open static method

DVAssetPack? open(String file, { required int offset, required int length, })

The pack at offset in file, length bytes long, or null when the bytes there are not one. Reads the index and nothing else.

Implementation

static DVAssetPack? open(String file, {required int offset, required int length}) {
  final RandomAccessFile raf;
  try {
    raf = File(file).openSync();
  } on FileSystemException {
    return null;
  }
  try {
    if (length < 12) return null;
    raf.setPositionSync(offset);
    final Uint8List head = raf.readSync(12);
    if (head.length < 12 || ascii.decode(head.sublist(0, 8), allowInvalid: true) != _magic) {
      return null;
    }
    final int indexLength = ByteData.sublistView(head).getUint32(8, Endian.little);
    if (indexLength > length - 12) return null;
    final Object? index = jsonDecode(utf8.decode(raf.readSync(indexLength)));
    if (index is! Map || index['entries'] is! List || index['build'] is! String) {
      return null;
    }
    final int data = offset + 12 + indexLength;
    final int dataLength = length - 12 - indexLength;
    final Map<String, DVPackedAsset> entries = <String, DVPackedAsset>{};
    for (final Object? row in index['entries'] as List) {
      if (row is! List || row.length < 7) return null;
      final int at = row[1] as int;
      final int stored = row[2] as int;
      if (at < 0 || stored < 0 || at + stored > dataLength) return null;
      final int encoding = row[4] as int;
      if (encoding < 0 || encoding >= DVAssetEncoding.values.length) return null;
      final String path = row[0] as String;
      entries[path] = DVPackedAsset._(
        path: path,
        offset: data + at,
        storedLength: stored,
        size: row[3] as int,
        encoding: DVAssetEncoding.values[encoding],
        hash: row[5] as String,
        protected: (row[6] as int) & _protectedFlag != 0,
      );
    }
    return DVAssetPack._(file, index['build'] as String, entries);
  } on FormatException {
    return null;
  } on TypeError {
    return null;
  } on FileSystemException {
    return null;
  } finally {
    raf.closeSync();
  }
}