Dart

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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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // 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.

  final ssh = CkSsh();

  final sshPort = 22;
  try {
    ssh.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 {
    ssh.authenticatePw('mySshLogin', password);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

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

  print('Opened direct-tcpip channel: $channelNum');

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

  ssh.disconnect();
}