* [SockJS-node](https://github.com/sockjs/sockjs-node) Node.js server
* [SockJS-erlang](https://github.com/sockjs/sockjs-erlang) Erlang server
* [SockJS-lua](https://github.com/luvit/sockjs-luvit) Lua/Luvit server
* [SockJS-tornado](https://github.com/MrJoes/sockjs-tornado) Python/Tornado server
* [vert.x](https://github.com/purplefox/vert.x) Java/vert.x server
Work in progress:
which creates a low latency, full duplex, cross-domain communication
channel between the browser and the web server.
Under the hood SockJS tries to use native WebSockets first. If that
fails it can use a variety of browser-specific transport protocols and
presents them through WebSocket-like abstractions.
SockJS is intended to work for all modern browsers and in environments
which don't support WebSocket protcol, for example behind restrictive
SockJS-client does require a server counterpart:
* [SockJS-node](https://github.com/sockjs/sockjs-node) is a SockJS
server for Node.js.
* The API should follow
[HTML5 Websockets API](http://dev.w3.org/html5/websockets/) as
closely as possible.
* All the transports must support cross domain connections out of the
box. It's possible and recommended to host SockJS server on
different server than your main web site.
* There is a support for at least one streaming protocol for every
* Streaming transports should work cross-domain and
should support cookies (for cookie-based sticky sessions).
* Polling transports are be used as a fallback for old browsers and
hosts behind restrictive proxies.
* Connection establishment should be fast and lightweight.
* No Flash inside (no need to open port 843 - which doesn't work
through proxies, no need to host 'crossdomain.xml', no need
[to wait for 3 seconds](https://github.com/gimite/web-socket-js/issues/49)
in order to detect problems)
[SockJS mailing list](https://groups.google.com/forum/#!forum/sockjs) for
discussions and support.
Live QUnit tests and smoke tests
SockJS comes with some QUnit tests and a few smoke tests (using
[SockJS-node](https://github.com/sockjs/sockjs-client) on the server
side). At the moment they are deployed in few places:
* http://sockjs.popcnt.org/ and https://sockjs.popcnt.org/ (hosted in Europe)
* http://sockjs.cloudfoundry.com/ (CloudFoundry, websockets disabled, loadbalanced)
* https://sockjs.cloudfoundry.com/ (CloudFoundry SSL, websockets disabled, loadbalanced)
SockJS mimics [WebSockets API](http://dev.w3.org/html5/websockets/)
put that in your http head:
After the script is loaded you can establish a connection with the
SockJS server. Here's a simple example:
### SockJS class
Similar to 'WebSocket' class 'SockJS' constructor takes one, or more arguments:
var sockjs = new SockJS(url, _reserved, options);
Where `options` is a hash which can contain:
* **debug (boolean)**
Print some debugging messages using 'console.log'.
* **devel (boolean)**
Development mode. Currently setting it disables caching of the
* **protocols_whitelist (list of strings)**
Sometimes it is useful to disable some fallback protocols. This
option allows you to supply a list protocols that may be used by
SockJS. By default all available protocols will be used, which is
equivalent to supplying: "['websocket', 'xdr-streaming', 'xhr-streaming',
'iframe-eventsource', 'iframe-htmlfile', 'xdr-polling', 'xhr-polling',
Although the 'SockJS' object tries to emulate the 'WebSocket'
behaviour, it's impossible to support all features. One of the
important SockJS limitations is the fact that you're not allowed to
open more than one SockJS connection to a single domain at a time.
This limitation is caused by a in-browser limit of outgoing
connections - usually [browsers don't allow opening more than two
outgoing connections to a single domain](http://stackoverflow.com/questions/985431/max-parallel-http-connections-in-a-browser). Single SockJS session
requires those two connections - one for downloading data, other for
sending messages. Opening second SockJS session at the same time
would most probably block and can result in both sessions timing out.
Opening more than one SockJS connection at a time is generally a
bad practice. If you absolutely must do it, you can use
mutliple subdomains, using different subdomain for every
Supported transports, by browser (html served from http:// or https://)
_Browser_ | _Websockets_ | _Streaming_ | _Polling_
IE 6, 7 | no | no | jsonp-polling
IE 8, 9 (cookies=no) | no | xdr-streaming † | xdr-polling †
IE 8, 9 (cookies=yes)| no | iframe-htmlfile | iframe-xhr-polling
IE 10 | rfc6455 | xhr-streaming | xhr-polling
Chrome 6-13 | hixie-76 | xhr-streaming | xhr-polling
Chrome 14+ | hybi-10 / rfc6455| xhr-streaming | xhr-polling
Firefox <10 | no ‡ | xhr-streaming | xhr-polling
Firefox 10+ | hybi-10 / rfc6455| xhr-streaming | xhr-polling
Safari 5 | hixie-76 | xhr-streaming | xhr-polling
Opera 10.70+ | no ‡ | iframe-eventsource | iframe-xhr-polling
Konqueror | no | no | jsonp-polling
* **†**: IE 8+ supports [XDomainRequest][^9], which is
esentially a modified AJAX/XHR that can do requests across
domains. But unfortunately it doesn't send any cookies, which
makes it inaproppriate for deployments when the load balancer uses
JSESSIONID cookie to do sticky sessions.
* **‡**: Firefox 4.0 and Opera 11.00 and shipped with disabled
Websockets "hixie-76". They can still be enabled by manually
changing a browser setting.
Supported transports, by browser (html served from file://)
Sometimes you may want to serve your html from "file://" address - for
development or if you're using PhoneGap or similar technologies. But
due to the Cross Origin Policy files served from "file://" have no
Origin, and that means some of SockJS transports won't work. For this
reason the SockJS protocol table is different than usually, major
_Browser_ | _Websockets_ | _Streaming_ | _Polling_
IE 8, 9 | same as above | iframe-htmlfile | iframe-xhr-polling
Other | same as above | iframe-eventsource | iframe-xhr-polling
Supported transports, by name
_Transport_ | _References_
websocket (rfc6455) | [rfc 6455][^10]
websocket (hixie-76) | [draft-hixie-thewebsocketprotocol-76][^1]
websocket (hybi-10) | [draft-ietf-hybi-thewebsocketprotocol-10][^2]
xhr-streaming | Transport using [Cross domain XHR][^5] [streaming][^7] capability (readyState=3).
xdr-streaming | Transport using [XDomainRequest][^9] [streaming][^7] capability (readyState=3).
iframe-eventsource | [EventSource][^4] used from an [iframe via postMessage][^3].
iframe-htmlfile | [HtmlFile][^8] used from an [iframe via postMessage][^3].
xhr-polling | Long-polling using [cross domain XHR][^5].
xdr-polling | Long-polling using [XDomainRequest][^9].
iframe-xhr-polling | Long-polling using normal AJAX from an [iframe via postMessage][^3].
jsonp-polling | Slow and old fashioned [JSONP polling][^6]. This transport will show "busy indicator" (aka: "spinning wheel") when sending data.
Connecting to SockJS without the client
Although the main point of SockJS it to enable browser-to-server
connectivity, it is possible to connect to SockJS from an external
application. Any SockJS server complying with 0.3 protocol does
support a raw WebSocket url. The raw WebSocket url for the test server
You can connect any WebSocket RFC 6455 compliant WebSocket client to
this url. This can be a command line client, external application,
third party code or even a browser (though I don't know why you would
want to do so).
In order to utilize best performance you should use the SockJS-client
releases hosted on SockJS CDN. You should use a version of sockjs-client
that supports the protocol used by your server. For example:
A list of files hosted on a CDN is available here: http://sockjs.github.com/sockjs-client/ .
You can also use or CDN via https (using Cloud Front domain name):
For server-side deployment tricks, especially about load balancing and
session stickiness, take a look at the
Development and testing
SockJS-client needs [Node.js](http://nodejs.org/) for running a test
SockJS-client source code, check out the git repo and follow this
npm install --dev
(To generate both run `make build`.)
Once you compiled SockJS-client you may want to check if your changes
pass all the tests. To run the tests you need a server that can answer
various SockJS requests. A common way is to use `SockJS-node` test
server for that. To run it (by default it will be listening on port 8081):
npm install --dev
At this point you're ready to run a SockJS-client server that will
javscript files (by default it will run on port 8080).
At that point you should have two web servers running: sockjs-node on
8081 and sockjs-client on 8080. When you open the browser on
[http://localhost:8080/](http://localhost:8080/) you should be able
run the QUnit tests against your sockjs-node server.
If you look at your browser console you will see warnings like that:
Incompatibile SockJS! Main site uses: "a", the iframe: "b".
This is due to a fact that SockJS-node test server is using compiled
that you must amend `sockjs_url` that is used by SockJS-node test
server. Edit the [`config.js`](https://github.com/sockjs/sockjs-node/blob/master/examples/test_server/config.js) file:
And replace `sockjs_url` setting which by default points to CDN:
to a freshly compiled sockjs, for example:
Also, if you want to run tests agains SockJS server not running on
`localhost:8081` you may want to edit the
Additionally, if you're doing more serious development consider using
`make serve`, which will automatically reload the server when you
modify the source code.
There are various browser quirks which we don't intend to address:
* Pressing ESC in Firefox closes SockJS connection. For a workaround
and discussion see [#18](https://github.com/sockjs/sockjs-client/issues/18).
* Jsonp-polling transport will show a "spinning wheel" (aka. "busy indicator")
when sending data.
* You can't open more than one SockJS connection to one domain at the
same time due to [the browsers limit of consurrent connections](http://stackoverflow.com/questions/985431/max-parallel-http-connections-in-a-browser)
(this limit is not counting native websockets connections).
* Although SockJS is trying to escape any strange Unicode characters
(even invalid ones - [like surrogates \xD800-\xDBFF](http://en.wikipedia.org/wiki/Mapping_of_Unicode_characters#Surrogates) or [\xFFFE and \xFFFF](https://en.wikipedia.org/wiki/Unicode#Character_General_Category))
it's advisable to use only valid characters. Using invalid
characters is a bit slower, and may not work with SockJS servers
that have a proper Unicode support.
* Having a global function called `onmessage` or such is probably a
bad idea, as it could be called by the built-in `postMessage` API.
* From SockJS point of view there is nothing special about
SSL/HTTPS. Connecting between unencrypted and encrypted sites
should work just fine.
* Although SockJS does best to support both prefix and cookie based
sticky sessions, the latter may not work well cross-domain with
browsers that don't accept third-party cookies by default (Safari).
In order to get around this make sure you're connecting to sockjs
from the same parent domain as the main site. For example
'sockjs.a.com' is able to set cookies if you're connecting from
'www.a.com' or 'a.com'.
* Trying to connect from secure "https://" to insecure "http://" is
not good idea. The other way around should be fine.
* Long polling is known to cause problems on Heroku, but
[workaround for SockJS is available](https://github.com/sockjs/sockjs-node/issues/57#issuecomment-5242187).
some reason clickling on this type of link breaks XDR/XHR requests
on IE (see [#90](https://github.com/sockjs/sockjs-client/issues/90)).