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 backend 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.

Protocol support
Installing
- Opt-in for performance
  - Legacy opt-in for performance
API docs
WebSocket compression
Usage examples
FAQ
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

bufferutil is an optional module that can be installed alongside the ws module:

npm install --save-optional bufferutil

This is a binary addon that improves the performance of certain operations such as masking and unmasking the data payload of the WebSocket frames. Prebuilt binaries are available for the most popular platforms, so you don't necessarily need to have a C++ compiler installed on your machine.

To force ws to not use bufferutil, use the WS_NO_BUFFER_UTIL environment variable. This can be useful to enhance security in systems where a user can put a package in the package search path of an application of another user, due to how the Node.js resolver algorithm works.

Legacy opt-in for performance

If you are running on an old version of Node.js (prior to v18.14.0), ws also supports the utf-8-validate module:

npm install --save-optional utf-8-validate

This contains a binary polyfill for buffer.isUtf8().

To force ws not to use utf-8-validate, use the WS_NO_UTF_8_VALIDATE environment variable.

API docs

See /doc/ws.md for Node.js-like documentation of ws classes and utility functions.

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.

import WebSocket, { WebSocketServer } from 'ws';

const wss = new WebSocketServer({
  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 if context takeover is disabled.
  }
});

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.

import WebSocket from 'ws';

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

Usage examples

Sending and receiving text data

import WebSocket from 'ws';

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

ws.on('error', console.error);

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

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

Sending binary data

import WebSocket from 'ws';

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

ws.on('error', console.error);

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

import { WebSocketServer } from 'ws';

const wss = new WebSocketServer({ port: 8080 });

wss.on('connection', function connection(ws) {
  ws.on('error', console.error);

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

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

External HTTP/S server

import { createServer } from 'https';
import { readFileSync } from 'fs';
import { WebSocketServer } from 'ws';

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

wss.on('connection', function connection(ws) {
  ws.on('error', console.error);

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

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

server.listen(8080);

Multiple servers sharing a single HTTP/S server

import { createServer } from 'http';
import { WebSocketServer } from 'ws';

const server = createServer();
const wss1 = new WebSocketServer({ noServer: true });
const wss2 = new WebSocketServer({ noServer: true });

wss1.on('connection', function connection(ws) {
  ws.on('error', console.error);

  // ...
});

wss2.on('connection', function connection(ws) {
  ws.on('error', console.error);

  // ...
});

server.on('upgrade', function upgrade(request, socket, head) {
  const { pathname } = new URL(request.url, 'wss://base.url');

  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);

Client authentication

import { createServer } from 'http';
import { WebSocketServer } from 'ws';

function onSocketError(err) {
  console.error(err);
}

const server = createServer();
const wss = new WebSocketServer({ noServer: true });

wss.on('connection', function connection(ws, request, client) {
  ws.on('error', console.error);

  ws.on('message', function message(data) {
    console.log(`Received message ${data} from user ${client}`);
  });
});

server.on('upgrade', function upgrade(request, socket, head) {
  socket.on('error', onSocketError);

  // This function is not defined on purpose. Implement it with your own logic.
  authenticate(request, function next(err, client) {
    if (err || !client) {
      socket.write('HTTP/1.1 401 Unauthorized\r\n\r\n');
      socket.destroy();
      return;
    }

    socket.removeListener('error', onSocketError);

    wss.handleUpgrade(request, socket, head, function done(ws) {
      wss.emit('connection', ws, request, client);
    });
  });
});

server.listen(8080);

Also see the provided example using express-session.

Server broadcast

A client WebSocket broadcasting to all connected WebSocket clients, including itself.

import WebSocket, { WebSocketServer } from 'ws';

const wss = new WebSocketServer({ port: 8080 });

wss.on('connection', function connection(ws) {
  ws.on('error', console.error);

  ws.on('message', function message(data, isBinary) {
    wss.clients.forEach(function each(client) {
      if (client.readyState === WebSocket.OPEN) {
        client.send(data, { binary: isBinary });
      }
    });
  });
});

A client WebSocket broadcasting to every other connected WebSocket clients, excluding itself.

import WebSocket, { WebSocketServer } from 'ws';

const wss = new WebSocketServer({ port: 8080 });

wss.on('connection', function connection(ws) {
  ws.on('error', console.error);

  ws.on('message', function message(data, isBinary) {
    wss.clients.forEach(function each(client) {
      if (client !== ws && client.readyState === WebSocket.OPEN) {
        client.send(data, { binary: isBinary });
      }
    });
  });
});

Round-trip time

import WebSocket from 'ws';

const ws = new WebSocket('wss://websocket-echo.com/');

ws.on('error', console.error);

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

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

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

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

Use the Node.js streams API

import WebSocket, { createWebSocketStream } from 'ws';

const ws = new WebSocket('wss://websocket-echo.com/');

const duplex = createWebSocketStream(ws, { encoding: 'utf8' });

duplex.on('error', console.error);

duplex.pipe(process.stdout);
process.stdin.pipe(duplex);

Other examples

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

Otherwise, see the test cases.

FAQ

How to get the IP address of the client?

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

import { WebSocketServer } from 'ws';

const wss = new WebSocketServer({ port: 8080 });

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

  ws.on('error', console.error);
});

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(',')[0].trim();

  ws.on('error', console.error);
});

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.

import { WebSocketServer } from 'ws';

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

const wss = new WebSocketServer({ port: 8080 });

wss.on('connection', function connection(ws) {
  ws.isAlive = true;
  ws.on('error', console.error);
  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();
  });
}, 30000);

wss.on('close', function close() {
  clearInterval(interval);
});

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:

import WebSocket from 'ws';

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

  // Use `WebSocket#terminate()`, which immediately destroys the connection,
  // instead of `WebSocket#close()`, which waits for the close timer.
  // 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://websocket-echo.com/');

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