code: func (prw *PssReadWriter) WriteMsg(msg p2p.Msg) error {
  	log.Trace("pssrw writemsg", "msg", msg)
  	if prw.closed {
  		return fmt.Errorf("connection closed")
  	}
  	rlpdata := make([]byte, msg.Size)
  	msg.Payload.Read(rlpdata)
  	pmsg, err := rlp.EncodeToBytes(ProtocolMsg{
  		Code:    msg.Code,
  		Size:    msg.Size,
  		Payload: rlpdata,
  	})
  	if err != nil {
  		return err
  	}
  	return prw.sendFunc(prw.key, *prw.topic, pmsg)
  }
docs: // Implements p2p.MsgWriter