ws

What is ws?

The 'ws' npm package is a simple to use, fast, and thoroughly tested WebSocket client and server implementation. It provides the necessary tools to build real-time applications with WebSocket support in Node.js.

What are ws's main functionalities?

Creating a WebSocket server

This code sample demonstrates how to create a WebSocket server that listens on port 8080. When a client connects, it sets up an event listener for messages and logs them. It also sends a message 'something' to the client.

const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 8080 });
wss.on('connection', function connection(ws) {
  ws.on('message', function incoming(message) {
    console.log('received: %s', message);
  });
  ws.send('something');
});

Creating a WebSocket client

This code sample shows how to create a WebSocket client that connects to a WebSocket server. Once the connection is open, it sends a message 'something' to the server and logs any messages received from the server.

const WebSocket = require('ws');
const ws = new WebSocket('ws://www.host.com/path');
ws.on('open', function open() {
  ws.send('something');
});
ws.on('message', function incoming(data) {
  console.log(data);
});

Broadcasting to all clients

This code sample illustrates how to broadcast a message to all connected clients except the sender. It loops through all clients and sends the message if the client is not the sender and the connection is open.

const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 8080 });
wss.on('connection', function connection(ws) {
  ws.on('message', function incoming(data) {
    wss.clients.forEach(function each(client) {
      if (client !== ws && client.readyState === WebSocket.OPEN) {
        client.send(data);
      }
    });
  });
});

Other packages similar to ws

socket.io

Socket.IO is a library that enables real-time, bidirectional and event-based communication between web clients and servers. It's more feature-rich than 'ws', providing built-in support for broadcasting to multiple sockets, handling reconnection, and other high-level features. However, it's also heavier and less minimalistic than 'ws'.

faye-websocket

Faye is a WebSocket (and EventSource) implementation that is designed for ease of use and compatibility across a wide range of browsers. It's similar to 'ws' but also works in client-side JavaScript, unlike 'ws' which is Node.js only.

websocket

The 'websocket' package provides both client and server implementations of the WebSocket protocol. It offers a similar API to 'ws' but also includes a fallback option for older browsers that do not support WebSockets, using Flash sockets or other transport protocols.

README

ws: a Node.js WebSocket library

ws is a simple to use, blazing fast, and thoroughly tested WebSocket client and server implementation.

Passes the quite extensive Autobahn test suite: server, client.

Note: This module does not work in the browser. The client in the docs is a reference to a back end with the role of a client in the WebSocket communication. Browser clients must use the native WebSocket object. To make the same code work seamlessly on Node.js and the browser, you can use one of the many wrappers available on npm, like isomorphic-ws.

Table of Contents

• Protocol support
• Installing
  • Opt-in for performance and spec compliance
• API docs
• WebSocket compression
• Usage examples
  • Sending and receiving text data
  • Sending binary data
  • Simple server
  • External HTTP/S server
  • Multiple servers sharing a single HTTP/S server
  • Server broadcast
  • echo.websocket.org demo
  • Other examples
• Error handling best practices
• FAQ
  • How to get the IP address of the client?
  • How to detect and close broken connections?
  • How to connect via a proxy?
• Changelog
• License

Protocol support

• HyBi drafts 07-12 (Use the option protocolVersion: 8)
• HyBi drafts 13-17 (Current default, alternatively option protocolVersion: 13)

Installing

npm install ws

Opt-in for performance and spec compliance

There are 2 optional modules that can be installed along side with the ws module. These modules are binary addons which improve certain operations. Prebuilt binaries are available for the most popular platforms so you don't necessarily need to have a C++ compiler installed on your machine.

• npm install --save-optional bufferutil: Allows to efficiently perform operations such as masking and unmasking the data payload of the WebSocket frames.
• npm install --save-optional utf-8-validate: Allows to efficiently check if a message contains valid UTF-8 as required by the spec.

API docs

See /doc/ws.md for Node.js-like docs for the ws classes.

WebSocket compression

ws supports the permessage-deflate extension which enables the client and server to negotiate a compression algorithm and its parameters, and then selectively apply it to the data payloads of each WebSocket message.

The extension is disabled by default on the server and enabled by default on the client. It adds a significant overhead in terms of performance and memory consumption so we suggest to enable it only if it is really needed.

Note that Node.js has a variety of issues with high-performance compression, where increased concurrency, especially on Linux, can lead to catastrophic memory fragmentation and slow performance. If you intend to use permessage-deflate in production, it is worthwhile to set up a test representative of your workload and ensure Node.js/zlib will handle it with acceptable performance and memory usage.

Tuning of permessage-deflate can be done via the options defined below. You can also use zlibDeflateOptions and zlibInflateOptions, which is passed directly into the creation of raw deflate/inflate streams.

See the docs for more options.

const WebSocket = require('ws');

const wss = new WebSocket.Server({
  port: 8080,
  perMessageDeflate: {
    zlibDeflateOptions: {
      // See zlib defaults.
      chunkSize: 1024,
      memLevel: 7,
      level: 3
    },
    zlibInflateOptions: {
      chunkSize: 10 * 1024
    },
    // Other options settable:
    clientNoContextTakeover: true, // Defaults to negotiated value.
    serverNoContextTakeover: true, // Defaults to negotiated value.
    serverMaxWindowBits: 10, // Defaults to negotiated value.
    // Below options specified as default values.
    concurrencyLimit: 10, // Limits zlib concurrency for perf.
    threshold: 1024 // Size (in bytes) below which messages
    // should not be compressed.
  }
});

The client will only use the extension if it is supported and enabled on the server. To always disable the extension on the client set the perMessageDeflate option to false.

const WebSocket = require('ws');

const ws = new WebSocket('ws://www.host.com/path', {
  perMessageDeflate: false
});

Usage examples

Sending and receiving text data

const WebSocket = require('ws');

const ws = new WebSocket('ws://www.host.com/path');

ws.on('open', function open() {
  ws.send('something');
});

ws.on('message', function incoming(data) {
  console.log(data);
});

Sending binary data

const WebSocket = require('ws');

const ws = new WebSocket('ws://www.host.com/path');

ws.on('open', function open() {
  const array = new Float32Array(5);

  for (var i = 0; i < array.length; ++i) {
    array[i] = i / 2;
  }

  ws.send(array);
});

Simple server

const WebSocket = require('ws');

const wss = new WebSocket.Server({ port: 8080 });

wss.on('connection', function connection(ws) {
  ws.on('message', function incoming(message) {
    console.log('received: %s', message);
  });

  ws.send('something');
});

External HTTP/S server

const fs = require('fs');
const https = require('https');
const WebSocket = require('ws');

const server = new https.createServer({
  cert: fs.readFileSync('/path/to/cert.pem'),
  key: fs.readFileSync('/path/to/key.pem')
});
const wss = new WebSocket.Server({ server });

wss.on('connection', function connection(ws) {
  ws.on('message', function incoming(message) {
    console.log('received: %s', message);
  });

  ws.send('something');
});

server.listen(8080);

Multiple servers sharing a single HTTP/S server

const http = require('http');
const WebSocket = require('ws');

const server = http.createServer();
const wss1 = new WebSocket.Server({ noServer: true });
const wss2 = new WebSocket.Server({ noServer: true });

wss1.on('connection', function connection(ws) {
  // ...
});

wss2.on('connection', function connection(ws) {
  // ...
});

server.on('upgrade', function upgrade(request, socket, head) {
  const pathname = url.parse(request.url).pathname;

  if (pathname === '/foo') {
    wss1.handleUpgrade(request, socket, head, function done(ws) {
      wss1.emit('connection', ws, request);
    });
  } else if (pathname === '/bar') {
    wss2.handleUpgrade(request, socket, head, function done(ws) {
      wss2.emit('connection', ws, request);
    });
  } else {
    socket.destroy();
  }
});

server.listen(8080);

Server broadcast

const WebSocket = require('ws');

const wss = new WebSocket.Server({ port: 8080 });

// Broadcast to all.
wss.broadcast = function broadcast(data) {
  wss.clients.forEach(function each(client) {
    if (client.readyState === WebSocket.OPEN) {
      client.send(data);
    }
  });
};

wss.on('connection', function connection(ws) {
  ws.on('message', function incoming(data) {
    // Broadcast to everyone else.
    wss.clients.forEach(function each(client) {
      if (client !== ws && client.readyState === WebSocket.OPEN) {
        client.send(data);
      }
    });
  });
});

echo.websocket.org demo

const WebSocket = require('ws');

const ws = new WebSocket('wss://echo.websocket.org/', {
  origin: 'https://websocket.org'
});

ws.on('open', function open() {
  console.log('connected');
  ws.send(Date.now());
});

ws.on('close', function close() {
  console.log('disconnected');
});

ws.on('message', function incoming(data) {
  console.log(`Roundtrip time: ${Date.now() - data} ms`);

  setTimeout(function timeout() {
    ws.send(Date.now());
  }, 500);
});

Other examples

For a full example with a browser client communicating with a ws server, see the examples folder.

Otherwise, see the test cases.

Error handling best practices

// If the WebSocket is closed before the following send is attempted
ws.send('something');

// Errors (both immediate and async write errors) can be detected in an optional
// callback. The callback is also the only way of being notified that data has
// actually been sent.
ws.send('something', function ack(error) {
  // If error is not defined, the send has been completed, otherwise the error
  // object will indicate what failed.
});

// Immediate errors can also be handled with `try...catch`, but **note** that
// since sends are inherently asynchronous, socket write failures will *not* be
// captured when this technique is used.
try {
  ws.send('something');
} catch (e) {
  /* handle error */
}

FAQ

How to get the IP address of the client?

The remote IP address can be obtained from the raw socket.

const WebSocket = require('ws');

const wss = new WebSocket.Server({ port: 8080 });

wss.on('connection', function connection(ws, req) {
  const ip = req.connection.remoteAddress;
});

When the server runs behind a proxy like NGINX, the de-facto standard is to use the X-Forwarded-For header.

wss.on('connection', function connection(ws, req) {
  const ip = req.headers['x-forwarded-for'].split(/\s*,\s*/)[0];
});

How to detect and close broken connections?

Sometimes the link between the server and the client can be interrupted in a way that keeps both the server and the client unaware of the broken state of the connection (e.g. when pulling the cord).

In these cases ping messages can be used as a means to verify that the remote endpoint is still responsive.

const WebSocket = require('ws');

function noop() {}

function heartbeat() {
  this.isAlive = true;
}

const wss = new WebSocket.Server({ port: 8080 });

wss.on('connection', function connection(ws) {
  ws.isAlive = true;
  ws.on('pong', heartbeat);
});

const interval = setInterval(function ping() {
  wss.clients.forEach(function each(ws) {
    if (ws.isAlive === false) return ws.terminate();

    ws.isAlive = false;
    ws.ping(noop);
  });
}, 30000);

Pong messages are automatically sent in response to ping messages as required by the spec.

Just like the server example above your clients might as well lose connection without knowing it. You might want to add a ping listener on your clients to prevent that. A simple implementation would be:

const WebSocket = require('ws');

function heartbeat() {
  clearTimeout(this.pingTimeout);

  // Use `WebSocket#terminate()` and not `WebSocket#close()`. Delay should be
  // equal to the interval at which your server sends out pings plus a
  // conservative assumption of the latency.
  this.pingTimeout = setTimeout(() => {
    this.terminate();
  }, 30000 + 1000);
}

const client = new WebSocket('wss://echo.websocket.org/');

client.on('open', heartbeat);
client.on('ping', heartbeat);
client.on('close', function clear() {
  clearTimeout(this.pingTimeout);
});

How to connect via a proxy?

Use a custom http.Agent implementation like https-proxy-agent or socks-proxy-agent.

Changelog

We're using the GitHub releases for changelog entries.

License

MIT