id3v2: tolerate odd-length UTF-16 text frames

id3v2frames.go

@@ -408,7 +408,9 @@ func decodeUTF16WithBOM(b []byte) (string, error) {
 
 func decodeUTF16(b []byte, bo binary.ByteOrder) (string, error) {
 	if len(b)%2 != 0 {
-		return "", errors.New("invalid encoding: expected even number of bytes for UTF-16 encoded text")
+		// Some encoders append a stray trailing byte (often a null
+		// terminator); drop it rather than failing.
+		b = b[:len(b)-1]
 	}
 	s := make([]uint16, 0, len(b)/2)
 	for i := 0; i < len(b); i += 2 {

id3v2frames_test.go

@@ -0,0 +1,34 @@
+// Copyright 2024, David Howden
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tag
+
+import (
+	"encoding/binary"
+	"testing"
+)
+
+func TestDecodeUTF16OddLength(t *testing.T) {
+	// "AB" in UTF-16BE with a stray trailing null byte appended by the encoder.
+	b := []byte{0x00, 0x41, 0x00, 0x42, 0x00}
+	got, err := decodeUTF16(b, binary.BigEndian)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "AB" {
+		t.Fatalf("got %q, want %q", got, "AB")
+	}
+}
+
+func TestDecodeTextUTF16OddLength(t *testing.T) {
+	// encoding byte 0x01 (UTF-16 with BOM), little-endian BOM, "AB", stray null.
+	b := []byte{0x01, 0xFF, 0xFE, 0x41, 0x00, 0x42, 0x00, 0x00}
+	got, err := decodeText(b[0], b[1:])
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "AB" {
+		t.Fatalf("got %q, want %q", got, "AB")
+	}
+}