code: func (m *Memberlist) SendBestEffort(to *Node, msg []byte) error {
  	// Encode as a user message
  	buf := make([]byte, 1, len(msg)+1)
  	buf[0] = byte(userMsg)
  	buf = append(buf, msg...)
  
  	// Send the message
  	return m.rawSendMsgPacket(to.Address(), to, buf)
  }
docs: // SendBestEffort uses the unreliable packet-oriented interface of the transport
  // to target a user message at the given node (this does not use the gossip
  // mechanism). The maximum size of the message depends on the configured
  // UDPBufferSize for this memberlist instance.