How to Create a Simple SSH Port Forward Using Golang?

Simple SSH Port Forwarding in Golang

Problem:

Programmatically creating a basic TCP port forward over SSH in Golang for users familiar with Ruby.

Solution:

To tackle this challenge, it's essential to understand the crucial steps involved:

1. Establishing a local listener (net.Listener) to accept connections on the local port.
2. Upon a connection attempt, accepting it and acquiring local io.Reader and io.Writer objects.
3. Establishing a remote connection to the server and remote port, obtaining its io.Reader and io.Writer objects.
4. Continuously transferring bytes bidirectionally between the local and remote io.Readers and io.Writers.

Code:

<code class="go">package main

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

// Configuration parameters for SSH connection
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) {
    // Establish SSH connection to remote server
    sshClientConn, err := ssh.Dial("tcp", serverAddrString, config)
    if err != nil {
        log.Fatalf("ssh.Dial failed: %s", err)
    }

    // Connect to remote port
    sshConn, err := sshClientConn.Dial("tcp", remoteAddrString)
    if err != nil {
        log.Fatalf("sshConn.Dial failed: %s", err)
    }

    // Create goroutines for bidirectional data transfer
    go func() {
        _, err = io.Copy(sshConn, localConn)
        if err != nil {
            log.Fatalf("io.Copy failed: %v", err)
        }

    }()

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

    }()
}

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

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

    // Monitor listener for new connections
    for {
        localConn, err := localListener.Accept()
        if err != nil {
            log.Fatalf("localListener.Accept failed: %v", err)
        }

        go forward(localConn, config)
    }
}</code>

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