Dart Requires Chilkat v11.0.0+

TCP Socket through SSH Tunnel (Port Forwarding)

See more Socket/SSL/TLS Examples

Demonstrates using Chilkat Socket to communicate to a TCP service through an SSH tunnel. This example will connect to an NIST time server and (using the old Time Protocol (RFC 868)), will read the current GMT time.

Note: This is not necessarily a recommended means for getting the current date/time. The most commonly used time protocol is the Network Time Protocol (RFC-1305). The intent of this example is to show how TCP communications can occur through an SSH tunnel.

Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // This example requires the Chilkat API to have been previously unlocked.
  // See Global Unlock Sample for sample code.

  final tunnel = CkSocket();

  final sshHostname = 'sftp.example.com';
  final sshPort = 22;

  // Connect to an SSH server and establish the SSH tunnel:
  try {
    tunnel.sshOpenTunnel(sshHostname, sshPort);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Authenticate with the SSH server via a login/password
  // or with a public key.
  // This example demonstrates SSH password authentication.
  try {
    tunnel.sshAuthenticatePw('mySshLogin', 'mySshPassword');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // OK, the SSH tunnel is setup.  Now open a channel within the tunnel.
  // Once the channel is obtained, the Socket API may
  // be used exactly the same as usual, except all communications
  // are sent through the channel in the SSH tunnel.
  // Any number of channels may be created from the same SSH tunnel.
  // Multiple channels may coexist at the same time.

  // Connect to an NIST time server and read the current date/time
  final maxWaitMs = 4000;
  final useTls = false;
  final channel = CkSocket();
  try {
    tunnel.sshNewChannel('time-c.nist.gov', 37, useTls, maxWaitMs, channel);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // The time server will send a big-endian 32-bit integer representing
  // the number of seconds since since 00:00 (midnight) 1 January 1900 GMT.
  // The ReceiveInt32 method will receive a 4-byte integer, but returns
  // true or false to indicate success.  If successful, the integer
  // is obtained via the ReceivedInt property.
  final bigEndian = true;
  try {
    channel.receiveInt32(bigEndian);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  final dt = CkDateTime();
  dt.setFromNtpTime(channel.receivedInt);

  // Show the current local date/time
  final bLocalTime = true;
  print('Current local date/time: ${dt.getAsRfc822(bLocalTime)}');

  // Close the SSH channel.
  try {
    channel.close(maxWaitMs);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // It is possible to create a new channel from the existing SSH tunnel for the next connection:
  // Any number of channels may be created from the same SSH tunnel.
  // Multiple channels may coexist at the same time.
  try {
    tunnel.sshNewChannel('time-a.nist.gov', 37, useTls, maxWaitMs, channel);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Review the LastErrorText to see that the connection was made via the SSH tunnel:
  print(tunnel.lastErrorText);

  // Close the connection to time-a.nist.gov.  This is actually closing our channel
  // within the SSH tunnel, but keeps the tunnel open for the next port-forwarded connection.
  try {
    channel.close(maxWaitMs);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Finally, close the SSH tunnel.
  try {
    tunnel.sshCloseTunnel();
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('TCP SSH tunneling example completed.');
}