Dart

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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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // 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.

  final tunnel = CkSshTunnel();

  // The fixed destination that accepted connections are forwarded to.
  tunnel.destHostname = 'db.internal.example.com';
  tunnel.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.listenBindIpAddress = '127.0.0.1';

  final sshPort = 22;
  try {
    tunnel.connect('ssh.example.com', sshPort);
  } on ChilkatException catch (e) {
    print(e.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.
  final password = 'mySshPassword';

  try {
    tunnel.authenticatePw('mySshLogin', password);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Pass 0 to let the operating system choose an available port.  After BeginAccepting succeeds,
  // ListenPort contains the actual port that was bound.
  try {
    tunnel.beginAccepting(0);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('Listening on 127.0.0.1 port ${tunnel.listenPort}');

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

  final waitForThreadExit = true;
  try {
    tunnel.closeTunnel(waitForThreadExit);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }
}