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// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
// SPDX-License-Identifier: MIT
// Package main implements a simple CLI tools to perform NAT traversal via STUN
package main
import (
"bufio"
"flag"
"fmt"
"log"
"net"
"os"
"strings"
"time"
"github.com/pion/stun"
)
var server = flag.String("server", "stun:stun.voipgate.com:3478", "Stun server address") //nolint:gochecknoglobals
const (
udp = "udp4"
pingMsg = "ping"
pongMsg = "pong"
timeoutMillis = 500
)
func main() { //nolint:gocognit
flag.Parse()
srvAddr, err := net.ResolveUDPAddr(udp, *server)
if err != nil {
log.Fatalf("Failed to resolve server addr: %s", err)
}
conn, err := net.ListenUDP(udp, nil)
if err != nil {
log.Fatalf("Failed to listen: %s", err)
}
defer func() {
_ = conn.Close()
}()
log.Printf("Listening on %s", conn.LocalAddr())
var publicAddr stun.XORMappedAddress
var peerAddr *net.UDPAddr
messageChan := listen(conn)
var peerAddrChan <-chan string
keepalive := time.Tick(timeoutMillis * time.Millisecond)
keepaliveMsg := pingMsg
var quit <-chan time.Time
gotPong := false
sentPong := false
for {
select {
case message, ok := <-messageChan:
if !ok {
return
}
switch {
case string(message) == pingMsg:
keepaliveMsg = pongMsg
case string(message) == pongMsg:
if !gotPong {
log.Println("Received pong message.")
}
// One client may skip sending ping if it receives
// a ping message before knowning the peer address.
keepaliveMsg = pongMsg
gotPong = true
case stun.IsMessage(message):
m := new(stun.Message)
m.Raw = message
decErr := m.Decode()
if decErr != nil {
log.Println("decode:", decErr)
break
}
var xorAddr stun.XORMappedAddress
if getErr := xorAddr.GetFrom(m); getErr != nil {
log.Println("getFrom:", getErr)
break
}
if publicAddr.String() != xorAddr.String() {
log.Printf("My public address: %s\n", xorAddr)
publicAddr = xorAddr
peerAddrChan = getPeerAddr()
}
default:
log.Panicln("unknown message", message)
}
case peerStr := <-peerAddrChan:
peerAddr, err = net.ResolveUDPAddr(udp, peerStr)
if err != nil {
log.Panicln("resolve peeraddr:", err)
}
case <-keepalive:
// Keep NAT binding alive using STUN server or the peer once it's known
if peerAddr == nil {
err = sendBindingRequest(conn, srvAddr)
} else {
err = sendStr(keepaliveMsg, conn, peerAddr)
if keepaliveMsg == pongMsg {
sentPong = true
}
}
if err != nil {
log.Panicln("keepalive:", err)
}
case <-quit:
_ = conn.Close()
}
if quit == nil && gotPong && sentPong {
log.Println("Success! Quitting in two seconds.")
quit = time.After(2 * time.Second)
}
}
}
func getPeerAddr() <-chan string {
result := make(chan string)
go func() {
reader := bufio.NewReader(os.Stdin)
log.Println("Enter remote peer address:")
peer, _ := reader.ReadString('\n')
result <- strings.Trim(peer, " \r\n")
}()
return result
}
func listen(conn *net.UDPConn) <-chan []byte {
messages := make(chan []byte)
go func() {
for {
buf := make([]byte, 1024)
n, _, err := conn.ReadFromUDP(buf)
if err != nil {
close(messages)
return
}
buf = buf[:n]
messages <- buf
}
}()
return messages
}
func sendBindingRequest(conn *net.UDPConn, addr *net.UDPAddr) error {
m := stun.MustBuild(stun.TransactionID, stun.BindingRequest)
err := send(m.Raw, conn, addr)
if err != nil {
return fmt.Errorf("binding: %w", err)
}
return nil
}
func send(msg []byte, conn *net.UDPConn, addr *net.UDPAddr) error {
_, err := conn.WriteToUDP(msg, addr)
if err != nil {
return fmt.Errorf("send: %w", err)
}
return nil
}
func sendStr(msg string, conn *net.UDPConn, addr *net.UDPAddr) error {
return send([]byte(msg), conn, addr)
}
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