SockJS-client
SockJS for enterprise
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Summary
SockJS is a browser JavaScript library that provides a WebSocket-like
object. SockJS gives you a coherent, cross-browser, Javascript API
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 the WebSocket protocol -- for example, behind restrictive
corporate proxies.
SockJS-client does require a server counterpart:
Philosophy:
- The API should follow
HTML5 Websockets API as
closely as possible.
- All the transports must support cross domain connections out of the
box. It's possible and recommended to host a SockJS server on a
different server than your main web site.
- There is support for at least one streaming protocol for every
major browser.
- Streaming transports should work cross-domain and
should support cookies (for cookie-based sticky sessions).
- Polling transports are 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
in order to detect problems)
Subscribe to
SockJS mailing list for
discussions and support.
SockJS family
Work in progress:
Getting Started
SockJS mimics the WebSockets API,
but instead of WebSocket there is a SockJS Javascript object.
First, you need to load the SockJS JavaScript library. For example, you can
put that in your HTML head:
<script src="https://cdn.jsdelivr.net/npm/sockjs-client@1/dist/sockjs.min.js"></script>
After the script is loaded you can establish a connection with the
SockJS server. Here's a simple example:
var sock = new SockJS('https://mydomain.com/my_prefix');
sock.onopen = function() {
console.log('open');
sock.send('test');
};
sock.onmessage = function(e) {
console.log('message', e.data);
sock.close();
};
sock.onclose = function() {
console.log('close');
};
SockJS-client API
SockJS class
Similar to the 'WebSocket' API, the 'SockJS' constructor takes one, or more arguments:
var sockjs = new SockJS(url, _reserved, options);
url may contain a query string, if one is desired.
Where options is a hash which can contain:
-
server (string)
String to append to url for actual data connection. Defaults to a random 4 digit number.
-
transports (string OR array of strings)
Sometimes it is useful to disable some fallback transports. This
option allows you to supply a list transports that may be used by
SockJS. By default all available transports will be used.
-
sessionId (number OR function)
Both client and server use session identifiers to distinguish connections.
If you specify this option as a number, SockJS will use its random string
generator function to generate session ids that are N-character long
(where N corresponds to the number specified by sessionId).
When you specify this option as a function, the function must return a
randomly generated string. Every time SockJS needs to generate a session
id it will call this function and use the returned string directly.
If you don't specify this option, the default is to use the default random
string generator to generate 8-character long session ids.
-
timeout (number)
Specify a minimum timeout in milliseconds to use for the transport connections.
By default this is dynamically calculated based on the measured RTT and
the number of expected round trips. This setting will establish a minimum,
but if the calculated timeout is higher, that will be used.
Although the 'SockJS' object tries to emulate the 'WebSocket'
behaviour, it's impossible to support all of its features. An
important SockJS limitation 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 an in-browser limit of outgoing
connections - usually browsers don't allow opening more than two
outgoing connections to a single domain. A single SockJS session
requires those two connections - one for downloading data, the other for
sending messages. Opening a second SockJS session at the same time
would most likely 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
multiple subdomains, using a different subdomain for every
SockJS connection.
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.x | hixie-76 | xhr-streaming | xhr-polling |
| Safari 6+ | rfc6455 | xhr-streaming | xhr-polling |
| Opera 10.70+ | no ‡ | iframe-eventsource | iframe-xhr-polling |
| Opera 12.10+ | rfc6455 | xhr-streaming | xhr-polling |
| Konqueror | no | no | jsonp-polling |
-
†: IE 8+ supports [XDomainRequest]1, which is
essentially a modified AJAX/XHR that can do requests across
domains. But unfortunately it doesn't send any cookies, which
makes it inappropriate 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 transport table is different than usually, major
differences are:
| 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]2 |
| websocket (hixie-76) | [draft-hixie-thewebsocketprotocol-76]3 |
| websocket (hybi-10) | [draft-ietf-hybi-thewebsocketprotocol-10]4 |
| xhr-streaming | Transport using [Cross domain XHR]5 [streaming]6 capability (readyState=3). |
| xdr-streaming | Transport using [XDomainRequest]1 [streaming]6 capability (readyState=3). |
| eventsource | [EventSource/Server-sent events]7. |
| iframe-eventsource | [EventSource/Server-sent events]7 used from an [iframe via postMessage]8. |
| htmlfile | [HtmlFile]9. |
| iframe-htmlfile | [HtmlFile]9 used from an [iframe via postMessage]8. |
| xhr-polling | Long-polling using [cross domain XHR]5. |
| xdr-polling | Long-polling using [XDomainRequest]1. |
| iframe-xhr-polling | Long-polling using normal AJAX from an [iframe via postMessage]8. |
| jsonp-polling | Slow and old fashioned [JSONP polling]10. This transport will show "busy indicator" (aka: "spinning wheel") when sending data. |
Connecting to SockJS without the client
Although the main point of SockJS is 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
looks like:
- ws://localhost:8081/echo/websocket
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).
Deployment
You should use a version of sockjs-client
that supports the protocol used by your server. For example:
<script src="https://cdn.jsdelivr.net/npm/sockjs-client@1/dist/sockjs.min.js"></script>
For server-side deployment tricks, especially about load balancing and
session stickiness, take a look at the
SockJS-node readme.
Development and testing
SockJS-client needs node.js for running a test
server and JavaScript minification. If you want to work on
SockJS-client source code, checkout the git repo and follow these
steps:
cd sockjs-client
npm install
To generate JavaScript, run:
gulp browserify
To generate minified JavaScript, run:
gulp browserify:min
Both commands output into the build directory.
Testing
Automated testing provided by:
Once you've compiled the SockJS-client you may want to check if your changes
pass all the tests.
npm run test:browser_local
This will start karma and a test support server.
Browser Quirks
There are various browser quirks which we don't intend to address:
- Pressing ESC in Firefox, before Firefox 20, closes the SockJS connection. For a workaround
and discussion see #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 browser's limit of concurrent connections
(this limit is not counting native WebSocket connections).
- Although SockJS is trying to escape any strange Unicode characters
(even invalid ones - like surrogates \xD800-\xDBFF or \xFFFE and \xFFFF)
it's advisable to use only valid characters. Using invalid
characters is a bit slower, and may not work with SockJS servers
that have 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 its 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 a good idea. The other way around should be fine.
- Long polling is known to cause problems on Heroku, but a
workaround for SockJS is available.
- SockJS websocket transport is more stable over SSL. If
you're a serious SockJS user then consider using SSL
(more info).
