code: func (w *PktlineWriter) Flush() error {
  	if w == nil {
  		return nil
  	}
  
  	if _, err := w.flush(); err != nil {
  		return err
  	}
  
  	if err := w.pl.writeFlush(); err != nil {
  		return err
  	}
  
  	return nil
  }
docs: // Flush empties the internal buffer used to store data temporarily and then
  // writes the pkt-line's FLUSH packet, to signal that it is done writing this
  // chunk of data.