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Reject encoding nil inside CBOR indefinite-length string #750

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Merged
fxamacker merged 1 commit into from
Mar 22, 2026
+113 −5
Merged

Reject encoding nil inside CBOR indefinite-length string #750

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16 changes: 11 additions & 5 deletions stream.go
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Original file line number Diff line number Diff line change
Expand Up @@ -171,14 +171,20 @@ func NewEncoder(w io.Writer) *Encoder {

// Encode writes the CBOR encoding of v.
func (enc *Encoder) Encode(v any) error {
if len(enc.indefTypes) > 0 && v != nil {
indefType := enc.indefTypes[len(enc.indefTypes)-1]
if indefType == cborTypeTextString {
if len(enc.indefTypes) > 0 {
switch enc.indefTypes[len(enc.indefTypes)-1] {
case cborTypeTextString:
if v == nil {
return errors.New("cbor: cannot encode nil for indefinite-length text string")
}
k := reflect.TypeOf(v).Kind()
if k != reflect.String {
return errors.New("cbor: cannot encode item type " + k.String() + " for indefinite-length text string")
}
} else if indefType == cborTypeByteString {
case cborTypeByteString:
if v == nil {
return errors.New("cbor: cannot encode nil for indefinite-length byte string")
}
t := reflect.TypeOf(v)
k := t.Kind()
if (k != reflect.Array && k != reflect.Slice) || t.Elem().Kind() != reflect.Uint8 {
Expand Down Expand Up @@ -219,7 +225,7 @@ func (enc *Encoder) StartIndefiniteArray() error {
return enc.startIndefinite(cborTypeArray)
}

// StartIndefiniteMap starts array encoding of indefinite length.
// StartIndefiniteMap starts map encoding of indefinite length.
// Subsequent calls of (*Encoder).Encode() encodes elements of the map
// until EndIndefinite is called.
func (enc *Encoder) StartIndefiniteMap() error {
Expand Down
102 changes: 102 additions & 0 deletions stream_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -883,6 +883,19 @@ func TestIndefiniteTextString(t *testing.T) {
}
}

func TestIndefiniteByteStringNilError(t *testing.T) {
var w bytes.Buffer
encoder := NewEncoder(&w)
if err := encoder.StartIndefiniteByteString(); err != nil {
t.Fatalf("StartIndefiniteByteString() returned error %v", err)
}
if err := encoder.Encode(nil); err == nil {
t.Errorf("Encode() didn't return an error")
} else if err.Error() != "cbor: cannot encode nil for indefinite-length byte string" {
t.Errorf("Encode() returned error %q, want %q", err.Error(), "cbor: cannot encode nil for indefinite-length byte string")
}
}

func TestIndefiniteTextStringError(t *testing.T) {
var w bytes.Buffer
encoder := NewEncoder(&w)
Expand All @@ -894,6 +907,24 @@ func TestIndefiniteTextStringError(t *testing.T) {
} else if err.Error() != "cbor: cannot encode item type slice for indefinite-length text string" {
t.Errorf("Encode() returned error %q, want %q", err.Error(), "cbor: cannot encode item type slice for indefinite-length text string")
}
if err := encoder.Encode(123); err == nil {
t.Errorf("Encode() didn't return an error")
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@x448 x448 Mar 22, 2026 •
edited
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This error message is confusing to me. It's easier to understand if it says something like "expected error foo but got nil error".

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@fxamacker fxamacker Mar 22, 2026

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Good point! I found more of these, so I will open separate PR to clean them up.

} else if err.Error() != "cbor: cannot encode item type int for indefinite-length text string" {
t.Errorf("Encode() returned error %q, want %q", err.Error(), "cbor: cannot encode item type int for indefinite-length text string")
}
}

func TestIndefiniteTextStringNilError(t *testing.T) {
var w bytes.Buffer
encoder := NewEncoder(&w)
if err := encoder.StartIndefiniteTextString(); err != nil {
t.Fatalf("StartIndefiniteTextString() returned error %v", err)
}
if err := encoder.Encode(nil); err == nil {
t.Errorf("Encode() didn't return an error")
} else if err.Error() != "cbor: cannot encode nil for indefinite-length text string" {
t.Errorf("Encode() returned error %q, want %q", err.Error(), "cbor: cannot encode nil for indefinite-length text string")
}
}

func TestIndefiniteArray(t *testing.T) {
Expand Down Expand Up @@ -929,6 +960,41 @@ func TestIndefiniteArray(t *testing.T) {
}
}

func TestIndefiniteArrayWithNilElement(t *testing.T) {
want := mustHexDecode("9f01f6ff") // [1, null]
var w bytes.Buffer
encoder := NewEncoder(&w)
if err := encoder.StartIndefiniteArray(); err != nil {
t.Fatalf("StartIndefiniteArray() returned error %v", err)
}
if err := encoder.Encode(1); err != nil {
t.Fatalf("Encode() returned error %v", err)
}
if err := encoder.Encode(nil); err != nil {
t.Fatalf("Encode() returned error %v", err)
}
if err := encoder.EndIndefinite(); err != nil {
t.Fatalf("EndIndefinite() returned error %v", err)
}
if !bytes.Equal(w.Bytes(), want) {
t.Errorf("Encoding mismatch: got %v, want %v", w.Bytes(), want)
}

var decoded []any
if err := Unmarshal(w.Bytes(), &decoded); err != nil {
t.Fatalf("Unmarshal() returned error %v", err)
}
if len(decoded) != 2 {
t.Fatalf("Unmarshal() returned %d elements, want 2", len(decoded))
}
if decoded[0] != uint64(1) {
t.Errorf("decoded[0] = %v (%T), want uint64(1)", decoded[0], decoded[0])
}
if decoded[1] != nil {
t.Errorf("decoded[1] = %v (%T), want nil", decoded[1], decoded[1])
}
}

func TestIndefiniteMap(t *testing.T) {
want := mustHexDecode("bf61610161629f0203ffff")
var w bytes.Buffer
Expand Down Expand Up @@ -969,6 +1035,42 @@ func TestIndefiniteMap(t *testing.T) {
}
}

func TestIndefiniteMapWithNilElement(t *testing.T) {
want := mustHexDecode("bf6161f6ff") // {"a": null}
var w bytes.Buffer
encoder := NewEncoder(&w)
if err := encoder.StartIndefiniteMap(); err != nil {
t.Fatalf("StartIndefiniteMap() returned error %v", err)
}
if err := encoder.Encode("a"); err != nil {
t.Fatalf("Encode() returned error %v", err)
}
if err := encoder.Encode(nil); err != nil {
t.Fatalf("Encode() returned error %v", err)
}
if err := encoder.EndIndefinite(); err != nil {
t.Fatalf("EndIndefinite() returned error %v", err)
}
if !bytes.Equal(w.Bytes(), want) {
t.Errorf("Encoding mismatch: got %v, want %v", w.Bytes(), want)
}

var decoded map[string]any
if err := Unmarshal(w.Bytes(), &decoded); err != nil {
t.Fatalf("Unmarshal() returned error %v", err)
}
if len(decoded) != 1 {
t.Fatalf("Unmarshal() returned %d entries, want 1", len(decoded))
}
v, ok := decoded["a"]
if !ok {
t.Fatalf("decoded map missing key \"a\"")
}
if v != nil {
t.Errorf("decoded[\"a\"] = %v (%T), want nil", v, v)
}
}

func TestIndefiniteLengthError(t *testing.T) {
var w bytes.Buffer
encoder := NewEncoder(&w)
Expand Down
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