code: func (msg *MsgPong) BtcEncode(w io.Writer, pver uint32, enc MessageEncoding) error {
  	// NOTE: <= is not a mistake here.  The BIP0031 was defined as AFTER
  	// the version unlike most others.
  	if pver <= BIP0031Version {
  		str := fmt.Sprintf("pong message invalid for protocol "+
  			"version %d", pver)
  		return messageError("MsgPong.BtcEncode", str)
  	}
  
  	return writeElement(w, msg.Nonce)
  }
docs: // BtcEncode encodes the receiver to w using the bitcoin protocol encoding.
  // This is part of the Message interface implementation.