Android™

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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// Important: Don't forget to include the call to System.loadLibrary
// as shown at the bottom of this code sample.
package com.test;

import android.app.Activity;
import com.chilkatsoft.*;

import android.widget.TextView;
import android.os.Bundle;

public class SimpleActivity extends Activity {

  private static final String TAG = "Chilkat";

  // Called when the activity is first created.
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    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) {
        Log.i(TAG, 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) {
        Log.i(TAG, 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) {
        Log.i(TAG, tunnel.lastErrorText());
        return;
        }

    Log.i(TAG, "Listening on 127.0.0.1 port " + String.valueOf(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) {
        Log.i(TAG, tunnel.lastErrorText());
        return;
        }


  }

  static {
      System.loadLibrary("chilkat");

      // Note: If the incorrect library name is passed to System.loadLibrary,
      // then you will see the following error message at application startup:
      //"The application <your-application-name> has stopped unexpectedly. Please try again."
  }
}