socket.io

How to use


The following example attaches socket.io to a plain Node.JS HTTP server listening on port 3000.


var server = require('http').createServer();
var io = require('socket.io')(server);
io.on('connection', function(socket){
  socket.on('event', function(data){});
  socket.on('disconnect', function(){});
});
server.listen(3000);
Standalone


var io = require('socket.io')();
io.on('connection', function(socket){});
io.listen(3000);
In conjunction with Express


Starting with 3.0, express applications have become request handler functions that you pass to http or http Server instances. You need to pass the Server to socket.io, and not the express application function.


var app = require('express')();
var server = require('http').createServer(app);
var io = require('socket.io')(server);
io.on('connection', function(){ /* … */ });
server.listen(3000);
In conjunction with Koa


Like Express.JS, Koa works by exposing an application as a request handler function, but only by calling the callback method.


var app = require('koa')();
var server = require('http').createServer(app.callback());
var io = require('socket.io')(server);
io.on('connection', function(){ /* … */ });
server.listen(3000);
API


Server


Exposed by require('socket.io').


Server()


Creates a new Server. Works with and without new:


  var io = require('socket.io')();
  // or
  var Server = require('socket.io');
  var io = new Server();
Server(opts:Object)


Optionally, the first or second argument (see below) of the Server constructor can be an options object.


The following options are supported:


serveClient sets the value for Server#serveClient()
path sets the value for Server#path()


The same options passed to socket.io are always passed to the engine.io Server that gets created. See engine.io options as reference.


Server(srv:http#Server, opts:Object)


Creates a new Server and attaches it to the given srv. Optionally opts can be passed.


Server(port:Number, opts:Object)


Binds socket.io to a new http.Server that listens on port.


Server#serveClient(v:Boolean):Server


If v 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.


  // 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);
If no arguments are supplied this method returns the current value.


Server#path(v:String):Server


Sets the path v 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(v:Adapter):Server


Sets the adapter v. Defaults to an instance of the Adapter that ships with socket.io which is memory based. See socket.io-adapter.


If no arguments are supplied this method returns the current value.


Server#origins(v:String):Server


Sets the allowed origins v. Defaults to any origins being allowed.


If no arguments are supplied this method returns the current value.


Server#origins(v:Function):Server


Sets the allowed origins as dynamic function. Function takes 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
Server#sockets:Namespace


The default (/) namespace.


Server#attach(srv:http#Server, opts:Object):Server


Attaches the Server to an engine.io instance on srv with the supplied opts (optionally).


Server#attach(port:Number, opts:Object):Server


Attaches the Server to an engine.io instance that is bound to port with the given opts (optionally).


Server#listen


Synonym of Server#attach.


Server#bind(srv:engine#Server):Server


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


Server#onconnection(socket:engine#Socket):Server


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


Server#of(nsp:String):Namespace


Initializes and retrieves the given Namespace by its pathname identifier nsp.


If the namespace was already initialized it returns it right away.


Server#emit


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


  var io = require('socket.io')();
  io.sockets.emit('an event sent to all connected clients');
  io.emit('an event sent to all connected clients');
For other available methods, see Namespace below.


Server#close


Closes socket server


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


  io(PORT);


  io.close(); // Close current server


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


  io(server);
Server#use


See Namespace#use below.


Namespace


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


By default the client always connects to /.


Events


connection / connect. Fired upon a connection.


Parameters:


Socket the incoming socket.
Namespace#name:String


The namespace identifier property.


Namespace#connected:Object


Hash of Socket objects that are connected to this namespace indexed by id.


Namespace#use(fn:Function):Namespace


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


  var io = require('socket.io')();
  io.use(function(socket, next){
    if (socket.request.headers.cookie) return next();
    next(new Error('Authentication error'));
  });
Errors passed to middleware callbacks are sent as special error packets to clients.


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.


Socket#rooms:Array


A list of strings identifying the rooms this socket is in.


Socket#client:Client


A reference to the underlying Client object.


Socket#conn:Socket


A reference to the underyling Client transport connection (engine.io Socket object).


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#id:String


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


Socket#emit(name:String[, …]):Socket


Emits an event to the socket identified by the string name. Any other parameters can be included.


All datastructures are supported, including Buffer. JavaScript functions can't be serialized/deserialized.


  var io = require('socket.io')();
  io.on('connection', function(socket){
    socket.emit('an event', { some: 'data' });
  });
Socket#join(name:String[, fn:Function]):Socket


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


The socket is automatically a member of a room identified with its session id (see Socket#id).


The mechanics of joining rooms are handled by the Adapter that has been configured (see Server#adapter above), defaulting to socket.io-adapter.


Socket#leave(name:String[, fn:Function]):Socket


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


Rooms are left automatically upon disconnection.


The mechanics of leaving rooms are handled by the Adapter that has been configured (see Server#adapter above), defaulting to socket.io-adapter.


Socket#to(room:String):Socket


Socket#in(room:String):Socket


Sets a modifier for a subsequent event emission that the event will only be broadcasted to sockets that have joined the given room.


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


  var io = require('socket.io')();
  io.on('connection', function(socket){
    socket.to('others').emit('an event', { some: 'data' });
  });
Client


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


Client#conn


A reference to the underlying engine.io Socket connection.


Client#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.


Debug / logging


Socket.IO is powered by debug. In order to see all the debug output, run your app with the environment variable DEBUG including the desired scope.


To see the output from all of Socket.IO's debugging scopes you can use:


DEBUG=socket.io* node myapp