# ws: a Node.js WebSocket library

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

Passes the quite extensive Autobahn test suite: [server][server-report],
[client][client-report].

**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`](https://developer.mozilla.org/en-US/docs/Web/API/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](https://github.com/heineiuo/isomorphic-ws).

## Table of Contents

* [Protocol support](#protocol-support)
* [Installing](#installing)
  + [Opt-in for performance and spec compliance](#opt-in-for-performance-and-spec-compliance)
* [API docs](#api-docs)
* [WebSocket compression](#websocket-compression)
* [Usage examples](#usage-examples)
  + [Sending and receiving text data](#sending-and-receiving-text-data)
  + [Sending binary data](#sending-binary-data)
  + [Server example](#server-example)
  + [Broadcast example](#broadcast-example)
  + [ExpressJS example](#expressjs-example)
  + [echo.websocket.org demo](#echowebsocketorg-demo)
  + [Other examples](#other-examples)
* [Error handling best practices](#error-handling-best-practices)
* [FAQ](#faq)
  + [How to get the IP address of the client?](#how-to-get-the-ip-address-of-the-client)
  + [How to detect and close broken connections?](#how-to-detect-and-close-broken-connections)
  + [How to connect via a proxy?](#how-to-connect-via-a-proxy)
* [Changelog](#changelog)
* [License](#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`](./doc/ws.md) for Node.js-like docs for the ws classes.

## WebSocket compression

ws supports the [permessage-deflate extension][permessage-deflate] 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][node-zlib-bug] 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][node-zlib-deflaterawdocs].

See [the docs][ws-server-options] for more options.

```js
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.
    clientMaxWindowBits: 10,       // 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`.

```js
const WebSocket = require('ws');

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

## Usage examples

### Sending and receiving text data

```js
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

```js
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

```js
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

```js
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

```js
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

```js
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

```js
// 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.

```js
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.

```js
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.

```js
const WebSocket = require('ws');

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

function noop() {}

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(noop);
  });
}, 30000);
```

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

### 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][changelog] for changelog entries.

## License

[MIT](LICENSE)

[https-proxy-agent]: https://github.com/TooTallNate/node-https-proxy-agent
[socks-proxy-agent]: https://github.com/TooTallNate/node-socks-proxy-agent
[client-report]: http://websockets.github.io/ws/autobahn/clients/
[server-report]: http://websockets.github.io/ws/autobahn/servers/
[permessage-deflate]: https://tools.ietf.org/html/rfc7692
[changelog]: https://github.com/websockets/ws/releases
[node-zlib-bug]: https://github.com/nodejs/node/issues/8871
[node-zlib-deflaterawdocs]: https://nodejs.org/api/zlib.html#zlib_zlib_createdeflateraw_options
[ws-server-options]: https://github.com/websockets/ws/blob/master/doc/ws.md#new-websocketserveroptions-callback