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.

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);
});

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, req) {
  const location = url.parse(req.url, true);
  // You might use location.query.access_token to authenticate or share sessions
  // or req.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) {
  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'];
});

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');

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 response to ping messages as required by the spec.

How to connect via a proxy?

Changelog

We're using the GitHub releases for changelog entries.