code: def _request_next_buffer(self):
      
      self._buffer_future = None
      next_offset = self._offset + self._buffer.remaining()
      if next_offset != self._file_size:
        self._buffer_future = self._get_segment(next_offset,
                                                self._buffer_size)
docs: Request next buffer.
  
      Requires self._offset and self._buffer are in consistent state.