## Table of Contents

  - [Class: Server](#server)
    - [new Server(httpServer[, options])](#new-serverhttpserver-options)
    - [new Server(port[, options])](#new-serverport-options)
    - [new Server(options)](#new-serveroptions)
    - [server.sockets](#serversockets)
    - [server.engine.generateId](#serverenginegenerateid)
    - [server.serveClient([value])](#serverserveclientvalue)
    - [server.path([value])](#serverpathvalue)
    - [server.adapter([value])](#serveradaptervalue)
    - [server.origins([value])](#serveroriginsvalue)
    - [server.origins(fn)](#serveroriginsfn)
    - [server.attach(httpServer[, options])](#serverattachhttpserver-options)
    - [server.attach(port[, options])](#serverattachport-options)
    - [server.listen(httpServer[, options])](#serverlistenhttpserver-options)
    - [server.listen(port[, options])](#serverlistenport-options)
    - [server.bind(engine)](#serverbindengine)
    - [server.onconnection(socket)](#serveronconnectionsocket)
    - [server.of(nsp)](#serverofnsp)
    - [server.close([callback])](#serverclosecallback)
  - [Class: Namespace](#namespace)
    - [namespace.name](#namespacename)
    - [namespace.connected](#namespaceconnected)
    - [namespace.emit(eventName[, ...args])](#namespaceemiteventname-args)
    - [namespace.clients(callback)](#namespaceclientscallback)
    - [namespace.use(fn)](#namespaceusefn)
    - [Event: 'connect'](#event-connect)
    - [Event: 'connection'](#event-connect)
    - [Flag: 'volatile'](#flag-volatile)
    - [Flag: 'local'](#flag-local)
  - [Class: Socket](#socket)
    - [socket.id](#socketid)
    - [socket.rooms](#socketrooms)
    - [socket.client](#socketclient)
    - [socket.conn](#socketconn)
    - [socket.request](#socketrequest)
    - [socket.use(fn)](#socketusefn)
    - [socket.send([...args][, ack])](#socketsendargs-ack)
    - [socket.emit(eventName[, ...args][, ack])](#socketemiteventname-args-ack)
    - [socket.on(eventName, callback)](#socketoneventname-callback)
    - [socket.once(eventName, listener)](#socketonceeventname-listener)
    - [socket.removeListener(eventName, listener)](#socketremovelistenereventname-listener)
    - [socket.removeAllListeners([eventName])](#socketremovealllistenerseventname)
    - [socket.eventNames()](#socketeventnames)
    - [socket.join(room[, callback])](#socketjoinroom-callback)
    - [socket.join(rooms[, callback])](#socketjoinrooms-callback)
    - [socket.leave(room[, callback])](#socketleaveroom-callback)
    - [socket.to(room)](#sockettoroom)
    - [socket.in(room)](#socketinroom)
    - [socket.compress(value)](#socketcompressvalue)
    - [socket.disconnect(close)](#socketdisconnectclose)
    - [Flag: 'broadcast'](#flag-broadcast)
    - [Flag: 'volatile'](#flag-volatile-1)
    - [Event: 'disconnect'](#event-disconnect)
    - [Event: 'error'](#event-error)
    - [Event: 'disconnecting'](#event-disconnecting)
  - [Class: Client](#client)
    - [client.conn](#clientconn)
    - [client.request](#clientrequest)


### Server

Exposed by `require('socket.io')`.

#### new Server(httpServer[, options])

  - `httpServer` _(http.Server)_ the server to bind to.
  - `options` _(Object)_
    - `path` _(String)_: name of the path to capture (`/socket.io`)
    - `serveClient` _(Boolean)_: whether to serve the client files (`true`)
    - `adapter` _(Adapter)_: the adapter to use. Defaults to an instance of the `Adapter` that ships with socket.io which is memory based. See [socket.io-adapter](https://github.com/socketio/socket.io-adapter)
    - `origins` _(String)_: the allowed origins (`*`)
    - `allowRequest` _(Function)_: A function that receives a given handshake or upgrade request as its first parameter, and can decide whether to continue or not. The second argument is a function that needs to be called with the decided information: `fn(err, success)`, where `success` is a boolean value where false means that the request is rejected, and err is an error code.
    - `parser` _(Parser)_: the parser to use. Defaults to an instance of the `Parser` that ships with socket.io. See [socket.io-parser](https://github.com/socketio/socket.io-parser).

Works with and without `new`:

```js
var io = require('socket.io')();
// or
var Server = require('socket.io');
var io = new Server();
```

The same options passed to socket.io are always passed to the `engine.io` `Server` that gets created. See engine.io [options](https://github.com/socketio/engine.io#methods-1) as reference.

Among those options:

  - `pingTimeout` _(Number)_: how many ms without a pong packet to consider the connection closed (`60000`)
  - `pingInterval` _(Number)_: how many ms before sending a new ping packet (`25000`).

Those two parameters will impact the delay before a client knows the server is not available anymore. For example, if the underlying TCP connection is not closed properly due to a network issue, a client may have to wait up to `pingTimeout + pingInterval` ms before getting a `disconnect` event.

  - `transports` _(Array<String>)_: transports to allow connections to (`['polling', 'websocket']`).

**Note:** The order is important. By default, a long-polling connection is established first, and then upgraded to WebSocket if possible. Using `['websocket']` means there will be no fallback if a WebSocket connection cannot be opened.

#### new Server(port[, options])

  - `port` _(Number)_ a port to listen to (a new `http.Server` will be created)
  - `options` _(Object)_

See [above](#new-serverhttpserver-options) for available options.

#### new Server(options)

  - `options` _(Object)_

See [above](#new-serverhttpserver-options) for available options.

#### server.sockets

  * _(Namespace)_

The default (`/`) namespace.

#### server.serveClient([value])

  - `value` _(Boolean)_
  - **Returns** `Server|Boolean`

If `value` is `true` the attached server (see `Server#attach`) will serve the client files. Defaults to `true`. This method has no effect after `attach` is called. If no arguments are supplied this method returns the current value.

```js
// pass a server and the `serveClient` option
var io = require('socket.io')(http, { serveClient: false });

// or pass no server and then you can call the method
var io = require('socket.io')();
io.serveClient(false);
io.attach(http);
```

#### server.path([value])

  - `value` _(String)_
  - **Returns** `Server|String`

Sets the path `value` under which `engine.io` and the static files will be served. Defaults to `/socket.io`. If no arguments are supplied this method returns the current value.

#### server.adapter([value])

  - `value` _(Adapter)_
  - **Returns** `Server|Adapter`

Sets the adapter `value`. Defaults to an instance of the `Adapter` that ships with socket.io which is memory based. See [socket.io-adapter](https://github.com/socketio/socket.io-adapter). If no arguments are supplied this method returns the current value.

#### server.origins([value])

  - `value` _(String)_
  - **Returns** `Server|String`

Sets the allowed origins `value`. Defaults to any origins being allowed. If no arguments are supplied this method returns the current value.

#### server.origins(fn)

  - `fn` _(Function)_
  - **Returns** `Server`

Provides a function taking two arguments `origin:String` and `callback(error, success)`, where `success` is a boolean value indicating whether origin is allowed or not.

__Potential drawbacks__:
* in some situations, when it is not possible to determine `origin` it may have value of `*`
* As this function will be executed for every request, it is advised to make this function work as fast as possible
* If `socket.io` is used together with `Express`, the CORS headers will be affected only for `socket.io` requests. For Express can use [cors](https://github.com/expressjs/cors).

#### server.attach(httpServer[, options])

  - `httpServer` _(http.Server)_ the server to attach to
  - `options` _(Object)_

Attaches the `Server` to an engine.io instance on `httpServer` with the supplied `options` (optionally).

### server.attach(port[, options])

  - `port` _(Number)_ the port to listen on
  - `options` _(Object)_

Attaches the `Server` to an engine.io instance on a new http.Server with the supplied `options` (optionally).

#### server.listen(httpServer[, options])

Synonym of [server.attach(httpServer[, options])](#serverattachhttpserver-options).

#### server.listen(port[, options])

Synonym of [server.attach(port[, options])](#serverattachport-options).

#### server.bind(engine)

  - `engine` _(engine.Server)_
  - **Returns** `Server`

Advanced use only. Binds the server to a specific engine.io `Server` (or compatible API) instance.

#### server.onconnection(socket)

  - `socket` _(engine.Socket)_
  - **Returns** `Server`

Advanced use only. Creates a new `socket.io` client from the incoming engine.io (or compatible API) `Socket`.

#### server.of(nsp)

  - `nsp` _(String)_
  - **Returns** `Namespace`

Initializes and retrieves the given `Namespace` by its pathname identifier `nsp`. If the namespace was already initialized it returns it immediately.

#### server.close([callback])

  - `callback` _(Function)_

Closes the socket.io server. The `callback` argument is optional and will be called when all connections are closed.

```js
var Server = require('socket.io');
var PORT   = 3030;
var server = require('http').Server();

var io = Server(PORT);

io.close(); // Close current server

server.listen(PORT); // PORT is free to use

io = Server(server);
```

#### server.engine.generateId

Overwrites the default method to generate your custom socket id.

The function is called with a node request object (`http.IncomingMessage`) as first parameter.

```js
io.engine.generateId = function (req) {
  return "custom:id:" + custom_id++; // custom id must be unique
}
```

### Namespace

Represents a pool of sockets connected under a given scope identified
by a pathname (eg: `/chat`).

By default the client always connects to `/`.

#### namespace.name

  * _(String)_

The namespace identifier property.

#### namespace.connected

  * _(Object<Socket>)_

The hash of `Socket` objects that are connected to this namespace, indexed by `id`.

#### namespace.emit(eventName[, ...args])

  - `eventName` _(String)_
  - `args`

Emits an event to all connected clients. The following two are equivalent:

```js
var io = require('socket.io')();

io.emit('an event sent to all connected clients'); // main namespace

var chat = io.of('/chat');
chat.emit('an event sent to all connected clients in chat namespace');
```

#### namespace.clients(callback)

  - `callback` _(Function)_

Gets a list of client IDs connected to this namespace (across all nodes if applicable).

```js
var io = require('socket.io')();
io.of('/chat').clients(function(error, clients){
  if (error) throw error;
  console.log(clients); // => [PZDoMHjiu8PYfRiKAAAF, Anw2LatarvGVVXEIAAAD]
});
```

An example to get all clients in namespace's room:

```js
var io = require('socket.io')();
io.of('/chat').in('general').clients(function(error, clients){
  if (error) throw error;
  console.log(clients); // => [Anw2LatarvGVVXEIAAAD]
});
```

As with broadcasting, the default is all clients from the default namespace ('/'):

```js
var io = require('socket.io')();
io.clients(function(error, clients){
  if (error) throw error;
  console.log(clients); // => [6em3d4TJP8Et9EMNAAAA, G5p55dHhGgUnLUctAAAB]
});
```

#### namespace.use(fn)

  - `fn` _(Function)_

Registers a middleware, which is a function that gets executed for every incoming `Socket`, and receives as parameters the socket and a function to optionally defer execution to the next registered middleware.

Errors passed to middleware callbacks are sent as special `error` packets to clients.

```js
var io = require('socket.io')();
io.use(function(socket, next){
  if (socket.request.headers.cookie) return next();
  next(new Error('Authentication error'));
});
```

#### Event: 'connect'

  - `socket` _(Socket)_ socket connection with client

Fired upon a connection from client.

#### Event: 'connection'

Synonym of [Event: 'connect'](#event-connect).

#### Flag: 'volatile'

Sets a modifier for a subsequent event emission that the event data may be lost if the clients are not ready to receive messages (because of network slowness or other issues, or because they’re connected through long polling and is in the middle of a request-response cycle).

```js
io.volatile.emit('an event', { some: 'data' }); // the clients may or may not receive it
```

#### Flag: 'local'

Sets a modifier for a subsequent event emission that the event data will only be _broadcast_ to the current node (when the [Redis adapter](https://github.com/socketio/socket.io-redis) is used).

```js
io.local.emit('an event', { some: 'data' });
```

### Socket

A `Socket` is the fundamental class for interacting with browser clients. A `Socket` belongs to a certain `Namespace` (by default `/`) and uses an underlying `Client` to communicate.

It should be noted the `Socket` doesn't relate directly to the actual underlying TCP/IP `socket` and it is only the name of the class.

Within each `Namespace`, you can also define arbitrary channels (called `room`) that the `Socket` can join and leave. That provides a convenient way to broadcast to a group of `Socket`s (see `Socket#to` below).

The `Socket` class inherits from [EventEmitter](https://nodejs.org/api/events.html#events_class_eventemitter). The `Socket` class overrides the `emit` method, and does not modify any other `EventEmitter` method. All methods documented here which also appear as `EventEmitter` methods (apart from `emit`) are implemented by `EventEmitter`, and documentation for `EventEmitter` applies.

#### socket.id

  * _(String)_

A unique identifier for the session, that comes from the underlying `Client`.

#### socket.rooms

  * _(Object)_

A hash of strings identifying the rooms this client is in, indexed by room name.

#### socket.client

  * _(Client)_

A reference to the underlying `Client` object.

#### socket.conn

  * _(engine.Socket)_

A reference to the underlying `Client` transport connection (engine.io `Socket` object). This allows access to the IO transport layer, which still (mostly) abstracts the actual TCP/IP socket.

#### socket.request

  * _(Request)_

A getter proxy that returns the reference to the `request` that originated the underlying engine.io `Client`. Useful for accessing request headers such as `Cookie` or `User-Agent`.

#### socket.use(fn)

  - `fn` _(Function)_

Registers a middleware, which is a function that gets executed for every incoming `Packet` and receives as parameter the packet and a function to optionally defer execution to the next registered middleware.

Errors passed to middleware callbacks are sent as special `error` packets to clients.

```js
var io = require('socket.io')();
io.on('connection', function(socket){
  socket.use(function(packet, next){
    if (packet.doge === true) return next();
    next(new Error('Not a doge error'));
  });
});
```

#### socket.send([...args][, ack])

  - `args`
  - `ack` _(Function)_
  - **Returns** `Socket`

Sends a `message` event. See [socket.emit(eventName[, ...args][, ack])](#socketemiteventname-args-ack).

#### socket.emit(eventName[, ...args][, ack])

*(overrides `EventEmitter.emit`)*
  - `eventName` _(String)_
  - `args`
  - `ack` _(Function)_
  - **Returns** `Socket`

Emits an event to the socket identified by the string name. Any other parameters can be included. All serializable datastructures are supported, including `Buffer`.

```js
socket.emit('hello', 'world');
socket.emit('with-binary', 1, '2', { 3: '4', 5: new Buffer(6) });
```

The `ack` argument is optional and will be called with the client's answer.

```js
var io = require('socket.io')();
io.on('connection', function(client){
  client.emit('an event', { some: 'data' });

  client.emit('ferret', 'tobi', function (data) {
    console.log(data); // data will be 'woot'
  });

  // the client code
  // client.on('ferret', function (name, fn) {
  //   fn('woot');
  // });

});
```

#### socket.on(eventName, callback)

*(inherited from `EventEmitter`)*
  - `eventName` _(String)_
  - `callback` _(Function)_
  - **Returns** `Socket`

Register a new handler for the given event.

```js
socket.on('news', function (data) {
  console.log(data);
});
```

#### socket.once(eventName, listener)
#### socket.removeListener(eventName, listener)
#### socket.removeAllListeners([eventName])
#### socket.eventNames()

Inherited from `EventEmitter` (along with other methods not mentioned here). See Node.js documentation for the `events` module.

#### socket.join(room[, callback])

  - `room` _(String)_
  - `callback` _(Function)_
  - **Returns** `Socket` for chaining

Adds the client to the `room`, and fires optionally a callback with `err` signature (if any).

```js
io.on('connection', function(socket){
  socket.join('room 237', function(){
    console.log(socket.rooms); // [ <socket.id>, 'room 237' ]
    io.to('room 237', 'a new user has joined the room'); // broadcast to everyone in the room
  });
});
```

The mechanics of joining rooms are handled by the `Adapter` that has been configured (see `Server#adapter` above), defaulting to [socket.io-adapter](https://github.com/socketio/socket.io-adapter).

For your convenience, each socket automatically joins a room identified by this id (see `Socket#id`). This makes it easy to broadcast messages to other sockets:

```js
io.on('connection', function(client){
  client.on('say to someone', function(id, msg){
    // send a private message to the socket with the given id
    client.broadcast.to(id).emit('my message', msg);
  });
});
```

#### socket.join(rooms[, callback])

  - `rooms` _(Array)_
  - `callback` _(Function)_
  - **Returns** `Socket` for chaining

Adds the client to the list of room, and fires optionally a callback with `err` signature (if any).

#### socket.leave(room[, callback])

  - `room` _(String)_
  - `callback` _(Function)_
  - **Returns** `Socket` for chaining

Removes the client from `room`, and fires optionally a callback with `err` signature (if any).

**Rooms are left automatically upon disconnection**.

#### socket.to(room)

  - `room` _(String)_
  - **Returns** `Socket` for chaining

Sets a modifier for a subsequent event emission that the event will only be _broadcasted_ to clients that have joined the given `room`.

To emit to multiple rooms, you can call `to` several times.

```js
var io = require('socket.io')();
io.on('connection', function(client){
  // to one room
  client.to('others').emit('an event', { some: 'data' });
  // to multiple rooms
  client.to('room1').to('room2').emit('hello');
});
```

#### socket.in(room)

Synonym of [socket.to(room)](#sockettoroom).

#### socket.compress(value)

  - `value` _(Boolean)_ whether to following packet will be compressed
  - **Returns** `Socket` for chaining

Sets a modifier for a subsequent event emission that the event data will only be _compressed_ if the value is `true`. Defaults to `true` when you don't call the method.

#### socket.disconnect(close)

  - `close` _(Boolean)_ whether to close the underlying connection
  - **Returns** `Socket`

Disconnects this client. If value of close is `true`, closes the underlying connection. Otherwise, it just disconnects the namespace.

#### Flag: 'broadcast'

Sets a modifier for a subsequent event emission that the event data will only be _broadcast_ to every sockets but the sender.

```js
var io = require('socket.io')();
io.on('connection', function(socket){
  socket.broadcast.emit('an event', { some: 'data' }); // everyone gets it but the sender
});
```

#### Flag: 'volatile'

Sets a modifier for a subsequent event emission that the event data may be lost if the client is not ready to receive messages (because of network slowness or other issues, or because they’re connected through long polling and is in the middle of a request-response cycle).

```js
var io = require('socket.io')();
io.on('connection', function(socket){
  socket.volatile.emit('an event', { some: 'data' }); // the client may or may not receive it
});
```

#### Event: 'disconnect'

  - `reason` _(String)_ the reason of the disconnection (either client or server-side)

Fired upon disconnection.

#### Event: 'error'

  - `error` _(Object)_ error object

Fired when an error occurs.

#### Event: 'disconnecting'

  - `reason` _(String)_ the reason of the disconnection (either client or server-side)

Fired when the client is going to be disconnected (but hasn't left its `rooms` yet).

These are reserved events (along with `connect`, `newListener` and `removeListener`) which cannot be used as event names.

### Client

The `Client` class represents an incoming transport (engine.io) connection. A `Client` can be associated with many multiplexed `Socket`s that belong to different `Namespace`s.

#### client.conn

  * _(engine.Socket)_

A reference to the underlying `engine.io` `Socket` connection.

#### client.request

  * _(Request)_

A getter proxy that returns the reference to the `request` that originated the engine.io connection. Useful for accessing request headers such as `Cookie` or `User-Agent`.