# Engine.IO client

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This is the client for [Engine.IO](http://github.com/automattic/engine.io),
the implementation of transport-based cross-browser/cross-device
bi-directional communication layer for [Socket.IO](http://github.com/automattic/socket.io).

## How to use

### Standalone

You can find an `engine.io.js` file in this repository, which is a
standalone build you can use as follows:

```html
<script src="/path/to/engine.io.js"></script>
<script>
  // eio = Socket
  var socket = eio('ws://localhost');
  socket.on('open', function(){
    socket.on('message', function(data){});
    socket.on('close', function(){});
  });
</script>
```

### With browserify

Engine.IO is a commonjs module, which means you can include it by using
`require` on the browser and package using [browserify](http://browserify.org/):

1. install the client package

    ```bash
    $ npm install engine.io-client
    ```

1. write your app code

    ```js
    var socket = require('engine.io-client')('ws://localhost');
    socket.on('open', function(){
      socket.on('message', function(data){});
      socket.on('close', function(){});
    });
    ```

1. build your app bundle

    ```bash
    $ browserify app.js > bundle.js
    ```

1. include on your page

    ```html
    <script src="/path/to/bundle.js"></script>
    ```

### Sending and receiving binary

```html
<script src="/path/to/engine.io.js"></script>
<script>
  var socket = new eio.Socket('ws://localhost/');
  socket.binaryType = 'blob';
  socket.on('open', function () {
    socket.send(new Int8Array(5));
    socket.on('message', function(blob){});
    socket.on('close', function(){ });
  });
</script>
```

### Node.JS

Add `engine.io-client` to your `package.json` and then:

```js
var socket = require('engine.io-client')('ws://localhost');
socket.on('open', function(){
  socket.on('message', function(data){});
  socket.on('close', function(){});
});
```

## Features

- Lightweight
- Runs on browser and node.js seamlessly
- Transports are independent of `Engine`
  - Easy to debug
  - Easy to unit test
- Runs inside HTML5 WebWorker
- Can send and receive binary data
  - Receives as ArrayBuffer or Blob when in browser, and Buffer or ArrayBuffer
    in Node
  - When XHR2 or WebSockets are used, binary is emitted directly. Otherwise
    binary is encoded into base64 strings, and decoded when binary types are
    supported.
  - With browsers that don't support ArrayBuffer, an object { base64: true,
    data: dataAsBase64String } is emitted on the `message` event.

## API

### Socket

The client class. Mixes in [Emitter](http://github.com/component/emitter).
Exposed as `eio` in the browser standalone build.

#### Properties

- `protocol` _(Number)_: protocol revision number
- `binaryType` _(String)_ : can be set to 'arraybuffer' or 'blob' in browsers,
  and `buffer` or `arraybuffer` in Node. Blob is only used in browser if it's
  supported.

#### Events

- `open`
  - Fired upon successful connection.
- `message`
  - Fired when data is received from the server.
  - **Arguments**
    - `String` | `ArrayBuffer`: utf-8 encoded data or ArrayBuffer containing
      binary data
- `close`
  - Fired upon disconnection. In compliance with the WebSocket API spec, this event may be 
    fired even if the `open` event does not occur (i.e. due to connection error or `close()`).
- `error`
  - Fired when an error occurs.
- `flush`
  - Fired upon completing a buffer flush
- `drain`
  - Fired after `drain` event of transport if writeBuffer is empty
- `upgradeError`
  - Fired if an error occurs with a transport we're trying to upgrade to.
- `upgrade`
  - Fired upon upgrade success, after the new transport is set

#### Methods

- **constructor**
    - Initializes the client
    - **Parameters**
      - `String` uri
      - `Object`: optional, options object
    - **Options**
      - `agent` (`http.Agent`): `http.Agent` to use, defaults to `false` (NodeJS only)
      - `upgrade` (`Boolean`): defaults to true, whether the client should try
      to upgrade the transport from long-polling to something better.
      - `forceJSONP` (`Boolean`): forces JSONP for polling transport.
      - `jsonp` (`Boolean`): determines whether to use JSONP when
        necessary for polling. If disabled (by settings to false) an error will
        be emitted (saying "No transports available") if no other transports
        are available. If another transport is available for opening a
        connection (e.g. WebSocket) that transport
        will be used instead.
      - `forceBase64` (`Boolean`): forces base 64 encoding for polling transport even when XHR2 responseType is available and WebSocket even if the used standard supports binary.
      - `enablesXDR` (`Boolean`): enables XDomainRequest for IE8 to avoid loading bar flashing with click sound. default to `false` because XDomainRequest has a flaw of not sending cookie.
      - `timestampRequests` (`Boolean`): whether to add the timestamp with
        each transport request. Note: this is ignored if the browser is
        IE or Android, in which case requests are always stamped (`false`)
      - `timestampParam` (`String`): timestamp parameter (`t`)
      - `policyPort` (`Number`): port the policy server listens on (`843`)
      - `path` (`String`): path to connect to, default is `/engine.io`
      - `transports` (`Array`): a list of transports to try (in order).
      Defaults to `['polling', 'websocket']`. `Engine`
      always attempts to connect directly with the first one, provided the
      feature detection test for it passes.
      - `rememberUpgrade` (`Boolean`): defaults to false.
        If true and if the previous websocket connection to the server succeeded,
        the connection attempt will bypass the normal upgrade process and will initially
        try websocket. A connection attempt following a transport error will use the 
        normal upgrade process. It is recommended you turn this on only when using
        SSL/TLS connections, or if you know that your network does not block websockets.
- `send`
    - Sends a message to the server
    - **Parameters**
      - `String` | `ArrayBuffer` | `ArrayBufferView` | `Blob`: data to send
      - `Function`: optional, callback upon `drain`
- `close`
    - Disconnects the client.

### Transport

The transport class. Private. _Inherits from EventEmitter_.

#### Events

- `poll`: emitted by polling transports upon starting a new request
- `pollComplete`: emitted by polling transports upon completing a request
- `drain`: emitted by polling transports upon a buffer drain

## Tests

`engine.io-client` is used to test
[engine](http://github.com/automattic/engine.io). Running the `engine.io`
test suite ensures the client works and vice-versa.

Browser tests are run using [zuul](https://github.com/defunctzombie/zuul). You can
run the tests locally using the following command.

```
./node_modules/.bin/zuul --local 8080 -- test/index.js
```

Additionally, `engine.io-client` has a standalone test suite you can run
with `make test` which will run node.js and browser tests. You must have zuul setup with
a saucelabs account.

## Support

The support channels for `engine.io-client` are the same as `socket.io`:
  - irc.freenode.net **#socket.io**
  - [Google Groups](http://groups.google.com/group/socket_io)
  - [Website](http://socket.io)

## Development

To contribute patches, run tests or benchmarks, make sure to clone the
repository:

```bash
git clone git://github.com/automattic/engine.io-client.git
```

Then:

```bash
cd engine.io-client
npm install
```

See the `Tests` section above for how to run tests before submitting any patches.

## License

MIT - Copyright (c) 2014 Automattic, Inc.