Repository: xmtp/xmtpd
Pull request #712: Add pkg merkle
Author: login: fbac
Created: 2025-04-11T17:37:45Z | Merged: 2025-04-21T15:26:54Z

### Implement Merkle tree data structure with proof generation and verification in `pkg/merkle`
* Introduces core Merkle tree implementation in [tree.go](https://github.com/xmtp/xmtpd/pull/712/files#diff-4a0ec8af27f891e4481136ec6a06b2eea6423d8992b8ea8c5c14d841b05b4d9a) with `MerkleTree` struct and tree construction logic
* Adds Keccak-256 hashing functions in [hash.go](https://github.com/xmtp/xmtpd/pull/712/files#diff-4381bdd78bb0be4de1b1e9d2b8a01153fb880ab9a8ac307d30baaa3307ccd38d) for leaf and internal node hashing
* Implements proof generation and verification in [proof.go](https://github.com/xmtp/xmtpd/pull/712/files#diff-c26afbea2e9b24a09656eaec6e2b648112cb8cf19fc1d0405b9f686e6530397d) with `MultiProof` struct
* Creates specialized proof handling for sequential elements in [proof_sequential.go](https://github.com/xmtp/xmtpd/pull/712/files#diff-f8864c26a7c602c0264a8e986cb80773e07ef20ffbf13989ee464788aecf837a)
* Adds index-based proof generation and verification in [proof_indices.go](https://github.com/xmtp/xmtpd/pull/712/files#diff-df289bc46e3f57b4c03db92365856f8c84e600ad2b9b7d8119640f2f113537c3)
* Includes comprehensive test coverage in [tree_test.go](https://github.com/xmtp/xmtpd/pull/712/files#diff-aa27c0aa647f6683e3d149d6596a81a4837849a512296c4f6419f26e088a8c7d)

#### 📍Where to Start
Start with the `NewMerkleTree` function in [tree.go](https://github.com/xmtp/xmtpd/pull/712/files#diff-4a0ec8af27f891e4481136ec6a06b2eea6423d8992b8ea8c5c14d841b05b4d9a) which implements the core tree construction logic and serves as the entry point for the package.

----

_[Macroscope](https://app.macroscope.com) summarized 5eb4a35._

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **New Features**
	- Introduced cryptographic hashing functions with distinct prefixes for leaf and node data to support Merkle tree integrity.
	- Added a Merkle tree data structure with balanced tree construction and multi-proof generation for both sequential and arbitrary leaf indices.
	- Implemented comprehensive multi-proof verification with robust validation and error handling.
- **Tests**
	- Added extensive tests covering tree construction, hashing correctness, multi-proof generation and verification, edge cases, and utility functions to ensure reliability and correctness.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->


Diff:
diff --git a/pkg/merkle/hash.go b/pkg/merkle/hash.go
new file mode 100644
index 000000000..b8b10909d
--- /dev/null
+++ b/pkg/merkle/hash.go
@@ -0,0 +1,47 @@
+package merkle
+
+import (
+	"golang.org/x/crypto/sha3"
+)
+
+const (
+	LEAF_PREFIX = "leaf|"
+	NODE_PREFIX = "node|"
+)
+
+var (
+	leafPrefixBytes = []byte(LEAF_PREFIX)
+	nodePrefixBytes = []byte(NODE_PREFIX)
+)
+
+// Hash computes the Keccak-256 hash of a buffer.
+func Hash(buffer []byte) []byte {
+	hash := sha3.NewLegacyKeccak256()
+	hash.Write(buffer)
+	return hash.Sum(nil)
+}
+
+func HashNode(left, right []byte) []byte {
+	nodePrefixLen := len(nodePrefixBytes)
+	buffer := make([]byte, nodePrefixLen+len(left)+len(right))
+
+	copy(buffer[:nodePrefixLen], nodePrefixBytes)
+	copy(buffer[nodePrefixLen:], left)
+	copy(buffer[nodePrefixLen+len(left):], right)
+
+	return Hash(buffer)
+}
+
+func HashLeaf(leaf []byte) []byte {
+	leafPrefixLen := len(leafPrefixBytes)
+	buffer := make([]byte, leafPrefixLen+len(leaf))
+
+	copy(buffer[:leafPrefixLen], leafPrefixBytes)
+	copy(buffer[leafPrefixLen:], leaf)
+
+	return Hash(buffer)
+}
+
+func HashEmptyLeaf() []byte {
+	return HashLeaf([]byte{})
+}
diff --git a/pkg/merkle/proof.go b/pkg/merkle/proof.go
new file mode 100644
index 000000000..28c8cb9aa
--- /dev/null
+++ b/pkg/merkle/proof.go
@@ -0,0 +1,337 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrDuplicateIndices   = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds = errors.New("indices out of bounds")
+	ErrInvalidRange       = errors.New("invalid range")
+	ErrInvalidLeafCount   = errors.New("invalid leaf count")
+	ErrNilProof           = errors.New("nil proof")
+	ErrNilRoot            = errors.New("nil root")
+	ErrNilElement         = errors.New("nil element")
+	ErrNoElements         = errors.New("no elements")
+	ErrNoIndices          = errors.New("no indices")
+	ErrNoProofs           = errors.New("no proofs provided")
+)
+
+type MultiProof struct {
+	values    IndexedValues
+	proofs    []Node
+	leafCount int
+}
+
+func (p *MultiProof) GetLeafCount() int {
+	return p.leafCount
+}
+
+func (p *MultiProof) GetProofs() []Node {
+	return p.proofs
+}
+
+func (p *MultiProof) GetValues() IndexedValues {
+	return p.values
+}
+
+type IndexedValues []IndexedValue
+
+type IndexedValue struct {
+	value []byte
+	index int
+}
+
+func (iv IndexedValue) GetValue() []byte {
+	return iv.value
+}
+
+func (iv IndexedValue) GetIndex() int {
+	return iv.index
+}
+
+func (iv IndexedValues) Indices() []int {
+	indices := make([]int, len(iv))
+	for i, v := range iv {
+		indices[i] = v.index
+	}
+	return indices
+}
+
+func (iv IndexedValues) ToLeaves() []Leaf {
+	leaves := make([]Leaf, len(iv))
+	for i, v := range iv {
+		leaves[i] = Leaf(v.value)
+	}
+	return leaves
+}
+
+// Verify verifies a MultiProof against the given tree root.
+func Verify(root []byte, proof *MultiProof) (bool, error) {
+	if len(root) == 0 {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
+	}
+
+	if err := proof.validate(); err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	// Handle single-element trees.
+	if proof.leafCount == 1 {
+		return bytes.Equal(root, HashLeaf(proof.values[0].value)), nil
+	}
+
+	// If all the elements are provided, we can directly reconstruct the tree.
+	if len(proof.values) == proof.leafCount {
+		leaves := proof.values.ToLeaves()
+
+		tree, err := NewMerkleTree(leaves)
+		if err != nil {
+			return false, fmt.Errorf(ErrVerifyProof, err)
+		}
+
+		return bytes.Equal(tree.Root(), root), nil
+	}
+
+	computedRoot, err := proof.computeRoot()
+	if err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	return bytes.Equal(computedRoot, root), nil
+}
+
+// validate performs common validation for Merkle proofs.
+func (p *MultiProof) validate() error {
+	if len(p.values) == 0 {
+		return ErrNoElements
+	}
+
+	if p.leafCount <= 0 {
+		return ErrInvalidLeafCount
+	}
+
+	if err := validateIndices(p.values.Indices(), p.leafCount); err != nil {
+		return err
+	}
+
+	for _, elem := range p.values {
+		if elem.value == nil {
+			return ErrNilElement
+		}
+	}
+
+	for _, proof := range p.proofs {
+		if proof.hash == nil {
+			return ErrNilProof
+		}
+	}
+
+	isPartialProof := len(p.values) < p.leafCount
+	isNonTrivialTree := p.leafCount > 1
+	needsProofs := isPartialProof && isNonTrivialTree
+
+	if needsProofs && len(p.proofs) == 0 {
+		return ErrNoProofs
+	}
+
+	return nil
+}
+
+// getNextProof safely retrieves the next proof and increments the index.
+func (p *MultiProof) getNextProof(index *int) ([]byte, error) {
+	if *index >= len(p.proofs) {
+		return nil, ErrNoProofs
+	}
+	proof := p.proofs[*index]
+	*index++
+	return proof.Hash(), nil
+}
+
+// nodeQueue represents a node in the computation queue with its tree index and hash value.
+// It's used during proof verification to track nodes as they are processed.
+type nodeQueue struct {
+	index int
+	hash  []byte
+}
+
+// buildNodeQueue builds the node queue for the proof computation.
+func (p *MultiProof) buildNodeQueue(balancedLeafCount int) ([]nodeQueue, error) {
+	leaves := p.values.ToLeaves()
+
+	nodes, err := makeNodes(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	indices := p.values.Indices()
+	n := len(indices)
+
+	queue := make([]nodeQueue, n)
+	for i, idx := range indices {
+		insertPos := n - 1 - i
+		queue[insertPos] = nodeQueue{
+			index: balancedLeafCount + idx,
+			hash:  nodes[i].Hash(),
+		}
+	}
+
+	return queue, nil
+}
+
+// computeRoot computes the root of the Merkle tree from the given proof.
+func (p *MultiProof) computeRoot() ([]byte, error) {
+	// 1. Prepare the queue.
+	blc, err := CalculateBalancedNodesCount(p.leafCount)
+	if err != nil {
+		return nil, err
+	}
+
+	queue, err := p.buildNodeQueue(blc)
+	if err != nil {
+		return nil, err
+	}
+
+	var (
+		head, proofIdx = 0, 0
+		lowerBound     = queue[len(queue)-1].index
+		left, right    []byte
+	)
+
+	// 2. Process queue until we hit the root.
+	for head < len(queue) {
+		current := queue[head]
+		head++
+
+		// Exit condition - return the root.
+		if current.index == 1 {
+			return current.hash, nil
+		}
+
+		// Detect level-up.
+		if current.index == lowerBound ||
+			(head < len(queue) && queue[head].index == lowerBound) {
+			lowerBound >>= 1
+		}
+
+		if isLeftChild(current.index) {
+			// Handle left-child branch.
+			left = current.hash
+			if head < len(queue) && queue[head].index == current.index+1 {
+				right = queue[head].hash
+				head++
+			} else {
+				right, err = p.getNextProof(&proofIdx)
+				if err != nil {
+					return nil, err
+				}
+			}
+		} else {
+			// Handle right-child branch.
+			right = current.hash
+			if head < len(queue) && queue[head].index == current.index-1 {
+				left = queue[head].hash
+				head++
+			} else {
+				left, err = p.getNextProof(&proofIdx)
+				if err != nil {
+					return nil, err
+				}
+			}
+		}
+
+		queue = append(queue, nodeQueue{
+			index: current.index >> 1,
+			hash:  HashNode(left, right),
+		})
+	}
+
+	return nil, ErrNilRoot
+}
+
+// makeIndexedValues creates indexed values from elements and their indices.
+func makeIndexedValues(leaves []Leaf, indices []int) (IndexedValues, error) {
+	result := make(IndexedValues, len(indices))
+
+	for i, idx := range indices {
+		result[i] = IndexedValue{
+			value: leaves[idx],
+			index: idx,
+		}
+	}
+
+	return result, nil
+}
+
+// makeIndices returns a slice of ascending ordered indices for the given starting index and count.
+func makeIndices(startingIndex, count int) ([]int, error) {
+	if startingIndex < 0 || count <= 0 {
+		return nil, ErrInvalidRange
+	}
+
+	indices := make([]int, count)
+	for i := 0; i < count; i++ {
+		indices[i] = startingIndex + i
+	}
+
+	return indices, nil
+}
+
+// validateIndices validates the indices slice of a proof.
+func validateIndices(indices []int, leafCount int) error {
+	balancedLeafCount, err := CalculateBalancedNodesCount(leafCount)
+	if err != nil {
+		return err
+	}
+
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	if len(sortedIndices) == 0 {
+		return ErrNoIndices
+	}
+
+	if hasDuplicates(sortedIndices) {
+		return ErrDuplicateIndices
+	}
+
+	if hasOutOfBounds(sortedIndices, balancedLeafCount) {
+		return ErrIndicesOutOfBounds
+	}
+
+	return nil
+}
+
+// hasDuplicates checks if the sorted indices slice contains duplicates.
+func hasDuplicates(indices []int) bool {
+	for i := 1; i < len(indices); i++ {
+		if indices[i] == indices[i-1] {
+			return true
+		}
+	}
+	return false
+}
+
+// hasOutOfBounds checks if all indices are within the valid range [0, leafCount).
+func hasOutOfBounds(indices []int, leafCount int) bool {
+	for _, idx := range indices {
+		if idx < 0 || idx >= leafCount {
+			return true
+		}
+	}
+	return false
+}
+
+// isLeftChild returns true if the given index is odd (right child).
+func isLeftChild(index int) bool {
+	return index%2 == 0
+}
diff --git a/pkg/merkle/proof_test.go b/pkg/merkle/proof_test.go
new file mode 100644
index 000000000..9c02e9ffb
--- /dev/null
+++ b/pkg/merkle/proof_test.go
@@ -0,0 +1,446 @@
+package merkle_test
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/xmtp/xmtpd/pkg/merkle"
+)
+
+func TestVerifyMultiProofSequential(t *testing.T) {
+	cases := []struct {
+		name            string
+		leaves          []merkle.Leaf
+		startIdx        int
+		count           int
+		wantErrCreate   bool
+		wantErrGenerate bool
+		wantErrVerify   bool
+		wantProofCount  int
+	}{
+		{
+			name:            "Balanced tree - 8 leaves - consecutive leaves from middle",
+			leaves:          createLeaves(t, 8),
+			startIdx:        2,
+			count:           3,
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  3,
+		},
+		{
+			name:            "Balanced tree - 8 leaves - consecutive leaves from start",
+			leaves:          createLeaves(t, 8),
+			startIdx:        0,
+			count:           3,
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  2,
+		},
+		{
+			name:            "Balanced tree - 8 leaves - consecutive leaves from end",
+			leaves:          createLeaves(t, 8),
+			startIdx:        5,
+			count:           3,
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  2,
+		},
+		{
+			name:            "Balanced tree - 16 leaves - large range",
+			leaves:          createLeaves(t, 16),
+			startIdx:        2,
+			count:           8,
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  3,
+		},
+		{
+			name:            "Balanced tree - 4 leaves - all leaves",
+			leaves:          createLeaves(t, 4),
+			startIdx:        0,
+			count:           4,
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  0,
+		},
+		{
+			name:            "Single leaf tree",
+			leaves:          createLeaves(t, 1),
+			startIdx:        0,
+			count:           1,
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  1,
+		},
+		{
+			name:            "Unbalanced tree - 3 leaves - last leaf",
+			leaves:          createLeaves(t, 3),
+			startIdx:        2,
+			count:           1,
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  2,
+		},
+		{
+			name:            "Unbalanced tree - 7 leaves - middle leaves",
+			leaves:          createLeaves(t, 7),
+			startIdx:        2,
+			count:           3,
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  3,
+		},
+		{
+			name:            "Out of bounds - start index negative",
+			leaves:          createLeaves(t, 8),
+			startIdx:        -1,
+			count:           3,
+			wantErrCreate:   false,
+			wantErrGenerate: true,
+			wantErrVerify:   false,
+			wantProofCount:  0,
+		},
+		{
+			name:            "Out of bounds - count exceeds leaves",
+			leaves:          createLeaves(t, 8),
+			startIdx:        6,
+			count:           3,
+			wantErrCreate:   false,
+			wantErrGenerate: true,
+			wantErrVerify:   false,
+			wantProofCount:  0,
+		},
+		{
+			name:            "Invalid input - zero count",
+			leaves:          createLeaves(t, 8),
+			startIdx:        2,
+			count:           0,
+			wantErrCreate:   false,
+			wantErrGenerate: true,
+			wantErrVerify:   false,
+			wantProofCount:  0,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			tree, err := merkle.NewMerkleTree(tc.leaves)
+			if tc.wantErrCreate {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+
+			proof, err := tree.GenerateMultiProofSequential(tc.startIdx, tc.count)
+			if tc.wantErrGenerate {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+
+			ok, err := merkle.Verify(tree.Root(), proof)
+			if tc.wantErrVerify {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			require.True(t, ok)
+
+			assert.Equal(t, tc.wantProofCount, len(proof.GetProofs()), "Invalid proof count")
+			assert.Equal(t, tc.count, len(proof.GetValues()), "Invalid values count")
+		})
+	}
+}
+
+func TestVerifyMultiProofWithIndices(t *testing.T) {
+	cases := []struct {
+		name            string
+		leaves          []merkle.Leaf
+		indices         []int
+		wantErrCreate   bool
+		wantErrGenerate bool
+		wantErrVerify   bool
+		wantProofCount  int
+	}{
+		{
+			name:            "Balanced tree - 8 leaves - out-of-order indices",
+			leaves:          createLeaves(t, 8),
+			indices:         []int{3, 1, 6},
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  4,
+		},
+		{
+			name:            "Balanced tree - 8 leaves - all indices",
+			leaves:          createLeaves(t, 8),
+			indices:         []int{0, 1, 2, 3, 4, 5, 6, 7},
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  0, // No proofs needed when all leaves included
+		},
+		{
+			name:            "Balanced tree - 8 leaves - single index",
+			leaves:          createLeaves(t, 8),
+			indices:         []int{4},
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  3,
+		},
+		{
+			name:            "Balanced tree - 8 leaves - sibling pairs",
+			leaves:          createLeaves(t, 8),
+			indices:         []int{2, 3}, // Siblings at the same parent
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  2,
+		},
+		{
+			name:            "Balanced tree - 8 leaves - different subtrees",
+			leaves:          createLeaves(t, 8),
+			indices:         []int{1, 6}, // From different parts of the tree
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  4,
+		},
+		{
+			name:            "Balanced tree - 16 leaves - various positions",
+			leaves:          createLeaves(t, 16),
+			indices:         []int{2, 7, 9, 15},
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  8,
+		},
+		{
+			name:            "Unbalanced tree - 5 leaves - odd indices",
+			leaves:          createLeaves(t, 5),
+			indices:         []int{1, 3},
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  3,
+		},
+		{
+			name:            "Unbalanced tree - 6 leaves - edge positions",
+			leaves:          createLeaves(t, 6),
+			indices:         []int{0, 5},
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  4,
+		},
+		{
+			name:            "Unbalanced tree - 7 leaves - first and last",
+			leaves:          createLeaves(t, 7),
+			indices:         []int{0, 6},
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  4,
+		},
+		{
+			name:            "Unbalanced tree - 9 leaves - mixed positions",
+			leaves:          createLeaves(t, 9),
+			indices:         []int{0, 6, 8},
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  7,
+		},
+		{
+			name:            "Single leaf tree",
+			leaves:          createLeaves(t, 1),
+			indices:         []int{0},
+			wantErrCreate:   false,
+			wantErrGenerate: false,
+			wantErrVerify:   false,
+			wantProofCount:  1,
+		},
+		{
+			name:            "Invalid input - empty indices",
+			leaves:          createLeaves(t, 8),
+			indices:         []int{},
+			wantErrCreate:   false,
+			wantErrGenerate: true, // Should error on empty indices
+			wantErrVerify:   false,
+			wantProofCount:  0,
+		},
+		{
+			name:            "Invalid input - duplicate indices",
+			leaves:          createLeaves(t, 8),
+			indices:         []int{1, 1, 3},
+			wantErrCreate:   false,
+			wantErrGenerate: true, // Should error on duplicate indices
+			wantErrVerify:   false,
+			wantProofCount:  0,
+		},
+		{
+			name:            "Invalid input - out of bounds indices",
+			leaves:          createLeaves(t, 8),
+			indices:         []int{1, 9, 3},
+			wantErrCreate:   false,
+			wantErrGenerate: true, // Should error on out of bounds
+			wantErrVerify:   false,
+			wantProofCount:  0,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			tree, err := merkle.NewMerkleTree(tc.leaves)
+			if tc.wantErrCreate {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+
+			proof, err := tree.GenerateMultiProofWithIndices(tc.indices)
+			if tc.wantErrGenerate {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+
+			ok, err := merkle.Verify(tree.Root(), proof)
+			if tc.wantErrVerify {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			require.True(t, ok)
+
+			assert.Equal(t, tc.wantProofCount, len(proof.GetProofs()), "Invalid proof count")
+			assert.Equal(t, len(tc.indices), len(proof.GetValues()), "Invalid values count")
+
+			vals := proof.GetValues()
+			for i := 1; i < len(vals); i++ {
+				assert.LessOrEqual(t, vals[i-1].GetIndex(), vals[i].GetIndex())
+			}
+		})
+	}
+}
+
+func TestVerifyEdgeCases(t *testing.T) {
+	testCases := []struct {
+		name      string
+		setupFunc func() ([]byte, *merkle.MultiProof, error)
+		wantOK    bool
+		wantErr   string
+		errorIs   error
+	}{
+		{
+			name: "NilRoot",
+			setupFunc: func() ([]byte, *merkle.MultiProof, error) {
+				tree, err := merkle.NewMerkleTree(createLeaves(t, 4))
+				if err != nil {
+					return nil, nil, err
+				}
+				multiProof, err := tree.GenerateMultiProofSequential(0, 1)
+				return nil, multiProof, err
+			},
+			wantOK:  false,
+			wantErr: "nil root",
+			errorIs: merkle.ErrNilRoot,
+		},
+		{
+			name: "TamperedRoot",
+			setupFunc: func() ([]byte, *merkle.MultiProof, error) {
+				tree, err := merkle.NewMerkleTree(createLeaves(t, 4))
+				if err != nil {
+					return nil, nil, err
+				}
+				multiProof, err := tree.GenerateMultiProofSequential(0, 1)
+				if err != nil {
+					return nil, nil, err
+				}
+
+				// Tamper with the root
+				tamperedRoot := make([]byte, len(tree.Root()))
+				copy(tamperedRoot, tree.Root())
+				tamperedRoot[0] ^= 0xFF
+
+				return tamperedRoot, multiProof, nil
+			},
+			wantOK: false,
+		},
+		{
+			name: "TamperedProofValues",
+			setupFunc: func() ([]byte, *merkle.MultiProof, error) {
+				tree, err := merkle.NewMerkleTree(createLeaves(t, 4))
+				if err != nil {
+					return nil, nil, err
+				}
+				multiProof, err := tree.GenerateMultiProofSequential(0, 1)
+				if err != nil {
+					return nil, nil, err
+				}
+
+				return tree.Root(), multiProof, nil
+			},
+			wantOK: true,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			root, multiProof, err := tc.setupFunc()
+			require.NoError(t, err)
+
+			verified, err := merkle.Verify(root, multiProof)
+
+			if tc.wantErr != "" {
+				assert.Error(t, err)
+				assert.ErrorContains(t, err, tc.wantErr)
+				if tc.errorIs != nil {
+					assert.ErrorIs(t, err, tc.errorIs)
+				}
+				return
+			}
+
+			assert.NoError(t, err)
+			assert.Equal(t, tc.wantOK, verified)
+		})
+	}
+}
+
+func TestMultiProofManipulation(t *testing.T) {
+	leaves := createLeaves(t, 8)
+	tree, err := merkle.NewMerkleTree(leaves)
+	require.NoError(t, err)
+
+	multiProof, err := tree.GenerateMultiProofWithIndices([]int{0, 3})
+	require.NoError(t, err)
+
+	verified, err := merkle.Verify(tree.Root(), multiProof)
+	require.NoError(t, err)
+	assert.True(t, verified)
+
+	values := multiProof.GetValues()
+	assert.Equal(t, 2, len(values))
+	assert.True(t, bytes.Equal(leaves[0], values[0].GetValue()))
+	assert.True(t, bytes.Equal(leaves[3], values[1].GetValue()))
+}
+
+func createLeaves(t *testing.T, count int) []merkle.Leaf {
+	t.Helper()
+	leaves := make([]merkle.Leaf, count)
+	for i := 0; i < count; i++ {
+		leaves[i] = []byte{byte(i + 1)}
+	}
+	return leaves
+}
diff --git a/pkg/merkle/tree.go b/pkg/merkle/tree.go
new file mode 100644
index 000000000..f0f023290
--- /dev/null
+++ b/pkg/merkle/tree.go
@@ -0,0 +1,318 @@
+package merkle
+
+import (
+	"errors"
+	"fmt"
+	"math/bits"
+	"sort"
+)
+
+type Node struct {
+	hash []byte
+}
+
+func (n *Node) Hash() []byte {
+	if n.hash == nil {
+		return nil
+	}
+
+	cp := make([]byte, len(n.hash))
+	copy(cp, n.hash)
+
+	return cp
+}
+
+type Leaf []byte
+
+// MerkleTree is a binary Merkle tree.
+//
+// tree has the collection of nodes, where:
+// - The tree is 1-indexed, so root is at index 1.
+// - The internal nodes are at index 1 to N-1.
+// - The leaves are at index N to 2N-1.
+//
+// leaves contains the raw elements of the tree.
+type MerkleTree struct {
+	tree   []Node
+	leaves []Leaf
+}
+
+var (
+	ErrNoLeaves  = errors.New("no leaves provided")
+	ErrTreeEmpty = errors.New("tree is empty")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(leaves []Leaf) (*MerkleTree, error) {
+	if len(leaves) == 0 {
+		return nil, ErrNoLeaves
+	}
+
+	balancedLeaves, err := makeLeaves(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	nodes, err := makeNodes(balancedLeaves)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(nodes)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{tree, balancedLeaves}, nil
+}
+
+// GenerateMultiProofSequential generates a sequential multi-proof starting from the given index.
+func (m *MerkleTree) GenerateMultiProofSequential(startingIndex, count int) (*MultiProof, error) {
+	indices, err := makeIndices(startingIndex, count)
+	if err != nil {
+		return nil, err
+	}
+
+	proof, err := m.makeProof(indices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// GenerateMultiProofWithIndices generates a multi-proof for the given indices.
+func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	proof, err := m.makeProof(sortedIndices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// makeProof returns a MultiProof for the given indices.
+func (m *MerkleTree) makeProof(indices []int) (MultiProof, error) {
+	err := validateIndices(indices, m.LeafCount())
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	indexedValues, err := makeIndexedValues(m.leaves, indices)
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	// Handle single-element trees.
+	if m.LeafCount() == 1 {
+		return MultiProof{
+			values:    indexedValues,
+			proofs:    []Node{{hash: m.Root()}},
+			leafCount: m.LeafCount(),
+		}, nil
+	}
+
+	var (
+		startLeafIdx = len(m.tree) >> 1
+		proofs       []Node
+		known        = make([]bool, len(m.tree))
+	)
+
+	// Mark provided indices as known.
+	for _, idx := range indices {
+		known[startLeafIdx+idx] = true
+	}
+
+	// Calculate proofs to prove the existence of the indices.
+	for i := startLeafIdx - 1; i > 0; i-- {
+		leftChildIdx := GetLeftChild(i)
+		rightChildIdx := GetRightChild(i)
+
+		left := known[leftChildIdx]
+		right := known[rightChildIdx]
+
+		// Only one of children is known, so we need the sibling as a proof.
+		if left != right {
+			if right {
+				proofs = append(proofs, m.tree[leftChildIdx])
+			} else {
+				proofs = append(proofs, m.tree[rightChildIdx])
+			}
+		}
+
+		// If at least one of the children is known, the parent is known.
+		known[i] = left || right
+	}
+
+	return MultiProof{
+		values:    indexedValues,
+		proofs:    proofs,
+		leafCount: len(m.leaves),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() []Node {
+	return m.tree
+}
+
+// Leaves returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Leaves() []Leaf {
+	return m.leaves
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.tree[1].Hash()
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return len(m.leaves)
+}
+
+// makeTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func makeTree(nodes []Node) ([]Node, error) {
+	if len(nodes) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	balancedLeafCount, err := CalculateBalancedNodesCount(len(nodes))
+	if err != nil {
+		return nil, err
+	}
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([]Node, balancedLeafCount<<1)
+
+	lowerBound := balancedLeafCount
+	upperBound := balancedLeafCount + len(nodes) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(nodes); i++ {
+		tree[lowerBound+i] = nodes[i]
+	}
+
+	for i := len(nodes); i < balancedLeafCount; i++ {
+		tree[lowerBound+i] = Node{hash: HashEmptyLeaf()}
+	}
+
+	// Build the tree.
+	for i := balancedLeafCount - 1; i >= 1; i-- {
+		leftChildIndex := GetLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := GetRightChild(i)
+
+		tree[i] = Node{
+			hash: HashNode(tree[leftChildIndex].Hash(), tree[rightChildIndex].Hash()),
+		}
+
+	}
+
+	return tree, nil
+}
+
+// makeNodes returns the hashed leaves of the tree,
+// ordered in the same order as the provided elements.
+func makeNodes(leaves []Leaf) ([]Node, error) {
+	if len(leaves) == 0 {
+		return nil, ErrNoLeaves
+	}
+
+	nodes := make([]Node, len(leaves))
+	for i, element := range leaves {
+		nodes[i] = Node{hash: HashLeaf(element)}
+	}
+
+	return nodes, nil
+}
+
+// makeLeaves creates a balanced leaves count for the given leaves.
+// It fills empty leaves with an empty leaf hash.
+func makeLeaves(leaves []Leaf) ([]Leaf, error) {
+	balancedLeafCount, err := CalculateBalancedNodesCount(len(leaves))
+	if err != nil {
+		return nil, err
+	}
+
+	balancedLeaves := make([]Leaf, balancedLeafCount)
+
+	copy(balancedLeaves, leaves)
+
+	for i := len(leaves); i < balancedLeafCount; i++ {
+		balancedLeaves[i] = []byte{}
+	}
+
+	return balancedLeaves, nil
+}
+
+// CalculateBalancedNodesCount returns the number of nodes in a balanced tree.
+// To calculate the number of nodes in a tree, we need to round up to the next power of 2.
+// Returns an error if the element count is too large to be represented in a uint32.
+func CalculateBalancedNodesCount(count int) (int, error) {
+	if count <= 0 {
+		return 0, fmt.Errorf("count must be greater than 0")
+	}
+
+	if count > int(1<<31) {
+		return 0, fmt.Errorf("count must be less than or equal to 2^31")
+	}
+
+	return int(roundUpToPowerOf2(uint32(count))), nil
+}
+
+// roundUpToPowerOf2 rounds up a number to the next power of 2.
+func roundUpToPowerOf2(n uint32) uint32 {
+	if bits.OnesCount32(n) == 1 {
+		return n
+	}
+
+	n |= n >> 1
+	n |= n >> 2
+	n |= n >> 4
+	n |= n >> 8
+	n |= n >> 16
+
+	return n + 1
+}
+
+// GetLeftChild returns the index of the left child for a node at the given index
+func GetLeftChild(index int) int {
+	return index << 1 // index * 2
+}
+
+// GetRightChild returns the index of the right child for a node at the given index
+func GetRightChild(index int) int {
+	return (index << 1) + 1 // index * 2 + 1
+}
diff --git a/pkg/merkle/tree_test.go b/pkg/merkle/tree_test.go
new file mode 100644
index 000000000..d5db9ef1a
--- /dev/null
+++ b/pkg/merkle/tree_test.go
@@ -0,0 +1,441 @@
+package merkle_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/xmtp/xmtpd/pkg/merkle"
+)
+
+func TestEmptyTree(t *testing.T) {
+	_, err := merkle.NewMerkleTree([]merkle.Leaf{})
+	assert.Error(t, err, "Should error on empty elements")
+	assert.ErrorAs(t, err, &merkle.ErrTreeEmpty)
+}
+
+func TestBalancedTrees(t *testing.T) {
+	testCases := []struct {
+		name          string
+		numElements   int
+		expectedDepth int
+	}{
+		{"TwoElements", 2, 1},
+		{"FourElements", 4, 2},
+		{"EightElements", 8, 3},
+		{"SixteenElements", 16, 4},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			// Create elements.
+			elements := make([]merkle.Leaf, tc.numElements)
+			for i := 0; i < tc.numElements; i++ {
+				elements[i] = []byte(tc.name + "_element" + string(rune('A'+i)))
+			}
+
+			tree, err := merkle.NewMerkleTree(elements)
+			require.NoError(t, err)
+
+			// Check structure.
+			assert.Equal(
+				t,
+				tc.numElements,
+				tree.LeafCount(),
+				"Leaf count should match element count",
+			)
+			assert.NotNil(t, tree.Root(), "Root should not be nil")
+
+			// For balanced trees, the array size is exactly 2*n where n is the next power of 2 >= numElements.
+			leafCount, err := merkle.CalculateBalancedNodesCount(tc.numElements)
+			require.NoError(t, err)
+			expectedArraySize := leafCount * 2
+			assert.Equal(
+				t,
+				expectedArraySize,
+				len(tree.Tree()),
+				"Tree array size should be 2*leafCount",
+			)
+
+			// Check that all leaves are present.
+			for i := 0; i < tc.numElements; i++ {
+				leafIndex := leafCount + i
+				assert.NotNil(t, tree.Tree()[leafIndex], "Leaf node should not be nil")
+				assert.Equal(
+					t,
+					merkle.HashLeaf(elements[i]),
+					tree.Tree()[leafIndex].Hash(),
+					"Leaf hash should match",
+				)
+			}
+
+			// Check that all internal nodes up to the root are not nil.
+			for i := 1; i < leafCount; i++ {
+				assert.NotNil(
+					t,
+					tree.Tree()[i].Hash(),
+					"Internal node should not be nil in a balanced tree",
+				)
+			}
+		})
+	}
+}
+
+func TestUnbalancedTrees(t *testing.T) {
+	testCases := []struct {
+		name        string
+		numElements int
+	}{
+		{"SingleElement", 1},
+		{"ThreeElements", 3},
+		{"FiveElements", 5},
+		{"SevenElements", 7},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			elements := make([]merkle.Leaf, tc.numElements)
+			for i := 0; i < tc.numElements; i++ {
+				elements[i] = []byte(tc.name + "_element" + string(rune('A'+i)))
+			}
+
+			tree, err := merkle.NewMerkleTree(elements)
+			require.NoError(t, err)
+
+			leafCount, err := merkle.CalculateBalancedNodesCount(tc.numElements)
+			require.NoError(t, err)
+			for i := 0; i < tc.numElements; i++ {
+				leafIdx := leafCount + i
+				assert.Equal(t, merkle.HashLeaf(elements[i]), tree.Tree()[leafIdx].Hash(),
+					"Leaf %d should be at tree[%d]", i, leafIdx)
+			}
+
+			verifyUnbalancedTreeStructure(t, tree.Tree(), leafCount, tc.numElements)
+		})
+	}
+}
+
+func TestLargeTrees(t *testing.T) {
+	testCases := []struct {
+		name           string
+		providedLeaves int
+		expectedLeaves int
+	}{
+		{"TreeSize100", 100, 128},
+		{"TreeSize1023", 1023, 1024},
+		{"TreeSize2048", 2048, 2048},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			elements := make([]merkle.Leaf, tc.providedLeaves)
+			for i := 0; i < tc.providedLeaves; i++ {
+				elements[i] = []byte{
+					byte(i & 0xFF),
+					byte((i >> 8) & 0xFF),
+					byte((i >> 16) & 0xFF),
+					byte((i >> 24) & 0xFF),
+				}
+			}
+
+			tree, err := merkle.NewMerkleTree(elements)
+			require.NoError(t, err)
+
+			// Verify basic properties.
+			assert.Equal(
+				t,
+				tc.expectedLeaves,
+				tree.LeafCount(),
+				"Leaf count should match element count",
+			)
+			assert.NotNil(t, tree.Root(), "Root should not be nil")
+
+			// Verify tree structure size.
+			leafCount, err := merkle.CalculateBalancedNodesCount(tc.providedLeaves)
+			require.NoError(t, err)
+			expectedArraySize := leafCount * 2
+			assert.Equal(
+				t,
+				expectedArraySize,
+				len(tree.Tree()),
+				"Tree array size should be 2*leafCount",
+			)
+
+			// Sample testing.
+			for i := 0; i < 5; i++ {
+				idx := i * (tc.providedLeaves / 5)
+				if idx >= tc.providedLeaves {
+					idx = tc.providedLeaves - 1
+				}
+				leafIndex := leafCount + idx
+				assert.NotNil(t, tree.Tree()[leafIndex], "Sampled leaf should not be nil")
+				assert.Equal(
+					t,
+					merkle.HashLeaf(elements[idx]),
+					tree.Tree()[leafIndex].Hash(),
+					"Sampled leaf hash should match",
+				)
+			}
+		})
+	}
+}
+
+func TestTreeWithDuplicateElements(t *testing.T) {
+	elements := []merkle.Leaf{
+		[]byte("same"),
+		[]byte("same"),
+		[]byte("same"),
+		[]byte("different"),
+	}
+
+	tree, err := merkle.NewMerkleTree(elements)
+	require.NoError(t, err)
+
+	leafCount, err := merkle.CalculateBalancedNodesCount(len(elements))
+	require.NoError(t, err)
+	leafHash1 := tree.Tree()[leafCount].Hash()
+	leafHash2 := tree.Tree()[leafCount+1].Hash()
+	leafHash3 := tree.Tree()[leafCount+2].Hash()
+	leafHash4 := tree.Tree()[leafCount+3].Hash()
+
+	assert.Equal(t, leafHash1, leafHash2, "Identical elements should have identical leaf hashes")
+	assert.Equal(t, leafHash2, leafHash3, "Identical elements should have identical leaf hashes")
+	assert.NotEqual(t, leafHash3, leafHash4, "Different elements should have different leaf hashes")
+
+	assert.NotNil(t, tree.Root(), "Tree with duplicate elements should have a valid root")
+}
+
+func TestTreeWithLargeElements(t *testing.T) {
+	bigElement := make([]byte, 1024*1024)
+	for i := range bigElement {
+		bigElement[i] = byte(i & 0xFF)
+	}
+
+	elements := []merkle.Leaf{
+		bigElement,
+		bigElement[:len(bigElement)/2],
+	}
+
+	tree, err := merkle.NewMerkleTree(elements)
+	require.NoError(t, err)
+	assert.NotNil(
+		t,
+		tree.Root(),
+		"Root should be calculated correctly even with large elements",
+	)
+}
+
+func TestTreeWithEmptyElements(t *testing.T) {
+	elements := []merkle.Leaf{
+		{},
+		{},
+		[]byte("non-empty"),
+	}
+
+	tree, err := merkle.NewMerkleTree(elements)
+	require.NoError(t, err)
+	assert.NotNil(t, tree.Root(), "Root should be calculated correctly with empty elements")
+
+	leafCount, err := merkle.CalculateBalancedNodesCount(len(elements))
+	require.NoError(t, err)
+	for i := 0; i < 2; i++ {
+		leafIndex := leafCount + i
+		assert.Equal(
+			t,
+			merkle.HashLeaf([]byte{}),
+			tree.Tree()[leafIndex].Hash(),
+			"Empty element should be properly hashed",
+		)
+	}
+}
+
+func TestTreeInternals(t *testing.T) {
+	// Test with a 3-element tree (unbalanced)
+	// Check everything "manually".
+	//
+	// Tree structure:
+	//        [1]
+	//       /   \
+	//     [2]    [3]
+	//    /  \    /
+	//  [4]  [5] [6]
+	//  A    B    C
+
+	elements := []merkle.Leaf{
+		[]byte("A"),
+		[]byte("B"),
+		[]byte("C"),
+	}
+
+	tree, err := merkle.NewMerkleTree(elements)
+	require.NoError(t, err)
+
+	internalTree := tree.Tree()
+
+	// For a 3-element tree, the balanced leaf count is 4
+	// So the tree array should have size 8 (2*4)
+	assert.Equal(t, 8, len(internalTree), "Tree array should have size 2*leafCount")
+	assert.Equal(t, tree.Root(), internalTree[1].Hash(), "Root should be at index 1")
+
+	// Check that all leaves are present.
+	leafStartIdx := 4
+	assert.Equal(
+		t,
+		merkle.HashLeaf(elements[0]),
+		internalTree[leafStartIdx].Hash(),
+		"Leaf 0 should match hash",
+	)
+	assert.Equal(
+		t,
+		merkle.HashLeaf(elements[1]),
+		internalTree[leafStartIdx+1].Hash(),
+		"Leaf 1 should match hash",
+	)
+	assert.Equal(
+		t,
+		merkle.HashLeaf(elements[2]),
+		internalTree[leafStartIdx+2].Hash(),
+		"Leaf 2 should match hash",
+	)
+	assert.Equal(
+		t,
+		internalTree[leafStartIdx+3].Hash(),
+		merkle.HashLeaf([]byte{}),
+		"Leaf 3 should match empty element hash",
+	)
+
+	verifyUnbalancedTreeStructure(t, internalTree, 4, len(elements))
+}
+
+// Helper function to verify the structure of an unbalanced tree
+func verifyUnbalancedTreeStructure(
+	t *testing.T,
+	tree []merkle.Node,
+	leafCount, actualElements int,
+) {
+	t.Helper()
+
+	// Handle single element trees.
+	if actualElements == 1 {
+		assert.Nil(t, tree[0].Hash(), "Merkle Tree 1-indexed, index 0 should be nil")
+		assert.Equal(
+			t,
+			tree[leafCount].Hash(),
+			tree[1].Hash(),
+			"For single element tree, root should equal leaf",
+		)
+		return
+	}
+
+	// Starting from the leaf parents, check nodes up to the root.
+	for i := leafCount - 1; i > 0; i-- {
+		leftIdx := merkle.GetLeftChild(i)
+		rightIdx := merkle.GetRightChild(i)
+
+		if leftIdx >= len(tree) {
+			continue
+		}
+
+		// If both children exist
+		if leftIdx < len(tree) && rightIdx < len(tree) {
+			assert.NotNil(t, tree[i], "Parent node should not be nil when both children exist")
+			assert.Equal(
+				t,
+				merkle.HashNode(tree[leftIdx].Hash(), tree[rightIdx].Hash()),
+				tree[i].Hash(),
+				"Node at index %d should be equal to its children at %d and %d",
+				i,
+				leftIdx,
+				rightIdx,
+			)
+		}
+	}
+
+	// Check the root is valid.
+	expectedRoot := tree[1].Hash()
+	assert.NotNil(t, expectedRoot, "Root should not be nil")
+	assert.NotNil(
+		t,
+		merkle.HashNode(tree[1].Hash(), tree[2].Hash()),
+		"Root should be calculated when both children exist",
+	)
+}
+
+func TestRoundUpToPowerOf2Values(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    int
+		expected int
+		wantErr  bool
+	}{
+		{"zero", 0, 0, true},
+		{"one", 1, 1, false},
+		{"already power of 2", 4, 4, false},
+		{"already power of 2 (large)", 16384, 16384, false},
+		{"regular case", 5, 8, false},
+		{"regular case (large)", 5000, 8192, false},
+		{"large number", 1<<30 - 1, 1 << 30, false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, err := merkle.CalculateBalancedNodesCount(tt.input)
+			if tt.wantErr {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+				if result != tt.expected {
+					t.Errorf(
+						"Power of 2 rounding for %d = %d, expected %d",
+						tt.input,
+						result,
+						tt.expected,
+					)
+				}
+			}
+		})
+	}
+}
+
+func TestCalculateBalancedLeafCount(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    int
+		expected int
+		wantErr  bool
+	}{
+		{"negative", -1, 0, true},
+		{"zero", 0, 0, true},
+		{"one", 1, 1, false},
+		{"power of 2", 16, 16, false},
+		{"not power of 2", 15, 16, false},
+		{"large number", 1000000, 1048576, false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, err := merkle.CalculateBalancedNodesCount(tt.input)
+			if tt.wantErr {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+				if result != tt.expected {
+					t.Errorf("CalculateBalancedLeafCount(%d) = %d, expected %d", tt.input, result, tt.expected)
+				}
+			}
+		})
+	}
+}
+
+// TestCalculateBalancedLeafCountError tests that the function returns an error with large inputs
+func TestCalculateBalancedLeafCountError(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode - requires large values")
+	}
+
+	// This is larger than max uint32 and should cause an error
+	massiveInput := int(^uint32(0)) + 1
+	_, err := merkle.CalculateBalancedNodesCount(massiveInput)
+	assert.Error(t, err)
+	assert.Equal(t, "count must be less than or equal to 2^31", err.Error())
+}


Reviews:
user: login: coderabbitai[bot]
body: **Actionable comments posted: 1**

<details>
<summary>🧹 Nitpick comments (8)</summary><blockquote>

<details>
<summary>pkg/merkle/hash.go (1)</summary><blockquote>

`11-16`: **Consider using the direct Summation-based Keccak256 helper for clarity.**
Using `sha3.NewLegacyKeccak256()` and `hash.Write(buffer)` is totally valid here. However, if performance or simplicity is desired when hashing single buffers, you might consider using a direct summation approach such as `sha3.SumLegacyKeccak256(buffer)` to avoid manual hasher creation and writing.

</blockquote></details>
<details>
<summary>pkg/merkle/proof_indices.go (3)</summary><blockquote>

`43-43`: **Consolidation TODO.**
The plan to abstract out shared logic from both sequential and index-based verification is laudable. This can reduce code duplication in future.

---

`44-81`: **Verification quietly returns (false, nil) on invalid proof.**
When `getRootIndices` returns `nil`, the code returns `(false, nil)` rather than an error. Consider returning `(false, error)` to provide clearer diagnostic feedback to callers.

---

`83-212`: **Complex but logical root computation.**
While thorough and correct, this routine is quite large. You could consider modularizing it into smaller functions to simplify readability and maintenance.

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

`28-36`: **Consider validating out-of-range or duplicate indices in `generateProof`.**

Currently, `generateProof` does not explicitly check whether indices exceed the tree’s range or if they contain duplicates. Although these checks may be performed in the calling functions, you might strengthen error safety by ensuring that indices are valid here as well, preventing potential out-of-bounds access on line 60 (`leafCount + idx`).

---

`155-183`: **Potential performance bottleneck in `combineLeaves`.**

For very large sets of leaves, repeatedly creating a new level by hashing adjacent pairs could be optimized via parallel processing or by minimizing intermediate slice allocations. If performance at scale becomes a concern, consider a more efficient approach or concurrency in safe contexts.

</blockquote></details>
<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`19-26`: **Validate non-nil elements on tree creation.**

In `NewMerkleTree`, there is no check for nil elements in the input slice. If an element is nil, `HashLeaf(nil)` might behave unexpectedly or degrade security. Consider validating them here to ensure consistent leaf data.

</blockquote></details>
<details>
<summary>pkg/merkle/proof_sequential.go (1)</summary><blockquote>

`89-200`: **Simplify or further document `getRootSequentially`.**

The circular queue approach is correct but quite complex, potentially impacting maintainability and readability. Adding more explanatory comments or breaking out sub-steps into helper functions may help future contributors understand and maintain this logic.

</blockquote></details>

</blockquote></details>

<details>
<summary>📜 Review details</summary>

**Configuration used: CodeRabbit UI**
**Review profile: CHILL**
**Plan: Pro**

<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between 95c58dd1bb8b055b8fe781ecf109a465e843e53d and 5eb4a3517bbcd467c63bae1c1f18c3f373be0538.

</details>

<details>
<summary>📒 Files selected for processing (6)</summary>

* `pkg/merkle/hash.go` (1 hunks)
* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/proof_indices.go` (1 hunks)
* `pkg/merkle/proof_sequential.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)
* `pkg/merkle/tree_test.go` (1 hunks)

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧬 Code Graph Analysis (3)</summary>

<details>
<summary>pkg/merkle/proof_indices.go (3)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary>

* `MerkleTree` (10-16)

</details>
<details>
<summary>pkg/merkle/proof.go (1)</summary>

* `MultiProof` (9-16)

</details>
<details>
<summary>pkg/merkle/hash.go (2)</summary>

* `HashLeaf` (24-26)
* `HashNode` (19-21)

</details>

</blockquote></details>
<details>
<summary>pkg/merkle/proof_sequential.go (3)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary>

* `MerkleTree` (10-16)

</details>
<details>
<summary>pkg/merkle/proof.go (1)</summary>

* `MultiProof` (9-16)

</details>
<details>
<summary>pkg/merkle/hash.go (2)</summary>

* `HashLeaf` (24-26)
* `HashNode` (19-21)

</details>

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (1)</summary><blockquote>

<details>
<summary>pkg/merkle/hash.go (1)</summary>

* `HashNode` (19-21)

</details>

</blockquote></details>

</details>

</details>

<details>
<summary>⏰ Context from checks skipped due to timeout of 90000ms (5)</summary>

* GitHub Check: Code Review
* GitHub Check: Push Docker Images to GitHub Packages (xmtpd-cli)
* GitHub Check: Push Docker Images to GitHub Packages (xmtpd)
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</details>

<details>
<summary>🔇 Additional comments (15)</summary><blockquote>

<details>
<summary>pkg/merkle/hash.go (3)</summary>

`7-9`: **Good use of a dedicated leaf prefix.**
This clear separation of leaf nodes helps avoid potential collision or ambiguity in hashing different node types.

---

`18-21`: **Straightforward node-hashing approach.**
No functional concerns; this is a neat and consistent way to combine child nodes.

---

`23-26`: **Good leaf-hashing pattern with the prefix.**
This ensures that leaf nodes cannot collide with internal node concatenations, which is critical for Merkle tree security.

</details>
<details>
<summary>pkg/merkle/tree_test.go (9)</summary>

`10-18`: **Meaningful empty-tree test case.**
Properly ensures that constructing an empty Merkle tree returns an error as expected.

---

`20-81`: **Comprehensive balanced-tree scenarios.**
These tests methodically verify that the tree’s depth, leaf count, and array size are computed accurately for powers-of-two element counts.

---

`83-114`: **Robust unbalanced-tree testing.**
Validates correctness when the element count isn’t a power of two. This coverage prevents overlooking off-by-one or indexing errors.

---

`116-172`: **Large-tree stress tests.**
These scenarios provide excellent coverage for performance and correctness under higher loads. Sampling leaves is a practical approach to keep tests efficient.

---

`174-196`: **Duplicate elements test.**
Well-handled test verifying that identical leaves yield identical hashes, while unique elements differ. Great for ensuring collision correctness.

---

`198-216`: **Validation of large byte-slice elements.**
Ensures the process scales to significant input sizes and the final root remains correct.

---

`218-239`: **Empty-element handling.**
Shows that empty leaves still result in a valid hash, which is critical for flexible usage scenarios.

---

`241-285`: **Manual verification of internal nodes.**
Covers indexing logic thoroughly in a small, unbalanced tree. Excellent approach for verifying complex tree structures.

---

`286-332`: **Helper function for unbalanced structure integrity.**
This function effectively checks parent-child relationships, ensuring no corner cases are missed.

</details>
<details>
<summary>pkg/merkle/proof_indices.go (2)</summary>

`9-41`: **Efficient multi-proof generation with early validations.**
Duplicates and out-of-range checks guard correctness by ensuring that proof generation starts only with valid indices.

---

`214-247`: **Robust proof indices validation.**
Ensures the indices match the elements and fall within valid bounds, detecting duplicates early. This is crucial for the multi-proof’s reliability.

</details>
<details>
<summary>pkg/merkle/proof.go (1)</summary>

`98-132`: **Good coverage in `validateProofBase`.**

This function thoroughly checks for nil roots, missing elements, invalid element counts, and partial proof decommitments. It effectively prevents many common proof pitfalls.

</details>

</blockquote></details>

</details>

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state: COMMENTED
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submitted_at: 2025-04-11T22:10:38Z
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body: **Actionable comments posted: 1**

<details>
<summary>🧹 Nitpick comments (11)</summary><blockquote>

<details>
<summary>pkg/merkle/proof_indices.go (2)</summary><blockquote>

`9-16`: **Check negative indices in a dedicated error branch**  
While `hasOutOfBounds` likely covers negative indices by extension, consider adding an explicit negative-index check to provide clearer error messages for invalid inputs.

---

`57-185`: **Consider refactoring `getRootIndices`**  
This function is lengthy, with multiple index variables. Extracting chunks of logic (e.g., sibling checks, proof consumption) into helper functions or adding in-code comments can improve long-term maintenance and reduce confusion.

</blockquote></details>
<details>
<summary>pkg/merkle/proof_sequential.go (2)</summary><blockquote>

`7-18`: **Check for negative or zero `count`**  
Lines 11-12 only validate that `startingIndex+count <= leafCount`. If a caller mistakenly passes a negative or zero value for `count`, the error might be cryptic. Consider adding an explicit check for `count <= 0` to fail fast.

---

`57-168`: **Large function complexity**  
The nested index manipulations can be tricky to follow. Splitting out repeated logic (e.g., sibling detection, proof consumption) might help reduce complexity for future maintainers.

</blockquote></details>
<details>
<summary>pkg/merkle/tree.go (2)</summary><blockquote>

`9-16`: **Consider a custom node type**  
Storing raw `[][]byte` is flexible yet can hinder readability. A small wrapper type—like `type Node struct { Hash []byte }`—can make it clearer where each element is used as a node.

---

`120-155`: **Edge case for a single leaf**  
`getDepth(1)` returns 0, which is valid unless your application expects a baseline depth of 1. You might clarify in docs or error-check if single-element trees pose any special constraints.

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (5)</summary><blockquote>

`19-29`: **Consider removing or consolidating unused error constants.**

Some of these declared constants (e.g., `ErrProofInvalidElementCount`, `ErrProofInvalidRange`, etc.) do not appear to be used, while other errors are declared inside the functions using `fmt.Errorf(...)`. For clarity, either remove the unused constants or standardize their usage throughout the file.

---

`118-135`: **Rename "leafs" to "leaves" for clarity.**

For readability and consistency, consider renaming the `leafs` variable to `leaves`, which is more standard English usage.

```diff
- root := HashLeaf(proof.Elements[0])
...
- leafs := make([][]byte, len(proof.Elements))
- for i, element := range proof.Elements {
-   leafs[i] = HashLeaf(element)
- }
+ leaves := make([][]byte, len(proof.Elements))
+ for i, element := range proof.Elements {
+   leaves[i] = HashLeaf(element)
+ }
  ...
- root = combineLeaves(leafs)
+ root = combineLeaves(leaves)
```

---

`150-184`: **Standardize error handling for proof validation.**

This block uses `fmt.Errorf(...)` to create new errors, whereas multiple proof-related error constants are declared globally. For consistency, either replace these inline errors with the existing constants (e.g., `ErrProofNoElements`, etc.) or remove the unused constants.

---

`206-235`: **Consider parallelizing leaf combination for large inputs.**

In `combineLeaves`, the algorithm sequentially calculates parent hashes. If you anticipate very large input sets and need higher performance, parallelizing this level-building process (e.g., using goroutines) may significantly reduce computation time. This is optional and depends on performance requirements.

---

`237-244`: **Evaluate whether buffer cloning is necessary.**

`cloneBuffer` duplicates each byte slice. If you can guarantee no modifications to the original slice after this function call, skipping the clone operation would improve performance and reduce allocations.

</blockquote></details>

</blockquote></details>

<details>
<summary>📜 Review details</summary>

**Configuration used: CodeRabbit UI**
**Review profile: CHILL**
**Plan: Pro**

<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between 5eb4a3517bbcd467c63bae1c1f18c3f373be0538 and dcc177c63fb7b3d66f303b5152c6742410a7b686.

</details>

<details>
<summary>📒 Files selected for processing (5)</summary>

* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/proof_indices.go` (1 hunks)
* `pkg/merkle/proof_sequential.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)
* `pkg/merkle/tree_test.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (1)</summary>

* pkg/merkle/tree_test.go

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧬 Code Graph Analysis (3)</summary>

<details>
<summary>pkg/merkle/proof_indices.go (3)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary>

* `MerkleTree` (10-16)

</details>
<details>
<summary>pkg/merkle/proof.go (1)</summary>

* `MultiProof` (10-17)

</details>
<details>
<summary>pkg/merkle/hash.go (1)</summary>

* `HashNode` (19-21)

</details>

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (1)</summary><blockquote>

<details>
<summary>pkg/merkle/hash.go (2)</summary>

* `HashLeaf` (24-26)
* `HashNode` (19-21)

</details>

</blockquote></details>
<details>
<summary>pkg/merkle/proof_sequential.go (3)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary>

* `MerkleTree` (10-16)

</details>
<details>
<summary>pkg/merkle/proof.go (1)</summary>

* `MultiProof` (10-17)

</details>
<details>
<summary>pkg/merkle/hash.go (1)</summary>

* `HashNode` (19-21)

</details>

</blockquote></details>

</details>

</details>

<details>
<summary>⏰ Context from checks skipped due to timeout of 90000ms (5)</summary>

* GitHub Check: Push Docker Images to GitHub Packages (xmtpd-cli)
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* GitHub Check: Test (Node)
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</details>

<details>
<summary>🔇 Additional comments (7)</summary><blockquote>

<details>
<summary>pkg/merkle/proof_indices.go (2)</summary>

`30-38`: **Sorting modifies the proof indices**  
Because the proof is returned with sorted indices, the user’s original index ordering will differ. If the intended behavior is to preserve the exact ordering, you might keep a separate unsorted copy or document that the proof uses sorted indices.

---

`189-220`: **Thorough validation**  
The index validation logic (checking for out-of-range, duplicates, etc.) is solid and ensures data integrity for multi-proof verification.

</details>
<details>
<summary>pkg/merkle/proof_sequential.go (2)</summary>

`30-35`: **Verifying array boundaries**  
This loop retrieves `m.elements[startingIndex + i]`. Although line 11 covers the range, it’s prudent in critical systems to re-validate in the loop or add an explanatory comment ensuring that `i` won’t exceed bounds.

---

`170-208`: **Neat sequential validation**  
The checks for sequential coherence (`StartingIndex + i`) are logical, and optional index validation is well thought out.

</details>
<details>
<summary>pkg/merkle/tree.go (2)</summary>

`18-38`: **Tree initialization is straightforward**  
Instantiating leaves, building the tree, and storing the root is logically consistent and meets common Merkle tree expectations.

---

`65-118`: **Confirm partial coverage handling**  
The loop skips building certain parent nodes when `leftChildIndex > upperBound`. This is often correct for Merkle trees with unpopulated leaves, but please confirm it aligns with your usage requirements (e.g., no unexpected nil parents).

</details>
<details>
<summary>pkg/merkle/proof.go (1)</summary>

`65-72`: **Ensure out-of-bounds protection for 'leafCount + idx'.**

When marking known leaves, the code does not guard against cases in which `leafCount + idx` might exceed the array bounds of `tree`. Relying on the caller to validate the indices can be risky because a single invalid index can panic the entire function. Consider a protective check or an explicit error if the sum exceeds the slice length.

</details>

</blockquote></details>

</details>

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author_association: CONTRIBUTOR
submitted_at: 2025-04-11T22:55:52Z
user: login: coderabbitai[bot]
body: **Actionable comments posted: 0**

<details>
<summary>♻️ Duplicate comments (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`139-153`: _🛠️ Refactor suggestion_

**Check for overflow after bit-smearing**  
`roundUpToPowerOf2` can overflow if `n` is near the maximum of `uint32`. Currently, the code wraps around without explicit checks. If large inputs are within scope, consider verifying that `n + 1` does not exceed `^uint32(0)` to avoid unexpected wraparounds.  

```diff
+	// If rounding causes overflow, cap at ^uint32(0)
+	if n == ^uint32(0) {
+		return n
+	}
```

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (1)</summary><blockquote>

`53-57`: _⚠️ Potential issue_

**Validate indices for duplicates/out-of-bounds**  
Sorting the indices is good, but you never explicitly call `hasDuplicates` or `hasOutOfBounds` here. This can lead to panics if upstream validations are skipped. For a robust library, consider verifying within `generateProof` itself or ensuring upstream calls always handle it.  

```diff
// Validate indices before sorting.
+if hasDuplicates(indices) {
+	return MultiProof{}, ErrProofDuplicateIndices
+}
+if hasOutOfBounds(indices, elementCount) {
+	return MultiProof{}, ErrProofIndicesOutOfBounds
+}

sort.Ints(idxs)
```

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (9)</summary><blockquote>

<details>
<summary>pkg/merkle/proof_sequential.go (3)</summary><blockquote>

`7-9`: **Validate error message for out-of-range inputs**  
The check correctly returns `ErrProofInvalidRange` when the multi-proof range is out of bounds. However, consider clarifying the returned error message or adding contextual information (e.g., the actual invalid range). This can help callers diagnose issues more easily without diving into deep logs or stack traces.

---

`16-19`: **Add index-validation checks before proof generation**  
Although this function enforces a valid range, it might be safer to check for unwanted duplicate indices or any potential inconsistencies (similar to how other proofs guard against them). For sequential proofs, duplicates are less likely, but an extra check would improve robustness.

---

`26-33`: **Avoid depending on `proof.Indices[0]`**  
Here, you set `StartingIndex` to `proof.Indices[0]`. For sequential use cases, it's logically equivalent to `startingIndex`, so consider assigning it directly from the function parameter. Doing so clarifies the flow without assuming a sorted or unmodified indices array in `generateProof`.  

```diff
- StartingIndex: proof.Indices[0],
+ StartingIndex: startingIndex,
```

</blockquote></details>
<details>
<summary>pkg/merkle/tree.go (3)</summary><blockquote>

`19-21`: **Explicitly handle extremely large inputs**  
The error for empty elements is helpful. However, for very large arrays, allocating a `2N` slice in `buildTree` (called below) can lead to excessive memory usage or potential overflows on 32-bit platforms. If extremely large Merkle trees are within scope, consider safe-guarding with upper bounds or memory-usage checks.

---

`75-88`: **Document the indexing scheme**  
The code uses a well-known 1-indexed layout for the internal nodes and leaves. While the in-code comments are good, adding a short note regarding how `leafCount << 1` and the `lowerBound/upperBound` references map to this scheme could make the logic easier to maintain and debug.

---

`110-113`: **Consider hashing child nodes**  
When only the left child exists, the node inherits its hash. This approach is correct but may unexpectedly cause single-sided trees for incomplete levels. If partial coverage is acceptable, leave as is. Otherwise, consider a more explicit approach (e.g., hashing the solitary child with an empty node).

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (3)</summary><blockquote>

`73-97`: **Verify sibling existence**  
The current logic appends non-nil sibling nodes to `proofs`. If for some reason a sibling is unexpectedly nil, it silently skips. While it may be valid to skip empty siblings, consider logging or returning an error to help detect erroneous or incomplete trees.

---

`121-138`: **Avoid single-element fallback if verifying multiple leaves**  
When `len(proof.Elements)` equals `proof.ElementCount`, the code recalculates the root purely by combining leaves in memory. This is correct, but there's a separate code path for single-element trees. Combining them might simplify the logic, ensuring uniformity.

---

`153-191`: **Add a nil-check for `proof`**  
`validateProofBase` already checks if `proof` is nil, but if future code modifies or bypasses this function, we risk a panic. Consider using a public entry function or pattern ensuring that all `verifyProof` calls pass through `validateProofBase` to avoid future regressions.

</blockquote></details>

</blockquote></details>

<details>
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<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between a25224580b8652a84e0c111459b1b587accae5cd and a4b966f9bc588f4fdf713419e87062d539e514b7.

</details>

<details>
<summary>📒 Files selected for processing (5)</summary>

* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/proof_indices.go` (1 hunks)
* `pkg/merkle/proof_sequential.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)
* `pkg/merkle/tree_test.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (2)</summary>

* pkg/merkle/proof_indices.go
* pkg/merkle/tree_test.go

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧬 Code Graph Analysis (3)</summary>

<details>
<summary>pkg/merkle/proof_sequential.go (3)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary>

* `MerkleTree` (9-15)

</details>
<details>
<summary>pkg/merkle/proof.go (3)</summary>

* `MultiProof` (10-17)
* `ErrProofInvalidRange` (26-26)
* `ErrProofInvalidStartingIndex` (24-24)

</details>
<details>
<summary>pkg/merkle/hash.go (1)</summary>

* `HashNode` (19-21)

</details>

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (2)</summary>

* `GetLeftChild` (156-158)
* `GetRightChild` (161-163)

</details>
<details>
<summary>pkg/merkle/hash.go (2)</summary>

* `HashLeaf` (24-26)
* `HashNode` (19-21)

</details>

</blockquote></details>
<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

<details>
<summary>pkg/merkle/hash.go (2)</summary>

* `HashLeaf` (24-26)
* `HashNode` (19-21)

</details>

</blockquote></details>

</details>

</details>

<details>
<summary>⏰ Context from checks skipped due to timeout of 90000ms (5)</summary>

* GitHub Check: Push Docker Images to GitHub Packages (xmtpd-cli)
* GitHub Check: Test (Node)
* GitHub Check: Push Docker Images to GitHub Packages (xmtpd)
* GitHub Check: Upgrade Tests
* GitHub Check: Code Review

</details>

<details>
<summary>🔇 Additional comments (3)</summary><blockquote>

<details>
<summary>pkg/merkle/proof_sequential.go (2)</summary>

`46-157`: **Ensure termination in `getRootSequentially`**  
The infinite `for {}` loop terminates when `nodeIndex == 1`, but intermediate conditions could theoretically lead to a scenario where `nodeIndex` or `lowestTreeIndex` never gets updated sufficiently. While this logic likely works as intended with valid proofs, consider documenting potential edge cases or adding checks for guaranteed progress to reassure maintainers that it cannot hang.

---

`159-175`: **Consistent argument validation**  
`validateProofSequential` partially duplicates the out-of-range checks found in `GenerateMultiProofSequential`. This redundancy is acceptable for security, but please confirm both are always in sync to avoid gaps if one is updated without the other.

</details>
<details>
<summary>pkg/merkle/tree.go (1)</summary>

`120-132`: **Leverage bit operations for depth**  
`getDepth` efficiently uses `bits.Len32`. This is good for performance. If there's an edge case where `elementCount` is extremely large (≥ 2^31), keep in mind that casting to `uint32` truncates it. Document or restrict usage if you expect bigger sizes.

</details>

</blockquote></details>

</details>

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submitted_at: 2025-04-11T22:56:24Z
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body: **Actionable comments posted: 2**

<details>
<summary>♻️ Duplicate comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (1)</summary><blockquote>

`54-57`: _⚠️ Potential issue_

**Add duplicate or out-of-bounds check for indices ().**

Just as previously noted in past comments, sorting the indices (line 56) without validating them can lead to runtime panics when referencing `leafCount+idx` if `idx` is greater or equal to `leafCount` or if duplicates exist. Consider integrating `hasDuplicates(...)` and `hasOutOfBounds(...)` here, or ensure they are invoked upstream.  


```diff
 idxs := make([]int, len(indices))
 copy(idxs, indices)
+if hasDuplicates(idxs) {
+	return MultiProof{}, ErrProofDuplicateIndices
+}
+if hasOutOfBounds(idxs, elementCount) {
+	return MultiProof{}, ErrProofIndicesOutOfBounds
+}
 sort.Ints(idxs)
```

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/proof_sequential.go (1)</summary><blockquote>

`46-157`: **Refactor or document the complexity of `getRootSequentially`.**

The function’s circular queue logic is quite intricate, risking confusion or maintenance errors. Splitting it into smaller, well-named helper functions (e.g., handling sibling merges, verifying remaining proofs) can improve readability and make it easier to debug.

</blockquote></details>

</blockquote></details>

<details>
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<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between a4b966f9bc588f4fdf713419e87062d539e514b7 and 3e94d04df0ac6dd38c7ea91dcdc98585f77201fd.

</details>

<details>
<summary>📒 Files selected for processing (5)</summary>

* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/proof_indices.go` (1 hunks)
* `pkg/merkle/proof_sequential.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)
* `pkg/merkle/tree_test.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (3)</summary>

* pkg/merkle/tree_test.go
* pkg/merkle/proof_indices.go
* pkg/merkle/tree.go

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧬 Code Graph Analysis (2)</summary>

<details>
<summary>pkg/merkle/proof_sequential.go (3)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary>

* `MerkleTree` (9-15)

</details>
<details>
<summary>pkg/merkle/proof.go (3)</summary>

* `MultiProof` (10-17)
* `ErrProofInvalidRange` (26-26)
* `ErrProofInvalidStartingIndex` (24-24)

</details>
<details>
<summary>pkg/merkle/hash.go (1)</summary>

* `HashNode` (19-21)

</details>

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (2)</summary>

* `GetLeftChild` (156-158)
* `GetRightChild` (161-163)

</details>
<details>
<summary>pkg/merkle/hash.go (2)</summary>

* `HashLeaf` (24-26)
* `HashNode` (19-21)

</details>

</blockquote></details>

</details>

</details>

<details>
<summary>⏰ Context from checks skipped due to timeout of 90000ms (4)</summary>

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</details>

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author_association: CONTRIBUTOR
submitted_at: 2025-04-11T23:00:10Z
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submitted_at: 2025-04-11T23:31:52Z
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body: **Actionable comments posted: 0**

<details>
<summary>♻️ Duplicate comments (4)</summary><blockquote>

<details>
<summary>pkg/merkle/proof_sequential.go (1)</summary><blockquote>

`7-8`: **Validate `count` is strictly positive.**

This check ensures that generating a proof with a zero or negative count doesn’t return an empty or invalid proof. An explicit `count <= 0` check would safeguard against undesired behavior.

</blockquote></details>
<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`140-140`: **Beware of integer overflow in `GetLeafCount`.**

Casting `roundUpToPowerOf2(uint32(elementCount))` to `int` for large `elementCount` can risk overflow on some platforms. This issue has been raised before and may still need addressing if extremely large trees are expected.

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

`73-75`: **Validate index bounds when marking nodes as known.**

Assigning `known[leafCount+idx] = true` can go out-of-bounds if any `idx >= leafCount`. Confirm that indices are genuinely within `[0, leafCount)` or add checks here as well.

---

`53-57`: _🛠️ Refactor suggestion_

**Add out-of-bounds and duplicate index checks before sorting.**

Although the code sorts the indices, it does not call `hasOutOfBounds` or `hasDuplicates` here. If `idx >= leafCount` or duplicates exist, later references (e.g., `known[leafCount+idx]`) may panic or produce an incorrect proof. Integrating these checks would further harden the proof generation.


```diff
 idxs := make([]int, len(indices))
 copy(idxs, indices)
+if hasOutOfBounds(idxs, elementCount) {
+	return MultiProof{}, ErrProofIndicesOutOfBounds
+}
+if hasDuplicates(idxs) {
+	return MultiProof{}, ErrProofDuplicateIndices
+}
 sort.Ints(idxs)
```

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (3)</summary><blockquote>

<details>
<summary>pkg/merkle/proof_sequential.go (1)</summary><blockquote>

`47-158`: **Consider splitting up or documenting the loop logic to enhance readability.**

The ring-buffer approach for computing the root is highly involved and can be difficult to follow, especially with shifting bounds (`lowestTreeIndex` and `upperBound`). Breaking out these operations or adding inline documentation would improve maintainability and reduce the chance of off-by-one errors.

</blockquote></details>
<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`91-114`: **Clarify shifting logic around `lowerBound` and `upperBound`.**

Within the loop that re-hashes internal nodes, the shifting of bounds can be confusing. Consider adding detailed comments or restructuring to better highlight when and why the boundary variables are updated. This will help future maintainers understand how the tree levels are being traversed.

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (1)</summary><blockquote>

`126-134`: **Constructing a new Merkle tree for entire proof verification might be costly.**

When `len(proof.Elements) == proof.ElementCount`, building a separate Merkle tree is correct but may be expensive for large datasets. As a future enhancement, you might consider a specialized check that reuses the existing partial calculations.

</blockquote></details>

</blockquote></details>

<details>
<summary>📜 Review details</summary>

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<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between 3e94d04df0ac6dd38c7ea91dcdc98585f77201fd and 7cdbc70ff5956c6f11355c91fad10f933ddbfdb1.

</details>

<details>
<summary>📒 Files selected for processing (4)</summary>

* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/proof_indices.go` (1 hunks)
* `pkg/merkle/proof_sequential.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (1)</summary>

* pkg/merkle/proof_indices.go

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧬 Code Graph Analysis (2)</summary>

<details>
<summary>pkg/merkle/proof_sequential.go (3)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary>

* `MerkleTree` (9-15)

</details>
<details>
<summary>pkg/merkle/proof.go (3)</summary>

* `MultiProof` (10-17)
* `ErrProofInvalidRange` (26-26)
* `ErrProofInvalidStartingIndex` (24-24)

</details>
<details>
<summary>pkg/merkle/hash.go (1)</summary>

* `HashNode` (19-21)

</details>

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (3)</summary>

* `GetLeftChild` (160-162)
* `GetRightChild` (165-167)
* `NewMerkleTree` (18-37)

</details>
<details>
<summary>pkg/merkle/hash.go (1)</summary>

* `HashLeaf` (24-26)

</details>

</blockquote></details>

</details>

</details>

<details>
<summary>⏰ Context from checks skipped due to timeout of 90000ms (5)</summary>

* GitHub Check: Push Docker Images to GitHub Packages (xmtpd-cli)
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* GitHub Check: Test (Node)
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</details>

<details>
<summary>🔇 Additional comments (3)</summary><blockquote>

<details>
<summary>pkg/merkle/proof_sequential.go (1)</summary>

`160-175`: **Validation logic appears consistent.**

The additional checks for `StartingIndex` and combined range align with the base proof validation approach. The method cleanly prevents out-of-bounds proofs for sequential checks.

</details>
<details>
<summary>pkg/merkle/tree.go (1)</summary>

`17-37`: **Constructor logic looks good.**

Handling of empty `elements` and assigning `tree[1]` as the root ensures the tree is built correctly in both single- and multiple-element cases.

</details>
<details>
<summary>pkg/merkle/proof.go (1)</summary>

`112-148`: **Overall verification flow looks robust.**

The single-element and partial-proof logic provide comprehensive coverage, and leveraging common helper functions keeps the code organized.

</details>

</blockquote></details>

</details>

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submitted_at: 2025-04-11T23:33:17Z
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body: **Actionable comments posted: 0**

<details>
<summary>♻️ Duplicate comments (2)</summary><blockquote>

<details>
<summary>pkg/merkle/proof_sequential.go (1)</summary><blockquote>

`7-9`: **Validate positive `count`.**

You only check the range `startingIndex+count > m.leafCount`, but do not explicitly enforce that `count` must be positive. Negative or zero counts can produce empty or invalid proofs. This repeats a suggestion from previous reviews.

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (1)</summary><blockquote>

`55-59`: **Add duplicate/bounds checks before sorting indices.**

Sorting `idxs` without validating for duplicates or out-of-bounds can lead to panics (e.g., `leafCount+idx` out of slice range). This repeats a past review comment that recommended calling validation helpers (`hasDuplicates`, `hasOutOfBounds`) prior to sorting.

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`143-157`: **Consider handling overflow in `roundUpToPowerOf2`.**

Adding `n + 1` at line 156 can overflow if `n` is near `math.MaxUint32`. While uncommon, consider an overflow guard or documentation clarifying potential limits on tree sizes.

</blockquote></details>

</blockquote></details>

<details>
<summary>📜 Review details</summary>

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<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between 7cdbc70ff5956c6f11355c91fad10f933ddbfdb1 and 813bceab130a7386ddc03233221d8fb54c7d67d1.

</details>

<details>
<summary>📒 Files selected for processing (4)</summary>

* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/proof_indices.go` (1 hunks)
* `pkg/merkle/proof_sequential.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (1)</summary>

* pkg/merkle/proof_indices.go

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧬 Code Graph Analysis (2)</summary>

<details>
<summary>pkg/merkle/proof_sequential.go (3)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary>

* `MerkleTree` (9-15)

</details>
<details>
<summary>pkg/merkle/proof.go (3)</summary>

* `MultiProof` (10-17)
* `ErrProofInvalidRange` (28-28)
* `ErrProofInvalidStartingIndex` (26-26)

</details>
<details>
<summary>pkg/merkle/hash.go (1)</summary>

* `HashNode` (19-21)

</details>

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (3)</summary>

* `GetLeftChild` (160-162)
* `GetRightChild` (165-167)
* `NewMerkleTree` (18-37)

</details>
<details>
<summary>pkg/merkle/hash.go (1)</summary>

* `HashLeaf` (24-26)

</details>

</blockquote></details>

</details>

</details>

<details>
<summary>⏰ Context from checks skipped due to timeout of 90000ms (5)</summary>

* GitHub Check: Push Docker Images to GitHub Packages (xmtpd-cli)
* GitHub Check: Push Docker Images to GitHub Packages (xmtpd)
* GitHub Check: Test (Node)
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</details>

<details>
<summary>🔇 Additional comments (6)</summary><blockquote>

<details>
<summary>pkg/merkle/proof_sequential.go (2)</summary>

`84-158`: **Ensure the loop always terminates.**

The infinite `for {}` loop in `getRootSequentially` relies on reaching `nodeIndex == 1` or exhausting proofs to exit. Under unexpected conditions (e.g., mismatched tree indices or insufficient proofs), you might never break out, risking an infinite loop.  

Would you like to run a randomized stress test, forcing pathological scenarios (e.g., partial proofs with misaligned indices) to confirm we always reach a return statement?

---

`160-175`: **Good sequential validation logic.**

Your checks for `proof.StartingIndex < 0` and `proof.StartingIndex+len(proof.Elements) > proof.ElementCount` handle sequential proof ranges well, and the method is succinct.

</details>
<details>
<summary>pkg/merkle/tree.go (2)</summary>

`18-37`: **Constructor looks good.**

The checks for non-empty elements, hashing each leaf, and returning a populated `MerkleTree` appear correct with no obvious issues.

---

`74-117`: **Verify parent assignment in `buildTree`.**

When iterating internal nodes backward, the logic for hashing children or copying the left child might skip certain parent nodes if leaves exist only beyond `upperBound`. There’s a risk of partially built parent levels if leaf distribution is uneven.  

Consider adding a test with uneven leaf sets to verify that final parents and root indices are correctly formed.

</details>
<details>
<summary>pkg/merkle/proof.go (2)</summary>

`114-150`: **Well-structured proof verification.**

The single-element fast path, fallback to rebuilding the tree for complete sets, and partial proof root calculation via `getRoot` is clean and logically consistent.

---

`152-189`: **Robust base proof validation.**

Your checks thoroughly cover nil proofs, missing roots, missing elements, and incomplete proofs, which helps prevent runtime errors.

</details>

</blockquote></details>

</details>

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submitted_at: 2025-04-11T23:44:08Z
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submitted_at: 2025-04-12T17:25:51Z
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<details>
<summary>🧹 Nitpick comments (3)</summary><blockquote>

<details>
<summary>pkg/merkle/proof_indices.go (2)</summary><blockquote>

`9-16`: **Clarify sorted vs. original ordering of elements**  
This code returns `Elements` sorted by the internally sorted `Indices`, which may differ from the caller’s original order of `indices`. This is correct for many multi-proof scenarios, but if a specific ordering is needed in the final proof, consider either preserving the original order or documenting that the output is sorted.

---

`44-173`: **Consider splitting large function into smaller helpers**  
The `getRootIndices` function is quite large, handling multiple stages of proof reconstruction, index manipulation, sibling checks, etc. Splitting it into smaller functions (e.g., a helper for reading the next node, a helper for merging hashes, etc.) could make the code easier to read and maintain.

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (1)</summary><blockquote>

`49-53`: **Avoid repeated sorting of indices**  
Currently, `generateProof` (lines 50–52) and `hasDuplicates` (lines 208–219) both sort the indices slice. This repeated sort adds minor overhead. If you pass a pre-sorted slice to `hasDuplicates`, you can avoid sorting again.  

Apply a small diff in `hasDuplicates` to remove the second sort if you guarantee that the input slice is already sorted:

```diff
 func hasDuplicates(indices []int) bool {
-	sortedIndices := make([]int, len(indices))
-	copy(sortedIndices, indices)
-	sort.Ints(sortedIndices)
-	for i := 1; i < len(sortedIndices); i++ {
-		if sortedIndices[i] == sortedIndices[i-1] {
+	for i := 1; i < len(indices); i++ {
+		if indices[i] == indices[i-1] {
			return true
		}
	}
	return false
}
```


Also applies to: 208-219

</blockquote></details>

</blockquote></details>

<details>
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</details>

<details>
<summary>📒 Files selected for processing (3)</summary>

* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/proof_indices.go` (1 hunks)
* `pkg/merkle/proof_sequential.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (1)</summary>

* pkg/merkle/proof_sequential.go

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧬 Code Graph Analysis (2)</summary>

<details>
<summary>pkg/merkle/proof_indices.go (3)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary>

* `MerkleTree` (9-15)

</details>
<details>
<summary>pkg/merkle/proof.go (4)</summary>

* `MultiProof` (10-17)
* `ErrProofInvalidElementCount` (25-25)
* `ErrProofIndicesOutOfBounds` (23-23)
* `ErrProofDuplicateIndices` (22-22)

</details>
<details>
<summary>pkg/merkle/hash.go (1)</summary>

* `HashNode` (19-21)

</details>

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (3)</summary>

* `GetLeftChild` (160-162)
* `GetRightChild` (165-167)
* `NewMerkleTree` (18-37)

</details>
<details>
<summary>pkg/merkle/hash.go (1)</summary>

* `HashLeaf` (24-26)

</details>

</blockquote></details>

</details>

</details>

<details>
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</details>

<details>
<summary>🔇 Additional comments (2)</summary><blockquote>

<details>
<summary>pkg/merkle/proof_indices.go (1)</summary>

`31-42`: **Multi-proof verification approach looks solid**  
Delegating the actual proof verification to the `verifyProof` helper is clean and consistent. The implementation is straightforward and appears correct.

</details>
<details>
<summary>pkg/merkle/proof.go (1)</summary>

`114-150`: **Proof verification logic is consistent**  
The function performs common-sense checks: handling single-element trees, verifying the entire set of elements if given, or rebuilding the root from partial data. It cleanly delegates the final root calculation to the provided function.

</details>

</blockquote></details>

</details>

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submitted_at: 2025-04-12T17:26:54Z
user: login: coderabbitai[bot]
body: **Actionable comments posted: 3**

<details>
<summary>♻️ Duplicate comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`146-160`: _🛠️ Refactor suggestion_

**Address potential overflow in `roundUpToPowerOf2`.**
If `n` is close to `math.MaxUint32`, `n + 1` can wrap around to `0`. While unlikely in practical usage, adding a boundary check helps ensure correctness in extreme edge cases.

```diff
 if n == ^uint32(0) {
     // choose an approach, e.g.:
     return n
 }
 return n + 1
```

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (3)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (2)</summary><blockquote>

`16-19`: **Ensure error variables are documented if they can be returned externally.**
These error variables are well-defined, but it would be helpful to document when each error is returned. This clarifies usage for other developers.

---

`28-31`: **Acknowledge the reasons for returning lightweight error wrappers.**
Using informative error variables is good. Consider prefixing error messages in the error returns to provide even more context in part of the normal error chain. For example: `"makeTree: %w"`.

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (1)</summary><blockquote>

`114-150`: **Improve single-element logic and partial proofs coverage.**
While the code handles single-element trees separately, consider adding an assertion if multiple indices are provided for `elementCount == 1` to detect potential misuse. For partial proofs, ensure that all edge cases (e.g., partially known single-element usage) are covered by tests.

</blockquote></details>

</blockquote></details>

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</details>

<details>
<summary>📒 Files selected for processing (3)</summary>

* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)
* `pkg/merkle/tree_test.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (1)</summary>

* pkg/merkle/tree_test.go

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧬 Code Graph Analysis (1)</summary>

<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (3)</summary>

* `GetLeftChild` (163-165)
* `GetRightChild` (168-170)
* `NewMerkleTree` (22-39)

</details>
<details>
<summary>pkg/merkle/hash.go (1)</summary>

* `HashLeaf` (24-26)

</details>

</blockquote></details>

</details>

</details>

<details>
<summary>🔇 Additional comments (2)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (2)</summary>

`87-101`: **Clarify handling when both children are known.**
Here, a proof segment is only added if exactly one child is known. If both children are known, no sibling is added to `proofs`. Confirm this is intentional behavior. If both children are valid leaves, you may still need to account for their sibling data. Otherwise, document why it isn't needed.

---

`191-205`: **Confirm that `validateIndices` usage aligns with downstream assumptions.**
`validateIndices` checks duplicates and out-of-bounds for `[0, elementCount)`, but the proof logic later assumes `elementCount <= leafCount`. Consider either:
1. Checking `elementCount <= leafCount` here as well, or
2. Explicitly documenting that `elementCount` must not exceed the number of leaves.

</details>

</blockquote></details>

</details>

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<details>
<summary>♻️ Duplicate comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (1)</summary><blockquote>

`124-133`: _⚠️ Potential issue_

**Missing safeguard against elementCount > leafCount causes potential out-of-bounds access.**  
This repeats a previously noted concern: if `elementCount` exceeds `leafCount`, index values that pass `validateIndices` might still be valid in the range `[0, elementCount)` but become invalid for `leafCount + idx` (potentially exceeding the `known` slice length).  
You should explicitly ensure `elementCount <= leafCount` before this loop, or handle the mismatch with an error.  

```diff
+   if elementCount > leafCount {
+       return MultiProof{}, fmt.Errorf("elementCount (%d) > leafCount (%d)", elementCount, leafCount)
+   }
    for _, idx := range idxs {
        known[leafCount+idx] = true
    }
```

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (2)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

`205-334`: **Consider splitting or documenting the complex logic in `getRoot`.**  
`getRoot` performs a large set of operations, including sorted pairing, checking sibling nodes, and building partial hashes. While it may be correct, it could benefit from extra inline comments or extraction of subroutines to improve readability and maintainability.

---

`1-432`: **Add or reference a thorough, randomized stress test.**  
Given that Merkle trees and proofs can fail under edge or large-scale scenarios, a stress test that continuously generates random trees and requests proofs would be helpful to ensure no hidden panics or index misalignments occur. Please let me know if you’d like assistance creating such a test harness.

</blockquote></details>

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<details>
<summary>📒 Files selected for processing (1)</summary>

* `pkg/merkle/proof.go` (1 hunks)

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<details>
<summary>🔇 Additional comments (3)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (3)</summary>

`1-31`: **Structs and error definitions look solid.**  
No immediate issues found with the `MultiProof` struct or error variables. The errors are well-labeled and self-explanatory.

---

`33-65`: **Correct usage of range checks in sequential proofs.**  
Your logic for checking `startingIndex+count > m.leafCount` and constructing `indices` is clear and consistent. No obvious concerns.

---

`67-88`: **Index-driven proof generation is straightforward.**  
The method carefully delegates core validation and proof composition to `generateProof`. Looks good.

</details>

</blockquote></details>

</details>

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submitted_at: 2025-04-12T20:00:17Z
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state: COMMENTED
author_association: COLLABORATOR
submitted_at: 2025-04-14T10:32:19Z
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<details>
<summary>🧹 Nitpick comments (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (2)</summary><blockquote>

`21-45`: **Consider adding a dedicated stress test for large inputs and continuous proof requests.**

The user “mkysel” requested a stress test that generates random trees, inserts nodes, and verifies proofs for a configurable duration. This helps uncover edge cases like extremely large trees or unusual insertion orders that might trigger bugs or boundary issues.  


I can help by creating a basic stress test script or code snippet that randomly generates elements, builds the tree, and runs proof verifications in a loop. Let me know if you'd like me to open a new issue or provide an example test.

---

`68-77`: **Align the documentation with the actual indexing.**

The doc comments mention a 1-indexed layout with leaves at indexes N+1 to 2N-1, but the code places leaves at [leafCount..(leafCount+len(leaves)-1)]. Update the doc comments or adjust the indexing logic to avoid confusion.

</blockquote></details>

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</details>

<details>
<summary>📒 Files selected for processing (3)</summary>

* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)
* `pkg/merkle/tree_test.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (2)</summary>

* pkg/merkle/tree_test.go
* pkg/merkle/proof.go

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<details>
<summary>🔇 Additional comments (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (2)</summary>

`47-65`: **Getters are clear and concise.**

These trivial getter methods improve encapsulation by exposing only necessary read-only access to the internal structures without duplicating logic.

---

`100-108`: **Verify the shift of bounds during tree construction.**

When `leftChildIndex > upperBound`, the loop continues, but if `leftChildIndex <= lowerBound`, you shift `lowerBound` and `upperBound` by one level. Ensure this logic correctly handles all leaf and internal node placements, particularly in edge cases with unbalanced or minimal leaves.  

Would you like assistance creating a specialized test or script to confirm that no nodes get skipped or incorrectly assigned?

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submitted_at: 2025-04-14T12:54:20Z
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body: **Actionable comments posted: 1**

<details>
<summary>🧹 Nitpick comments (3)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (3)</summary><blockquote>

`93-100`: **Building a new Merkle tree for full proofs.**

Rebuilding the entire tree when `len(proof.Elements) == proof.LeafCount` is a straightforward approach to verify the root. Though potentially more expensive for large trees, it's clear and correct for verifying a complete set of leaves.

If performance becomes a concern for large full proofs, consider reusing partial structures or ephemeral hashing rather than constructing the entire tree.

---

`118-123`: **Silent error on out-of-bounds might hinder debugging.**

When `computeRoot` detects an index `< 0 || >= elementCount`, it returns `nil` without a descriptive error. This can complicate debugging for downstream callers.  

Return a descriptive error (e.g., `ErrIndicesOutOfBounds`) instead of `nil`, so callers can distinguish invalid indices from other failures.

---

`197-200`: **Minor check is redundant.**

`if nextReadIndex < len(treeIndices) { nextNodeIndex = treeIndices[nextReadIndex] }` is always true since `nextReadIndex` is `(readIndex + 1) % count` and `count` == `len(treeIndices)`. This check can be removed safely to reduce confusion.

```diff
- if nextReadIndex < len(treeIndices) {
-     nextNodeIndex = treeIndices[nextReadIndex]
- }
+ nextNodeIndex = treeIndices[nextReadIndex]
```

</blockquote></details>

</blockquote></details>

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</details>

<details>
<summary>📒 Files selected for processing (1)</summary>

* `pkg/merkle/proof.go` (1 hunks)

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧠 Learnings (1)</summary>

<details>
<summary>pkg/merkle/proof.go (1)</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:0-0
Timestamp: 2025-04-14T12:55:15.436Z
Learning: In Merkle tree implementations, when indices are validated using a function like `validateIndices(indices, elementCount)` which checks that indices are less than the element count, additional bounds checking for accessing tree nodes at `leafCount+idx` is redundant because the element count corresponds to the number of leaf nodes.
```

</details>

</details><details>
<summary>🧬 Code Graph Analysis (1)</summary>

<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (4)</summary>

* `MerkleTree` (9-14)
* `NewMerkleTree` (22-45)
* `GetLeftChild` (171-173)
* `GetRightChild` (176-178)

</details>
<details>
<summary>pkg/merkle/hash.go (2)</summary>

* `HashLeaf` (24-26)
* `HashNode` (19-21)

</details>

</blockquote></details>

</details>

</details>

<details>
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</details>

<details>
<summary>🔇 Additional comments (12)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (12)</summary>

`10-16`: **Struct naming and clarity look good.**

The `MultiProof` struct is well-organized and named clearly, reflecting its purpose for multi-proof data. Good job including fields like `Elements`, `Proofs`, `Root`, etc. This aligns well with typical Merkle proof needs.

---

`39-60`: **Implementation clarity for sequential proofs.**

The `GenerateMultiProofSequential` method is straightforward. After generating indices with `makeIndices`, you construct and validate the proof. Returning `&proof` is a clean approach. This maintains good separation of concerns: index preparation, proof creation, and final validation.

---

`62-79`: **Separate code paths for index-based proofs are well-structured.**

`GenerateMultiProofWithIndices` follows a similar flow as the sequential method but accommodates a custom indices list. This separation further enhances clarity. It’s beneficial to see both approaches share the same proof-making logic in `makeProof`, promoting DRY.

---

`81-90`: **Single-leaf verification is consistent.**

When `proof.LeafCount == 1`, the direct comparison of `proof.Root` with `HashLeaf(proof.Elements[0])` is an elegant short-circuit. This avoids unnecessary overhead in building or recalculating a full Merkle tree.

---

`131-155`: **Index-leaf pairing flow is logical.**

Sorting the `(Index, Leaf)` pairs ensures leaves and indices align for proof calculation. This approach is a neat way to avoid the complexity of parallel sorting. The inline struct usage is concise and readable.

---

`247-259`: **Index generation is intuitive.**

`makeIndices` is simple and does exactly what its name implies. Validating for negative start or non-positive count with `ErrInvalidRange` ensures correct usage. Approved.

---

`261-339`: **`makeProof` logic is methodical and well-structured.**

1. **Index handling**: Creating a copy of indices is good practice to avoid side effects.  
2. **Edge case**: Handling `leafCount == 1` gracefully.  
3. **Known map**: Marking known leaves and collecting siblings is a clean approach.  
4. **Proof array**: Storing siblings in `proofs` fosters simpler merging logic.  

Overall, it effectively addresses partial and single-element trees while returning a consistent `MultiProof`.

---

`341-388`: **Proof validation covers critical checks.**

`validateProof` checks for nil pointers, out-of-bounds elements/indices, mismatch between `Indices` and `Elements`, and partial proofs needing sibling hashes. This thorough approach mitigates many typical Merkle proof pitfalls.

---

`390-409`: **Index validation method is robust.**

By sorting and checking duplicates plus bounding each index, `validateIndices` ensures proofs won’t break with invalid input. This approach is essential to avoid panics later in the codebase.

---

`411-419`: **Duplicate check for sorted array.**

The linear scan in `hasDuplicates` is efficient and clear for a sorted slice. This approach is typical in index-based validations.

---

`421-429`: **Bounds checking synergy with `leafCount`.**

`hasOutOfBounds` complements `validateIndices` to restrict indices to `[0, elementCount)`. As per your stored learnings, additional checks in `makeProof` are redundant since the function ensures correctness.

---

`431-438`: **Byte slice clone to avoid side effects.**

`cloneBuffer` is straightforward and eliminates the risk of shared memory. This is especially helpful in cryptographic contexts where passing references can lead to subtle bugs.

</details>

</blockquote></details>

</details>

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author_association: CONTRIBUTOR
submitted_at: 2025-04-14T12:58:56Z
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state: COMMENTED
author_association: CONTRIBUTOR
submitted_at: 2025-04-14T12:59:00Z
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body: **Actionable comments posted: 0**

<details>
<summary>🧹 Nitpick comments (4)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (4)</summary><blockquote>

`38-61`: **Consider unifying the proof generation logic.**

Both `GenerateMultiProofSequential` (lines 38–61) and `GenerateMultiProofWithIndices` (lines 63–80) internally call `makeProof` and perform similar validations and assignments with slight variations. To avoid duplication and reduce maintenance overhead, consider refactoring them into a shared helper that accepts either an index range or custom indices, and then composes the final proof.

---

`56-58`: **Double-check redundant proof validation.**

After building the proof in `GenerateMultiProofSequential` (line 45) and `GenerateMultiProofWithIndices` (line 65), the function calls `validateProof(&proof)` (lines 56–58 and 75–77). This is also repeated in `VerifyProof`. If the proof is always re-validated at the call site, you could streamline or remove one of the validations to reduce overhead.

---

`103-107`: **Optimize repeated leaf hashing for partial proofs.**

Recomputing leaves (via `makeLeaves(proof.elements)`) in `VerifyProof` (lines 103–107) may add overhead if elements are already hashed elsewhere. If performance is critical, consider allowing pre-hashed leaves or caching the result to avoid duplicative hashing operations.

---

`274-281`: **Check single-element proof design.**

When `leafCount == 1`, the returned `MultiProof` (lines 274–281) includes the tree’s root as the sole proof node. Although functionally correct (the single element is indeed the root), you might alternatively store an empty `proofs` slice to indicate that no Merkle path data is necessary for a single-leaf tree. Consider clarifying this design in your documentation for consistency with typical Merkle representations.

</blockquote></details>

</blockquote></details>

<details>
<summary>📜 Review details</summary>

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<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between d6656390507a208f6aeaf3fe87c5213688758068 and fef7c0ba6e66b5c3634f4ffe135c1900cc648c47.

</details>

<details>
<summary>📒 Files selected for processing (1)</summary>

* `pkg/merkle/proof.go` (1 hunks)

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧠 Learnings (1)</summary>

<details>
<summary>pkg/merkle/proof.go (1)</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:0-0
Timestamp: 2025-04-14T12:55:15.436Z
Learning: In Merkle tree implementations, when indices are validated using a function like `validateIndices(indices, elementCount)` which checks that indices are less than the element count, additional bounds checking for accessing tree nodes at `leafCount+idx` is redundant because the element count corresponds to the number of leaf nodes.
```

</details>

</details><details>
<summary>🧬 Code Graph Analysis (1)</summary>

<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (4)</summary>

* `MerkleTree` (9-14)
* `NewMerkleTree` (22-45)
* `GetLeftChild` (171-173)
* `GetRightChild` (176-178)

</details>
<details>
<summary>pkg/merkle/hash.go (2)</summary>

* `HashLeaf` (24-26)
* `HashNode` (19-21)

</details>

</blockquote></details>

</details>

</details>

<details>
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</details>

<details>
<summary>🔇 Additional comments (4)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (4)</summary>

`88-92`: **Ensure coverage for single-element trees.**

When `proof.leafCount == 1`, the logic returns whether the single-element hash matches `proof.root`. This is correct for a tree of size 1. However, ensure your test suite covers edge cases where `elements[0]` might be empty or nil to prevent potential corner-case oversights.

---

`117-233`: **Review potential infinite loop in `computeRoot`.**

`computeRoot` has a `for {}` loop that exits when `nodeIndex == 1` (the root) or returns `nil` on error. Ensure there's always a path to one of these exits. In certain unexpected edge cases (e.g., incomplete data or incorrectly formed proof arrays), you might never hit `nodeIndex == 1` or a `nil` return, which could hang the function. Consider adding a safety check or clearly documenting invariants ensuring eventual termination.

---

`295-319`: **Validate sibling presence only if needed.**

Within the loop (lines 295–319), you selectively fetch sibling nodes if one child is known. This is appropriate. However, be mindful if the tree or a child is nil in a partially populated scenario. Your existing `tree[leftChildIdx] != nil` checks guard against adding nil siblings. This logic appears correct, but ensure that any future expansions (e.g., partial data sets) thoroughly handle missing or nil child nodes.

---

`379-417`: **Indices validation approach is consistent with retrieved learnings.**

The `validateIndices`, `hasDuplicates`, and `hasOutOfBounds` functions collectively ensure that indices are within `[0, leafCount)` and do not contain duplicates (lines 379–417). Given your earlier note that `elementCount` matches the leaf count, additional checks in `computeRoot` are indeed redundant. This implementation is efficient and straightforward.

</details>

</blockquote></details>

</details>

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<details>
<summary>♻️ Duplicate comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`196-210`: **Potential integer overflow in `roundUpToPowerOf2`.**  
This function may overflow if `n` is close to `math.MaxUint32` because `n + 1` can wrap around to `0`.  

Below is the previously suggested fix from past reviews for reference:

```diff
 func roundUpToPowerOf2(n uint32) uint32 {
     if bits.OnesCount32(n) == 1 {
         return n
     }
     n |= n >> 1
     n |= n >> 2
     n |= n >> 4
     n |= n >> 8
     n |= n >> 16
-    return n + 1
+    if n == ^uint32(0) {
+        // Overflow scenario: can't add 1 safely
+        return n
+    }
+    return n + 1
 }
```

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`9-15`: **Consider adding doc comments for the MerkleTree fields.**  
While the fields are self-explanatory, adding Go-style doc comments (e.g., `// tree is ...`) can improve readability and maintainability.

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (1)</summary><blockquote>

`108-203`: **`computeRoot` is functionally correct but quite complex.**  
The circular queue approach works, but consider splitting it into smaller helper functions or adding more comments for clarity. This would improve readability and maintainability.

</blockquote></details>

</blockquote></details>

<details>
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<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between fef7c0ba6e66b5c3634f4ffe135c1900cc648c47 and 6672b7dbad31f80cae384ab475dcbcb50da97491.

</details>

<details>
<summary>📒 Files selected for processing (2)</summary>

* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧠 Learnings (1)</summary>

<details>
<summary>pkg/merkle/proof.go (1)</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:0-0
Timestamp: 2025-04-14T12:55:15.436Z
Learning: In Merkle tree implementations, when indices are validated using a function like `validateIndices(indices, elementCount)` which checks that indices are less than the element count, additional bounds checking for accessing tree nodes at `leafCount+idx` is redundant because the element count corresponds to the number of leaf nodes.
```

</details>

</details><details>
<summary>🧬 Code Graph Analysis (2)</summary>

<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/hash.go (2)</summary>

* `HashLeaf` (24-26)
* `HashNode` (19-21)

</details>
<details>
<summary>pkg/merkle/tree.go (4)</summary>

* `NewMerkleTree` (23-46)
* `CalculateBalancedLeafCount` (188-194)
* `GetLeftChild` (213-215)
* `GetRightChild` (218-220)

</details>

</blockquote></details>
<details>
<summary>pkg/merkle/tree.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (1)</summary>

* `MultiProof` (30-35)

</details>
<details>
<summary>pkg/merkle/hash.go (2)</summary>

* `HashNode` (19-21)
* `HashLeaf` (24-26)

</details>

</blockquote></details>

</details>

</details>

<details>
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</details>

<details>
<summary>🔇 Additional comments (26)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (10)</summary>

`1-7`: **Package and imports look good.**  
No issues detected with the package declaration and imports.

---

`17-20`: **Error definitions are clear.**  
The custom error variables are well-defined and promote consistent error handling.

---

`22-46`: **Merkle tree constructor logic is solid.**  
The deep copy preserves immutability, and the error checks from `makeLeaves` and `makeTree` are correctly propagated.

---

`48-67`: **Multi-proof generation using sequential indices looks good.**  
The method properly constructs indices, creates the proof, and validates it.

---

`69-87`: **Multi-proof generation with index list is well-structured.**  
Sorting the indices before generating the proof is sensible, and validation is performed properly afterwards.

---

`89-107`: **Accessors are straightforward.**  
Returning slices and fields directly is acceptable; no issues found.

---

`109-169`: **Tree building logic is robust.**  
Your approach for populating leaves and computing internal nodes from bottom-up is correct. The fallback to `tree[1]` as root is validated, preventing nil-root issues.

---

`171-184`: **Leaf creation is nicely encapsulated.**  
Hashing each element with `HashLeaf` is correct and helps keep the rest of the code clean.

---

`186-194`: **Balanced leaf count calculation is concise.**  
The function appropriately returns 0 for empty input and otherwise rounds up to the nearest power of two.

---

`212-220`: **Child index helpers are straightforward.**  
Shifting bits to compute child indices is efficient and aligns with typical binary tree indexing approaches.

</details>
<details>
<summary>pkg/merkle/proof.go (16)</summary>

`1-8`: **Package and imports are standard.**  
No issues found with the package declaration and basic imports.

---

`10-13`: **Error constants for proof generation and verification.**  
Well-defined and help wrap underlying errors with context.

---

`15-28`: **Error variable definitions are comprehensive.**  
The variety of custom errors ensures clarity in different failure scenarios.

---

`30-35`: **MultiProof struct is concise.**  
Storing elements, proofs, root, and leaf count is sufficient for representing a Merkle proof.

---

`37-51`: **Accessor methods are clear and idiomatic.**  
No concerns with returning the underlying slices and values.

---

`53-58`: **indexedValues definitions.**  
No issues found; it’s a reasonable wrapper for values and indices.

---

`60-67`: **Values() method logic is correct.**  
Copying into a new slice ensures no unintended modifications.

---

`69-76`: **Indices() method is straightforward.**  
Implementation is direct and correctly preserves order.

---

`78-106`: **Proof verification logic is comprehensive.**  
It handles single-element trees, full-element re-checks, and partial proofs with a computed root.

---

`205-244`: **Validation is thorough and covers edge cases.**  
Nil checks, partial-proof checks, and index validations are all in place.

---

`246-256`: **`makeIndexedValues` approach is clean.**  
It pairs each element with its index effectively.

---

`258-270`: **Index creation utility is well-defined.**  
It rejects negative or zero counts, then generates a consecutive range of indices.

---

`272-343`: **`makeProof` logic is accurate.**  
Marking known nodes and collecting siblings into `proofs` is correct for partial proof generation.

---

`345-364`: **`validateIndices` properly detects invalid or duplicate indices.**  
Sorting first ensures efficient duplicate checks and consistent out-of-bounds detection.

---

`366-384`: **`hasDuplicates` and `hasOutOfBounds` are straightforward.**  
They fulfill their purposes with minimal overhead.

---

`386-393`: **`cloneBuffer` ensures safe copies.**  
This reuse of memory patterns for proof generation is a good defensive practice.

</details>

</blockquote></details>

</details>

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<details>
<summary>♻️ Duplicate comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (1)</summary><blockquote>

`204-216`: _🛠️ Refactor suggestion_

**Reorder validation checks for more accurate error reporting.**

The function validates indices before checking if `leafCount` is positive, which could lead to returning `ErrIndicesOutOfBounds` when the more relevant error is `ErrInvalidLeafCount`. Validating `leafCount` first would provide a more accurate error.

```diff
func (p *MultiProof) validate() error {
    if len(p.elements) == 0 {
        return ErrNoElements
    }

+   if p.leafCount <= 0 {
+       return ErrInvalidLeafCount
+   }
+
    if err := validateIndices(p.elements.Indices(), p.leafCount); err != nil {
        return err
    }

-   if p.leafCount <= 0 {
-       return ErrInvalidLeafCount
-   }
```

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (5)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (5)</summary><blockquote>

`10-13`: **Improve error constant naming and pattern.**

The error constants use uppercase with underscores, but Go's convention for constants is to use MixedCaps. Additionally, these are string constants that are only used for formatting. Consider making them private or using a more idiomatic approach.

```diff
const (
-   ErrGenerateProof string = "cannot generate proof: %w"
-   ErrVerifyProof   string = "cannot verify proof: %w"
+   errGenerateProofFmt string = "cannot generate proof: %w"
+   errVerifyProofFmt   string = "cannot verify proof: %w"
)
```

Then update references to these constants throughout the file.

---

`307-308`: **Rename `Get` prefixed functions to follow Go conventions.**

Function names like `GetLeftChild` and `GetRightChild` don't follow Go's naming conventions, which typically avoid the `Get` prefix. Consider renaming these functions to `LeftChild` and `RightChild` for more idiomatic Go code.

```diff
-   leftChildIdx := GetLeftChild(i)
-   rightChildIdx := GetRightChild(i)
+   leftChildIdx := LeftChild(i)
+   rightChildIdx := RightChild(i)
```

This would require changing the function definitions elsewhere in the package.

---

`74-105`: **Consider adding nil check for proof parameter.**

The `Verify` function doesn't check if the `proof` parameter is nil before accessing its fields through the `validate` method. While the `validate` method will catch some issues, adding an explicit nil check at the beginning would prevent a potential panic.

```diff
func Verify(root []byte, proof *MultiProof) (bool, error) {
    if len(root) == 0 {
        return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
    }

+   if proof == nil {
+       return false, fmt.Errorf(ErrVerifyProof, ErrNilProof)
+   }

    if err := proof.validate(); err != nil {
        return false, fmt.Errorf(ErrVerifyProof, err)
    }
```

---

`107-202`: **Consider breaking down complex computeRoot method.**

The `computeRoot` method is quite complex with multiple nested conditionals and a large loop. Consider refactoring it into smaller, more focused functions to improve readability and maintainability.

For example, you could extract the sibling handling logic (lines 162-195) into a separate function:

```go
func (p *MultiProof) processSiblings(nodeIndex int, readIndex int, proofIndex int, count int, 
                                     hashes [][]byte, nextIsPair bool) (int, int, []byte, error) {
    var right, left []byte
    indexIsOdd := nodeIndex&1 == 1
    
    if indexIsOdd {
        right = hashes[readIndex]
        readIndex = (readIndex + 1) % count
        if !nextIsPair {
            if proofIndex >= len(p.proofs) {
                return readIndex, proofIndex, nil, ErrNilProof
            }
            left = p.proofs[proofIndex]
            proofIndex++
        } else {
            left = hashes[readIndex]
            readIndex = (readIndex + 1) % count
        }
    } else {
        if proofIndex >= len(p.proofs) {
            return readIndex, proofIndex, nil, ErrNilProof
        }
        right = p.proofs[proofIndex]
        proofIndex++
        left = hashes[readIndex]
        readIndex = (readIndex + 1) % count
    }
    
    if left == nil || right == nil {
        return readIndex, proofIndex, nil, ErrNilProof
    }
    
    return readIndex, proofIndex, HashNode(left, right), nil
}
```

Then call this function from the main loop.

---

`267-336`: **Improve docstring on makeProof function.**

The `makeProof` function's purpose is not fully explained in its comment. Consider adding details about what the function does, what each parameter means, and what the returned `MultiProof` contains.

```diff
-// makeProof returns a MultiProof for the given indices.
+// makeProof generates a MultiProof for the given indices in a Merkle tree.
+// Parameters:
+//   - tree: The complete Merkle tree represented as a slice of hash byte slices
+//   - root: The Merkle root hash
+//   - indices: The indices of the leaves to include in the proof
+//   - leafCount: The total number of leaves in the tree
+// Returns a MultiProof that contains:
+//   - The provided indices and their respective values
+//   - The minimal set of proof hashes needed for verification
+//   - The total leaf count
+// The function will return an error if the tree is empty, the root is nil,
+// or if the indices are invalid.
```

</blockquote></details>

</blockquote></details>

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</details>

<details>
<summary>📒 Files selected for processing (1)</summary>

* `pkg/merkle/proof.go` (1 hunks)

</details>

<details>
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<details>
<summary>🧠 Learnings (1)</summary>

<details>
<summary>pkg/merkle/proof.go (1)</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:0-0
Timestamp: 2025-04-14T12:55:15.436Z
Learning: In Merkle tree implementations, when indices are validated using a function like `validateIndices(indices, elementCount)` which checks that indices are less than the element count, additional bounds checking for accessing tree nodes at `leafCount+idx` is redundant because the element count corresponds to the number of leaf nodes.
```

</details>

</details>

</details>

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<details>
<summary>♻️ Duplicate comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`266-280`: _⚠️ Potential issue_

**Avoid integer overflow in `roundUpToPowerOf2`**  
If `n` is near `math.MaxUint32`, adding 1 will overflow (wrap to 0). This silently breaks tree sizing for extremely large inputs. One fix might be:

```diff
 func roundUpToPowerOf2(n uint32) uint32 {
     if bits.OnesCount32(n) == 1 {
         return n
     }
     n |= n >> 1
     n |= n >> 2
     n |= n >> 4
     n |= n >> 8
     n |= n >> 16
-    return n + 1
+    if n == ^uint32(0) {
+        // Overflow scenario: can't safely increment
+        return n
+    }
+    return n + 1
 }
```

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (3)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

`86-96`: **Consider avoiding full Merkle tree reconstruction for large proofs**  
Rebuilding the entire Merkle tree for verification (when all leaves are present) may be costly for large datasets. You could optimize by verifying each leaf’s hash incrementally or by reusing partial logic.

---

`105-200`: **Reduce complexity or add documentation to `computeRoot`**  
The `computeRoot` method is lengthy and has complex indexing logic. Splitting it into smaller helper functions or adding in-line comments would improve maintainability and reduce cognitive load.

</blockquote></details>
<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`24-29`: **Evaluate memory usage for large inputs**  
A full element-by-element deep copy is performed, which can be expensive for large inputs. If immutability is not strictly required, consider referencing the original slices or using a more memory-efficient approach.

</blockquote></details>

</blockquote></details>

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<details>
<summary>📥 Commits</summary>

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</details>

<details>
<summary>📒 Files selected for processing (2)</summary>

* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧠 Learnings (1)</summary>

<details>
<summary>pkg/merkle/proof.go (1)</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:0-0
Timestamp: 2025-04-14T12:55:15.436Z
Learning: In Merkle tree implementations, when indices are validated using a function like `validateIndices(indices, elementCount)` which checks that indices are less than the element count, additional bounds checking for accessing tree nodes at `leafCount+idx` is redundant because the element count corresponds to the number of leaf nodes.
```

</details>

</details>

</details>

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<summary>⏰ Context from checks skipped due to timeout of 90000ms (5)</summary>

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</details>

<details>
<summary>🔇 Additional comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary>

`227-231`: **Confirm no scenario where only the right child is non-nil**  
The code handles both children present or only the left child present, but there's no branch for a lone right child. If that situation can’t occur due to left-to-right filling, add a comment clarifying this invariant. Otherwise, consider adding a condition for the right-child-only case.

</details>

</blockquote></details>

</details>

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submitted_at: 2025-04-15T11:28:35Z
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submitted_at: 2025-04-15T11:29:05Z
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state: COMMENTED
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submitted_at: 2025-04-15T11:37:27Z
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submitted_at: 2025-04-15T11:38:06Z
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body: **Actionable comments posted: 0**

<details>
<summary>♻️ Duplicate comments (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`266-280`: _⚠️ Potential issue_

**Prevent potential overflow in `roundUpToPowerOf2`.**

If `n` is extremely large (close to `math.MaxUint32`), `n + 1` could wrap around to 0. This silently breaks the leaf count calculation for very large input sizes. Consider adding an overflow guard to avoid returning 0 unintentionally.


Example fix:

```diff
 if n == ^uint32(0) {
     // Overflow scenario
     return n
 }
 return n + 1
```

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (1)</summary><blockquote>

`71-72`: **Check for nil `proof` argument to avoid panic.**  
This was mentioned in earlier reviews, but remains unresolved. Calling `proof.validate()` at line 77 will panic if `proof` is nil.

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (4)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (2)</summary><blockquote>

`24-29`: **Consider early validation for empty input elements.**

Right now, the constructor copies elements before delegating an empty check to `makeLeaves`. As an optional optimization, you could perform a quick `if len(elements) == 0 { return nil, ErrTreeEmpty }` at the start of `NewMerkleTree` to fail early and avoid unnecessary copying.

---

`256-264`: **Edge case handling for negative element counts.**

`CalculateBalancedLeafCount` returns 0 when `elementCount == 0`, but negative inputs would skip that check and pass a negative cast to `uint32`. Although likely not an issue in normal usage, consider validating non-negative values just to avoid unexpected large outcomes in `roundUpToPowerOf2`.

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

`86-94`: **Potential performance overhead when reconstructing the entire tree.**

When the proof includes all elements (`len(proof.elements) == proof.leafCount`), you reconstruct the entire Merkle tree for verification. This approach is correct but can be expensive for large trees. You could skip building the full tree since the proof contains all leaves (though it may not be necessary). If performance becomes an issue, consider a partial or in-place rehash approach.

---

`130-197`: **Complex parent-hash logic could benefit from smaller helper functions.**

`computeRoot` covers a lot of ground while juggling multiple indices (`readIndex`, `writeIndex`, `proofIndex`) and boundary logic (`lowestTreeIndex`, `upperBound`). Consider extracting some of these steps (like sibling retrieval) into smaller helper methods to improve readability and maintainability.

</blockquote></details>

</blockquote></details>

<details>
<summary>📜 Review details</summary>

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**Plan: Pro**

<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between 6548572c51bd80696dfa001ff416f5acd3e9d65b and 6eea74e632e22838579445e6189755220088463b.

</details>

<details>
<summary>📒 Files selected for processing (2)</summary>

* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧠 Learnings (1)</summary>

<details>
<summary>pkg/merkle/proof.go (2)</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:0-0
Timestamp: 2025-04-14T12:55:15.436Z
Learning: In Merkle tree implementations, when indices are validated using a function like `validateIndices(indices, elementCount)` which checks that indices are less than the element count, additional bounds checking for accessing tree nodes at `leafCount+idx` is redundant because the element count corresponds to the number of leaf nodes.
```

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:71-72
Timestamp: 2025-04-15T11:29:03.575Z
Learning: In Go, when a byte slice (`[]byte`) is nil, `len(slice)` returns 0. Therefore, checking `if len(slice) == 0` will catch both nil slices and empty slices (initialized but with no elements).
```

</details>

</details>

</details>

<details>
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</details>

<details>
<summary>🔇 Additional comments (3)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary>

`180-239`: **Good bottom-up tree construction approach.**

The logic for building the 1-indexed Merkle tree from the leaf level up (bit-shifting index boundaries) is correct and well-structured. This straightforward design helps in verifying boundary conditions for smaller and larger trees. The fallback case for `tree[i] = tree[leftChildIndex]` when the right child is nil is consistent with your left-to-right fill assumption.

</details>
<details>
<summary>pkg/merkle/proof.go (2)</summary>

`82-84`: **Single-element verification looks correct.**

By hashing the single element again via `HashLeaf`, you ensure the reconstructed root matches the original. This is straightforward and logically consistent for the simplest tree scenario.

---

`217-252`: **Thorough validation checks.**

The validation function ensures no nil elements, verifies the required proofs for partial trees, and calls `validateIndices` to catch duplicates or out-of-bounds. These safeguards make the proof generation and verification logic more robust.

</details>

</blockquote></details>

</details>

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submitted_at: 2025-04-15T19:12:09Z
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submitted_at: 2025-04-16T10:34:35Z
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submitted_at: 2025-04-16T10:37:05Z
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body: **Actionable comments posted: 0**

<details>
<summary>♻️ Duplicate comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`286-299`: **Prevent potential overflow when rounding up to power of 2.**

If `n` is near the maximum `uint32` value (e.g., `0xFFFFFFFF`), `n + 1` will overflow to 0. This silently breaks the tree's size calculation.

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`18-18`: **Consider using idiomatic Go naming convention for constants.**

The constant `TREE_MAX_LEAVES` uses uppercase with underscores, which doesn't follow Go's typical naming convention. In idiomatic Go, constants use MixedCaps rather than SNAKE_CASE.

```diff
-const TREE_MAX_LEAVES = 4096
+const TreeMaxLeaves = 4096
```

Remember to update all references to this constant if you make this change.

</blockquote></details>

</blockquote></details>

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<details>
<summary>📥 Commits</summary>

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</details>

<details>
<summary>📒 Files selected for processing (3)</summary>

* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)
* `pkg/merkle/tree_test.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (2)</summary>

* pkg/merkle/tree_test.go
* pkg/merkle/proof.go

</details>

<details>
<summary>⏰ Context from checks skipped due to timeout of 90000ms (5)</summary>

* GitHub Check: Push Docker Images to GitHub Packages (xmtpd-cli)
* GitHub Check: Push Docker Images to GitHub Packages (xmtpd)
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* GitHub Check: Test (Node)
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</details>

<details>
<summary>🔇 Additional comments (5)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (5)</summary>

`242-246`: **The logic for handling child nodes looks good.**

The implementation correctly handles the cases when both children exist, only the left child exists, or no children exist. The condition order is now correct, fixing a previous issue where the tree would never hash both children.

---

`271-284`: **The leaf count calculation handles edge cases properly.**

The function correctly handles negative or zero element counts and checks for potential overflow. Good defensive programming!

---

`61-96`: **Proof generation methods are well-structured.**

Both `GenerateMultiProofSequential` and `GenerateMultiProofWithIndices` follow good patterns with proper validation and error handling. The sorting of indices in the latter ensures consistent behavior regardless of input order.

---

`27-59`: **The tree construction process is robust.**

The `NewMerkleTree` function includes proper validation, deep copying of input elements for immutability, and clear error handling. Good implementation!

---

`98-169`: <details>
<summary>✅ Verification successful</summary>

**Verify the cloneBuffer function is available.**

The `makeProof` method uses a function called `cloneBuffer` at lines 150 and 155, but this function isn't defined in this file. Ensure that this function is defined elsewhere in the package and properly exported if needed.

---

🏁 Script executed:

```shell
#!/bin/bash
# Check if cloneBuffer is defined somewhere in the package
rg -p "func cloneBuffer" --type go
```

Length of output: 101

---



</details>

**Confirmation: `cloneBuffer` is correctly defined and accessible**

The verification confirms that the `cloneBuffer` function is defined in `pkg/merkle/proof.go` at line 304, making it accessible to the `makeProof` method within the same package. No further action is required on this point.

</details>

</blockquote></details>

</details>

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<details>
<summary>🧹 Nitpick comments (6)</summary><blockquote>

<details>
<summary>pkg/merkle/tree_test.go (6)</summary><blockquote>

`113-113`: **Consider enhancing the helper function documentation.**

The call to `verifyUnbalancedTreeStructure` isn't immediately clear on what's being validated without examining the helper function implementation. Consider adding a brief comment before this line explaining what aspects of the tree structure are being verified.

```diff
-			verifyUnbalancedTreeStructure(t, tree.Tree(), leafCount, tc.numElements)
+			// Verify parent-child relationships and hash consistency in the unbalanced tree
+			verifyUnbalancedTreeStructure(t, tree.Tree(), leafCount, tc.numElements)
```

---

`164-177`: **Sampling approach for large trees is effective.**

Using sampling to verify large trees is a good approach to balance thoroughness with test run time. However, consider adding a comment explaining why only 5 samples are checked.


```diff
-			// Sample testing.
+			// Sample testing - check only a few elements to keep test runtime reasonable.
+			// For large trees, we verify 5 evenly distributed elements rather than all elements.
```

---

`310-358`: **Consider improving helper function resilience.**

The helper function could be more resilient by checking array bounds before accessing elements.

```diff
-	if tree[1] != nil && tree[2] != nil {
+	if len(tree) > 2 && tree[1] != nil && tree[2] != nil {
```

Additionally, the assertion regarding the root calculation contains a logic error - it uses `assert.NotNil` when it should verify the hash equals the root:
```diff
-		assert.NotNil(
-			t,
-			merkle.HashNode(tree[1], tree[2]),
-			"Root should be calculated when both children exist",
-		)
+		assert.Equal(
+			t,
+			merkle.HashNode(tree[2], tree[3]),
+			tree[1],
+			"Root should equal hash of its children",
+		)
```

---

`325-327`: **Early continue could be clearer.**

This early continue skips iterations where the left child is out of bounds, but the intent isn't immediately clear.

```diff
-		if leftIdx >= len(tree) {
-			continue
-		}
+		// Skip if left child index is out of bounds - this node has no children
+		if leftIdx >= len(tree) {
+			continue
+		}
```

---

`360-389`: **TestRoundUpToPowerOf2Values and TestCalculateBalancedLeafCount are partially redundant.**

There's some overlap between these two test functions. Consider merging them or making the distinction clearer in their names and comments.


Additionally, you could use `assert.Equal` instead of custom error messages for consistency with the rest of the test suite:

```diff
-			if result != tt.expected {
-				t.Errorf(
-					"Power of 2 rounding for %d = %d, expected %d",
-					tt.input,
-					result,
-					tt.expected,
-				)
-			}
+			assert.Equal(
+				t, 
+				tt.expected, 
+				result, 
+				"Power of 2 rounding for %d incorrect", 
+				tt.input,
+			)
```

---

`427-431`: **Overflow test could be more explicit.**

The test for overflow could be more explicit about why this specific value causes an overflow.

```diff
-	// This is larger than max uint32 and should cause an error
-	massiveInput := int(^uint32(0)) + 1
+	// Test with a value just beyond uint32's maximum (2^32)
+	// This should trigger ErrTreeLeavesOverflow since the implementation uses uint32 internally
+	massiveInput := int(^uint32(0)) + 1
```

</blockquote></details>

</blockquote></details>

<details>
<summary>📜 Review details</summary>

**Configuration used: CodeRabbit UI**
**Review profile: CHILL**
**Plan: Pro**

<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between 1c9ae32ac2caebcf2c92d8e1980ff7b5de01a102 and 07b9d11247c5500c95237324ee161fc007ee818f.

</details>

<details>
<summary>📒 Files selected for processing (3)</summary>

* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)
* `pkg/merkle/tree_test.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (2)</summary>

* pkg/merkle/tree.go
* pkg/merkle/proof.go

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧬 Code Graph Analysis (1)</summary>

<details>
<summary>pkg/merkle/tree_test.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (6)</summary>

* `NewMerkleTree` (28-59)
* `ErrTreeEmpty` (21-21)
* `CalculateBalancedLeafCount` (274-284)
* `GetLeftChild` (302-304)
* `GetRightChild` (307-309)
* `ErrTreeLeavesOverflow` (24-24)

</details>
<details>
<summary>pkg/merkle/hash.go (2)</summary>

* `HashLeaf` (37-45)
* `HashNode` (25-34)

</details>

</blockquote></details>

</details>

</details>

<details>
<summary>⏰ Context from checks skipped due to timeout of 90000ms (5)</summary>

* GitHub Check: Push Docker Images to GitHub Packages (xmtpd-cli)
* GitHub Check: Test (Node)
* GitHub Check: Upgrade Tests
* GitHub Check: Push Docker Images to GitHub Packages (xmtpd)
* GitHub Check: Code Review

</details>

<details>
<summary>🔇 Additional comments (7)</summary><blockquote>

<details>
<summary>pkg/merkle/tree_test.go (7)</summary>

`1-1`: **Package naming is correctly set for external testing.**

The use of `package merkle_test` instead of `package merkle` is a good practice for black-box testing, ensuring tests only access exported members of the package. This aligns with the team's preference as noted in previous review comments.

---

`11-15`: **Empty tree test looks good.**

This test correctly verifies that attempting to create a Merkle tree with an empty slice of elements results in the expected error.

---

`17-82`: **Comprehensive balanced trees test cases.**

The test provides good coverage for balanced trees of various sizes and verifies essential properties including:
- Correct leaf count
- Non-nil root
- Accurate array size calculation
- Correct leaf node hashing
- Presence of all internal nodes

The table-driven approach makes it easy to add more test cases in the future.

---

`182-205`: **Thorough test for duplicate elements.**

This test nicely verifies that identical elements produce identical leaf hashes while maintaining different hashes for distinct elements - an important property for a Merkle tree implementation.

---

`207-225`: **Good edge case testing with large elements.**

Testing with a 1MB element is a good edge case to verify that the implementation handles large data efficiently. This helps ensure the implementation doesn't break with realistic payloads.

---

`227-249`: **Empty elements test is thorough.**

Testing empty byte slices is an important edge case that could cause issues in hash calculation. This test correctly verifies that empty elements are properly hashed and included in the tree.

---

`251-307`: **Excellent manual verification of tree structure with detailed comments.**

The ASCII diagram and detailed node-by-node verification provide a clear understanding of the expected tree structure. This test serves as both verification and documentation of how the tree is organized.

</details>

</blockquote></details>

</details>

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author_association: CONTRIBUTOR
submitted_at: 2025-04-16T11:35:28Z
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submitted_at: 2025-04-16T19:44:51Z
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body: **Actionable comments posted: 1**

<details>
<summary>♻️ Duplicate comments (3)</summary><blockquote>

<details>
<summary>pkg/merkle/proof.go (2)</summary><blockquote>

`336-339`: **Comment contradicts implementation**  

`isLeftChild` returns `true` for *even* indices (left child), yet the comment claims the opposite. Please update the comment (or the code) for clarity.

---

`77-85`: _⚠️ Potential issue_

**Add a nil–check for `proof` to prevent panics**  
`Verify` dereferences `proof` immediately (`proof.validate()`), so a caller that accidentally passes `nil` will trigger a runtime panic. A tiny guard avoids the crash and surfaces a clear error:

```diff
 func Verify(root []byte, proof *MultiProof) (bool, error) {
-	if len(root) == 0 {
+	if proof == nil {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilProof)
+	}
+	if len(root) == 0 {
 		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
 	}
 
 	if err := proof.validate(); err != nil {
 		return false, fmt.Errorf(ErrVerifyProof, err)
 	}
```

</blockquote></details>
<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`294-306`: _🛠️ Refactor suggestion_

**`roundUpToPowerOf2` still overflows for `math.MaxUint32`**  

`n + 1` wraps to `0` for `0xFFFFFFFF`, which later converts to a negative `int` on 32‑bit builds.  
Either cap the input earlier or guard here:

```diff
-	return n + 1
+	if n == ^uint32(0) {
+		return n // already max; cannot round further
+	}
+	return n + 1
```

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (4)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (3)</summary><blockquote>

`24-27`: **Fix off‑by‑one / typo in public documentation**  

The comment says  
```
- The hashed are at index N+1 to 2N-1.
```  
but leaves actually occupy indices `N` … `2N‑1` (see `lowerBound := balancedLeafCount`). Mis‑documenting the layout makes the public API harder to reason about—please adjust.

---

`10-16`: **Expose a copy to keep node hashes immutable**  

`Hash()` returns the backing slice, so callers can mutate it and silently corrupt the tree/proofs:

```diff
 func (n *Node) Hash() []byte {
-	return n.hash
+	dup := make([]byte, len(n.hash))
+	copy(dup, n.hash)
+	return dup
 }
```

Alternatively, document that callers must treat the slice as read‑only.

---

`46-54`: **Deep‑copy individual leaves to avoid shared mutability**  

`copy(leavesDeepCopy, leaves)` duplicates the slice header only; each `[]byte` element still aliases the caller’s buffer.  
Either:

1. Clarify in docs that the caller must not mutate after construction, or  
2. Perform a per‑element copy:

```go
leavesDeepCopy := make([]Leaf, len(leaves))
for i, l := range leaves {
    cpy := make([]byte, len(l))
    copy(cpy, l)
    leavesDeepCopy[i] = cpy
}
```

</blockquote></details>
<details>
<summary>pkg/merkle/proof_test.go (1)</summary><blockquote>

`441-445`: **Optional: assert immutability rather than equality only**  

The test correctly checks value equality, but not that the returned slices are *copies* (immutable).  
If you adopt the earlier `Hash()` / leaf‑copy changes, consider extending the test:

```go
orig := values[0].GetValue()
orig[0] ^= 0xFF
require.False(t, bytes.Equal(values[0].GetValue(), orig), "proof exposes mutable slice")
```

</blockquote></details>

</blockquote></details>

<details>
<summary>📜 Review details</summary>

**Configuration used: CodeRabbit UI**
**Review profile: CHILL**
**Plan: Pro**

<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between 79f8c1289f32effbe2d61b04eaf0bd5b56def877 and 1371d83c20bcb79c1d919008e88a90c43047b759.

</details>

<details>
<summary>📒 Files selected for processing (5)</summary>

* `pkg/merkle/hash.go` (1 hunks)
* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/proof_test.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)
* `pkg/merkle/tree_test.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (2)</summary>

* pkg/merkle/hash.go
* pkg/merkle/tree_test.go

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧠 Learnings (1)</summary>

<details>
<summary>pkg/merkle/proof.go (2)</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:0-0
Timestamp: 2025-04-14T12:55:15.436Z
Learning: In Merkle tree implementations, when indices are validated using a function like `validateIndices(indices, elementCount)` which checks that indices are less than the element count, additional bounds checking for accessing tree nodes at `leafCount+idx` is redundant because the element count corresponds to the number of leaf nodes.
```

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:71-72
Timestamp: 2025-04-15T11:29:03.575Z
Learning: In Go, when a byte slice (`[]byte`) is nil, `len(slice)` returns 0. Therefore, checking `if len(slice) == 0` will catch both nil slices and empty slices (initialized but with no elements).
```

</details>

</details><details>
<summary>🧬 Code Graph Analysis (1)</summary>

<details>
<summary>pkg/merkle/tree.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/hash.go (4)</summary>

* `Hash` (18-22)
* `HashEmptyLeaf` (45-47)
* `HashNode` (24-33)
* `HashLeaf` (35-43)

</details>
<details>
<summary>pkg/merkle/proof.go (2)</summary>

* `MultiProof` (28-32)
* `ErrGenerateProof` (11-11)

</details>

</blockquote></details>

</details>

</details>

<details>
<summary>⏰ Context from checks skipped due to timeout of 90000ms (5)</summary>

* GitHub Check: Push Docker Images to GitHub Packages (xmtpd-cli)
* GitHub Check: Push Docker Images to GitHub Packages (xmtpd)
* GitHub Check: Test (Node)
* GitHub Check: Upgrade Tests
* GitHub Check: Code Review

</details>

</details>

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author_association: CONTRIBUTOR
submitted_at: 2025-04-17T11:31:52Z
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submitted_at: 2025-04-17T11:33:15Z
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body: **Actionable comments posted: 0**

<details>
<summary>♻️ Duplicate comments (4)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`294-306`: **Potential overflow in `roundUpToPowerOf2` remains unaddressed**  

Prior reviews noted that `n + 1` can wrap to 0 when `n == ^uint32(0)`.  
Although `CalculateBalancedNodesCount` now caps inputs, the helper is still callable elsewhere and is safer with an explicit guard.

(See earlier comment; not repeated here.)

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (3)</summary><blockquote>

`77-85`: **Nil‑proof dereference can panic**

`Verify` dereferences `proof` without checking for `nil`; passing a `nil` pointer will panic.

```diff
 func Verify(root []byte, proof *MultiProof) (bool, error) {
+	if proof == nil {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilProof)
+	}
 	if len(root) == 0 {
 		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
 	}
```
(This issue was flagged previously and is still outstanding.)

---

`291-311`: **Indices are validated against padded leaf count, allowing empty‑leaf proofs**

`validateIndices` bounds‑checks against `balancedLeafCount`, which includes the synthetic padding leaves.  
Callers can therefore request proofs for indices that have no real data (e.g. index 3 in a 3‑leaf tree padded to 4).

Re–use the actual `leafCount` instead:

```diff
-	balancedLeafCount, err := CalculateBalancedNodesCount(leafCount)
-	if err != nil {
-		return err
-	}
 ...
-	if hasOutOfBounds(sortedIndices, balancedLeafCount) {
+	if hasOutOfBounds(sortedIndices, leafCount) {
 		return ErrIndicesOutOfBounds
 	}
```
Prevents silent acceptance of invalid proofs.

---

`336-339`: **Comment contradicts implementation**

`isLeftChild` returns `true` for **even** indices, but the comment claims the opposite. Correcting the comment avoids mental traps.

```diff
-// isLeftChild returns true if the given index is odd (right child).
+// isLeftChild returns true if the given index is even (left child).
```

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (4)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (3)</summary><blockquote>

`20-26`: **Fix inaccurate documentation of slice layout**

The comments describing the 1‑indexed layout are off by one:

* Internal nodes occupy indices 2 … N‑1 (not 2 … N).
* Leaves sit at indices N … 2N‑1 (not N+1 … 2N‑1).
* “…​hashed” → “…​leaves”.

Keeping these doc‑strings correct prevents future off‑by‑one bugs for anyone maintaining the code.

```diff
-// - The internal nodes are at index 2 to N.
-// - The hashed are at index N+1 to 2N-1.
+// - Internal nodes are at indices 2 to N‑1.
+// - Leaves are at indices N to 2N‑1.
```

---

`14-16`: **Return a defensive copy to prevent external mutation**

`Hash()` exposes the internal byte‐slice directly. A caller can mutate the slice in‑place and corrupt the tree.

```diff
-func (n *Node) Hash() []byte {
-	return n.hash
+func (n *Node) Hash() []byte {
+	// Return a copy so callers cannot mutate internal state.
+	if n.hash == nil {
+		return nil
+	}
+	cp := make([]byte, len(n.hash))
+	copy(cp, n.hash)
+	return cp
 }
```

---

`46-57`: **Double copying of leaves is unnecessary**

`NewMerkleTree` deep‑copies `leaves` into `leavesDeepCopy`, then `makeLeaves` copies again.  
Unless the original slice must remain untouched, a single copy inside `makeLeaves` suffices and avoids an extra allocation.

Refactor idea:

1. Drop `leavesDeepCopy` altogether.
2. Let `makeLeaves` handle the copy/padding.

This reduces allocations for large trees.

</blockquote></details>
<details>
<summary>pkg/merkle/proof.go (1)</summary><blockquote>

`203-206`: **Remove unused variable to silence `go vet`**

`upperBound` is declared but never referenced after this point.

```diff
-		upperBound     = blc + p.leafCount - 1
+		// upperBound was part of an earlier algorithm; remove to avoid dead code.
```

An unused local will trigger `go vet` warnings.

</blockquote></details>

</blockquote></details>

<details>
<summary>📜 Review details</summary>

**Configuration used: CodeRabbit UI**
**Review profile: CHILL**
**Plan: Pro**

<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between 1371d83c20bcb79c1d919008e88a90c43047b759 and 5aed727dc5656ec4c9a9aa5c8d4fbd8a96ced02f.

</details>

<details>
<summary>📒 Files selected for processing (5)</summary>

* `pkg/merkle/hash.go` (1 hunks)
* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/proof_test.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)
* `pkg/merkle/tree_test.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (3)</summary>

* pkg/merkle/hash.go
* pkg/merkle/tree_test.go
* pkg/merkle/proof_test.go

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧠 Learnings (1)</summary>

<details>
<summary>pkg/merkle/proof.go (2)</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:0-0
Timestamp: 2025-04-14T12:55:15.436Z
Learning: In Merkle tree implementations, when indices are validated using a function like `validateIndices(indices, elementCount)` which checks that indices are less than the element count, additional bounds checking for accessing tree nodes at `leafCount+idx` is redundant because the element count corresponds to the number of leaf nodes.
```

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:71-72
Timestamp: 2025-04-15T11:29:03.575Z
Learning: In Go, when a byte slice (`[]byte`) is nil, `len(slice)` returns 0. Therefore, checking `if len(slice) == 0` will catch both nil slices and empty slices (initialized but with no elements).
```

</details>

</details>

</details>

</details>

<!-- This is an auto-generated comment by CodeRabbit for review status -->
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author_association: CONTRIBUTOR
submitted_at: 2025-04-17T11:36:43Z
user: login: fbac
state: COMMENTED
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submitted_at: 2025-04-17T11:37:35Z
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submitted_at: 2025-04-17T11:38:13Z
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body: **Actionable comments posted: 1**

<details>
<summary>♻️ Duplicate comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`297-309`: **Potential overflow in `roundUpToPowerOf2` remains unhandled**

The function still does `return n + 1` after the bit‑smearing step.  
For inputs such as `0xFFFF_FFFF` this wraps to `0`, breaking subsequent size calculations.  Previous review threads already highlighted this; please address it or document why the current behaviour is acceptable.

```diff
-	return n + 1
+	if n == ^uint32(0) {
+		// Overflow would wrap to zero – reject or cap explicitly.
+		return n // or: panic("overflow in roundUpToPowerOf2")
+	}
+	return n + 1
```

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary><blockquote>

`14-23`: **Avoid repeated allocations in `Node.Hash()`**

`Node.Hash()` defensively copies the underlying slice on every call.  
While this guarantees immutability, it also allocates `O(n)` memory for *every* hash access, which becomes expensive when walking large trees or generating proofs.

If the tree is treated as immutable after construction (which appears to be the case), you can safely return the slice itself and document it as *read‑only*.  A middle ground is to expose both a zero‑allocation accessor (`HashNoCopy`) and keep the safe variant for external callers.

```diff
-func (n *Node) Hash() []byte {
-	if n.hash == nil {
-		return nil
-	}
-
-	cp := make([]byte, len(n.hash))
-	copy(cp, n.hash)
-	return cp
-}
+// Hash returns the node hash. The slice **must not** be mutated.
+func (n *Node) Hash() []byte {
+	return n.hash
+}
```

If total immutability is required, consider caching the copy once and re‑using it instead of re‑allocating each time.

</blockquote></details>

</blockquote></details>

<details>
<summary>📜 Review details</summary>

**Configuration used: CodeRabbit UI**
**Review profile: CHILL**
**Plan: Pro**

<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between 5aed727dc5656ec4c9a9aa5c8d4fbd8a96ced02f and 0b0be338da219cd4df69358e657794c7ecdd8ebf.

</details>

<details>
<summary>📒 Files selected for processing (5)</summary>

* `pkg/merkle/hash.go` (1 hunks)
* `pkg/merkle/proof.go` (1 hunks)
* `pkg/merkle/proof_test.go` (1 hunks)
* `pkg/merkle/tree.go` (1 hunks)
* `pkg/merkle/tree_test.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (4)</summary>

* pkg/merkle/proof_test.go
* pkg/merkle/hash.go
* pkg/merkle/tree_test.go
* pkg/merkle/proof.go

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧬 Code Graph Analysis (1)</summary>

<details>
<summary>pkg/merkle/tree.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/hash.go (4)</summary>

* `Hash` (18-22)
* `HashEmptyLeaf` (45-47)
* `HashNode` (24-33)
* `HashLeaf` (35-43)

</details>
<details>
<summary>pkg/merkle/proof.go (2)</summary>

* `MultiProof` (28-32)
* `ErrGenerateProof` (11-11)

</details>

</blockquote></details>

</details>

</details>

<details>
<summary>⏰ Context from checks skipped due to timeout of 90000ms (5)</summary>

* GitHub Check: Push Docker Images to GitHub Packages (xmtpd-cli)
* GitHub Check: Test (Node)
* GitHub Check: Upgrade Tests
* GitHub Check: Push Docker Images to GitHub Packages (xmtpd)
* GitHub Check: Code Review

</details>

<details>
<summary>🔇 Additional comments (1)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (1)</summary>

`129-160`: **Proof sibling ordering might break verification – please double‑check**

`makeProof` appends a sibling **as soon as exactly one child is known**.  
The resulting order of `proofs` depends on the traversal sequence (`i` descending) rather than on the position of the sibling in the tree.  Many multi‑proof verification algorithms expect a *deterministic* left‑to‑right (or bottom‑up) ordering of proof hashes; a mismatch will yield false‑negative verification.

Please verify that `MultiProof.validate()` (and the public verifier) consume the `proofs` slice according to this exact production order.  If not, you may need to:

1. Collect the sibling hashes first, then reverse or sort them to the expected order, **or**
2. Switch to a breadth‑first / left‑to‑right traversal when building `proofs`.

Failing to align the orders will surface only under certain index combinations, so an explicit test is advisable.

</details>

</blockquote></details>

</details>

<!-- This is an auto-generated comment by CodeRabbit for review status -->
state: COMMENTED
author_association: CONTRIBUTOR
submitted_at: 2025-04-17T11:54:40Z
user: login: neekolas
state: COMMENTED
author_association: CONTRIBUTOR
submitted_at: 2025-04-17T14:54:15Z
user: login: neekolas
state: APPROVED
author_association: CONTRIBUTOR
submitted_at: 2025-04-17T15:11:03Z
user: login: mkysel
state: COMMENTED
author_association: COLLABORATOR
submitted_at: 2025-04-17T15:12:28Z
user: login: mkysel
state: COMMENTED
author_association: COLLABORATOR
submitted_at: 2025-04-17T15:24:32Z
user: login: mkysel
state: COMMENTED
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submitted_at: 2025-04-17T15:25:00Z
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state: COMMENTED
author_association: COLLABORATOR
submitted_at: 2025-04-17T15:31:26Z
user: login: coderabbitai[bot]
body: **Actionable comments posted: 0**

<details>
<summary>♻️ Duplicate comments (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (2)</summary><blockquote>

`177-179`: _🛠️ Refactor suggestion_

**Add bounds check for Root() method.**

The `Root()` method directly accesses `m.tree[1]` without checking if the tree slice has sufficient length. This could lead to a panic if the tree is empty or malformed.

```diff
func (m *MerkleTree) Root() []byte {
+	if len(m.tree) <= 1 {
+		return nil
+	}
	return m.tree[1].Hash()
}
```

---

`295-308`: _⚠️ Potential issue_

**Handle potential overflow in roundUpToPowerOf2.**

When `n` is close to the maximum uint32 value (`0xFFFFFFFF`), adding 1 could cause an overflow, resulting in a value of 0. This would cause unexpected behavior when calculating the balanced node count.

```diff
func roundUpToPowerOf2(n uint32) uint32 {
	if bits.OnesCount32(n) == 1 {
		return n
	}

	n |= n >> 1
	n |= n >> 2
	n |= n >> 4
	n |= n >> 8
	n |= n >> 16

+	// Check for potential overflow
+	if n == math.MaxUint32 {
+		return n
+	}
	return n + 1
}
```

Don't forget to add the import: `import "math"`

</blockquote></details>

</blockquote></details>

<details>
<summary>🧹 Nitpick comments (4)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (4)</summary><blockquote>

`106-164`: **Simplify nested conditional logic in makeProof.**

The nested if statements in the makeProof function could be simplified for better readability while preserving the same logic.

```diff
// Only one of children is known, so we need the sibling as a proof.
if left != right {
-	if right {
-		proofs = append(proofs, m.tree[leftChildIdx])
-	} else {
-		proofs = append(proofs, m.tree[rightChildIdx])
-	}
+	siblingIdx := rightChildIdx
+	if right {
+		siblingIdx = leftChildIdx
+	}
+	proofs = append(proofs, m.tree[siblingIdx])
}
```

---

`280-293`: **Error message improvement in CalculateBalancedNodesCount.**

The error messages could be more informative to help diagnose issues. Consider adding details about the actual input value that caused the error.

```diff
func CalculateBalancedNodesCount(count int) (int, error) {
	if count <= 0 {
-		return 0, fmt.Errorf("count must be greater than 0")
+		return 0, fmt.Errorf("count must be greater than 0, got %d", count)
	}

	if count > int(1<<31) {
-		return 0, fmt.Errorf("count must be less than or equal to 2^31")
+		return 0, fmt.Errorf("count must be less than or equal to 2^31, got %d", count)
	}

	return int(roundUpToPowerOf2(uint32(count))), nil
}
```

---

`69-104`: **Consider adding validation for negative indices in GenerateMultiProofWithIndices.**

While the `makeProof` function validates indices, adding an early check for negative values in the public API methods would provide clearer error messages.

```diff
func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	// Early validation for negative indices
+	for _, idx := range indices {
+		if idx < 0 {
+			return nil, fmt.Errorf("negative index %d is invalid", idx)
+		}
+	}
+
	sortedIndices := make([]int, len(indices))
	copy(sortedIndices, indices)
	sort.Ints(sortedIndices)
```

---

`209-219`: **Consider using constants for clarity in makeTree.**

The tree building logic relies on understanding the 1-indexed representation. Using named constants could make the code more readable.

```diff
+	// Constants for clarity
+	const ROOT_INDEX = 1

	lowerBound := balancedLeafCount
	upperBound := balancedLeafCount + len(nodes) - 1

	// Copy leaves into the tree, starting at index N.
	for i := 0; i < len(nodes); i++ {
		tree[lowerBound+i] = nodes[i]
	}
```

</blockquote></details>

</blockquote></details>

<details>
<summary>📜 Review details</summary>

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<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between 0b0be338da219cd4df69358e657794c7ecdd8ebf and d34a3ebfb00185f3913fdb5fe5fb05d457eaad5e.

</details>

<details>
<summary>📒 Files selected for processing (1)</summary>

* `pkg/merkle/tree.go` (1 hunks)

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧬 Code Graph Analysis (1)</summary>

<details>
<summary>pkg/merkle/tree.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/hash.go (4)</summary>

* `Hash` (18-22)
* `HashEmptyLeaf` (45-47)
* `HashNode` (24-33)
* `HashLeaf` (35-43)

</details>
<details>
<summary>pkg/merkle/proof.go (2)</summary>

* `MultiProof` (28-32)
* `ErrGenerateProof` (11-11)

</details>

</blockquote></details>

</details>

</details>

<details>
<summary>⏰ Context from checks skipped due to timeout of 90000ms (5)</summary>

* GitHub Check: Push Docker Images to GitHub Packages (xmtpd-cli)
* GitHub Check: Test (Node)
* GitHub Check: Push Docker Images to GitHub Packages (xmtpd)
* GitHub Check: Upgrade Tests
* GitHub Check: Code Review

</details>

<details>
<summary>🔇 Additional comments (4)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (4)</summary>

`14-23`: **Defensive copy in Hash() method is a good practice.**

Creating a defensive copy of the hash ensures that external code cannot modify the internal state of the tree nodes. This immutability helps prevent subtle bugs that could arise from accidental modifications.

---

`27-38`: **Well-documented data structure design.**

The documentation clearly explains the 1-indexed array structure of the Merkle tree, which makes the code easier to understand. This implementation choice follows a common approach for binary trees where parent-child relationships can be calculated using simple arithmetic.

---

`45-67`: **Proper error handling in NewMerkleTree.**

The constructor properly propagates errors from helper functions, ensuring that any issues during tree construction are reported accurately to the caller.

---

`220-240`: <details>
<summary>❌ Incorrect review comment</summary>

**Check for nil hash before dereferencing in makeTree.**

When building the tree, the code doesn't check if `Hash()` returns nil before using it in `HashNode()`. This could lead to a panic if one of the child nodes has a nil hash.

```diff
tree[i] = Node{
-	hash: HashNode(tree[leftChildIndex].Hash(), tree[rightChildIndex].Hash()),
+	hash: HashNode(
+		getNonNilHash(tree[leftChildIndex].Hash()), 
+		getNonNilHash(tree[rightChildIndex].Hash()),
+	),
}

// Add this helper function:
// func getNonNilHash(hash []byte) []byte {
//     if hash == nil {
//         return []byte{}
//     }
//     return hash
// }
```

Let's verify if a nil hash can actually occur in practice:

---

🏁 Script executed:

```shell
#!/bin/bash
# Search for any places where a Node is created with a nil hash
rg -A 2 -B 2 "Node\s*{(\s*hash:\s*nil|\s*}\s*)" pkg/merkle/
```

Length of output: 184

---

Let’s inspect the `Node` type, its `Hash()` method, the `HashNode` function, and the surrounding `makeTree` logic to confirm whether a nil‐slice can flow through:

---

🏁 Script executed:

```shell
#!/bin/bash
echo "=== Node struct definition ==="
rg -n 'type Node' -n pkg/merkle

echo
echo "=== HashNode function ==="
rg -n 'func HashNode' -n pkg/merkle

echo
echo "=== Hash() method ==="
rg -n 'func .*Hash()' -n pkg/merkle

echo
echo "=== makeTree snippet (lines 200–260) ==="
sed -n '200,260p' pkg/merkle/tree.go
```

Length of output: 2157

---

Let’s confirm the implementations of `HashNode`, `HashLeaf`, and `HashEmptyLeaf` to see if they ever return `nil`:

---

🏁 Script executed:

```shell
#!/bin/bash
echo "=== pkg/merkle/hash.go ==="
sed -n '1,200p' pkg/merkle/hash.go
```

Length of output: 1051

---



</details>

**Drop the nil‐check guard: hashes are always non‐nil**  
All `Node.hash` fields are seeded via `HashLeaf`, `HashEmptyLeaf`, or `HashNode`—and each of those calls `Hash(buffer)`, which always returns a non‑nil `[]byte`. Additionally, `func (n *Node) Hash()` is called on a value receiver (never `nil`). The proposed `getNonNilHash` helper isn’t needed.  


> Likely an incorrect or invalid review comment.

</details>

</blockquote></details>

</details>

<!-- This is an auto-generated comment by CodeRabbit for review status -->
state: COMMENTED
author_association: CONTRIBUTOR
submitted_at: 2025-04-21T11:22:38Z
user: login: fbac
state: COMMENTED
author_association: COLLABORATOR
submitted_at: 2025-04-21T11:24:56Z
user: login: coderabbitai[bot]
body: **Actionable comments posted: 0**

<details>
<summary>🧹 Nitpick comments (2)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (2)</summary><blockquote>

`295-308`: **Consider adding a const for the maximum accepted value.**

While the overflow check in CalculateBalancedNodesCount prevents integer overflow by limiting the count to 2^31, consider adding a named constant for this maximum value to make the code more readable and maintainable.

```diff
+ const MaxNodeCount = 1 << 31 // Maximum node count to prevent overflow

  func CalculateBalancedNodesCount(count int) (int, error) {
      if count <= 0 {
          return 0, fmt.Errorf("count must be greater than 0")
      }

-     if count > int(1<<31) {
+     if count > MaxNodeCount {
          return 0, fmt.Errorf("count must be less than or equal to 2^31")
      }

      return int(roundUpToPowerOf2(uint32(count))), nil
  }
```

---

`310-318`: **Consider using more idiomatic Go function names.**

The functions `GetLeftChild` and `GetRightChild` follow traditional OOP naming conventions. In Go, the "Get" prefix is typically omitted. Consider renaming to `LeftChild` and `RightChild` to follow idiomatic Go naming conventions.

```diff
- func GetLeftChild(index int) int {
+ func LeftChild(index int) int {
      return index << 1 // index * 2
  }

- func GetRightChild(index int) int {
+ func RightChild(index int) int {
      return (index << 1) + 1 // index * 2 + 1
  }
```

</blockquote></details>

</blockquote></details>

<details>
<summary>📜 Review details</summary>

**Configuration used: CodeRabbit UI**
**Review profile: CHILL**
**Plan: Pro**

<details>
<summary>📥 Commits</summary>

Reviewing files that changed from the base of the PR and between d34a3ebfb00185f3913fdb5fe5fb05d457eaad5e and 439d038928efff83c3f35060b97ddfee04b8f17b.

</details>

<details>
<summary>📒 Files selected for processing (2)</summary>

* `pkg/merkle/tree.go` (1 hunks)
* `pkg/merkle/tree_test.go` (1 hunks)

</details>

<details>
<summary>🚧 Files skipped from review as they are similar to previous changes (1)</summary>

* pkg/merkle/tree_test.go

</details>

<details>
<summary>🧰 Additional context used</summary>

<details>
<summary>🧬 Code Graph Analysis (1)</summary>

<details>
<summary>pkg/merkle/tree.go (2)</summary><blockquote>

<details>
<summary>pkg/merkle/hash.go (4)</summary>

* `Hash` (18-22)
* `HashEmptyLeaf` (45-47)
* `HashNode` (24-33)
* `HashLeaf` (35-43)

</details>
<details>
<summary>pkg/merkle/proof.go (2)</summary>

* `MultiProof` (28-32)
* `ErrGenerateProof` (11-11)

</details>

</blockquote></details>

</details>

</details>

<details>
<summary>⏰ Context from checks skipped due to timeout of 90000ms (1)</summary>

* GitHub Check: Test (Node)

</details>

<details>
<summary>🔇 Additional comments (8)</summary><blockquote>

<details>
<summary>pkg/merkle/tree.go (8)</summary>

`10-23`: **LGTM: Node struct with defensive Hash method.**

The Node struct definition is clean and the Hash() method correctly handles nil values and defensively returns a copy of the hash value to prevent accidental modifications of the internal state. This is a good practice for immutability.

---

`27-38`: **LGTM: Well-documented MerkleTree struct with clear indexing explanation.**

The struct definition and comments clearly explain the 1-indexed nature of the tree array representation. This explicit documentation of the indexing scheme is essential for understanding the implementation.

---

`45-67`: **LGTM: Clean constructor with proper error handling.**

The NewMerkleTree function follows a clear step-by-step construction process with appropriate error handling at each stage. The delegation to helper functions keeps the constructor clean and focused.

---

`69-86`: **LGTM: Sequential multi-proof generation with proper validation.**

The GenerateMultiProofSequential method properly creates and validates indices before generating the proof. The final validation step ensures the generated proof is correct.

---

`88-104`: **LGTM: Multi-proof generation for arbitrary indices with sorting.**

The GenerateMultiProofWithIndices method correctly sorts the indices to ensure consistent proof generation. This is important for the internal algorithm and allows for verification using the canonical ordering.

---

`106-164`: **LGTM: Well-implemented proof generation algorithm.**

The makeProof method correctly validates inputs, handles the single-element tree edge case, and implements the proof generation algorithm. The approach of marking nodes as known and walking up the tree is efficient and matches the standard Merkle proof generation approach.

---

`186-244`: **LGTM: Thorough tree construction implementation.**

The makeTree function correctly implements the bottom-up tree construction algorithm with proper error handling and empty tree checks. The algorithm efficiently builds the tree by calculating hashes from the leaf level up.

---

`176-179`: <details>
<summary>❌ Incorrect review comment</summary>

**Ensure Root() works with empty trees.**

The Root() method directly accesses index 1 without checking if the tree array has at least 2 elements. While the constructor ensures non-empty trees, defensive programming would suggest adding a bounds check.

---

🏁 Script executed:

```shell
#!/bin/bash
# Check if there are any functions that call Root() that might not verify the tree is non-empty first
rg -A 5 "Root\(\)" pkg/merkle
```

Length of output: 4860

---



</details>

**No change needed: `Root()` is safe for empty trees**  

The MerkleTree constructor uses `CalculateBalancedNodesCount`, which guarantees a minimum leaf count of 1 (so `m.tree` is always at least length 2). Existing tests—especially `TestTreeWithEmptyElements`—already exercise `Root()` on an empty tree and assert it’s non‑nil. A bounds check isn’t required here.  


> Likely an incorrect or invalid review comment.

</details>

</blockquote></details>

</details>

<!-- This is an auto-generated comment by CodeRabbit for review status -->
state: COMMENTED
author_association: CONTRIBUTOR
submitted_at: 2025-04-21T11:25:30Z
user: login: mkysel
state: APPROVED
author_association: COLLABORATOR
submitted_at: 2025-04-21T13:07:29Z

Review comments:
diff_hunk: @@ -0,0 +1,150 @@
+package merkle
+
+import (
+	"errors"
+	"math"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	depth     int
+	leafCount int
+}
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	tree, depth := buildTree(leaves)
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[0],
+		depth:     depth,
+		leafCount: len(elements),
+	}, nil
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// Elements returns the elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Depth returns the depth of the Merkle tree.
+func (m *MerkleTree) Depth() int {
+	return m.depth
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+// The matrix representation has the root at index 0.
+// The internal nodes are at index 1 to N-1.
+// The leaves are at index N to 2N-1.
+// For any node at index i:
+// - its left child is at index 2*i and its right child is at index 2*i+1.
+// - its parent is at index i/2.
+func buildTree(leaves [][]byte) ([][]byte, int) {
+	depth := getDepth(len(leaves))
+	leafCount := getLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		if i == 0 {
+			if tree[1] != nil {
+				tree[0] = tree[1]
+			} else if tree[1] != nil && tree[2] != nil {
+				tree[0] = HashNode(tree[1], tree[2])
+			}
+			break
path: pkg/merkle/tree.go
user: login: coderabbitai[bot]
body: _⚠️ Potential issue_

**Fix dead code branch for root calculation.**

The condition at line 81 checks `if tree[1] != nil`, and the `else if tree[1] != nil && tree[2] != nil` block at line 83 is never reached. This suggests a logic error that prevents hashing both children when both are non-nil:

Please consider a fix similar to:

```diff
- if tree[1] != nil {
-   tree[0] = tree[1]
- } else if tree[1] != nil && tree[2] != nil {
-   tree[0] = HashNode(tree[1], tree[2])
- }
+ if tree[1] != nil && tree[2] != nil {
+   tree[0] = HashNode(tree[1], tree[2])
+ } else if tree[1] != nil {
+   tree[0] = tree[1]
+ } else if tree[2] != nil {
+   tree[0] = tree[2]
+ }
```


<!-- suggestion_start -->

<details>
<summary>📝 Committable suggestion</summary>

> ‼️ **IMPORTANT**
> Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

`````suggestion
		if i == 0 {
			if tree[1] != nil && tree[2] != nil {
				tree[0] = HashNode(tree[1], tree[2])
			} else if tree[1] != nil {
				tree[0] = tree[1]
			} else if tree[2] != nil {
				tree[0] = tree[2]
			}
			break
`````

</details>

<!-- suggestion_end -->

<!-- This is an auto-generated comment by CodeRabbit -->
created_at: 2025-04-11T17:41:16Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,150 @@
+package merkle
+
+import (
+	"errors"
+	"math"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	depth     int
+	leafCount int
+}
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	tree, depth := buildTree(leaves)
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[0],
+		depth:     depth,
+		leafCount: len(elements),
+	}, nil
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// Elements returns the elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Depth returns the depth of the Merkle tree.
+func (m *MerkleTree) Depth() int {
+	return m.depth
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+// The matrix representation has the root at index 0.
+// The internal nodes are at index 1 to N-1.
+// The leaves are at index N to 2N-1.
+// For any node at index i:
+// - its left child is at index 2*i and its right child is at index 2*i+1.
+// - its parent is at index i/2.
+func buildTree(leaves [][]byte) ([][]byte, int) {
+	depth := getDepth(len(leaves))
+	leafCount := getLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		if i == 0 {
+			if tree[1] != nil {
+				tree[0] = tree[1]
+			} else if tree[1] != nil && tree[2] != nil {
+				tree[0] = HashNode(tree[1], tree[2])
+			}
+			break
+		}
+
+		leftChildIndex := getLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := getRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	return tree, depth
+}
+
+// getDepth calculates the depth of a Merkle tree based on element count.
+func getDepth(elementCount int) int {
+	return int(math.Ceil(math.Log2(float64(elementCount))))
path: pkg/merkle/tree.go
user: login: macroscopeapp[bot]
body: The `getDepth` function currently computes the logarithm without checking that `elementCount` is positive. If `elementCount` is 0 or negative, calling `math.Log2` can result in `-Inf` or `NaN`, which is likely not the intended behavior. Consider adding a condition to validate that `elementCount` is greater than 0, and handle cases when it isn't.

```diff
+	if elementCount <= 0 { return 0 }
```
> 🚀 Reply to ask Macroscope to explain or update this suggestion.

> 👍 Helpful? React to give us feedback.
created_at: 2025-04-11T17:41:17Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,150 @@
+package merkle
+
+import (
+	"errors"
+	"math"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	depth     int
+	leafCount int
+}
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	tree, depth := buildTree(leaves)
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[0],
+		depth:     depth,
+		leafCount: len(elements),
+	}, nil
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// Elements returns the elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Depth returns the depth of the Merkle tree.
+func (m *MerkleTree) Depth() int {
+	return m.depth
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+// The matrix representation has the root at index 0.
+// The internal nodes are at index 1 to N-1.
+// The leaves are at index N to 2N-1.
+// For any node at index i:
+// - its left child is at index 2*i and its right child is at index 2*i+1.
+// - its parent is at index i/2.
+func buildTree(leaves [][]byte) ([][]byte, int) {
+	depth := getDepth(len(leaves))
+	leafCount := getLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		if i == 0 {
+			if tree[1] != nil {
+				tree[0] = tree[1]
+			} else if tree[1] != nil && tree[2] != nil {
+				tree[0] = HashNode(tree[1], tree[2])
+			}
+			break
+		}
path: pkg/merkle/tree.go
user: login: macroscopeapp[bot]
body: The logic in the `buildTree` function for handling the root node appears to use a condition where if `tree[1]` is non-nil, it assigns that value to the root without checking if `tree[2]` is also available. In scenarios where both `tree[1]` and `tree[2]` are non-nil, this prevents the use of `HashNode` to combine both children. Consider reversing the condition order to first check that both children are available before falling back to only one child. This diff swaps the condition checks, ensuring that if both `tree[1]` and `tree[2]` exist, the root is computed using `HashNode`.

```diff
-		if tree[1] != nil {
-			tree[0] = tree[1]
-		} else if tree[1] != nil && tree[2] != nil {
-			tree[0] = HashNode(tree[1], tree[2])
-		}
+		if tree[1] != nil && tree[2] != nil {
+			tree[0] = HashNode(tree[1], tree[2])
+		} else if tree[1] != nil {
+			tree[0] = tree[1]
+		}
```
> 🚀 Reply to ask Macroscope to explain or update this suggestion.

> 👍 Helpful? React to give us feedback.
created_at: 2025-04-11T17:41:17Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,150 @@
+package merkle
+
+import (
+	"errors"
+	"math"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	depth     int
+	leafCount int
+}
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	tree, depth := buildTree(leaves)
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[0],
+		depth:     depth,
+		leafCount: len(elements),
+	}, nil
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// Elements returns the elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Depth returns the depth of the Merkle tree.
+func (m *MerkleTree) Depth() int {
+	return m.depth
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+// The matrix representation has the root at index 0.
+// The internal nodes are at index 1 to N-1.
+// The leaves are at index N to 2N-1.
+// For any node at index i:
+// - its left child is at index 2*i and its right child is at index 2*i+1.
+// - its parent is at index i/2.
+func buildTree(leaves [][]byte) ([][]byte, int) {
+	depth := getDepth(len(leaves))
+	leafCount := getLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		if i == 0 {
+			if tree[1] != nil {
+				tree[0] = tree[1]
+			} else if tree[1] != nil && tree[2] != nil {
+				tree[0] = HashNode(tree[1], tree[2])
+			}
+			break
+		}
+
+		leftChildIndex := getLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := getRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	return tree, depth
+}
+
+// getDepth calculates the depth of a Merkle tree based on element count.
+func getDepth(elementCount int) int {
+	return int(math.Ceil(math.Log2(float64(elementCount))))
+}
+
+// getLeafCount returns the number of leaves in a tree.
+func getLeafCount(elementCount int) int {
+	return int(roundUpToPowerOf2(uint32(elementCount)))
+}
+
+// roundUpToPowerOf2 rounds up a number to the next power of 2.
+// Rounding up to the next power of 2 is necessary to ensure that the tree is balanced.
+func roundUpToPowerOf2(number uint32) uint32 {
path: pkg/merkle/tree.go
user: login: mkysel
body: fancy bit smearing! 

I like this one more than the [btcd](https://github.com/btcsuite/btcd/blob/master/blockchain/merkle.go#L48) float conversion
created_at: 2025-04-11T19:26:33Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,150 @@
+package merkle
+
+import (
+	"errors"
+	"math"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	depth     int
+	leafCount int
+}
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	tree, depth := buildTree(leaves)
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[0],
+		depth:     depth,
+		leafCount: len(elements),
+	}, nil
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// Elements returns the elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Depth returns the depth of the Merkle tree.
+func (m *MerkleTree) Depth() int {
+	return m.depth
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+// The matrix representation has the root at index 0.
+// The internal nodes are at index 1 to N-1.
+// The leaves are at index N to 2N-1.
+// For any node at index i:
+// - its left child is at index 2*i and its right child is at index 2*i+1.
+// - its parent is at index i/2.
+func buildTree(leaves [][]byte) ([][]byte, int) {
+	depth := getDepth(len(leaves))
+	leafCount := getLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		if i == 0 {
+			if tree[1] != nil {
+				tree[0] = tree[1]
+			} else if tree[1] != nil && tree[2] != nil {
+				tree[0] = HashNode(tree[1], tree[2])
+			}
+			break
+		}
+
+		leftChildIndex := getLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := getRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	return tree, depth
+}
+
+// getDepth calculates the depth of a Merkle tree based on element count.
+func getDepth(elementCount int) int {
+	return int(math.Ceil(math.Log2(float64(elementCount))))
path: pkg/merkle/tree.go
user: login: mkysel
body: I would recommend this
```
func getDepth(n uint32) int {
	if n <= 1 {
		return 0
	}
	// Round up to next power of 2 if not already a power of 2
	if bits.OnesCount32(n) > 1 {
		n = roundUpToPowerOf2(n)
	}
	// bits.Len32 gives position of highest bit + 1
	return bits.Len32(n) - 1
}
```

does that sound better?
created_at: 2025-04-11T19:29:44Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,150 @@
+package merkle
+
+import (
+	"errors"
+	"math"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	depth     int
+	leafCount int
+}
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	tree, depth := buildTree(leaves)
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[0],
+		depth:     depth,
+		leafCount: len(elements),
+	}, nil
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// Elements returns the elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Depth returns the depth of the Merkle tree.
+func (m *MerkleTree) Depth() int {
+	return m.depth
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+// The matrix representation has the root at index 0.
+// The internal nodes are at index 1 to N-1.
+// The leaves are at index N to 2N-1.
+// For any node at index i:
+// - its left child is at index 2*i and its right child is at index 2*i+1.
+// - its parent is at index i/2.
+func buildTree(leaves [][]byte) ([][]byte, int) {
+	depth := getDepth(len(leaves))
+	leafCount := getLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		if i == 0 {
+			if tree[1] != nil {
+				tree[0] = tree[1]
+			} else if tree[1] != nil && tree[2] != nil {
+				tree[0] = HashNode(tree[1], tree[2])
+			}
+			break
+		}
+
+		leftChildIndex := getLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := getRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	return tree, depth
+}
+
+// getDepth calculates the depth of a Merkle tree based on element count.
+func getDepth(elementCount int) int {
+	return int(math.Ceil(math.Log2(float64(elementCount))))
path: pkg/merkle/tree.go
user: login: macroscopeapp[bot]
body: Yes, that's a much better approach! Your solution not only addresses the original issue with invalid inputs but also improves efficiency by using bit manipulation instead of floating-point operations. The type change to `uint32` naturally prevents negative inputs, and the explicit check for `n <= 1` handles edge cases correctly. Using `bits.Len32` is also more precise for this use case. Well done!
created_at: 2025-04-11T19:30:05Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,150 @@
+package merkle
+
+import (
+	"errors"
+	"math"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	depth     int
+	leafCount int
+}
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	tree, depth := buildTree(leaves)
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[0],
+		depth:     depth,
+		leafCount: len(elements),
+	}, nil
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// Elements returns the elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Depth returns the depth of the Merkle tree.
+func (m *MerkleTree) Depth() int {
+	return m.depth
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+// The matrix representation has the root at index 0.
+// The internal nodes are at index 1 to N-1.
+// The leaves are at index N to 2N-1.
+// For any node at index i:
+// - its left child is at index 2*i and its right child is at index 2*i+1.
+// - its parent is at index i/2.
+func buildTree(leaves [][]byte) ([][]byte, int) {
+	depth := getDepth(len(leaves))
+	leafCount := getLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		if i == 0 {
+			if tree[1] != nil {
+				tree[0] = tree[1]
+			} else if tree[1] != nil && tree[2] != nil {
+				tree[0] = HashNode(tree[1], tree[2])
+			}
+			break
+		}
+
+		leftChildIndex := getLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := getRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	return tree, depth
+}
+
+// getDepth calculates the depth of a Merkle tree based on element count.
+func getDepth(elementCount int) int {
+	return int(math.Ceil(math.Log2(float64(elementCount))))
+}
+
+// getLeafCount returns the number of leaves in a tree.
+func getLeafCount(elementCount int) int {
+	return int(roundUpToPowerOf2(uint32(elementCount)))
+}
+
+// roundUpToPowerOf2 rounds up a number to the next power of 2.
+// Rounding up to the next power of 2 is necessary to ensure that the tree is balanced.
+func roundUpToPowerOf2(number uint32) uint32 {
path: pkg/merkle/tree.go
user: login: mkysel
body: This might be even faster:
```
func roundUpToPowerOf2(n uint32) uint32 {
	n--
	n |= n >> 1
	n |= n >> 2
	n |= n >> 4
	n |= n >> 8
	n |= n >> 16
	n++
	return n
}
```
created_at: 2025-04-11T19:31:16Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,26 @@
+package merkle
+
+import (
+	"golang.org/x/crypto/sha3"
+)
+
+// LEAF_PREFIX is the prefix for leaf nodes.
+// It is used to distinguish leaf nodes from other types of nodes.
+const LEAF_PREFIX = "leaf|"
path: pkg/merkle/hash.go
user: login: mkysel
body: you can't really retrieve the fact that some cryptographic hash has a `LEAF|` prefix by looking at the hash. So you can write it, but you can't ever read it out again.

What purpose does it serve?
created_at: 2025-04-11T19:34:07Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,150 @@
+package merkle
+
+import (
+	"errors"
+	"math"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
path: pkg/merkle/tree.go
user: login: mkysel
body: my brain refuses to process anything related to `[][]`. 

If I were writing this, I would typedef the node so at least its `tree []Node`

Even if it is as simple as 
```
type Node struct {
	Hash []byte
}
```
created_at: 2025-04-11T19:40:25Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,26 @@
+package merkle
+
+import (
+	"golang.org/x/crypto/sha3"
+)
+
+// LEAF_PREFIX is the prefix for leaf nodes.
+// It is used to distinguish leaf nodes from other types of nodes.
+const LEAF_PREFIX = "leaf|"
path: pkg/merkle/hash.go
user: login: mkysel
body: we can get into the weeds of cryptography here, but a standalone `prefix` can not solve domain `separation`.

If we assume that the purpose of this prefix is to prevent a malicious `leaf input` from colliding with an internal node operation, it does not quite work that way.

`leaf|` aka `0x4C4541467C` is just a prefix. If you can find an internal node that starts with exactly these bytes you can craft a payload that is "(nothing instead of leaf|) || leaf1-suffix || leaf2) and you will get a collision.

I think that you need to prefix both the leaf and the internal node to achieve true domain separation.
created_at: 2025-04-11T20:02:18Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,26 @@
+package merkle
+
+import (
+	"golang.org/x/crypto/sha3"
+)
+
+// LEAF_PREFIX is the prefix for leaf nodes.
+// It is used to distinguish leaf nodes from other types of nodes.
+const LEAF_PREFIX = "leaf|"
path: pkg/merkle/hash.go
user: login: mkysel
body: or just double hash :D https://github.com/OpenZeppelin/merkle-tree/blob/master/src/hashes.ts
created_at: 2025-04-11T20:02:26Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,26 @@
+package merkle
+
+import (
+	"golang.org/x/crypto/sha3"
+)
+
+// LEAF_PREFIX is the prefix for leaf nodes.
+// It is used to distinguish leaf nodes from other types of nodes.
+const LEAF_PREFIX = "leaf|"
path: pkg/merkle/hash.go
user: login: mkysel
body: Hey @macroscopeapp. Hey @coderabbitai. Compare the correctness, structural integrity and safety of Hash(LEAF|payload) == Hash(leftHash || rightHash) vs Hash(LEAF|payload) == Hash(NODE|leftHash || rightHash) vs Hash(payload) == Hash(leftHash || rightHash)
created_at: 2025-04-11T20:13:33Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,26 @@
+package merkle
+
+import (
+	"golang.org/x/crypto/sha3"
+)
+
+// LEAF_PREFIX is the prefix for leaf nodes.
+// It is used to distinguish leaf nodes from other types of nodes.
+const LEAF_PREFIX = "leaf|"
path: pkg/merkle/hash.go
user: login: coderabbitai[bot]
body: @mkysel Let me compare the three hashing approaches:

1. **Hash(LEAF|payload) == Hash(leftHash || rightHash)** (current implementation):
   - **Security**: Vulnerable to second preimage attacks. An attacker could potentially craft a payload that when hashed without the LEAF prefix produces a hash that collides with an internal node hash.
   - **Integrity**: Only partially protects the tree structure by distinguishing leaves from internal nodes in one direction.
   - **Safety**: Insufficient domain separation as internal nodes aren't prefixed.

2. **Hash(LEAF|payload) == Hash(NODE|leftHash || rightHash)**:
   - **Security**: Much stronger. Creates true domain separation by ensuring leaf and internal node hashes come from distinct domains.
   - **Integrity**: Fully protects the tree structure as neither node type can be substituted for the other.
   - **Safety**: Prevents an attacker from constructing a leaf whose hash could be mistaken for a node hash and vice versa.

3. **Hash(payload) == Hash(leftHash || rightHash)**:
   - **Security**: Most vulnerable to second preimage attacks.
   - **Integrity**: No structural protection; leaf nodes could be confused with internal nodes.
   - **Safety**: Allows for potential substitution attacks.

The second approach with both prefixes is the most secure option as it implements true domain separation. Alternatively, the double hashing approach used by OpenZeppelin (that you referenced) also provides strong security by hashing twice rather than using prefixes.

For cryptographic security in Merkle trees, I would recommend either using both prefixes or implementing the double hashing approach.
---
<details>
<summary>✏️ Learnings added</summary>

```
Learnt from: mkysel
PR: xmtp/xmtpd#712
File: pkg/merkle/hash.go:7-9
Timestamp: 2025-04-11T20:14:15.760Z
Learning: In Merkle tree implementations, domain separation is important for security. Use either explicit prefixes for both leaf and internal nodes (e.g., "leaf|" and "node|") or double hashing to prevent second preimage attacks. Simply prefixing leaf nodes without prefixing internal nodes doesn't provide true domain separation and could be vulnerable to attacks.
```

> Note: Learnings are effective only in the context of similar code segments. To apply general coding guidelines, please configure [review instructions](https://docs.coderabbit.ai/guides/review-instructions). You can manage existing learnings in the [app](https://app.coderabbit.ai/learnings).

</details>



<!-- <agentComponentType>chat-answer</agentComponentType> -->

<!-- <rawResChunk><answer>@mkysel Let me compare the three hashing approaches:

1. **Hash(LEAF|payload) == Hash(leftHash || rightHash)** (current implementation):
   - **Security**: Vulnerable to second preimage attacks. An attacker could potentially craft a payload that when hashed without the LEAF prefix produces a hash that collides with an internal node hash.
   - **Integrity**: Only partially protects the tree structure by distinguishing leaves from internal nodes in one direction.
   - **Safety**: Insufficient domain separation as internal nodes aren't prefixed.

2. **Hash(LEAF|payload) == Hash(NODE|leftHash || rightHash)**:
   - **Security**: Much stronger. Creates true domain separation by ensuring leaf and internal node hashes come from distinct domains.
   - **Integrity**: Fully protects the tree structure as neither node type can be substituted for the other.
   - **Safety**: Prevents an attacker from constructing a leaf whose hash could be mistaken for a node hash and vice versa.

3. **Hash(payload) == Hash(leftHash || rightHash)**:
   - **Security**: Most vulnerable to second preimage attacks.
   - **Integrity**: No structural protection; leaf nodes could be confused with internal nodes.
   - **Safety**: Allows for potential substitution attacks.

The second approach with both prefixes is the most secure option as it implements true domain separation. Alternatively, the double hashing approach used by OpenZeppelin (that you referenced) also provides strong security by hashing twice rather than using prefixes.

For cryptographic security in Merkle trees, I would recommend either using both prefixes or implementing the double hashing approach.
---

<details>
<summary>✏️ Learnings added</summary>

```
Learnt from: mkysel
PR: xmtp/xmtpd#712
File: pkg/merkle/hash.go:7-9
Timestamp: 2025-04-11T20:14:15.760Z
Learning: In Merkle tree implementations, domain separation is important for security. Use either explicit prefixes for both leaf and internal nodes (e.g., "leaf|" and "node|") or double hashing to prevent second preimage attacks. Simply prefixing leaf nodes without prefixing internal nodes doesn't provide true domain separation and could be vulnerable to attacks.
```

> Note: Learnings are effective only in the context of similar code segments. To apply general coding guidelines, please configure [review instructions](https://docs.coderabbit.ai/guides/review-instructions). You can manage existing learnings in the [app](https://app.coderabbit.ai/learnings).

</details></answer></rawResChunk> -->

<!-- This is an auto-generated reply by CodeRabbit -->
created_at: 2025-04-11T20:14:17Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,331 @@
+package merkle
path: pkg/merkle/tree_test.go
user: login: mkysel
body: Nit: I prefer using `merkle_test` so you can't muck with the internals of the package. There is no right or wrong way, we have just been moving a lot of tests from the the same package into its own (_test) for exactly this reason.
created_at: 2025-04-11T20:25:45Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,154 @@
+package merkle
+
+import (
+	"errors"
+	"math"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	depth     int
+	leafCount int
+}
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	tree, depth := buildTree(leaves)
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[1],
+		depth:     depth,
+		leafCount: len(elements),
+	}, nil
+}
+
+// Tree returns the tree of the Merkle tree.
+func (m *MerkleTree) Tree() [][]byte {
+	return m.tree
+}
+
+// Elements returns the elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// Depth returns the depth of the Merkle tree.
+func (m *MerkleTree) Depth() int {
+	return m.depth
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return m.leafCount
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func buildTree(leaves [][]byte) ([][]byte, int) {
+	depth := getDepth(len(leaves))
+	leafCount := getLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		leftChildIndex := getLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := getRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	return tree, depth
+}
+
+// getDepth calculates the depth of a Merkle tree based on element count.
+func getDepth(elementCount int) int {
+	return int(math.Ceil(math.Log2(float64(elementCount))))
+}
+
+// getLeafCount returns the number of leaves in a tree.
+func getLeafCount(elementCount int) int {
+	return int(roundUpToPowerOf2(uint32(elementCount)))
+}
+
+// roundUpToPowerOf2 rounds up a number to the next power of 2.
+// Rounding up to the next power of 2 is necessary to ensure that the tree is balanced.
+func roundUpToPowerOf2(number uint32) uint32 {
+	if bits.OnesCount32(number) == 1 {
+		return number
+	}
+
+	number |= number >> 1
+	number |= number >> 2
+	number |= number >> 4
+	number |= number >> 8
+	number |= number >> 16
+
+	return number + 1
path: pkg/merkle/tree.go
user: login: macroscopeapp[bot]
body: The function `roundUpToPowerOf2` currently adds 1 to the bit-propagated number which can result in an integer overflow (e.g. for inputs greater than 0x80000000). This might lead to an unintended result since `uint32` wraps around to 0 when overflow occurs. Consider adding a check for the maximum `uint32` value (using `^uint32(0)`) before adding 1 to avoid the overflow, unless this behavior is deliberate. If it is intentional, consider documenting the rationale behind this overflow behavior.

```diff
-	return number + 1
+	if number == ^uint32(0) {
+		return number
+	}
+	return number + 1
```
> 🚀 Reply to ask Macroscope to explain or update this suggestion.

> 👍 Helpful? React to give us feedback.
created_at: 2025-04-11T22:10:36Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,220 @@
+package merkle
+
+import (
+	"fmt"
+	"sort"
+)
+
+// GenerateMultiProofWithIndices generates a multi-proof for the given indices
+func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	if hasDuplicates(indices) {
+		return nil, fmt.Errorf("found duplicate indices")
+	}
+
+	if hasOutOfBounds(indices, m.leafCount) {
+		return nil, fmt.Errorf("found indices out of range")
+	}
+
+	proof, err := generateProof(m.tree, m.root, indices, m.leafCount)
+	if err != nil {
+		return nil, err
+	}
+
+	// Extract elements at the specified indices.
path: pkg/merkle/proof_indices.go
user: login: macroscopeapp[bot]
body: In `GenerateMultiProofWithIndices`, the extraction of `elements` from `m.elements` is done before sorting the `indices` slice, but the returned `MultiProof` uses the sorted `Indices` (with the sort call occurring later). This may cause the `Elements` array to be misaligned with its corresponding indices. Consider moving the `sort.Ints(indices)` call so that `indices` are sorted before extracting the corresponding elements, ensuring that the order of `Elements` matches the sorted `Indices`.

```diff
+    sort.Ints(indices)
-    sort.Ints(indices)
```
> 🚀 Reply to ask Macroscope to explain or update this suggestion.

> 👍 Helpful? React to give us feedback.
created_at: 2025-04-11T22:10:36Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,244 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+type MultiProof struct {
+	Elements      [][]byte
+	Proofs        [][]byte
+	Root          []byte
+	Indices       []int
+	StartingIndex int
+	ElementCount  int
+}
+
+var (
+	ErrProofNilRoot              = errors.New("proof root cannot be nil")
+	ErrProofNoElements           = errors.New("proof has no elements")
+	ErrProofNoIndices            = errors.New("proof has no indices")
+	ErrProofNoProofs             = errors.New("proof has no proofs")
+	ErrProofInvalidStartingIndex = errors.New("proof has invalid starting index")
+	ErrProofInvalidElementCount  = errors.New("proof has invalid element count")
+	ErrProofInvalidRange         = errors.New("proof has invalid range")
+	ErrProofEmptyTree            = errors.New("proof has empty tree")
+	ErrProofEmptyIndices         = errors.New("proof has empty indices")
+)
+
+// generateProof returns a MultiProof for the given indices.
+func generateProof(
+	tree [][]byte,
+	root []byte,
+	indices []int,
+	elementCount int,
+) (MultiProof, error) {
+	if len(tree) == 0 {
+		return MultiProof{}, ErrProofEmptyTree
+	}
+
+	if root == nil {
+		return MultiProof{}, ErrProofNilRoot
+	}
+
+	if len(indices) == 0 {
+		return MultiProof{}, ErrProofEmptyIndices
+	}
+
+	// Do not modify the original indices slice.
+	idxs := make([]int, len(indices))
+	copy(idxs, indices)
+	sort.Ints(idxs)
+
path: pkg/merkle/proof.go
user: login: coderabbitai[bot]
body: _💡 Verification agent_

<details>
<summary>🧩 Analysis chain</summary>

**Add duplicate or range-check for indices before sorting.**

Currently, the code sorts `idxs` but does not check for duplicates or out-of-bounds. As a result, if the caller provides invalid indices (e.g., duplicates, indices outside the valid range), the function may panic when accessing `known[leafCount + idx]`. Consider calling `hasDuplicates(...)` and `hasOutOfBounds(...)` here to ensure safe proof generation, or confirm they are called upstream.

---

🏁 Script executed:

```shell
#!/bin/bash
# Check if generateProof calls hasDuplicates or hasOutOfBounds anywhere in the codebase.
rg "generateProof" -A 10
```

Length of output: 1775

---



</details>

**Indices validation required: Add duplicate and range-checks before sorting**

The current implementation in `pkg/merkle/proof.go` (lines 50-54) copies and sorts the indices without verifying their validity. Our search through the codebase (e.g., in `pkg/merkle/proof_indices.go` and `pkg/merkle/proof_sequential.go`) indicates that no upstream duplicate or range-checks are being performed before calling `generateProof`. This omission exposes the function to potential panics when invalid indices (duplicates or out-of-bounds) are provided.

Please ensure that you add checks here—using helper functions like `hasDuplicates(...)` and `hasOutOfBounds(...)`—or explicitly document that these validations occur upstream if that is indeed the case. For example, a suggested change could be:

```go
// Do not modify the original indices slice.
idxs := make([]int, len(indices))
copy(idxs, indices)

// Validate indices before sorting.
if hasDuplicates(idxs) {
	return MultiProof{}, errors.New("duplicate indices not allowed")
}
if hasOutOfBounds(idxs, elementCount) {
	return MultiProof{}, errors.New("index out of bounds")
}

sort.Ints(idxs)
```

<!-- This is an auto-generated comment by CodeRabbit -->
created_at: 2025-04-11T22:11:16Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,244 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+type MultiProof struct {
+	Elements      [][]byte
+	Proofs        [][]byte
+	Root          []byte
+	Indices       []int
+	StartingIndex int
+	ElementCount  int
+}
+
+var (
+	ErrProofNilRoot              = errors.New("proof root cannot be nil")
+	ErrProofNoElements           = errors.New("proof has no elements")
+	ErrProofNoIndices            = errors.New("proof has no indices")
+	ErrProofNoProofs             = errors.New("proof has no proofs")
+	ErrProofInvalidStartingIndex = errors.New("proof has invalid starting index")
+	ErrProofInvalidElementCount  = errors.New("proof has invalid element count")
+	ErrProofInvalidRange         = errors.New("proof has invalid range")
+	ErrProofEmptyTree            = errors.New("proof has empty tree")
+	ErrProofEmptyIndices         = errors.New("proof has empty indices")
+)
+
+// generateProof returns a MultiProof for the given indices.
+func generateProof(
+	tree [][]byte,
+	root []byte,
+	indices []int,
+	elementCount int,
+) (MultiProof, error) {
+	if len(tree) == 0 {
+		return MultiProof{}, ErrProofEmptyTree
+	}
+
+	if root == nil {
+		return MultiProof{}, ErrProofNilRoot
+	}
+
+	if len(indices) == 0 {
+		return MultiProof{}, ErrProofEmptyIndices
+	}
+
+	// Do not modify the original indices slice.
+	idxs := make([]int, len(indices))
+	copy(idxs, indices)
+	sort.Ints(idxs)
+
+	// Handle single-element trees.
+	if elementCount == 1 {
+		return MultiProof{
+			Root:         root,
+			Indices:      idxs,
+			ElementCount: elementCount,
+			Proofs:       [][]byte{root},
+		}, nil
+	}
+
+	// Mark provided indices as known.
+	leafCount := len(tree) >> 1
+	known := make([]bool, len(tree))
+	var proofs [][]byte
+
+	for _, idx := range idxs {
+		known[leafCount+idx] = true
+	}
+
+	// Calculate proofs to prove the existence of the indices.
+	for i := leafCount - 1; i > 0; i-- {
+		leftChildIdx := getLeftChild(i)
+		rightChildIdx := getRightChild(i)
+
+		left := known[leftChildIdx]
+		right := known[rightChildIdx]
+
+		// Only one of children would be known, so we need the sibling as a proof
+		if left != right {
+			if right {
+				// Only add non-nil sibling nodes
+				if tree[leftChildIdx] != nil {
+					proofs = append(proofs, cloneBuffer(tree[leftChildIdx]))
+				}
+			} else {
+				// Only add non-nil sibling nodes
+				if tree[rightChildIdx] != nil {
+					proofs = append(proofs, cloneBuffer(tree[rightChildIdx]))
+				}
+			}
+		}
+
+		// If at least one of the children is known, the parent is known
+		known[i] = left || right
+	}
+
+	return MultiProof{
+		Root:         root,
+		Indices:      idxs,
+		ElementCount: elementCount,
+		Proofs:       proofs,
+	}, nil
+}
+
+func verifyProof(
+	proof *MultiProof,
+	validateProof func(proof *MultiProof) error,
+	getRoot func(leafs [][]byte, proofs [][]byte, startingIndex, elementCount int) []byte,
+) (bool, error) {
+	if err := validateProof(proof); err != nil {
+		return false, err
+	}
+
+	// If this is a single-element tree or we're verifying all elements, we don't need proofs.
+	if len(proof.Elements) == proof.ElementCount || proof.ElementCount == 1 {
+		// Just verify that the proof's root matches the recalculated root
+		root := HashLeaf(proof.Elements[0])
+
+		// For multiple elements, we need to combine them
+		if len(proof.Elements) > 1 {
+			leafs := make([][]byte, len(proof.Elements))
+			for i, element := range proof.Elements {
+				leafs[i] = HashLeaf(element)
+			}
+
+			// Combine the leaves into a root
+			root = combineLeaves(leafs)
+		}
+
+		return bytes.Equal(root, proof.Root), nil
+	}
+
+	leafs := make([][]byte, len(proof.Elements))
+	for i, element := range proof.Elements {
+		leafs[i] = HashLeaf(element)
+	}
+
+	result := getRoot(leafs, proof.Proofs, proof.StartingIndex, proof.ElementCount)
+	if result == nil {
+		return false, nil
+	}
+
+	return bytes.Equal(result, proof.Root), nil
+}
+
+// validateProofBase performs common validation for all types of Merkle proofs.
+// This covers the validation requirements shared between indices and sequential proofs.
+func validateProofBase(proof *MultiProof) error {
+	if proof.Root == nil {
+		return fmt.Errorf("proof has nil root")
path: pkg/merkle/proof.go
user: login: macroscopeapp[bot]
body: In the `validateProofBase` function, there is no nil check for the `proof` parameter before its fields are accessed, which could result in a runtime panic when a nil pointer is passed. Consider adding a nil check at the beginning of the function to prevent such dereferencing. If this behavior is intentional, please consider documenting the rationale for omitting the nil check.

```diff
+	if proof == nil {
		return fmt.Errorf("nil proof")
	}

```
> 🚀 Reply to ask Macroscope to explain or update this suggestion.

> 👍 Helpful? React to give us feedback.
created_at: 2025-04-11T22:14:10Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,163 @@
+package merkle
+
+import (
+	"errors"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	depth     int
+	leafCount int
+}
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	tree, depth := buildTree(leaves)
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[1],
+		depth:     depth,
+		leafCount: len(elements),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() [][]byte {
+	return m.tree
+}
+
+// Elements returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// Depth returns the depth of the Merkle tree.
+func (m *MerkleTree) Depth() int {
+	return m.depth
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return m.leafCount
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func buildTree(leaves [][]byte) ([][]byte, int) {
+	depth := getDepth(uint32(len(leaves)))
+	leafCount := GetLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		leftChildIndex := GetLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := GetRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	return tree, depth
+}
+
+// getDepth calculates the depth of a Merkle tree based on element count.
+func getDepth(n uint32) int {
+	if n <= 1 {
+		return 0
+	}
+
+	// Round up to next power of 2 if not already a power of 2.
+	if bits.OnesCount32(n) > 1 {
+		n = roundUpToPowerOf2(n)
+	}
+
+	// bits.Len32 gives position of highest bit + 1.
+	return bits.Len32(n) - 1
+}
+
+// GetLeafCount returns the number of leaves in a tree.
+func GetLeafCount(elementCount int) int {
+	return int(roundUpToPowerOf2(uint32(elementCount)))
path: pkg/merkle/tree.go
user: login: macroscopeapp[bot]
body: The current implementation in both `GetLeafCount` and `roundUpToPowerOf2` may lead to integer overflow for very large input values. In `GetLeafCount`, converting the result of `roundUpToPowerOf2` from `uint32` to `int` could overflow on platforms where `int` is smaller than 32 bits, and in `roundUpToPowerOf2`, the raw addition (`n + 1`) risks overflow when `n` is close to the maximum `uint32` value. Consider adding explicit overflow checks as shown in the diff to prevent unexpected behavior and potential runtime errors.

```diff
-	return int(roundUpToPowerOf2(uint32(elementCount)))
+ 	r := roundUpToPowerOf2(uint32(elementCount))
+ 	if r > uint32(math.MaxInt32) {
+ 		panic("element count too high, overflow in GetLeafCount")
+ 	}
+ 	return int(r)
 
-	return n + 1
+ 	if n == math.MaxUint32 {
+ 		panic("roundUpToPowerOf2 overflow risk: n is math.MaxUint32")
+ 	}
+ 	return n + 1
```
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> 👍 Helpful? React to give us feedback.
created_at: 2025-04-11T22:55:51Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,175 @@
+package merkle
+
+// GenerateMultiProofSequential generates a sequential multi-proof starting from the given index.
+func (m *MerkleTree) GenerateMultiProofSequential(
+	startingIndex, count int,
+) (*MultiProof, error) {
+	if startingIndex < 0 || startingIndex+count > m.leafCount {
+		return nil, ErrProofInvalidRange
path: pkg/merkle/proof_sequential.go
user: login: coderabbitai[bot]
body: _🛠️ Refactor suggestion_

**Consider validating that `count` is positive before range-check.**

If `count` is zero or negative, the function will create an empty or invalid proof. Adding a check here can prevent generating proofs with no elements or negative counts.  


```diff
 if startingIndex < 0 || startingIndex+count > m.leafCount {
+	if count <= 0 {
+		return nil, ErrProofInvalidRange
+	}
 	return nil, ErrProofInvalidRange
 }
```


> Committable suggestion skipped: line range outside the PR's diff.

<!-- This is an auto-generated comment by CodeRabbit -->

✅ Addressed in commit 7cdbc70
created_at: 2025-04-11T23:00:09Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,251 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+type MultiProof struct {
+	Elements      [][]byte
+	Proofs        [][]byte
+	Root          []byte
+	Indices       []int
+	StartingIndex int
+	ElementCount  int
+}
+
+var (
+	ErrProofEmptyTree            = errors.New("proof has empty tree")
+	ErrProofEmptyIndices         = errors.New("proof has empty indices")
+	ErrProofDuplicateIndices     = errors.New("proof has duplicate indices")
+	ErrProofIndicesOutOfBounds   = errors.New("proof has indices out of bounds")
+	ErrProofInvalidStartingIndex = errors.New("proof has invalid starting index")
+	ErrProofInvalidElementCount  = errors.New("proof has invalid element count")
+	ErrProofInvalidRange         = errors.New("proof has invalid range")
+	ErrProofNil                  = errors.New("proof is nil")
+	ErrProofNilRoot              = errors.New("proof root cannot be nil")
+	ErrProofNoElements           = errors.New("proof has no elements")
+	ErrProofNoIndices            = errors.New("proof has no indices")
+	ErrProofNoProofs             = errors.New("proof has no proofs")
+)
+
+// generateProof returns a MultiProof for the given indices.
+func generateProof(
+	tree [][]byte,
+	root []byte,
+	indices []int,
+	elementCount int,
+) (MultiProof, error) {
+	if len(tree) == 0 {
+		return MultiProof{}, ErrProofEmptyTree
+	}
+
+	if root == nil {
+		return MultiProof{}, ErrProofNilRoot
+	}
+
+	if len(indices) == 0 {
+		return MultiProof{}, ErrProofEmptyIndices
+	}
+
+	// Do not modify the original indices slice.
+	idxs := make([]int, len(indices))
+	copy(idxs, indices)
+	sort.Ints(idxs)
+
+	// Handle single-element trees.
+	if elementCount == 1 {
+		return MultiProof{
+			Root:         root,
+			Indices:      idxs,
+			ElementCount: elementCount,
+			Proofs:       [][]byte{root},
+		}, nil
+	}
+
+	// Mark provided indices as known.
+	leafCount := len(tree) >> 1
+	known := make([]bool, len(tree))
+	var proofs [][]byte
+
+	for _, idx := range idxs {
+		known[leafCount+idx] = true
+	}
path: pkg/merkle/proof.go
user: login: coderabbitai[bot]
body: _💡 Verification agent_

<details>
<summary>🧩 Analysis chain</summary>

**Consider verifying `idx < leafCount` before marking `known[leafCount+idx]`.**

Because `leafCount` is derived as `len(tree) >> 1`, but `elementCount` can differ, referencing `known[leafCount+idx]` might cause a panic if `idx` >= `leafCount`. Confirm that `elementCount` always matches `leafCount` or add a safeguard here.

---

🏁 Script executed:

```shell
#!/bin/bash
# Verify that leafCount matches elementCount across the codebase.
rg --multiline "leafCount\s:=\slen\(tree\)\s*>>\s*1" -A 10
```

Length of output: 559

---



</details>

**Action Required: Validate Index Bounds in Proof Generation**

In **pkg/merkle/proof.go** (lines 68–75), the loop that marks indices as known uses:

```go
for _, idx := range idxs {
    known[leafCount+idx] = true
}
```

Since `leafCount` is computed as `len(tree) >> 1`, there’s a potential risk of a runtime panic if any `idx` is greater than or equal to `leafCount`. To mitigate this risk, please add a safeguard to ensure that every index in `idxs` satisfies `idx < leafCount`—for example:

```go
for _, idx := range idxs {
    if idx < leafCount {
        known[leafCount+idx] = true
    } else {
        // Optionally, handle the error or log a warning.
    }
}
```

Alternatively, if there is a guaranteed invariant elsewhere that assures `idx < leafCount` (i.e. that `elementCount` always equals `leafCount`), please document that assumption explicitly.

<!-- This is an auto-generated comment by CodeRabbit -->
created_at: 2025-04-11T23:00:09Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,212 @@
+package merkle
+
+import (
+	"sort"
+)
+
+// GenerateMultiProofWithIndices generates a multi-proof for the given indices.
+func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	if hasDuplicates(indices) {
+		return nil, ErrProofDuplicateIndices
path: pkg/merkle/proof_indices.go
user: login: macroscopeapp[bot]
body: The duplicate check in `GenerateMultiProofWithIndices` currently calls `hasDuplicates` on the unsorted `indices` slice. Since `hasDuplicates` expects a sorted slice to reliably detect adjacent duplicate entries, this may lead to undetected duplicate indices (e.g. [1, 3, 1]). Consider sorting a copy of the `indices` slice before performing the duplicate check, as shown in the diff.

```diff
-	if hasDuplicates(indices) {
-		return nil, ErrProofDuplicateIndices
-	}
+	sortedIndices := append([]int(nil), indices...)
+	sort.Ints(sortedIndices)
+	if hasDuplicates(sortedIndices) {
+		return nil, ErrProofDuplicateIndices
+	}
```
> 🚀 Reply to ask Macroscope to explain or update this suggestion.

> 👍 Helpful? React to give us feedback.
created_at: 2025-04-11T23:31:51Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,167 @@
+package merkle
+
+import (
+	"errors"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	depth     int
+	leafCount int
+}
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	tree, depth := buildTree(leaves)
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[1],
+		depth:     depth,
+		leafCount: len(elements),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() [][]byte {
+	return m.tree
+}
+
+// Elements returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// Depth returns the depth of the Merkle tree.
+func (m *MerkleTree) Depth() int {
+	return m.depth
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return m.leafCount
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func buildTree(leaves [][]byte) ([][]byte, int) {
+	depth := getDepth(uint32(len(leaves)))
+	leafCount := GetLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		leftChildIndex := GetLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := GetRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	return tree, depth
+}
+
+// getDepth calculates the depth of a Merkle tree based on element count.
+func getDepth(n uint32) int {
+	if n <= 1 {
+		return 0
+	}
+
+	// Round up to next power of 2 if not already a power of 2.
+	if bits.OnesCount32(n) > 1 {
+		n = roundUpToPowerOf2(n)
+	}
+
+	// bits.Len32 gives position of highest bit + 1.
+	return bits.Len32(n) - 1
+}
+
+// GetLeafCount returns the number of leaves in a tree.
+func GetLeafCount(elementCount int) int {
+	if elementCount == 0 {
+		return 0
+	}
+
+	return int(roundUpToPowerOf2(uint32(elementCount)))
+}
+
+// roundUpToPowerOf2 rounds up a number to the next power of 2.
+// Rounding up to the next power of 2 is necessary to ensure that the tree is balanced.
+func roundUpToPowerOf2(n uint32) uint32 {
+	if bits.OnesCount32(n) == 1 {
+		return n
+	}
+
+	n |= n >> 1
+	n |= n >> 2
+	n |= n >> 4
+	n |= n >> 8
+	n |= n >> 16
+
path: pkg/merkle/tree.go
user: login: macroscopeapp[bot]
body: In `roundUpToPowerOf2`, when `n` is near the maximum representable value and is not already a power of 2, the operation `n + 1` can overflow, wrapping back to 0 and leading to an incorrect tree depth in `getDepth`. This behavior is likely unintentional. Consider adding an explicit check for values of `n` that would cause an overflow and capping the result at the largest power of 2 representable in a 32-bit unsigned integer (i.e. `1 << 31`).

```diff
-	return n + 1
+	if n >= (1 << 31) {
+		return 1 << 31
+	}
+	return n + 1
```
> 🚀 Reply to ask Macroscope to explain or update this suggestion.

> 👍 Helpful? React to give us feedback.
created_at: 2025-04-12T17:25:49Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,238 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+type MultiProof struct {
+	Elements      [][]byte
+	Proofs        [][]byte
+	Root          []byte
+	Indices       []int
+	StartingIndex int
+	ElementCount  int
+}
+
+var (
+	ErrProofEmptyTree            = errors.New("proof has empty tree")
+	ErrProofEmptyIndices         = errors.New("proof has empty indices")
+	ErrProofDuplicateIndices     = errors.New("proof has duplicate indices")
+	ErrProofIndicesOutOfBounds   = errors.New("proof has indices out of bounds")
+	ErrProofInvalidStartingIndex = errors.New("proof has invalid starting index")
+	ErrProofInvalidElementCount  = errors.New("proof has invalid element count")
+	ErrProofInvalidRange         = errors.New("proof has invalid range")
+	ErrProofNil                  = errors.New("proof is nil")
+	ErrProofNilRoot              = errors.New("proof root cannot be nil")
+	ErrProofNoElements           = errors.New("proof has no elements")
+	ErrProofNoIndices            = errors.New("proof has no indices")
+	ErrProofNoProofs             = errors.New("proof has no proofs")
+)
+
+// generateProof returns a MultiProof for the given indices.
+func generateProof(
+	tree [][]byte,
+	root []byte,
+	indices []int,
+	elementCount int,
+) (MultiProof, error) {
+	if len(tree) == 0 {
+		return MultiProof{}, fmt.Errorf("cannot generate proof: %w", ErrProofEmptyTree)
+	}
+
+	if root == nil {
+		return MultiProof{}, fmt.Errorf("cannot generate proof: %w", ErrProofNilRoot)
+	}
+
+	// Do not modify the original indices slice.
+	idxs := make([]int, len(indices))
+	copy(idxs, indices)
+	sort.Ints(idxs)
+
+	if err := validateIndices(idxs, elementCount); err != nil {
+		return MultiProof{}, fmt.Errorf("cannot generate proof: %w", err)
+	}
+
+	// Handle single-element trees.
+	if elementCount == 1 {
+		return MultiProof{
+			Root:         root,
+			Indices:      idxs,
+			ElementCount: elementCount,
+			Proofs:       [][]byte{root},
+		}, nil
+	}
+
+	// Mark provided indices as known.
+	var (
+		leafCount = len(tree) >> 1
+		proofs    [][]byte
+		known     = make([]bool, len(tree))
+	)
+
+	for _, idx := range idxs {
+		known[leafCount+idx] = true
+	}
path: pkg/merkle/proof.go
user: login: coderabbitai[bot]
body: _💡 Verification agent_

<details>
<summary>🧩 Analysis chain</summary>

**Validate alignment between `elementCount` and `leafCount`**  
`leafCount` is derived from `len(tree) >> 1`, while `elementCount` can come from elsewhere. If `elementCount` exceeds `leafCount`, referencing `known[leafCount+idx]` (line 76) could panic. Although you validate indices against `elementCount`, you might confirm that `elementCount <= leafCount` to avoid runtime errors.

---

🏁 Script executed:

```shell
#!/bin/bash
# Check for potential mismatch between leafCount and elementCount across the codebase.
rg "leafCount|elementCount" -A 5
```

Length of output: 15340

---



</details>

**Ensure `elementCount` is bounded by `leafCount` to prevent potential panics**  
The current snippet computes `leafCount` as `len(tree) >> 1` and then marks indices via `known[leafCount+idx] = true`. Although the code validates that each `idx` is in the range `[0, elementCount)`, there’s no explicit guarantee that `elementCount` is ≤ `leafCount`. If it isn’t, adding any index (`leafCount + idx`) may exceed the bounds of the `known` slice, leading to a runtime panic.

**Recommendations:**  
- **Add a guard check:** Before iterating over `idxs`, insert a check (or assert) to ensure that `elementCount` does not exceed `leafCount`.  
- **Example diff snippet:**  
  ```diff
  	leafCount = len(tree) >> 1
  		proofs    [][]byte
  		known     = make([]bool, len(tree))
  	)
  +	// Ensure that elementCount (number of actual leaves) does not exceed the padded leafCount.
  +	if elementCount > leafCount {
  +	    return MultiProof{}, fmt.Errorf("elementCount (%d) exceeds computed leafCount (%d)", elementCount, leafCount)
  +	}
  
  	for _, idx := range idxs {
  		known[leafCount+idx] = true
  	}
  ```
- **Verify consistency:** Double-check that all callers of this function are passing an appropriate `elementCount` (i.e. one that reflects the actual number of leaves and not an inflated value).

This small adjustment will help safeguard against out-of-bounds access in cases where the tree’s structure or the provided parameters might be misaligned.



<!-- suggestion_start -->

<details>
<summary>📝 Committable suggestion</summary>

> ‼️ **IMPORTANT**
> Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

`````suggestion
		leafCount = len(tree) >> 1
		proofs    [][]byte
		known     = make([]bool, len(tree))
	)

	// Ensure that elementCount (number of actual leaves) does not exceed the padded leafCount.
	if elementCount > leafCount {
	    return MultiProof{}, fmt.Errorf("elementCount (%d) exceeds computed leafCount (%d)", elementCount, leafCount)
	}

	for _, idx := range idxs {
		known[leafCount+idx] = true
	}
`````

</details>

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<!-- This is an auto-generated comment by CodeRabbit -->

✅ Addressed in commit 88f6e99
created_at: 2025-04-12T17:26:53Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,170 @@
+package merkle
+
+import (
+	"errors"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	leafCount int
+}
+
+var (
+	ErrTreeEmpty   = errors.New("tree is empty")
+	ErrTreeRootNil = errors.New("tree root is nil")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	leaves, err := makeLeaves(elements)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[1],
+		leafCount: len(elements),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() [][]byte {
+	return m.tree
+}
+
+// Elements returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return m.leafCount
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func makeTree(leaves [][]byte) ([][]byte, error) {
+	if len(leaves) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	leafCount := GetLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		leftChildIndex := GetLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := GetRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	if tree[1] == nil {
+		return nil, ErrTreeRootNil
+	}
+
+	return tree, nil
+}
+
+func makeLeaves(elements [][]byte) ([][]byte, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	return leaves, nil
+}
+
+// GetLeafCount returns the number of leaves in a tree.
+// Rounding up to the next power of 2 is necessary to ensure that the tree is balanced. This allows to handle unbalanced trees.
+func GetLeafCount(elementCount int) int {
+	if elementCount == 0 {
+		return 0
+	}
+
+	return int(roundUpToPowerOf2(uint32(elementCount)))
+}
path: pkg/merkle/tree.go
user: login: coderabbitai[bot]
body: _🛠️ Refactor suggestion_

**Consider overflow checks in `GetLeafCount`.**
When the tree is extremely large, casting the result of `roundUpToPowerOf2(uint32(elementCount))` to `int` may overflow on some platforms. If large Merkle trees are expected, consider adding explicit overflow checks to guard against unexpected behavior.

<!-- This is an auto-generated comment by CodeRabbit -->
created_at: 2025-04-12T17:40:51Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,170 @@
+package merkle
+
+import (
+	"errors"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	leafCount int
+}
+
+var (
+	ErrTreeEmpty   = errors.New("tree is empty")
+	ErrTreeRootNil = errors.New("tree root is nil")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	leaves, err := makeLeaves(elements)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[1],
+		leafCount: len(elements),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() [][]byte {
+	return m.tree
+}
+
+// Elements returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return m.leafCount
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func makeTree(leaves [][]byte) ([][]byte, error) {
+	if len(leaves) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	leafCount := GetLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		leftChildIndex := GetLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := GetRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	if tree[1] == nil {
+		return nil, ErrTreeRootNil
+	}
+
+	return tree, nil
+}
path: pkg/merkle/tree.go
user: login: coderabbitai[bot]
body: _⚠️ Potential issue_

**Handle the scenario where the right child is non-nil but the left child is nil.**
Within the loop, there's no branch that assigns `tree[i]` if only the right child is non-nil. This can lead to a situation where the right child is ignored if the left child is nil. If that scenario is possible in practice, consider adding a conditional to handle it:
```diff
} else if tree[rightChildIndex] != nil {
    tree[i] = tree[rightChildIndex]
}
```
Otherwise, document why it's intentionally omitted.



<!-- suggestion_start -->

<details>
<summary>📝 Committable suggestion</summary>

> ‼️ **IMPORTANT**
> Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

`````suggestion
// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
//
// The tree is 1-indexed, so root is at index 1.
// The internal nodes are at index 2 to N.
// The leaves are at index N+1 to 2N-1.
//
// For any node at index i:
// - left child is at index 2*i
// - right child is at index 2*i+1
// - parent is at floor(i/2)
func makeTree(leaves [][]byte) ([][]byte, error) {
	if len(leaves) == 0 {
		return nil, ErrTreeEmpty
	}

	leafCount := GetLeafCount(len(leaves))

	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
	tree := make([][]byte, leafCount<<1)

	lowerBound := leafCount
	upperBound := leafCount + len(leaves) - 1

	// Copy leaves into the tree, starting at index N.
	for i := 0; i < len(leaves); i++ {
		tree[lowerBound+i] = leaves[i]
	}

	// Build the tree.
	// Start from the last internal node and work our way up to the root.
	for i := leafCount - 1; i >= 0; i-- {
		leftChildIndex := GetLeftChild(i)

		if leftChildIndex > upperBound {
			continue
		}

		// Detect the level is processed.
		if leftChildIndex <= lowerBound {
			lowerBound >>= 1
			upperBound >>= 1
		}

		rightChildIndex := GetRightChild(i)

		// Hash both children if they exist.
		// If only left child exists, use it.
		// If only right child exists, use it.
		// If no children exist, leave it as nil.
		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
		} else if tree[leftChildIndex] != nil {
			tree[i] = tree[leftChildIndex]
		} else if tree[rightChildIndex] != nil {
			tree[i] = tree[rightChildIndex]
		}
	}

	if tree[1] == nil {
		return nil, ErrTreeRootNil
	}

	return tree, nil
}
`````

</details>

<!-- suggestion_end -->

<!-- This is an auto-generated reply by CodeRabbit -->
created_at: 2025-04-12T17:40:52Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,238 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+type MultiProof struct {
+	Elements      [][]byte
+	Proofs        [][]byte
+	Root          []byte
+	Indices       []int
+	StartingIndex int
+	ElementCount  int
+}
+
+var (
+	ErrProofEmptyTree            = errors.New("proof has empty tree")
+	ErrProofEmptyIndices         = errors.New("proof has empty indices")
+	ErrProofDuplicateIndices     = errors.New("proof has duplicate indices")
+	ErrProofIndicesOutOfBounds   = errors.New("proof has indices out of bounds")
+	ErrProofInvalidStartingIndex = errors.New("proof has invalid starting index")
+	ErrProofInvalidElementCount  = errors.New("proof has invalid element count")
+	ErrProofInvalidRange         = errors.New("proof has invalid range")
+	ErrProofNil                  = errors.New("proof is nil")
+	ErrProofNilRoot              = errors.New("proof root cannot be nil")
+	ErrProofNoElements           = errors.New("proof has no elements")
+	ErrProofNoIndices            = errors.New("proof has no indices")
+	ErrProofNoProofs             = errors.New("proof has no proofs")
+)
+
+// generateProof returns a MultiProof for the given indices.
+func generateProof(
+	tree [][]byte,
+	root []byte,
+	indices []int,
+	elementCount int,
+) (MultiProof, error) {
+	if len(tree) == 0 {
+		return MultiProof{}, fmt.Errorf("cannot generate proof: %w", ErrProofEmptyTree)
+	}
+
+	if root == nil {
+		return MultiProof{}, fmt.Errorf("cannot generate proof: %w", ErrProofNilRoot)
+	}
+
+	// Do not modify the original indices slice.
+	idxs := make([]int, len(indices))
+	copy(idxs, indices)
+	sort.Ints(idxs)
+
+	if err := validateIndices(idxs, elementCount); err != nil {
+		return MultiProof{}, fmt.Errorf("cannot generate proof: %w", err)
+	}
+
+	// Handle single-element trees.
+	if elementCount == 1 {
+		return MultiProof{
+			Root:         root,
+			Indices:      idxs,
+			ElementCount: elementCount,
+			Proofs:       [][]byte{root},
+		}, nil
+	}
+
+	// Mark provided indices as known.
+	var (
+		leafCount = len(tree) >> 1
+		proofs    [][]byte
+		known     = make([]bool, len(tree))
+	)
+
+	for _, idx := range idxs {
+		known[leafCount+idx] = true
+	}
path: pkg/merkle/proof.go
user: login: coderabbitai[bot]
body: _⚠️ Potential issue_

**Validate that `elementCount` does not exceed `leafCount`.**
Although `validateIndices` ensures `idx < elementCount`, there's no explicit check to confirm `elementCount <= leafCount`. If `elementCount` is larger, the assignment `known[leafCount+idx]` may go out of bounds. Consider enforcing:
```go
if elementCount > leafCount {
    return MultiProof{}, errors.New("elementCount exceeds internal leaf count")
}
```
before the loop that marks indices.

<!-- This is an auto-generated reply by CodeRabbit -->
created_at: 2025-04-12T17:40:52Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,170 @@
+package merkle
+
+import (
+	"errors"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	leafCount int
+}
+
+var (
+	ErrTreeEmpty   = errors.New("tree is empty")
+	ErrTreeRootNil = errors.New("tree root is nil")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	leaves, err := makeLeaves(elements)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[1],
+		leafCount: len(elements),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() [][]byte {
+	return m.tree
+}
+
+// Elements returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return m.leafCount
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func makeTree(leaves [][]byte) ([][]byte, error) {
+	if len(leaves) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	leafCount := GetLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		leftChildIndex := GetLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := GetRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	if tree[1] == nil {
+		return nil, ErrTreeRootNil
+	}
+
+	return tree, nil
+}
path: pkg/merkle/tree.go
user: login: fbac
body: Study this algorithm again and check if the scenario can exist, where rightChildIndex is not nil while leftChildIndex is nil.
Note that the algorithm fill leaf nodes from left to right, so in my opinion this won't ever happen.
created_at: 2025-04-14T10:32:19Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,170 @@
+package merkle
+
+import (
+	"errors"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	leafCount int
+}
+
+var (
+	ErrTreeEmpty   = errors.New("tree is empty")
+	ErrTreeRootNil = errors.New("tree root is nil")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	leaves, err := makeLeaves(elements)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[1],
+		leafCount: len(elements),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() [][]byte {
+	return m.tree
+}
+
+// Elements returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return m.leafCount
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func makeTree(leaves [][]byte) ([][]byte, error) {
+	if len(leaves) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	leafCount := GetLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		leftChildIndex := GetLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := GetRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	if tree[1] == nil {
+		return nil, ErrTreeRootNil
+	}
+
+	return tree, nil
+}
path: pkg/merkle/tree.go
user: login: coderabbitai[bot]
body: @fbac You're absolutely correct. After carefully reanalyzing the algorithm, I can confirm that the scenario where the right child exists but the left child doesn't is impossible in this implementation.

Since the leaf nodes are filled from left to right starting at index `leafCount` (i.e., `tree[lowerBound+i] = leaves[i]`), there's no way to have gaps where a right child would exist without its corresponding left child also existing.

For example, with 3 leaf nodes:
- Leaves would be at indices 4, 5, 6
- Index 7 would be nil
- For node at index 3, left child (6) exists but right child (7) doesn't

My suggested fix isn't necessary, as the algorithm correctly handles all possible cases. Thanks for pointing this out!

(￣^￣)ゞ



<!-- <agentComponentType>chat-answer</agentComponentType> -->

<!-- <rawResChunk><answer>@fbac You're absolutely correct. After carefully reanalyzing the algorithm, I can confirm that the scenario where the right child exists but the left child doesn't is impossible in this implementation.

Since the leaf nodes are filled from left to right starting at index `leafCount` (i.e., `tree[lowerBound+i] = leaves[i]`), there's no way to have gaps where a right child would exist without its corresponding left child also existing.

For example, with 3 leaf nodes:
- Leaves would be at indices 4, 5, 6
- Index 7 would be nil
- For node at index 3, left child (6) exists but right child (7) doesn't

My suggested fix isn't necessary, as the algorithm correctly handles all possible cases. Thanks for pointing this out!

(￣^￣)ゞ</answer></rawResChunk> -->

<!-- This is an auto-generated reply by CodeRabbit -->
created_at: 2025-04-14T10:32:57Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,178 @@
+package merkle
+
+import (
+	"errors"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	leafCount int
+}
+
+var (
+	ErrTreeEmpty   = errors.New("tree is empty")
+	ErrTreeRootNil = errors.New("tree root is nil")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	elementsDeepCopy := make([][]byte, len(elements))
+	for i, element := range elements {
+		elementsDeepCopy[i] = make([]byte, len(element))
+		copy(elementsDeepCopy[i], element)
+	}
+
+	leaves, err := makeLeaves(elementsDeepCopy)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elementsDeepCopy,
+		root:      tree[1],
+		leafCount: len(elementsDeepCopy),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() [][]byte {
+	return m.tree
+}
+
+// Elements returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return m.leafCount
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func makeTree(leaves [][]byte) ([][]byte, error) {
+	if len(leaves) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	leafCount := CalculateBalancedLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		leftChildIndex := GetLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := GetRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	if tree[1] == nil {
+		return nil, ErrTreeRootNil
+	}
+
+	return tree, nil
+}
+
+// makeLeaves returns the leaves of the tree,
+// ordered in the same order as the provided elements.
+func makeLeaves(elements [][]byte) ([][]byte, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	return leaves, nil
+}
+
+// CalculateBalancedLeafCount returns the number of leaves in a balanced tree.
+// To calculate the number of leaves in a tree, we need to round up to the next power of 2.
+func CalculateBalancedLeafCount(elementCount int) int {
+	if elementCount == 0 {
+		return 0
+	}
+
+	return int(roundUpToPowerOf2(uint32(elementCount)))
+}
+
+// roundUpToPowerOf2 rounds up a number to the next power of 2.
+// Rounding up to the next power of 2 is necessary to ensure that the tree is balanced.
+func roundUpToPowerOf2(n uint32) uint32 {
+	if bits.OnesCount32(n) == 1 {
+		return n
+	}
+
+	n |= n >> 1
+	n |= n >> 2
+	n |= n >> 4
+	n |= n >> 8
+	n |= n >> 16
+
+	return n + 1
+}
path: pkg/merkle/tree.go
user: login: coderabbitai[bot]
body: _⚠️ Potential issue_

**Prevent potential overflow when rounding up to power of 2.**

If `n` is near the maximum `uint32` value (e.g. `0xFFFFFFFF`), `n + 1` will overflow to 0. This silently breaks the tree’s size calculation.  


Below is a possible fix to cap the result or return an error if overflow occurs:

```diff
 func roundUpToPowerOf2(n uint32) uint32 {
     if bits.OnesCount32(n) == 1 {
         return n
     }
     n |= n >> 1
     n |= n >> 2
     n |= n >> 4
     n |= n >> 8
     n |= n >> 16
-    return n + 1
+    if n == ^uint32(0) {
+        // Overflow scenario: can't add 1 safely
+        return n
+    }
+    return n + 1
 }
```


<!-- suggestion_start -->

<details>
<summary>📝 Committable suggestion</summary>

> ‼️ **IMPORTANT**
> Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

`````suggestion
// roundUpToPowerOf2 rounds up a number to the next power of 2.
// Rounding up to the next power of 2 is necessary to ensure that the tree is balanced.
func roundUpToPowerOf2(n uint32) uint32 {
    if bits.OnesCount32(n) == 1 {
        return n
    }

    n |= n >> 1
    n |= n >> 2
    n |= n >> 4
    n |= n >> 8
    n |= n >> 16

    if n == ^uint32(0) {
        // Overflow scenario: can't add 1 safely
        return n
    }
    return n + 1
}
`````

</details>

<!-- suggestion_end -->

<!-- This is an auto-generated comment by CodeRabbit -->
created_at: 2025-04-14T12:35:33Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,238 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+type MultiProof struct {
+	Elements      [][]byte
+	Proofs        [][]byte
+	Root          []byte
+	Indices       []int
+	StartingIndex int
+	ElementCount  int
+}
+
+var (
+	ErrProofEmptyTree            = errors.New("proof has empty tree")
+	ErrProofEmptyIndices         = errors.New("proof has empty indices")
+	ErrProofDuplicateIndices     = errors.New("proof has duplicate indices")
+	ErrProofIndicesOutOfBounds   = errors.New("proof has indices out of bounds")
+	ErrProofInvalidStartingIndex = errors.New("proof has invalid starting index")
+	ErrProofInvalidElementCount  = errors.New("proof has invalid element count")
+	ErrProofInvalidRange         = errors.New("proof has invalid range")
+	ErrProofNil                  = errors.New("proof is nil")
+	ErrProofNilRoot              = errors.New("proof root cannot be nil")
+	ErrProofNoElements           = errors.New("proof has no elements")
+	ErrProofNoIndices            = errors.New("proof has no indices")
+	ErrProofNoProofs             = errors.New("proof has no proofs")
+)
+
+// generateProof returns a MultiProof for the given indices.
+func generateProof(
+	tree [][]byte,
+	root []byte,
+	indices []int,
+	elementCount int,
+) (MultiProof, error) {
+	if len(tree) == 0 {
+		return MultiProof{}, fmt.Errorf("cannot generate proof: %w", ErrProofEmptyTree)
+	}
+
+	if root == nil {
+		return MultiProof{}, fmt.Errorf("cannot generate proof: %w", ErrProofNilRoot)
+	}
+
+	// Do not modify the original indices slice.
+	idxs := make([]int, len(indices))
+	copy(idxs, indices)
+	sort.Ints(idxs)
+
+	if err := validateIndices(idxs, elementCount); err != nil {
+		return MultiProof{}, fmt.Errorf("cannot generate proof: %w", err)
+	}
+
+	// Handle single-element trees.
+	if elementCount == 1 {
+		return MultiProof{
+			Root:         root,
+			Indices:      idxs,
+			ElementCount: elementCount,
+			Proofs:       [][]byte{root},
+		}, nil
+	}
+
+	// Mark provided indices as known.
+	var (
+		leafCount = len(tree) >> 1
+		proofs    [][]byte
+		known     = make([]bool, len(tree))
+	)
+
+	for _, idx := range idxs {
+		known[leafCount+idx] = true
+	}
path: pkg/merkle/proof.go
user: login: fbac
body: leafCount (len(tree) / 2) is used to access the known map (len(tree)) with leafCount+idx. Indices are previously validated to be inside bounds of the tree.
Further checks seems redundant.
created_at: 2025-04-14T12:54:20Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,238 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+type MultiProof struct {
+	Elements      [][]byte
+	Proofs        [][]byte
+	Root          []byte
+	Indices       []int
+	StartingIndex int
+	ElementCount  int
+}
+
+var (
+	ErrProofEmptyTree            = errors.New("proof has empty tree")
+	ErrProofEmptyIndices         = errors.New("proof has empty indices")
+	ErrProofDuplicateIndices     = errors.New("proof has duplicate indices")
+	ErrProofIndicesOutOfBounds   = errors.New("proof has indices out of bounds")
+	ErrProofInvalidStartingIndex = errors.New("proof has invalid starting index")
+	ErrProofInvalidElementCount  = errors.New("proof has invalid element count")
+	ErrProofInvalidRange         = errors.New("proof has invalid range")
+	ErrProofNil                  = errors.New("proof is nil")
+	ErrProofNilRoot              = errors.New("proof root cannot be nil")
+	ErrProofNoElements           = errors.New("proof has no elements")
+	ErrProofNoIndices            = errors.New("proof has no indices")
+	ErrProofNoProofs             = errors.New("proof has no proofs")
+)
+
+// generateProof returns a MultiProof for the given indices.
+func generateProof(
+	tree [][]byte,
+	root []byte,
+	indices []int,
+	elementCount int,
+) (MultiProof, error) {
+	if len(tree) == 0 {
+		return MultiProof{}, fmt.Errorf("cannot generate proof: %w", ErrProofEmptyTree)
+	}
+
+	if root == nil {
+		return MultiProof{}, fmt.Errorf("cannot generate proof: %w", ErrProofNilRoot)
+	}
+
+	// Do not modify the original indices slice.
+	idxs := make([]int, len(indices))
+	copy(idxs, indices)
+	sort.Ints(idxs)
+
+	if err := validateIndices(idxs, elementCount); err != nil {
+		return MultiProof{}, fmt.Errorf("cannot generate proof: %w", err)
+	}
+
+	// Handle single-element trees.
+	if elementCount == 1 {
+		return MultiProof{
+			Root:         root,
+			Indices:      idxs,
+			ElementCount: elementCount,
+			Proofs:       [][]byte{root},
+		}, nil
+	}
+
+	// Mark provided indices as known.
+	var (
+		leafCount = len(tree) >> 1
+		proofs    [][]byte
+		known     = make([]bool, len(tree))
+	)
+
+	for _, idx := range idxs {
+		known[leafCount+idx] = true
+	}
path: pkg/merkle/proof.go
user: login: coderabbitai[bot]
body: @fbac You're absolutely right. I reviewed the code more carefully and see that the validation through `validateIndices()` is already ensuring that indices are within bounds. Since `validateIndices()` checks that `idx

< elementCount` and `elementCount` corresponds to the number of leaf nodes, the access to `known[leafCount+idx]` is already guaranteed to be safe. My suggested additional check would indeed be redundant.
---
<details>
<summary>✏️ Learnings added</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:0-0
Timestamp: 2025-04-14T12:55:15.436Z
Learning: In Merkle tree implementations, when indices are validated using a function like `validateIndices(indices, elementCount)` which checks that indices are less than the element count, additional bounds checking for accessing tree nodes at `leafCount+idx` is redundant because the element count corresponds to the number of leaf nodes.
```

> Note: Learnings are effective only in the context of similar code segments. To apply general coding guidelines, please configure [review instructions](https://docs.coderabbit.ai/guides/review-instructions). You can manage existing learnings in the [app](https://app.coderabbit.ai/learnings).

</details>



<!-- <agentComponentType>chat-answer</agentComponentType> -->

<!-- <rawResChunk><answer>@fbac You're absolutely right. I reviewed the code more carefully and see that the validation through `validateIndices()` is already ensuring that indices are within bounds. Since `validateIndices()` checks that `idx < elementCount` and `elementCount` corresponds to the number of leaf nodes, the access to `known[leafCount+idx]` is already guaranteed to be safe. My suggested additional check would indeed be redundant.
---

<details>
<summary>✏️ Learnings added</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:0-0
Timestamp: 2025-04-14T12:55:15.436Z
Learning: In Merkle tree implementations, when indices are validated using a function like `validateIndices(indices, elementCount)` which checks that indices are less than the element count, additional bounds checking for accessing tree nodes at `leafCount+idx` is redundant because the element count corresponds to the number of leaf nodes.
```

> Note: Learnings are effective only in the context of similar code segments. To apply general coding guidelines, please configure [review instructions](https://docs.coderabbit.ai/guides/review-instructions). You can manage existing learnings in the [app](https://app.coderabbit.ai/learnings).

</details></answer></rawResChunk> -->

<!-- This is an auto-generated reply by CodeRabbit -->
created_at: 2025-04-14T12:55:16Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,438 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+type MultiProof struct {
+	Elements  [][]byte
+	Proofs    [][]byte
+	Root      []byte
+	Indices   []int
+	LeafCount int
+}
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrEmptyTree           = errors.New("empty tree")
+	ErrDuplicateIndices    = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds  = errors.New("indices out of bounds")
+	ErrInvalidRange        = errors.New("invalid range")
+	ErrInvalidElementCount = errors.New("invalid element count")
+	ErrElementMismatch     = errors.New("element mismatch")
+	ErrNilProof            = errors.New("nil proof")
+	ErrNilRoot             = errors.New("nil root")
+	ErrNilElement          = errors.New("nil element")
+	ErrNoElements          = errors.New("no elements")
+	ErrNoIndices           = errors.New("no indices")
+	ErrNoProofs            = errors.New("no proofs provided")
+)
+
+// GenerateMultiProofSequential generates a sequential multi-proof starting from the given index.
+func (m *MerkleTree) GenerateMultiProofSequential(startingIndex, count int) (*MultiProof, error) {
+	indices, err := makeIndices(startingIndex, count)
+	if err != nil {
+		return nil, err
+	}
+
+	proof, err := makeProof(m.tree, m.root, indices, m.leafCount)
+	if err != nil {
+		return nil, err
+	}
+
+	proof.Elements = make([][]byte, count)
+	for i := 0; i < count; i++ {
+		proof.Elements[i] = m.elements[startingIndex+i]
+	}
+
+	if err := validateProof(&proof); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// GenerateMultiProofWithIndices generates a multi-proof for the given indices.
+func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	proof, err := makeProof(m.tree, m.root, indices, m.leafCount)
+	if err != nil {
+		return nil, err
+	}
+
+	proof.Elements = make([][]byte, len(proof.Indices))
+	for i, index := range proof.Indices {
+		proof.Elements[i] = m.elements[index]
+	}
+
+	if err := validateProof(&proof); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// VerifyProof verifies a proof.
+func VerifyProof(proof *MultiProof) (bool, error) {
+	if err := validateProof(proof); err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	// Handle single-element trees.
+	if proof.LeafCount == 1 {
+		return bytes.Equal(proof.Root, HashLeaf(proof.Elements[0])), nil
+	}
+
+	// If all the elements are provided, we can verify the proof by recalculating the root.
+	if len(proof.Elements) == proof.LeafCount {
+		tree, err := NewMerkleTree(proof.Elements)
+		if err != nil {
+			return false, fmt.Errorf(ErrVerifyProof, err)
+		}
+
+		return bytes.Equal(tree.Root(), proof.Root), nil
+	}
+
+	// If only some of the elements are provided, we need to calculate the root.
+	leaves, err := makeLeaves(proof.Elements)
+	if err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	result := computeRoot(leaves, proof.Indices, proof.LeafCount, proof.Proofs)
+	if result == nil {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
+	}
+
+	return bytes.Equal(result, proof.Root), nil
+}
+
+// computeRoot computes the root given the leaves, their indices, and proofs.
+func computeRoot(leaves [][]byte, indices []int, elementCount int, proofs [][]byte) []byte {
+	// Ensure indices are valid
+	for _, index := range indices {
+		if index < 0 || index >= elementCount {
+			return nil
+		}
+	}
+
+	// Validate input
+	if len(leaves) == 0 || len(indices) == 0 ||
+		len(leaves) != len(indices) {
+		return nil
+	}
+
+	// Sort indices and corresponding leaves
+	indexLeafPairs := make([]struct {
+		Index int
+		Leaf  []byte
+	}, len(indices))
+
+	for i, index := range indices {
+		indexLeafPairs[i] = struct {
+			Index int
+			Leaf  []byte
+		}{Index: index, Leaf: leaves[i]}
+	}
+
+	sort.Slice(indexLeafPairs, func(i, j int) bool {
+		return indexLeafPairs[i].Index < indexLeafPairs[j].Index
+	})
+
+	// Update sorted indices and leaves
+	sortedIndices := make([]int, len(indexLeafPairs))
+	sortedLeaves := make([][]byte, len(indexLeafPairs))
+	for i, pair := range indexLeafPairs {
+		sortedIndices[i] = pair.Index
+		sortedLeaves[i] = pair.Leaf
+	}
+
+	// Original GetRoot implementation using balanced tree
+	balancedLeafCount := int(roundUpToPowerOf2(uint32(elementCount)))
+
path: pkg/merkle/proof.go
user: login: coderabbitai[bot]
body: _💡 Verification agent_

<details>
<summary>🧩 Analysis chain</summary>

**Check coverage of `roundUpToPowerOf2`.**

`roundUpToPowerOf2` is crucial for computing `balancedLeafCount`. Ensure it’s sufficiently tested in your unit tests, especially corner cases (e.g., leaf counts already a power of two vs. not).  

Please verify testing coverage with a script:

---

🏁 Script executed:

```shell
#!/bin/bash
# Search for roundUpToPowerOf2 references and check associated tests
rg --context 5 "roundUpToPowerOf2"
rg "func TestRoundUpToPowerOf2"
```

Length of output: 1314

---



</details>

**RoundUpToPowerOf2 Test Coverage Check**  
Our repository search did not reveal any direct unit tests (e.g., a function named `TestRoundUpToPowerOf2`) for the `roundUpToPowerOf2` function defined in `pkg/merkle/tree.go`. Since this function underpins the calculation of `balancedLeafCount` (as seen in both `pkg/merkle/proof.go` and `pkg/merkle/tree.go`), it's important to ensure that its behavior is thoroughly validated.

**Please ensure that:**
- **Edge case coverage:** The scenario where the input is already a power of 2 (i.e., the branch that returns early) is explicitly tested.
- **Rounding behavior:** Inputs that are not powers of two correctly trigger the bitwise rounding logic to compute the next power of 2.

If the function is being indirectly validated via tests for `CalculateBalancedLeafCount`, confirm that these tests cover the above scenarios. Otherwise, please add dedicated tests for `roundUpToPowerOf2` to ensure robust coverage.

<!-- This is an auto-generated comment by CodeRabbit -->
created_at: 2025-04-14T12:58:55Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,438 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+type MultiProof struct {
+	Elements  [][]byte
+	Proofs    [][]byte
+	Root      []byte
+	Indices   []int
+	LeafCount int
+}
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrEmptyTree           = errors.New("empty tree")
+	ErrDuplicateIndices    = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds  = errors.New("indices out of bounds")
+	ErrInvalidRange        = errors.New("invalid range")
+	ErrInvalidElementCount = errors.New("invalid element count")
+	ErrElementMismatch     = errors.New("element mismatch")
+	ErrNilProof            = errors.New("nil proof")
+	ErrNilRoot             = errors.New("nil root")
+	ErrNilElement          = errors.New("nil element")
+	ErrNoElements          = errors.New("no elements")
+	ErrNoIndices           = errors.New("no indices")
+	ErrNoProofs            = errors.New("no proofs provided")
+)
+
+// GenerateMultiProofSequential generates a sequential multi-proof starting from the given index.
+func (m *MerkleTree) GenerateMultiProofSequential(startingIndex, count int) (*MultiProof, error) {
+	indices, err := makeIndices(startingIndex, count)
+	if err != nil {
+		return nil, err
+	}
+
+	proof, err := makeProof(m.tree, m.root, indices, m.leafCount)
+	if err != nil {
+		return nil, err
+	}
+
+	proof.Elements = make([][]byte, count)
+	for i := 0; i < count; i++ {
+		proof.Elements[i] = m.elements[startingIndex+i]
+	}
+
+	if err := validateProof(&proof); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// GenerateMultiProofWithIndices generates a multi-proof for the given indices.
+func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	proof, err := makeProof(m.tree, m.root, indices, m.leafCount)
+	if err != nil {
+		return nil, err
+	}
+
+	proof.Elements = make([][]byte, len(proof.Indices))
+	for i, index := range proof.Indices {
+		proof.Elements[i] = m.elements[index]
+	}
+
+	if err := validateProof(&proof); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// VerifyProof verifies a proof.
+func VerifyProof(proof *MultiProof) (bool, error) {
+	if err := validateProof(proof); err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	// Handle single-element trees.
+	if proof.LeafCount == 1 {
+		return bytes.Equal(proof.Root, HashLeaf(proof.Elements[0])), nil
+	}
+
+	// If all the elements are provided, we can verify the proof by recalculating the root.
+	if len(proof.Elements) == proof.LeafCount {
+		tree, err := NewMerkleTree(proof.Elements)
+		if err != nil {
+			return false, fmt.Errorf(ErrVerifyProof, err)
+		}
+
+		return bytes.Equal(tree.Root(), proof.Root), nil
+	}
+
+	// If only some of the elements are provided, we need to calculate the root.
+	leaves, err := makeLeaves(proof.Elements)
+	if err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	result := computeRoot(leaves, proof.Indices, proof.LeafCount, proof.Proofs)
+	if result == nil {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
+	}
+
+	return bytes.Equal(result, proof.Root), nil
+}
+
+// computeRoot computes the root given the leaves, their indices, and proofs.
+func computeRoot(leaves [][]byte, indices []int, elementCount int, proofs [][]byte) []byte {
+	// Ensure indices are valid
+	for _, index := range indices {
+		if index < 0 || index >= elementCount {
+			return nil
+		}
+	}
+
+	// Validate input
+	if len(leaves) == 0 || len(indices) == 0 ||
+		len(leaves) != len(indices) {
+		return nil
+	}
+
+	// Sort indices and corresponding leaves
+	indexLeafPairs := make([]struct {
+		Index int
+		Leaf  []byte
+	}, len(indices))
+
+	for i, index := range indices {
+		indexLeafPairs[i] = struct {
+			Index int
+			Leaf  []byte
+		}{Index: index, Leaf: leaves[i]}
+	}
+
+	sort.Slice(indexLeafPairs, func(i, j int) bool {
+		return indexLeafPairs[i].Index < indexLeafPairs[j].Index
+	})
+
+	// Update sorted indices and leaves
+	sortedIndices := make([]int, len(indexLeafPairs))
+	sortedLeaves := make([][]byte, len(indexLeafPairs))
+	for i, pair := range indexLeafPairs {
+		sortedIndices[i] = pair.Index
+		sortedLeaves[i] = pair.Leaf
+	}
+
+	// Original GetRoot implementation using balanced tree
+	balancedLeafCount := int(roundUpToPowerOf2(uint32(elementCount)))
+
+	// Prepare circular queues
+	count := len(sortedIndices)
+	treeIndices := make([]int, count)
+	hashes := make([][]byte, count)
+
+	// Initialize queues
+	for i := 0; i < count; i++ {
+		treeIndices[count-1-i] = balancedLeafCount + sortedIndices[i]
+		hashes[count-1-i] = cloneBuffer(sortedLeaves[i])
+	}
+
+	readIndex := 0
+	writeIndex := 0
+	proofIndex := 0
+	upperBound := balancedLeafCount + elementCount - 1
+	lowestTreeIndex := treeIndices[count-1]
+	var nextNodeIndex int
+
+	for {
+		nodeIndex := treeIndices[readIndex]
+
+		if nodeIndex == 1 {
+			// Reached the root
+			rootIndex := writeIndex - 1
+			if writeIndex == 0 {
+				rootIndex = count - 1
+			}
+			return hashes[rootIndex]
+		}
+
+		indexIsOdd := nodeIndex&1 == 1
+
+		if nodeIndex == upperBound && !indexIsOdd {
+			treeIndices[writeIndex] = nodeIndex >> 1
+			hashes[writeIndex] = hashes[readIndex]
+			writeIndex = (writeIndex + 1) % count
+			readIndex = (readIndex + 1) % count
+		} else {
path: pkg/merkle/proof.go
user: login: macroscopeapp[bot]
body: In the function `computeRoot`, the variable `nextNodeIndex` is updated only in the else branch, which means that when the branch for `nodeIndex == upperBound && !indexIsOdd` is executed, `nextNodeIndex` is not refreshed and may hold an old value. This could lead to unexpected behavior when `nextNodeIndex` is compared later in the loop. Consider updating `nextNodeIndex` in that branch to ensure its value is current, or if this is intentional, please document the reasoning behind this conditional update.

```diff
readIndex = (readIndex + 1) % count
+		nextNodeIndex = treeIndices[readIndex]
```
> 🚀 Reply to ask Macroscope to explain or update this suggestion.

> 👍 Helpful? React to give us feedback.
created_at: 2025-04-14T12:58:59Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,393 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrEmptyTree          = errors.New("empty tree")
+	ErrDuplicateIndices   = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds = errors.New("indices out of bounds")
+	ErrInvalidRange       = errors.New("invalid range")
+	ErrInvalidLeafCount   = errors.New("invalid leaf count")
+	ErrElementMismatch    = errors.New("element and indices mismatch")
+	ErrNilProof           = errors.New("nil proof")
+	ErrNilRoot            = errors.New("nil root")
+	ErrNilElement         = errors.New("nil element")
+	ErrNoElements         = errors.New("no elements")
+	ErrNoIndices          = errors.New("no indices")
+	ErrNoProofs           = errors.New("no proofs provided")
+)
+
+type MultiProof struct {
+	elements  indexedValues
+	proofs    [][]byte
+	root      []byte
+	leafCount int
+}
+
+func (p *MultiProof) Elements() indexedValues {
+	return p.elements
+}
+
+func (p *MultiProof) Proofs() [][]byte {
+	return p.proofs
+}
+
+func (p *MultiProof) Root() []byte {
+	return p.root
+}
+
+func (p *MultiProof) LeafCount() int {
+	return p.leafCount
+}
+
+type indexedValues []indexedValue
+
+type indexedValue struct {
+	value []byte
+	index int
+}
+
+// Values returns all leaf values
+func (iv indexedValues) Values() [][]byte {
+	values := make([][]byte, len(iv))
+	for i, v := range iv {
+		values[i] = v.value
+	}
+	return values
+}
+
+// Indices returns all index values
+func (iv indexedValues) Indices() []int {
+	indices := make([]int, len(iv))
+	for i, v := range iv {
+		indices[i] = v.index
+	}
+	return indices
+}
+
+// Verify verifies a proof.
+func Verify(proof *MultiProof) (bool, error) {
+	if err := proof.validate(); err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	// Handle single-element trees.
+	if proof.leafCount == 1 {
+		return bytes.Equal(proof.root, HashLeaf(proof.elements[0].value)), nil
+	}
+
+	// If all the elements are provided, we can verify the proof by recalculating the root.
+	if len(proof.elements) == proof.leafCount {
+		// Extract just the leaves for tree creation
+		tree, err := NewMerkleTree(proof.elements.Values())
+		if err != nil {
+			return false, fmt.Errorf(ErrVerifyProof, err)
+		}
+
+		return bytes.Equal(tree.Root(), proof.root), nil
+	}
+
+	result, err := proof.computeRoot()
+	if err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	return bytes.Equal(result, proof.root), nil
+}
+
+// computeRoot computes the root given the leaves, their indices, and proofs.
+func (p *MultiProof) computeRoot() ([]byte, error) {
+	leaves, err := makeLeaves(p.elements.Values())
+	if err != nil {
+		return nil, err
+	}
+
+	balancedLeafCount := CalculateBalancedLeafCount(p.leafCount)
+
+	// Prepare circular queues
+	count := len(p.elements.Indices())
+	treeIndices := make([]int, count)
+	hashes := make([][]byte, count)
+
+	// Initialize queues
+	for i := 0; i < count; i++ {
+		treeIndices[count-1-i] = balancedLeafCount + p.elements.Indices()[i]
+		hashes[count-1-i] = cloneBuffer(leaves[i])
+	}
+
+	readIndex := 0
+	writeIndex := 0
+	proofIndex := 0
+	upperBound := balancedLeafCount + p.leafCount - 1
+	lowestTreeIndex := treeIndices[count-1]
+	var nextNodeIndex int
+
+	for {
+		nodeIndex := treeIndices[readIndex]
+
+		if nodeIndex == 1 {
+			// Reached the root
+			rootIndex := writeIndex - 1
+			if writeIndex == 0 {
+				rootIndex = count - 1
+			}
+			return hashes[rootIndex], nil
+		}
+
+		indexIsOdd := nodeIndex&1 == 1
+
+		if nodeIndex == upperBound && !indexIsOdd {
+			treeIndices[writeIndex] = nodeIndex >> 1
+			hashes[writeIndex] = hashes[readIndex]
+			writeIndex = (writeIndex + 1) % count
+			readIndex = (readIndex + 1) % count
+		} else {
+			nextReadIndex := (readIndex + 1) % count
+			if nextReadIndex < len(treeIndices) {
+				nextNodeIndex = treeIndices[nextReadIndex]
+			}
+
+			// Check if the next node is a sibling
+			nextIsPair := nextNodeIndex == nodeIndex-1
+
+			var right, left []byte
+			if indexIsOdd {
+				right = hashes[readIndex]
+				readIndex = (readIndex + 1) % count
+				if !nextIsPair {
+					if proofIndex >= len(p.proofs) {
+						return nil, ErrNilProof
+					}
+					left = p.proofs[proofIndex]
+					proofIndex++
+				} else {
+					left = hashes[readIndex]
+					readIndex = (readIndex + 1) % count
+				}
+			} else {
+				if proofIndex >= len(p.proofs) {
+					return nil, ErrNilProof
+				}
+				right = p.proofs[proofIndex]
+				proofIndex++
+				left = hashes[readIndex]
+				readIndex = (readIndex + 1) % count
+			}
+
+			if left == nil || right == nil {
+				return nil, ErrNilProof
+			}
+
+			parentIndex := nodeIndex >> 1
+			treeIndices[writeIndex] = parentIndex
+			parentHash := HashNode(left, right)
+			hashes[writeIndex] = parentHash
+			writeIndex = (writeIndex + 1) % count
+		}
+
+		if nodeIndex == lowestTreeIndex || nextNodeIndex == lowestTreeIndex {
+			lowestTreeIndex >>= 1
+			upperBound >>= 1
+		}
+	}
+}
+
+// validate performs common validation for Merkle proofs.
+func (p *MultiProof) validate() error {
+	if p.root == nil {
+		return ErrNilRoot
+	}
+
+	if len(p.elements) == 0 {
+		return ErrNoElements
path: pkg/merkle/proof.go
user: login: macroscopeapp[bot]
body: In the `validate` method, the check for a valid `leafCount` is performed after calling `validateIndices`. This could result in an error like `ErrIndicesOutOfBounds` being returned rather than the more relevant `ErrInvalidLeafCount` when `leafCount` is non-positive. Consider reordering the validation so that `leafCount` is validated before calling `validateIndices` to ensure the error is more accurate.

```diff
-	if err := validateIndices(p.elements.Indices(), p.leafCount); err != nil {
-		return err
-	}
-
-	if p.leafCount <= 0 {
-		return ErrInvalidLeafCount
-	}
+	if p.leafCount <= 0 {
+		return ErrInvalidLeafCount
+	}
+
+	if err := validateIndices(p.elements.Indices(), p.leafCount); err != nil {
+		return err
+	}
```
> 🚀 Reply to ask Macroscope to explain or update this suggestion.

> 👍 Helpful? React to give us feedback.
created_at: 2025-04-14T19:05:45Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,386 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrEmptyTree          = errors.New("empty tree")
+	ErrDuplicateIndices   = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds = errors.New("indices out of bounds")
+	ErrInvalidRange       = errors.New("invalid range")
+	ErrInvalidLeafCount   = errors.New("invalid leaf count")
+	ErrElementMismatch    = errors.New("element and indices mismatch")
+	ErrNilProof           = errors.New("nil proof")
+	ErrNilRoot            = errors.New("nil root")
+	ErrNilElement         = errors.New("nil element")
+	ErrNoElements         = errors.New("no elements")
+	ErrNoIndices          = errors.New("no indices")
+	ErrNoProofs           = errors.New("no proofs provided")
+)
+
+type MultiProof struct {
+	elements  indexedValues
+	proofs    [][]byte
+	leafCount int
+}
+
+func (p *MultiProof) Elements() indexedValues {
+	return p.elements
+}
+
+func (p *MultiProof) Proofs() [][]byte {
+	return p.proofs
+}
+
+func (p *MultiProof) LeafCount() int {
+	return p.leafCount
+}
+
+type indexedValues []indexedValue
+
+type indexedValue struct {
+	value []byte
+	index int
+}
+
+// Values returns all leaf values
+func (iv indexedValues) Values() [][]byte {
+	values := make([][]byte, len(iv))
+	for i, v := range iv {
+		values[i] = v.value
+	}
+	return values
+}
+
+// Indices returns all index values
+func (iv indexedValues) Indices() []int {
+	indices := make([]int, len(iv))
+	for i, v := range iv {
+		indices[i] = v.index
+	}
+	return indices
+}
+
+// Verify verifies a proof.
+func Verify(root []byte, proof *MultiProof) (bool, error) {
+	if len(root) == 0 {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
+	}
+
+	if err := proof.validate(); err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	// Handle single-element trees.
+	if proof.leafCount == 1 {
+		return bytes.Equal(root, HashLeaf(proof.elements[0].value)), nil
+	}
+
+	// If all the elements are provided, we can verify the proof by recalculating the root.
+	if len(proof.elements) == proof.leafCount {
+		// Extract just the leaves for tree creation
+		tree, err := NewMerkleTree(proof.elements.Values())
+		if err != nil {
+			return false, fmt.Errorf(ErrVerifyProof, err)
+		}
+
+		return bytes.Equal(tree.Root(), root), nil
+	}
+
+	result, err := proof.computeRoot()
+	if err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	return bytes.Equal(result, root), nil
+}
+
+// computeRoot computes the root given the leaves, their indices, and proofs.
+func (p *MultiProof) computeRoot() ([]byte, error) {
+	leaves, err := makeLeaves(p.elements.Values())
+	if err != nil {
+		return nil, err
+	}
+
+	balancedLeafCount := CalculateBalancedLeafCount(p.leafCount)
+
+	// Prepare circular queues
+	count := len(p.elements.Indices())
+	treeIndices := make([]int, count)
+	hashes := make([][]byte, count)
+
+	// Initialize queues
+	for i := 0; i < count; i++ {
+		treeIndices[count-1-i] = balancedLeafCount + p.elements.Indices()[i]
+		hashes[count-1-i] = cloneBuffer(leaves[i])
+	}
+
+	readIndex := 0
+	writeIndex := 0
+	proofIndex := 0
+	upperBound := balancedLeafCount + p.leafCount - 1
+	lowestTreeIndex := treeIndices[count-1]
+	var nextNodeIndex int
+
+	for {
+		nodeIndex := treeIndices[readIndex]
+
+		if nodeIndex == 1 {
+			// Reached the root
+			rootIndex := writeIndex - 1
+			if writeIndex == 0 {
+				rootIndex = count - 1
+			}
+			return hashes[rootIndex], nil
+		}
+
+		indexIsOdd := nodeIndex&1 == 1
+
+		if nodeIndex == upperBound && !indexIsOdd {
+			treeIndices[writeIndex] = nodeIndex >> 1
+			hashes[writeIndex] = hashes[readIndex]
+			writeIndex = (writeIndex + 1) % count
+			readIndex = (readIndex + 1) % count
+		} else {
path: pkg/merkle/proof.go
user: login: coderabbitai[bot]
body: _⚠️ Potential issue_

**Fix the missing `nextNodeIndex` update in the first branch.**

The variable `nextNodeIndex` is only updated in the else branch (lines 154-157), but not in the first branch where `nodeIndex == upperBound && !indexIsOdd`. This can lead to using a stale value when checking `nextIsPair` in subsequent iterations, potentially causing unexpected behavior.

Apply this fix:

```diff
if nodeIndex == upperBound && !indexIsOdd {
    treeIndices[writeIndex] = nodeIndex >> 1
    hashes[writeIndex] = hashes[readIndex]
    writeIndex = (writeIndex + 1) % count
    readIndex = (readIndex + 1) % count
+   if readIndex < len(treeIndices) {
+       nextNodeIndex = treeIndices[readIndex]
+   }
} else {
```


<!-- suggestion_start -->

<details>
<summary>📝 Committable suggestion</summary>

> ‼️ **IMPORTANT**
> Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

`````suggestion
		indexIsOdd := nodeIndex&1 == 1

		if nodeIndex == upperBound && !indexIsOdd {
			treeIndices[writeIndex] = nodeIndex >> 1
			hashes[writeIndex] = hashes[readIndex]
			writeIndex = (writeIndex + 1) % count
			readIndex = (readIndex + 1) % count
			if readIndex < len(treeIndices) {
				nextNodeIndex = treeIndices[readIndex]
			}
		} else {
			// ... existing logic in the else branch
`````

</details>

<!-- suggestion_end -->

<!-- This is an auto-generated comment by CodeRabbit -->

✅ Addressed in commit 79f8c12
created_at: 2025-04-15T11:02:04Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,313 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrEmptyTree          = errors.New("empty tree")
+	ErrDuplicateIndices   = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds = errors.New("indices out of bounds")
+	ErrInvalidRange       = errors.New("invalid range")
+	ErrInvalidLeafCount   = errors.New("invalid leaf count")
+	ErrElementMismatch    = errors.New("element and indices mismatch")
+	ErrNilProof           = errors.New("nil proof")
+	ErrNilRoot            = errors.New("nil root")
+	ErrNilElement         = errors.New("nil element")
+	ErrNoElements         = errors.New("no elements")
+	ErrNoIndices          = errors.New("no indices")
+	ErrNoProofs           = errors.New("no proofs provided")
+)
+
+type MultiProof struct {
+	elements  indexedValues
+	proofs    [][]byte
+	leafCount int
+}
+
+func (p *MultiProof) Elements() indexedValues {
+	return p.elements
+}
+
+func (p *MultiProof) Proofs() [][]byte {
+	return p.proofs
+}
+
+func (p *MultiProof) LeafCount() int {
+	return p.leafCount
+}
+
+type indexedValues []indexedValue
+
+type indexedValue struct {
+	value []byte
+	index int
+}
+
+func (iv indexedValues) Values() [][]byte {
+	values := make([][]byte, len(iv))
+	for i, v := range iv {
+		values[i] = v.value
+	}
+	return values
+}
+
+func (iv indexedValues) Indices() []int {
+	indices := make([]int, len(iv))
+	for i, v := range iv {
+		indices[i] = v.index
+	}
+	return indices
+}
+
+// Verify verifies a MultiProof against the given tree root.
+func Verify(root []byte, proof *MultiProof) (bool, error) {
path: pkg/merkle/proof.go
user: login: coderabbitai[bot]
body: _⚠️ Potential issue_

**Check for nil `proof` to avoid potential panic**  
When `proof` is `nil`, calling `proof.validate()` at line 77 will panic. Consider adding a nil check here:

```diff
 func Verify(root []byte, proof *MultiProof) (bool, error) {
+	if proof == nil {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilProof)
+	}
 	if len(root) == 0 {
 		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
 	}
```



<!-- suggestion_start -->

<details>
<summary>📝 Committable suggestion</summary>

> ‼️ **IMPORTANT**
> Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

`````suggestion
// Verify verifies a MultiProof against the given tree root.
func Verify(root []byte, proof *MultiProof) (bool, error) {
	if proof == nil {
		return false, fmt.Errorf(ErrVerifyProof, ErrNilProof)
	}
	if len(root) == 0 {
		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
	}
	// ... rest of the function implementation ...
}
`````

</details>

<!-- suggestion_end -->

<!-- This is an auto-generated reply by CodeRabbit -->
created_at: 2025-04-15T11:19:52Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,313 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrEmptyTree          = errors.New("empty tree")
+	ErrDuplicateIndices   = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds = errors.New("indices out of bounds")
+	ErrInvalidRange       = errors.New("invalid range")
+	ErrInvalidLeafCount   = errors.New("invalid leaf count")
+	ErrElementMismatch    = errors.New("element and indices mismatch")
+	ErrNilProof           = errors.New("nil proof")
+	ErrNilRoot            = errors.New("nil root")
+	ErrNilElement         = errors.New("nil element")
+	ErrNoElements         = errors.New("no elements")
+	ErrNoIndices          = errors.New("no indices")
+	ErrNoProofs           = errors.New("no proofs provided")
+)
+
+type MultiProof struct {
+	elements  indexedValues
+	proofs    [][]byte
+	leafCount int
+}
+
+func (p *MultiProof) Elements() indexedValues {
+	return p.elements
+}
+
+func (p *MultiProof) Proofs() [][]byte {
+	return p.proofs
+}
+
+func (p *MultiProof) LeafCount() int {
+	return p.leafCount
+}
+
+type indexedValues []indexedValue
+
+type indexedValue struct {
+	value []byte
+	index int
+}
+
+func (iv indexedValues) Values() [][]byte {
+	values := make([][]byte, len(iv))
+	for i, v := range iv {
+		values[i] = v.value
+	}
+	return values
+}
+
+func (iv indexedValues) Indices() []int {
+	indices := make([]int, len(iv))
+	for i, v := range iv {
+		indices[i] = v.index
+	}
+	return indices
+}
+
+// Verify verifies a MultiProof against the given tree root.
+func Verify(root []byte, proof *MultiProof) (bool, error) {
path: pkg/merkle/proof.go
user: login: fbac
body: The check len(root) == nil also checks for nil, as a nil []byte has length 0.
created_at: 2025-04-15T11:28:35Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,313 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrEmptyTree          = errors.New("empty tree")
+	ErrDuplicateIndices   = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds = errors.New("indices out of bounds")
+	ErrInvalidRange       = errors.New("invalid range")
+	ErrInvalidLeafCount   = errors.New("invalid leaf count")
+	ErrElementMismatch    = errors.New("element and indices mismatch")
+	ErrNilProof           = errors.New("nil proof")
+	ErrNilRoot            = errors.New("nil root")
+	ErrNilElement         = errors.New("nil element")
+	ErrNoElements         = errors.New("no elements")
+	ErrNoIndices          = errors.New("no indices")
+	ErrNoProofs           = errors.New("no proofs provided")
+)
+
+type MultiProof struct {
+	elements  indexedValues
+	proofs    [][]byte
+	leafCount int
+}
+
+func (p *MultiProof) Elements() indexedValues {
+	return p.elements
+}
+
+func (p *MultiProof) Proofs() [][]byte {
+	return p.proofs
+}
+
+func (p *MultiProof) LeafCount() int {
+	return p.leafCount
+}
+
+type indexedValues []indexedValue
+
+type indexedValue struct {
+	value []byte
+	index int
+}
+
+func (iv indexedValues) Values() [][]byte {
+	values := make([][]byte, len(iv))
+	for i, v := range iv {
+		values[i] = v.value
+	}
+	return values
+}
+
+func (iv indexedValues) Indices() []int {
+	indices := make([]int, len(iv))
+	for i, v := range iv {
+		indices[i] = v.index
+	}
+	return indices
+}
+
+// Verify verifies a MultiProof against the given tree root.
+func Verify(root []byte, proof *MultiProof) (bool, error) {
path: pkg/merkle/proof.go
user: login: coderabbitai[bot]
body: @fbac You're absolutely right. In Go, a nil byte slice does have length 0, so the `len(root) == 0` check effectively catches both nil slices and empty slices. 

To clarify, the suggestion was actually about adding a nil check for the `proof` parameter (which is a pointer to `MultiProof`), not for the `root` parameter. Since `proof` is a struct pointer rather than a slice, calling `proof.validate()` would panic if `proof` were nil.
---
<details>
<summary>✏️ Learnings added</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:71-72
Timestamp: 2025-04-15T11:29:03.575Z
Learning: In Go, when a byte slice (`[]byte`) is nil, `len(slice)` returns 0. Therefore, checking `if len(slice) == 0` will catch both nil slices and empty slices (initialized but with no elements).
```

> Note: Learnings are effective only in the context of similar code segments. To apply general coding guidelines, please configure [review instructions](https://docs.coderabbit.ai/guides/review-instructions). You can manage existing learnings in the [app](https://app.coderabbit.ai/learnings).

</details>



<!-- <agentComponentType>chat-answer</agentComponentType> -->

<!-- <rawResChunk><answer>@fbac You're absolutely right. In Go, a nil byte slice does have length 0, so the `len(root) == 0` check effectively catches both nil slices and empty slices. 

To clarify, the suggestion was actually about adding a nil check for the `proof` parameter (which is a pointer to `MultiProof`), not for the `root` parameter. Since `proof` is a struct pointer rather than a slice, calling `proof.validate()` would panic if `proof` were nil.
---

<details>
<summary>✏️ Learnings added</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:71-72
Timestamp: 2025-04-15T11:29:03.575Z
Learning: In Go, when a byte slice (`[]byte`) is nil, `len(slice)` returns 0. Therefore, checking `if len(slice) == 0` will catch both nil slices and empty slices (initialized but with no elements).
```

> Note: Learnings are effective only in the context of similar code segments. To apply general coding guidelines, please configure [review instructions](https://docs.coderabbit.ai/guides/review-instructions). You can manage existing learnings in the [app](https://app.coderabbit.ai/learnings).

</details></answer></rawResChunk> -->

<!-- This is an auto-generated reply by CodeRabbit -->
created_at: 2025-04-15T11:29:04Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,150 @@
+package merkle
+
+import (
+	"errors"
+	"math"
+	"math/bits"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	depth     int
+	leafCount int
+}
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	tree, depth := buildTree(leaves)
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elements,
+		root:      tree[0],
+		depth:     depth,
+		leafCount: len(elements),
+	}, nil
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// Elements returns the elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Depth returns the depth of the Merkle tree.
+func (m *MerkleTree) Depth() int {
+	return m.depth
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+// The matrix representation has the root at index 0.
+// The internal nodes are at index 1 to N-1.
+// The leaves are at index N to 2N-1.
+// For any node at index i:
+// - its left child is at index 2*i and its right child is at index 2*i+1.
+// - its parent is at index i/2.
+func buildTree(leaves [][]byte) ([][]byte, int) {
+	depth := getDepth(len(leaves))
+	leafCount := getLeafCount(len(leaves))
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		if i == 0 {
+			if tree[1] != nil {
+				tree[0] = tree[1]
+			} else if tree[1] != nil && tree[2] != nil {
+				tree[0] = HashNode(tree[1], tree[2])
+			}
+			break
+		}
+
+		leftChildIndex := getLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := getRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	return tree, depth
+}
+
+// getDepth calculates the depth of a Merkle tree based on element count.
+func getDepth(elementCount int) int {
+	return int(math.Ceil(math.Log2(float64(elementCount))))
path: pkg/merkle/tree.go
user: login: fbac
body: In the end getDepth is not needed, so I removed the code.
created_at: 2025-04-15T11:37:27Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,331 @@
+package merkle
path: pkg/merkle/tree_test.go
user: login: fbac
body: Done.
created_at: 2025-04-15T11:38:06Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,345 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrEmptyTree          = errors.New("empty tree")
+	ErrDuplicateIndices   = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds = errors.New("indices out of bounds")
+	ErrInvalidRange       = errors.New("invalid range")
+	ErrInvalidLeafCount   = errors.New("invalid leaf count")
+	ErrElementMismatch    = errors.New("element and indices mismatch")
+	ErrNilProof           = errors.New("nil proof")
+	ErrNilRoot            = errors.New("nil root")
+	ErrNilElement         = errors.New("nil element")
+	ErrNoElements         = errors.New("no elements")
+	ErrNoIndices          = errors.New("no indices")
+	ErrNoProofs           = errors.New("no proofs provided")
+)
+
+type MultiProof struct {
+	elements  indexedValues
+	proofs    [][]byte
+	leafCount int
+}
+
+func (p *MultiProof) Elements() indexedValues {
+	return p.elements
+}
+
+func (p *MultiProof) Proofs() [][]byte {
+	return p.proofs
+}
+
+func (p *MultiProof) LeafCount() int {
+	return p.leafCount
+}
+
+type indexedValues []indexedValue
+
+type indexedValue struct {
+	value []byte
+	index int
+}
+
+func (iv indexedValues) Values() [][]byte {
+	values := make([][]byte, len(iv))
+	for i, v := range iv {
+		values[i] = v.value
+	}
+	return values
+}
+
+func (iv indexedValues) Indices() []int {
+	indices := make([]int, len(iv))
+	for i, v := range iv {
+		indices[i] = v.index
+	}
+	return indices
+}
+
+// Verify verifies a MultiProof against the given tree root.
+func Verify(root []byte, proof *MultiProof) (bool, error) {
+	if len(root) == 0 {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
+	}
+
+	if err := proof.validate(); err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	// Handle single-element trees.
+	if proof.leafCount == 1 {
+		return bytes.Equal(root, HashLeaf(proof.elements[0].value)), nil
+	}
+
+	// If all the elements are provided, we can directly reconstruct the tree.
+	if len(proof.elements) == proof.leafCount {
+		tree, err := NewMerkleTree(proof.elements.Values())
+		if err != nil {
+			return false, fmt.Errorf(ErrVerifyProof, err)
+		}
+
+		return bytes.Equal(tree.Root(), root), nil
+	}
+
+	result, err := proof.computeRoot()
+	if err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	return bytes.Equal(result, root), nil
+}
+
+func (p *MultiProof) computeRoot() ([]byte, error) {
+	balancedLeafCount := CalculateBalancedLeafCount(p.leafCount)
+
+	leaves, err := makeLeaves(p.elements.Values())
+	if err != nil {
+		return nil, err
+	}
+
+	indices := p.elements.Indices()
+	numElements := len(indices)
+
+	// nodeQueue is populated with the indices we want to prove, from right to left.
+	nodeQueue := make([]int, numElements)
+	hashQueue := make([][]byte, numElements)
+	for i := 0; i < numElements; i++ {
+		reverseIdx := numElements - 1 - i
+		nodeQueue[reverseIdx] = balancedLeafCount + indices[i]
+		hashQueue[reverseIdx] = cloneBuffer(leaves[i])
+	}
+
+	var (
+		readIndex, writeIndex, proofIndex = 0, 0, 0
+		upperBound                        = balancedLeafCount + p.leafCount - 1
+		lowestTreeIndex                   = nodeQueue[numElements-1]
+		nextNodeIndex                     int
+		leftHash, rightHash               []byte
+	)
+
+	for {
+		currentIndex := nodeQueue[readIndex]
+
+		// When the root is reached, return the hash.
+		if currentIndex == 1 {
+			rootIdx := (writeIndex + numElements - 1) % numElements
+			return hashQueue[rootIdx], nil
+		}
+
+		// A left child is even, a right child is odd.
+		isOdd := isOddIndex(currentIndex)
+
+		// A left child at the boundary might not have a right sibling.
+		// The sibling of a left child (even index) would be at index+1.
+		shouldPromoteDirectly := isLeftNodeAtUpperBound(currentIndex, upperBound)
+
+		// Promote node if it's a left child at the boundary with no sibling
+		if shouldPromoteDirectly {
+			nodeQueue[writeIndex] = currentIndex >> 1
+			hashQueue[writeIndex] = hashQueue[readIndex]
+			writeIndex = (writeIndex + 1) % numElements
+			readIndex = (readIndex + 1) % numElements
+		} else {
+			nextReadIndex := (readIndex + 1) % numElements
+			nextNodeIndex = nodeQueue[nextReadIndex]
+			nextIsSibling := nextNodeIndex == currentIndex-1
+
+			if isOdd {
+				// Current node is right child
+				rightHash = hashQueue[readIndex]
+				readIndex = (readIndex + 1) % numElements
+
+				if nextIsSibling {
+					// Get left sibling from queue
+					leftHash = hashQueue[readIndex]
+					readIndex = (readIndex + 1) % numElements
+				} else {
+					// Get left sibling from proof
+					leftHash, err = p.getNextProof(&proofIndex)
+					if err != nil {
+						return nil, err
+					}
+				}
+			} else {
+				// Current node is left child
+				leftHash = hashQueue[readIndex]
+				readIndex = (readIndex + 1) % numElements
+
+				// Always get right sibling from proof
+				rightHash, err = p.getNextProof(&proofIndex)
+				if err != nil {
+					return nil, err
+				}
+			}
+
+			if leftHash == nil || rightHash == nil {
+				return nil, ErrNilProof
+			}
+
+			// Compute parent hash and add to queue
+			parentIndex := currentIndex >> 1
+			parentHash := HashNode(leftHash, rightHash)
+			nodeQueue[writeIndex] = parentIndex
+			hashQueue[writeIndex] = parentHash
+			writeIndex = (writeIndex + 1) % numElements
+		}
+
+		// Update level tracking when processing the lowest index.
+		if currentIndex == lowestTreeIndex || nextNodeIndex == lowestTreeIndex {
+			lowestTreeIndex >>= 1
+			upperBound >>= 1
+		}
+	}
+}
+
+// getNextProof safely retrieves the next proof and increments the index.
+func (p *MultiProof) getNextProof(proofIndex *int) ([]byte, error) {
+	if *proofIndex >= len(p.proofs) {
+		return nil, ErrNilProof
+	}
+	proof := p.proofs[*proofIndex]
+	*proofIndex++
+	return proof, nil
+}
+
+// validate performs common validation for Merkle proofs.
+func (p *MultiProof) validate() error {
+	if len(p.elements) == 0 {
+		return ErrNoElements
+	}
+
+	if p.leafCount <= 0 {
+		return ErrInvalidLeafCount
+	}
+
+	if err := validateIndices(p.elements.Indices(), p.leafCount); err != nil {
+		return err
+	}
+
+	for _, elem := range p.elements {
+		if elem.value == nil {
+			return ErrNilElement
+		}
+	}
+
+	for _, proof := range p.proofs {
+		if proof == nil {
+			return ErrNilProof
+		}
+	}
+
+	isPartialProof := len(p.elements) < p.leafCount
+	isNonTrivialTree := p.leafCount > 1
+	needsProofs := isPartialProof && isNonTrivialTree
+
+	if needsProofs && len(p.proofs) == 0 {
+		return ErrNoProofs
+	}
+
+	return nil
+}
+
+// makeIndexedValues creates indexed values from elements and their indices.
+func makeIndexedValues(elements [][]byte, indices []int) indexedValues {
+	result := make(indexedValues, len(indices))
+	for i, idx := range indices {
+		result[i] = indexedValue{
+			value: elements[idx],
+			index: idx,
+		}
+	}
+	return result
+}
+
+// makeIndices returns a slice of ascending ordered indices for the given starting index and count.
+func makeIndices(startingIndex, count int) ([]int, error) {
+	if startingIndex < 0 || count <= 0 {
+		return nil, ErrInvalidRange
+	}
+
+	indices := make([]int, count)
+	for i := 0; i < count; i++ {
+		indices[i] = startingIndex + i
+	}
+
+	return indices, nil
+}
+
+// validateIndices validates the indices slice of a proof.
+func validateIndices(indices []int, leafCount int) error {
path: pkg/merkle/proof.go
user: login: neekolas
body: What about gaps in the list. For example, if I provide `1, 2, 4`. Those would not have duplicates, or out of bounds, but should be invalid for a sequential multi-proof.

Or is the goal to handle that validation elsewhere so that we can generate adversarial test cases?
created_at: 2025-04-15T18:17:16Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,26 @@
+package merkle
+
+import (
+	"golang.org/x/crypto/sha3"
+)
+
+// LEAF_PREFIX is the prefix for leaf nodes.
+// It is used to distinguish leaf nodes from other types of nodes.
+const LEAF_PREFIX = "leaf|"
path: pkg/merkle/hash.go
user: login: neekolas
body: Great call out
created_at: 2025-04-15T19:12:03Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,26 @@
+package merkle
+
+import (
+	"golang.org/x/crypto/sha3"
+)
+
+// LEAF_PREFIX is the prefix for leaf nodes.
+// It is used to distinguish leaf nodes from other types of nodes.
+const LEAF_PREFIX = "leaf|"
path: pkg/merkle/hash.go
user: login: coderabbitai[bot]
body: > Seems like the humans are having a chat. I'll hop back into my burrow for now. If you need me again, just tag @coderabbitai in a new comment, and I'll come hopping out!

<!-- This is an auto-generated mute comment by CodeRabbit -->
created_at: 2025-04-15T19:12:09Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,26 @@
+package merkle
+
+import (
+	"golang.org/x/crypto/sha3"
+)
+
+// LEAF_PREFIX is the prefix for leaf nodes.
+// It is used to distinguish leaf nodes from other types of nodes.
+const LEAF_PREFIX = "leaf|"
path: pkg/merkle/hash.go
user: login: fbac
body: This is really interesting. :)

I wrote a new HashNode which uses a prefix for nodes, and also uses a buffer for easy optimizations:

```
func HashNode(left, right []byte) []byte {
	nodePrefixLen := len(nodePrefixBytes)
	buffer := make([]byte, nodePrefixLen+len(left)+len(right))

	copy(buffer[:nodePrefixLen], nodePrefixBytes)
	copy(buffer[nodePrefixLen:], left)
	copy(buffer[nodePrefixLen+len(left):], right)

	return Hash(buffer)
}
```

It settles around ~278.0 ns/op with improved security, while the old HashNode marks 280 ns/op.


created_at: 2025-04-16T10:34:35Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,345 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrEmptyTree          = errors.New("empty tree")
+	ErrDuplicateIndices   = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds = errors.New("indices out of bounds")
+	ErrInvalidRange       = errors.New("invalid range")
+	ErrInvalidLeafCount   = errors.New("invalid leaf count")
+	ErrElementMismatch    = errors.New("element and indices mismatch")
+	ErrNilProof           = errors.New("nil proof")
+	ErrNilRoot            = errors.New("nil root")
+	ErrNilElement         = errors.New("nil element")
+	ErrNoElements         = errors.New("no elements")
+	ErrNoIndices          = errors.New("no indices")
+	ErrNoProofs           = errors.New("no proofs provided")
+)
+
+type MultiProof struct {
+	elements  indexedValues
+	proofs    [][]byte
+	leafCount int
+}
+
+func (p *MultiProof) Elements() indexedValues {
+	return p.elements
+}
+
+func (p *MultiProof) Proofs() [][]byte {
+	return p.proofs
+}
+
+func (p *MultiProof) LeafCount() int {
+	return p.leafCount
+}
+
+type indexedValues []indexedValue
+
+type indexedValue struct {
+	value []byte
+	index int
+}
+
+func (iv indexedValues) Values() [][]byte {
+	values := make([][]byte, len(iv))
+	for i, v := range iv {
+		values[i] = v.value
+	}
+	return values
+}
+
+func (iv indexedValues) Indices() []int {
+	indices := make([]int, len(iv))
+	for i, v := range iv {
+		indices[i] = v.index
+	}
+	return indices
+}
+
+// Verify verifies a MultiProof against the given tree root.
+func Verify(root []byte, proof *MultiProof) (bool, error) {
+	if len(root) == 0 {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
+	}
+
+	if err := proof.validate(); err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	// Handle single-element trees.
+	if proof.leafCount == 1 {
+		return bytes.Equal(root, HashLeaf(proof.elements[0].value)), nil
+	}
+
+	// If all the elements are provided, we can directly reconstruct the tree.
+	if len(proof.elements) == proof.leafCount {
+		tree, err := NewMerkleTree(proof.elements.Values())
+		if err != nil {
+			return false, fmt.Errorf(ErrVerifyProof, err)
+		}
+
+		return bytes.Equal(tree.Root(), root), nil
+	}
+
+	result, err := proof.computeRoot()
+	if err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	return bytes.Equal(result, root), nil
+}
+
+func (p *MultiProof) computeRoot() ([]byte, error) {
+	balancedLeafCount := CalculateBalancedLeafCount(p.leafCount)
+
+	leaves, err := makeLeaves(p.elements.Values())
+	if err != nil {
+		return nil, err
+	}
+
+	indices := p.elements.Indices()
+	numElements := len(indices)
+
+	// nodeQueue is populated with the indices we want to prove, from right to left.
+	nodeQueue := make([]int, numElements)
+	hashQueue := make([][]byte, numElements)
+	for i := 0; i < numElements; i++ {
+		reverseIdx := numElements - 1 - i
+		nodeQueue[reverseIdx] = balancedLeafCount + indices[i]
+		hashQueue[reverseIdx] = cloneBuffer(leaves[i])
+	}
+
+	var (
+		readIndex, writeIndex, proofIndex = 0, 0, 0
+		upperBound                        = balancedLeafCount + p.leafCount - 1
+		lowestTreeIndex                   = nodeQueue[numElements-1]
+		nextNodeIndex                     int
+		leftHash, rightHash               []byte
+	)
+
+	for {
+		currentIndex := nodeQueue[readIndex]
+
+		// When the root is reached, return the hash.
+		if currentIndex == 1 {
+			rootIdx := (writeIndex + numElements - 1) % numElements
+			return hashQueue[rootIdx], nil
+		}
+
+		// A left child is even, a right child is odd.
+		isOdd := isOddIndex(currentIndex)
+
+		// A left child at the boundary might not have a right sibling.
+		// The sibling of a left child (even index) would be at index+1.
+		shouldPromoteDirectly := isLeftNodeAtUpperBound(currentIndex, upperBound)
+
+		// Promote node if it's a left child at the boundary with no sibling
+		if shouldPromoteDirectly {
+			nodeQueue[writeIndex] = currentIndex >> 1
+			hashQueue[writeIndex] = hashQueue[readIndex]
+			writeIndex = (writeIndex + 1) % numElements
+			readIndex = (readIndex + 1) % numElements
+		} else {
+			nextReadIndex := (readIndex + 1) % numElements
+			nextNodeIndex = nodeQueue[nextReadIndex]
+			nextIsSibling := nextNodeIndex == currentIndex-1
+
+			if isOdd {
+				// Current node is right child
+				rightHash = hashQueue[readIndex]
+				readIndex = (readIndex + 1) % numElements
+
+				if nextIsSibling {
+					// Get left sibling from queue
+					leftHash = hashQueue[readIndex]
+					readIndex = (readIndex + 1) % numElements
+				} else {
+					// Get left sibling from proof
+					leftHash, err = p.getNextProof(&proofIndex)
+					if err != nil {
+						return nil, err
+					}
+				}
+			} else {
+				// Current node is left child
+				leftHash = hashQueue[readIndex]
+				readIndex = (readIndex + 1) % numElements
+
+				// Always get right sibling from proof
+				rightHash, err = p.getNextProof(&proofIndex)
+				if err != nil {
+					return nil, err
+				}
+			}
+
+			if leftHash == nil || rightHash == nil {
+				return nil, ErrNilProof
+			}
+
+			// Compute parent hash and add to queue
+			parentIndex := currentIndex >> 1
+			parentHash := HashNode(leftHash, rightHash)
+			nodeQueue[writeIndex] = parentIndex
+			hashQueue[writeIndex] = parentHash
+			writeIndex = (writeIndex + 1) % numElements
+		}
+
+		// Update level tracking when processing the lowest index.
+		if currentIndex == lowestTreeIndex || nextNodeIndex == lowestTreeIndex {
+			lowestTreeIndex >>= 1
+			upperBound >>= 1
+		}
+	}
+}
+
+// getNextProof safely retrieves the next proof and increments the index.
+func (p *MultiProof) getNextProof(proofIndex *int) ([]byte, error) {
+	if *proofIndex >= len(p.proofs) {
+		return nil, ErrNilProof
+	}
+	proof := p.proofs[*proofIndex]
+	*proofIndex++
+	return proof, nil
+}
+
+// validate performs common validation for Merkle proofs.
+func (p *MultiProof) validate() error {
+	if len(p.elements) == 0 {
+		return ErrNoElements
+	}
+
+	if p.leafCount <= 0 {
+		return ErrInvalidLeafCount
+	}
+
+	if err := validateIndices(p.elements.Indices(), p.leafCount); err != nil {
+		return err
+	}
+
+	for _, elem := range p.elements {
+		if elem.value == nil {
+			return ErrNilElement
+		}
+	}
+
+	for _, proof := range p.proofs {
+		if proof == nil {
+			return ErrNilProof
+		}
+	}
+
+	isPartialProof := len(p.elements) < p.leafCount
+	isNonTrivialTree := p.leafCount > 1
+	needsProofs := isPartialProof && isNonTrivialTree
+
+	if needsProofs && len(p.proofs) == 0 {
+		return ErrNoProofs
+	}
+
+	return nil
+}
+
+// makeIndexedValues creates indexed values from elements and their indices.
+func makeIndexedValues(elements [][]byte, indices []int) indexedValues {
+	result := make(indexedValues, len(indices))
+	for i, idx := range indices {
+		result[i] = indexedValue{
+			value: elements[idx],
+			index: idx,
+		}
+	}
+	return result
+}
+
+// makeIndices returns a slice of ascending ordered indices for the given starting index and count.
+func makeIndices(startingIndex, count int) ([]int, error) {
+	if startingIndex < 0 || count <= 0 {
+		return nil, ErrInvalidRange
+	}
+
+	indices := make([]int, count)
+	for i := 0; i < count; i++ {
+		indices[i] = startingIndex + i
+	}
+
+	return indices, nil
+}
+
+// validateIndices validates the indices slice of a proof.
+func validateIndices(indices []int, leafCount int) error {
path: pkg/merkle/proof.go
user: login: fbac
body: Currently we support two multi proofs; sequential and indices based. That's why we don't explicitly check the provided indices are always sequential.

We can be more opinionated and just do sequential indices.
created_at: 2025-04-16T10:37:05Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,309 @@
+package merkle
+
+import (
+	"errors"
+	"fmt"
+	"math/bits"
+	"sort"
+)
+
+// MerkleTree represents a Merkle tree data structure.
+type MerkleTree struct {
+	tree      [][]byte
+	elements  [][]byte
+	root      []byte
+	leafCount int
+}
+
+const TREE_MAX_LEAVES = 4096
+
+var (
+	ErrTreeEmpty          = errors.New("tree is empty")
+	ErrTreeRootNil        = errors.New("tree root is nil")
+	ErrTreeTooLarge       = errors.New("tree size exceeds maximum supported size")
+	ErrTreeLeavesOverflow = errors.New("amount of leaves overflows uint32")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(elements [][]byte) (*MerkleTree, error) {
+	if len(elements) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	if len(elements) > TREE_MAX_LEAVES {
+		return nil, ErrTreeTooLarge
+	}
+
+	elementsDeepCopy := make([][]byte, len(elements))
+	for i, element := range elements {
+		elementsDeepCopy[i] = make([]byte, len(element))
+		copy(elementsDeepCopy[i], element)
+	}
+
+	leaves, err := makeLeaves(elementsDeepCopy)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{
+		tree:      tree,
+		elements:  elementsDeepCopy,
+		root:      tree[1],
+		leafCount: len(elementsDeepCopy),
+	}, nil
+}
+
+// GenerateMultiProofSequential generates a sequential multi-proof starting from the given index.
+func (m *MerkleTree) GenerateMultiProofSequential(startingIndex, count int) (*MultiProof, error) {
+	indices, err := makeIndices(startingIndex, count)
+	if err != nil {
+		return nil, err
+	}
+
+	proof, err := m.makeProof(indices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// GenerateMultiProofWithIndices generates a multi-proof for the given indices.
+func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	proof, err := m.makeProof(sortedIndices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// makeProof returns a MultiProof for the given indices.
+func (m *MerkleTree) makeProof(indices []int) (MultiProof, error) {
+	if len(m.tree) == 0 {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, ErrEmptyTree)
+	}
+
+	if len(m.root) == 0 {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, ErrNilRoot)
+	}
+
+	if err := validateIndices(indices, m.leafCount); err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	indexedValues := makeIndexedValues(m.elements, indices)
+	if len(indexedValues) != len(indices) {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, ErrElementMismatch)
+	}
+
+	// Handle single-element trees.
+	if m.leafCount == 1 {
+		return MultiProof{
+			elements:  indexedValues,
+			proofs:    [][]byte{m.root},
+			leafCount: m.leafCount,
+		}, nil
+	}
+
+	var (
+		startLeafIdx = len(m.tree) >> 1
+		proofs       [][]byte
+		known        = make([]bool, len(m.tree))
+	)
+
+	// Mark provided indices as known.
+	for _, idx := range indices {
+		known[startLeafIdx+idx] = true
+	}
+
+	// Calculate proofs to prove the existence of the indices.
+	for i := startLeafIdx - 1; i > 0; i-- {
+		leftChildIdx := GetLeftChild(i)
+		rightChildIdx := GetRightChild(i)
+
+		left := known[leftChildIdx]
+		right := known[rightChildIdx]
+
+		// Only one of children would be known, so we need the sibling as a proof
+		if left != right {
+			if right {
+				// Only add non-nil sibling nodes
+				if m.tree[leftChildIdx] != nil {
+					proofs = append(proofs, cloneBuffer(m.tree[leftChildIdx]))
+				}
+			} else {
+				// Only add non-nil sibling nodes
+				if m.tree[rightChildIdx] != nil {
+					proofs = append(proofs, cloneBuffer(m.tree[rightChildIdx]))
+				}
+			}
+		}
+
+		// If at least one of the children is known, the parent is known
+		known[i] = left || right
+	}
+
+	return MultiProof{
+		elements:  indexedValues,
+		proofs:    proofs,
+		leafCount: m.leafCount,
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() [][]byte {
+	return m.tree
+}
+
+// Elements returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Elements() [][]byte {
+	return m.elements
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.root
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return m.leafCount
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func makeTree(leaves [][]byte) ([][]byte, error) {
+	if len(leaves) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	leafCount, err := CalculateBalancedLeafCount(len(leaves))
+	if err != nil {
+		return nil, err
+	}
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([][]byte, leafCount<<1)
+
+	lowerBound := leafCount
+	upperBound := leafCount + len(leaves) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(leaves); i++ {
+		tree[lowerBound+i] = leaves[i]
+	}
+
+	// Build the tree.
+	// Start from the last internal node and work our way up to the root.
+	for i := leafCount - 1; i >= 0; i-- {
+		leftChildIndex := GetLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := GetRightChild(i)
+
+		// Hash both children if they exist.
+		// If only left children exists, use it.
+		// If no children exist, leave it as nil.
+		if tree[leftChildIndex] != nil && tree[rightChildIndex] != nil {
+			tree[i] = HashNode(tree[leftChildIndex], tree[rightChildIndex])
+		} else if tree[leftChildIndex] != nil {
+			tree[i] = tree[leftChildIndex]
+		}
+	}
+
+	if tree[1] == nil {
+		return nil, ErrTreeRootNil
+	}
+
+	return tree, nil
+}
+
+// makeLeaves returns the leaves of the tree,
+// ordered in the same order as the provided elements.
+func makeLeaves(elements [][]byte) ([][]byte, error) {
+	if len(elements) == 0 {
+		return nil, errors.New("elements cannot be empty")
+	}
+
+	leaves := make([][]byte, len(elements))
+	for i, element := range elements {
+		leaves[i] = HashLeaf(element)
+	}
+
+	return leaves, nil
+}
+
+// CalculateBalancedLeafCount returns the number of leaves in a balanced tree.
+// To calculate the number of leaves in a tree, we need to round up to the next power of 2.
+// Returns an error if the element count is too large to be represented in a uint32.
+func CalculateBalancedLeafCount(elementCount int) (int, error) {
+	if elementCount <= 0 {
+		return 0, nil
+	}
+
+	if elementCount > int(^uint32(0)) {
+		return 0, ErrTreeLeavesOverflow
+	}
+
path: pkg/merkle/tree.go
user: login: macroscopeapp[bot]
body: The current implementation of `roundUpToPowerOf2` can overflow for inputs greater than 2^31 and which are not already a power of two, resulting in a return value of 0 due to wrapping when adding 1. This behavior may lead to unexpected tree construction errors later on. Consider changing the overflow check in `CalculateBalancedLeafCount` to ensure that inputs which would cause the overflow are rejected. For example, replacing the check from `int(^uint32(0))` with `1<<31` would ensure the function only handles values that can safely be rounded to the next power of 2.

```diff
-	if elementCount > int(^uint32(0)) {
+	if elementCount > int(1<<31) {
```
> 🚀 Reply to ask Macroscope to explain or update this suggestion.

> 👍 Helpful? React to give us feedback.
created_at: 2025-04-16T11:30:36Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,432 @@
+package merkle_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/xmtp/xmtpd/pkg/merkle"
+)
+
+func TestEmptyTree(t *testing.T) {
+	_, err := merkle.NewMerkleTree([][]byte{})
+	assert.Error(t, err, "Should error on empty elements")
+	assert.ErrorAs(t, err, &merkle.ErrTreeEmpty)
+}
+
+func TestBalancedTrees(t *testing.T) {
+	testCases := []struct {
+		name          string
+		numElements   int
+		expectedDepth int
+	}{
+		{"TwoElements", 2, 1},
+		{"FourElements", 4, 2},
+		{"EightElements", 8, 3},
+		{"SixteenElements", 16, 4},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			// Create elements.
+			elements := make([][]byte, tc.numElements)
+			for i := 0; i < tc.numElements; i++ {
+				elements[i] = []byte(tc.name + "_element" + string(rune('A'+i)))
+			}
+
+			tree, err := merkle.NewMerkleTree(elements)
+			require.NoError(t, err)
+
+			// Check structure.
+			assert.Equal(
+				t,
+				tc.numElements,
+				tree.LeafCount(),
+				"Leaf count should match element count",
+			)
+			assert.NotNil(t, tree.Root(), "Root should not be nil")
+
+			// For balanced trees, the array size is exactly 2*n where n is the next power of 2 >= numElements.
+			leafCount, err := merkle.CalculateBalancedLeafCount(tc.numElements)
+			require.NoError(t, err)
+			expectedArraySize := leafCount * 2
+			assert.Equal(
+				t,
+				expectedArraySize,
+				len(tree.Tree()),
+				"Tree array size should be 2*leafCount",
+			)
+
+			// Check that all leaves are present.
+			for i := 0; i < tc.numElements; i++ {
+				leafIndex := leafCount + i
+				assert.NotNil(t, tree.Tree()[leafIndex], "Leaf node should not be nil")
+				assert.Equal(
+					t,
+					merkle.HashLeaf(elements[i]),
+					tree.Tree()[leafIndex],
+					"Leaf hash should match",
+				)
+			}
+
+			// Check that all internal nodes up to the root are not nil.
+			for i := 1; i < leafCount; i++ {
+				assert.NotNil(
+					t,
+					tree.Tree()[i],
+					"Internal node should not be nil in a balanced tree",
+				)
+			}
+		})
+	}
+}
+
+func TestUnbalancedTrees(t *testing.T) {
+	testCases := []struct {
+		name        string
+		numElements int
+	}{
+		{"SingleElement", 1},
+		{"ThreeElements", 3},
+		{"FiveElements", 5},
+		{"SevenElements", 7},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			elements := make([][]byte, tc.numElements)
+			for i := 0; i < tc.numElements; i++ {
+				elements[i] = []byte(tc.name + "_element" + string(rune('A'+i)))
+			}
+
+			tree, err := merkle.NewMerkleTree(elements)
+			require.NoError(t, err)
+
+			leafCount, err := merkle.CalculateBalancedLeafCount(tc.numElements)
+			require.NoError(t, err)
+			for i := 0; i < tc.numElements; i++ {
+				leafIdx := leafCount + i
+				assert.Equal(t, merkle.HashLeaf(elements[i]), tree.Tree()[leafIdx],
+					"Leaf %d should be at tree[%d]", i, leafIdx)
+			}
+
+			verifyUnbalancedTreeStructure(t, tree.Tree(), leafCount, tc.numElements)
+		})
+	}
+}
+
+func TestLargeTrees(t *testing.T) {
+	testCases := []struct {
+		name        string
+		numElements int
+	}{
+		{"TreeSize100", 100},
+		{"TreeSize1023", 1023},
+		{"TreeSize2048", 2048},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			elements := make([][]byte, tc.numElements)
+			for i := 0; i < tc.numElements; i++ {
+				elements[i] = []byte{
+					byte(i & 0xFF),
+					byte((i >> 8) & 0xFF),
+					byte((i >> 16) & 0xFF),
+					byte((i >> 24) & 0xFF),
+				}
+			}
+
+			tree, err := merkle.NewMerkleTree(elements)
+			require.NoError(t, err)
+
+			// Verify basic properties.
+			assert.Equal(
+				t,
+				tc.numElements,
+				tree.LeafCount(),
+				"Leaf count should match element count",
+			)
+			assert.NotNil(t, tree.Root(), "Root should not be nil")
+
+			// Verify tree structure size.
+			leafCount, err := merkle.CalculateBalancedLeafCount(tc.numElements)
+			require.NoError(t, err)
+			expectedArraySize := leafCount * 2
+			assert.Equal(
+				t,
+				expectedArraySize,
+				len(tree.Tree()),
+				"Tree array size should be 2*leafCount",
+			)
+
+			// Sample testing.
+			for i := 0; i < 5; i++ {
+				idx := i * (tc.numElements / 5)
+				if idx >= tc.numElements {
+					idx = tc.numElements - 1
+				}
+				leafIndex := leafCount + idx
+				assert.NotNil(t, tree.Tree()[leafIndex], "Sampled leaf should not be nil")
+				assert.Equal(
+					t,
+					merkle.HashLeaf(elements[idx]),
+					tree.Tree()[leafIndex],
+					"Sampled leaf hash should match",
+				)
+			}
+		})
+	}
+}
+
+func TestTreeWithDuplicateElements(t *testing.T) {
+	elements := [][]byte{
+		[]byte("same"),
+		[]byte("same"),
+		[]byte("same"),
+		[]byte("different"),
+	}
+
+	tree, err := merkle.NewMerkleTree(elements)
+	require.NoError(t, err)
+
+	leafCount, err := merkle.CalculateBalancedLeafCount(len(elements))
+	require.NoError(t, err)
+	leafHash1 := tree.Tree()[leafCount]
+	leafHash2 := tree.Tree()[leafCount+1]
+	leafHash3 := tree.Tree()[leafCount+2]
+	leafHash4 := tree.Tree()[leafCount+3]
+
+	assert.Equal(t, leafHash1, leafHash2, "Identical elements should have identical leaf hashes")
+	assert.Equal(t, leafHash2, leafHash3, "Identical elements should have identical leaf hashes")
+	assert.NotEqual(t, leafHash3, leafHash4, "Different elements should have different leaf hashes")
+
+	assert.NotNil(t, tree.Root(), "Tree with duplicate elements should have a valid root")
+}
+
+func TestTreeWithLargeElements(t *testing.T) {
+	bigElement := make([]byte, 1024*1024)
+	for i := range bigElement {
+		bigElement[i] = byte(i & 0xFF)
+	}
+
+	elements := [][]byte{
+		bigElement,
+		bigElement[:len(bigElement)/2],
+	}
+
+	tree, err := merkle.NewMerkleTree(elements)
+	require.NoError(t, err)
+	assert.NotNil(
+		t,
+		tree.Root(),
+		"Root should be calculated correctly even with large elements",
+	)
+}
+
+func TestTreeWithEmptyElements(t *testing.T) {
+	elements := [][]byte{
+		{},
+		{},
+		[]byte("non-empty"),
+	}
+
+	tree, err := merkle.NewMerkleTree(elements)
+	require.NoError(t, err)
+	assert.NotNil(t, tree.Root(), "Root should be calculated correctly with empty elements")
+
+	leafCount, err := merkle.CalculateBalancedLeafCount(len(elements))
+	require.NoError(t, err)
+	for i := 0; i < 2; i++ {
+		leafIndex := leafCount + i
+		assert.Equal(
+			t,
+			merkle.HashLeaf([]byte{}),
+			tree.Tree()[leafIndex],
+			"Empty element should be properly hashed",
+		)
+	}
+}
+
+func TestTreeInternals(t *testing.T) {
+	// Test with a 3-element tree (unbalanced)
+	// Check everything "manually".
+	//
+	// Tree structure:
+	//        [1]
+	//       /   \
+	//     [2]    [3]
+	//    /  \    /
+	//  [4]  [5] [6]
+	//  A    B    C
+
+	elements := [][]byte{
+		[]byte("A"),
+		[]byte("B"),
+		[]byte("C"),
+	}
+
+	tree, err := merkle.NewMerkleTree(elements)
+	require.NoError(t, err)
+
+	internalTree := tree.Tree()
+
+	// For a 3-element tree, the balanced leaf count is 4
+	// So the tree array should have size 8 (2*4)
+	assert.Equal(t, 8, len(internalTree), "Tree array should have size 2*leafCount")
+	assert.Equal(t, tree.Root(), internalTree[1], "Root should be at index 1")
+
+	// Check that all nodes are present.
+	assert.Nil(t, internalTree[0], "Node 0 should be nil")
+	assert.NotNil(t, internalTree[1], "Root should not be nil")
+	assert.NotNil(t, internalTree[2], "Node 1 should not be nil")
+	assert.NotNil(t, internalTree[3], "Node 2 should not be nil")
+	assert.NotNil(t, internalTree[4], "Node 3 should not be nil")
+	assert.NotNil(t, internalTree[5], "Node 5 should not be nil")
+	assert.NotNil(t, internalTree[6], "Node 6 should not be nil")
+	assert.Nil(t, internalTree[7], "Node 7 should be nil")
+
+	// Check that all leaves are present.
+	leafStartIdx := 4
+	assert.Equal(t, merkle.HashLeaf(elements[0]), internalTree[leafStartIdx], "Leaf 0 should match")
+	assert.Equal(
+		t,
+		merkle.HashLeaf(elements[1]),
+		internalTree[leafStartIdx+1],
+		"Leaf 1 should match",
+	)
+	assert.Equal(
+		t,
+		merkle.HashLeaf(elements[2]),
+		internalTree[leafStartIdx+2],
+		"Leaf 2 should match",
+	)
+	assert.Nil(t, internalTree[leafStartIdx+3], "Leaf 3 should be nil (not in original elements)")
+
+	verifyUnbalancedTreeStructure(t, internalTree, 4, len(elements))
+}
+
+// Helper function to verify the structure of an unbalanced tree
+func verifyUnbalancedTreeStructure(t *testing.T, tree [][]byte, leafCount, actualElements int) {
+	t.Helper()
+
+	// Handle single element trees.
+	if actualElements == 1 {
+		assert.Nil(t, tree[0], "Merkle Tree 1-index, index 0 should be nil")
+		assert.Equal(t, tree[leafCount], tree[1], "For single element tree, root should equal leaf")
+		return
+	}
+
+	// Starting from the leaf parents, check nodes up to the root.
+	for i := leafCount - 1; i > 0; i-- {
+		leftIdx := merkle.GetLeftChild(i)
+		rightIdx := merkle.GetRightChild(i)
+
+		if leftIdx >= len(tree) {
+			continue
+		}
+
+		// If both children exist
+		if leftIdx < len(tree) && rightIdx < len(tree) &&
+			tree[leftIdx] != nil && tree[rightIdx] != nil {
+			assert.NotNil(t, tree[i], "Parent node should not be nil when both children exist")
+			assert.Equal(
+				t,
+				merkle.HashNode(tree[leftIdx], tree[rightIdx]),
+				tree[i],
+				"Node at index %d should be equal to its children at %d and %d",
+				i,
+				leftIdx,
+				rightIdx,
+			)
+		} else if leftIdx < len(tree) && tree[leftIdx] != nil {
+			assert.Equal(t, tree[leftIdx], tree[i],
+				"Node at index %d should be equal to its only child at %d", i, leftIdx)
+		}
+	}
+
+	// Check the root is valid.
+	expectedRoot := tree[1]
+	assert.NotNil(t, expectedRoot, "Root should not be nil")
+	if tree[1] != nil && tree[2] != nil {
+		assert.NotNil(
+			t,
+			merkle.HashNode(tree[1], tree[2]),
+			"Root should be calculated when both children exist",
+		)
+	}
+}
+
+func TestRoundUpToPowerOf2Values(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    int
+		expected int
+	}{
+		{"zero", 0, 0},
+		{"one", 1, 1},
+		{"already power of 2", 4, 4},
+		{"already power of 2 (large)", 16384, 16384},
+		{"regular case", 5, 8},
+		{"regular case (large)", 5000, 8192},
+		{"large number", 1<<30 - 1, 1 << 30},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, err := merkle.CalculateBalancedLeafCount(tt.input)
+			require.NoError(t, err)
+			if result != tt.expected {
+				t.Errorf(
+					"Power of 2 rounding for %d = %d, expected %d",
+					tt.input,
+					result,
+					tt.expected,
+				)
+			}
+		})
+	}
+}
+
+func TestCalculateBalancedLeafCount(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    int
+		expected int
+		wantErr  bool
+	}{
+		{"negative", -1, 0, false},
+		{"zero", 0, 0, false},
+		{"one", 1, 1, false},
+		{"power of 2", 16, 16, false},
+		{"not power of 2", 15, 16, false},
+		{"large number", 1000000, 1048576, false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, err := merkle.CalculateBalancedLeafCount(tt.input)
+			if tt.wantErr {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+				if result != tt.expected {
+					t.Errorf("CalculateBalancedLeafCount(%d) = %d, expected %d", tt.input, result, tt.expected)
+				}
+			}
+		})
+	}
+}
+
+// TestCalculateBalancedLeafCountError tests that the function returns an error with large inputs
+func TestCalculateBalancedLeafCountError(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode - requires large values")
+	}
path: pkg/merkle/tree_test.go
user: login: coderabbitai[bot]
body: _💡 Verification agent_

<details>
<summary>❓ Verification inconclusive</summary>

**Consider adding a stress test as requested in PR comments.**

There was a specific request in the PR comments for a comprehensive stress test. Consider adding a `TestStressMerkleTree` function that generates random trees, adds nodes, and requests proofs for a configurable duration.

---

🏁 Script executed:

```shell
#!/bin/bash
# Check if any stress tests were added to the package
rg "func TestStress" pkg/merkle/
```

Length of output: 34

---



</details>

**Action Required: Add the requested stress test**

The current test file (pkg/merkle/tree_test.go) does not include any function to perform a comprehensive stress test for the Merkle tree, as requested in the PR comments. Please add a new test function—such as `TestStressMerkleTree`—that generates random trees, adds nodes, and requests proofs over a configurable duration. Ensure that this test properly checks for scalability and correctness, while still respecting the short-test mode (i.e. skipping when `testing.Short()` is enabled).

- **Location:** pkg/merkle/tree_test.go (around lines 423–425)
- **Action:** Create a dedicated stress test function to simulate heavy workloads and validate edge cases.

<!-- This is an auto-generated comment by CodeRabbit -->
created_at: 2025-04-16T11:35:27Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,348 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrEmptyTree          = errors.New("empty tree")
+	ErrDuplicateIndices   = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds = errors.New("indices out of bounds")
+	ErrInvalidRange       = errors.New("invalid range")
+	ErrInvalidLeafCount   = errors.New("invalid leaf count")
+	ErrElementMismatch    = errors.New("element and indices mismatch")
+	ErrNilProof           = errors.New("nil proof")
+	ErrNilRoot            = errors.New("nil root")
+	ErrNilElement         = errors.New("nil element")
+	ErrNoElements         = errors.New("no elements")
+	ErrNoIndices          = errors.New("no indices")
+	ErrNoProofs           = errors.New("no proofs provided")
+)
+
+type MultiProof struct {
+	values    IndexedValues
+	proofs    []Proof
+	leafCount int
+}
+
+type Proof []byte
+
+type IndexedValues []IndexedValue
+
+type IndexedValue struct {
+	value []byte
+	index int
+}
+
+func (iv IndexedValues) Indices() []int {
+	indices := make([]int, len(iv))
+	for i, v := range iv {
+		indices[i] = v.index
+	}
+	return indices
+}
+
+func (iv IndexedValues) ToLeaves() []Leaf {
+	leaves := make([]Leaf, len(iv))
+	for i, v := range iv {
+		leaves[i] = Leaf(v.value)
+	}
+	return leaves
+}
+
+// Verify verifies a MultiProof against the given tree root.
+func Verify(root []byte, proof *MultiProof) (bool, error) {
+	if len(root) == 0 {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
+	}
+
+	if err := proof.validate(); err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	// Handle single-element trees.
+	if proof.leafCount == 1 {
+		return bytes.Equal(root, HashLeaf(proof.values[0].value)), nil
+	}
+
+	// If all the elements are provided, we can directly reconstruct the tree.
+	if len(proof.values) == proof.leafCount {
+		leaves := proof.values.ToLeaves()
+
+		tree, err := NewMerkleTree(leaves)
+		if err != nil {
+			return false, fmt.Errorf(ErrVerifyProof, err)
+		}
+
+		return bytes.Equal(tree.Root(), root), nil
+	}
+
+	computedRoot, err := proof.computeRoot()
+	if err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	return bytes.Equal(computedRoot, root), nil
+}
+
+// validate performs common validation for Merkle proofs.
+func (p *MultiProof) validate() error {
+	if len(p.values) == 0 {
+		return ErrNoElements
+	}
+
+	if p.leafCount <= 0 {
+		return ErrInvalidLeafCount
+	}
+
+	if err := validateIndices(p.values.Indices(), p.leafCount); err != nil {
+		return err
+	}
+
+	for _, elem := range p.values {
+		if elem.value == nil {
+			return ErrNilElement
+		}
+	}
+
+	for _, proof := range p.proofs {
+		if proof == nil {
+			return ErrNilProof
+		}
+	}
+
+	isPartialProof := len(p.values) < p.leafCount
+	isNonTrivialTree := p.leafCount > 1
+	needsProofs := isPartialProof && isNonTrivialTree
+
+	if needsProofs && len(p.proofs) == 0 {
+		return ErrNoProofs
+	}
+
+	return nil
+}
+
+// getNextProof safely retrieves the next proof and increments the index.
+func (p *MultiProof) getNextProof(index *int) ([]byte, error) {
+	if *index >= len(p.proofs) {
+		return nil, ErrNilProof
+	}
+	proof := p.proofs[*index]
+	*index++
+	return proof, nil
+}
+
+// NodeQueue represents a node in the computation queue with its tree index and hash value.
+// It's used during proof verification to track nodes as they are processed.
+type NodeQueue struct {
+	index int
+	hash  []byte
+}
+
+// buildNodeQueue builds the node queue for the proof computation.
+func (p *MultiProof) buildNodeQueue(balancedLeafCount int) ([]NodeQueue, error) {
+	leaves := p.values.ToLeaves()
+
+	nodes, err := makeNodes(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	indices := p.values.Indices()
+	n := len(indices)
+
+	queue := make([]NodeQueue, n)
+	for i, idx := range indices {
+		insertPos := n - 1 - i
+		queue[insertPos] = NodeQueue{
+			index: balancedLeafCount + idx,
+			hash:  nodes[i].Hash(),
+		}
+	}
+
+	return queue, nil
+}
+
+// computeRoot computes the root of the Merkle tree from the given proof.
+func (p *MultiProof) computeRoot() ([]byte, error) {
+	// 1. Prepare the queue.
+	blc, err := CalculateBalancedLeafCount(p.leafCount)
+	if err != nil {
+		return nil, err
+	}
+
+	nodeQueue, err := p.buildNodeQueue(blc)
+	if err != nil {
+		return nil, err
+	}
+
+	var (
+		head, proofIdx = 0, 0
+		upperBound     = blc + p.leafCount - 1
+		lowerBound     = nodeQueue[len(nodeQueue)-1].index
+		left, right    []byte
+	)
+
+	// 2. Process queue until we hit the root.
+	for head < len(nodeQueue) {
+		current := nodeQueue[head]
+		head++
+
+		if current.index == 1 {
+			return current.hash, nil
+		}
+
+		// Detect level-up.
+		if current.index == lowerBound ||
+			(head < len(nodeQueue) && nodeQueue[head].index == lowerBound) {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		// Detect solo-left at tree edge.
+		if isLeftNodeAtUpperBound(current.index, upperBound) {
+			nodeQueue = append(nodeQueue, NodeQueue{
+				index: current.index >> 1,
+				hash:  current.hash,
+			})
+			continue
+		}
+
+		if isLeftChild(current.index) {
+			// Handle left-child branch.
+			left = current.hash
+			if head < len(nodeQueue) && nodeQueue[head].index == current.index+1 {
+				right = nodeQueue[head].hash
+				head++
+			} else {
+				right, err = p.getNextProof(&proofIdx)
+				if err != nil {
+					return nil, err
+				}
+			}
+		} else {
+			// Handle right-child branch.
+			right = current.hash
+			if head < len(nodeQueue) && nodeQueue[head].index == current.index-1 {
+				left = nodeQueue[head].hash
+				head++
+			} else {
+				left, err = p.getNextProof(&proofIdx)
+				if err != nil {
+					return nil, err
+				}
+			}
+		}
+
+		parentHash := HashNode(left, right)
+
+		nodeQueue = append(nodeQueue, NodeQueue{
+			index: current.index >> 1,
+			hash:  parentHash,
+		})
+	}
+
+	return nil, ErrNilRoot
+}
+
+// makeIndexedValues creates indexed values from elements and their indices.
+func makeIndexedValues(leaves []Leaf, indices []int) IndexedValues {
+	result := make(IndexedValues, len(indices))
+	for i, idx := range indices {
+		result[i] = IndexedValue{
+			value: leaves[idx],
+			index: idx,
+		}
+	}
+	return result
+}
+
+// makeIndices returns a slice of ascending ordered indices for the given starting index and count.
+func makeIndices(startingIndex, count int) ([]int, error) {
+	if startingIndex < 0 || count <= 0 {
+		return nil, ErrInvalidRange
+	}
+
+	indices := make([]int, count)
+	for i := 0; i < count; i++ {
+		indices[i] = startingIndex + i
+	}
+
+	return indices, nil
+}
+
+// validateIndices validates the indices slice of a proof.
+func validateIndices(indices []int, leafCount int) error {
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	if len(sortedIndices) == 0 {
+		return ErrNoIndices
+	}
+
+	if hasDuplicates(sortedIndices) {
+		return ErrDuplicateIndices
+	}
+
+	if hasOutOfBounds(sortedIndices, leafCount) {
+		return ErrIndicesOutOfBounds
+	}
+
+	return nil
+}
+
+func cloneBuffer(buffer []byte) []byte {
+	if buffer == nil {
+		return nil
+	}
+	clone := make([]byte, len(buffer))
+	copy(clone, buffer)
+	return clone
+}
+
+// hasDuplicates checks if the sorted indices slice contains duplicates.
+func hasDuplicates(indices []int) bool {
+	for i := 1; i < len(indices); i++ {
+		if indices[i] == indices[i-1] {
+			return true
+		}
+	}
+	return false
+}
+
+// hasOutOfBounds checks if all indices are within the valid range [0, leafCount).
+func hasOutOfBounds(indices []int, leafCount int) bool {
+	for _, idx := range indices {
+		if idx < 0 || idx >= leafCount {
+			return true
+		}
+	}
+	return false
+}
+
+// isLeftChild returns true if the given index is odd (right child).
+func isLeftChild(index int) bool {
path: pkg/merkle/proof.go
user: login: macroscopeapp[bot]
body: The comment for the `isLeftChild` function seems to be incorrect: it currently claims that the function returns true for odd indices (right child), but the implementation returns true for even indices (left child). This change aligns the comment with the behavior of the function. Consider documenting the rationale behind the naming and behavior if this is an intentional design decision.

```diff
-// isLeftChild returns true if the given index is odd (right child).
+// isLeftChild returns true if the given index is even (left child).
```
> 🚀 Reply to ask Macroscope to explain or update this suggestion.

> 👍 Helpful? React to give us feedback.
created_at: 2025-04-16T19:44:49Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,310 @@
+package merkle
+
+import (
+	"errors"
+	"fmt"
+	"math/bits"
+	"sort"
+)
+
+type Node struct {
+	hash []byte
+}
+
+func (n *Node) Hash() []byte {
+	return n.hash
+}
+
+func (n *Node) IsNil() bool {
+	return n.hash == nil
+}
+
+type Leaf []byte
+
+type MerkleTree struct {
+	tree   []Node
+	leaves []Leaf
+}
+
+var (
+	ErrTreeEmpty          = errors.New("tree is empty")
+	ErrTreeRootNil        = errors.New("tree root is nil")
+	ErrTreeLeavesOverflow = errors.New("amount of leaves overflows uint32")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(leaves []Leaf) (*MerkleTree, error) {
+	if len(leaves) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	leavesDeepCopy := make([]Leaf, len(leaves))
+	copy(leavesDeepCopy, leaves)
+
+	nodes, err := makeNodes(leavesDeepCopy)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(nodes)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{
+		tree:   tree,
+		leaves: leavesDeepCopy,
+	}, nil
+}
+
+// GenerateMultiProofSequential generates a sequential multi-proof starting from the given index.
+func (m *MerkleTree) GenerateMultiProofSequential(startingIndex, count int) (*MultiProof, error) {
+	indices, err := makeIndices(startingIndex, count)
+	if err != nil {
+		return nil, err
+	}
+
+	proof, err := m.makeProof(indices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// GenerateMultiProofWithIndices generates a multi-proof for the given indices.
+func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	proof, err := m.makeProof(sortedIndices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// makeProof returns a MultiProof for the given indices.
+func (m *MerkleTree) makeProof(indices []int) (MultiProof, error) {
+	if len(m.tree) == 0 {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, ErrEmptyTree)
+	}
+
+	if len(m.Root()) == 0 {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, ErrNilRoot)
+	}
+
+	if err := validateIndices(indices, m.LeafCount()); err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	indexedValues := makeIndexedValues(m.leaves, indices)
+	if len(indexedValues) != len(indices) {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, ErrElementMismatch)
+	}
+
+	// Handle single-element trees.
+	if m.LeafCount() == 1 {
+		return MultiProof{
+			values:    indexedValues,
+			proofs:    []Proof{m.Root()},
+			leafCount: m.LeafCount(),
+		}, nil
+	}
+
+	var (
+		startLeafIdx = len(m.tree) >> 1
+		proofs       []Proof
+		known        = make([]bool, len(m.tree))
+	)
+
+	// Mark provided indices as known.
+	for _, idx := range indices {
+		known[startLeafIdx+idx] = true
+	}
+
+	// Calculate proofs to prove the existence of the indices.
+	for i := startLeafIdx - 1; i > 0; i-- {
+		leftChildIdx := GetLeftChild(i)
+		rightChildIdx := GetRightChild(i)
+
+		left := known[leftChildIdx]
+		right := known[rightChildIdx]
+
+		// Only one of children would be known, so we need the sibling as a proof
+		if left != right {
+			if right {
+				// Only add non-nil sibling nodes
+				if !m.tree[leftChildIdx].IsNil() {
+					proofs = append(proofs, cloneBuffer(m.tree[leftChildIdx].Hash()))
+				}
+			} else {
+				// Only add non-nil sibling nodes
+				if !m.tree[rightChildIdx].IsNil() {
+					proofs = append(proofs, cloneBuffer(m.tree[rightChildIdx].Hash()))
+				}
+			}
+		}
+
+		// If at least one of the children is known, the parent is known
+		known[i] = left || right
+	}
+
+	return MultiProof{
+		values:    indexedValues,
+		proofs:    proofs,
+		leafCount: len(m.leaves),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() []Node {
+	return m.tree
+}
+
+// Leaves returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Leaves() []Leaf {
+	return m.leaves
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.tree[1].Hash()
path: pkg/merkle/tree.go
user: login: macroscopeapp[bot]
body: The `Root()` method currently accesses `m.tree[1]` without checking if the slice contains more than one element. This can potentially lead to an index-out-of-range error when the tree has exactly one element. Consider adding a condition to check for a single-element tree and return `m.tree[0].Hash()` in that case. If this behavior is deliberate, you might document the design rationale to clarify the expected input and usage.

```diff
if len(m.tree) == 1 {
	return m.tree[0].Hash()
}
return m.tree[1].Hash()
```
> 🚀 Reply to ask Macroscope to explain or update this suggestion.

> 👍 Helpful? React to give us feedback.
created_at: 2025-04-16T19:44:50Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,339 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrDuplicateIndices   = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds = errors.New("indices out of bounds")
+	ErrInvalidRange       = errors.New("invalid range")
+	ErrInvalidLeafCount   = errors.New("invalid leaf count")
+	ErrNilProof           = errors.New("nil proof")
+	ErrNilRoot            = errors.New("nil root")
+	ErrNilElement         = errors.New("nil element")
+	ErrNoElements         = errors.New("no elements")
+	ErrNoIndices          = errors.New("no indices")
+	ErrNoProofs           = errors.New("no proofs provided")
+)
+
+type MultiProof struct {
+	values    IndexedValues
+	proofs    []Node
+	leafCount int
+}
+
+func (p *MultiProof) GetLeafCount() int {
+	return p.leafCount
+}
+
+func (p *MultiProof) GetProofs() []Node {
+	return p.proofs
+}
+
+func (p *MultiProof) GetValues() IndexedValues {
+	return p.values
+}
+
+type IndexedValues []IndexedValue
+
+type IndexedValue struct {
+	value []byte
+	index int
+}
+
+func (iv IndexedValue) GetValue() []byte {
+	return iv.value
+}
+
+func (iv IndexedValue) GetIndex() int {
+	return iv.index
+}
+
+func (iv IndexedValues) Indices() []int {
+	indices := make([]int, len(iv))
+	for i, v := range iv {
+		indices[i] = v.index
+	}
+	return indices
+}
+
+func (iv IndexedValues) ToLeaves() []Leaf {
+	leaves := make([]Leaf, len(iv))
+	for i, v := range iv {
+		leaves[i] = Leaf(v.value)
+	}
+	return leaves
+}
+
+// Verify verifies a MultiProof against the given tree root.
+func Verify(root []byte, proof *MultiProof) (bool, error) {
+	if len(root) == 0 {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
+	}
+
+	if err := proof.validate(); err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	// Handle single-element trees.
+	if proof.leafCount == 1 {
+		return bytes.Equal(root, HashLeaf(proof.values[0].value)), nil
+	}
+
+	// If all the elements are provided, we can directly reconstruct the tree.
+	if len(proof.values) == proof.leafCount {
+		leaves := proof.values.ToLeaves()
+
+		tree, err := NewMerkleTree(leaves)
+		if err != nil {
+			return false, fmt.Errorf(ErrVerifyProof, err)
+		}
+
+		return bytes.Equal(tree.Root(), root), nil
+	}
+
+	computedRoot, err := proof.computeRoot()
+	if err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	return bytes.Equal(computedRoot, root), nil
+}
+
+// validate performs common validation for Merkle proofs.
+func (p *MultiProof) validate() error {
+	if len(p.values) == 0 {
+		return ErrNoElements
+	}
+
+	if p.leafCount <= 0 {
+		return ErrInvalidLeafCount
+	}
+
+	if err := validateIndices(p.values.Indices(), p.leafCount); err != nil {
+		return err
+	}
+
+	for _, elem := range p.values {
+		if elem.value == nil {
+			return ErrNilElement
+		}
+	}
+
+	for _, proof := range p.proofs {
+		if proof.hash == nil {
+			return ErrNilProof
+		}
+	}
+
+	isPartialProof := len(p.values) < p.leafCount
+	isNonTrivialTree := p.leafCount > 1
+	needsProofs := isPartialProof && isNonTrivialTree
+
+	if needsProofs && len(p.proofs) == 0 {
+		return ErrNoProofs
+	}
+
+	return nil
+}
+
+// getNextProof safely retrieves the next proof and increments the index.
+func (p *MultiProof) getNextProof(index *int) ([]byte, error) {
+	if *index >= len(p.proofs) {
+		return nil, ErrNoProofs
+	}
+	proof := p.proofs[*index]
+	*index++
+	return proof.Hash(), nil
+}
+
+// nodeQueue represents a node in the computation queue with its tree index and hash value.
+// It's used during proof verification to track nodes as they are processed.
+type nodeQueue struct {
+	index int
+	hash  []byte
+}
+
+// buildNodeQueue builds the node queue for the proof computation.
+func (p *MultiProof) buildNodeQueue(balancedLeafCount int) ([]nodeQueue, error) {
+	leaves := p.values.ToLeaves()
+
+	nodes, err := makeNodes(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	indices := p.values.Indices()
+	n := len(indices)
+
+	queue := make([]nodeQueue, n)
+	for i, idx := range indices {
+		insertPos := n - 1 - i
+		queue[insertPos] = nodeQueue{
+			index: balancedLeafCount + idx,
+			hash:  nodes[i].Hash(),
+		}
+	}
+
+	return queue, nil
+}
+
+// computeRoot computes the root of the Merkle tree from the given proof.
+func (p *MultiProof) computeRoot() ([]byte, error) {
+	// 1. Prepare the queue.
+	blc, err := CalculateBalancedNodesCount(p.leafCount)
+	if err != nil {
+		return nil, err
+	}
+
+	queue, err := p.buildNodeQueue(blc)
+	if err != nil {
+		return nil, err
+	}
+
+	var (
+		head, proofIdx = 0, 0
+		upperBound     = blc + p.leafCount - 1
+		lowerBound     = queue[len(queue)-1].index
+		left, right    []byte
+	)
+
+	// 2. Process queue until we hit the root.
+	for head < len(queue) {
+		current := queue[head]
+		head++
+
+		// Exit condition - return the root.
+		if current.index == 1 {
+			return current.hash, nil
+		}
+
+		// Detect level-up.
+		if current.index == lowerBound ||
+			(head < len(queue) && queue[head].index == lowerBound) {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		if isLeftChild(current.index) {
+			// Handle left-child branch.
+			left = current.hash
+			if head < len(queue) && queue[head].index == current.index+1 {
+				right = queue[head].hash
+				head++
+			} else {
+				right, err = p.getNextProof(&proofIdx)
+				if err != nil {
+					return nil, err
+				}
+			}
+		} else {
+			// Handle right-child branch.
+			right = current.hash
+			if head < len(queue) && queue[head].index == current.index-1 {
+				left = queue[head].hash
+				head++
+			} else {
+				left, err = p.getNextProof(&proofIdx)
+				if err != nil {
+					return nil, err
+				}
+			}
+		}
+
+		queue = append(queue, nodeQueue{
+			index: current.index >> 1,
+			hash:  HashNode(left, right),
+		})
+	}
+
+	return nil, ErrNilRoot
+}
+
+// makeIndexedValues creates indexed values from elements and their indices.
+func makeIndexedValues(leaves []Leaf, indices []int) (IndexedValues, error) {
+	result := make(IndexedValues, len(indices))
+
+	for i, idx := range indices {
+		result[i] = IndexedValue{
+			value: leaves[idx],
+			index: idx,
+		}
+	}
+
+	return result, nil
+}
+
+// makeIndices returns a slice of ascending ordered indices for the given starting index and count.
+func makeIndices(startingIndex, count int) ([]int, error) {
+	if startingIndex < 0 || count <= 0 {
+		return nil, ErrInvalidRange
+	}
+
+	indices := make([]int, count)
+	for i := 0; i < count; i++ {
+		indices[i] = startingIndex + i
+	}
+
+	return indices, nil
+}
+
+// validateIndices validates the indices slice of a proof.
+func validateIndices(indices []int, leafCount int) error {
+	balancedLeafCount, err := CalculateBalancedNodesCount(leafCount)
+	if err != nil {
+		return err
+	}
+
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	if len(sortedIndices) == 0 {
+		return ErrNoIndices
+	}
+
+	if hasDuplicates(sortedIndices) {
+		return ErrDuplicateIndices
+	}
+
+	if hasOutOfBounds(sortedIndices, balancedLeafCount) {
+		return ErrIndicesOutOfBounds
+	}
path: pkg/merkle/proof.go
user: login: coderabbitai[bot]
body: _⚠️ Potential issue_

**`validateIndices` should bound‑check against *actual* leaves, not padded leaves**  

`hasOutOfBounds` currently compares indices with `balancedLeafCount`, which may be larger than the real leaf count when padding is added (e.g., 3 real leaves → 4 padded).  
This lets callers request proofs for non‑existent (empty) leaves without error.

```diff
-	balancedLeafCount, err := CalculateBalancedNodesCount(leafCount)
-	if err != nil {
-		return err
-	}
...
-	if hasOutOfBounds(sortedIndices, balancedLeafCount) {
+	if hasOutOfBounds(sortedIndices, leafCount) {
 		return ErrIndicesOutOfBounds
 	}
```

Using the true `leafCount` keeps the API intuitive and prevents accidental acceptance of invalid proofs.



<!-- suggestion_start -->

<details>
<summary>📝 Committable suggestion</summary>

> ‼️ **IMPORTANT**
> Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

`````suggestion
func validateIndices(indices []int, leafCount int) error {
    sortedIndices := make([]int, len(indices))
    copy(sortedIndices, indices)
    sort.Ints(sortedIndices)

    if len(sortedIndices) == 0 {
        return ErrNoIndices
    }

    if hasDuplicates(sortedIndices) {
        return ErrDuplicateIndices
    }

    if hasOutOfBounds(sortedIndices, leafCount) {
        return ErrIndicesOutOfBounds
    }

    // ... the rest of the function unchanged ...
}
`````

</details>

<!-- suggestion_end -->

<!-- This is an auto-generated reply by CodeRabbit -->
created_at: 2025-04-17T11:31:51Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,316 @@
+package merkle
+
+import (
+	"errors"
+	"fmt"
+	"math/bits"
+	"sort"
+)
+
+type Node struct {
+	hash []byte
+}
+
+func (n *Node) Hash() []byte {
+	return n.hash
+}
+
+type Leaf []byte
+
+// MerkleTree is a binary Merkle tree.
+//
+// tree has the collection of nodes, where:
+// - The tree is 1-indexed, so root is at index 1.
+// - The internal nodes are at index 2 to N.
+// - The hashed are at index N+1 to 2N-1.
+//
+// leaves contains the raw elements of the tree.
+type MerkleTree struct {
+	tree   []Node
+	leaves []Leaf
+}
+
+var (
+	ErrNoLeaves           = errors.New("no leaves provided")
+	ErrTreeEmpty          = errors.New("tree is empty")
+	ErrTreeRootNil        = errors.New("tree root is nil")
+	ErrTreeLeavesOverflow = errors.New("amount of leaves overflows uint32")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(leaves []Leaf) (*MerkleTree, error) {
+	if len(leaves) == 0 {
+		return nil, ErrNoLeaves
+	}
+
+	leavesDeepCopy := make([]Leaf, len(leaves))
+	copy(leavesDeepCopy, leaves)
+
+	balancedLeaves, err := makeLeaves(leavesDeepCopy)
+	if err != nil {
+		return nil, err
+	}
+
+	nodes, err := makeNodes(balancedLeaves)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(nodes)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{tree, balancedLeaves}, nil
+}
+
+// GenerateMultiProofSequential generates a sequential multi-proof starting from the given index.
+func (m *MerkleTree) GenerateMultiProofSequential(startingIndex, count int) (*MultiProof, error) {
+	indices, err := makeIndices(startingIndex, count)
+	if err != nil {
+		return nil, err
+	}
+
+	proof, err := m.makeProof(indices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// GenerateMultiProofWithIndices generates a multi-proof for the given indices.
+func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	proof, err := m.makeProof(sortedIndices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// makeProof returns a MultiProof for the given indices.
+func (m *MerkleTree) makeProof(indices []int) (MultiProof, error) {
+	err := validateIndices(indices, m.LeafCount())
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	indexedValues, err := makeIndexedValues(m.leaves, indices)
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	// Handle single-element trees.
+	if m.LeafCount() == 1 {
+		return MultiProof{
+			values:    indexedValues,
+			proofs:    []Node{{hash: m.Root()}},
+			leafCount: m.LeafCount(),
+		}, nil
+	}
+
+	var (
+		startLeafIdx = len(m.tree) >> 1
+		proofs       []Node
+		known        = make([]bool, len(m.tree))
+	)
+
+	// Mark provided indices as known.
+	for _, idx := range indices {
+		known[startLeafIdx+idx] = true
+	}
+
+	// Calculate proofs to prove the existence of the indices.
+	for i := startLeafIdx - 1; i > 0; i-- {
+		leftChildIdx := GetLeftChild(i)
+		rightChildIdx := GetRightChild(i)
+
+		left := known[leftChildIdx]
+		right := known[rightChildIdx]
+
+		// Only one of children is known, so we need the sibling as a proof.
+		if left != right {
+			if right {
+				proofs = append(proofs, m.tree[leftChildIdx])
+			} else {
+				proofs = append(proofs, m.tree[rightChildIdx])
+			}
+		}
+
+		// If at least one of the children is known, the parent is known.
+		known[i] = left || right
+	}
+
+	return MultiProof{
+		values:    indexedValues,
+		proofs:    proofs,
+		leafCount: len(m.leaves),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() []Node {
+	return m.tree
+}
+
+// Leaves returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Leaves() []Leaf {
+	return m.leaves
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.tree[1].Hash()
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return len(m.leaves)
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func makeTree(nodes []Node) ([]Node, error) {
+	if len(nodes) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	balancedLeafCount, err := CalculateBalancedNodesCount(len(nodes))
+	if err != nil {
+		return nil, err
+	}
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([]Node, balancedLeafCount<<1)
+
+	lowerBound := balancedLeafCount
+	upperBound := balancedLeafCount + len(nodes)
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(nodes); i++ {
+		tree[lowerBound+i] = nodes[i]
+	}
+
+	for i := len(nodes); i < balancedLeafCount; i++ {
+		tree[lowerBound+i] = Node{hash: HashEmptyLeaf()}
+	}
+
path: pkg/merkle/tree.go
user: login: macroscopeapp[bot]
body: The initialization of `upperBound` in the `makeTree` function looks like it may result in a logic error: by setting it to `balancedLeafCount + len(nodes)`, some valid internal node computations could be skipped, leaving nodes with uninitialized hash values. If the intended behavior is to process all nodes up to the last valid index in the tree (which is `(balancedLeafCount << 1) - 1`), consider updating the initialization of `upperBound`. If instead this behavior is deliberate, please document the rationale behind using the current value.

```diff
-	upperBound := balancedLeafCount + len(nodes)
+	upperBound := (balancedLeafCount << 1) - 1
```
> 🚀 Reply to ask Macroscope to explain or update this suggestion.

> 👍 Helpful? React to give us feedback.
created_at: 2025-04-17T11:33:14Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,339 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrDuplicateIndices   = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds = errors.New("indices out of bounds")
+	ErrInvalidRange       = errors.New("invalid range")
+	ErrInvalidLeafCount   = errors.New("invalid leaf count")
+	ErrNilProof           = errors.New("nil proof")
+	ErrNilRoot            = errors.New("nil root")
+	ErrNilElement         = errors.New("nil element")
+	ErrNoElements         = errors.New("no elements")
+	ErrNoIndices          = errors.New("no indices")
+	ErrNoProofs           = errors.New("no proofs provided")
+)
+
+type MultiProof struct {
+	values    IndexedValues
+	proofs    []Node
+	leafCount int
+}
+
+func (p *MultiProof) GetLeafCount() int {
+	return p.leafCount
+}
+
+func (p *MultiProof) GetProofs() []Node {
+	return p.proofs
+}
+
+func (p *MultiProof) GetValues() IndexedValues {
+	return p.values
+}
+
+type IndexedValues []IndexedValue
+
+type IndexedValue struct {
+	value []byte
+	index int
+}
+
+func (iv IndexedValue) GetValue() []byte {
+	return iv.value
+}
+
+func (iv IndexedValue) GetIndex() int {
+	return iv.index
+}
+
+func (iv IndexedValues) Indices() []int {
+	indices := make([]int, len(iv))
+	for i, v := range iv {
+		indices[i] = v.index
+	}
+	return indices
+}
+
+func (iv IndexedValues) ToLeaves() []Leaf {
+	leaves := make([]Leaf, len(iv))
+	for i, v := range iv {
+		leaves[i] = Leaf(v.value)
+	}
+	return leaves
+}
+
+// Verify verifies a MultiProof against the given tree root.
+func Verify(root []byte, proof *MultiProof) (bool, error) {
+	if len(root) == 0 {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
+	}
+
+	if err := proof.validate(); err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	// Handle single-element trees.
+	if proof.leafCount == 1 {
+		return bytes.Equal(root, HashLeaf(proof.values[0].value)), nil
+	}
+
+	// If all the elements are provided, we can directly reconstruct the tree.
+	if len(proof.values) == proof.leafCount {
+		leaves := proof.values.ToLeaves()
+
+		tree, err := NewMerkleTree(leaves)
+		if err != nil {
+			return false, fmt.Errorf(ErrVerifyProof, err)
+		}
+
+		return bytes.Equal(tree.Root(), root), nil
+	}
+
+	computedRoot, err := proof.computeRoot()
+	if err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	return bytes.Equal(computedRoot, root), nil
+}
+
+// validate performs common validation for Merkle proofs.
+func (p *MultiProof) validate() error {
+	if len(p.values) == 0 {
+		return ErrNoElements
+	}
+
+	if p.leafCount <= 0 {
+		return ErrInvalidLeafCount
+	}
+
+	if err := validateIndices(p.values.Indices(), p.leafCount); err != nil {
+		return err
+	}
+
+	for _, elem := range p.values {
+		if elem.value == nil {
+			return ErrNilElement
+		}
+	}
+
+	for _, proof := range p.proofs {
+		if proof.hash == nil {
+			return ErrNilProof
+		}
+	}
+
+	isPartialProof := len(p.values) < p.leafCount
+	isNonTrivialTree := p.leafCount > 1
+	needsProofs := isPartialProof && isNonTrivialTree
+
+	if needsProofs && len(p.proofs) == 0 {
+		return ErrNoProofs
+	}
+
+	return nil
+}
+
+// getNextProof safely retrieves the next proof and increments the index.
+func (p *MultiProof) getNextProof(index *int) ([]byte, error) {
+	if *index >= len(p.proofs) {
+		return nil, ErrNoProofs
+	}
+	proof := p.proofs[*index]
+	*index++
+	return proof.Hash(), nil
+}
+
+// nodeQueue represents a node in the computation queue with its tree index and hash value.
+// It's used during proof verification to track nodes as they are processed.
+type nodeQueue struct {
+	index int
+	hash  []byte
+}
+
+// buildNodeQueue builds the node queue for the proof computation.
+func (p *MultiProof) buildNodeQueue(balancedLeafCount int) ([]nodeQueue, error) {
+	leaves := p.values.ToLeaves()
+
+	nodes, err := makeNodes(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	indices := p.values.Indices()
+	n := len(indices)
+
+	queue := make([]nodeQueue, n)
+	for i, idx := range indices {
+		insertPos := n - 1 - i
+		queue[insertPos] = nodeQueue{
+			index: balancedLeafCount + idx,
+			hash:  nodes[i].Hash(),
+		}
+	}
+
+	return queue, nil
+}
+
+// computeRoot computes the root of the Merkle tree from the given proof.
+func (p *MultiProof) computeRoot() ([]byte, error) {
+	// 1. Prepare the queue.
+	blc, err := CalculateBalancedNodesCount(p.leafCount)
+	if err != nil {
+		return nil, err
+	}
+
+	queue, err := p.buildNodeQueue(blc)
+	if err != nil {
+		return nil, err
+	}
+
+	var (
+		head, proofIdx = 0, 0
+		upperBound     = blc + p.leafCount - 1
+		lowerBound     = queue[len(queue)-1].index
+		left, right    []byte
+	)
+
+	// 2. Process queue until we hit the root.
+	for head < len(queue) {
+		current := queue[head]
+		head++
+
+		// Exit condition - return the root.
+		if current.index == 1 {
+			return current.hash, nil
+		}
+
+		// Detect level-up.
+		if current.index == lowerBound ||
+			(head < len(queue) && queue[head].index == lowerBound) {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		if isLeftChild(current.index) {
+			// Handle left-child branch.
+			left = current.hash
+			if head < len(queue) && queue[head].index == current.index+1 {
+				right = queue[head].hash
+				head++
+			} else {
+				right, err = p.getNextProof(&proofIdx)
+				if err != nil {
+					return nil, err
+				}
+			}
+		} else {
+			// Handle right-child branch.
+			right = current.hash
+			if head < len(queue) && queue[head].index == current.index-1 {
+				left = queue[head].hash
+				head++
+			} else {
+				left, err = p.getNextProof(&proofIdx)
+				if err != nil {
+					return nil, err
+				}
+			}
+		}
+
+		queue = append(queue, nodeQueue{
+			index: current.index >> 1,
+			hash:  HashNode(left, right),
+		})
+	}
+
+	return nil, ErrNilRoot
+}
+
+// makeIndexedValues creates indexed values from elements and their indices.
+func makeIndexedValues(leaves []Leaf, indices []int) (IndexedValues, error) {
+	result := make(IndexedValues, len(indices))
+
+	for i, idx := range indices {
+		result[i] = IndexedValue{
+			value: leaves[idx],
+			index: idx,
+		}
+	}
+
+	return result, nil
+}
+
+// makeIndices returns a slice of ascending ordered indices for the given starting index and count.
+func makeIndices(startingIndex, count int) ([]int, error) {
+	if startingIndex < 0 || count <= 0 {
+		return nil, ErrInvalidRange
+	}
+
+	indices := make([]int, count)
+	for i := 0; i < count; i++ {
+		indices[i] = startingIndex + i
+	}
+
+	return indices, nil
+}
+
+// validateIndices validates the indices slice of a proof.
+func validateIndices(indices []int, leafCount int) error {
+	balancedLeafCount, err := CalculateBalancedNodesCount(leafCount)
+	if err != nil {
+		return err
+	}
+
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	if len(sortedIndices) == 0 {
+		return ErrNoIndices
+	}
+
+	if hasDuplicates(sortedIndices) {
+		return ErrDuplicateIndices
+	}
+
+	if hasOutOfBounds(sortedIndices, balancedLeafCount) {
+		return ErrIndicesOutOfBounds
+	}
path: pkg/merkle/proof.go
user: login: fbac
body: padded leaves are stil valid and should be taken in account, they're initialized as []byte{}.
created_at: 2025-04-17T11:37:35Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,339 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrDuplicateIndices   = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds = errors.New("indices out of bounds")
+	ErrInvalidRange       = errors.New("invalid range")
+	ErrInvalidLeafCount   = errors.New("invalid leaf count")
+	ErrNilProof           = errors.New("nil proof")
+	ErrNilRoot            = errors.New("nil root")
+	ErrNilElement         = errors.New("nil element")
+	ErrNoElements         = errors.New("no elements")
+	ErrNoIndices          = errors.New("no indices")
+	ErrNoProofs           = errors.New("no proofs provided")
+)
+
+type MultiProof struct {
+	values    IndexedValues
+	proofs    []Node
+	leafCount int
+}
+
+func (p *MultiProof) GetLeafCount() int {
+	return p.leafCount
+}
+
+func (p *MultiProof) GetProofs() []Node {
+	return p.proofs
+}
+
+func (p *MultiProof) GetValues() IndexedValues {
+	return p.values
+}
+
+type IndexedValues []IndexedValue
+
+type IndexedValue struct {
+	value []byte
+	index int
+}
+
+func (iv IndexedValue) GetValue() []byte {
+	return iv.value
+}
+
+func (iv IndexedValue) GetIndex() int {
+	return iv.index
+}
+
+func (iv IndexedValues) Indices() []int {
+	indices := make([]int, len(iv))
+	for i, v := range iv {
+		indices[i] = v.index
+	}
+	return indices
+}
+
+func (iv IndexedValues) ToLeaves() []Leaf {
+	leaves := make([]Leaf, len(iv))
+	for i, v := range iv {
+		leaves[i] = Leaf(v.value)
+	}
+	return leaves
+}
+
+// Verify verifies a MultiProof against the given tree root.
+func Verify(root []byte, proof *MultiProof) (bool, error) {
+	if len(root) == 0 {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
+	}
+
+	if err := proof.validate(); err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	// Handle single-element trees.
+	if proof.leafCount == 1 {
+		return bytes.Equal(root, HashLeaf(proof.values[0].value)), nil
+	}
+
+	// If all the elements are provided, we can directly reconstruct the tree.
+	if len(proof.values) == proof.leafCount {
+		leaves := proof.values.ToLeaves()
+
+		tree, err := NewMerkleTree(leaves)
+		if err != nil {
+			return false, fmt.Errorf(ErrVerifyProof, err)
+		}
+
+		return bytes.Equal(tree.Root(), root), nil
+	}
+
+	computedRoot, err := proof.computeRoot()
+	if err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	return bytes.Equal(computedRoot, root), nil
+}
+
+// validate performs common validation for Merkle proofs.
+func (p *MultiProof) validate() error {
+	if len(p.values) == 0 {
+		return ErrNoElements
+	}
+
+	if p.leafCount <= 0 {
+		return ErrInvalidLeafCount
+	}
+
+	if err := validateIndices(p.values.Indices(), p.leafCount); err != nil {
+		return err
+	}
+
+	for _, elem := range p.values {
+		if elem.value == nil {
+			return ErrNilElement
+		}
+	}
+
+	for _, proof := range p.proofs {
+		if proof.hash == nil {
+			return ErrNilProof
+		}
+	}
+
+	isPartialProof := len(p.values) < p.leafCount
+	isNonTrivialTree := p.leafCount > 1
+	needsProofs := isPartialProof && isNonTrivialTree
+
+	if needsProofs && len(p.proofs) == 0 {
+		return ErrNoProofs
+	}
+
+	return nil
+}
+
+// getNextProof safely retrieves the next proof and increments the index.
+func (p *MultiProof) getNextProof(index *int) ([]byte, error) {
+	if *index >= len(p.proofs) {
+		return nil, ErrNoProofs
+	}
+	proof := p.proofs[*index]
+	*index++
+	return proof.Hash(), nil
+}
+
+// nodeQueue represents a node in the computation queue with its tree index and hash value.
+// It's used during proof verification to track nodes as they are processed.
+type nodeQueue struct {
+	index int
+	hash  []byte
+}
+
+// buildNodeQueue builds the node queue for the proof computation.
+func (p *MultiProof) buildNodeQueue(balancedLeafCount int) ([]nodeQueue, error) {
+	leaves := p.values.ToLeaves()
+
+	nodes, err := makeNodes(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	indices := p.values.Indices()
+	n := len(indices)
+
+	queue := make([]nodeQueue, n)
+	for i, idx := range indices {
+		insertPos := n - 1 - i
+		queue[insertPos] = nodeQueue{
+			index: balancedLeafCount + idx,
+			hash:  nodes[i].Hash(),
+		}
+	}
+
+	return queue, nil
+}
+
+// computeRoot computes the root of the Merkle tree from the given proof.
+func (p *MultiProof) computeRoot() ([]byte, error) {
+	// 1. Prepare the queue.
+	blc, err := CalculateBalancedNodesCount(p.leafCount)
+	if err != nil {
+		return nil, err
+	}
+
+	queue, err := p.buildNodeQueue(blc)
+	if err != nil {
+		return nil, err
+	}
+
+	var (
+		head, proofIdx = 0, 0
+		upperBound     = blc + p.leafCount - 1
+		lowerBound     = queue[len(queue)-1].index
+		left, right    []byte
+	)
+
+	// 2. Process queue until we hit the root.
+	for head < len(queue) {
+		current := queue[head]
+		head++
+
+		// Exit condition - return the root.
+		if current.index == 1 {
+			return current.hash, nil
+		}
+
+		// Detect level-up.
+		if current.index == lowerBound ||
+			(head < len(queue) && queue[head].index == lowerBound) {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		if isLeftChild(current.index) {
+			// Handle left-child branch.
+			left = current.hash
+			if head < len(queue) && queue[head].index == current.index+1 {
+				right = queue[head].hash
+				head++
+			} else {
+				right, err = p.getNextProof(&proofIdx)
+				if err != nil {
+					return nil, err
+				}
+			}
+		} else {
+			// Handle right-child branch.
+			right = current.hash
+			if head < len(queue) && queue[head].index == current.index-1 {
+				left = queue[head].hash
+				head++
+			} else {
+				left, err = p.getNextProof(&proofIdx)
+				if err != nil {
+					return nil, err
+				}
+			}
+		}
+
+		queue = append(queue, nodeQueue{
+			index: current.index >> 1,
+			hash:  HashNode(left, right),
+		})
+	}
+
+	return nil, ErrNilRoot
+}
+
+// makeIndexedValues creates indexed values from elements and their indices.
+func makeIndexedValues(leaves []Leaf, indices []int) (IndexedValues, error) {
+	result := make(IndexedValues, len(indices))
+
+	for i, idx := range indices {
+		result[i] = IndexedValue{
+			value: leaves[idx],
+			index: idx,
+		}
+	}
+
+	return result, nil
+}
+
+// makeIndices returns a slice of ascending ordered indices for the given starting index and count.
+func makeIndices(startingIndex, count int) ([]int, error) {
+	if startingIndex < 0 || count <= 0 {
+		return nil, ErrInvalidRange
+	}
+
+	indices := make([]int, count)
+	for i := 0; i < count; i++ {
+		indices[i] = startingIndex + i
+	}
+
+	return indices, nil
+}
+
+// validateIndices validates the indices slice of a proof.
+func validateIndices(indices []int, leafCount int) error {
+	balancedLeafCount, err := CalculateBalancedNodesCount(leafCount)
+	if err != nil {
+		return err
+	}
+
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	if len(sortedIndices) == 0 {
+		return ErrNoIndices
+	}
+
+	if hasDuplicates(sortedIndices) {
+		return ErrDuplicateIndices
+	}
+
+	if hasOutOfBounds(sortedIndices, balancedLeafCount) {
+		return ErrIndicesOutOfBounds
+	}
path: pkg/merkle/proof.go
user: login: coderabbitai[bot]
body: @fbac Thank you for the clarification. I understand now - in your implementation, padded leaves (initialized as `[]byte{}`) are intentionally considered valid parts of the tree. In this case, using `balancedLeafCount` for bounds checking is indeed the correct approach, as it allows accessing both actual and padded leaves.

---

<details>
<summary>✏️ Learnings added</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:291-311
Timestamp: 2025-04-17T11:38:12.267Z
Learning: In the Merkle tree implementation, padded leaves (added to make leaf count a power of 2) are considered valid and should be taken into account for bounds checking. These padded leaves are initialized as empty byte arrays (`[]byte{}`) and can be accessed through indices. The validation should use `balancedLeafCount` (which includes padding) rather than just `leafCount` (actual leaves).
```

> Note: Learnings are effective only in the context of similar code segments. To apply general coding guidelines, please configure [review instructions](https://docs.coderabbit.ai/guides/review-instructions). You can manage existing learnings in the [app](https://app.coderabbit.ai/learnings).

</details>




<!-- <agentComponentType>chat-answer</agentComponentType> -->

<!-- <rawResChunk><answer>@fbac Thank you for the clarification. I understand now - in your implementation, padded leaves (initialized as `[]byte{}`) are intentionally considered valid parts of the tree. In this case, using `balancedLeafCount` for bounds checking is indeed the correct approach, as it allows accessing both actual and padded leaves.

---

<details>
<summary>✏️ Learnings added</summary>

```
Learnt from: fbac
PR: xmtp/xmtpd#712
File: pkg/merkle/proof.go:291-311
Timestamp: 2025-04-17T11:38:12.267Z
Learning: In the Merkle tree implementation, padded leaves (added to make leaf count a power of 2) are considered valid and should be taken into account for bounds checking. These padded leaves are initialized as empty byte arrays (`[]byte{}`) and can be accessed through indices. The validation should use `balancedLeafCount` (which includes padding) rather than just `leafCount` (actual leaves).
```

> Note: Learnings are effective only in the context of similar code segments. To apply general coding guidelines, please configure [review instructions](https://docs.coderabbit.ai/guides/review-instructions). You can manage existing learnings in the [app](https://app.coderabbit.ai/learnings).

</details>

</answer></rawResChunk> -->

<!-- This is an auto-generated reply by CodeRabbit -->
created_at: 2025-04-17T11:38:13Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,320 @@
+package merkle
+
+import (
+	"errors"
+	"fmt"
+	"math/bits"
+	"sort"
+)
+
+type Node struct {
+	hash []byte
+}
+
+func (n *Node) Hash() []byte {
+	if n.hash == nil {
+		return nil
+	}
+
+	cp := make([]byte, len(n.hash))
+	copy(cp, n.hash)
+
+	return cp
+}
+
+type Leaf []byte
+
+// MerkleTree is a binary Merkle tree.
+//
+// tree has the collection of nodes, where:
+// - The tree is 1-indexed, so root is at index 1.
+// - The internal nodes are at index 1 to N-1.
+// - The leaves are at index N to 2N-1.
+//
+// leaves contains the raw elements of the tree.
+type MerkleTree struct {
+	tree   []Node
+	leaves []Leaf
+}
+
+var (
+	ErrNoLeaves           = errors.New("no leaves provided")
+	ErrTreeEmpty          = errors.New("tree is empty")
+	ErrTreeRootNil        = errors.New("tree root is nil")
+	ErrTreeLeavesOverflow = errors.New("amount of leaves overflows uint32")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(leaves []Leaf) (*MerkleTree, error) {
+	if len(leaves) == 0 {
+		return nil, ErrNoLeaves
+	}
+
+	balancedLeaves, err := makeLeaves(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	nodes, err := makeNodes(balancedLeaves)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(nodes)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{tree, balancedLeaves}, nil
+}
+
+// GenerateMultiProofSequential generates a sequential multi-proof starting from the given index.
+func (m *MerkleTree) GenerateMultiProofSequential(startingIndex, count int) (*MultiProof, error) {
+	indices, err := makeIndices(startingIndex, count)
+	if err != nil {
+		return nil, err
+	}
+
+	proof, err := m.makeProof(indices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// GenerateMultiProofWithIndices generates a multi-proof for the given indices.
+func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	proof, err := m.makeProof(sortedIndices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// makeProof returns a MultiProof for the given indices.
+func (m *MerkleTree) makeProof(indices []int) (MultiProof, error) {
+	err := validateIndices(indices, m.LeafCount())
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	indexedValues, err := makeIndexedValues(m.leaves, indices)
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	// Handle single-element trees.
+	if m.LeafCount() == 1 {
+		return MultiProof{
+			values:    indexedValues,
+			proofs:    []Node{{hash: m.Root()}},
+			leafCount: m.LeafCount(),
+		}, nil
+	}
+
+	var (
+		startLeafIdx = len(m.tree) >> 1
+		proofs       []Node
+		known        = make([]bool, len(m.tree))
+	)
+
+	// Mark provided indices as known.
+	for _, idx := range indices {
+		known[startLeafIdx+idx] = true
+	}
+
+	// Calculate proofs to prove the existence of the indices.
+	for i := startLeafIdx - 1; i > 0; i-- {
+		leftChildIdx := GetLeftChild(i)
+		rightChildIdx := GetRightChild(i)
+
+		left := known[leftChildIdx]
+		right := known[rightChildIdx]
+
+		// Only one of children is known, so we need the sibling as a proof.
+		if left != right {
+			if right {
+				proofs = append(proofs, m.tree[leftChildIdx])
+			} else {
+				proofs = append(proofs, m.tree[rightChildIdx])
+			}
+		}
+
+		// If at least one of the children is known, the parent is known.
+		known[i] = left || right
+	}
+
+	return MultiProof{
+		values:    indexedValues,
+		proofs:    proofs,
+		leafCount: len(m.leaves),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() []Node {
+	return m.tree
+}
+
+// Leaves returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Leaves() []Leaf {
+	return m.leaves
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.tree[1].Hash()
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return len(m.leaves)
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func makeTree(nodes []Node) ([]Node, error) {
+	if len(nodes) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	balancedLeafCount, err := CalculateBalancedNodesCount(len(nodes))
+	if err != nil {
+		return nil, err
+	}
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([]Node, balancedLeafCount<<1)
+
+	lowerBound := balancedLeafCount
+	upperBound := balancedLeafCount + len(nodes) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(nodes); i++ {
+		tree[lowerBound+i] = nodes[i]
+	}
+
+	for i := len(nodes); i < balancedLeafCount; i++ {
+		tree[lowerBound+i] = Node{hash: HashEmptyLeaf()}
+	}
+
+	// Build the tree.
+	for i := balancedLeafCount - 1; i >= 1; i-- {
+		leftChildIndex := GetLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := GetRightChild(i)
+
+		tree[i] = Node{
+			hash: HashNode(tree[leftChildIndex].Hash(), tree[rightChildIndex].Hash()),
+		}
+
+	}
+
+	return tree, nil
+}
+
+// makeNodes returns the hashed leaves of the tree,
+// ordered in the same order as the provided elements.
+func makeNodes(leaves []Leaf) ([]Node, error) {
+	if len(leaves) == 0 {
+		return nil, ErrNoLeaves
+	}
+
+	nodes := make([]Node, len(leaves))
+	for i, element := range leaves {
+		nodes[i] = Node{hash: HashLeaf(element)}
+	}
+
+	return nodes, nil
+}
+
+// makeLeaves creates a balanced leaves count for the given leaves.
+// It fills empty leaves with an empty leaf hash.
+func makeLeaves(leaves []Leaf) ([]Leaf, error) {
+	balancedLeafCount, err := CalculateBalancedNodesCount(len(leaves))
+	if err != nil {
+		return nil, err
+	}
+
+	balancedLeaves := make([]Leaf, balancedLeafCount)
+
+	copy(balancedLeaves, leaves)
+
+	for i := len(leaves); i < balancedLeafCount; i++ {
+		balancedLeaves[i] = []byte{}
+	}
+
+	return balancedLeaves, nil
+}
+
+// CalculateBalancedNodesCount returns the number of nodes in a balanced tree.
+// To calculate the number of nodes in a tree, we need to round up to the next power of 2.
+// Returns an error if the element count is too large to be represented in a uint32.
+func CalculateBalancedNodesCount(count int) (int, error) {
+	if count <= 0 {
+		return 0, nil
+	}
+
+	if count > int(1<<31) {
+		return 0, ErrTreeLeavesOverflow
+	}
+
+	return int(roundUpToPowerOf2(uint32(count))), nil
+}
path: pkg/merkle/tree.go
user: login: coderabbitai[bot]
body: _🛠️ Refactor suggestion_

**Return an error for non‑positive counts instead of silently returning 0**

`CalculateBalancedNodesCount` currently returns `(0, nil)` when `count <= 0`.  
Down‑stream callers (present or future) may treat a zero as valid and attempt to build an empty tree, leading to a panic or a mysterious “root nil” error later.

Consider treating non‑positive input as programmer error:

```diff
-	if count <= 0 {
-		return 0, nil
-	}
+	if count <= 0 {
+		return 0, fmt.Errorf("element count must be positive")
+	}
```

This defensive check fails fast and pin‑points the issue at the correct call site.  



<!-- suggestion_start -->

<details>
<summary>📝 Committable suggestion</summary>

> ‼️ **IMPORTANT**
> Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

`````suggestion
	if count <= 0 {
		return 0, fmt.Errorf("element count must be positive")
	}

	if count > int(1<<31) {
		return 0, ErrTreeLeavesOverflow
	}

	return int(roundUpToPowerOf2(uint32(count))), nil
}
`````

</details>

<!-- suggestion_end -->

<!-- This is an auto-generated comment by CodeRabbit -->

✅ Addressed in commit d34a3eb
created_at: 2025-04-17T11:54:40Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,345 @@
+package merkle
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+)
+
+const (
+	ErrGenerateProof string = "cannot generate proof: %w"
+	ErrVerifyProof   string = "cannot verify proof: %w"
+)
+
+var (
+	ErrEmptyTree          = errors.New("empty tree")
+	ErrDuplicateIndices   = errors.New("duplicate indices")
+	ErrIndicesOutOfBounds = errors.New("indices out of bounds")
+	ErrInvalidRange       = errors.New("invalid range")
+	ErrInvalidLeafCount   = errors.New("invalid leaf count")
+	ErrElementMismatch    = errors.New("element and indices mismatch")
+	ErrNilProof           = errors.New("nil proof")
+	ErrNilRoot            = errors.New("nil root")
+	ErrNilElement         = errors.New("nil element")
+	ErrNoElements         = errors.New("no elements")
+	ErrNoIndices          = errors.New("no indices")
+	ErrNoProofs           = errors.New("no proofs provided")
+)
+
+type MultiProof struct {
+	elements  indexedValues
+	proofs    [][]byte
+	leafCount int
+}
+
+func (p *MultiProof) Elements() indexedValues {
+	return p.elements
+}
+
+func (p *MultiProof) Proofs() [][]byte {
+	return p.proofs
+}
+
+func (p *MultiProof) LeafCount() int {
+	return p.leafCount
+}
+
+type indexedValues []indexedValue
+
+type indexedValue struct {
+	value []byte
+	index int
+}
+
+func (iv indexedValues) Values() [][]byte {
+	values := make([][]byte, len(iv))
+	for i, v := range iv {
+		values[i] = v.value
+	}
+	return values
+}
+
+func (iv indexedValues) Indices() []int {
+	indices := make([]int, len(iv))
+	for i, v := range iv {
+		indices[i] = v.index
+	}
+	return indices
+}
+
+// Verify verifies a MultiProof against the given tree root.
+func Verify(root []byte, proof *MultiProof) (bool, error) {
+	if len(root) == 0 {
+		return false, fmt.Errorf(ErrVerifyProof, ErrNilRoot)
+	}
+
+	if err := proof.validate(); err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	// Handle single-element trees.
+	if proof.leafCount == 1 {
+		return bytes.Equal(root, HashLeaf(proof.elements[0].value)), nil
+	}
+
+	// If all the elements are provided, we can directly reconstruct the tree.
+	if len(proof.elements) == proof.leafCount {
+		tree, err := NewMerkleTree(proof.elements.Values())
+		if err != nil {
+			return false, fmt.Errorf(ErrVerifyProof, err)
+		}
+
+		return bytes.Equal(tree.Root(), root), nil
+	}
+
+	result, err := proof.computeRoot()
+	if err != nil {
+		return false, fmt.Errorf(ErrVerifyProof, err)
+	}
+
+	return bytes.Equal(result, root), nil
+}
+
+func (p *MultiProof) computeRoot() ([]byte, error) {
+	balancedLeafCount := CalculateBalancedLeafCount(p.leafCount)
+
+	leaves, err := makeLeaves(p.elements.Values())
+	if err != nil {
+		return nil, err
+	}
+
+	indices := p.elements.Indices()
+	numElements := len(indices)
+
+	// nodeQueue is populated with the indices we want to prove, from right to left.
+	nodeQueue := make([]int, numElements)
+	hashQueue := make([][]byte, numElements)
+	for i := 0; i < numElements; i++ {
+		reverseIdx := numElements - 1 - i
+		nodeQueue[reverseIdx] = balancedLeafCount + indices[i]
+		hashQueue[reverseIdx] = cloneBuffer(leaves[i])
+	}
+
+	var (
+		readIndex, writeIndex, proofIndex = 0, 0, 0
+		upperBound                        = balancedLeafCount + p.leafCount - 1
+		lowestTreeIndex                   = nodeQueue[numElements-1]
+		nextNodeIndex                     int
+		leftHash, rightHash               []byte
+	)
+
+	for {
+		currentIndex := nodeQueue[readIndex]
+
+		// When the root is reached, return the hash.
+		if currentIndex == 1 {
+			rootIdx := (writeIndex + numElements - 1) % numElements
+			return hashQueue[rootIdx], nil
+		}
+
+		// A left child is even, a right child is odd.
+		isOdd := isOddIndex(currentIndex)
+
+		// A left child at the boundary might not have a right sibling.
+		// The sibling of a left child (even index) would be at index+1.
+		shouldPromoteDirectly := isLeftNodeAtUpperBound(currentIndex, upperBound)
+
+		// Promote node if it's a left child at the boundary with no sibling
+		if shouldPromoteDirectly {
+			nodeQueue[writeIndex] = currentIndex >> 1
+			hashQueue[writeIndex] = hashQueue[readIndex]
+			writeIndex = (writeIndex + 1) % numElements
+			readIndex = (readIndex + 1) % numElements
+		} else {
+			nextReadIndex := (readIndex + 1) % numElements
+			nextNodeIndex = nodeQueue[nextReadIndex]
+			nextIsSibling := nextNodeIndex == currentIndex-1
+
+			if isOdd {
+				// Current node is right child
+				rightHash = hashQueue[readIndex]
+				readIndex = (readIndex + 1) % numElements
+
+				if nextIsSibling {
+					// Get left sibling from queue
+					leftHash = hashQueue[readIndex]
+					readIndex = (readIndex + 1) % numElements
+				} else {
+					// Get left sibling from proof
+					leftHash, err = p.getNextProof(&proofIndex)
+					if err != nil {
+						return nil, err
+					}
+				}
+			} else {
+				// Current node is left child
+				leftHash = hashQueue[readIndex]
+				readIndex = (readIndex + 1) % numElements
+
+				// Always get right sibling from proof
+				rightHash, err = p.getNextProof(&proofIndex)
+				if err != nil {
+					return nil, err
+				}
+			}
+
+			if leftHash == nil || rightHash == nil {
+				return nil, ErrNilProof
+			}
+
+			// Compute parent hash and add to queue
+			parentIndex := currentIndex >> 1
+			parentHash := HashNode(leftHash, rightHash)
+			nodeQueue[writeIndex] = parentIndex
+			hashQueue[writeIndex] = parentHash
+			writeIndex = (writeIndex + 1) % numElements
+		}
+
+		// Update level tracking when processing the lowest index.
+		if currentIndex == lowestTreeIndex || nextNodeIndex == lowestTreeIndex {
+			lowestTreeIndex >>= 1
+			upperBound >>= 1
+		}
+	}
+}
+
+// getNextProof safely retrieves the next proof and increments the index.
+func (p *MultiProof) getNextProof(proofIndex *int) ([]byte, error) {
+	if *proofIndex >= len(p.proofs) {
+		return nil, ErrNilProof
+	}
+	proof := p.proofs[*proofIndex]
+	*proofIndex++
+	return proof, nil
+}
+
+// validate performs common validation for Merkle proofs.
+func (p *MultiProof) validate() error {
+	if len(p.elements) == 0 {
+		return ErrNoElements
+	}
+
+	if p.leafCount <= 0 {
+		return ErrInvalidLeafCount
+	}
+
+	if err := validateIndices(p.elements.Indices(), p.leafCount); err != nil {
+		return err
+	}
+
+	for _, elem := range p.elements {
+		if elem.value == nil {
+			return ErrNilElement
+		}
+	}
+
+	for _, proof := range p.proofs {
+		if proof == nil {
+			return ErrNilProof
+		}
+	}
+
+	isPartialProof := len(p.elements) < p.leafCount
+	isNonTrivialTree := p.leafCount > 1
+	needsProofs := isPartialProof && isNonTrivialTree
+
+	if needsProofs && len(p.proofs) == 0 {
+		return ErrNoProofs
+	}
+
+	return nil
+}
+
+// makeIndexedValues creates indexed values from elements and their indices.
+func makeIndexedValues(elements [][]byte, indices []int) indexedValues {
+	result := make(indexedValues, len(indices))
+	for i, idx := range indices {
+		result[i] = indexedValue{
+			value: elements[idx],
+			index: idx,
+		}
+	}
+	return result
+}
+
+// makeIndices returns a slice of ascending ordered indices for the given starting index and count.
+func makeIndices(startingIndex, count int) ([]int, error) {
+	if startingIndex < 0 || count <= 0 {
+		return nil, ErrInvalidRange
+	}
+
+	indices := make([]int, count)
+	for i := 0; i < count; i++ {
+		indices[i] = startingIndex + i
+	}
+
+	return indices, nil
+}
+
+// validateIndices validates the indices slice of a proof.
+func validateIndices(indices []int, leafCount int) error {
path: pkg/merkle/proof.go
user: login: neekolas
body: For sequential proofs, we need to check _somewhere_ that they are actually sequential or someone could exclude a Payer from settlement. Unclear whether to me whether that should be here or elsewhere.
created_at: 2025-04-17T14:54:15Z
author_association: CONTRIBUTOR
diff_hunk: @@ -0,0 +1,320 @@
+package merkle
+
+import (
+	"errors"
+	"fmt"
+	"math/bits"
+	"sort"
+)
+
+type Node struct {
+	hash []byte
+}
+
+func (n *Node) Hash() []byte {
+	if n.hash == nil {
+		return nil
+	}
+
+	cp := make([]byte, len(n.hash))
+	copy(cp, n.hash)
+
+	return cp
+}
+
+type Leaf []byte
+
+// MerkleTree is a binary Merkle tree.
+//
+// tree has the collection of nodes, where:
+// - The tree is 1-indexed, so root is at index 1.
+// - The internal nodes are at index 1 to N-1.
+// - The leaves are at index N to 2N-1.
+//
+// leaves contains the raw elements of the tree.
+type MerkleTree struct {
+	tree   []Node
+	leaves []Leaf
+}
+
+var (
+	ErrNoLeaves           = errors.New("no leaves provided")
+	ErrTreeEmpty          = errors.New("tree is empty")
+	ErrTreeRootNil        = errors.New("tree root is nil")
+	ErrTreeLeavesOverflow = errors.New("amount of leaves overflows uint32")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(leaves []Leaf) (*MerkleTree, error) {
+	if len(leaves) == 0 {
+		return nil, ErrNoLeaves
+	}
+
+	balancedLeaves, err := makeLeaves(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	nodes, err := makeNodes(balancedLeaves)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(nodes)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{tree, balancedLeaves}, nil
+}
+
+// GenerateMultiProofSequential generates a sequential multi-proof starting from the given index.
+func (m *MerkleTree) GenerateMultiProofSequential(startingIndex, count int) (*MultiProof, error) {
+	indices, err := makeIndices(startingIndex, count)
+	if err != nil {
+		return nil, err
+	}
+
+	proof, err := m.makeProof(indices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// GenerateMultiProofWithIndices generates a multi-proof for the given indices.
+func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	proof, err := m.makeProof(sortedIndices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// makeProof returns a MultiProof for the given indices.
+func (m *MerkleTree) makeProof(indices []int) (MultiProof, error) {
+	err := validateIndices(indices, m.LeafCount())
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	indexedValues, err := makeIndexedValues(m.leaves, indices)
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	// Handle single-element trees.
+	if m.LeafCount() == 1 {
+		return MultiProof{
+			values:    indexedValues,
+			proofs:    []Node{{hash: m.Root()}},
+			leafCount: m.LeafCount(),
+		}, nil
+	}
+
+	var (
+		startLeafIdx = len(m.tree) >> 1
+		proofs       []Node
+		known        = make([]bool, len(m.tree))
+	)
+
+	// Mark provided indices as known.
+	for _, idx := range indices {
+		known[startLeafIdx+idx] = true
+	}
+
+	// Calculate proofs to prove the existence of the indices.
+	for i := startLeafIdx - 1; i > 0; i-- {
+		leftChildIdx := GetLeftChild(i)
+		rightChildIdx := GetRightChild(i)
+
+		left := known[leftChildIdx]
+		right := known[rightChildIdx]
+
+		// Only one of children is known, so we need the sibling as a proof.
+		if left != right {
+			if right {
+				proofs = append(proofs, m.tree[leftChildIdx])
+			} else {
+				proofs = append(proofs, m.tree[rightChildIdx])
+			}
+		}
+
+		// If at least one of the children is known, the parent is known.
+		known[i] = left || right
+	}
+
+	return MultiProof{
+		values:    indexedValues,
+		proofs:    proofs,
+		leafCount: len(m.leaves),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() []Node {
+	return m.tree
+}
+
+// Leaves returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Leaves() []Leaf {
+	return m.leaves
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.tree[1].Hash()
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return len(m.leaves)
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
path: pkg/merkle/tree.go
user: login: mkysel
body: seems to be called `makeTree` now
created_at: 2025-04-17T15:12:28Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,320 @@
+package merkle
+
+import (
+	"errors"
+	"fmt"
+	"math/bits"
+	"sort"
+)
+
+type Node struct {
+	hash []byte
+}
+
+func (n *Node) Hash() []byte {
+	if n.hash == nil {
+		return nil
+	}
+
+	cp := make([]byte, len(n.hash))
+	copy(cp, n.hash)
+
+	return cp
+}
+
+type Leaf []byte
+
+// MerkleTree is a binary Merkle tree.
+//
+// tree has the collection of nodes, where:
+// - The tree is 1-indexed, so root is at index 1.
+// - The internal nodes are at index 1 to N-1.
+// - The leaves are at index N to 2N-1.
+//
+// leaves contains the raw elements of the tree.
+type MerkleTree struct {
+	tree   []Node
+	leaves []Leaf
+}
+
+var (
+	ErrNoLeaves           = errors.New("no leaves provided")
+	ErrTreeEmpty          = errors.New("tree is empty")
+	ErrTreeRootNil        = errors.New("tree root is nil")
+	ErrTreeLeavesOverflow = errors.New("amount of leaves overflows uint32")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(leaves []Leaf) (*MerkleTree, error) {
+	if len(leaves) == 0 {
+		return nil, ErrNoLeaves
+	}
+
+	balancedLeaves, err := makeLeaves(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	nodes, err := makeNodes(balancedLeaves)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(nodes)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{tree, balancedLeaves}, nil
+}
+
+// GenerateMultiProofSequential generates a sequential multi-proof starting from the given index.
+func (m *MerkleTree) GenerateMultiProofSequential(startingIndex, count int) (*MultiProof, error) {
+	indices, err := makeIndices(startingIndex, count)
+	if err != nil {
+		return nil, err
+	}
+
+	proof, err := m.makeProof(indices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// GenerateMultiProofWithIndices generates a multi-proof for the given indices.
+func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	proof, err := m.makeProof(sortedIndices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// makeProof returns a MultiProof for the given indices.
+func (m *MerkleTree) makeProof(indices []int) (MultiProof, error) {
+	err := validateIndices(indices, m.LeafCount())
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	indexedValues, err := makeIndexedValues(m.leaves, indices)
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	// Handle single-element trees.
+	if m.LeafCount() == 1 {
+		return MultiProof{
+			values:    indexedValues,
+			proofs:    []Node{{hash: m.Root()}},
+			leafCount: m.LeafCount(),
+		}, nil
+	}
+
+	var (
+		startLeafIdx = len(m.tree) >> 1
+		proofs       []Node
+		known        = make([]bool, len(m.tree))
+	)
+
+	// Mark provided indices as known.
+	for _, idx := range indices {
+		known[startLeafIdx+idx] = true
+	}
+
+	// Calculate proofs to prove the existence of the indices.
+	for i := startLeafIdx - 1; i > 0; i-- {
+		leftChildIdx := GetLeftChild(i)
+		rightChildIdx := GetRightChild(i)
+
+		left := known[leftChildIdx]
+		right := known[rightChildIdx]
+
+		// Only one of children is known, so we need the sibling as a proof.
+		if left != right {
+			if right {
+				proofs = append(proofs, m.tree[leftChildIdx])
+			} else {
+				proofs = append(proofs, m.tree[rightChildIdx])
+			}
+		}
+
+		// If at least one of the children is known, the parent is known.
+		known[i] = left || right
+	}
+
+	return MultiProof{
+		values:    indexedValues,
+		proofs:    proofs,
+		leafCount: len(m.leaves),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() []Node {
+	return m.tree
+}
+
+// Leaves returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Leaves() []Leaf {
+	return m.leaves
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.tree[1].Hash()
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return len(m.leaves)
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func makeTree(nodes []Node) ([]Node, error) {
+	if len(nodes) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	balancedLeafCount, err := CalculateBalancedNodesCount(len(nodes))
+	if err != nil {
+		return nil, err
+	}
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([]Node, balancedLeafCount<<1)
+
+	lowerBound := balancedLeafCount
+	upperBound := balancedLeafCount + len(nodes) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(nodes); i++ {
+		tree[lowerBound+i] = nodes[i]
+	}
+
+	for i := len(nodes); i < balancedLeafCount; i++ {
+		tree[lowerBound+i] = Node{hash: HashEmptyLeaf()}
+	}
+
+	// Build the tree.
+	for i := balancedLeafCount - 1; i >= 1; i-- {
+		leftChildIndex := GetLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := GetRightChild(i)
+
+		tree[i] = Node{
+			hash: HashNode(tree[leftChildIndex].Hash(), tree[rightChildIndex].Hash()),
+		}
+
+	}
+
+	return tree, nil
+}
+
+// makeNodes returns the hashed leaves of the tree,
+// ordered in the same order as the provided elements.
+func makeNodes(leaves []Leaf) ([]Node, error) {
+	if len(leaves) == 0 {
+		return nil, ErrNoLeaves
+	}
+
+	nodes := make([]Node, len(leaves))
+	for i, element := range leaves {
+		nodes[i] = Node{hash: HashLeaf(element)}
+	}
+
+	return nodes, nil
+}
+
+// makeLeaves creates a balanced leaves count for the given leaves.
+// It fills empty leaves with an empty leaf hash.
+func makeLeaves(leaves []Leaf) ([]Leaf, error) {
+	balancedLeafCount, err := CalculateBalancedNodesCount(len(leaves))
+	if err != nil {
+		return nil, err
+	}
+
+	balancedLeaves := make([]Leaf, balancedLeafCount)
+
+	copy(balancedLeaves, leaves)
+
+	for i := len(leaves); i < balancedLeafCount; i++ {
+		balancedLeaves[i] = []byte{}
+	}
+
+	return balancedLeaves, nil
+}
+
+// CalculateBalancedNodesCount returns the number of nodes in a balanced tree.
+// To calculate the number of nodes in a tree, we need to round up to the next power of 2.
+// Returns an error if the element count is too large to be represented in a uint32.
path: pkg/merkle/tree.go
user: login: mkysel
body: these type casts here... It's such a shame that Go `len()` is `int` instead of `uint`. I understand the design decision, but it makes some things a bit more annoying to cast.

I would assume that all of our code will be running on 64-bit architecture and so int will be int64. `roundUpToPowerOf2` can be easily adapted to accept and return `uint64`. Just add a few more shifts :) Or make it accept `int` and handle both architectures.

That might remove the need for the overflow check and a bunch of these casts.
created_at: 2025-04-17T15:24:32Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,320 @@
+package merkle
+
+import (
+	"errors"
+	"fmt"
+	"math/bits"
+	"sort"
+)
+
+type Node struct {
+	hash []byte
+}
+
+func (n *Node) Hash() []byte {
+	if n.hash == nil {
+		return nil
+	}
+
+	cp := make([]byte, len(n.hash))
+	copy(cp, n.hash)
+
+	return cp
+}
+
+type Leaf []byte
+
+// MerkleTree is a binary Merkle tree.
+//
+// tree has the collection of nodes, where:
+// - The tree is 1-indexed, so root is at index 1.
+// - The internal nodes are at index 1 to N-1.
+// - The leaves are at index N to 2N-1.
+//
+// leaves contains the raw elements of the tree.
+type MerkleTree struct {
+	tree   []Node
+	leaves []Leaf
+}
+
+var (
+	ErrNoLeaves           = errors.New("no leaves provided")
+	ErrTreeEmpty          = errors.New("tree is empty")
+	ErrTreeRootNil        = errors.New("tree root is nil")
+	ErrTreeLeavesOverflow = errors.New("amount of leaves overflows uint32")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(leaves []Leaf) (*MerkleTree, error) {
+	if len(leaves) == 0 {
+		return nil, ErrNoLeaves
+	}
+
+	balancedLeaves, err := makeLeaves(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	nodes, err := makeNodes(balancedLeaves)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(nodes)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{tree, balancedLeaves}, nil
+}
+
+// GenerateMultiProofSequential generates a sequential multi-proof starting from the given index.
+func (m *MerkleTree) GenerateMultiProofSequential(startingIndex, count int) (*MultiProof, error) {
+	indices, err := makeIndices(startingIndex, count)
+	if err != nil {
+		return nil, err
+	}
+
+	proof, err := m.makeProof(indices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// GenerateMultiProofWithIndices generates a multi-proof for the given indices.
+func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	proof, err := m.makeProof(sortedIndices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// makeProof returns a MultiProof for the given indices.
+func (m *MerkleTree) makeProof(indices []int) (MultiProof, error) {
+	err := validateIndices(indices, m.LeafCount())
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	indexedValues, err := makeIndexedValues(m.leaves, indices)
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	// Handle single-element trees.
+	if m.LeafCount() == 1 {
+		return MultiProof{
+			values:    indexedValues,
+			proofs:    []Node{{hash: m.Root()}},
+			leafCount: m.LeafCount(),
+		}, nil
+	}
+
+	var (
+		startLeafIdx = len(m.tree) >> 1
+		proofs       []Node
+		known        = make([]bool, len(m.tree))
+	)
+
+	// Mark provided indices as known.
+	for _, idx := range indices {
+		known[startLeafIdx+idx] = true
+	}
+
+	// Calculate proofs to prove the existence of the indices.
+	for i := startLeafIdx - 1; i > 0; i-- {
+		leftChildIdx := GetLeftChild(i)
+		rightChildIdx := GetRightChild(i)
+
+		left := known[leftChildIdx]
+		right := known[rightChildIdx]
+
+		// Only one of children is known, so we need the sibling as a proof.
+		if left != right {
+			if right {
+				proofs = append(proofs, m.tree[leftChildIdx])
+			} else {
+				proofs = append(proofs, m.tree[rightChildIdx])
+			}
+		}
+
+		// If at least one of the children is known, the parent is known.
+		known[i] = left || right
+	}
+
+	return MultiProof{
+		values:    indexedValues,
+		proofs:    proofs,
+		leafCount: len(m.leaves),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() []Node {
+	return m.tree
+}
+
+// Leaves returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Leaves() []Leaf {
+	return m.leaves
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.tree[1].Hash()
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return len(m.leaves)
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func makeTree(nodes []Node) ([]Node, error) {
+	if len(nodes) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	balancedLeafCount, err := CalculateBalancedNodesCount(len(nodes))
+	if err != nil {
+		return nil, err
+	}
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([]Node, balancedLeafCount<<1)
+
+	lowerBound := balancedLeafCount
+	upperBound := balancedLeafCount + len(nodes) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(nodes); i++ {
+		tree[lowerBound+i] = nodes[i]
+	}
+
+	for i := len(nodes); i < balancedLeafCount; i++ {
+		tree[lowerBound+i] = Node{hash: HashEmptyLeaf()}
+	}
+
+	// Build the tree.
+	for i := balancedLeafCount - 1; i >= 1; i-- {
+		leftChildIndex := GetLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := GetRightChild(i)
+
+		tree[i] = Node{
+			hash: HashNode(tree[leftChildIndex].Hash(), tree[rightChildIndex].Hash()),
+		}
+
+	}
+
+	return tree, nil
+}
+
+// makeNodes returns the hashed leaves of the tree,
+// ordered in the same order as the provided elements.
+func makeNodes(leaves []Leaf) ([]Node, error) {
+	if len(leaves) == 0 {
+		return nil, ErrNoLeaves
+	}
+
+	nodes := make([]Node, len(leaves))
+	for i, element := range leaves {
+		nodes[i] = Node{hash: HashLeaf(element)}
+	}
+
+	return nodes, nil
+}
+
+// makeLeaves creates a balanced leaves count for the given leaves.
+// It fills empty leaves with an empty leaf hash.
+func makeLeaves(leaves []Leaf) ([]Leaf, error) {
+	balancedLeafCount, err := CalculateBalancedNodesCount(len(leaves))
+	if err != nil {
+		return nil, err
+	}
+
+	balancedLeaves := make([]Leaf, balancedLeafCount)
+
+	copy(balancedLeaves, leaves)
+
+	for i := len(leaves); i < balancedLeafCount; i++ {
+		balancedLeaves[i] = []byte{}
+	}
+
+	return balancedLeaves, nil
+}
+
+// CalculateBalancedNodesCount returns the number of nodes in a balanced tree.
+// To calculate the number of nodes in a tree, we need to round up to the next power of 2.
+// Returns an error if the element count is too large to be represented in a uint32.
+func CalculateBalancedNodesCount(count int) (int, error) {
+	if count <= 0 {
+		return 0, nil
+	}
+
+	if count > int(1<<31) {
path: pkg/merkle/tree.go
user: login: mkysel
body: this does not work on 32bit architecture. It will overflow and hence go negative.
created_at: 2025-04-17T15:25:00Z
author_association: COLLABORATOR
path: pkg/merkle/tree_test.go
user: login: mkysel
body: Slapping this comment here.

I would love to see a randomized test. This code is really complex and my human eyes can't see all edge cases.
created_at: 2025-04-17T15:31:25Z
author_association: COLLABORATOR
diff_hunk: @@ -0,0 +1,320 @@
+package merkle
+
+import (
+	"errors"
+	"fmt"
+	"math/bits"
+	"sort"
+)
+
+type Node struct {
+	hash []byte
+}
+
+func (n *Node) Hash() []byte {
+	if n.hash == nil {
+		return nil
+	}
+
+	cp := make([]byte, len(n.hash))
+	copy(cp, n.hash)
+
+	return cp
+}
+
+type Leaf []byte
+
+// MerkleTree is a binary Merkle tree.
+//
+// tree has the collection of nodes, where:
+// - The tree is 1-indexed, so root is at index 1.
+// - The internal nodes are at index 1 to N-1.
+// - The leaves are at index N to 2N-1.
+//
+// leaves contains the raw elements of the tree.
+type MerkleTree struct {
+	tree   []Node
+	leaves []Leaf
+}
+
+var (
+	ErrNoLeaves           = errors.New("no leaves provided")
+	ErrTreeEmpty          = errors.New("tree is empty")
+	ErrTreeRootNil        = errors.New("tree root is nil")
+	ErrTreeLeavesOverflow = errors.New("amount of leaves overflows uint32")
+)
+
+// NewMerkleTree creates a new Merkle tree from the given elements.
+func NewMerkleTree(leaves []Leaf) (*MerkleTree, error) {
+	if len(leaves) == 0 {
+		return nil, ErrNoLeaves
+	}
+
+	balancedLeaves, err := makeLeaves(leaves)
+	if err != nil {
+		return nil, err
+	}
+
+	nodes, err := makeNodes(balancedLeaves)
+	if err != nil {
+		return nil, err
+	}
+
+	tree, err := makeTree(nodes)
+	if err != nil {
+		return nil, err
+	}
+
+	return &MerkleTree{tree, balancedLeaves}, nil
+}
+
+// GenerateMultiProofSequential generates a sequential multi-proof starting from the given index.
+func (m *MerkleTree) GenerateMultiProofSequential(startingIndex, count int) (*MultiProof, error) {
+	indices, err := makeIndices(startingIndex, count)
+	if err != nil {
+		return nil, err
+	}
+
+	proof, err := m.makeProof(indices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// GenerateMultiProofWithIndices generates a multi-proof for the given indices.
+func (m *MerkleTree) GenerateMultiProofWithIndices(indices []int) (*MultiProof, error) {
+	sortedIndices := make([]int, len(indices))
+	copy(sortedIndices, indices)
+	sort.Ints(sortedIndices)
+
+	proof, err := m.makeProof(sortedIndices)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := proof.validate(); err != nil {
+		return nil, err
+	}
+
+	return &proof, nil
+}
+
+// makeProof returns a MultiProof for the given indices.
+func (m *MerkleTree) makeProof(indices []int) (MultiProof, error) {
+	err := validateIndices(indices, m.LeafCount())
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	indexedValues, err := makeIndexedValues(m.leaves, indices)
+	if err != nil {
+		return MultiProof{}, fmt.Errorf(ErrGenerateProof, err)
+	}
+
+	// Handle single-element trees.
+	if m.LeafCount() == 1 {
+		return MultiProof{
+			values:    indexedValues,
+			proofs:    []Node{{hash: m.Root()}},
+			leafCount: m.LeafCount(),
+		}, nil
+	}
+
+	var (
+		startLeafIdx = len(m.tree) >> 1
+		proofs       []Node
+		known        = make([]bool, len(m.tree))
+	)
+
+	// Mark provided indices as known.
+	for _, idx := range indices {
+		known[startLeafIdx+idx] = true
+	}
+
+	// Calculate proofs to prove the existence of the indices.
+	for i := startLeafIdx - 1; i > 0; i-- {
+		leftChildIdx := GetLeftChild(i)
+		rightChildIdx := GetRightChild(i)
+
+		left := known[leftChildIdx]
+		right := known[rightChildIdx]
+
+		// Only one of children is known, so we need the sibling as a proof.
+		if left != right {
+			if right {
+				proofs = append(proofs, m.tree[leftChildIdx])
+			} else {
+				proofs = append(proofs, m.tree[rightChildIdx])
+			}
+		}
+
+		// If at least one of the children is known, the parent is known.
+		known[i] = left || right
+	}
+
+	return MultiProof{
+		values:    indexedValues,
+		proofs:    proofs,
+		leafCount: len(m.leaves),
+	}, nil
+}
+
+// Tree returns the 1-indexed representation of the Merkle tree.
+func (m *MerkleTree) Tree() []Node {
+	return m.tree
+}
+
+// Leaves returns the raw elements of the Merkle tree.
+func (m *MerkleTree) Leaves() []Leaf {
+	return m.leaves
+}
+
+// Root returns the root hash of the Merkle tree.
+func (m *MerkleTree) Root() []byte {
+	return m.tree[1].Hash()
+}
+
+// LeafCount returns the number of leaves in the Merkle tree.
+func (m *MerkleTree) LeafCount() int {
+	return len(m.leaves)
+}
+
+// BuildTree builds a serialized Merkle tree from an array of leaf nodes.
+//
+// The tree is 1-indexed, so root is at index 1.
+// The internal nodes are at index 2 to N.
+// The leaves are at index N+1 to 2N-1.
+//
+// For any node at index i:
+// - left child is at index 2*i
+// - right child is at index 2*i+1
+// - parent is at floor(i/2)
+func makeTree(nodes []Node) ([]Node, error) {
+	if len(nodes) == 0 {
+		return nil, ErrTreeEmpty
+	}
+
+	balancedLeafCount, err := CalculateBalancedNodesCount(len(nodes))
+	if err != nil {
+		return nil, err
+	}
+
+	// Allocate 2N space for the tree. (N leaf nodes, N-1 internal nodes)
+	tree := make([]Node, balancedLeafCount<<1)
+
+	lowerBound := balancedLeafCount
+	upperBound := balancedLeafCount + len(nodes) - 1
+
+	// Copy leaves into the tree, starting at index N.
+	for i := 0; i < len(nodes); i++ {
+		tree[lowerBound+i] = nodes[i]
+	}
+
+	for i := len(nodes); i < balancedLeafCount; i++ {
+		tree[lowerBound+i] = Node{hash: HashEmptyLeaf()}
+	}
+
+	// Build the tree.
+	for i := balancedLeafCount - 1; i >= 1; i-- {
+		leftChildIndex := GetLeftChild(i)
+
+		if leftChildIndex > upperBound {
+			continue
+		}
+
+		// Detect the level is processed.
+		if leftChildIndex <= lowerBound {
+			lowerBound >>= 1
+			upperBound >>= 1
+		}
+
+		rightChildIndex := GetRightChild(i)
+
+		tree[i] = Node{
+			hash: HashNode(tree[leftChildIndex].Hash(), tree[rightChildIndex].Hash()),
+		}
+
+	}
+
+	return tree, nil
+}
+
+// makeNodes returns the hashed leaves of the tree,
+// ordered in the same order as the provided elements.
+func makeNodes(leaves []Leaf) ([]Node, error) {
+	if len(leaves) == 0 {
+		return nil, ErrNoLeaves
+	}
+
+	nodes := make([]Node, len(leaves))
+	for i, element := range leaves {
+		nodes[i] = Node{hash: HashLeaf(element)}
+	}
+
+	return nodes, nil
+}
+
+// makeLeaves creates a balanced leaves count for the given leaves.
+// It fills empty leaves with an empty leaf hash.
+func makeLeaves(leaves []Leaf) ([]Leaf, error) {
+	balancedLeafCount, err := CalculateBalancedNodesCount(len(leaves))
+	if err != nil {
+		return nil, err
+	}
+
+	balancedLeaves := make([]Leaf, balancedLeafCount)
+
+	copy(balancedLeaves, leaves)
+
+	for i := len(leaves); i < balancedLeafCount; i++ {
+		balancedLeaves[i] = []byte{}
+	}
+
+	return balancedLeaves, nil
+}
+
+// CalculateBalancedNodesCount returns the number of nodes in a balanced tree.
+// To calculate the number of nodes in a tree, we need to round up to the next power of 2.
+// Returns an error if the element count is too large to be represented in a uint32.
path: pkg/merkle/tree.go
user: login: fbac
body: > I would assume that all of our code will be running on 64-bit architecture and so int will be int64. roundUpToPowerOf2 can be easily adapted to accept and return uint64. Just add a few more shifts :) Or make it accept int and handle both architectures.

My assumption too, extracting this to an issue to work on it.
created_at: 2025-04-21T11:24:56Z
author_association: COLLABORATOR

PR comments:
user: login: coderabbitai[bot]
created_at: 2025-04-11T17:37:54Z
body: <!-- This is an auto-generated comment: summarize by coderabbit.ai -->
<!-- walkthrough_start -->

## Walkthrough
This pull request introduces several new files in the `pkg/merkle` package, implementing hashing operations, a Merkle tree data structure, and multi-proof generation and verification for Merkle trees. It adds new constants, functions, methods, and utility functions that support reliable tree creation, proof generation, and proof validation. Additionally, comprehensive test suites are provided for both the Merkle tree and multi-proof functionalities, covering various tree configurations, edge cases, and error conditions.

## Changes

| File(s)                     | Change Summary                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| pkg/merkle/hash.go          | New file implementing hashing operations for Merkle trees. Introduces the `LEAF_PREFIX` and `NODE_PREFIX` constants and functions `Hash`, `HashNode`, `HashLeaf`, and `HashEmptyLeaf` which use the Keccak-256 hash algorithm from the `sha3` package with prefixed inputs for leaf and node hashing.                                                                                  |
| pkg/merkle/proof.go         | New file providing a comprehensive implementation for Merkle multi-proofs. Introduces the `MultiProof` struct and supporting types (`IndexedValue`, `IndexedValues`, `nodeQueue`). Implements methods for proof validation, root computation using balanced leaf counts and queue-based traversal, and error handling. Provides the `Verify` function to validate multi-proofs against a given root. Includes helper functions for indices validation and child position determination.                                    |
| pkg/merkle/tree.go          | New file implementing the Merkle tree data structure. Defines the `MerkleTree`, `Node`, and `Leaf` types. Implements tree construction with balanced leaf counts, hashing of leaves and internal nodes, and methods to generate multi-proofs for sequential or arbitrary leaf indices. Includes utility functions for tree balancing, child node indexing, and error handling.                                                           |
| pkg/merkle/tree_test.go     | New test file providing extensive unit tests for the Merkle tree implementation. Tests cover empty trees, balanced and unbalanced trees of various sizes, large trees, duplicate and empty elements, and internal tree structure validation. Also tests utility functions related to leaf count balancing and power-of-two rounding. Uses the `testify` package for assertions and error checking.                                  |
| pkg/merkle/proof_test.go    | New test file providing comprehensive unit tests for Merkle multi-proof generation and verification. Tests cover sequential and arbitrary multi-proof generation, verification success and failure scenarios, edge cases like single-leaf trees, invalid inputs, and proof immutability. Uses helper functions for deterministic leaves and asserts correctness with the `testify` package.                                                                 |

## Sequence Diagram(s)

```mermaid
sequenceDiagram
    participant U as User
    participant MT as MerkleTree
    participant ML as makeNodes
    participant MTREE as makeTree

    U->>MT: NewMerkleTree(leaves)
    MT->>ML: makeNodes(leaves)
    ML-->>MT: nodes (hashed leaves)
    MT->>MTREE: makeTree(nodes)
    MTREE-->>MT: tree structure & root
    MT-->>U: MerkleTree instance
```

```mermaid
sequenceDiagram
    participant U as User
    participant MT as MerkleTree
    participant GP as GenerateMultiProof
    participant VP as Verify

    U->>MT: GenerateMultiProofSequential(startIndex, count)
    MT->>GP: makeProof(tree, root, indices, leafCount)
    GP-->>MT: MultiProof instance
    MT-->>U: MultiProof instance

    U->>VP: Verify(root, MultiProof)
    VP->>VP: validate inputs and proof
    VP->>VP: computeRoot from elements and proofs
    VP-->>U: Verification result (true/false, error)
```

```mermaid
sequenceDiagram
    participant U as User
    participant MT as MerkleTree
    participant GP as GenerateMultiProofWithIndices
    participant VP as Verify

    U->>MT: GenerateMultiProofWithIndices(indices)
    MT->>GP: makeProof(tree, root, indices, leafCount)
    GP-->>MT: MultiProof instance
    MT-->>U: MultiProof instance

    U->>VP: Verify(root, MultiProof)
    VP->>VP: validate inputs and proof
    VP->>VP: computeRoot from elements and proofs
    VP-->>U: Verification result (true/false, error)
```

<!-- walkthrough_end -->
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> 
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> 
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<!-- internal state start -->


<!-- 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 -->

<!-- internal state end -->
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<details>
<summary>✨ Finishing Touches</summary>

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<!-- tips_end -->
author_association: CONTRIBUTOR
user: login: mkysel
created_at: 2025-04-11T20:18:21Z
body: @coderabbitai can you generate a random stress test for the merkle tree implementation? Keep generating trees, adding nodes and asking for proofs for a configurable duration. The purpose of the stress test is to look for edge conditions and out-of-bounds errors. If you can, sanity check as much as possible.
author_association: COLLABORATOR
user: login: coderabbitai[bot]
created_at: 2025-04-11T20:21:38Z
body: <!-- This is an auto-generated reply by CodeRabbit -->
> [!TIP]
> For best results, initiate chat on the files or code changes.

<details>
<summary>🧩 Analysis chain</summary>

@mkysel I'll create a comprehensive stress test for the Merkle tree implementation. First, let me check the code to understand the API properly.

---

🏁 Script executed:
```
#!/bin/bash
# Let's examine the Merkle tree implementation to understand its API
echo "Examining tree.go to understand the core structure and API"
cat pkg/merkle/tree.go
```

Length of output: 3933

---

🏁 Script executed:
```
#!/bin/bash
# Let's examine the proof-related files to understand how proofs are constructed
echo "Examining proof.go for the MultiProof structure"
cat pkg/merkle/proof.go

echo -e "\nExamining proof_indices.go for index-based proof generation"
cat pkg/merkle/proof_indices.go

echo -e "\nExamining proof_sequential.go for sequential proof generation"
cat pkg/merkle/proof_sequential.go
```

Length of output: 17615

---

🏁 Script executed:
```
#!/bin/bash
# Let's examine the hash functions and test files to understand how to properly test the implementation
echo "Examining hash.go for hashing functions"
cat pkg/merkle/hash.go

echo -e "\nExamining tree_test.go to understand existing test patterns"
cat pkg/merkle/tree_test.go
```

Length of output: 9737

---
</details>
```mermaid
flowchart TB
    A["Generate Merkle Tree Stress Test"] --o B["Main Test Function Structure"]
    B --o C["Random Element Generation"]
    B --o D["Tree Creation

& Validation"]
    B --o E["Proof Generation & Verification"]
    E --o F["Sequential Proofs"]
    E --o G["Index-based Proofs"]
    B --o H["Edge Case Testing"]
    H --o I["Empty Elements"]
    H --o J["Duplicate Elements"]
    H --o K["Large Elements"]
    H --o L["Boundary Indices"]
    B --o M["Stress Test Duration Control"]
    M --o N["Configurable Parameters"]
    B --o O["Test Result Statistics"]
```
<!-- <requirement>
[requirement stress_test_1/3 create_test_file]
Create a Merkle tree stress test file that can run for a configurable duration, testing various edge cases and potential failures.

[propose_code_change]
File: `pkg/merkle/stress_test.go`

```go
package merkle

import (
	"bytes"
	"crypto/rand"
	"fmt"
	"math/big"
	"testing"
	"time"
)

// TestMerkleTreeStress performs a stress test on the Merkle tree implementation.
// The test creates trees of random sizes, generates proofs, and verifies them.
// It runs for a configurable duration to catch potential memory leaks or concurrency issues.
func TestMerkleTreeStress(t *testing.T) {
	if testing.Short() {
		t.Skip("Skipping stress test in short mode")
	}

	// Configuration
	duration := 5 * time.Second    // How long to run the stress test
	maxElements := 1000            // Maximum number of elements in a tree
	maxElementSize := 1024         // Maximum size of an element in bytes
	iterations := 0                // Count of iterations (for reporting)
	treeCount := 0                 // Count of trees created
	proofCount := 0                // Count of proofs generated
	verificationCount := 0         // Count of verifications performed
	failureCount := 0              // Count of verification failures

	// For time-limited tests
	start := time.Now()
	deadline := start.Add(duration)

	t.Logf("Starting Merkle tree stress test for %v...", duration)

	for time.Now().Before(deadline) {
		iterations++

		// 1. Generate a random tree size (1 to maxElements)
		treeSize := randomInt(1, maxElements)

		// 2. Create random elements
		elements := generateRandomElements(treeSize, maxElementSize)

		// 3. Occasionally include edge cases
		if iterations%5 == 0 {
			elements = incorporateEdgeCases(elements)
		}

		// 4. Create the Merkle tree
		tree, err := NewMerkleTree(elements)
		if err != nil {
			t.Fatalf("Failed to create Merkle tree: %v", err)
		}
		treeCount++

		// 5. Test sequential proofs
		if err := testSequentialProofs(t, tree, &proofCount, &verificationCount, &failureCount); err != nil {
			t.Fatalf("Sequential proof test failed: %v", err)
		}

		// 6. Test index-based proofs
		if err := testIndexBasedProofs(t, tree, &proofCount, &verificationCount, &failureCount); err != nil {
			t.Fatalf("Index-based proof test failed: %v", err)
		}

		// 7. Occasionally perform garbage collection to simulate real-world conditions
		if iterations%100 == 0 {
			t.Logf("Progress: %d iterations, %d trees, %d proofs, %d verifications (%d failures)",
				iterations, treeCount, proofCount, verificationCount, failureCount)
		}
	}

	elapsed := time.Since(start)
	t.Logf("Stress test completed in %v", elapsed)
	t.Logf("Total iterations: %d", iterations)
	t.Logf("Trees created: %d", treeCount)
	t.Logf("Proofs generated: %d", proofCount)
	t.Logf("Verifications performed: %d", verificationCount)
	t.Logf("Verification failures: %d", failureCount)

	if failureCount > 0 {
		t.Errorf("Encountered %d verification failures during stress test", failureCount)
	}
}

// testSequentialProofs tests sequential proofs for the given tree.
func testSequentialProofs(t *testing.T, tree *MerkleTree, proofCount, verificationCount, failureCount *int) error {
	t.Helper()
	elements := tree.Elements()
	elementCount := len(elements)

	// Test cases to cover edge cases and random scenarios
	testCases := []struct {
		name          string
		startingIndex int
		count         int
	}{
		{"SingleElement", 0, 1}, // First element
	}

	// Add edge case: last element
	if elementCount > 1 {
		testCases = append(testCases, struct {
			name          string
			startingIndex int
			count         int
		}{"LastElement", elementCount - 1, 1})
	}

	// Add edge case: all elements
	testCases = append(testCases, struct {
		name          string
		startingIndex int
		count         int
	}{"AllElements", 0, elementCount})

	// Add random ranges if there are enough elements
	if elementCount > 2 {
		// Random middle element
		startIdx := randomInt(1, elementCount-1)
		testCases = append(testCases, struct {
			name          string
			startingIndex int
			count         int
		}{"RandomMiddleElement", startIdx, 1})

		// Random range
		if elementCount > 3 {
			startIdx = randomInt(0, elementCount-2)
			count := randomInt(1, elementCount-startIdx)
			testCases = append(testCases, struct {
				name          string
				startingIndex int
				count         int
			}{"RandomRange", startIdx, count})
		}
	}

	// Execute all test cases
	for _, tc := range testCases {
		proof, err := tree.GenerateMultiProofSequential(tc.startingIndex, tc.count)
		if err != nil {
			return fmt.Errorf("failed to generate sequential proof (%s): %v", tc.name, err)
		}
		(*proofCount)++

		// Verify the proof
		valid, err := VerifyMultiProofSequential(proof)
		(*verificationCount)++
		if err != nil {
			return fmt.Errorf("failed to verify sequential proof (%s): %v", tc.name, err)
		}
		if !valid {
			(*failureCount)++
			return fmt.Errorf("sequential proof verification failed (%s)", tc.name)
		}

		// Sanity check: Modify root and ensure verification fails
		if tc.count > 0 {
			invalidProof := *proof
			invalidProof.Root = bytes.Repeat([]byte{0xFF}, len(proof.Root))
			valid, _ = VerifyMultiProofSequential(&invalidProof)
			(*verificationCount)++
			if valid {
				(*failureCount)++
				return fmt.Errorf("verification succeeded with invalid root (%s)", tc.name)
			}
		}
	}

	return nil
}

// testIndexBasedProofs tests index-based proofs for the given tree.
func testIndexBasedProofs(t *testing.T, tree *MerkleTree, proofCount, verificationCount, failureCount *int) error {
	t.Helper()
	elements := tree.Elements()
	elementCount := len(elements)

	// Test cases to cover edge cases and random scenarios
	testCases := []struct {
		name    string
		indices []int
	}{
		{"FirstElement", []int{0}}, // First element
	}

	// Add edge case: last element
	if elementCount > 1 {
		testCases = append(testCases, struct {
			name    string
			indices []int
		}{"LastElement", []int{elementCount - 1}})
	}

	// Add edge case: all elements
	if elementCount > 0 {
		allIndices := make([]int, elementCount)
		for i := 0; i < elementCount; i++ {
			allIndices[i] = i
		}
		testCases = append(testCases, struct {
			name    string
			indices []int
		}{"AllElements", allIndices})
	}

	// Add random selections if there are enough elements
	if elementCount > 2 {
		// Random middle element
		middleIdx := randomInt(1, elementCount-1)
		testCases = append(testCases, struct {
			name    string
			indices []int
		}{"RandomMiddleElement", []int{middleIdx}})

		// Random set of elements (if there are enough elements)
		if elementCount > 3 {
			count := randomInt(2, (elementCount+1)/2)
			randomIndices := generateRandomIndices(elementCount, count)
			testCases = append(testCases, struct {
				name    string
				indices []int
			}{"RandomIndices", randomIndices})
		}
	}

	// Execute all test cases
	for _, tc := range testCases {
		proof, err := tree.GenerateMultiProofWithIndices(tc.indices)
		if err != nil {
			return fmt.Errorf("failed to generate index-based proof (%s): %v", tc.name, err)
		}
		(*proofCount)++

		// Verify the proof
		valid, err := VerifyMultiProofWithIndices(proof)
		(*verificationCount)++
		if err != nil {
			return fmt.Errorf("failed to verify index-based proof (%s): %v", tc.name, err)
		}
		if !valid {
			(*failureCount)++
			return fmt.Errorf("index-based proof verification failed (%s)", tc.name)
		}

		// Sanity check: Modify root and ensure verification fails
		if len(tc.indices) > 0 {
			invalidProof := *proof
			invalidProof.Root = bytes.Repeat([]byte{0xFF}, len(proof.Root))
			valid, _ = VerifyMultiProofWithIndices(&invalidProof)
			(*verificationCount)++
			if valid {
				(*failureCount)++
				return fmt.Errorf("verification succeeded with invalid root (%s)", tc.name)
			}
		}
	}

	return nil
}

// generateRandomElements creates a slice of random byte slices.
func generateRandomElements(count, maxSize int) [][]byte {
	result := make([][]byte, count)
	for i := 0; i < count; i++ {
		size := randomInt(1, maxSize)
		element := make([]byte, size)
		_, _ = rand.Read(element)
		result[i] = element
	}
	return result
}

// incorporateEdgeCases adds edge cases to the elements.
func incorporateEdgeCases(elements [][]byte) [][]byte {
	result := make([][]byte, len(elements))
	copy(result, elements)

	// Randomly decide which edge cases to include
	switch randomInt(0, 4) {
	case 0:
		// Replace a random element with an empty slice
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			result[idx] = []byte{}
		}
	case 1:
		// Add duplicate elements
		if len(result) > 1 {
			srcIdx := randomInt(0, len(result)-1)
			dstIdx := (srcIdx + 1) % len(result)
			result[dstIdx] = make([]byte, len(result[srcIdx]))
			copy(result[dstIdx], result[srcIdx])
		}
	case 2:
		// Add a large element
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			largeElement := make([]byte, 1024*1024) // 1MB
			_, _ = rand.Read(largeElement)
			result[idx] = largeElement
		}
	case 3:
		// Add a very small element
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			result[idx] = []byte{0x42}
		}
	}

	return result
}

// generateRandomIndices creates a random set of unique indices.
func generateRandomIndices(max, count int) []int {
	if count > max {
		count = max
	}

	// Generate all possible indices
	indices := make([]int, max)
	for i := 0; i < max; i++ {
		indices[i] = i
	}

	// Shuffle using Fisher-Yates algorithm
	for i := max - 1; i > 0; i-- {
		j := randomInt(0, i)
		indices[i], indices[j] = indices[j], indices[i]
	}

	// Take the first 'count' indices
	return indices[:count]
}

// randomInt returns a random integer in the range [min, max).
func randomInt(min, max int) int {
	if min >= max {
		return min
	}
	n, _ := rand.Int(rand.Reader, big.NewInt(int64(max-min)))
	return int(n.Int64()) + min
}
```
</requirement> -->
<!-- <requirement>
[requirement stress_test_2/3 create_advanced_test_file]
Create a more comprehensive test file that includes parallel testing and additional edge cases for Merkle tree stress testing.

[propose_code_change]
File: `pkg/merkle/advanced_stress_test.go`

```go
package merkle

import (
	"bytes"
	"crypto/rand"
	"fmt"
	"math/big"
	"runtime"
	"sync"
	"sync/atomic"
	"testing"
	"time"
)

// TestMerkleTreeParallelStress performs a stress test with concurrent operations
// to test the thread safety and performance under load.
func TestMerkleTreeParallelStress(t *testing.T) {
	if testing.Short() {
		t.Skip("Skipping parallel stress test in short mode")
	}

	// Configuration
	duration := 5 * time.Second
	numWorkers := runtime.NumCPU()
	maxTreeSize := 500
	
	var (
		treeCount         int64
		proofCount        int64
		verificationCount int64
		failureCount      int64
	)

	// Channel to signal workers to stop
	stopCh := make(chan struct{})
	var wg sync.WaitGroup

	t.Logf("Starting parallel Merkle tree stress test with %d workers for %v...", numWorkers, duration)
	
	// Start worker goroutines
	for i := 0; i < numWorkers; i++ {
		wg.Add(1)
		go func(workerID int) {
			defer wg.Done()
			
			for {
				select {
				case <-stopCh:
					return
				default:
					// Create a random tree
					treeSize := randomInt(1, maxTreeSize)
					elements := generateRandomElements(treeSize, 256)
					
					// Add edge cases occasionally
					if randomInt(0, 10) == 0 {
						elements = incorporateEdgeCases(elements)
					}
					
					tree, err := NewMerkleTree(elements)
					if err != nil {
						t.Errorf("Worker %d: Failed to create tree: %v", workerID, err)
						continue
					}
					atomic.AddInt64(&treeCount, 1)
					
					// Test proofs
					if err := runSequentialProofs(tree, &proofCount, &verificationCount, &failureCount); err != nil {
						t.Errorf("Worker %d: Sequential proof error: %v", workerID, err)
					}
					
					if err := runIndexBasedProofs(tree, &proofCount, &verificationCount, &failureCount); err != nil {
						t.Errorf("Worker %d: Index-based proof error: %v", workerID, err)
					}
				}
			}
		}(i)
	}

	// Let the test run for the specified duration
	time.Sleep(duration)
	close(stopCh)
	
	// Wait for all workers to finish
	wg.Wait()
	
	// Report results
	t.Logf("Parallel stress test completed")
	t.Logf("Trees created: %d", treeCount)
	t.Logf("Proofs generated: %d", proofCount)
	t.Logf("Verifications performed: %d", verificationCount)
	t.Logf("Verification failures: %d", failureCount)
	
	if failureCount > 0 {
		t.Errorf("Encountered %d verification failures during parallel stress test", failureCount)
	}
}

// TestMerkleTreeEdgeCases focuses specifically on testing edge cases
func TestMerkleTreeEdgeCases(t *testing.T) {
	testCases := []struct {
		name     string
		elements [][]byte
	}{
		{
			name: "Single Empty Element",
			elements: [][]byte{{}},
		},
		{
			name: "Many Empty Elements",
			elements: bytes.Split(bytes.Repeat([]byte{0}, 100), []byte{0})[1:],
		},
		{
			name: "Mixed Empty and Non-Empty",
			elements: [][]byte{
				{},
				{1, 2, 3},
				{},
				{4, 5, 6},
				{},
			},
		},
		{
			name: "All Same Elements",
			elements: func() [][]byte {
				elems := make([][]byte, 50)
				for i := range elems {
					elems[i] = []byte{1, 2, 3, 4}
				}
				return elems
			}(),
		},
		{
			name: "Alternating Patterns",
			elements: func() [][]byte {
				elems := make([][]byte, 50)
				for i := range elems {
					if i%2 == 0 {
						elems[i] = []byte{1, 2}
					} else {
						elems[i] = []byte{3, 4}
					}
				}
				return elems
			}(),
		},
		{
			name: "Power of Two + 1",
			elements: func() [][]byte {
				elems := make([][]byte, 17) // 16 + 1
				for i := range elems {
					elems[i] = []byte{byte(i)}
				}
				return elems
			}(),
		},
		{
			name: "Power of Two - 1",
			elements: func() [][]byte {
				elems := make([][]byte, 15) // 16 - 1
				for i := range elems {
					elems[i] = []byte{byte(i)}
				}
				return elems
			}(),
		},
	}
	
	for _, tc := range testCases {
		t.Run(tc.name, func(t *testing.T) {
			// Create the tree
			tree, err := NewMerkleTree(tc.elements)
			if err != nil {
				t.Fatalf("Failed to create tree: %v", err)
			}
			
			// Test exhaustively for small trees, or sample for larger ones
			var indices [][]int
			if len(tc.elements) <= 10 {
				// For small trees, test all possible index combinations
				indices = generateAllIndexCombinations(len(tc.elements))
			} else {
				// For larger trees, test a representative sample
				indices = generateIndexSamples(len(tc.elements))
			}
			
			// Test index-based proofs
			for _, idxSet := range indices {
				proof, err := tree.GenerateMultiProofWithIndices(idxSet)
				if err != nil {
					t.Fatalf("Failed to generate proof for indices %v: %v", idxSet, err)
				}
				
				valid, err := VerifyMultiProofWithIndices(proof)
				if err != nil {
					t.Fatalf("Failed to verify proof for indices %v: %v", idxSet, err)
				}
				if !valid {
					t.Errorf("Invalid proof for indices %v", idxSet)
				}
			}
			
			// Test sequential proofs - try all possible ranges
			if len(tc.elements) <= 10 {
				for start := 0; start < len(tc.elements); start++ {
					for count := 1; start+count <= len(tc.elements); count++ {
						proof, err := tree.GenerateMultiProofSequential(start, count)
						if err != nil {
							t.Fatalf("Failed to generate sequential proof (start=%d, count=%d): %v", 
								start, count, err)
						}
						
						valid, err := VerifyMultiProofSequential(proof)
						if err != nil {
							t.Fatalf("Failed to verify sequential proof (start=%d, count=%d): %v", 
								start, count, err)
						}
						if !valid {
							t.Errorf("Invalid sequential proof (start=%d, count=%d)", start, count)
						}
					}
				}
			} else {
				// Sample some ranges for larger trees
				ranges := []struct {
					start int
					count int
				}{
					{0, 1},                       // First element
					{len(tc.elements) - 1, 1},    // Last element
					{0, len(tc.elements)},        // All elements
					{len(tc.elements) / 2, 1},    // Middle element
					{0, len(tc.elements) / 2},    // First half
					{len(tc.elements) / 2, len(tc.elements) - len(tc.elements) / 2}, // Second half
				}
				
				for _, r := range ranges {
					proof, err := tree.GenerateMultiProofSequential(r.start, r.count)
					if err != nil {
						t.Fatalf("Failed to generate sequential proof (start=%d, count=%d): %v", 
							r.start, r.count, err)
					}
					
					valid, err := VerifyMultiProofSequential(proof)
					if err != nil {
						t.Fatalf("Failed to verify sequential proof (start=%d, count=%d): %v", 
							r.start, r.count, err)
					}
					if !valid {
						t.Errorf("Invalid sequential proof (start=%d, count=%d)", r.start, r.count)
					}
				}
			}
		})
	}
}

// runSequentialProofs is a helper function for testing sequential proofs
func runSequentialProofs(tree *MerkleTree, proofCount, verificationCount, failureCount *int64) error {
	elements := tree.Elements()
	elementCount := len(elements)
	
	// Generate a few random test cases
	testCases := []struct {
		startingIndex int
		count         int
	}{
		{0, 1}, // First element
	}
	
	// Add last element if there's more than one
	if elementCount > 1 {
		testCases = append(testCases, struct {
			startingIndex int
			count         int
		}{elementCount - 1, 1})
	}
	
	// Add random ranges
	if elementCount > 2 {
		startIdx := randomInt(0, elementCount-1)
		count := randomInt(1, elementCount-startIdx)
		testCases = append(testCases, struct {
			startingIndex int
			count         int
		}{startIdx, count})
	}
	
	// Run the test cases
	for _, tc := range testCases {
		proof, err := tree.GenerateMultiProofSequential(tc.startingIndex, tc.count)
		if err != nil {
			return fmt.Errorf("failed to generate sequential proof: %v", err)
		}
		atomic.AddInt64(proofCount, 1)
		
		valid, err := VerifyMultiProofSequential(proof)
		atomic.AddInt64(verificationCount, 1)
		if err != nil {
			return fmt.Errorf("failed to verify sequential proof: %v", err)
		}
		if !valid {
			atomic.AddInt64(failureCount, 1)
			return fmt.Errorf("sequential proof verification failed")
		}
	}
	
	return nil
}

// runIndexBasedProofs is a helper function for testing index-based proofs
func runIndexBasedProofs(tree *MerkleTree, proofCount, verificationCount, failureCount *int64) error {
	elements := tree.Elements()
	elementCount := len(elements)
	
	// Generate test cases
	var testCases [][]int
	
	// Single indices
	if elementCount > 0 {
		testCases = append(testCases, []int{0}) // First element
		if elementCount > 1 {
			testCases = append(testCases, []int{elementCount - 1}) // Last element
			if elementCount > 2 {
				testCases = append(testCases, []int{elementCount / 2}) // Middle element
			}
		}
	}
	
	// Multiple random indices
	if elementCount > 3 {
		count := randomInt(2, (elementCount+1)/2)
		randomIndices := generateRandomIndices(elementCount, count)
		testCases = append(testCases, randomIndices)
	}
	
	// Run the test cases
	for _, indices := range testCases {
		proof, err := tree.GenerateMultiProofWithIndices(indices)
		if err != nil {
			return fmt.Errorf("failed to generate index-based proof: %v", err)
		}
		atomic.AddInt64(proofCount, 1)
		
		valid, err := VerifyMultiProofWithIndices(proof)
		atomic.AddInt64(verificationCount, 1)
		if err != nil {
			return fmt.Errorf("failed to verify index-based proof: %v", err)
		}
		if !valid {
			atomic.AddInt64(failureCount, 1)
			return fmt.Errorf("index-based proof verification failed")
		}
	}
	
	return nil
}

// generateAllIndexCombinations generates all possible combinations of indices
// (for small trees only, as this grows exponentially)
func generateAllIndexCombinations(size int) [][]int {
	if size <= 0 {
		return nil
	}
	
	// Start with individual indices
	result := make([][]int, size)
	for i := 0; i < size; i++ {
		result[i] = []int{i}
	}
	
	// For small trees, add some combinations (limit to avoid explosion)
	if size <= 5 {
		// Add all pairs
		for i := 0; i < size; i++ {
			for j := i + 1; j < size; j++ {
				result = append(result, []int{i, j})
			}
		}
		
		// Add all triplets for very small trees
		if size <= 4 {
			for i := 0; i < size; i++ {
				for j := i + 1; j < size; j++ {
					for k := j + 1; k < size; k++ {
						result = append(result, []int{i, j, k})
					}
				}
			}
		}
	}
	
	return result
}

// generateIndexSamples generates a representative sample of index combinations
func generateIndexSamples(size int) [][]int {
	result := [][]int{
		{0},                    // First element
		{size - 1},             // Last element
		{size / 2},             // Middle element
		{0, size - 1},          // First and last
	}
	
	// Add some random single and multiple indices
	for i := 0; i < 5; i++ {
		count := randomInt(1, min(5, size))
		result = append(result, generateRandomIndices(size, count))
	}
	
	return result
}

// min returns the minimum of two integers
func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}
```
</requirement> -->
<!-- <requirement>
[requirement stress_test_3/3 create_cli_stress_test]
Create a standalone command-line tool to run stress tests on the Merkle tree implementation with configurable parameters.

[propose_code_change]
File: `cmd/merkle_stress/main.go`

```go
package main

import (
	"bytes"
	"crypto/rand"
	"flag"
	"fmt"
	"math/big"
	"os"
	"os/signal"
	"runtime"
	"sync"
	"sync/atomic"
	"syscall"
	"time"

	"github.com/xmtp/xmtpd/pkg/merkle"
)

type StressTestStats struct {
	TreesCreated        int64
	ProofsGenerated     int64
	VerificationsRun    int64
	VerificationFailures int64
	Errors              int64
}

func main() {
	// Parse command line flags
	duration := flag.Duration("duration", 10*time.Second, "Duration to run the stress test")
	workers := flag.Int("workers", runtime.NumCPU(), "Number of concurrent workers")
	maxElements := flag.Int("max-elements", 1000, "Maximum number of elements in a tree")
	maxElementSize := flag.Int("max-element-size", 1024, "Maximum size of an element in bytes")
	quiet := flag.Bool("quiet", false, "Reduce output verbosity")
	flag.Parse()

	fmt.Printf("Merkle Tree Stress Test\n")
	fmt.Printf("=======================\n")
	fmt.Printf("Duration: %v\n", *duration)
	fmt.Printf("Workers: %d\n", *workers)
	fmt.Printf("Max Elements: %d\n", *maxElements)
	fmt.Printf("Max Element Size: %d bytes\n", *maxElementSize)
	fmt.Printf("\nStarting test...\n\n")

	// Set up signal handling for graceful shutdown
	sigCh := make(chan os.Signal, 1)
	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)

	// Create channels for coordination
	stopCh := make(chan struct{})
	statsCh := make(chan StressTestStats, *workers)

	// Start workers
	var wg sync.WaitGroup
	for i := 0; i < *workers; i++ {
		wg.Add(1)
		go runWorker(i, stopCh, statsCh, &wg, *maxElements, *maxElementSize, *quiet)
	}

	// Set up ticker for progress updates
	ticker := time.NewTicker(1 * time.Second)
	defer ticker.Stop()

	// Initialize aggregate statistics
	stats := StressTestStats{}

	// Set deadline
	deadline := time.Now().Add(*duration)
	timeRemaining := *duration

	// Main control loop
	running := true
	for running {
		select {
		case <-ticker.C:
			timeRemaining = time.Until(deadline)
			if timeRemaining <= 0 {
				close(stopCh)
				running = false
			} else if !*quiet {
				fmt.Printf("\rRunning... %v remaining | Trees: %d | Proofs: %d | Verifications: %d | Failures: %d | Errors: %d",
					timeRemaining.Round(time.Second),
					stats.TreesCreated, stats.ProofsGenerated,
					stats.VerificationsRun, stats.VerificationFailures, stats.Errors)
			}

		case workerStats := <-statsCh:
			// Aggregate worker statistics
			stats.TreesCreated += workerStats.TreesCreated
			stats.ProofsGenerated += workerStats.ProofsGenerated
			stats.VerificationsRun += workerStats.VerificationsRun
			stats.VerificationFailures += workerStats.VerificationFailures
			stats.Errors += workerStats.Errors

		case sig := <-sigCh:
			fmt.Printf("\nReceived signal %v, shutting down...\n", sig)
			close(stopCh)
			running = false
		}
	}

	fmt.Printf("\nWaiting for workers to finish...\n")
	wg.Wait()

	// Drain any remaining stats
	close(statsCh)
	for workerStats := range statsCh {
		stats.TreesCreated += workerStats.TreesCreated
		stats.ProofsGenerated += workerStats.ProofsGenerated
		stats.VerificationsRun += workerStats.VerificationsRun
		stats.VerificationFailures += workerStats.VerificationFailures
		stats.Errors += workerStats.Errors
	}

	// Print final statistics
	fmt.Printf("\nStress Test Results\n")
	fmt.Printf("===================\n")
	fmt.Printf("Trees Created: %d\n", stats.TreesCreated)
	fmt.Printf("Proofs Generated: %d\n", stats.ProofsGenerated)
	fmt.Printf("Verifications Run: %d\n", stats.VerificationsRun)
	fmt.Printf("Verification Failures: %d\n", stats.VerificationFailures)
	fmt.Printf("Errors: %d\n", stats.Errors)

	if stats.VerificationFailures > 0 || stats.Errors > 0 {
		fmt.Printf("\nTest FAILED with %d verification failures and %d errors\n",
			stats.VerificationFailures, stats.Errors)
		os.Exit(1)
	} else {
		fmt.Printf("\nTest PASSED successfully\n")
	}
}

func runWorker(id int, stopCh <-chan struct{}, statsCh chan<- StressTestStats, wg *sync.WaitGroup, maxElements, maxElementSize int, quiet bool) {
	defer wg.Done()

	stats := StressTestStats{}
	localStats := StressTestStats{} // For periodic reporting

	reportTicker := time.NewTicker(1 * time.Second)
	defer reportTicker.Stop()

	for {
		select {
		case <-stopCh:
			statsCh <- stats
			return

		case <-reportTicker.C:
			// Report accumulated stats if there are any
			if localStats.TreesCreated > 0 {
				statsCh <- localStats
				// Reset local stats after reporting
				localStats = StressTestStats{}
			}

		default:
			// Do stress test work
			runSingleIteration(maxElements, maxElementSize, &stats, &localStats, quiet)
		}
	}
}

func runSingleIteration(maxElements, maxElementSize int, stats, localStats *StressTestStats, quiet bool) {
	// 1. Generate a random tree size
	treeSize := randomInt(1, maxElements)

	// 2. Create random elements
	elements := generateRandomElements(treeSize, maxElementSize)

	// 3. Occasionally include edge cases
	if randomInt(0, 5) == 0 {
		elements = incorporateEdgeCases(elements)
	}

	// 4. Create the Merkle tree
	tree, err := merkle.NewMerkleTree(elements)
	if err != nil {
		if !quiet {
			fmt.Printf("\nError creating tree: %v\n", err)
		}
		atomic.AddInt64(&stats.Errors, 1)
		atomic.AddInt64(&localStats.Errors, 1)
		return
	}
	atomic.AddInt64(&stats.TreesCreated, 1)
	atomic.AddInt64(&localStats.TreesCreated, 1)

	// 5. Test sequential proofs
	if err := testSequentialProofs(tree, stats, localStats); err != nil && !quiet {
		fmt.Printf("\nSequential proof error: %v\n", err)
	}

	// 6. Test index-based proofs
	if err := testIndexBasedProofs(tree, stats, localStats); err != nil && !quiet {
		fmt.Printf("\nIndex-based proof error: %v\n", err)
	}
}

func testSequentialProofs(tree *merkle.MerkleTree, stats, localStats *StressTestStats) error {
	elements := tree.Elements()
	elementCount := len(elements)

	// Test cases to cover edge cases and random scenarios
	testCases := []struct {
		startingIndex int
		count         int
	}{
		{0, 1}, // First element
	}

	// Add edge case: last element
	if elementCount > 1 {
		testCases = append(testCases, struct {
			startingIndex int
			count         int
		}{elementCount - 1, 1})
	}

	// Add edge case: all elements
	testCases = append(testCases, struct {
		startingIndex int
		count         int
	}{0, elementCount})

	// Add random ranges if there are enough elements
	if elementCount > 2 {
		// Random middle element
		startIdx := randomInt(1, elementCount-1)
		testCases = append(testCases, struct {
			startingIndex int
			count         int
		}{startIdx, 1})

		// Random range
		if elementCount > 3 {
			startIdx = randomInt(0, elementCount-2)
			count := randomInt(1, elementCount-startIdx)
			testCases = append(testCases, struct {
				startingIndex int
				count         int
			}{startIdx, count})
		}
	}

	// Execute all test cases
	for _, tc := range testCases {
		proof, err := tree.GenerateMultiProofSequential(tc.startingIndex, tc.count)
		if err != nil {
			atomic.AddInt64(&stats.Errors, 1)
			atomic.AddInt64(&localStats.Errors, 1)
			return fmt.Errorf("failed to generate sequential proof: %v", err)
		}
		atomic.AddInt64(&stats.ProofsGenerated, 1)
		atomic.AddInt64(&localStats.ProofsGenerated, 1)

		// Verify the proof
		valid, err := merkle.VerifyMultiProofSequential(proof)
		atomic.AddInt64(&stats.VerificationsRun, 1)
		atomic.AddInt64(&localStats.VerificationsRun, 1)
		if err != nil {
			atomic.AddInt64(&stats.Errors, 1)
			atomic.AddInt64(&localStats.Errors, 1)
			return fmt.Errorf("failed to verify sequential proof: %v", err)
		}
		if !valid {
			atomic.AddInt64(&stats.VerificationFailures, 1)
			atomic.AddInt64(&localStats.VerificationFailures, 1)
			return fmt.Errorf("sequential proof verification failed")
		}

		// Sanity check: Modify root and ensure verification fails
		if tc.count > 0 {
			invalidProof := *proof
			invalidProof.Root = bytes.Repeat([]byte{0xFF}, len(proof.Root))
			valid, _ = merkle.VerifyMultiProofSequential(&invalidProof)
			atomic.AddInt64(&stats.VerificationsRun, 1)
			atomic.AddInt64(&localStats.VerificationsRun, 1)
			if valid {
				atomic.AddInt64(&stats.VerificationFailures, 1)
				atomic.AddInt64(&localStats.VerificationFailures, 1)
				return fmt.Errorf("verification succeeded with invalid root")
			}
		}
	}

	return nil
}

func testIndexBasedProofs(tree *merkle.MerkleTree, stats, localStats *StressTestStats) error {
	elements := tree.Elements()
	elementCount := len(elements)

	// Test cases to cover edge cases and random scenarios
	testCases := []struct {
		indices []int
	}{
		{[]int{0}}, // First element
	}

	// Add edge case: last element
	if elementCount > 1 {
		testCases = append(testCases, struct {
			indices []int
		}{[]int{elementCount - 1}})
	}

	// Add edge case: all elements
	if elementCount > 0 {
		allIndices := make([]int, elementCount)
		for i := 0; i < elementCount; i++ {
			allIndices[i] = i
		}
		testCases = append(testCases, struct {
			indices []int
		}{allIndices})
	}

	// Add random selections if there are enough elements
	if elementCount > 2 {
		// Random middle element
		middleIdx := randomInt(1, elementCount-1)
		testCases = append(testCases, struct {
			indices []int
		}{[]int{middleIdx}})

		// Random set of elements (if there are enough elements)
		if elementCount > 3 {
			count := randomInt(2, (elementCount+1)/2)
			randomIndices := generateRandomIndices(elementCount, count)
			testCases = append(testCases, struct {
				indices []int
			}{randomIndices})
		}
	}

	// Execute all test cases
	for _, tc := range testCases {
		proof, err := tree.GenerateMultiProofWithIndices(tc.indices)
		if err != nil {
			atomic.AddInt64(&stats.Errors, 1)
			atomic.AddInt64(&localStats.Errors, 1)
			return fmt.Errorf("failed to generate index-based proof: %v", err)
		}
		atomic.AddInt64(&stats.ProofsGenerated, 1)
		atomic.AddInt64(&localStats.ProofsGenerated, 1)

		// Verify the proof
		valid, err := merkle.VerifyMultiProofWithIndices(proof)
		atomic.AddInt64(&stats.VerificationsRun, 1)
		atomic.AddInt64(&localStats.VerificationsRun, 1)
		if err != nil {
			atomic.AddInt64(&stats.Errors, 1)
			atomic.AddInt64(&localStats.Errors, 1)
			return fmt.Errorf("failed to verify index-based proof: %v", err)
		}
		if !valid {
			atomic.AddInt64(&stats.VerificationFailures, 1)
			atomic.AddInt64(&localStats.VerificationFailures, 1)
			return fmt.Errorf("index-based proof verification failed")
		}

		// Sanity check: Modify root and ensure verification fails
		if len(tc.indices) > 0 {
			invalidProof := *proof
			invalidProof.Root = bytes.Repeat([]byte{0xFF}, len(proof.Root))
			valid, _ = merkle.VerifyMultiProofWithIndices(&invalidProof)
			atomic.AddInt64(&stats.VerificationsRun, 1)
			atomic.AddInt64(&localStats.VerificationsRun, 1)
			if valid {
				atomic.AddInt64(&stats.VerificationFailures, 1)
				atomic.AddInt64(&localStats.VerificationFailures, 1)
				return fmt.Errorf("verification succeeded with invalid root")
			}
		}
	}

	return nil
}

// Helper functions from previous implementation

func generateRandomElements(count, maxSize int) [][]byte {
	result := make([][]byte, count)
	for i := 0; i < count; i++ {
		size := randomInt(1, maxSize)
		element := make([]byte, size)
		_, _ = rand.Read(element)
		result[i] = element
	}
	return result
}

func incorporateEdgeCases(elements [][]byte) [][]byte {
	result := make([][]byte, len(elements))
	copy(result, elements)

	// Randomly decide which edge cases to include
	switch randomInt(0, 4) {
	case 0:
		// Replace a random element with an empty slice
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			result[idx] = []byte{}
		}
	case 1:
		// Add duplicate elements
		if len(result) > 1 {
			srcIdx := randomInt(0, len(result)-1)
			dstIdx := (srcIdx + 1) % len(result)
			result[dstIdx] = make([]byte, len(result[srcIdx]))
			copy(result[dstIdx], result[srcIdx])
		}
	case 2:
		// Add a large element
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			largeElement := make([]byte, 1024*16) // 16KB
			_, _ = rand.Read(largeElement)
			result[idx] = largeElement
		}
	case 3:
		// Add a very small element
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			result[idx] = []byte{0x42}
		}
	}

	return result
}

func generateRandomIndices(max, count int) []int {
	if count > max {
		count = max
	}

	// Generate all possible indices
	indices := make([]int, max)
	for i := 0; i < max; i++ {
		indices[i] = i
	}

	// Shuffle using Fisher-Yates algorithm
	for i := max - 1; i > 0; i-- {
		j := randomInt(0, i)
		indices[i], indices[j] = indices[j], indices[i]
	}

	// Take the first 'count' indices
	return indices[:count]
}

func randomInt(min, max int) int {
	if min >= max {
		return min
	}
	n, _ := rand.Int(rand.Reader, big.NewInt(int64(max-min)))
	return int(n.Int64()) + min
}
```
</requirement> -->

@mkysel I'll create a comprehensive stress test for the Merkle tree implementation. After examining the code, I've designed a stress test that will thoroughly exercise the implementation to find any potential edge cases or out-of-bounds errors.

The stress test will:

1. Generate trees of various sizes (from single element to thousands)
2. Test both sequential and index-based proofs
3. Include edge cases (empty elements, duplicates, large elements)
4. Verify all proofs for correctness
5. Run for a configurable duration to catch any memory leaks or concurrency issues

Another agent will come along to implement this plan. The stress test will include comprehensive reporting to help identify any potential issues.

---

⏳ Preparing changes...



<!-- <agentComponentType>chat-answer</agentComponentType> -->

<!-- <rawResChunk><nextState>plan-edits</nextState></rawResChunk> -->

<!-- <rawResChunk><answer><details>
<summary>🧩 Analysis chain</summary>

@mkysel I'll create a comprehensive stress test for the Merkle tree implementation. First, let me check the code to understand the API properly.

---

🏁 Script executed:
```
#!/bin/bash
# Let's examine the Merkle tree implementation to understand its API
echo "Examining tree.go to understand the core structure and API"
cat pkg/merkle/tree.go
```

Length of output: 3933

---

🏁 Script executed:
```
#!/bin/bash
# Let's examine the proof-related files to understand how proofs are constructed
echo "Examining proof.go for the MultiProof structure"
cat pkg/merkle/proof.go

echo -e "\nExamining proof_indices.go for index-based proof generation"
cat pkg/merkle/proof_indices.go

echo -e "\nExamining proof_sequential.go for sequential proof generation"
cat pkg/merkle/proof_sequential.go
```

Length of output: 17615

---

🏁 Script executed:
```
#!/bin/bash
# Let's examine the hash functions and test files to understand how to properly test the implementation
echo "Examining hash.go for hashing functions"
cat pkg/merkle/hash.go

echo -e "\nExamining tree_test.go to understand existing test patterns"
cat pkg/merkle/tree_test.go
```

Length of output: 9737

---



</details>



```mermaid
flowchart TB
    A["Generate Merkle Tree Stress Test"] --o B["Main Test Function Structure"]
    B --o C["Random Element Generation"]
    B --o D["Tree Creation & Validation"]
    B --o E["Proof Generation & Verification"]
    E --o F["Sequential Proofs"]
    E --o G["Index-based Proofs"]
    B --o H["Edge Case Testing"]
    H --o I["Empty Elements"]
    H --o J["Duplicate Elements"]
    H --o K["Large Elements"]
    H --o L["Boundary Indices"]
    B --o M["Stress Test Duration Control"]
    M --o N["Configurable Parameters"]
    B --o O["Test Result Statistics"]
```

&lt;!-- <requirement>
[requirement stress_test_1/3 create_test_file]
Create a Merkle tree stress test file that can run for a configurable duration, testing various edge cases and potential failures.

[propose_code_change]
File: `pkg/merkle/stress_test.go`

```go
package merkle

import (
	"bytes"
	"crypto/rand"
	"fmt"
	"math/big"
	"testing"
	"time"
)

// TestMerkleTreeStress performs a stress test on the Merkle tree implementation.
// The test creates trees of random sizes, generates proofs, and verifies them.
// It runs for a configurable duration to catch potential memory leaks or concurrency issues.
func TestMerkleTreeStress(t *testing.T) {
	if testing.Short() {
		t.Skip("Skipping stress test in short mode")
	}

	// Configuration
	duration := 5 * time.Second    // How long to run the stress test
	maxElements := 1000            // Maximum number of elements in a tree
	maxElementSize := 1024         // Maximum size of an element in bytes
	iterations := 0                // Count of iterations (for reporting)
	treeCount := 0                 // Count of trees created
	proofCount := 0                // Count of proofs generated
	verificationCount := 0         // Count of verifications performed
	failureCount := 0              // Count of verification failures

	// For time-limited tests
	start := time.Now()
	deadline := start.Add(duration)

	t.Logf("Starting Merkle tree stress test for %v...", duration)

	for time.Now().Before(deadline) {
		iterations++

		// 1. Generate a random tree size (1 to maxElements)
		treeSize := randomInt(1, maxElements)

		// 2. Create random elements
		elements := generateRandomElements(treeSize, maxElementSize)

		// 3. Occasionally include edge cases
		if iterations%5 == 0 {
			elements = incorporateEdgeCases(elements)
		}

		// 4. Create the Merkle tree
		tree, err := NewMerkleTree(elements)
		if err != nil {
			t.Fatalf("Failed to create Merkle tree: %v", err)
		}
		treeCount++

		// 5. Test sequential proofs
		if err := testSequentialProofs(t, tree, &proofCount, &verificationCount, &failureCount); err != nil {
			t.Fatalf("Sequential proof test failed: %v", err)
		}

		// 6. Test index-based proofs
		if err := testIndexBasedProofs(t, tree, &proofCount, &verificationCount, &failureCount); err != nil {
			t.Fatalf("Index-based proof test failed: %v", err)
		}

		// 7. Occasionally perform garbage collection to simulate real-world conditions
		if iterations%100 == 0 {
			t.Logf("Progress: %d iterations, %d trees, %d proofs, %d verifications (%d failures)",
				iterations, treeCount, proofCount, verificationCount, failureCount)
		}
	}

	elapsed := time.Since(start)
	t.Logf("Stress test completed in %v", elapsed)
	t.Logf("Total iterations: %d", iterations)
	t.Logf("Trees created: %d", treeCount)
	t.Logf("Proofs generated: %d", proofCount)
	t.Logf("Verifications performed: %d", verificationCount)
	t.Logf("Verification failures: %d", failureCount)

	if failureCount > 0 {
		t.Errorf("Encountered %d verification failures during stress test", failureCount)
	}
}

// testSequentialProofs tests sequential proofs for the given tree.
func testSequentialProofs(t *testing.T, tree *MerkleTree, proofCount, verificationCount, failureCount *int) error {
	t.Helper()
	elements := tree.Elements()
	elementCount := len(elements)

	// Test cases to cover edge cases and random scenarios
	testCases := []struct {
		name          string
		startingIndex int
		count         int
	}{
		{"SingleElement", 0, 1}, // First element
	}

	// Add edge case: last element
	if elementCount > 1 {
		testCases = append(testCases, struct {
			name          string
			startingIndex int
			count         int
		}{"LastElement", elementCount - 1, 1})
	}

	// Add edge case: all elements
	testCases = append(testCases, struct {
		name          string
		startingIndex int
		count         int
	}{"AllElements", 0, elementCount})

	// Add random ranges if there are enough elements
	if elementCount > 2 {
		// Random middle element
		startIdx := randomInt(1, elementCount-1)
		testCases = append(testCases, struct {
			name          string
			startingIndex int
			count         int
		}{"RandomMiddleElement", startIdx, 1})

		// Random range
		if elementCount > 3 {
			startIdx = randomInt(0, elementCount-2)
			count := randomInt(1, elementCount-startIdx)
			testCases = append(testCases, struct {
				name          string
				startingIndex int
				count         int
			}{"RandomRange", startIdx, count})
		}
	}

	// Execute all test cases
	for _, tc := range testCases {
		proof, err := tree.GenerateMultiProofSequential(tc.startingIndex, tc.count)
		if err != nil {
			return fmt.Errorf("failed to generate sequential proof (%s): %v", tc.name, err)
		}
		(*proofCount)++

		// Verify the proof
		valid, err := VerifyMultiProofSequential(proof)
		(*verificationCount)++
		if err != nil {
			return fmt.Errorf("failed to verify sequential proof (%s): %v", tc.name, err)
		}
		if !valid {
			(*failureCount)++
			return fmt.Errorf("sequential proof verification failed (%s)", tc.name)
		}

		// Sanity check: Modify root and ensure verification fails
		if tc.count > 0 {
			invalidProof := *proof
			invalidProof.Root = bytes.Repeat([]byte{0xFF}, len(proof.Root))
			valid, _ = VerifyMultiProofSequential(&invalidProof)
			(*verificationCount)++
			if valid {
				(*failureCount)++
				return fmt.Errorf("verification succeeded with invalid root (%s)", tc.name)
			}
		}
	}

	return nil
}

// testIndexBasedProofs tests index-based proofs for the given tree.
func testIndexBasedProofs(t *testing.T, tree *MerkleTree, proofCount, verificationCount, failureCount *int) error {
	t.Helper()
	elements := tree.Elements()
	elementCount := len(elements)

	// Test cases to cover edge cases and random scenarios
	testCases := []struct {
		name    string
		indices []int
	}{
		{"FirstElement", []int{0}}, // First element
	}

	// Add edge case: last element
	if elementCount > 1 {
		testCases = append(testCases, struct {
			name    string
			indices []int
		}{"LastElement", []int{elementCount - 1}})
	}

	// Add edge case: all elements
	if elementCount > 0 {
		allIndices := make([]int, elementCount)
		for i := 0; i < elementCount; i++ {
			allIndices[i] = i
		}
		testCases = append(testCases, struct {
			name    string
			indices []int
		}{"AllElements", allIndices})
	}

	// Add random selections if there are enough elements
	if elementCount > 2 {
		// Random middle element
		middleIdx := randomInt(1, elementCount-1)
		testCases = append(testCases, struct {
			name    string
			indices []int
		}{"RandomMiddleElement", []int{middleIdx}})

		// Random set of elements (if there are enough elements)
		if elementCount > 3 {
			count := randomInt(2, (elementCount+1)/2)
			randomIndices := generateRandomIndices(elementCount, count)
			testCases = append(testCases, struct {
				name    string
				indices []int
			}{"RandomIndices", randomIndices})
		}
	}

	// Execute all test cases
	for _, tc := range testCases {
		proof, err := tree.GenerateMultiProofWithIndices(tc.indices)
		if err != nil {
			return fmt.Errorf("failed to generate index-based proof (%s): %v", tc.name, err)
		}
		(*proofCount)++

		// Verify the proof
		valid, err := VerifyMultiProofWithIndices(proof)
		(*verificationCount)++
		if err != nil {
			return fmt.Errorf("failed to verify index-based proof (%s): %v", tc.name, err)
		}
		if !valid {
			(*failureCount)++
			return fmt.Errorf("index-based proof verification failed (%s)", tc.name)
		}

		// Sanity check: Modify root and ensure verification fails
		if len(tc.indices) > 0 {
			invalidProof := *proof
			invalidProof.Root = bytes.Repeat([]byte{0xFF}, len(proof.Root))
			valid, _ = VerifyMultiProofWithIndices(&invalidProof)
			(*verificationCount)++
			if valid {
				(*failureCount)++
				return fmt.Errorf("verification succeeded with invalid root (%s)", tc.name)
			}
		}
	}

	return nil
}

// generateRandomElements creates a slice of random byte slices.
func generateRandomElements(count, maxSize int) [][]byte {
	result := make([][]byte, count)
	for i := 0; i < count; i++ {
		size := randomInt(1, maxSize)
		element := make([]byte, size)
		_, _ = rand.Read(element)
		result[i] = element
	}
	return result
}

// incorporateEdgeCases adds edge cases to the elements.
func incorporateEdgeCases(elements [][]byte) [][]byte {
	result := make([][]byte, len(elements))
	copy(result, elements)

	// Randomly decide which edge cases to include
	switch randomInt(0, 4) {
	case 0:
		// Replace a random element with an empty slice
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			result[idx] = []byte{}
		}
	case 1:
		// Add duplicate elements
		if len(result) > 1 {
			srcIdx := randomInt(0, len(result)-1)
			dstIdx := (srcIdx + 1) % len(result)
			result[dstIdx] = make([]byte, len(result[srcIdx]))
			copy(result[dstIdx], result[srcIdx])
		}
	case 2:
		// Add a large element
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			largeElement := make([]byte, 1024*1024) // 1MB
			_, _ = rand.Read(largeElement)
			result[idx] = largeElement
		}
	case 3:
		// Add a very small element
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			result[idx] = []byte{0x42}
		}
	}

	return result
}

// generateRandomIndices creates a random set of unique indices.
func generateRandomIndices(max, count int) []int {
	if count > max {
		count = max
	}

	// Generate all possible indices
	indices := make([]int, max)
	for i := 0; i < max; i++ {
		indices[i] = i
	}

	// Shuffle using Fisher-Yates algorithm
	for i := max - 1; i > 0; i-- {
		j := randomInt(0, i)
		indices[i], indices[j] = indices[j], indices[i]
	}

	// Take the first 'count' indices
	return indices[:count]
}

// randomInt returns a random integer in the range [min, max).
func randomInt(min, max int) int {
	if min >= max {
		return min
	}
	n, _ := rand.Int(rand.Reader, big.NewInt(int64(max-min)))
	return int(n.Int64()) + min
}
```
</requirement> --&gt;

&lt;!-- <requirement>
[requirement stress_test_2/3 create_advanced_test_file]
Create a more comprehensive test file that includes parallel testing and additional edge cases for Merkle tree stress testing.

[propose_code_change]
File: `pkg/merkle/advanced_stress_test.go`

```go
package merkle

import (
	"bytes"
	"crypto/rand"
	"fmt"
	"math/big"
	"runtime"
	"sync"
	"sync/atomic"
	"testing"
	"time"
)

// TestMerkleTreeParallelStress performs a stress test with concurrent operations
// to test the thread safety and performance under load.
func TestMerkleTreeParallelStress(t *testing.T) {
	if testing.Short() {
		t.Skip("Skipping parallel stress test in short mode")
	}

	// Configuration
	duration := 5 * time.Second
	numWorkers := runtime.NumCPU()
	maxTreeSize := 500
	
	var (
		treeCount         int64
		proofCount        int64
		verificationCount int64
		failureCount      int64
	)

	// Channel to signal workers to stop
	stopCh := make(chan struct{})
	var wg sync.WaitGroup

	t.Logf("Starting parallel Merkle tree stress test with %d workers for %v...", numWorkers, duration)
	
	// Start worker goroutines
	for i := 0; i < numWorkers; i++ {
		wg.Add(1)
		go func(workerID int) {
			defer wg.Done()
			
			for {
				select {
				case <-stopCh:
					return
				default:
					// Create a random tree
					treeSize := randomInt(1, maxTreeSize)
					elements := generateRandomElements(treeSize, 256)
					
					// Add edge cases occasionally
					if randomInt(0, 10) == 0 {
						elements = incorporateEdgeCases(elements)
					}
					
					tree, err := NewMerkleTree(elements)
					if err != nil {
						t.Errorf("Worker %d: Failed to create tree: %v", workerID, err)
						continue
					}
					atomic.AddInt64(&treeCount, 1)
					
					// Test proofs
					if err := runSequentialProofs(tree, &proofCount, &verificationCount, &failureCount); err != nil {
						t.Errorf("Worker %d: Sequential proof error: %v", workerID, err)
					}
					
					if err := runIndexBasedProofs(tree, &proofCount, &verificationCount, &failureCount); err != nil {
						t.Errorf("Worker %d: Index-based proof error: %v", workerID, err)
					}
				}
			}
		}(i)
	}

	// Let the test run for the specified duration
	time.Sleep(duration)
	close(stopCh)
	
	// Wait for all workers to finish
	wg.Wait()
	
	// Report results
	t.Logf("Parallel stress test completed")
	t.Logf("Trees created: %d", treeCount)
	t.Logf("Proofs generated: %d", proofCount)
	t.Logf("Verifications performed: %d", verificationCount)
	t.Logf("Verification failures: %d", failureCount)
	
	if failureCount > 0 {
		t.Errorf("Encountered %d verification failures during parallel stress test", failureCount)
	}
}

// TestMerkleTreeEdgeCases focuses specifically on testing edge cases
func TestMerkleTreeEdgeCases(t *testing.T) {
	testCases := []struct {
		name     string
		elements [][]byte
	}{
		{
			name: "Single Empty Element",
			elements: [][]byte{{}},
		},
		{
			name: "Many Empty Elements",
			elements: bytes.Split(bytes.Repeat([]byte{0}, 100), []byte{0})[1:],
		},
		{
			name: "Mixed Empty and Non-Empty",
			elements: [][]byte{
				{},
				{1, 2, 3},
				{},
				{4, 5, 6},
				{},
			},
		},
		{
			name: "All Same Elements",
			elements: func() [][]byte {
				elems := make([][]byte, 50)
				for i := range elems {
					elems[i] = []byte{1, 2, 3, 4}
				}
				return elems
			}(),
		},
		{
			name: "Alternating Patterns",
			elements: func() [][]byte {
				elems := make([][]byte, 50)
				for i := range elems {
					if i%2 == 0 {
						elems[i] = []byte{1, 2}
					} else {
						elems[i] = []byte{3, 4}
					}
				}
				return elems
			}(),
		},
		{
			name: "Power of Two + 1",
			elements: func() [][]byte {
				elems := make([][]byte, 17) // 16 + 1
				for i := range elems {
					elems[i] = []byte{byte(i)}
				}
				return elems
			}(),
		},
		{
			name: "Power of Two - 1",
			elements: func() [][]byte {
				elems := make([][]byte, 15) // 16 - 1
				for i := range elems {
					elems[i] = []byte{byte(i)}
				}
				return elems
			}(),
		},
	}
	
	for _, tc := range testCases {
		t.Run(tc.name, func(t *testing.T) {
			// Create the tree
			tree, err := NewMerkleTree(tc.elements)
			if err != nil {
				t.Fatalf("Failed to create tree: %v", err)
			}
			
			// Test exhaustively for small trees, or sample for larger ones
			var indices [][]int
			if len(tc.elements) <= 10 {
				// For small trees, test all possible index combinations
				indices = generateAllIndexCombinations(len(tc.elements))
			} else {
				// For larger trees, test a representative sample
				indices = generateIndexSamples(len(tc.elements))
			}
			
			// Test index-based proofs
			for _, idxSet := range indices {
				proof, err := tree.GenerateMultiProofWithIndices(idxSet)
				if err != nil {
					t.Fatalf("Failed to generate proof for indices %v: %v", idxSet, err)
				}
				
				valid, err := VerifyMultiProofWithIndices(proof)
				if err != nil {
					t.Fatalf("Failed to verify proof for indices %v: %v", idxSet, err)
				}
				if !valid {
					t.Errorf("Invalid proof for indices %v", idxSet)
				}
			}
			
			// Test sequential proofs - try all possible ranges
			if len(tc.elements) <= 10 {
				for start := 0; start < len(tc.elements); start++ {
					for count := 1; start+count <= len(tc.elements); count++ {
						proof, err := tree.GenerateMultiProofSequential(start, count)
						if err != nil {
							t.Fatalf("Failed to generate sequential proof (start=%d, count=%d): %v", 
								start, count, err)
						}
						
						valid, err := VerifyMultiProofSequential(proof)
						if err != nil {
							t.Fatalf("Failed to verify sequential proof (start=%d, count=%d): %v", 
								start, count, err)
						}
						if !valid {
							t.Errorf("Invalid sequential proof (start=%d, count=%d)", start, count)
						}
					}
				}
			} else {
				// Sample some ranges for larger trees
				ranges := []struct {
					start int
					count int
				}{
					{0, 1},                       // First element
					{len(tc.elements) - 1, 1},    // Last element
					{0, len(tc.elements)},        // All elements
					{len(tc.elements) / 2, 1},    // Middle element
					{0, len(tc.elements) / 2},    // First half
					{len(tc.elements) / 2, len(tc.elements) - len(tc.elements) / 2}, // Second half
				}
				
				for _, r := range ranges {
					proof, err := tree.GenerateMultiProofSequential(r.start, r.count)
					if err != nil {
						t.Fatalf("Failed to generate sequential proof (start=%d, count=%d): %v", 
							r.start, r.count, err)
					}
					
					valid, err := VerifyMultiProofSequential(proof)
					if err != nil {
						t.Fatalf("Failed to verify sequential proof (start=%d, count=%d): %v", 
							r.start, r.count, err)
					}
					if !valid {
						t.Errorf("Invalid sequential proof (start=%d, count=%d)", r.start, r.count)
					}
				}
			}
		})
	}
}

// runSequentialProofs is a helper function for testing sequential proofs
func runSequentialProofs(tree *MerkleTree, proofCount, verificationCount, failureCount *int64) error {
	elements := tree.Elements()
	elementCount := len(elements)
	
	// Generate a few random test cases
	testCases := []struct {
		startingIndex int
		count         int
	}{
		{0, 1}, // First element
	}
	
	// Add last element if there's more than one
	if elementCount > 1 {
		testCases = append(testCases, struct {
			startingIndex int
			count         int
		}{elementCount - 1, 1})
	}
	
	// Add random ranges
	if elementCount > 2 {
		startIdx := randomInt(0, elementCount-1)
		count := randomInt(1, elementCount-startIdx)
		testCases = append(testCases, struct {
			startingIndex int
			count         int
		}{startIdx, count})
	}
	
	// Run the test cases
	for _, tc := range testCases {
		proof, err := tree.GenerateMultiProofSequential(tc.startingIndex, tc.count)
		if err != nil {
			return fmt.Errorf("failed to generate sequential proof: %v", err)
		}
		atomic.AddInt64(proofCount, 1)
		
		valid, err := VerifyMultiProofSequential(proof)
		atomic.AddInt64(verificationCount, 1)
		if err != nil {
			return fmt.Errorf("failed to verify sequential proof: %v", err)
		}
		if !valid {
			atomic.AddInt64(failureCount, 1)
			return fmt.Errorf("sequential proof verification failed")
		}
	}
	
	return nil
}

// runIndexBasedProofs is a helper function for testing index-based proofs
func runIndexBasedProofs(tree *MerkleTree, proofCount, verificationCount, failureCount *int64) error {
	elements := tree.Elements()
	elementCount := len(elements)
	
	// Generate test cases
	var testCases [][]int
	
	// Single indices
	if elementCount > 0 {
		testCases = append(testCases, []int{0}) // First element
		if elementCount > 1 {
			testCases = append(testCases, []int{elementCount - 1}) // Last element
			if elementCount > 2 {
				testCases = append(testCases, []int{elementCount / 2}) // Middle element
			}
		}
	}
	
	// Multiple random indices
	if elementCount > 3 {
		count := randomInt(2, (elementCount+1)/2)
		randomIndices := generateRandomIndices(elementCount, count)
		testCases = append(testCases, randomIndices)
	}
	
	// Run the test cases
	for _, indices := range testCases {
		proof, err := tree.GenerateMultiProofWithIndices(indices)
		if err != nil {
			return fmt.Errorf("failed to generate index-based proof: %v", err)
		}
		atomic.AddInt64(proofCount, 1)
		
		valid, err := VerifyMultiProofWithIndices(proof)
		atomic.AddInt64(verificationCount, 1)
		if err != nil {
			return fmt.Errorf("failed to verify index-based proof: %v", err)
		}
		if !valid {
			atomic.AddInt64(failureCount, 1)
			return fmt.Errorf("index-based proof verification failed")
		}
	}
	
	return nil
}

// generateAllIndexCombinations generates all possible combinations of indices
// (for small trees only, as this grows exponentially)
func generateAllIndexCombinations(size int) [][]int {
	if size <= 0 {
		return nil
	}
	
	// Start with individual indices
	result := make([][]int, size)
	for i := 0; i < size; i++ {
		result[i] = []int{i}
	}
	
	// For small trees, add some combinations (limit to avoid explosion)
	if size <= 5 {
		// Add all pairs
		for i := 0; i < size; i++ {
			for j := i + 1; j < size; j++ {
				result = append(result, []int{i, j})
			}
		}
		
		// Add all triplets for very small trees
		if size <= 4 {
			for i := 0; i < size; i++ {
				for j := i + 1; j < size; j++ {
					for k := j + 1; k < size; k++ {
						result = append(result, []int{i, j, k})
					}
				}
			}
		}
	}
	
	return result
}

// generateIndexSamples generates a representative sample of index combinations
func generateIndexSamples(size int) [][]int {
	result := [][]int{
		{0},                    // First element
		{size - 1},             // Last element
		{size / 2},             // Middle element
		{0, size - 1},          // First and last
	}
	
	// Add some random single and multiple indices
	for i := 0; i < 5; i++ {
		count := randomInt(1, min(5, size))
		result = append(result, generateRandomIndices(size, count))
	}
	
	return result
}

// min returns the minimum of two integers
func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}
```
</requirement> --&gt;

&lt;!-- <requirement>
[requirement stress_test_3/3 create_cli_stress_test]
Create a standalone command-line tool to run stress tests on the Merkle tree implementation with configurable parameters.

[propose_code_change]
File: `cmd/merkle_stress/main.go`

```go
package main

import (
	"bytes"
	"crypto/rand"
	"flag"
	"fmt"
	"math/big"
	"os"
	"os/signal"
	"runtime"
	"sync"
	"sync/atomic"
	"syscall"
	"time"

	"github.com/xmtp/xmtpd/pkg/merkle"
)

type StressTestStats struct {
	TreesCreated        int64
	ProofsGenerated     int64
	VerificationsRun    int64
	VerificationFailures int64
	Errors              int64
}

func main() {
	// Parse command line flags
	duration := flag.Duration("duration", 10*time.Second, "Duration to run the stress test")
	workers := flag.Int("workers", runtime.NumCPU(), "Number of concurrent workers")
	maxElements := flag.Int("max-elements", 1000, "Maximum number of elements in a tree")
	maxElementSize := flag.Int("max-element-size", 1024, "Maximum size of an element in bytes")
	quiet := flag.Bool("quiet", false, "Reduce output verbosity")
	flag.Parse()

	fmt.Printf("Merkle Tree Stress Test\n")
	fmt.Printf("=======================\n")
	fmt.Printf("Duration: %v\n", *duration)
	fmt.Printf("Workers: %d\n", *workers)
	fmt.Printf("Max Elements: %d\n", *maxElements)
	fmt.Printf("Max Element Size: %d bytes\n", *maxElementSize)
	fmt.Printf("\nStarting test...\n\n")

	// Set up signal handling for graceful shutdown
	sigCh := make(chan os.Signal, 1)
	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)

	// Create channels for coordination
	stopCh := make(chan struct{})
	statsCh := make(chan StressTestStats, *workers)

	// Start workers
	var wg sync.WaitGroup
	for i := 0; i < *workers; i++ {
		wg.Add(1)
		go runWorker(i, stopCh, statsCh, &wg, *maxElements, *maxElementSize, *quiet)
	}

	// Set up ticker for progress updates
	ticker := time.NewTicker(1 * time.Second)
	defer ticker.Stop()

	// Initialize aggregate statistics
	stats := StressTestStats{}

	// Set deadline
	deadline := time.Now().Add(*duration)
	timeRemaining := *duration

	// Main control loop
	running := true
	for running {
		select {
		case <-ticker.C:
			timeRemaining = time.Until(deadline)
			if timeRemaining <= 0 {
				close(stopCh)
				running = false
			} else if !*quiet {
				fmt.Printf("\rRunning... %v remaining | Trees: %d | Proofs: %d | Verifications: %d | Failures: %d | Errors: %d",
					timeRemaining.Round(time.Second),
					stats.TreesCreated, stats.ProofsGenerated,
					stats.VerificationsRun, stats.VerificationFailures, stats.Errors)
			}

		case workerStats := <-statsCh:
			// Aggregate worker statistics
			stats.TreesCreated += workerStats.TreesCreated
			stats.ProofsGenerated += workerStats.ProofsGenerated
			stats.VerificationsRun += workerStats.VerificationsRun
			stats.VerificationFailures += workerStats.VerificationFailures
			stats.Errors += workerStats.Errors

		case sig := <-sigCh:
			fmt.Printf("\nReceived signal %v, shutting down...\n", sig)
			close(stopCh)
			running = false
		}
	}

	fmt.Printf("\nWaiting for workers to finish...\n")
	wg.Wait()

	// Drain any remaining stats
	close(statsCh)
	for workerStats := range statsCh {
		stats.TreesCreated += workerStats.TreesCreated
		stats.ProofsGenerated += workerStats.ProofsGenerated
		stats.VerificationsRun += workerStats.VerificationsRun
		stats.VerificationFailures += workerStats.VerificationFailures
		stats.Errors += workerStats.Errors
	}

	// Print final statistics
	fmt.Printf("\nStress Test Results\n")
	fmt.Printf("===================\n")
	fmt.Printf("Trees Created: %d\n", stats.TreesCreated)
	fmt.Printf("Proofs Generated: %d\n", stats.ProofsGenerated)
	fmt.Printf("Verifications Run: %d\n", stats.VerificationsRun)
	fmt.Printf("Verification Failures: %d\n", stats.VerificationFailures)
	fmt.Printf("Errors: %d\n", stats.Errors)

	if stats.VerificationFailures > 0 || stats.Errors > 0 {
		fmt.Printf("\nTest FAILED with %d verification failures and %d errors\n",
			stats.VerificationFailures, stats.Errors)
		os.Exit(1)
	} else {
		fmt.Printf("\nTest PASSED successfully\n")
	}
}

func runWorker(id int, stopCh <-chan struct{}, statsCh chan<- StressTestStats, wg *sync.WaitGroup, maxElements, maxElementSize int, quiet bool) {
	defer wg.Done()

	stats := StressTestStats{}
	localStats := StressTestStats{} // For periodic reporting

	reportTicker := time.NewTicker(1 * time.Second)
	defer reportTicker.Stop()

	for {
		select {
		case <-stopCh:
			statsCh <- stats
			return

		case <-reportTicker.C:
			// Report accumulated stats if there are any
			if localStats.TreesCreated > 0 {
				statsCh <- localStats
				// Reset local stats after reporting
				localStats = StressTestStats{}
			}

		default:
			// Do stress test work
			runSingleIteration(maxElements, maxElementSize, &stats, &localStats, quiet)
		}
	}
}

func runSingleIteration(maxElements, maxElementSize int, stats, localStats *StressTestStats, quiet bool) {
	// 1. Generate a random tree size
	treeSize := randomInt(1, maxElements)

	// 2. Create random elements
	elements := generateRandomElements(treeSize, maxElementSize)

	// 3. Occasionally include edge cases
	if randomInt(0, 5) == 0 {
		elements = incorporateEdgeCases(elements)
	}

	// 4. Create the Merkle tree
	tree, err := merkle.NewMerkleTree(elements)
	if err != nil {
		if !quiet {
			fmt.Printf("\nError creating tree: %v\n", err)
		}
		atomic.AddInt64(&stats.Errors, 1)
		atomic.AddInt64(&localStats.Errors, 1)
		return
	}
	atomic.AddInt64(&stats.TreesCreated, 1)
	atomic.AddInt64(&localStats.TreesCreated, 1)

	// 5. Test sequential proofs
	if err := testSequentialProofs(tree, stats, localStats); err != nil && !quiet {
		fmt.Printf("\nSequential proof error: %v\n", err)
	}

	// 6. Test index-based proofs
	if err := testIndexBasedProofs(tree, stats, localStats); err != nil && !quiet {
		fmt.Printf("\nIndex-based proof error: %v\n", err)
	}
}

func testSequentialProofs(tree *merkle.MerkleTree, stats, localStats *StressTestStats) error {
	elements := tree.Elements()
	elementCount := len(elements)

	// Test cases to cover edge cases and random scenarios
	testCases := []struct {
		startingIndex int
		count         int
	}{
		{0, 1}, // First element
	}

	// Add edge case: last element
	if elementCount > 1 {
		testCases = append(testCases, struct {
			startingIndex int
			count         int
		}{elementCount - 1, 1})
	}

	// Add edge case: all elements
	testCases = append(testCases, struct {
		startingIndex int
		count         int
	}{0, elementCount})

	// Add random ranges if there are enough elements
	if elementCount > 2 {
		// Random middle element
		startIdx := randomInt(1, elementCount-1)
		testCases = append(testCases, struct {
			startingIndex int
			count         int
		}{startIdx, 1})

		// Random range
		if elementCount > 3 {
			startIdx = randomInt(0, elementCount-2)
			count := randomInt(1, elementCount-startIdx)
			testCases = append(testCases, struct {
				startingIndex int
				count         int
			}{startIdx, count})
		}
	}

	// Execute all test cases
	for _, tc := range testCases {
		proof, err := tree.GenerateMultiProofSequential(tc.startingIndex, tc.count)
		if err != nil {
			atomic.AddInt64(&stats.Errors, 1)
			atomic.AddInt64(&localStats.Errors, 1)
			return fmt.Errorf("failed to generate sequential proof: %v", err)
		}
		atomic.AddInt64(&stats.ProofsGenerated, 1)
		atomic.AddInt64(&localStats.ProofsGenerated, 1)

		// Verify the proof
		valid, err := merkle.VerifyMultiProofSequential(proof)
		atomic.AddInt64(&stats.VerificationsRun, 1)
		atomic.AddInt64(&localStats.VerificationsRun, 1)
		if err != nil {
			atomic.AddInt64(&stats.Errors, 1)
			atomic.AddInt64(&localStats.Errors, 1)
			return fmt.Errorf("failed to verify sequential proof: %v", err)
		}
		if !valid {
			atomic.AddInt64(&stats.VerificationFailures, 1)
			atomic.AddInt64(&localStats.VerificationFailures, 1)
			return fmt.Errorf("sequential proof verification failed")
		}

		// Sanity check: Modify root and ensure verification fails
		if tc.count > 0 {
			invalidProof := *proof
			invalidProof.Root = bytes.Repeat([]byte{0xFF}, len(proof.Root))
			valid, _ = merkle.VerifyMultiProofSequential(&invalidProof)
			atomic.AddInt64(&stats.VerificationsRun, 1)
			atomic.AddInt64(&localStats.VerificationsRun, 1)
			if valid {
				atomic.AddInt64(&stats.VerificationFailures, 1)
				atomic.AddInt64(&localStats.VerificationFailures, 1)
				return fmt.Errorf("verification succeeded with invalid root")
			}
		}
	}

	return nil
}

func testIndexBasedProofs(tree *merkle.MerkleTree, stats, localStats *StressTestStats) error {
	elements := tree.Elements()
	elementCount := len(elements)

	// Test cases to cover edge cases and random scenarios
	testCases := []struct {
		indices []int
	}{
		{[]int{0}}, // First element
	}

	// Add edge case: last element
	if elementCount > 1 {
		testCases = append(testCases, struct {
			indices []int
		}{[]int{elementCount - 1}})
	}

	// Add edge case: all elements
	if elementCount > 0 {
		allIndices := make([]int, elementCount)
		for i := 0; i < elementCount; i++ {
			allIndices[i] = i
		}
		testCases = append(testCases, struct {
			indices []int
		}{allIndices})
	}

	// Add random selections if there are enough elements
	if elementCount > 2 {
		// Random middle element
		middleIdx := randomInt(1, elementCount-1)
		testCases = append(testCases, struct {
			indices []int
		}{[]int{middleIdx}})

		// Random set of elements (if there are enough elements)
		if elementCount > 3 {
			count := randomInt(2, (elementCount+1)/2)
			randomIndices := generateRandomIndices(elementCount, count)
			testCases = append(testCases, struct {
				indices []int
			}{randomIndices})
		}
	}

	// Execute all test cases
	for _, tc := range testCases {
		proof, err := tree.GenerateMultiProofWithIndices(tc.indices)
		if err != nil {
			atomic.AddInt64(&stats.Errors, 1)
			atomic.AddInt64(&localStats.Errors, 1)
			return fmt.Errorf("failed to generate index-based proof: %v", err)
		}
		atomic.AddInt64(&stats.ProofsGenerated, 1)
		atomic.AddInt64(&localStats.ProofsGenerated, 1)

		// Verify the proof
		valid, err := merkle.VerifyMultiProofWithIndices(proof)
		atomic.AddInt64(&stats.VerificationsRun, 1)
		atomic.AddInt64(&localStats.VerificationsRun, 1)
		if err != nil {
			atomic.AddInt64(&stats.Errors, 1)
			atomic.AddInt64(&localStats.Errors, 1)
			return fmt.Errorf("failed to verify index-based proof: %v", err)
		}
		if !valid {
			atomic.AddInt64(&stats.VerificationFailures, 1)
			atomic.AddInt64(&localStats.VerificationFailures, 1)
			return fmt.Errorf("index-based proof verification failed")
		}

		// Sanity check: Modify root and ensure verification fails
		if len(tc.indices) > 0 {
			invalidProof := *proof
			invalidProof.Root = bytes.Repeat([]byte{0xFF}, len(proof.Root))
			valid, _ = merkle.VerifyMultiProofWithIndices(&invalidProof)
			atomic.AddInt64(&stats.VerificationsRun, 1)
			atomic.AddInt64(&localStats.VerificationsRun, 1)
			if valid {
				atomic.AddInt64(&stats.VerificationFailures, 1)
				atomic.AddInt64(&localStats.VerificationFailures, 1)
				return fmt.Errorf("verification succeeded with invalid root")
			}
		}
	}

	return nil
}

// Helper functions from previous implementation

func generateRandomElements(count, maxSize int) [][]byte {
	result := make([][]byte, count)
	for i := 0; i < count; i++ {
		size := randomInt(1, maxSize)
		element := make([]byte, size)
		_, _ = rand.Read(element)
		result[i] = element
	}
	return result
}

func incorporateEdgeCases(elements [][]byte) [][]byte {
	result := make([][]byte, len(elements))
	copy(result, elements)

	// Randomly decide which edge cases to include
	switch randomInt(0, 4) {
	case 0:
		// Replace a random element with an empty slice
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			result[idx] = []byte{}
		}
	case 1:
		// Add duplicate elements
		if len(result) > 1 {
			srcIdx := randomInt(0, len(result)-1)
			dstIdx := (srcIdx + 1) % len(result)
			result[dstIdx] = make([]byte, len(result[srcIdx]))
			copy(result[dstIdx], result[srcIdx])
		}
	case 2:
		// Add a large element
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			largeElement := make([]byte, 1024*16) // 16KB
			_, _ = rand.Read(largeElement)
			result[idx] = largeElement
		}
	case 3:
		// Add a very small element
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			result[idx] = []byte{0x42}
		}
	}

	return result
}

func generateRandomIndices(max, count int) []int {
	if count > max {
		count = max
	}

	// Generate all possible indices
	indices := make([]int, max)
	for i := 0; i < max; i++ {
		indices[i] = i
	}

	// Shuffle using Fisher-Yates algorithm
	for i := max - 1; i > 0; i-- {
		j := randomInt(0, i)
		indices[i], indices[j] = indices[j], indices[i]
	}

	// Take the first 'count' indices
	return indices[:count]
}

func randomInt(min, max int) int {
	if min >= max {
		return min
	}
	n, _ := rand.Int(rand.Reader, big.NewInt(int64(max-min)))
	return int(n.Int64()) + min
}
```
</requirement> --&gt;

@mkysel I'll create a comprehensive stress test for the Merkle tree implementation. After examining the code, I've designed a stress test that will thoroughly exercise the implementation to find any potential edge cases or out-of-bounds errors.

The stress test will:

1. Generate trees of various sizes (from single element to thousands)
2. Test both sequential and index-based proofs
3. Include edge cases (empty elements, duplicates, large elements)
4. Verify all proofs for correctness
5. Run for a configurable duration to catch any memory leaks or concurrency issues

Another agent will come along to implement this plan. The stress test will include comprehensive reporting to help identify any potential issues.

---

⏳ Preparing changes...

</answer></rawResChunk> -->
author_association: CONTRIBUTOR
user: login: coderabbitai[bot]
created_at: 2025-04-11T20:24:15Z
body: <!-- This is an auto-generated reply by CodeRabbit -->
A summary of the edits CodeRabbit can apply:

> We are going to create a new stress test file at pkg/merkle/stress_test.go. This test will run for a configurable duration and continuously generate random Merkle trees with random data; for each tree, it will generate both sequential and index‐based proofs, verify them, and also deliberately modify proofs (by falsifying the root) to assert that improper proofs are rejected. The test will exercise various edge cases – such as empty elements, duplicate elements, very large or very small elements – and will keep track of iteration counts and any verification failures.



A plan of each step that CodeRabbit will take in order to execute the edits for each file (with inline rough draft snippets):

<details>
<summary>📄 pkg/merkle/stress_test.go</summary>

Place the package declaration and necessary imports at the top of the file:

<code>package merkle

import (
	"bytes"
	"crypto/rand"
	"fmt"
	"math/big"
	"testing"
	"time"
)
</code>

---

Define the main stress test function TestMerkleTreeStress. Within this function, configure parameters such as:
         - duration (e.g. 5 seconds)
         - maximum number of elements in a tree (e.g. 1000)
         - maximum element size (in bytes)
         - counters for iterations, tree count, proof count, verification count, and failure count.
        Use a loop that runs until the configurable duration has elapsed.

<code>func TestMerkleTreeStress(t *testing.T) {
	if testing.Short() {
		t.Skip("Skipping stress test in short mode")
	}

	// Configuration
	duration := 5 * time.Second
	maxElements := 1000
	maxElementSize := 1024
	iterations, treeCount, proofCount, verificationCount, failureCount := 0, 0, 0, 0, 0

	start := time.Now()
	deadline := start.Add(duration)

	t.Logf("Starting Merkle tree stress test for %v...", duration)

	for time.Now().Before(deadline) {
		iterations++
		// (Implementation continues…)
	}
	// Log final results (omitted for brevity)
}
</code>

---

Implement helper functions:
         - generateRandomElements: to create a slice of random byte slices.
         - incorporateEdgeCases: to sometimes inject an empty slice, duplicate elements, very large elements, or very small elements.
         - randomInt and generateRandomIndices: for randomness support.
        Wrap the code in appropriate

<code>func</code>

definitions.

---

Add two testing helper functions:
         - testSequentialProofs: which uses tree.GenerateMultiProofSequential and VerifyMultiProofSequential to generate and verify sequential proofs and performs a sanity check by modifying the root.
         - testIndexBasedProofs: which uses tree.GenerateMultiProofWithIndices and VerifyMultiProofWithIndices to generate and verify index‐based proofs, also including a sanity check for invalid roots.
        Make sure to update counters passed by pointer to capture the number of proofs and verification attempts.

---

At strategic points (for example, every 100 iterations) log the progress (iteration count, tree count, proof count, verifications, and failures) using t.Logf.

---

After the loop, log the total elapsed time and the final statistics. If any verification failures were encountered, call t.Errorf with an appropriate message.

---

Combine all the code segments, ensuring that all the helper functions are included in this new file. The final file should be pasted in its entirety under pkg/merkle/stress_test.go.

</details>



A summary of the context that CodeRabbit is considering across the codebase:

> We are verifying that the NewMerkleTree constructor exists in the codebase and is used by the stress test.

> We are confirming that the verification functions (VerifyMultiProofSequential and VerifyMultiProofWithIndices) exist and are implemented; these are essential for the stress test to properly validate generated proofs.

- [ ] <!-- {"checkboxId": "32599f3c-a2a5-4bb9-b887-dee90db62b97", "radioGroupId": "edit-actions-group-2797936525"} --> ✅ Create PR with these edits

- [ ] <!-- {"checkboxId": "6b3df8e2-79f5-4eb8-9d4a-c7d3a6a5f7b1", "radioGroupId": "edit-actions-group-2797936525"} --> 📋 Get copyable edits

- [ ] <!-- {"checkboxId": "85e7c9f1-3a23-4b8e-9f25-d7a5b234a8c1", "radioGroupId": "edit-actions-group-2797936525"} --> 📌 Create commit in current branch

- [ ] <!-- {"checkboxId": "1ff584df-7767-46fe-8b5b-0980b49c465f", "radioGroupId": "edit-actions-group-2797936525"} --> 🔄 Try a different approach

<!-- <agentComponentType>plan-edits</agentComponentType> -->

<!-- <rawResChunk><rationale>The user requested a stress test for the Merkle tree implementation, which requires creating a new test file specifically for this purpose. The existing files related to the Merkle tree (like tree.go and tree_test.go) will be referenced to ensure the stress test interacts correctly with the current implementation. The new stress_test.go file will contain the logic for generating trees, adding nodes, and verifying proofs as specified in the user's request.</rationale><toCreateFile>pkg/merkle/stress_test.go</toCreateFile></rawResChunk> -->

<!-- <rawResChunk><generated_script>
```shell
#!/bin/bash
# This script searches the repository for files and code patterns 
# that are likely to be relevant to implementing a random stress test for the Merkle tree.
# The stress test is expected to generate random trees, add nodes, and request proofs repeatedly,
# with a configurable duration to stress test edge cases and out-of-bound errors.

echo "────────────────────────────"
echo "1. Searching for files mentioning 'stress' (e.g., potential stress test files)"
rg -i "stress" -tgo

echo "────────────────────────────"
echo "2. Searching for benchmark functions (they can be used for performance or stress testing)"
rg -i "func Benchmark" -tgo

echo "────────────────────────────"
echo "3. Looking for configurable duration or timeout parameters (likely used for test durations)"
rg -i "duration" -tgo
rg -i "timeout" -tgo

echo "────────────────────────────"
echo "4. Searching for randomization keywords (e.g., generating random trees/nodes)"
rg -i "random" -tgo

echo "────────────────────────────"
echo "5. Searching for 'edge' conditions and index boundaries in the code"
rg -i "edge" -tgo

echo "────────────────────────────"
echo "6. Listing all test files within the Merkle tree package (likely candidates for integration with a stress test)"
fd "merkle" -e "go" | grep -i "test"

echo "────────────────────────────"
echo "7. Checking for a dedicated file that might be intended as a stress test (e.g., stress_test.go)"
fd -e go "^stress_test\.go$"

echo "────────────────────────────"
echo "8. Reviewing documentation files for hints on testing configurations"
fd -e md "^README\.md$"
```
</generated_script>

<rationale>
- **Search for "stress":** This command scans all Go files for the keyword “stress” to identify any files, comments, or functions already related to stress testing. Such information can guide the implementation of the random stress test.
- **Benchmark Functions:** By searching for "func Benchmark", we aim to locate any benchmark tests that might be used to simulate heavy loads. These files can show how the Merkle tree handles performance stress.
- **Duration/Timeout Searches:** The user request mentions a configurable duration for the stress test. Searching for keywords like “duration” and “timeout” may reveal configuration options or patterns that govern how long tests run.
- **Randomization Keywords:** The test involves generating random trees and nodes so scanning for “random” helps identify existing random data generation utilities or patterns.
- **Edge Conditions:** Looking for "edge" within the code helps uncover any already-handled boundary conditions, which are critical for a stress test targeting out-of-bound errors.
- **Test Files Listing:** Listing test files in the Merkle tree package (by filtering files with “test” in their names) provides insight into where unit tests are defined. These files (e.g., pkg/merkle/tree_test.go) may be extended or referred to in a new stress test.
- **Dedicated Stress Test File:** Searching for a file specifically named “stress_test.go” can reveal if a preliminary stress test already exists or if the new test should be created.
- **Documentation Files:** Lastly, checking README.md or similar documentation might reveal any testing guidelines or configuration notes relevant to the stress test.
</rationale></rawResChunk> -->

<!-- <rawResChunk>```xml
<fileAction>
  <fileActionSummary>
    We are going to create a new stress test file at pkg/merkle/stress_test.go. This test will run for a configurable duration and continuously generate random Merkle trees with random data; for each tree, it will generate both sequential and index‐based proofs, verify them, and also deliberately modify proofs (by falsifying the root) to assert that improper proofs are rejected. The test will exercise various edge cases – such as empty elements, duplicate elements, very large or very small elements – and will keep track of iteration counts and any verification failures.
  </fileActionSummary>
  <file_name>pkg/merkle/stress_test.go</file_name>
  <type>CreateNewFile</type>
  <start_line>1</start_line>
  <end_line>300</end_line>
  <steps>
    <step>
      <stepNumber>1</stepNumber>
      <generated_instruction>
        Place the package declaration and necessary imports at the top of the file:
        <code>package merkle

import (
	"bytes"
	"crypto/rand"
	"fmt"
	"math/big"
	"testing"
	"time"
)
</code>
      </generated_instruction>
    </step>
    <step>
      <stepNumber>2</stepNumber>
      <generated_instruction>
        Define the main stress test function TestMerkleTreeStress. Within this function, configure parameters such as:
         - duration (e.g. 5 seconds)
         - maximum number of elements in a tree (e.g. 1000)
         - maximum element size (in bytes)
         - counters for iterations, tree count, proof count, verification count, and failure count.
        Use a loop that runs until the configurable duration has elapsed.
        <code>func TestMerkleTreeStress(t *testing.T) {
	if testing.Short() {
		t.Skip("Skipping stress test in short mode")
	}

	// Configuration
	duration := 5 * time.Second
	maxElements := 1000
	maxElementSize := 1024
	iterations, treeCount, proofCount, verificationCount, failureCount := 0, 0, 0, 0, 0

	start := time.Now()
	deadline := start.Add(duration)

	t.Logf("Starting Merkle tree stress test for %v...", duration)

	for time.Now().Before(deadline) {
		iterations++
		// (Implementation continues…)
	}
	// Log final results (omitted for brevity)
}
</code>
      </generated_instruction>
    </step>
    <step>
      <stepNumber>3</stepNumber>
      <generated_instruction>
        Implement helper functions:
         - generateRandomElements: to create a slice of random byte slices.
         - incorporateEdgeCases: to sometimes inject an empty slice, duplicate elements, very large elements, or very small elements.
         - randomInt and generateRandomIndices: for randomness support.
        Wrap the code in appropriate <code>func</code> definitions.
      </generated_instruction>
    </step>
    <step>
      <stepNumber>4</stepNumber>
      <generated_instruction>
        Add two testing helper functions:
         - testSequentialProofs: which uses tree.GenerateMultiProofSequential and VerifyMultiProofSequential to generate and verify sequential proofs and performs a sanity check by modifying the root.
         - testIndexBasedProofs: which uses tree.GenerateMultiProofWithIndices and VerifyMultiProofWithIndices to generate and verify index‐based proofs, also including a sanity check for invalid roots.
        Make sure to update counters passed by pointer to capture the number of proofs and verification attempts.
      </generated_instruction>
    </step>
    <step>
      <stepNumber>5</stepNumber>
      <generated_instruction>
        At strategic points (for example, every 100 iterations) log the progress (iteration count, tree count, proof count, verifications, and failures) using t.Logf.
      </generated_instruction>
    </step>
    <step>
      <stepNumber>6</stepNumber>
      <generated_instruction>
        After the loop, log the total elapsed time and the final statistics. If any verification failures were encountered, call t.Errorf with an appropriate message.
      </generated_instruction>
    </step>
    <step>
      <stepNumber>7</stepNumber>
      <generated_instruction>
        Combine all the code segments, ensuring that all the helper functions are included in this new file. The final file should be pasted in its entirety under pkg/merkle/stress_test.go.
      </generated_instruction>
    </step>
  </steps>
  <code>
// pkg/merkle/stress_test.go
package merkle

import (
	"bytes"
	"crypto/rand"
	"fmt"
	"math/big"
	"testing"
	"time"
)

// TestMerkleTreeStress performs a stress test on the Merkle tree implementation.
// The test creates trees of random sizes, generates proofs, and verifies them.
// It runs for a configurable duration to catch potential memory leaks or concurrency issues.
func TestMerkleTreeStress(t *testing.T) {
	if testing.Short() {
		t.Skip("Skipping stress test in short mode")
	}

	// Configuration
	duration := 5 * time.Second
	maxElements := 1000
	maxElementSize := 1024
	iterations, treeCount, proofCount, verificationCount, failureCount := 0, 0, 0, 0, 0

	start := time.Now()
	deadline := start.Add(duration)

	t.Logf("Starting Merkle tree stress test for %v...", duration)

	for time.Now().Before(deadline) {
		iterations++

		// 1. Generate a random tree size (1 to maxElements)
		treeSize := randomInt(1, maxElements)

		// 2. Create random elements
		elements := generateRandomElements(treeSize, maxElementSize)

		// 3. Occasionally include edge cases
		if iterations%5 == 0 {
			elements = incorporateEdgeCases(elements)
		}

		// 4. Create the Merkle tree
		tree, err := NewMerkleTree(elements)
		if err != nil {
			t.Fatalf("Failed to create Merkle tree: %v", err)
		}
		treeCount++

		// 5. Test sequential proofs
		if err := testSequentialProofs(t, tree, &proofCount, &verificationCount, &failureCount); err != nil {
			t.Fatalf("Sequential proof test failed: %v", err)
		}

		// 6. Test index-based proofs
		if err := testIndexBasedProofs(t, tree, &proofCount, &verificationCount, &failureCount); err != nil {
			t.Fatalf("Index-based proof test failed: %v", err)
		}

		// 7. Occasionally log progress
		if iterations%100 == 0 {
			t.Logf("Progress: %d iterations, %d trees, %d proofs, %d verifications (%d failures)",
				iterations, treeCount, proofCount, verificationCount, failureCount)
		}
	}

	elapsed := time.Since(start)
	t.Logf("Stress test completed in %v", elapsed)
	t.Logf("Total iterations: %d", iterations)
	t.Logf("Trees created: %d", treeCount)
	t.Logf("Proofs generated: %d", proofCount)
	t.Logf("Verifications performed: %d", verificationCount)
	t.Logf("Verification failures: %d", failureCount)

	if failureCount > 0 {
		t.Errorf("Encountered %d verification failures during stress test", failureCount)
	}
}

// testSequentialProofs tests sequential proofs for the given tree.
func testSequentialProofs(t *testing.T, tree *MerkleTree, proofCount, verificationCount, failureCount *int) error {
	t.Helper()
	elements := tree.Elements()
	elementCount := len(elements)

	// Prepare test cases
	testCases := []struct {
		name          string
		startingIndex int
		count         int
	}{
		{"SingleElement", 0, 1},
	}

	// Add edge case for last element
	if elementCount > 1 {
		testCases = append(testCases, struct {
			name          string
			startingIndex int
			count         int
		}{"LastElement", elementCount - 1, 1})
	}

	// Add test for all elements
	testCases = append(testCases, struct {
		name          string
		startingIndex int
		count         int
	}{"AllElements", 0, elementCount})

	// Add random test cases if possible
	if elementCount > 2 {
		startIdx := randomInt(1, elementCount-1)
		testCases = append(testCases, struct {
			name          string
			startingIndex int
			count         int
		}{"RandomMiddleElement", startIdx, 1})

		if elementCount > 3 {
			startIdx = randomInt(0, elementCount-2)
			count := randomInt(1, elementCount-startIdx)
			testCases = append(testCases, struct {
				name          string
				startingIndex int
				count         int
			}{"RandomRange", startIdx, count})
		}
	}

	for _, tc := range testCases {
		proof, err := tree.GenerateMultiProofSequential(tc.startingIndex, tc.count)
		if err != nil {
			return fmt.Errorf("failed to generate sequential proof (%s): %v", tc.name, err)
		}
		(*proofCount)++

		valid, err := VerifyMultiProofSequential(proof)
		(*verificationCount)++
		if err != nil {
			return fmt.Errorf("failed to verify sequential proof (%s): %v", tc.name, err)
		}
		if !valid {
			(*failureCount)++
			return fmt.Errorf("sequential proof verification failed (%s)", tc.name)
		}

		// Sanity check: modify the proof to ensure verification failure
		if tc.count > 0 {
			invalidProof := *proof
			invalidProof.Root = bytes.Repeat([]byte{0xFF}, len(proof.Root))
			valid, _ = VerifyMultiProofSequential(&invalidProof)
			(*verificationCount)++
			if valid {
				(*failureCount)++
				return fmt.Errorf("verification succeeded with invalid root (%s)", tc.name)
			}
		}
	}
	return nil
}

// testIndexBasedProofs tests index-based proofs for the given tree.
func testIndexBasedProofs(t *testing.T, tree *MerkleTree, proofCount, verificationCount, failureCount *int) error {
	t.Helper()
	elements := tree.Elements()
	elementCount := len(elements)

	testCases := []struct {
		name    string
		indices []int
	}{
		{"FirstElement", []int{0}},
	}

	if elementCount > 1 {
		testCases = append(testCases, struct {
			name    string
			indices []int
		}{"LastElement", []int{elementCount - 1}})
	}

	if elementCount > 0 {
		allIndices := make([]int, elementCount)
		for i := 0; i < elementCount; i++ {
			allIndices[i] = i
		}
		testCases = append(testCases, struct {
			name    string
			indices []int
		}{"AllElements", allIndices})
	}

	if elementCount > 2 {
		middleIdx := randomInt(1, elementCount-1)
		testCases = append(testCases, struct {
			name    string
			indices []int
		}{"RandomMiddleElement", []int{middleIdx}})
		if elementCount > 3 {
			count := randomInt(2, (elementCount+1)/2)
			randomIndices := generateRandomIndices(elementCount, count)
			testCases = append(testCases, struct {
				name    string
				indices []int
			}{"RandomIndices", randomIndices})
		}
	}

	for _, tc := range testCases {
		proof, err := tree.GenerateMultiProofWithIndices(tc.indices)
		if err != nil {
			return fmt.Errorf("failed to generate index-based proof (%s): %v", tc.name, err)
		}
		(*proofCount)++

		valid, err := VerifyMultiProofWithIndices(proof)
		(*verificationCount)++
		if err != nil {
			return fmt.Errorf("failed to verify index-based proof (%s): %v", tc.name, err)
		}
		if !valid {
			(*failureCount)++
			return fmt.Errorf("index-based proof verification failed (%s)", tc.name)
		}

		if len(tc.indices) > 0 {
			invalidProof := *proof
			invalidProof.Root = bytes.Repeat([]byte{0xFF}, len(proof.Root))
			valid, _ = VerifyMultiProofWithIndices(&invalidProof)
			(*verificationCount)++
			if valid {
				(*failureCount)++
				return fmt.Errorf("verification succeeded with invalid root (%s)", tc.name)
			}
		}
	}
	return nil
}

// generateRandomElements creates a slice of random byte slices.
func generateRandomElements(count, maxSize int) [][]byte {
	result := make([][]byte, count)
	for i := 0; i < count; i++ {
		size := randomInt(1, maxSize)
		element := make([]byte, size)
		_, _ = rand.Read(element)
		result[i] = element
	}
	return result
}

// incorporateEdgeCases adds edge cases to the elements.
func incorporateEdgeCases(elements [][]byte) [][]byte {
	result := make([][]byte, len(elements))
	copy(result, elements)

	switch randomInt(0, 4) {
	case 0:
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			result[idx] = []byte{}
		}
	case 1:
		if len(result) > 1 {
			srcIdx := randomInt(0, len(result)-1)
			dstIdx := (srcIdx + 1) % len(result)
			result[dstIdx] = make([]byte, len(result[srcIdx]))
			copy(result[dstIdx], result[srcIdx])
		}
	case 2:
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			largeElement := make([]byte, 1024*1024) // 1MB
			_, _ = rand.Read(largeElement)
			result[idx] = largeElement
		}
	case 3:
		if len(result) > 0 {
			idx := randomInt(0, len(result)-1)
			result[idx] = []byte{0x42}
		}
	}
	return result
}

// generateRandomIndices creates a random set of unique indices.
func generateRandomIndices(max, count int) []int {
	if count > max {
		count = max
	}
	indices := make([]int, max)
	for i := 0; i < max; i++ {
		indices[i] = i
	}
	for i := max - 1; i > 0; i-- {
		j := randomInt(0, i)
		indices[i], indices[j] = indices[j], indices[i]
	}
	return indices[:count]
}

// randomInt returns a random integer in the range [min, max).
func randomInt(min, max int) int {
	if min >= max {
		return min
	}
	n, _ := rand.Int(rand.Reader, big.NewInt(int64(max-min)))
	return int(n.Int64()) + min
}
  </code>
</fileAction>

<context><rationale>
    We are verifying that the NewMerkleTree constructor exists in the codebase and is used by the stress test.
  </rationale>

<generated_script>
    ```shell
    rg "func NewMerkleTree" -C5
    ```
  </generated_script>

<shell_result>
    (Sample output indicating that NewMerkleTree is defined appropriately in the repository)
  </shell_result></context>

<context><rationale>
    We are confirming that the verification functions (VerifyMultiProofSequential and VerifyMultiProofWithIndices) exist and are implemented; these are essential for the stress test to properly validate generated proofs.
  </rationale>

<generated_script>
    ```shell
    rg "func VerifyMultiProofSequential" -C5
    rg "func VerifyMultiProofWithIndices" -C5
    ```
  </generated_script>

<shell_result>
    (Sample output showing the definitions of these verification functions in the codebase)
  </shell_result></context>
```</rawResChunk> -->
author_association: CONTRIBUTOR
user: login: mkysel
created_at: 2025-04-11T20:28:44Z
body: @coderabbitai here is a set of rules https://github.com/xmtp/xmtpd/blob/main/.cursor/rules/100-go-mistakes.mdc, you can also find them here https://100go.co/. Can you check this PR for any violations and if you find any, make relevant comments inline?
author_association: COLLABORATOR
user: login: coderabbitai[bot]
created_at: 2025-04-11T20:32:16Z
body: <!-- This is an auto-generated reply by CodeRabbit -->
> [!TIP]
> For best results, initiate chat on the files or code changes.

<details>
<summary>🧩 Analysis chain</summary>

🏁 Script executed:
```
#!/bin/bash
# First, fetch the Go mistakes rules document
echo "Fetching the Go mistakes rules document..."
curl -s https://raw.githubusercontent.com/xmtp/xmtpd/main/.cursor/rules/100-go-mistakes.mdc

# Now, get a list of all files modified in the PR to analyze them
echo -e "\n\nFiles in the PR to analyze:"
find pkg/merkle -type f -name "*.go" | sort
```

Length of output: 3534

---

🏁 Script executed:
```
#!/bin/bash
echo "Examining pkg/merkle/hash.go:"
cat pkg/merkle/hash.go
```

Length of output: 729

---

🏁 Script executed:
```
#!/bin/bash
echo "Examining pkg/merkle/proof.go:"
cat pkg/merkle/proof.go
```

Length of output: 4780

---

🏁 Script executed:
```
#!/bin/bash
echo "Examining pkg/merkle/proof_indices.go:"
cat pkg/merkle/proof_indices.go
```

Length of output: 6512

---

🏁 Script executed:
```
#!/bin/bash
echo "Examining pkg/merkle/proof_sequential.go:"
cat pkg/merkle/proof_sequential.go
```

Length of output: 6193

---

🏁 Script executed:
```
#!/bin/bash
echo "Examining pkg/merkle/tree.go:"
cat pkg/merkle/tree.go
```

Length of output: 3875

---

🏁 Script executed:
```
#!/bin/bash
echo "Examining pkg/merkle/tree_test.go:"
cat pkg/merkle/tree_test.go
```

Length of output: 8931

---

🏁 Script executed:
```
#!/bin/bash
# Now let's look for specific issues in the code based on the 100 Go Mistakes rules
echo "Checking for TODO comments (potential unfinished work):"
grep -n "TODO" pkg/merkle/*.go

echo -e "\nChecking for potentially complex functions (long functions):"
awk 'length($0) > 100' pkg/merkle/*.go | wc -l

echo -e "\nChecking for proper error handling patterns:"
grep -n "return.*error" pkg/merkle/*.go

echo -e "\nChecking for potential nil pointer dereferences:"
grep -n "if .* == nil" pkg/merkle/*.go
```

Length of output: 1982

---
</details>

@mkysel I've reviewed the PR against the 100 Go Mistakes rules and found a few issues that could be addressed:

1. **TODO Comments**:
   There are two TODO comments in the code that should be addressed before merging:
   - In both `proof_indices.go` and `proof_sequential.go`: 
     ```go
     // TODO: Abstract VerifyMultiProofSequential and VerifyMultiProofWithIndices to use a common function.
     ```
   This indicates potential code duplication that should be refactored.

2. **Error Handling**:
   In `hash.go`, the `Hash` function doesn't check the error returned by `hash.Write()`:
   ```go
   func Hash(buffer []byte) []byte {
       hash := sha3.NewLegacyKeccak256()
       hash.Write(buffer) // This can potentially return an error but it's not checked
       return hash.Sum(nil)
   }
   ```
   Although `hash.Write()` rarely fails for in-memory operations, it's a good practice to handle all potential errors, especially in cryptographic code.

3. **Complex Functions**:
   Some functions are quite complex with deep nesting and many local variables:
   - `getRootIndices` in `proof_indices.go`
   - `getRootSequentially` in `proof_sequential.go`
   
   Breaking these down into smaller, more focused functions would improve readability and maintainability.

4. **Variable Names**:
   In several places (like `proof.go`), there are short, non-descriptive variable names:
   ```go
   // Variables like "i", "idxs" could be more descriptive
   for i := leafCount - 1; i

> 0; i-- {
       leftChildIdx := getLeftChild(i)
       rightChildIdx := getRightChild(i)
       // ...
   }
   ```

5. **Function Naming Conventions**:
   Some functions like `getLeftChild` and `getRightChild` use the "get" prefix, which is not typical in Go. Functions are typically named without "get" (e.g., `leftChild` and `rightChild`).

6. **Constants Naming**:
   The constant `LEAF_PREFIX` is using uppercase with underscores, while Go's convention is to use MixedCaps:
   ```go
   // Should be: LeafPrefix instead of LEAF_PREFIX
   const LEAF_PREFIX = "leaf|"
   ```

7. **Potential Over-nesting in Control Flow**:
   There are instances of nested if statements that could be simplified:
   ```go
   // Example from proof.go - could be simplified
   if left != right {
       if right {
           if tree[leftChildIdx] != nil {
               proofs = append(proofs, cloneBuffer(tree[leftChildIdx]))
           }
       } else {
           if tree[rightChildIdx] != nil {
               proofs = append(proofs, cloneBuffer(tree[rightChildIdx]))
           }
       }
   }
   ```

Would you like more detailed comments on any of these particular issues?



<!-- <agentComponentType>chat-answer</agentComponentType> -->

<!-- <rawResChunk><answer><details>
<summary>🧩 Analysis chain</summary>

🏁 Script executed:
```
#!/bin/bash
# First, fetch the Go mistakes rules document
echo "Fetching the Go mistakes rules document..."
curl -s https://raw.githubusercontent.com/xmtp/xmtpd/main/.cursor/rules/100-go-mistakes.mdc

# Now, get a list of all files modified in the PR to analyze them
echo -e "\n\nFiles in the PR to analyze:"
find pkg/merkle -type f -name "*.go" | sort
```

Length of output: 3534

---

🏁 Script executed:
```
#!/bin/bash
echo "Examining pkg/merkle/hash.go:"
cat pkg/merkle/hash.go
```

Length of output: 729

---

🏁 Script executed:
```
#!/bin/bash
echo "Examining pkg/merkle/proof.go:"
cat pkg/merkle/proof.go
```

Length of output: 4780

---

🏁 Script executed:
```
#!/bin/bash
echo "Examining pkg/merkle/proof_indices.go:"
cat pkg/merkle/proof_indices.go
```

Length of output: 6512

---

🏁 Script executed:
```
#!/bin/bash
echo "Examining pkg/merkle/proof_sequential.go:"
cat pkg/merkle/proof_sequential.go
```

Length of output: 6193

---

🏁 Script executed:
```
#!/bin/bash
echo "Examining pkg/merkle/tree.go:"
cat pkg/merkle/tree.go
```

Length of output: 3875

---

🏁 Script executed:
```
#!/bin/bash
echo "Examining pkg/merkle/tree_test.go:"
cat pkg/merkle/tree_test.go
```

Length of output: 8931

---

🏁 Script executed:
```
#!/bin/bash
# Now let's look for specific issues in the code based on the 100 Go Mistakes rules
echo "Checking for TODO comments (potential unfinished work):"
grep -n "TODO" pkg/merkle/*.go

echo -e "\nChecking for potentially complex functions (long functions):"
awk 'length($0) > 100' pkg/merkle/*.go | wc -l

echo -e "\nChecking for proper error handling patterns:"
grep -n "return.*error" pkg/merkle/*.go

echo -e "\nChecking for potential nil pointer dereferences:"
grep -n "if .* == nil" pkg/merkle/*.go
```

Length of output: 1982

---



</details>

@mkysel I've reviewed the PR against the 100 Go Mistakes rules and found a few issues that could be addressed:

1. **TODO Comments**:
   There are two TODO comments in the code that should be addressed before merging:
   - In both `proof_indices.go` and `proof_sequential.go`: 
     ```go
     // TODO: Abstract VerifyMultiProofSequential and VerifyMultiProofWithIndices to use a common function.
     ```
   This indicates potential code duplication that should be refactored.

2. **Error Handling**:
   In `hash.go`, the `Hash` function doesn't check the error returned by `hash.Write()`:
   ```go
   func Hash(buffer []byte) []byte {
       hash := sha3.NewLegacyKeccak256()
       hash.Write(buffer) // This can potentially return an error but it's not checked
       return hash.Sum(nil)
   }
   ```
   Although `hash.Write()` rarely fails for in-memory operations, it's a good practice to handle all potential errors, especially in cryptographic code.

3. **Complex Functions**:
   Some functions are quite complex with deep nesting and many local variables:
   - `getRootIndices` in `proof_indices.go`
   - `getRootSequentially` in `proof_sequential.go`
   
   Breaking these down into smaller, more focused functions would improve readability and maintainability.

4. **Variable Names**:
   In several places (like `proof.go`), there are short, non-descriptive variable names:
   ```go
   // Variables like "i", "idxs" could be more descriptive
   for i := leafCount - 1; i > 0; i-- {
       leftChildIdx := getLeftChild(i)
       rightChildIdx := getRightChild(i)
       // ...
   }
   ```

5. **Function Naming Conventions**:
   Some functions like `getLeftChild` and `getRightChild` use the "get" prefix, which is not typical in Go. Functions are typically named without "get" (e.g., `leftChild` and `rightChild`).

6. **Constants Naming**:
   The constant `LEAF_PREFIX` is using uppercase with underscores, while Go's convention is to use MixedCaps:
   ```go
   // Should be: LeafPrefix instead of LEAF_PREFIX
   const LEAF_PREFIX = "leaf|"
   ```

7. **Potential Over-nesting in Control Flow**:
   There are instances of nested if statements that could be simplified:
   ```go
   // Example from proof.go - could be simplified
   if left != right {
       if right {
           if tree[leftChildIdx] != nil {
               proofs = append(proofs, cloneBuffer(tree[leftChildIdx]))
           }
       } else {
           if tree[rightChildIdx] != nil {
               proofs = append(proofs, cloneBuffer(tree[rightChildIdx]))
           }
       }
   }
   ```

Would you like more detailed comments on any of these particular issues?</answer></rawResChunk> -->
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-11T22:08:58Z
body: ### Changes in dcc177c

- Refactored `merkle` package tree indexing from 0-based to 1-based indexing, moving root to index 1, internal nodes to indices 2-N, leaves to indices N+1 to 2N-1, and adding `Tree()` and `LeafCount()` accessor methods
- Implemented centralized proof verification in `merkle` package with new `verifyProof` function and error constants `ErrProofEmptyTree` and `ErrProofEmptyIndices`
- Modified proof generation in `merkle` package to accept explicit root parameter and improved error handling in `generateProof`, `GenerateMultiProofWithIndices`, and `GenerateMultiProofSequential` functions


----

_[Macroscope](https://app.macroscope.com) summarized dcc177c._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-11T22:11:37Z
body: ### Changes in a252245

- Reimplemented `merkle.getDepth` function to use bit manipulation with `bits.Len32` instead of floating-point math operations, handling edge cases for values ≤ 1 and non-power-of-2 inputs
- Modified `merkle.getDepth` function signature to accept `uint32` parameter and updated corresponding call in `merkle.buildTree`


----

_[Macroscope](https://app.macroscope.com) summarized a252245._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-11T22:53:25Z
body: ### Changes in a4b966f

- Added standardized error handling in `merkle` package by introducing eight new error variables and replacing `fmt.Errorf` calls with these predefined errors across proof validation functions
- Exposed internal tree navigation functions in `merkle` package by making `getLeafCount`, `getLeftChild`, and `getRightChild` public and converting test package to external `merkle_test`
- Modified `merkle` package proof generation functions to consistently use proof object properties instead of local variables for indices and element counts
- Removed unused imports and renamed parameters in `merkle` package


----

_[Macroscope](https://app.macroscope.com) summarized a4b966f._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-11T22:56:25Z
body: ### Implement Merkle tree data structure with proof verification in `pkg/merkle` package
* Adds core Merkle tree implementation in [tree.go](https://github.com/xmtp/xmtpd/pull/712/files#diff-4a0ec8af27f891e4481136ec6a06b2eea6423d8992b8ea8c5c14d841b05b4d9a) with 1-indexed array representation and methods for tree creation and proof generation
* Implements Keccak-256 hashing functions in [hash.go](https://github.com/xmtp/xmtpd/pull/712/files#diff-4381bdd78bb0be4de1b1e9d2b8a01153fb880ab9a8ac307d30baaa3307ccd38d) for leaf and node operations
* Creates `MultiProof` verification system in [proof.go](https://github.com/xmtp/xmtpd/pull/712/files#diff-c26afbea2e9b24a09656eaec6e2b648112cb8cf19fc1d0405b9f686e6530397d) for validating multiple elements against a tree root
* Includes comprehensive test suites in [tree_test.go](https://github.com/xmtp/xmtpd/pull/712/files#diff-aa27c0aa647f6683e3d149d6596a81a4837849a512296c4f6419f26e088a8c7d) and [proof_test.go](https://github.com/xmtp/xmtpd/pull/712/files#diff-cfbdb4b5ff23d147c944f1ad21ba263df19911f82ad2a968d68cdc586c4b5e9a) covering various tree configurations and edge cases

#### 📍Where to Start
Start with the `NewMerkleTree` function in [tree.go](https://github.com/xmtp/xmtpd/pull/712/files#diff-4a0ec8af27f891e4481136ec6a06b2eea6423d8992b8ea8c5c14d841b05b4d9a) which serves as the main entry point for creating Merkle trees and demonstrates the core data structure design.

----

_[Macroscope](https://app.macroscope.com) summarized 439d038._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-11T23:30:24Z
body: ### Changes in 7cdbc70

- Refactored `merkle` package proof verification to use `NewMerkleTree` instead of custom combining logic, standardized 'leaves' terminology, and improved single-element tree handling
- Added zero element count handling in `merkle` package `GetLeafCount` function
- Updated documentation in `merkle` package proof-related functions


----

_[Macroscope](https://app.macroscope.com) summarized 7cdbc70._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-12T17:23:46Z
body: ### Changes in 77602fe

- Refactored error handling and validation in `merkle` package by introducing `validateIndices` function, wrapping errors with context in `generateProof`, and removing `ErrInputDuplicateIndices` and `ErrInputIndicesOutOfBounds` error variables
- Renamed `validateProofBase` to `validateProof` in `merkle` package, updating all references in `validateProofIndices` and `validateProofSequential` functions
- Reorganized code structure in `merkle` package by consolidating variable declarations and removing duplicate validation checks


----

_[Macroscope](https://app.macroscope.com) summarized 77602fe._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-12T17:39:22Z
body: ### Changes in 75847c0

- Added new error types `ErrTreeEmpty`, `ErrTreeRootNil`, and `ErrProofNilRoot` to `merkle` package, implementing error wrapping with contextual messages for proof verification and tree creation operations
- Refactored `merkle` package tree creation by extracting leaf generation into `makeLeaves` function and tree building into `makeTree` function, adding error handling to both operations
- Removed depth tracking functionality from `merkle.MerkleTree` struct, including the `Depth()` method and associated test assertions


----

_[Macroscope](https://app.macroscope.com) summarized 75847c0._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-12T19:57:20Z
body: ### Changes in 84795e7

- Consolidated `merkle` package proof-related functionality by merging `proof_indices.go` and `proof_sequential.go` into `proof.go`, removing `StartingIndex` field from `MultiProof` struct
- Added `MerkleTree.GenerateMultiProofSequential` and `MerkleTree.GenerateMultiProofWithIndices` methods, replaced multiple verification functions with unified `VerifyProof` function in `merkle` package
- Modified proof validation logic in `merkle` package by updating `validateProof`, `validateIndices`, and `hasDuplicates` functions to handle sorted indices and implement streamlined root computation


----

_[Macroscope](https://app.macroscope.com) summarized 84795e7._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-14T12:31:33Z
body: ### Changes in 88f6e99

- Refactored `merkle` package proof implementation by renaming `MultiProof.ElementCount` to `LeafCount`, reorganizing error variables, adding `makeIndices` helper function, improving validation in `validateProof`, and renaming core functions including `generateProof` to `makeProof` and `getRoot` to `computeRoot`
- Modified `merkle` package tree implementation to add deep copying of input elements in `NewMerkleTree` and renamed `GetLeafCount` to `CalculateBalancedLeafCount`
- Updated `merkle` package test references from `GetLeafCount` to `CalculateBalancedLeafCount`


----

_[Macroscope](https://app.macroscope.com) summarized 88f6e99._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-14T12:56:13Z
body: ### Changes in d665639

- Added error formatting constants `ErrGenerateProof` and `ErrVerifyProof` in `merkle` package for standardizing proof-related error messages
- Renamed error variables in `merkle` package by removing 'Proof' prefix, fixing typo in `ErrProodIndicesDuplicated`, and adding new `ErrNilElement` error
- Modified `merkle.makeProof`, `merkle.VerifyProof`, and `merkle.validateProof` functions to use new error constants and improve variable naming


----

_[Macroscope](https://app.macroscope.com) summarized d665639._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-15T10:57:52Z
body: ### Changes in 314d211

- Removed `root` field and `Root()` method from `merkle.MultiProof` type
- Modified `merkle.Verify` function to accept root parameter and updated related validation logic


----

_[Macroscope](https://app.macroscope.com) summarized 314d211._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-15T11:16:09Z
body: ### Changes in 6548572

- Relocated `makeProof` function from standalone to `MerkleTree.makeProof()` method in `merkle` package, adding validation for indexed values count and integrating with `GenerateMultiProofSequential` and `GenerateMultiProofWithIndices` methods
- Updated documentation in `merkle` package to clarify `MultiProof.Verify()` and `MultiProof.computeRoot()` methods' functionality regarding tree root verification and reconstruction
- Removed redundant comments and standardized documentation formatting in `merkle` package


----

_[Macroscope](https://app.macroscope.com) summarized 6548572._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-16T10:32:49Z
body: ### Changes in 0b2e41c

- Added node prefix functionality to `merkle` package's hash computation, introducing `NODE_PREFIX` constant and modifying `HashNode` function to prepend `node|` prefix when computing internal node hashes
- Optimized hash computation in `merkle` package by pre-computing prefix byte slices and using pre-allocated buffers with `make()` and `copy()` instead of `append()`


----

_[Macroscope](https://app.macroscope.com) summarized 0b2e41c._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-16T11:28:05Z
body: ### Changes in 1c9ae32

- Added size validation to `merkle` package by introducing `TREE_MAX_LEAVES` constant (4096), `ErrTreeTooLarge` and `ErrTreeLeavesOverflow` errors, and size validation in `NewMerkleTree` function
- Modified error handling in `merkle` package's `MultiProof.computeRoot` and `CalculateBalancedLeafCount` functions to properly handle and propagate errors
- Added test cases for `merkle` package's `roundUpToPowerOf2` and `CalculateBalancedLeafCount` functions, updated existing tests to handle new error returns


----

_[Macroscope](https://app.macroscope.com) summarized 1c9ae32._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-16T15:50:59Z
body: ### Changes in 4350fd4

- Introduced new core types in `merkle` package including `Node` struct with `Hash()` and `IsNil()` methods, `Leaf` type as `[]byte`, `Proof` type as `[]byte`, `IndexedValues`, and `IndexedValue`
- Refactored `merkle.MerkleTree` struct to compute root and leaf count on demand, removed stored fields, renamed `elements` to `leaves`, and changed internal `tree` type from `[][]byte` to `[]Node`
- Modified `merkle.MultiProof` struct to remove getter methods and use direct field access with new `IndexedValues` and `Proof` types
- Updated test suite to use new type system, replacing byte slice operations with `Node.Hash()` and `Node.IsNil()` method calls


----

_[Macroscope](https://app.macroscope.com) summarized 4350fd4._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-16T19:42:46Z
body: ### Changes in 79f8c12

- Rewrote `merkle.Proof.computeRoot()` method implementation
- Renamed and inverted `merkle.Proof.isOddIndex()` method
- Reorganized code structure and documentation in `merkle` package


----

_[Macroscope](https://app.macroscope.com) summarized 79f8c12._
author_association: CONTRIBUTOR
user: login: macroscopeapp[bot]
created_at: 2025-04-17T11:29:24Z
body: ### Changes in 1371d83

- Restructured `merkle` package proof system
- Modified `merkle` package tree implementation
- Added test suite to `merkle` package
- Updated `merkle` package API and documentation


----

_[Macroscope](https://app.macroscope.com) summarized 1371d83._
author_association: CONTRIBUTOR
user: login: mkysel
created_at: 2025-04-17T15:50:20Z
body: I've been trying to figure out where a malicious actor can inject payloads. It's hard to reason about because so many functions are exposed (public). I assume you have done that because I suggested to have the tests live in their own package and test the externally exposed functionality. 

Can you explain what the entry points are? The two MultiProof functions?

We could always formalize that by using an `interface`.
author_association: COLLABORATOR
user: login: macroscopeapp[bot]
created_at: 2025-04-21T11:18:27Z
body: ### Changes in d34a3eb

- Modified error handling in `merkle` package
- Renamed tree construction function in `merkle` package


----

_[Macroscope](https://app.macroscope.com) summarized d34a3eb._
author_association: CONTRIBUTOR
user: login: fbac
created_at: 2025-04-21T12:01:01Z
body: > I've been trying to figure out where a malicious actor can inject payloads. It's hard to reason about because so many functions are exposed (public). I assume you have done that because I suggested to have the tests live in their own package and test the externally exposed functionality.
> 
> Can you explain what the entry points are? The two MultiProof functions?
> 
> We could always formalize that by using an `interface`.

This package aims to be a generic Merkle Tree implementation, in our case it means some limits should be enforced in the xmtpd main logic consuming this pkg.

The entrypoints are:

`NewMerkleTree(leaves []Leaf) (*MerkleTree, error)` returns a new MerkleTree struct.

Takes an arbitrary amount of leaves, the package only forces a positive amount of them. Ideally the consumer also forces a maximum amount of leaves, depending on the use case. It would make sense for our payer service constructing the tree to have a max size.

A `MerkleTree` is of type:

```
type MerkleTree struct {
	tree   []Node
	leaves []Leaf
}
```

- The `Node` only has a field `[]byte`. They're computed by the pkg using keccak.
- Leaf is just a type alias for `[]byte`. They're provided by the user and can be of arbitrary length, depending on how the consumer creates the data. Our use case is `append(address, amount)`.
- I believe some malicious actor could alter the tree by getting the `tree []Node` slice with `merkle.Tree()`, which would be possible in go because slices are reference values. But then, as `Verify` requires the original root the new data injected would not be verified. Anyway, this can be solved by just returning a copy of the slices in those specific methods.

`Verify(root []byte, proof *MultiProof) (bool, error)` verifies a MultiProof.

A `MultiProof` is of type:
```
type MultiProof struct {
	values    IndexedValues
	proofs    []Node
	leafCount int
}
```

- The root could be enforced to be `[32]byte`, as we're using keccak256. In the end, all the hashes used by the pkg could be typed as `[32]byte`. Happy to do it.
- A malicious actor could, again, alter a MultiProof, by altering the specific slices returned by the accessor methods... but then again those values won't verify against the original provided root.

MerkleTree methods:
- `GenerateMultiProofSequential(startingIndex, count int) (*MultiProof, error)`
- `GenerateMultiProofWithIndices(indices []int) (*MultiProof, error)`

This are only used to generate a `MultiProof` and will fail if indices or provided integers are invalid when compared to the tree.

Utility functions - I don't see any injection possibilities here:
- `CalculateBalancedNodesCount(count int) (int, error)`
- `GetLeftChild(index int) int`
- `GetRightChild(index int) int`

Interesting action items:
- Fix node hashes as `[32]byte`.
- Test which builds a merkle tree, alter values and tries to verify them.
- Test which builds a merkle tree, creates a proof and alter its, and tries to verify it.
- Random / fuzz testing.

@mkysel @neekolas any other suggestion here to harden the package?

For the sake of legibility I'll work on those in a separate PR. :)
author_association: COLLABORATOR