golang: tunnel tcp over socks5

main.go

package main

import (
	"flag"
	"io"
	"net"
	"time"

	log "github.com/sirupsen/logrus"
	"golang.org/x/net/proxy"
)

func pipe(src io.Reader, dst io.WriteCloser, result chan<- int64) {
	defer dst.Close()
	n, _ := io.Copy(dst, src)
	result <- int64(n)
}

func main() {
	local := flag.String("local", "127.0.0.1:8388", "address to listen")
	socks5 := flag.String("proxy", "127.0.0.1:1080", "socks5 proxy")
	target := flag.String("target", "www.google.com:80", "forwarding target")
	flag.Parse()
	lis, err := net.Listen("tcp", *local)
	if err != nil {
		log.WithError(err).Fatal("cannot listen")
	}
	for {
		conn, err := lis.Accept()
		if err != nil {
			log.WithError(err).Warn("cannot accept")
		}
		go func(conn net.Conn) {
			defer conn.Close()
			dailer, err := proxy.SOCKS5("tcp", *socks5, nil, &net.Dialer{
				Timeout:   60 * time.Second,
				KeepAlive: 30 * time.Second,
			})
			if err != nil {
				log.WithError(err).Warn("cannot initialize socks5 proxy")
				return
			}
			c, err := dailer.Dial("tcp", *target)
			if err != nil {
				log.WithError(err).WithField("target", *target).Warn("cannot dial")
				return
			}
			up, down := make(chan int64), make(chan int64)
			go pipe(conn, c, up)
			go pipe(c, conn, down)
			<-up
			<-down
			return
		}(conn)
	}
}