STUN server over UDP

main.go

package main

import (
	"flag"
	"fmt"
	"net"
	"os"
	"time"
)

var port = flag.Int("port", 0, "")

func main() {
	flag.Parse()

	uaddr, err := net.ResolveUDPAddr("udp4", fmt.Sprintf(":%d", *port))
	if err != nil {
		panic(err)
	}

	fmt.Println("stun server started")

	conn, err := net.ListenUDP("udp4", uaddr)
	if err != nil {
		panic(err)
	}

	buf := make([]byte, 1024)

	addrs := make([]net.Addr, 0)

	for {
		n, addr, err := conn.ReadFromUDP(buf)
		if err != nil {
			fmt.Println(err)
			os.Exit(1)
		}

		go func() {
			fmt.Println(addr.String(), string(buf[:n]))

			if len(addrs) == 0 {
				addrs = append(addrs, addr)
			} else {
				conn.WriteTo([]byte("addr:"+addr.String()), addrs[0])
				time.Sleep(1 * time.Second)
				conn.WriteTo([]byte("addr:"+addrs[0].String()), addr)
				addrs = make([]net.Addr, 0)
			}
		}()
	}
}