(Java) FTP through SSH Tunnel with Dynamic Port Forwarding

Demonstrates how to start a background thread that runs a portable SSH tunnel w/ dynamic port forwarding that the foreground thread can be used for establishing FTP sessions through an SSH tunnel.

Note: Some developers may be accustomed to starting an stunnel.exe proxy from https://www.stunnel.org. The stunnel.exe is not necessary here. Chilkat's background thread fulfills the task of what the external stunnel.exe does. Therefore, your application is self-contained, meaning that it can run anywhere because the SSH tunnel proxy is built-in.

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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[])
  {
    // Starting in v9.5.0.49, all Chilkat classes can be unlocked at once at the beginning of a program
    // by calling UnlockBundle.  It requires a Bundle unlock code.
    CkGlobal chilkatGlob = new CkGlobal();
    boolean success = chilkatGlob.UnlockBundle("Anything for 30-day trial.");
    if (success != true) {
        System.out.println(chilkatGlob.lastErrorText());
        return;
        }

    // This example requires Chilkat version 9.5.0.50 or greater.
    CkSshTunnel tunnel = new CkSshTunnel();

    String sshHostname = "sftp.example.com";
    int sshPort = 22;

    // Connect to an SSH server and establish the SSH tunnel:
    success = tunnel.Connect(sshHostname,sshPort);
    if (success != true) {
        System.out.println(tunnel.lastErrorText());
        return;
        }

    // Authenticate with the SSH server via a login/password
    // or with a public key.  
    // This example demonstrates SSH password authentication.
    success = tunnel.AuthenticatePw("mySshLogin","mySshPassword");
    if (success != true) {
        System.out.println(tunnel.lastErrorText());
        return;
        }

    // Indicate that the background SSH tunnel thread will behave as a SOCKS proxy server
    // with dynamic port forwarding:
    tunnel.put_DynamicPortForwarding(true);

    // We may optionally require that connecting clients authenticate with our SOCKS proxy server.
    // To do this, set an inbound username/password.  Any connecting clients would be required to 
    // use SOCKS5 with the correct username/password.
    // If no inbound username/password is set, then our SOCKS proxy server will accept both
    // SOCKS4 and SOCKS5 unauthenticated connections.

    tunnel.put_InboundSocksUsername("chilkat123");
    tunnel.put_InboundSocksPassword("password123");

    // Start the listen/accept thread to begin accepting SOCKS proxy client connections.
    // Listen on port 1080.
    success = tunnel.BeginAccepting(1080);
    if (success != true) {
        System.out.println(tunnel.lastErrorText());
        return;
        }

    // Now that a background thread is running a SOCKS proxy server that forwards connections
    // through an SSH tunnel, it is possible to use any Chilkat implemented protocol that is SOCKS capable,
    // such as HTTP, POP3, SMTP, IMAP, FTP, etc.  The protocol may use SSL/TLS because the SSL/TLS
    // will be passed through the SSH tunnel to the end-destination.  Also, any number of simultaneous
    // connections may be routed through the SSH tunnel.

    CkFtp2 ftp = new CkFtp2();

    // Indicate that the HTTP object is to use our portable SOCKS proxy/SSH tunnel running in our background thread.
    ftp.put_SocksHostname("localhost");
    // The SocksPort must equal the port passed to BeginAccepting above.
    ftp.put_SocksPort(1080);
    ftp.put_SocksVersion(5);
    // The SOCKS5 login/password set here must equal the InboundSocksUsername/Password set above.
    ftp.put_SocksUsername("chilkat123");
    ftp.put_SocksPassword("password123");

    // This is the actual FTP server domain or IP address, and the login/password for the user account on the destination FTP server.
    ftp.put_Hostname("ftp.someFtpServer.com");
    ftp.put_Username("myLogin");
    ftp.put_Password("myPassword");
    ftp.put_AuthTls(true);

    // Connect and login (via the SSH tunnel) to the FTP server.
    success = ftp.Connect();
    if (success != true) {
        System.out.println(ftp.lastErrorText());
        return;
        }

    // Change to the remote directory where the file is located.
    // This step is only necessary if the file is not in the root directory
    // for the FTP account.
    success = ftp.ChangeRemoteDir("junk");
    if (success != true) {
        System.out.println(ftp.lastErrorText());
        return;
        }

    String localFilename = "c:/temp/hamlet.xml";
    String remoteFilename = "hamlet.xml";

    // Download a file.  (the data connection is also automatically established through the 
    // SSH tunnel using dynamic port forwarding..)
    success = ftp.GetFile(remoteFilename,localFilename);
    if (success != true) {
        System.out.println(ftp.lastErrorText());
        return;
        }

    // The disconnect is disconnecting with the FTP server and closes the SSH tunnel.
    // The background tunnel thread is still running, and may be used for subsequent FTP connections,
    // or even connections for any other purpose, such as HTTP, IMAP, SMTP, POP3, etc.
    success = ftp.Disconnect();

    // When the app is finished with the tunnel, it can cleanup..

    // Stop the background listen/accept thread:
    boolean waitForThreadExit = true;
    success = tunnel.StopAccepting(waitForThreadExit);
    if (success != true) {
        System.out.println(tunnel.lastErrorText());
        return;
        }

    // Close the SSH tunnel (would also kick any remaining connected clients).
    success = tunnel.CloseTunnel(waitForThreadExit);
    if (success != true) {
        System.out.println(tunnel.lastErrorText());
        return;
        }
  }
}