Simple SSH port forward in Golang

Question

I\'m trying to create (and later close) a simple TCP port forward over SSH with Go. I\'m new to Golang and statically typed languages. (Coming from Ruby.)

In a termi

Answer 1

I finally figured out how to do this, I got hints from schmichael in an IRC channel. Thanks to all!

EDIT: A little explanation: A big part of the problem I was having was that I did not realize a local net.Listener (not just a local net.Conn) needed setup to receive a local request and create the net.Conn before forwarding the bytes. Also, there exist both port forwards and reverse port forwards and I hadn't previously thought in detail about the fact that a regular port forward also sends bytes back, so copying the remote reader to local writer was not something I had implemented, yet it's very much needed. Here is an attempt to relate the essence of what this code does:

• Listen on local port 9000.
• Upon attempted read from local port 9000: (listener.Accept()),
• Accept connection and return a local io.Reader and io.Writer and,
• Connect to remote server and,
• Connect to remote port 9999 returning a io.Reader and io.Writer.
• Continually copy local io.Reader bytes to remote io.Writer,
• Continually copy remote io.Reader bytes to local io.Writer.

Here is the code:

package main

// Forward from local port 9000 to remote port 9999

import (
    "io"
    "log"
    "net"
    "golang.org/x/crypto/ssh"
)

var (
    username         = "root"
    password         = "password"
    serverAddrString = "192.168.1.100:22"
    localAddrString  = "localhost:9000"
    remoteAddrString = "localhost:9999"
)

func forward(localConn net.Conn, config *ssh.ClientConfig) {
    // Setup sshClientConn (type *ssh.ClientConn)
    sshClientConn, err := ssh.Dial("tcp", serverAddrString, config)
    if err != nil {
        log.Fatalf("ssh.Dial failed: %s", err)
    }

    // Setup sshConn (type net.Conn)
    sshConn, err := sshClientConn.Dial("tcp", remoteAddrString)

    // Copy localConn.Reader to sshConn.Writer
    go func() {
        _, err = io.Copy(sshConn, localConn)
        if err != nil {
            log.Fatalf("io.Copy failed: %v", err)
        }
    }()

    // Copy sshConn.Reader to localConn.Writer
    go func() {
        _, err = io.Copy(localConn, sshConn)
        if err != nil {
            log.Fatalf("io.Copy failed: %v", err)
        }
    }()
}

func main() {
    // Setup SSH config (type *ssh.ClientConfig)
    config := &ssh.ClientConfig{
        User: username,
        Auth: []ssh.AuthMethod{
            ssh.Password(password),
        },
    }

    // Setup localListener (type net.Listener)
    localListener, err := net.Listen("tcp", localAddrString)
    if err != nil {
        log.Fatalf("net.Listen failed: %v", err)
    }

    for {
        // Setup localConn (type net.Conn)
        localConn, err := localListener.Accept()
        if err != nil {
            log.Fatalf("listen.Accept failed: %v", err)
        }
        go forward(localConn, config)
    }
}