engine.io-client

What is engine.io-client?

The engine.io-client npm package is a client-side library that provides bidirectional event-based communication between web clients and servers. It is the client component of the Engine.IO protocol, which is a transport layer built on top of WebSocket and other transport mechanisms to provide a reliable, low-latency connection for real-time applications.

What are engine.io-client's main functionalities?

Establishing a connection

This feature allows you to establish a connection to an Engine.IO server. The 'open' event is emitted when the connection is successfully established.

const eio = require('engine.io-client');
const socket = eio('ws://localhost');
socket.on('open', function(){
  console.log('Connection established');
});

Sending messages

Once a connection is established, you can send messages to the server using the 'send' method.

socket.send('Hello World!');

Receiving messages

You can listen for messages from the server with the 'message' event. The callback function receives the message data as its argument.

socket.on('message', function(data){
  console.log('Received message:', data);
});

Handling connection errors

The 'error' event is emitted when there is a connection error. The callback function receives the error object as its argument.

socket.on('error', function(error){
  console.error('Connection error:', error);
});

Closing the connection

The 'close' event is emitted when the connection is closed. The callback function receives the reason and a description as arguments.

socket.on('close', function(reason, description){
  console.log('Connection closed', reason, description);
});

Other packages similar to engine.io-client

socket.io-client

Socket.IO-client is a more feature-rich client-side library that provides real-time bidirectional event-based communication, similar to engine.io-client. It is built on top of engine.io-client and adds additional features like namespaces, rooms, and automatic reconnection.

ws

The 'ws' package is a simple WebSocket client and server implementation for Node.js. Unlike engine.io-client, it does not provide built-in mechanisms for features like automatic reconnection and binary data handling, but it allows for more control over the WebSocket connection.

faye-websocket

Faye-websocket is a WebSocket client and server for Node.js and Ruby. It provides a simple API for handling WebSocket connections but does not include the higher-level abstractions and fallback mechanisms that engine.io-client offers.

README

Engine.IO client

This is the client for Engine.IO, the implementation of transport-based cross-browser/cross-device bi-directional communication layer for Socket.IO.

How to use

Standalone

You can find an engine.io.js file in this repository, which is a standalone build you can use as follows:

<script src="/path/to/engine.io.js"></script>
<script>
  // eio = Socket
  const socket = eio('ws://localhost');
  socket.on('open', () => {
    socket.on('message', (data) => {});
    socket.on('close', () => {});
  });
</script>

With browserify

Engine.IO is a commonjs module, which means you can include it by using require on the browser and package using browserify:

1. install the client package

   $ npm install engine.io-client
   

2. write your app code

   const { Socket } = require('engine.io-client');
   const socket = new Socket('ws://localhost');
   socket.on('open', () => {
     socket.on('message', (data) => {});
     socket.on('close', () => {});
   });
   

3. build your app bundle

   $ browserify app.js > bundle.js
   

4. include on your page

   <script src="/path/to/bundle.js"></script>
   

Sending and receiving binary

<script src="/path/to/engine.io.js"></script>
<script>
  const socket = eio('ws://localhost/');
  socket.binaryType = 'blob';
  socket.on('open', () => {
    socket.send(new Int8Array(5));
    socket.on('message', (blob) => {});
    socket.on('close', () => {});
  });
</script>

Node.JS

Add engine.io-client to your package.json and then:

const { Socket } = require('engine.io-client');
const socket = new Socket('ws://localhost');
socket.on('open', () => {
  socket.on('message', (data) => {});
  socket.on('close', () => {});
});

Node.js with certificates

const opts = {
  key: fs.readFileSync('test/fixtures/client.key'),
  cert: fs.readFileSync('test/fixtures/client.crt'),
  ca: fs.readFileSync('test/fixtures/ca.crt')
};

const { Socket } = require('engine.io-client');
const socket = new Socket('ws://localhost', opts);
socket.on('open', () => {
  socket.on('message', (data) => {});
  socket.on('close', () => {});
});

Node.js with extraHeaders

const opts = {
  extraHeaders: {
    'X-Custom-Header-For-My-Project': 'my-secret-access-token',
    'Cookie': 'user_session=NI2JlCKF90aE0sJZD9ZzujtdsUqNYSBYxzlTsvdSUe35ZzdtVRGqYFr0kdGxbfc5gUOkR9RGp20GVKza; path=/; expires=Tue, 07-Apr-2015 18:18:08 GMT; secure; HttpOnly'
  }
};

const { Socket } = require('engine.io-client');
const socket = new Socket('ws://localhost', opts);
socket.on('open', () => {
  socket.on('message', (data) => {});
  socket.on('close', () => {});
});

In the browser, the WebSocket object does not support additional headers. In case you want to add some headers as part of some authentication mechanism, you can use the transportOptions attribute. Please note that in this case the headers won't be sent in the WebSocket upgrade request.

// WILL NOT WORK in the browser
const socket = new Socket('http://localhost', {
  extraHeaders: {
    'X-Custom-Header-For-My-Project': 'will not be sent'
  }
});
// WILL NOT WORK
const socket = new Socket('http://localhost', {
  transports: ['websocket'], // polling is disabled
  transportOptions: {
    polling: {
      extraHeaders: {
        'X-Custom-Header-For-My-Project': 'will not be sent'
      }
    }
  }
});
// WILL WORK
const socket = new Socket('http://localhost', {
  transports: ['polling', 'websocket'],
  transportOptions: {
    polling: {
      extraHeaders: {
        'X-Custom-Header-For-My-Project': 'will be used'
      }
    }
  }
});

Features

• Lightweight
• Runs on browser and node.js seamlessly
• Transports are independent of Engine
  • Easy to debug
  • Easy to unit test
• Runs inside HTML5 WebWorker
• Can send and receive binary data
  • Receives as ArrayBuffer or Blob when in browser, and Buffer or ArrayBuffer in Node
  • When XHR2 or WebSockets are used, binary is emitted directly. Otherwise binary is encoded into base64 strings, and decoded when binary types are supported.
  • With browsers that don't support ArrayBuffer, an object { base64: true, data: dataAsBase64String } is emitted on the message event.

API

Socket

The client class. Mixes in Emitter. Exposed as eio in the browser standalone build.

Properties

• protocol (Number): protocol revision number
• binaryType (String) : can be set to 'arraybuffer' or 'blob' in browsers, and buffer or arraybuffer in Node. Blob is only used in browser if it's supported.

Events

• open
  • Fired upon successful connection.
• message
  • Fired when data is received from the server.
  • Arguments
    • String | ArrayBuffer: utf-8 encoded data or ArrayBuffer containing binary data
• close
  • Fired upon disconnection. In compliance with the WebSocket API spec, this event may be fired even if the open event does not occur (i.e. due to connection error or close()).
• error
  • Fired when an error occurs.
• flush
  • Fired upon completing a buffer flush
• drain
  • Fired after drain event of transport if writeBuffer is empty
• upgradeError
  • Fired if an error occurs with a transport we're trying to upgrade to.
• upgrade
  • Fired upon upgrade success, after the new transport is set
• ping
  • Fired upon receiving a ping packet.
• pong
  • Fired upon flushing a pong packet (ie: actual packet write out)

Methods

• constructor
  • Initializes the client
  • Parameters
    • String uri
    • Object: optional, options object
  • Options
    • agent (http.Agent): http.Agent to use, defaults to false (NodeJS only)
    • upgrade (Boolean): defaults to true, whether the client should try to upgrade the transport from long-polling to something better.
    • forceBase64 (Boolean): forces base 64 encoding for polling transport even when XHR2 responseType is available and WebSocket even if the used standard supports binary.
    • withCredentials (Boolean): defaults to false, whether to include credentials (cookies, authorization headers, TLS client certificates, etc.) with cross-origin XHR polling requests.
    • timestampRequests (Boolean): whether to add the timestamp with each transport request. Note: polling requests are always stamped unless this option is explicitly set to false (false)
    • timestampParam (String): timestamp parameter (t)
    • path (String): path to connect to, default is /engine.io
    • transports (Array): a list of transports to try (in order). Defaults to ['polling', 'websocket', 'webtransport']. Engine always attempts to connect directly with the first one, provided the feature detection test for it passes.
    • transportOptions (Object): hash of options, indexed by transport name, overriding the common options for the given transport
    • rememberUpgrade (Boolean): defaults to false. If true and if the previous websocket connection to the server succeeded, the connection attempt will bypass the normal upgrade process and will initially try websocket. A connection attempt following a transport error will use the normal upgrade process. It is recommended you turn this on only when using SSL/TLS connections, or if you know that your network does not block websockets.
    • pfx (String|Buffer): Certificate, Private key and CA certificates to use for SSL. Can be used in Node.js client environment to manually specify certificate information.
    • key (String): Private key to use for SSL. Can be used in Node.js client environment to manually specify certificate information.
    • passphrase (String): A string of passphrase for the private key or pfx. Can be used in Node.js client environment to manually specify certificate information.
    • cert (String): Public x509 certificate to use. Can be used in Node.js client environment to manually specify certificate information.
    • ca (String|Array): An authority certificate or array of authority certificates to check the remote host against.. Can be used in Node.js client environment to manually specify certificate information.
    • ciphers (String): A string describing the ciphers to use or exclude. Consult the cipher format list for details on the format. Can be used in Node.js client environment to manually specify certificate information.
    • rejectUnauthorized (Boolean): If true, the server certificate is verified against the list of supplied CAs. An 'error' event is emitted if verification fails. Verification happens at the connection level, before the HTTP request is sent. Can be used in Node.js client environment to manually specify certificate information.
    • perMessageDeflate (Object|Boolean): parameters of the WebSocket permessage-deflate extension (see ws module api docs). Set to false to disable. (true)
      • threshold (Number): data is compressed only if the byte size is above this value. This option is ignored on the browser. (1024)
    • extraHeaders (Object): Headers that will be passed for each request to the server (via xhr-polling and via websockets). These values then can be used during handshake or for special proxies. Can only be used in Node.js client environment.
    • localAddress (String): the local IP address to connect to
    • autoUnref (Boolean): whether the transport should be unref'd upon creation. This calls unref on the underlying timers and sockets so that the program is allowed to exit if they are the only timers/sockets in the event system (Node.js only)
    • useNativeTimers (Boolean): Whether to always use the native timeouts. This allows the client to reconnect when the native timeout functions are overridden, such as when mock clocks are installed with @sinonjs/fake-timers.
  • Polling-only options
    • requestTimeout (Number): Timeout for xhr-polling requests in milliseconds (0)
  • Websocket-only options
    • protocols (Array): a list of subprotocols (see MDN reference)
    • closeOnBeforeunload (Boolean): whether to silently close the connection when the beforeunload event is emitted in the browser (defaults to false)
• send
  • Sends a message to the server
  • Parameters
    • String | ArrayBuffer | ArrayBufferView | Blob: data to send
    • Object: optional, options object
    • Function: optional, callback upon drain
  • Options
    • compress (Boolean): whether to compress sending data. This option is ignored and forced to be true on the browser. (true)
• close
  • Disconnects the client.

Transport

The transport class. Private. Inherits from EventEmitter.

Events

• poll: emitted by polling transports upon starting a new request
• pollComplete: emitted by polling transports upon completing a request
• drain: emitted by polling transports upon a buffer drain

Tests

engine.io-client is used to test engine. Running the engine.io test suite ensures the client works and vice-versa.

Browser tests are run using zuul. You can run the tests locally using the following command.

./node_modules/.bin/zuul --local 8080 -- test/index.js

Additionally, engine.io-client has a standalone test suite you can run with make test which will run node.js and browser tests. You must have zuul setup with a saucelabs account.

Support

The support channels for engine.io-client are the same as socket.io:

• irc.freenode.net #socket.io
• Google Groups
• Website

Development

To contribute patches, run tests or benchmarks, make sure to clone the repository:

git clone git://github.com/socketio/engine.io-client.git

Then:

cd engine.io-client
npm install

See the Tests section above for how to run tests before submitting any patches.

License

MIT - Copyright (c) 2014 Automattic, Inc.