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. See http://websockets.github.io/ws/ for the full reports.

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.

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
  • Server example
  • Broadcast example
  • ExpressJS example
  • 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?
• 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 --save 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 enabled by default but adds a significant overhead in terms of performance and memory comsumption. We suggest to use WebSocket compression only if it is really needed.

To disable the extension you can set the perMessageDeflate option to false. On the server:

const WebSocket = require('ws');

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

On the client:

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, flags) {
  // flags.binary will be set if a binary data is received.
  // flags.masked will be set if the data was masked.
});

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);
});

Server example

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');
});

Broadcast example

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);
      }
    });
  });
});

ExpressJS example

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

const app = express();

app.use(function (req, res) {
  res.send({ msg: "hello" });
});

const server = http.createServer(app);
const wss = new WebSocket.Server({ server });

wss.on('connection', function connection(ws) {
  const location = url.parse(ws.upgradeReq.url, true);
  // You might use location.query.access_token to authenticate or share sessions
  // or ws.upgradeReq.headers.cookie (see http://stackoverflow.com/a/16395220/151312)

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

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

server.listen(8080, function listening() {
  console.log('Listening on %d', server.address().port);
});

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, flags) {
  console.log(`Roundtrip time: ${Date.now() - data} ms`, flags);

  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) {
  const ip = ws.upgradeReq.connection.remoteAddress;
});

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

wss.on('connection', function connection(ws) {
  const ip = ws.upgradeReq.headers['x-forwarded-for'];
});

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 unware 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');

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

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

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('', false, true);
  });
}, 30000);

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

Changelog

We're using the GitHub releases for changelog entries.

License

MIT