readFileRange function

Future<ReadFileRangeResult?> readFileRange(String path, int offset, int maxBytes)

Read up to maxBytes from a file starting at offset. Returns a flat string from bytes -- no sliced string references to a larger parent. Returns null if the file is smaller than the offset.

Implementation

Future<ReadFileRangeResult?> readFileRange(
  String path,
  int offset,
  int maxBytes,
) async {
  final raf = await File(path).open(mode: FileMode.read);
  try {
    final size = await raf.length();
    if (size <= offset) {
      return null;
    }
    final bytesToRead = min(size - offset, maxBytes);
    final buffer = Uint8List(bytesToRead);
    await raf.setPosition(offset);

    int totalRead = 0;
    while (totalRead < bytesToRead) {
      final bytesRead = await raf.readInto(buffer, totalRead, bytesToRead);
      if (bytesRead == 0) break;
      totalRead += bytesRead;
    }

    return ReadFileRangeResult(
      content: String.fromCharCodes(buffer, 0, totalRead),
      bytesRead: totalRead,
      bytesTotal: size,
    );
  } finally {
    await raf.close();
  }
}