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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Java

import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    boolean success = 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.

    CkSshTunnel tunnel = new CkSshTunnel();

    //  The fixed destination that accepted connections are forwarded to.
    tunnel.put_DestHostname("db.internal.example.com");
    tunnel.put_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.put_ListenBindIpAddress("127.0.0.1");

    int sshPort = 22;
    success = tunnel.Connect("ssh.example.com",sshPort);
    if (success == false) {
        System.out.println(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.
    String password = "mySshPassword";

    success = tunnel.AuthenticatePw("mySshLogin",password);
    if (success == false) {
        System.out.println(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(0);
    if (success == false) {
        System.out.println(tunnel.lastErrorText());
        return;
        }

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

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

    boolean waitForThreadExit = true;
    success = tunnel.CloseTunnel(waitForThreadExit);
    if (success == false) {
        System.out.println(tunnel.lastErrorText());
        return;
        }
  }
}