code: func (p *Peer) handlePingMsg(msg *wire.MsgPing) {
  	// Only reply with pong if the message is from a new enough client.
  	if p.ProtocolVersion() > wire.BIP0031Version {
  		// Include nonce from ping so pong can be identified.
  		p.QueueMessage(wire.NewMsgPong(msg.Nonce), nil)
  	}
  }
docs: // handlePingMsg is invoked when a peer receives a ping bitcoin message.  For
  // recent clients (protocol version > BIP0031Version), it replies with a pong
  // message.  For older clients, it does nothing and anything other than failure
  // is considered a successful ping.