read method

@override Future<Uint8List> read(int offset, int length)

Exactly length bytes at offset, or a thrown error.

Returning a short read silently is the one behaviour that breaks every caller, so implementations must not do it.

Implementation

@override
Future<Uint8List> read(int offset, int length) async {
  if (offset < 0 || length < 0 || offset + length > _size) {
    throw RangeError(
      '4dgs: range [$offset, ${offset + length}) outside $_size bytes',
    );
  }
  await _handle.setPosition(offset);
  final out = await _handle.read(length);
  // A short read is the one behaviour that breaks every caller, and a file can
  // produce one — it may have been truncated between the size call and this
  // read. Reported rather than returned.
  if (out.length != length) {
    throw FourdgsTruncatedFile(
      'read $length bytes at $offset and got ${out.length}',
    );
  }
  return out;
}