Golang : Forwarding a local port to a remote server example


Tags : golang port-forwarding tcp-net io-copy remote-server

Got a strange request yesterday. A friend who is an IT manager in his company needs to implement some control over his local network. He needs to block all the staffs(his co-workers) access to Facebook during working hours, but at the same time open up a "secret" door access to Facebook for his boss.

It is pretty trivial to configure the local network firewall to block access to certain websites nowadays. However, he prefers not to configure the "secret" door in the local network firewall. The next best solution is to implement a local port forwarding to remote server.

Below is a simple port forwarding solution in Golang that will initiate a bi-directional communication with a remote server(Facebook for example).

Here you go!


 package main

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

 var localServerHost = "localhost:8880"
 var remoteServerHost = "www.facebook.com:80"

 func main() {

  ln, err := net.Listen("tcp", localServerHost)
  if err != nil {
 log.Fatal(err)
  }

  log.Println("Port forwarding server up and listening on ", localServerHost)

  for {
 conn, err := ln.Accept()
 if err != nil {
 log.Fatal(err)
 }

 go handleConnection(conn)
  }
 }

 func forward(src, dest net.Conn) {
  defer src.Close()
  defer dest.Close()
  io.Copy(src, dest)
 }

 func handleConnection(c net.Conn) {

  log.Println("Connection from : ", c.RemoteAddr())

  remote, err := net.Dial("tcp", remoteServerHost)
  if err != nil {
 log.Fatal(err)
  }

  log.Println("Connected to ", remoteServerHost)

  // go routines to initiate bi-directional communication for local server with a
  // remote server
  go forward(c, remote)
  go forward(remote, c)
 }

Sample output:

1) Run the program at the background and

2) On the browser, enter localhost:8880 in the address bar.

golang port forwarding localhost to facebook example

References:

https://www.socketloop.com/tutorials/golang-simple-client-server-example

https://www.socketloop.com/tutorials/golang-simple-client-server-hmac-authentication-without-ssl-example

  See also : Golang : Simple client-server HMAC authentication without SSL example



Tags : golang port-forwarding tcp-net io-copy remote-server

By Adam Ng

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