feat: import Chinese-localized Buzz source snapshot

Signed-off-by: cls_宁波本机 <908705107@qq.com>

mobile/test/shared/relay/mp4_fast_start_test.dart

@@ -0,0 +1,145 @@
+import 'dart:convert';
+import 'dart:io';
+import 'dart:typed_data';
+
+import 'package:buzz/shared/relay/mp4_fast_start.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  late Directory tempDirectory;
+
+  setUp(() async {
+    tempDirectory = await Directory.systemTemp.createTemp(
+      'buzz-faststart-test-',
+    );
+  });
+
+  tearDown(() async {
+    await tempDirectory.delete(recursive: true);
+  });
+
+  for (final offsetBox in ['stco', 'co64']) {
+    test('moves moov before mdat and patches $offsetBox offsets', () async {
+      final ftyp = _box('ftyp', [
+        ...ascii.encode('isom'),
+        0,
+        0,
+        0,
+        0,
+        ...ascii.encode('isom'),
+      ]);
+      final mdat = _box('mdat', [1, 2, 3, 4]);
+      final originalMediaOffset = ftyp.length + 8;
+      final offsetPayload = BytesBuilder()
+        ..add([0, 0, 0, 0])
+        ..add(_uint32(1))
+        ..add(
+          offsetBox == 'stco'
+              ? _uint32(originalMediaOffset)
+              : _uint64(originalMediaOffset),
+        );
+      final sampleTable = _box(offsetBox, offsetPayload.takeBytes());
+      final moov = _nestedMoov(sampleTable);
+      final sourceBytes = Uint8List.fromList([...ftyp, ...mdat, ...moov]);
+      final source = File('${tempDirectory.path}/source.mp4');
+      final destination = File('${tempDirectory.path}/output.mp4');
+      await source.writeAsBytes(sourceBytes);
+
+      await rewriteMp4ForFastStart(source, destination);
+
+      final output = await destination.readAsBytes();
+      expect(_topLevelTypes(output), ['ftyp', 'moov', 'mdat']);
+      expect(
+        output.sublist(ftyp.length + moov.length + 8),
+        equals([1, 2, 3, 4]),
+      );
+
+      final typeOffset = _findAscii(output, offsetBox);
+      expect(typeOffset, greaterThanOrEqualTo(4));
+      final entryOffset = typeOffset + 12;
+      final adjusted = offsetBox == 'stco'
+          ? _readUint32(output, entryOffset)
+          : _readUint64(output, entryOffset);
+      expect(adjusted, originalMediaOffset + moov.length);
+    });
+  }
+
+  test(
+    'rejects excessive nested box depth and deletes partial output',
+    () async {
+      final ftyp = _box('ftyp', [
+        ...ascii.encode('isom'),
+        0,
+        0,
+        0,
+        0,
+        ...ascii.encode('isom'),
+      ]);
+      final mdat = _box('mdat', [1]);
+      var nested = _box('stco', [0, 0, 0, 0, ..._uint32(0)]);
+      for (var index = 0; index < 34; index++) {
+        nested = _box('stbl', nested);
+      }
+      final source = File('${tempDirectory.path}/deep.mp4');
+      final destination = File('${tempDirectory.path}/output.mp4');
+      await source.writeAsBytes([...ftyp, ...mdat, ..._box('moov', nested)]);
+
+      await expectLater(
+        rewriteMp4ForFastStart(source, destination),
+        throwsA(isA<FormatException>()),
+      );
+      expect(await destination.exists(), isFalse);
+    },
+  );
+}
+
+Uint8List _nestedMoov(List<int> leaf) =>
+    _box('moov', _box('trak', _box('mdia', _box('minf', _box('stbl', leaf)))));
+
+Uint8List _box(String type, List<int> payload) => Uint8List.fromList([
+  ..._uint32(payload.length + 8),
+  ...ascii.encode(type),
+  ...payload,
+]);
+
+Uint8List _uint32(int value) {
+  final bytes = ByteData(4)..setUint32(0, value, Endian.big);
+  return bytes.buffer.asUint8List();
+}
+
+Uint8List _uint64(int value) {
+  final bytes = ByteData(8)..setUint64(0, value, Endian.big);
+  return bytes.buffer.asUint8List();
+}
+
+int _readUint32(Uint8List bytes, int offset) =>
+    ByteData.sublistView(bytes).getUint32(offset, Endian.big);
+
+int _readUint64(Uint8List bytes, int offset) =>
+    ByteData.sublistView(bytes).getUint64(offset, Endian.big);
+
+List<String> _topLevelTypes(Uint8List bytes) {
+  final types = <String>[];
+  var offset = 0;
+  while (offset < bytes.length) {
+    final size = _readUint32(bytes, offset);
+    types.add(ascii.decode(bytes.sublist(offset + 4, offset + 8)));
+    offset += size;
+  }
+  return types;
+}
+
+int _findAscii(Uint8List bytes, String value) {
+  final needle = ascii.encode(value);
+  for (var offset = 0; offset + needle.length <= bytes.length; offset++) {
+    var matches = true;
+    for (var index = 0; index < needle.length; index++) {
+      if (bytes[offset + index] != needle[index]) {
+        matches = false;
+        break;
+      }
+    }
+    if (matches) return offset;
+  }
+  return -1;
+}