transport

A private interface that used to establish a connection, send data, receive data and close the connection.

Full-duplex channel over HTTP

Whereas the WebSocket is a protocol designed for a full-duplex communications over a TCP connection, the HTTP is just a protocol based on the request-response paradigm and has nothing to do with real-time characteristics. To simulate a full-duplex connection over HTTP, the following methods defined in httpbase transport are used to send data to the server in order.

• XMLHttpRequest: works if the given url is from same-origin or if the given url is from the cross-origin and the browser supports CORS.
• XDomainRequest: works if the browser supports XDomainRequest and the .options.xdrURL(url) returns a appropriate url.
• Form element: always works but causes a clicking sound.

To receive data from the server, a.k.a. server-push, streaming and long polling are implemented. These mechanisms’ definition and known issues are well-explained in RFC 6202. You should read it to choose a fallback’s mechanism.

• Streaming: sse, stream, streamxhr, streamxdr, streamiframe.
• Long polling: longpoll, longpollajax, longpollxdr, longpolljsonp.

Implementation

The following implementations are ready to use.

ws

WebSocket. Works if the browser supports WebSocket. After the open, message, close and all the custom event, it’s possible to access a used WebSocket’s original event by calling .data('event').

sse

Server-Sent Events. Works if the browser supports EventSource. After the open, message, close whose the reason is done and all the custom event, it’s possible to access a used Event Source’s original event by calling .data('event'). By reason of the Server-Sent Events spec’s ambiguity, there is no way to determine whether a connection closed normally or not so that the close event’s reason will be done even though the connection closed due to an error.

stream

Means the streamxhr, streamxdr and streamiframe.

streamxhr

XMLHttpRequest streaming. Works if the browser supports XMLHttpRequest, if the browser is Internet Explorer, the browser version is equal to or higher than 10, or if if the given url is from the cross-origin and the XMLHttpRequest supports CORS.

streamxdr

XDomainRequest streaming. Works if the browser supports XDomainRequest and the .options.xdrURL(url) returns a appropriate url.

streamiframe

Hidden Iframe streaming. Works if the browser supports ActiveXObject and the given url is from the same-origin. This transport differs from the traditional Hidden Iframe in terms of fetching a response text. The traditional transport expects script tags, whereas this transport periodically polls the response text. And, disconnection is not detected.

longpoll

Means the longpollajax, longpollxdr and longpolljsonp.

longpollajax

AJAX long polling. Works if the given url is from same-origin or if the given url is from the cross-origin and the browser supports CORS.

longpollxdr

XDomainRequest long polling. Works if the browser supports XDomainRequest and the .options.xdrURL(url) returns a appropriate url.

longpolljsonp

JSONP long polling. Works without qualification, but disconnection is not detected.