Java

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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import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.SshTunnel;

public class ChilkatExample {

    public static void main(String[] args) {
        // 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.

        SshTunnel tunnel = new SshTunnel();

        // The fixed destination that accepted connections are forwarded to.
        tunnel.setDestHostname("db.internal.example.com");
        tunnel.setDestPort(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.setListenBindIpAddress("127.0.0.1");

        int sshPort = 22;
        try {
            tunnel.connect("ssh.example.com", sshPort);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            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.
        String password = "mySshPassword";

        try {
            tunnel.authenticatePw("mySshLogin", password);

            // Pass 0 to let the operating system choose an available port.  After BeginAccepting succeeds,
            // ListenPort contains the actual port that was bound.
            tunnel.beginAccepting(0);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        System.out.println("Listening on 127.0.0.1 port " + tunnel.getListenPort());

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

        boolean waitForThreadExit = true;
        try {
            tunnel.closeTunnel(waitForThreadExit);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }
    }
}