React Native 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.

React Native

import { CkDateTime, Socket } from '@chilkat/react-native'

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

  const tunnel = new Socket();

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

  // Connect to an SSH server and establish the SSH tunnel:
  try {
    await tunnel.sshOpenTunnelAsync(sshHostname, sshPort);
  } catch {
    console.log(tunnel.lastErrorText);
    return;
  }

  // Authenticate with the SSH server via a login/password
  // or with a public key.
  // This example demonstrates SSH password authentication.
  try {
    await tunnel.sshAuthenticatePwAsync('mySshLogin', 'mySshPassword');
  } catch {
    console.log(tunnel.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
  const maxWaitMs = 4000;
  const useTls = false;
  const channel = new Socket();
  try {
    await tunnel.sshNewChannelAsync('time-c.nist.gov', 37, useTls, maxWaitMs, channel);
  } catch {
    console.log(tunnel.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.
  const bigEndian = true;
  try {
    await channel.receiveInt32Async(bigEndian);
  } catch {
    console.log(channel.lastErrorText);
    return;
  }

  const dt = new CkDateTime();
  dt.setFromNtpTime(channel.receivedInt);

  // Show the current local date/time
  const bLocalTime = true;
  console.log(`Current local date/time: ${dt.getAsRfc822(bLocalTime)}`);

  // Close the SSH channel.
  try {
    await channel.closeAsync(maxWaitMs);
  } catch {
    console.log(channel.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 {
    await tunnel.sshNewChannelAsync('time-a.nist.gov', 37, useTls, maxWaitMs, channel);
  } catch {
    console.log(tunnel.lastErrorText);
    return;
  }

  // Review the LastErrorText to see that the connection was made via the SSH tunnel:
  console.log(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 {
    await channel.closeAsync(maxWaitMs);
  } catch {
    console.log(channel.lastErrorText);
    return;
  }

  // Finally, close the SSH tunnel.
  try {
    await tunnel.sshCloseTunnelAsync();
  } catch {
    console.log(tunnel.lastErrorText);
    return;
  }

  console.log('TCP SSH tunneling example completed.');
}