Repository: fxamacker/cbor (go)

Issue:
bug: prevent decoding other CBOR types to `cbor.SimpleValue`
Currently, decoder can decode CBOR integers (not CBOR simple value) to `cbor.SimpleValue`.  However, CBOR simple value (major type 7) is different from integers and shouldn't be used interchangeably.

Fix this by only allowing CBOR simple values (major type 7) to be decoded to `cbor.SimpleValue`.

Pull request description:
Fix cbor.SimpleValue encoding and decoding
Closes #462 #463

1.  Encoding `cbor.SimpleValue` with values 24..31 should fail because CBOR simple values 24..31 are reserved and they MUST NOT be encoded according to RFC 8949.

    This PR makes encoder return `UnsupportedValueError` when encoding `cbor.SimpleValue` with values 24..31 because that would not be a well-formed CBOR data item.

2. Decoding other CBOR types to `cbor.SimpleValue` should fail because `cbor.SimpleValue` represents CBOR simple value (major type 7) which is different from CBOR integers and shouldn't be used interchangeably.

    This PR makes decoder return `UnmarshalTypeError` when decoding other CBOR types to `cbor.SimpleValue`.


Patch:
diff --git a/decode.go b/decode.go
index 6102de6..ffb62e8 100644
--- a/decode.go
+++ b/decode.go
@@ -1002,11 +1002,6 @@ func (d *decoder) parseToValue(v reflect.Value, tInfo *typeInfo) error { //nolin
 			f := math.Float64frombits(val)
 			return fillFloat(t, f, v)
 		default: // ai <= 24
-			// Decode simple values (including false, true, null, and undefined)
-			if tInfo.nonPtrType == typeSimpleValue {
-				v.SetUint(val)
-				return nil
-			}
 			switch ai {
 			case 20, 21:
 				return fillBool(t, ai == 21, v)
diff --git a/encode.go b/encode.go
index f329f5d..d762ebb 100644
--- a/encode.go
+++ b/encode.go
@@ -110,6 +110,16 @@ func (e *UnsupportedTypeError) Error() string {
 	return "cbor: unsupported type: " + e.Type.String()
 }
 
+// UnsupportedValueError is returned by Marshal when attempting to encode an
+// unsupported value.
+type UnsupportedValueError struct {
+	msg string
+}
+
+func (e *UnsupportedValueError) Error() string {
+	return "cbor: unsupported value: " + e.msg
+}
+
 // SortMode identifies supported sorting order.
 type SortMode int
 
@@ -1269,14 +1279,6 @@ func encodeTag(e *encoderBuffer, em *encMode, v reflect.Value) error {
 	return encode(e, em, reflect.ValueOf(t.Content))
 }
 
-func encodeSimpleValue(e *encoderBuffer, em *encMode, v reflect.Value) error {
-	if b := em.encTagBytes(v.Type()); b != nil {
-		e.Write(b)
-	}
-	encodeHead(e, byte(cborTypePrimitives), v.Uint())
-	return nil
-}
-
 func encodeHead(e *encoderBuffer, t byte, n uint64) {
 	if n <= 23 {
 		e.WriteByte(t | byte(n))
@@ -1319,7 +1321,7 @@ func getEncodeFuncInternal(t reflect.Type) (encodeFunc, isEmptyFunc) {
 	}
 	switch t {
 	case typeSimpleValue:
-		return encodeSimpleValue, isEmptyUint
+		return encodeMarshalerType, isEmptyUint
 	case typeTag:
 		return encodeTag, alwaysNotEmpty
 	case typeTime:
diff --git a/simplevalue.go b/simplevalue.go
index 14fd147..6f93f67 100644
--- a/simplevalue.go
+++ b/simplevalue.go
@@ -1,6 +1,10 @@
 package cbor
 
-import "reflect"
+import (
+	"errors"
+	"fmt"
+	"reflect"
+)
 
 // SimpleValue represents CBOR simple value.
 // CBOR simple value is:
@@ -16,3 +20,50 @@ type SimpleValue uint8
 var (
 	typeSimpleValue = reflect.TypeOf(SimpleValue(0))
 )
+
+// MarshalCBOR encodes SimpleValue as CBOR simple value (major type 7).
+func (sv SimpleValue) MarshalCBOR() ([]byte, error) {
+	// RFC 8949 3.3. Floating-Point Numbers and Values with No Content says:
+	// "An encoder MUST NOT issue two-byte sequences that start with 0xf8
+	// (major type 7, additional information 24) and continue with a byte
+	// less than 0x20 (32 decimal). Such sequences are not well-formed.
+	// (This implies that an encoder cannot encode false, true, null, or
+	// undefined in two-byte sequences and that only the one-byte variants
+	// of these are well-formed; more generally speaking, each simple value
+	// only has a single representation variant)."
+
+	switch {
+	case sv <= 23:
+		return []byte{byte(cborTypePrimitives) | byte(sv)}, nil
+
+	case sv >= 32:
+		return []byte{byte(cborTypePrimitives) | byte(24), byte(sv)}, nil
+
+	default:
+		return nil, &UnsupportedValueError{msg: fmt.Sprintf("SimpleValue(%d)", sv)}
+	}
+}
+
+// UnmarshalCBOR decodes CBOR simple value (major type 7) to SimpleValue.
+func (sv *SimpleValue) UnmarshalCBOR(data []byte) error {
+	if sv == nil {
+		return errors.New("cbor.SimpleValue: UnmarshalCBOR on nil pointer")
+	}
+
+	d := decoder{data: data, dm: defaultDecMode}
+
+	typ, ai, val := d.getHead()
+
+	if typ != cborTypePrimitives {
+		return &UnmarshalTypeError{CBORType: typ.String(), GoType: "SimpleValue"}
+	}
+	if ai > 24 {
+		return &UnmarshalTypeError{CBORType: typ.String(), GoType: "SimpleValue", errorMsg: "not simple values"}
+	}
+
+	// It is safe to cast val to uint8 here because
+	// - data is already verified to be well-formed CBOR simple value and
+	// - val is <= math.MaxUint8.
+	*sv = SimpleValue(val)
+	return nil
+}


Test patch:
diff --git a/decode_test.go b/decode_test.go
index 5c655ee..c029f50 100644
--- a/decode_test.go
+++ b/decode_test.go
@@ -79,6 +79,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -108,6 +109,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -137,6 +139,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -166,6 +169,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -195,6 +199,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -224,6 +229,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -253,6 +259,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -282,6 +289,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -311,6 +319,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -340,6 +349,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -367,6 +377,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 
@@ -397,6 +408,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -425,6 +437,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -453,6 +466,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -481,6 +495,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -506,6 +521,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	}, // CBOR value -18446744073709551616 overflows Go's int64, see TestNegIntOverflow
 
@@ -537,6 +553,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeBigInt,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -566,6 +583,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeBigInt,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -596,6 +614,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeBigInt,
+			typeSimpleValue,
 		},
 	},
 
@@ -623,6 +642,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -648,6 +668,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -673,6 +694,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -698,6 +720,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -723,6 +746,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -748,6 +772,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -773,6 +798,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -798,6 +824,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 
@@ -834,6 +861,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -871,6 +899,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -900,6 +929,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -929,6 +959,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -958,6 +989,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -994,6 +1026,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1028,6 +1061,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1057,6 +1091,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1086,6 +1121,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1122,6 +1158,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1151,8 +1188,8 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeBigInt,
-
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1183,6 +1220,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 
@@ -1216,6 +1254,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1245,6 +1284,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1274,6 +1314,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1304,6 +1345,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1333,6 +1375,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1362,6 +1405,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 
@@ -1392,6 +1436,7 @@ var unmarshalTests = []unmarshalTest{
 			typeMapStringInt,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	}, // 0: standard date/time
 	{
@@ -1420,6 +1465,7 @@ var unmarshalTests = []unmarshalTest{
 			typeIntSlice,
 			typeMapStringInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	}, // 1: epoch-based date/time
 	{
@@ -1455,6 +1501,7 @@ var unmarshalTests = []unmarshalTest{
 			typeIntSlice,
 			typeMapStringInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	}, // 2: positive bignum: 18446744073709551616
 	{
@@ -1490,6 +1537,7 @@ var unmarshalTests = []unmarshalTest{
 			typeIntSlice,
 			typeMapStringInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	}, // 3: negative bignum: -18446744073709551617
 	{
@@ -1519,6 +1567,7 @@ var unmarshalTests = []unmarshalTest{
 			typeMapStringInt,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	}, // 1: epoch-based date/time
 	{
@@ -1550,6 +1599,7 @@ var unmarshalTests = []unmarshalTest{
 			typeMapStringInt,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	}, // 23: expected conversion to base16 encoding
 	{
@@ -1581,6 +1631,7 @@ var unmarshalTests = []unmarshalTest{
 			typeMapStringInt,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	}, // 24: encoded cborBytes data item
 	{
@@ -1608,6 +1659,7 @@ var unmarshalTests = []unmarshalTest{
 			typeMapStringInt,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	}, // 32: URI
 
@@ -1859,6 +1911,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeBigInt,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1884,6 +1937,7 @@ var unmarshalTests = []unmarshalTest{
 			typeRawTag,
 			typeBigInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1915,6 +1969,7 @@ var unmarshalTests = []unmarshalTest{
 			typeTag,
 			typeRawTag,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 
@@ -1945,6 +2000,7 @@ var unmarshalTests = []unmarshalTest{
 			typeIntSlice,
 			typeMapStringInt,
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 	{
@@ -1982,6 +2038,7 @@ var unmarshalTests = []unmarshalTest{
 			typeMapStringInt,
 			reflect.TypeOf([3]string{}),
 			typeByteString,
+			typeSimpleValue,
 		},
 	},
 }
@@ -2012,6 +2069,7 @@ var unmarshalFloatWrongTypes = []reflect.Type{
 	typeRawTag,
 	typeBigInt,
 	typeByteString,
+	typeSimpleValue,
 }
 
 // unmarshalFloatTests includes test values for float16, float32, and float64.
diff --git a/simplevalue_test.go b/simplevalue_test.go
new file mode 100644
index 0000000..67b1166
--- /dev/null
+++ b/simplevalue_test.go
@@ -0,0 +1,177 @@
+// Copyright (c) Faye Amacker. All rights reserved.
+// Licensed under the MIT License. See LICENSE in the project root for license information.
+
+package cbor
+
+import (
+	"bytes"
+	"reflect"
+	"testing"
+)
+
+func TestUnmarshalSimpleValue(t *testing.T) {
+	t.Run("0..23", func(t *testing.T) {
+		for i := 0; i <= 23; i++ {
+			data := []byte{byte(cborTypePrimitives) | byte(i)}
+			want := SimpleValue(i)
+
+			switch i {
+			case 20: // false
+				testUnmarshalSimpleValueToEmptyInterface(t, data, false)
+			case 21: // true
+				testUnmarshalSimpleValueToEmptyInterface(t, data, true)
+			case 22: // null
+				testUnmarshalSimpleValueToEmptyInterface(t, data, nil)
+			case 23: // undefined
+				testUnmarshalSimpleValueToEmptyInterface(t, data, nil)
+			default:
+				testUnmarshalSimpleValueToEmptyInterface(t, data, want)
+			}
+
+			testUnmarshalSimpleValue(t, data, want)
+		}
+	})
+
+	t.Run("24..31", func(t *testing.T) {
+		for i := 24; i <= 31; i++ {
+			data := []byte{byte(cborTypePrimitives) | byte(24), byte(i)}
+
+			testUnmarshalInvalidSimpleValueToEmptyInterface(t, data)
+			testUnmarshalInvalidSimpleValue(t, data)
+		}
+	})
+
+	t.Run("32..255", func(t *testing.T) {
+		for i := 32; i <= 255; i++ {
+			data := []byte{byte(cborTypePrimitives) | byte(24), byte(i)}
+			want := SimpleValue(i)
+			testUnmarshalSimpleValueToEmptyInterface(t, data, want)
+			testUnmarshalSimpleValue(t, data, want)
+		}
+	})
+}
+
+func testUnmarshalInvalidSimpleValueToEmptyInterface(t *testing.T, data []byte) {
+	var v interface{}
+	if err := Unmarshal(data, v); err == nil {
+		t.Errorf("Unmarshal(0x%x) didn't return an error", data)
+	} else if _, ok := err.(*SyntaxError); !ok {
+		t.Errorf("Unmarshal(0x%x) returned wrong error type %T, want (*SyntaxError)", data, err)
+	}
+}
+
+func testUnmarshalInvalidSimpleValue(t *testing.T, data []byte) {
+	var v SimpleValue
+	if err := Unmarshal(data, v); err == nil {
+		t.Errorf("Unmarshal(0x%x) didn't return an error", data)
+	} else if _, ok := err.(*SyntaxError); !ok {
+		t.Errorf("Unmarshal(0x%x) returned wrong error type %T, want (*SyntaxError)", data, err)
+	}
+}
+
+func testUnmarshalSimpleValueToEmptyInterface(t *testing.T, data []byte, want interface{}) {
+	var v interface{}
+	if err := Unmarshal(data, &v); err != nil {
+		t.Errorf("Unmarshal(0x%x) returned error %v", data, err)
+		return
+	}
+	if !reflect.DeepEqual(v, want) {
+		t.Errorf("Unmarshal(0x%x) = %v (%T), want %v (%T)", data, v, v, want, want)
+	}
+}
+
+func testUnmarshalSimpleValue(t *testing.T, data []byte, want SimpleValue) {
+	cborNil := isCBORNil(data)
+
+	// Decode to SimpleValue
+	var v SimpleValue
+	err := Unmarshal(data, &v)
+	if err != nil {
+		t.Errorf("Unmarshal(0x%x) returned error %v", data, err)
+		return
+	}
+	if !reflect.DeepEqual(v, want) {
+		t.Errorf("Unmarshal(0x%x) = %v (%T), want %v (%T)", data, v, v, want, want)
+	}
+
+	// Decode to uninitialized *SimpleValue
+	var pv *SimpleValue
+	err = Unmarshal(data, &pv)
+	if err != nil {
+		t.Errorf("Unmarshal(0x%x) returned error %v", data, err)
+		return
+	}
+	if cborNil {
+		if pv != nil {
+			t.Errorf("Unmarshal(0x%x) returned %v, want nil *SimpleValue", data, *pv)
+		}
+	} else {
+		if !reflect.DeepEqual(*pv, want) {
+			t.Errorf("Unmarshal(0x%x) = %v (%T), want %v (%T)", data, *pv, *pv, want, want)
+		}
+	}
+
+	// Decode to initialized *SimpleValue
+	v = SimpleValue(0)
+	pv = &v
+	err = Unmarshal(data, &pv)
+	if err != nil {
+		t.Errorf("Unmarshal(0x%x) returned error %v", data, err)
+		return
+	}
+	if cborNil {
+		if pv != nil {
+			t.Errorf("Unmarshal(0x%x) returned %v, want nil *SimpleValue", data, *pv)
+		}
+	} else {
+		if !reflect.DeepEqual(v, want) {
+			t.Errorf("Unmarshal(0x%x) = %v (%T), want %v (%T)", data, v, v, want, want)
+		}
+	}
+}
+
+func TestMarshalSimpleValue(t *testing.T) {
+	t.Run("0..23", func(t *testing.T) {
+		for i := 0; i <= 23; i++ {
+			wantData := []byte{byte(cborTypePrimitives) | byte(i)}
+			v := SimpleValue(i)
+
+			data, err := Marshal(v)
+			if err != nil {
+				t.Errorf("Marshal(%v) returned error %v", v, err)
+				continue
+			}
+			if !bytes.Equal(data, wantData) {
+				t.Errorf("Marshal(%v) = 0x%x, want 0x%x", v, data, wantData)
+			}
+		}
+	})
+
+	t.Run("24..31", func(t *testing.T) {
+		for i := 24; i <= 31; i++ {
+			v := SimpleValue(i)
+
+			if data, err := Marshal(v); err == nil {
+				t.Errorf("Marshal(%v) didn't return an error", data)
+			} else if _, ok := err.(*UnsupportedValueError); !ok {
+				t.Errorf("Marshal(%v) returned wrong error type %T, want (*UnsupportedValueError)", data, err)
+			}
+		}
+	})
+
+	t.Run("32..255", func(t *testing.T) {
+		for i := 32; i <= 255; i++ {
+			wantData := []byte{byte(cborTypePrimitives) | byte(24), byte(i)}
+			v := SimpleValue(i)
+
+			data, err := Marshal(v)
+			if err != nil {
+				t.Errorf("Marshal(%v) returned error %v", v, err)
+				continue
+			}
+			if !bytes.Equal(data, wantData) {
+				t.Errorf("Marshal(%v) = 0x%x, want 0x%x", v, data, wantData)
+			}
+		}
+	})
+}