Simplest Go TCP proxy

go_tcp_proxy.go

package main

import (
	"flag"
	"io"
	"log"
	"net"
)

var (
	addr  = flag.String("addr", ":8100", "Local proxy address")
	raddr = flag.String("raddr", "localhost:10000", "Remove endpoint address")
)

func main() {
	flag.Parse()

	list, err := net.Listen("tcp", *addr)
	if err != nil {
		log.Fatalf("cannot listen to %s: %v", *addr, err)
	}

	for {
		conn, err := list.Accept()
		if err != nil {
			log.Fatalf("cannot accept conn: %v", err)
		}

		go proxy(conn)
	}
}

// proxy proxies connection to remote service. Not that this is not production ready
// as it is missing timeouts, slow client atacks etc.
func proxy(conn net.Conn) {
	log.Printf("proxy %s: %s\n", conn.LocalAddr().String(), conn.RemoteAddr().String())
	remote, err := net.Dial("tcp", *raddr)
	if err != nil {
		log.Fatalf("cannot dial to remote: %v", err)
	}
	defer remote.Close()

	go io.Copy(remote, conn)
	io.Copy(conn, remote)
}