Repository: segmentio/parquet-go (go)
Issue: Panic (nil deref) when creating NewGenericBuffer[any]
As the title states, the library panics with a nil pointer panic when you attempt to create a GenericBuffer with `[any]` as the type.

Minimal example code:
```go
package main

import (
	parquet "github.com/segmentio/parquet-go"
)

func main() {
	parquet.NewGenericBuffer[any]()
}
```

Output:
```
 # ./parquet-panic 
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x98 pc=0x6cf1fc]

goroutine 1 [running]:
github.com/segmentio/parquet-go.dereference({0x0?, 0x0?})
	/go/pkg/mod/github.com/segmentio/parquet-go@v0.0.0-20220914210246-f80ef85197ed/schema.go:138 +0x3c
github.com/segmentio/parquet-go.NewGenericBuffer[...]({0x0, 0x722b60?, 0xc0000061a0?})
	/go/pkg/mod/github.com/segmentio/parquet-go@v0.0.0-20220914210246-f80ef85197ed/buffer_go18.go:37 +0x85
main.main()
	/parquet-panic/main.go:8 +0x27
```

According to the docs both `NewGenericBuffer`  _should_ work with `any` as the type parameter. Note that `NewGenericWriter[any]` fails in the same manner.
Pull request description: fix issue 343
Fixes #343 

Patch:
diff --git a/buffer_go18.go b/buffer_go18.go
index e393928..c073abf 100644
--- a/buffer_go18.go
+++ b/buffer_go18.go
@@ -33,7 +33,7 @@ func NewGenericBuffer[T any](options ...RowGroupOption) *GenericBuffer[T] {
 	}
 
 	t := typeOf[T]()
-	if config.Schema == nil {
+	if config.Schema == nil && t != nil {
 		config.Schema = schemaOf(dereference(t))
 	}
 
@@ -53,6 +53,9 @@ func typeOf[T any]() reflect.Type {
 type bufferFunc[T any] func(*GenericBuffer[T], []T) (int, error)
 
 func bufferFuncOf[T any](t reflect.Type, schema *Schema) bufferFunc[T] {
+	if t == nil {
+		return (*GenericBuffer[T]).writeRows
+	}
 	switch t.Kind() {
 	case reflect.Interface, reflect.Map:
 		return (*GenericBuffer[T]).writeRows
diff --git a/column.go b/column.go
index 8bb840a..08ccfba 100644
--- a/column.go
+++ b/column.go
@@ -561,24 +561,39 @@ func (c *Column) decodeDataPageV2(header DataPageHeaderV2, page *buffer, dict Di
 	var repetitionLevels *buffer
 	var definitionLevels *buffer
 
-	if c.maxRepetitionLevel > 0 {
-		encoding := lookupLevelEncoding(header.RepetitionLevelEncoding(), c.maxRepetitionLevel)
-		length := header.RepetitionLevelsByteLength()
-		repetitionLevels, pageData, err = decodeLevelsV2(encoding, numValues, pageData, length)
+	if length := header.RepetitionLevelsByteLength(); length > 0 {
+		if c.maxRepetitionLevel == 0 {
+			// In some cases we've observed files which have a non-zero
+			// repetition level despite the column not being repeated
+			// (nor nested within a repeated column).
+			//
+			// See https://github.com/apache/parquet-testing/pull/24
+			pageData, err = skipLevelsV2(pageData, length)
+		} else {
+			encoding := lookupLevelEncoding(header.RepetitionLevelEncoding(), c.maxRepetitionLevel)
+			repetitionLevels, pageData, err = decodeLevelsV2(encoding, numValues, pageData, length)
+		}
 		if err != nil {
 			return nil, fmt.Errorf("decoding repetition levels of data page v2: %w", io.ErrUnexpectedEOF)
 		}
-		defer repetitionLevels.unref()
+		if repetitionLevels != nil {
+			defer repetitionLevels.unref()
+		}
 	}
 
-	if c.maxDefinitionLevel > 0 {
-		encoding := lookupLevelEncoding(header.DefinitionLevelEncoding(), c.maxDefinitionLevel)
-		length := header.DefinitionLevelsByteLength()
-		definitionLevels, pageData, err = decodeLevelsV2(encoding, numValues, pageData, length)
+	if length := header.DefinitionLevelsByteLength(); length > 0 {
+		if c.maxDefinitionLevel == 0 {
+			pageData, err = skipLevelsV2(pageData, length)
+		} else {
+			encoding := lookupLevelEncoding(header.DefinitionLevelEncoding(), c.maxDefinitionLevel)
+			definitionLevels, pageData, err = decodeLevelsV2(encoding, numValues, pageData, length)
+		}
 		if err != nil {
 			return nil, fmt.Errorf("decoding definition levels of data page v2: %w", io.ErrUnexpectedEOF)
 		}
-		defer definitionLevels.unref()
+		if definitionLevels != nil {
+			defer definitionLevels.unref()
+		}
 	}
 
 	if isCompressed(c.compression) && header.IsCompressed() {
@@ -687,9 +702,6 @@ func decodeLevelsV1(enc encoding.Encoding, numValues int, data []byte) (*buffer,
 }
 
 func decodeLevelsV2(enc encoding.Encoding, numValues int, data []byte, length int64) (*buffer, []byte, error) {
-	if length > int64(len(data)) {
-		return nil, data, io.ErrUnexpectedEOF
-	}
 	levels, err := decodeLevels(enc, numValues, data[:length])
 	return levels, data[length:], err
 }
@@ -711,6 +723,13 @@ func decodeLevels(enc encoding.Encoding, numValues int, data []byte) (levels *bu
 	return levels, err
 }
 
+func skipLevelsV2(data []byte, length int64) ([]byte, error) {
+	if length >= int64(len(data)) {
+		return data, io.ErrUnexpectedEOF
+	}
+	return data[length:], nil
+}
+
 // DecodeDictionary decodes a data page from the header and compressed data
 // passed as arguments.
 func (c *Column) DecodeDictionary(header DictionaryPageHeader, page []byte) (Dictionary, error) {
diff --git a/file.go b/file.go
index 117a26f..846b912 100644
--- a/file.go
+++ b/file.go
@@ -696,6 +696,7 @@ func (f *filePages) Close() error {
 	f.chunk = nil
 	f.section = io.SectionReader{}
 	f.rbuf = nil
+	f.rbufpool = nil
 	f.baseOffset = 0
 	f.dataOffset = 0
 	f.dictOffset = 0
diff --git a/go.mod b/go.mod
index 54551e2..9804d55 100644
--- a/go.mod
+++ b/go.mod
@@ -6,7 +6,7 @@ require (
 	github.com/andybalholm/brotli v1.0.3
 	github.com/google/uuid v1.3.0
 	github.com/hexops/gotextdiff v1.0.3
-	github.com/klauspost/compress v1.15.5
+	github.com/klauspost/compress v1.15.9
 	github.com/olekukonko/tablewriter v0.0.5
 	github.com/pierrec/lz4/v4 v4.1.9
 	github.com/segmentio/encoding v0.3.5
diff --git a/go.sum b/go.sum
index dd857c4..5109074 100644
--- a/go.sum
+++ b/go.sum
@@ -4,8 +4,8 @@ github.com/google/uuid v1.3.0 h1:t6JiXgmwXMjEs8VusXIJk2BXHsn+wx8BZdTaoZ5fu7I=
 github.com/google/uuid v1.3.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/hexops/gotextdiff v1.0.3 h1:gitA9+qJrrTCsiCl7+kh75nPqQt1cx4ZkudSTLoUqJM=
 github.com/hexops/gotextdiff v1.0.3/go.mod h1:pSWU5MAI3yDq+fZBTazCSJysOMbxWL1BSow5/V2vxeg=
-github.com/klauspost/compress v1.15.5 h1:qyCLMz2JCrKADihKOh9FxnW3houKeNsp2h5OEz0QSEA=
-github.com/klauspost/compress v1.15.5/go.mod h1:PhcZ0MbTNciWF3rruxRgKxI5NkcHHrHUDtV4Yw2GlzU=
+github.com/klauspost/compress v1.15.9 h1:wKRjX6JRtDdrE9qwa4b/Cip7ACOshUI4smpCQanqjSY=
+github.com/klauspost/compress v1.15.9/go.mod h1:PhcZ0MbTNciWF3rruxRgKxI5NkcHHrHUDtV4Yw2GlzU=
 github.com/mattn/go-runewidth v0.0.9 h1:Lm995f3rfxdpd6TSmuVCHVb/QhupuXlYr8sCI/QdE+0=
 github.com/mattn/go-runewidth v0.0.9/go.mod h1:H031xJmbD/WCDINGzjvQ9THkh0rPKHF+m2gUSrubnMI=
 github.com/olekukonko/tablewriter v0.0.5 h1:P2Ga83D34wi1o9J6Wh1mRuqd4mF/x/lgBS7N7AbDhec=
diff --git a/internal/debug/debug.go b/internal/debug/debug.go
index a527ae6..bc6419c 100644
--- a/internal/debug/debug.go
+++ b/internal/debug/debug.go
@@ -1,6 +1,7 @@
 package debug
 
 import (
+	"encoding/hex"
 	"fmt"
 	"io"
 )
@@ -19,7 +20,7 @@ type ioReaderAt struct {
 
 func (d *ioReaderAt) ReadAt(b []byte, off int64) (int, error) {
 	n, err := d.reader.ReadAt(b, off)
-	fmt.Printf("%s: Read(%d) @%d => %d %v \n  %q\n", d.prefix, len(b), off, n, err, b[:n])
+	fmt.Printf("%s: Read(%d) @%d => %d %v \n%s\n", d.prefix, len(b), off, n, err, hex.Dump(b[:n]))
 	return n, err
 }
 
@@ -38,7 +39,7 @@ type ioReader struct {
 
 func (d *ioReader) Read(b []byte) (int, error) {
 	n, err := d.reader.Read(b)
-	fmt.Printf("%s: Read(%d) @%d => %d %v \n  %q\n", d.prefix, len(b), d.offset, n, err, b[:n])
+	fmt.Printf("%s: Read(%d) @%d => %d %v \n%s\n", d.prefix, len(b), d.offset, n, err, hex.Dump(b[:n]))
 	d.offset += int64(n)
 	return n, err
 }


Test patch:
diff --git a/buffer_go18_test.go b/buffer_go18_test.go
index 51e08bf..9a9548a 100644
--- a/buffer_go18_test.go
+++ b/buffer_go18_test.go
@@ -181,3 +181,8 @@ func TestIssue327(t *testing.T) {
 		_ = parquet.NewGenericBuffer[testType]()
 	})
 }
+
+func TestIssue343(t *testing.T) {
+	// must not panic
+	_ = parquet.NewGenericBuffer[any]()
+}