[TOC] > [参考](https://blog.csdn.net/qq_31967569/article/details/82704340) ## 实例 <details> <summary>client.go </summary> ``` package main import ( "fmt" "log" "net" "os" "strconv" "strings" "time" ) const HAND_SHAKE_MSG = "我是打洞消息" var ( tag string ) func main() { // 当前进程标记字符串,便于显示 tag = os.Args[1] port,_:= strconv.Atoi(tag) srcAddr := &net.UDPAddr{IP: net.IPv4zero, Port: port} // 注意端口必须固定 dstAddr := &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: 9981}// 实际中 127.0.0.1 改为 公网,即可打洞 conn, err := net.DialUDP("udp", srcAddr, dstAddr) if err != nil { fmt.Println(err) } if _, err = conn.Write([]byte("hello, I'm new peer:" + tag)); err != nil { log.Panic(err) } data := make([]byte, 1024) n, remoteAddr, err := conn.ReadFromUDP(data) if err != nil { fmt.Printf("error during read: %s", err) } conn.Close() anotherPeer := parseAddr(string(data[:n])) fmt.Printf("local:%s server:%s another:%s\n", srcAddr, remoteAddr, anotherPeer.String()) // 开始打洞 bidirectionHole(srcAddr, &anotherPeer) } func parseAddr(addr string) net.UDPAddr { t := strings.Split(addr, ":") port, _ := strconv.Atoi(t[1]) return net.UDPAddr{ IP: net.ParseIP(t[0]), Port: port, } } func bidirectionHole(srcAddr *net.UDPAddr, anotherAddr *net.UDPAddr) { conn, err := net.DialUDP("udp", srcAddr, anotherAddr) if err != nil { fmt.Println(err) } defer conn.Close() // 向另一个peer发送一条udp消息(对方peer的nat设备会丢弃该消息,非法来源),用意是在自身的nat设备打开一条可进入的通道,这样对方peer就可以发过来udp消息 if _, err = conn.Write([]byte(HAND_SHAKE_MSG)); err != nil { log.Println("send handshake:", err) } go func() { for { time.Sleep(10 * time.Second) if _, err = conn.Write([]byte("from [" + tag + "]")); err != nil { log.Println("send msg fail", err) } } }() for { data := make([]byte, 1024) n, _, err := conn.ReadFromUDP(data) if err != nil { log.Printf("error during read: %s\n", err) } else { log.Printf("收到数据:%s\n", data[:n]) } } } ``` </details> <br/> <details> <summary>peer_server.go</summary> ``` package main import ( "fmt" "log" "net" "time" ) func main() { listener, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4zero, Port: 9981}) if err != nil { fmt.Println(err) return } log.Printf("本地地址: <%s> \n", listener.LocalAddr().String()) peers := make([]net.UDPAddr, 0, 2) data := make([]byte, 1024) for { n, remoteAddr, err := listener.ReadFromUDP(data) if err != nil { fmt.Printf("error during read: %s", err) } log.Printf("<%s> %s\n", remoteAddr.String(), data[:n]) peers = append(peers, *remoteAddr) // 等待两个udp 建立连接就互相转发数据 if len(peers) == 2 { log.Printf("进行UDP打洞,建立 %s <--> %s 的连接\n", peers[0].String(), peers[1].String()) listener.WriteToUDP([]byte(peers[1].String()), &peers[0]) listener.WriteToUDP([]byte(peers[0].String()), &peers[1]) time.Sleep(time.Second * 8) log.Println("中转服务器退出,仍不影响peers间通信") return } } } ``` </details> <br/> 分别执行 ``` go run peer.go go run client.go 1998 go run client.go 1999 ``` 原理: peer作为打洞服务等待client 进行连接,第一个client 连接后继续等待,直到存在两个连接后让他们直接互相通讯,此时连接已经建立,取消 peer 服务也不影响发送消息