telnet-client

What is telnet-client?

The telnet-client npm package is a simple and easy-to-use library for creating and managing Telnet connections in Node.js. It allows you to connect to Telnet servers, send commands, and receive responses, making it useful for automating tasks, remote server management, and network device configuration.

What are telnet-client's main functionalities?

Establishing a Telnet Connection

This feature allows you to establish a connection to a Telnet server using specified parameters such as host, port, shell prompt, and timeout.

const Telnet = require('telnet-client');
let connection = new Telnet();

let params = {
  host: '127.0.0.1',
  port: 23,
  shellPrompt: '/ # ',
  timeout: 1500
};

connection.connect(params)
  .then(() => {
    console.log('Connected to the Telnet server');
  })
  .catch((error) => {
    console.error('Connection failed:', error);
  });

Sending Commands

Once connected, you can send commands to the Telnet server and handle the responses. This is useful for executing remote commands and automating tasks.

connection.send('ls -l')
  .then((response) => {
    console.log('Command response:', response);
  })
  .catch((error) => {
    console.error('Command failed:', error);
  });

Handling Connection Events

You can handle various connection events such as timeout and close to manage the connection lifecycle and handle errors or disconnections gracefully.

connection.on('timeout', () => {
  console.log('Connection timed out');
  connection.end();
});

connection.on('close', () => {
  console.log('Connection closed');
});

Other packages similar to telnet-client

node-telnet-client

node-telnet-client is another Telnet client library for Node.js. It offers similar functionalities to telnet-client, such as establishing connections, sending commands, and handling responses. However, it provides a more extensive set of options for connection parameters and event handling, making it a bit more flexible for advanced use cases.

telnet-stream

telnet-stream is a low-level Telnet client library that provides a stream-based interface for Telnet communication. It is more suitable for developers who need fine-grained control over the Telnet protocol and want to build custom Telnet clients. Compared to telnet-client, it requires more effort to set up and use but offers greater flexibility.

README

node-telnet-client

A simple telnet client for node.js

Installation

Locally in your project or globally:

npm install telnet-client
npm install -g telnet-client

Responsible disclosure

Since version 0.11.x, we have moved from using new Buffer to Buffer.from, because when the library is used with latest Node.js, it issues a deprecation warning (see PR #63). Also, since version 0.12.x, we have moved to ECMAScript 6 to utilize class and scoping features.

This means we have moved exclusively to Current and LTS Node.js releases. Should there be any problems with it, please check if the corresponding issue is opened, and if not, open it so we can reach out and try to solve the deprecation problem.

Usage example

Callback-style

var telnet = require('telnet-client');
var connection = new telnet();

var params = {
  host: '127.0.0.1',
  port: 23,
  shellPrompt: '/ # ',
  timeout: 1500,
  // removeEcho: 4
};

connection.on('ready', function(prompt) {
  connection.exec(cmd, function(err, response) {
    console.log(response);
  });
});

connection.on('timeout', function() {
  console.log('socket timeout!')
  connection.end();
});

connection.on('close', function() {
  console.log('connection closed');
});

connection.connect(params);

Promises

var telnet = require('telnet-client');
var connection = new telnet();

var params = {
  host: '127.0.0.1',
  port: 23,
  shellPrompt: '/ # ',
  timeout: 1500,
  // removeEcho: 4
};

connection.connect(params)
.then(function(prompt) {
  connection.exec(cmd)
  .then(function(res) {
    console.log('promises result:', res)
  })
}, function(error) {
  console.log('promises reject:', error)
});

Generators

var co = require('co')
var bluebird = require('bluebird')
var telnet = require('telnet-client');
var connection = new telnet();

var params = {
  host: '127.0.0.1',
  port: 23,
  shellPrompt: '/ # ',
  timeout: 1500,
  // removeEcho: 4
};

// using 'co'
co(function*() {
  yield connection.connect(params)

  let res = yield connection.exec(cmd)
  console.log('coroutine result:', res)
})

// using 'bluebird'
bluebird.coroutine(function*() {
  yield connection.connect(params)

  let res = yield connection.exec(cmd)
  console.log('coroutine result:', res)
})()

Async/Await (using babeljs)

'use strict'

const Promise = require('bluebird')
const telnet = require('telnet-client')

require('babel-runtime/core-js/promise').default = Promise

Promise.onPossiblyUnhandledRejection(function(error) {
  throw error
})

// also requires additional babeljs setup

async function run() {
  let connection = new telnet()

  let params = {
    host: '127.0.0.1',
    port: 23,
    shellPrompt: '/ # ',
    timeout: 1500
  }

  await connection.connect(params)

  let res = await connection.exec(cmd)
  console.log('async result:', res)
}

run()

API

var telnet = require('telnet-client');
var connection = new telnet();

connection.connect(options) -> Promise

Creates a new TCP connection to the specified host, where 'options' is an object which can include following properties:

• host: Host the client should connect to. Defaults to '127.0.0.1'.
• port: Port the client should connect to. Defaults to '23'.
• timeout: Sets the socket to timeout after the specified number of milliseconds of inactivity on the socket.
• shellPrompt: Shell prompt that the host is using. Can be a string or an instance of RegExp. Defaults to regex '/(?:/ )?#\s/'.
• loginPrompt: Username/login prompt that the host is using. Can be a string or an instance of RegExp. Defaults to regex '/login[: ]*$/i'.
• passwordPrompt: Username/login prompt that the host is using. Can be a string or an instance of RegExp. Defaults to regex '/Password: /i'.
• failedLoginMatch: String or regex to match if your host provides login failure messages. Defaults to undefined.
• username: Username used to login. Defaults to 'root'.
• password: Username used to login. Defaults to 'guest'.
• irs: Input record separator. A separator used to distinguish between lines of the response. Defaults to '\r\n'.
• ors: Output record separator. A separator used to execute commands (break lines on input). Defaults to '\n'.
• echoLines: The number of lines used to cut off the response. Defaults to 1.
• stripShellPrompt: Whether shell prompt should be excluded from the results. Defaults to true.
• pageSeparator: The pattern used (and removed from final output) for breaking the number of lines on output. Defaults to '---- More'.
• negotiationMandatory: Disable telnet negotiations if needed. Can be used with 'send' when telnet specification is not needed. Telnet client will then basically act like a simple TCP client. Defaults to true.
• execTimeout: A timeout used to wait for a server reply when the 'exec' method is used. Defaults to 2000 (ms).
• sendTimeout: A timeout used to wait for a server reply when the 'send' method is used. Defaults to 2000 (ms).
• maxBufferLength: Maximum buffer length in bytes which can be filled with response data. Defaults to 1M.
• debug: Enable/disable debug logs on console. Defaults to false.

connection.exec(data, [options], [callback]) -> Promise

Sends data on the socket (should be a compatible remote host's command if sane information is wanted). The optional callback parameter will be executed with an error and response when the command is finally written out and the response data has been received.
If there was no error when executing the command, 'error' as the first argument to the callback will be undefined. Command result will be passed as the second argument to the callback.

*** important notice/API change from 0.3.0 ***
The callback argument is now called with a signature of (error, [response])

Options:

• shellPrompt: Shell prompt that the host is using. Can be a string or an instance of RegExp. Defaults to regex '/(?:/ )?#\s/'.
• loginPrompt: Username/login prompt that the host is using. Can be a string or an instance of RegExp. Defaults to regex '/login[: ]*$/i'.
• failedLoginMatch: String or regex to match if your host provides login failure messages. Defaults to undefined.
• timeout: Sets the socket to timeout after the specified number of milliseconds of inactivity on the socket.
• execTimeout: A timeout used to wait for a server reply when this method is used. Defaults to 'undefined'.
• maxBufferLength: Maximum buffer length in bytes which can be filled with response data. Defaults to 1M.
• irs: Input record separator. A separator used to distinguish between lines of the response. Defaults to '\r\n'.
• ors: Output record separator. A separator used to execute commands (break lines on input). Defaults to '\n'.
• echoLines: The number of lines used to cut off the response. Defaults to 1.

connection.send(data, [options], [callback]) -> Promise

Sends data on the socket without requiring telnet negotiations.

Options:

• ors: Output record separator. A separator used to execute commands (break lines on input). Defaults to '\n'.
• waitfor: Wait for the given string before returning a response. If not defined, the timeout value will be used.
• timeout: A timeout used to wait for a server reply when the 'send' method is used. Defaults to 2000 (ms) or to sendTimeout ('connect' method) if set.
• maxBufferLength: Maximum buffer length in bytes which can be filled with response data. Defaults to 1M.

connection.shell(callback) -> Promise

Starts an interactive shell session. Returns a duplex stream which can be used to read and write data.

connection.end() -> Promise

Half-closes the socket. i.e., it sends a FIN packet. It is possible the server will still send some data.

connection.destroy() -> Promise

Ensures that no more I/O activity happens on this socket. Only necessary in case of errors (parse error or so).

Event: 'connect'

Emitted when a socket connection is successfully established.

Event: 'ready'

Emitted when a socket connection is successfully established and the client is successfully connected to the specified remote host. A value of prompt is passed as the first argument to the callback.

Event: 'writedone'

Emitted when the write of given data is sent to the socket.

Event: 'data'

This is a forwarded 'data' event from core 'net' library. A <buffer> is received when this event is triggered.

Event: 'timeout'

Emitted if the socket times out from inactivity. This is only to notify that the socket has been idle. The user must manually close the connection.

Event: 'failedlogin'

Emitted when the failedLoginMatch pattern is provided and a match is found from the host. The 'destroy()' method is called directly following this event.

Event: 'error'

Emitted when an error occurs. The 'close' event will be called directly following this event.

Event: 'end'

Emitted when the other end of the socket (remote host) sends a FIN packet.

Event: 'close'

Emitted once the socket is fully closed.