Swift

SSH Tunnel Static (Fixed-Destination) Port Forwarding

Demonstrates fixed-destination port forwarding with the DestHostname, DestPort, ListenBindIpAddress, and ListenPort properties. Every local connection accepted by the listener is forwarded to the same fixed destination through the SSH server.

Background: This is the classic ssh -L scenario: expose a single remote service — a database, an internal web app — at a local port. Binding the listener to 127.0.0.1 keeps the tunnel private to the local machine, whereas 0.0.0.0 would let other hosts route through it. Passing 0 to BeginAccepting lets the OS pick a free port, which ListenPort then reports — handy when a fixed port might already be in use.

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func chilkatTest() {
    var success: Bool = false

    //  Demonstrates fixed-destination (static) port forwarding with the SshTunnel properties
    //  DestHostname, DestPort, ListenBindIpAddress, and ListenPort.
    //  
    //  Every local connection accepted by the listener is forwarded to the same fixed destination
    //  through the SSH server.

    let tunnel = CkoSshTunnel()!

    //  The fixed destination that accepted connections are forwarded to.
    tunnel.destHostname = "db.internal.example.com"
    tunnel.destPort = 5432

    //  Bind the listener to loopback so only local processes can use the tunnel.  Use "0.0.0.0" to
    //  accept connections from other machines (less secure).
    tunnel.listenBindIpAddress = "127.0.0.1"

    var sshPort: Int = 22
    success = tunnel.connect(hostname: "ssh.example.com", port: sshPort)
    if success == false {
        print("\(tunnel.lastErrorText!)")
        return
    }

    //  Normally you would not hard-code the password in source.  You should instead obtain it
    //  from an interactive prompt, environment variable, or a secrets vault.
    var password: String? = "mySshPassword"

    success = tunnel.authenticatePw(login: "mySshLogin", password: password)
    if success == false {
        print("\(tunnel.lastErrorText!)")
        return
    }

    //  Pass 0 to let the operating system choose an available port.  After BeginAccepting succeeds,
    //  ListenPort contains the actual port that was bound.
    success = tunnel.beginAccepting(listenPort: 0)
    if success == false {
        print("\(tunnel.lastErrorText!)")
        return
    }

    print("Listening on 127.0.0.1 port \(tunnel.listenPort.intValue)")

    //  Applications now connect to 127.0.0.1:ListenPort as if it were the database server.

    var waitForThreadExit: Bool = true
    success = tunnel.closeTunnel(waitForThreads: waitForThreadExit)
    if success == false {
        print("\(tunnel.lastErrorText!)")
        return
    }


}