Port forwarding is a useful technique to establish a tunnel between two hosts, allowing traffic to be securely relayed through an intermediary server. In Go, port forwarding can be achieved using the golang.org/x/crypto/ssh package.
A basic port forward setup involves:
Here's a simple Go code example demonstrating port forwarding from a local port (9000) to a remote port (9999) on a remote server:
<code class="go">package main import ( "io" "log" "net" "golang.org/x/crypto/ssh" ) const ( localAddrString = "localhost:9000" remoteAddrString = "localhost:9999" serverAddrString = "192.168.1.100:22" username = "root" password = "password" ) 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) } defer sshClientConn.Close() // Establish connection to remote destination port sshConn, err := sshClientConn.Dial("tcp", remoteAddrString) if err != nil { log.Fatalf("sshClientConn.Dial failed: %s", err) } defer sshConn.Close() // Relay data between local and remote connections go func() { if _, err := io.Copy(sshConn, localConn); err != nil { log.Fatalf("io.Copy failed: %v", err) } }() go func() { if _, err := io.Copy(localConn, sshConn); 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) } // Accept incoming connections and forward them for { localConn, err := localListener.Accept() if err != nil { log.Fatalf("listener.Accept failed: %v", err) } go forward(localConn, config) } }</code>
This code starts by creating a local listener on port 9000, then establishes a client connection to the remote SSH server. Next, SSH connections are initiated to the destination port (9999) on the remote server. Finally, data is relayed between the local and remote connections via goroutines.
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