Android™

SSH Tunnel TCP Socket Options

Demonstrates tuning the underlying TCP socket with the SoRcvBuf, SoSndBuf, TcpNoDelay, OutboundBindIpAddress, and OutboundBindPort properties. These normally should be left at their defaults.

Background: These are low-level knobs for specific situations. Larger send/receive buffers can improve throughput on high-bandwidth, high-latency ("long fat") links; TcpNoDelay disables Nagle's algorithm to cut latency for small interactive packets at the cost of efficiency; and binding the outbound socket to a specific local address or port is occasionally required by firewall rules or multi-homed hosts. Change them only with a concrete reason, since the defaults are tuned for the common case.

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Android™

// 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 tuning the underlying TCP socket with the SshTunnel properties SoRcvBuf, SoSndBuf,
    //  TcpNoDelay, OutboundBindIpAddress, and OutboundBindPort.
    //  
    //  These normally should be left at their defaults; adjust them only for specific performance or
    //  networking requirements.

    CkSshTunnel tunnel = new CkSshTunnel();

    //  Socket send/receive buffer sizes, in bytes.  Larger buffers can help throughput on
    //  high-latency links.
    tunnel.put_SoRcvBuf(4194304);
    tunnel.put_SoSndBuf(262144);

    //  Disable Nagle's algorithm to reduce latency for small, interactive packets.
    tunnel.put_TcpNoDelay(true);

    //  Bind the outbound socket to a specific local address/port before connecting.  0 (the default)
    //  lets the OS choose the local port; an empty address lets the OS choose the interface.
    tunnel.put_OutboundBindIpAddress("192.168.1.50");
    tunnel.put_OutboundBindPort(0);

    tunnel.put_DestHostname("db.internal.example.com");
    tunnel.put_DestPort(5432);

    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;
        }

    int listenPort = 1080;
    success = tunnel.BeginAccepting(listenPort);
    if (success == false) {
        Log.i(TAG, tunnel.lastErrorText());
        return;
        }

    Log.i(TAG, "Tunnel established with custom socket options.");

    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."
  }
}