read method
Reads size bytes from the file starting at offset bytes from the beginning of the file.
Implementation
Future<List<int>> read(
  int offset,
  int size,
) async {
  final request = RequestFileRead(
    file: handle,
    offset: offset,
    size: size,
  );
  final response = await client.invoke(request);
  switch (response) {
    case ResponseBytes(value: final value): return value;
    default: throw UnexpectedResponse();
  }
}