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I notice an instant messenger using javascript/http/xmlhttprequest rather than tcp/websocket to communicate.

such as http://w.qq.com/login.html

I monitored its communication way in chrome developer tool. All are http requests. One request to server every minute.

The thing I confused is that if I send a message to the http client, it receives the message immediately.

As I know http client can not get message from others, it has to send request and get response.

Is there any way to make http client to get message from others without using tcp/socket or sending request and geting response?

Your comment welcome

arachide
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1 Answers1

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I don't get all this asian hieroglyphs, but they probably use long-polling: client asks server for new data and server holds answer (don't send anything, and don't close connection) while data is not ready (new message came) or until huge timeout expired. As soon as connection closed, client process response and sends next long poll request. The more common term for "permanent" connect via http called Comet. As you can see, Comet can be implemented via many techniques. As for me, the most modern is ajax streaming. It requires modern browser of course, but worth it. It's not so hard to implement streaming by yourself, but I believe there are few js libs which do the job for you.

Upd: Here is pretty good explanation with code source

and

here is one of many questions about streaming on SO (the answer in the bottom is most interesting I guess)

Community
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Tommi
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