Demo of tcp connection proxy with golang.

tcp-forward-golang.go

package main

import (
	"io"
	"log"
	"net"
	"os"
)

func forward(conn net.Conn) {
	forward, err := net.Dial("tcp", os.Args[2])
	if err != nil {
		log.Printf("Dial failed to target: %v\n", err)
	} else {
		log.Printf("Connected to target %v:%v\n", forward.RemoteAddr().(*net.TCPAddr).IP, forward.RemoteAddr().(*net.TCPAddr).Port)
		go func() {
			defer forward.Close()
			defer conn.Close()
			io.Copy(forward, conn)
		}()
		go func() {
			defer forward.Close()
			defer conn.Close()
			io.Copy(conn, forward)
		}()
	}

}

func main() {
	if len(os.Args) != 3 {
		log.Fatalf("Usage %s listen:port target:port\n", os.Args[0])
		return
	}

	listen, err := net.Listen("tcp", os.Args[1])
	if err != nil {
		log.Fatalf("Failed to create a forward : %v", err)
	}

	for {
		conn, err := listen.Accept()
		if err != nil {
			log.Fatalf("ERROR: failed to accept forward: %v", err)
		}
		log.Printf("Accepted incoming connection %v:%v\n", conn.RemoteAddr().(*net.TCPAddr).IP, conn.RemoteAddr().(*net.TCPAddr).Port)
		go forward(conn)
	}
}