perf(lyrics): stream MP3 audio when updating ID3 lyrics

2026-09-30 05:12:00 +02:00 · 2026-09-17 02:59:22 +07:00
parent cd4b8ead90
commit 39a3e680a4
3 changed files with 148 additions and 4 deletions
@@ -0,0 +1,86 @@
+import 'dart:io';
+import 'dart:typed_data';
+
+import 'package:crypto/crypto.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:spotiflac_android/services/id3v23_lyrics.dart';
+
+void main() {
+  late Directory root;
+  setUp(() async {
+    root = await Directory.systemTemp.createTemp('id3-lyrics-test-');
+  });
+  tearDown(() => root.delete(recursive: true));
+
+  test(
+    'streams audio unchanged across insertion and replacement of lyrics',
+    () async {
+      final file = File('${root.path}/track.mp3');
+      final chunk = Uint8List.fromList(List.generate(65536, (i) => i % 251));
+      final sink = file.openWrite();
+      for (var i = 0; i < 128; i++) {
+        sink.add(chunk);
+      }
+      await sink.close();
+      final audioSize = await file.length();
+      final audioHash = await sha256.bind(file.openRead()).single;
+
+      for (final lyrics in ['First lyrics', 'Replacement 歌詞']) {
+        expect(
+          await Id3v23Lyrics.writeUnsyncedLyricsToFile(file, lyrics),
+          isTrue,
+        );
+        final input = await file.open();
+        final header = await input.read(10);
+        final tagSize =
+            (header[6] << 21) |
+            (header[7] << 14) |
+            (header[8] << 7) |
+            header[9];
+        await input.setPosition(0);
+        final tag = await input.read(tagSize + 10);
+        await input.close();
+        expect(tag, Id3v23Lyrics.writeUnsyncedLyrics(Uint8List(0), lyrics));
+        expect(await file.length(), audioSize + tag.length);
+        expect(await sha256.bind(file.openRead(tag.length)).single, audioHash);
+        expect(await root.list().length, 1);
+      }
+    },
+  );
+
+  test('preserves other frames when updating an existing tag', () async {
+    final file = File('${root.path}/track.mp3');
+    final bytes = Id3v23Lyrics.writeUnsyncedLyrics(
+      Uint8List.fromList([1, 2, 3, 4]),
+      'old lyrics',
+    )!;
+    // Re-label the valid frame so it must be preserved alongside new USLT.
+    bytes.setRange(10, 14, [0x54, 0x49, 0x54, 0x32]);
+    await file.writeAsBytes(bytes);
+    expect(await Id3v23Lyrics.writeUnsyncedLyricsToFile(file, 'new'), isTrue);
+    expect(
+      await file.readAsBytes(),
+      Id3v23Lyrics.writeUnsyncedLyrics(bytes, 'new'),
+    );
+  });
+
+  test(
+    'unsupported, malformed and truncated tags leave the file intact',
+    () async {
+      for (final header in [
+        [73, 68, 51, 4, 0, 0, 0, 0, 0, 0],
+        [73, 68, 51, 3, 0, 0x80, 0, 0, 0, 0],
+        [73, 68, 51, 3, 0, 0, 0x80, 0, 0, 0],
+        [73, 68, 51, 3, 0, 0, 0, 0, 0, 100],
+      ]) {
+        final file = await File('${root.path}/track.mp3').writeAsBytes(header);
+        expect(
+          await Id3v23Lyrics.writeUnsyncedLyricsToFile(file, 'new'),
+          isFalse,
+        );
+        expect(await file.readAsBytes(), header);
+        expect(await root.list().length, 1);
+      }
+    },
+  );
+}