code: func (p *pktline) writeFlush() error {
  	if _, err := p.w.WriteString(fmt.Sprintf("%04x", 0)); err != nil {
  		return err
  	}
  
  	if err := p.w.Flush(); err != nil {
  		return err
  	}
  
  	return nil
  }
docs: // writeFlush writes the terminating "flush" packet and then flushes the
  // underlying buffered writer.
  //
  // If any error was encountered along the way, it will be returned immediately