Java

Open a direct-tcpip Channel (SSH Port Forwarding)

Demonstrates the Chilkat Ssh.OpenDirectTcpIpChannel method, which opens a direct-tcpip channel through the SSH server to a target host and port. The first argument is the target hostname and the second is the target port. It returns the channel number, or -1 on failure.

Background: This is SSH local port forwarding at the API level: the channel carries ordinary TCP traffic to a service that may be reachable only from the SSH server's network — a database, an internal web app, a message broker. The key detail is that the server resolves the target name, not your machine, so it must resolve and be reachable there. Supplying a numeric IPv4 address avoids remote DNS resolution entirely.

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import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.Ssh;

public class ChilkatExample {

    public static void main(String[] args) {
        // Demonstrates the Ssh.OpenDirectTcpIpChannel method, which opens a direct-tcpip channel
        // through the SSH server to a target host and port.  The 1st argument is the target hostname
        // and the 2nd is the target port.  It returns the channel number, or -1 on failure.

        Ssh ssh = new Ssh();

        int sshPort = 22;
        try {
            ssh.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 {
            ssh.authenticatePw("mySshLogin", password);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // The target name is resolved by the SSH server, not by this computer, so it must be
        // reachable from the server's network.
        String targetHostname = "db.internal.example.com";
        int targetPort = 5432;
        int channelNum = ssh.openDirectTcpIpChannel(targetHostname, targetPort);
        if (channelNum < 0) {
            System.out.println(ssh.getLastErrorText());
            return;
        }

        System.out.println("Opened direct-tcpip channel: " + channelNum);

        // The channel now carries ordinary TCP data to the target, tunneled over SSH.

        ssh.disconnect();
    }
}