344 lines
16 KiB
Markdown
344 lines
16 KiB
Markdown
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# SockJS-client
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[](https://www.npmjs.com/package/sockjs-client)[](https://travis-ci.org/sockjs/sockjs-client)[](https://david-dm.org/sockjs/sockjs-client)[](https://gitter.im/sockjs/sockjs-client)
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[](https://www.browserstack.com/automate/public-build/dW9YdlFsSEI5VzNBVVk5ZS9XT0xaTjJVQkhQMkRkNlZBQURiSWNWMC9jaz0tLXRJM05RbW1tTCt5TlhHaVgycFJUYmc9PQ==--e3ef9b9a9fa071084e6d87874b5fc65b71273821)
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SockJS is a browser JavaScript library that provides a WebSocket-like
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object. SockJS gives you a coherent, cross-browser, Javascript API
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which creates a low latency, full duplex, cross-domain communication
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channel between the browser and the web server.
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Under the hood SockJS tries to use native WebSockets first. If that
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fails it can use a variety of browser-specific transport protocols and
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presents them through WebSocket-like abstractions.
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SockJS is intended to work for all modern browsers and in environments
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which don't support the WebSocket protocol -- for example, behind restrictive
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corporate proxies.
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SockJS-client does require a server counterpart:
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* [SockJS-node](https://github.com/sockjs/sockjs-node) is a SockJS
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server for Node.js.
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Philosophy:
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* The API should follow
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[HTML5 Websockets API](https://www.w3.org/TR/websockets/) as
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closely as possible.
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* All the transports must support cross domain connections out of the
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box. It's possible and recommended to host a SockJS server on a
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different server than your main web site.
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* There is support for at least one streaming protocol for every
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major browser.
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* Streaming transports should work cross-domain and
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should support cookies (for cookie-based sticky sessions).
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* Polling transports are used as a fallback for old browsers and
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hosts behind restrictive proxies.
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* Connection establishment should be fast and lightweight.
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* No Flash inside (no need to open port 843 - which doesn't work
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through proxies, no need to host 'crossdomain.xml', no need
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[to wait for 3 seconds](https://github.com/gimite/web-socket-js/issues/49)
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in order to detect problems)
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Subscribe to
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[SockJS mailing list](https://groups.google.com/forum/#!forum/sockjs) for
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discussions and support.
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SockJS family:
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* [SockJS-client](https://github.com/sockjs/sockjs-client) JavaScript client library
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* [SockJS-node](https://github.com/sockjs/sockjs-node) Node.js server
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* [SockJS-erlang](https://github.com/sockjs/sockjs-erlang) Erlang server
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* [SockJS-cyclone](https://github.com/flaviogrossi/sockjs-cyclone) Python/Cyclone/Twisted server
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* [SockJS-tornado](https://github.com/MrJoes/sockjs-tornado) Python/Tornado server
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* [SockJS-twisted](https://github.com/DesertBus/sockjs-twisted/) Python/Twisted server
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* [SockJS-aiohttp](https://github.com/aio-libs/sockjs/) Python/Aiohttp server
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* [Spring Framework](https://projects.spring.io/spring-framework) Java [client](https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/web.html#websocket-fallback-sockjs-client) & server
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* [vert.x](https://github.com/vert-x/vert.x) Java/vert.x server
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* [Xitrum](https://xitrum-framework.github.io/) Scala server
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* [Atmosphere Framework](https://github.com/Atmosphere/atmosphere) JavaEE Server, Play Framework, Netty, Vert.x
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* [Actix SockJS](https://github.com/fafhrd91/actix-sockjs) Rust Server, Actix Framework
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Work in progress:
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* [SockJS-ruby](https://github.com/nyarly/sockjs-ruby)
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* [SockJS-netty](https://github.com/cgbystrom/sockjs-netty)
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* [SockJS-gevent](https://github.com/ksava/sockjs-gevent) ([SockJS-gevent fork](https://github.com/njoyce/sockjs-gevent))
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* [pyramid-SockJS](https://github.com/fafhrd91/pyramid_sockjs)
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* [wildcloud-websockets](https://github.com/wildcloud/wildcloud-websockets)
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* [wai-SockJS](https://github.com/Palmik/wai-sockjs)
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* [SockJS-perl](https://github.com/vti/sockjs-perl)
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* [SockJS-go](https://github.com/igm/sockjs-go/)
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Getting Started
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-------
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SockJS mimics the [WebSockets API](https://www.w3.org/TR/websockets/),
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but instead of `WebSocket` there is a `SockJS` Javascript object.
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First, you need to load the SockJS JavaScript library. For example, you can
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put that in your HTML head:
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```html
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<script src="https://cdn.jsdelivr.net/npm/sockjs-client@1/dist/sockjs.min.js"></script>
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```
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After the script is loaded you can establish a connection with the
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SockJS server. Here's a simple example:
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```javascript
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var sock = new SockJS('https://mydomain.com/my_prefix');
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sock.onopen = function() {
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console.log('open');
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sock.send('test');
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};
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sock.onmessage = function(e) {
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console.log('message', e.data);
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sock.close();
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};
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sock.onclose = function() {
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console.log('close');
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};
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```
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SockJS-client API
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-----------------
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### SockJS class
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Similar to the 'WebSocket' API, the 'SockJS' constructor takes one, or more arguments:
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```javascript
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var sockjs = new SockJS(url, _reserved, options);
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```
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`url` may contain a query string, if one is desired.
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Where `options` is a hash which can contain:
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* **server (string)**
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String to append to url for actual data connection. Defaults to a random 4 digit number.
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* **transports (string OR array of strings)**
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Sometimes it is useful to disable some fallback transports. This
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option allows you to supply a list transports that may be used by
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SockJS. By default all available transports will be used.
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* **sessionId (number OR function)**
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Both client and server use session identifiers to distinguish connections.
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If you specify this option as a number, SockJS will use its random string
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generator function to generate session ids that are N-character long
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(where N corresponds to the number specified by **sessionId**).
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When you specify this option as a function, the function must return a
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randomly generated string. Every time SockJS needs to generate a session
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id it will call this function and use the returned string directly.
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If you don't specify this option, the default is to use the default random
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string generator to generate 8-character long session ids.
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Although the 'SockJS' object tries to emulate the 'WebSocket'
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behaviour, it's impossible to support all of its features. An
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important SockJS limitation is the fact that you're not allowed to
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open more than one SockJS connection to a single domain at a time.
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This limitation is caused by an in-browser limit of outgoing
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connections - usually [browsers don't allow opening more than two
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outgoing connections to a single domain](https://stackoverflow.com/questions/985431/max-parallel-http-connections-in-a-browser). A single SockJS session
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requires those two connections - one for downloading data, the other for
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sending messages. Opening a second SockJS session at the same time
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would most likely block, and can result in both sessions timing out.
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Opening more than one SockJS connection at a time is generally a
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bad practice. If you absolutely must do it, you can use
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multiple subdomains, using a different subdomain for every
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SockJS connection.
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Supported transports, by browser (html served from http:// or https://)
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-----------------------------------------------------------------------
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_Browser_ | _Websockets_ | _Streaming_ | _Polling_
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----------------|------------------|-------------|-------------------
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IE 6, 7 | no | no | jsonp-polling
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IE 8, 9 (cookies=no) | no | xdr-streaming † | xdr-polling †
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IE 8, 9 (cookies=yes)| no | iframe-htmlfile | iframe-xhr-polling
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IE 10 | rfc6455 | xhr-streaming | xhr-polling
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Chrome 6-13 | hixie-76 | xhr-streaming | xhr-polling
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Chrome 14+ | hybi-10 / rfc6455| xhr-streaming | xhr-polling
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Firefox <10 | no ‡ | xhr-streaming | xhr-polling
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Firefox 10+ | hybi-10 / rfc6455| xhr-streaming | xhr-polling
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Safari 5.x | hixie-76 | xhr-streaming | xhr-polling
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Safari 6+ | rfc6455 | xhr-streaming | xhr-polling
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Opera 10.70+ | no ‡ | iframe-eventsource | iframe-xhr-polling
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Opera 12.10+ | rfc6455 | xhr-streaming | xhr-polling
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Konqueror | no | no | jsonp-polling
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* **†**: IE 8+ supports [XDomainRequest][^9], which is
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essentially a modified AJAX/XHR that can do requests across
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domains. But unfortunately it doesn't send any cookies, which
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makes it inappropriate for deployments when the load balancer uses
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JSESSIONID cookie to do sticky sessions.
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* **‡**: Firefox 4.0 and Opera 11.00 and shipped with disabled
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Websockets "hixie-76". They can still be enabled by manually
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changing a browser setting.
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Supported transports, by browser (html served from file://)
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-----------------------------------------------------------
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Sometimes you may want to serve your html from "file://" address - for
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development or if you're using PhoneGap or similar technologies. But
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due to the Cross Origin Policy files served from "file://" have no
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Origin, and that means some of SockJS transports won't work. For this
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reason the SockJS transport table is different than usually, major
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differences are:
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_Browser_ | _Websockets_ | _Streaming_ | _Polling_
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----------------|---------------|--------------------|-------------------
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IE 8, 9 | same as above | iframe-htmlfile | iframe-xhr-polling
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Other | same as above | iframe-eventsource | iframe-xhr-polling
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Supported transports, by name
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-----------------------------
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_Transport_ | _References_
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---------------------|---------------
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websocket (rfc6455) | [rfc 6455][^10]
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websocket (hixie-76) | [draft-hixie-thewebsocketprotocol-76][^1]
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websocket (hybi-10) | [draft-ietf-hybi-thewebsocketprotocol-10][^2]
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xhr-streaming | Transport using [Cross domain XHR][^5] [streaming][^7] capability (readyState=3).
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xdr-streaming | Transport using [XDomainRequest][^9] [streaming][^7] capability (readyState=3).
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eventsource | [EventSource/Server-sent events][^4].
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iframe-eventsource | [EventSource/Server-sent events][^4] used from an [iframe via postMessage][^3].
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htmlfile | [HtmlFile][^8].
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iframe-htmlfile | [HtmlFile][^8] used from an [iframe via postMessage][^3].
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xhr-polling | Long-polling using [cross domain XHR][^5].
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xdr-polling | Long-polling using [XDomainRequest][^9].
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iframe-xhr-polling | Long-polling using normal AJAX from an [iframe via postMessage][^3].
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jsonp-polling | Slow and old fashioned [JSONP polling][^6]. This transport will show "busy indicator" (aka: "spinning wheel") when sending data.
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[^1]: https://tools.ietf.org/html/draft-hixie-thewebsocketprotocol-76
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[^2]: https://tools.ietf.org/html/draft-ietf-hybi-thewebsocketprotocol-10
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[^3]: https://developer.mozilla.org/en/DOM/window.postMessage
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[^4]: https://html.spec.whatwg.org/multipage/comms.html#server-sent-events
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[^5]: https://secure.wikimedia.org/wikipedia/en/wiki/XMLHttpRequest#Cross-domain_requests
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[^6]: https://secure.wikimedia.org/wikipedia/en/wiki/JSONP
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[^7]: http://www.debugtheweb.com/test/teststreaming.aspx
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[^8]: http://cometdaily.com/2007/11/18/ie-activexhtmlfile-transport-part-ii/
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[^9]: https://blogs.msdn.microsoft.com/ieinternals/2010/05/13/xdomainrequest-restrictions-limitations-and-workarounds/
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[^10]: https://www.rfc-editor.org/rfc/rfc6455.txt
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Connecting to SockJS without the client
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---------------------------------------
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Although the main point of SockJS is to enable browser-to-server
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connectivity, it is possible to connect to SockJS from an external
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application. Any SockJS server complying with 0.3 protocol does
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support a raw WebSocket url. The raw WebSocket url for the test server
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looks like:
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* ws://localhost:8081/echo/websocket
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You can connect any WebSocket RFC 6455 compliant WebSocket client to
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this url. This can be a command line client, external application,
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third party code or even a browser (though I don't know why you would
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want to do so).
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Deployment
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----------
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You should use a version of sockjs-client
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that supports the protocol used by your server. For example:
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```html
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<script src="https://cdn.jsdelivr.net/npm/sockjs-client@1/dist/sockjs.min.js"></script>
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```
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For server-side deployment tricks, especially about load balancing and
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session stickiness, take a look at the
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[SockJS-node readme](https://github.com/sockjs/sockjs-node#readme).
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Development and testing
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-----------------------
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SockJS-client needs [node.js](https://nodejs.org/) for running a test
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server and JavaScript minification. If you want to work on
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SockJS-client source code, checkout the git repo and follow these
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steps:
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cd sockjs-client
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npm install
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To generate JavaScript, run:
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gulp browserify
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To generate minified JavaScript, run:
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gulp browserify:min
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Both commands output into the `build` directory.
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### Testing
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Automated testing provided by:
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<a href="https://browserstack.com"><img src="img/Browserstack-logo@2x.png" height="50"></a>
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Once you've compiled the SockJS-client you may want to check if your changes
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pass all the tests.
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npm run test:browser_local
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This will start [karma](https://karma-runner.github.io) and a test support server.
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Browser Quirks
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--------------
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There are various browser quirks which we don't intend to address:
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* Pressing ESC in Firefox, before Firefox 20, closes the SockJS connection. For a workaround
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and discussion see [#18](https://github.com/sockjs/sockjs-client/issues/18).
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* `jsonp-polling` transport will show a "spinning wheel" (aka. "busy indicator")
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when sending data.
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* You can't open more than one SockJS connection to one domain at the
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same time due to [the browser's limit of concurrent connections](https://stackoverflow.com/questions/985431/max-parallel-http-connections-in-a-browser)
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(this limit is not counting native WebSocket connections).
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* Although SockJS is trying to escape any strange Unicode characters
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(even invalid ones - [like surrogates \xD800-\xDBFF](https://en.wikipedia.org/wiki/Mapping_of_Unicode_characters#Surrogates) or [\xFFFE and \xFFFF](https://en.wikipedia.org/wiki/Unicode#Character_General_Category))
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it's advisable to use only valid characters. Using invalid
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characters is a bit slower, and may not work with SockJS servers
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that have proper Unicode support.
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* Having a global function called `onmessage` or such is probably a
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bad idea, as it could be called by the built-in `postMessage` API.
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* From SockJS' point of view there is nothing special about
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SSL/HTTPS. Connecting between unencrypted and encrypted sites
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should work just fine.
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* Although SockJS does its best to support both prefix and cookie based
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sticky sessions, the latter may not work well cross-domain with
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browsers that don't accept third-party cookies by default (Safari).
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In order to get around this make sure you're connecting to SockJS
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from the same parent domain as the main site. For example
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'sockjs.a.com' is able to set cookies if you're connecting from
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'www.a.com' or 'a.com'.
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* Trying to connect from secure "https://" to insecure "http://" is
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not a good idea. The other way around should be fine.
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* Long polling is known to cause problems on Heroku, but a
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[workaround for SockJS is available](https://github.com/sockjs/sockjs-node/issues/57#issuecomment-5242187).
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* SockJS [websocket transport is more stable over SSL](https://github.com/sockjs/sockjs-client/issues/94). If
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you're a serious SockJS user then consider using SSL
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([more info](https://www.ietf.org/mail-archive/web/hybi/current/msg01605.html)).
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