readRange method

@override Future<Uint8List> readRange(String key, { required int start, required int length, })

Read a byte range.

Returns bytes starting at start with the given length. For encrypted files, only the overlapping chunks are decrypted; for chunked files, only the overlapping chunk records are read.

Implementation

@override
Future<Uint8List> readRange(
  String key, {
  required int start,
  required int length,
}) async {
  checkNotDisposed();
  final manifest = await _readManifest(key);
  if (manifest == null) throw FileNotFoundError(key);

  final end = (start + length).clamp(0, manifest.totalSize);
  if (end <= start) return Uint8List(0);

  final firstChunk = start ~/ chunkSize;
  final lastChunk = (end - 1) ~/ chunkSize;

  final builder = BytesBuilder(copy: false);
  for (var i = firstChunk; i <= lastChunk; i++) {
    final chunk = await _readChunk(key, manifest.generation, i);
    final chunkStart = i * chunkSize;
    final sliceStart = (start > chunkStart) ? start - chunkStart : 0;
    final sliceEnd = (end < chunkStart + chunk.length)
        ? end - chunkStart
        : chunk.length;
    builder.add(chunk.sublist(sliceStart, sliceEnd));
  }
  return builder.takeBytes();
}