Is there a way using HTTP to allow the server to update the content in a client browser without client requesting for it?

It is quite easy to update the interface by sending jQuery ajax request and updating with new content. But I need something more specific.

I开发者_JAVA技巧 want to send the response to client without their having requested it and update the content when they have found something new on the server. No need to send an ajax request every time. When the server has new data it sends a response to every client.

Is there any way to do this using HTTP or some specific functionality inside the browser?

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Websockets, Comet, HTTP long polling.

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It has name server push (you can also find it under name Comet technology). Do search using these keywords and you will find bunch examples, tools and so on. No special protocol is required for that.

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Aaah! You are trying to break the principles of the web :) You see if the web was pure MVC (model-view-controller) the 'server' could actually send messages to the client(s) and ask them to update. The issue is that the server could be load balanced and the same request could be sent to different servers. Now if you were to send a message back to the client you'll have to know who all are connected to the server. Let's say the site is quite popular and you have about 100,000 people connecting to it every day. You'll actually have to store the IPs of each of them to know where on the internet they are located and to be able to "push" them a message.

Caveats:

• What if they are no longer browsing your website? You see currently there is no way to log out automatically if you close your browser. The server needs to check after a fixed timeout if you have logged out (or you send a new nonce with every response to prevent the server from doing that check)
• What about a system restart/crash etc? You'd lose all the IPs that you were keeping track of and you are back to square one - you have people connected to you but until you receive new requests you can't really "send" them data when they may be expecting it as per your model.
• Let's take an example of facebook's news feeds or "Most recent" link close to the top right - sometimes while you are browsing your wall you see the number next to most recent has gone up or a new 'feed' has come to the top of your wall post! It's the client sending periodic requests to the server to find out what was updated rather than the other way round

You see, it keeps it simple and restful. You may feel it's inefficient for the client to "poll" the server to pull the data and you'd prefer push, but the design of the server gets simplified :)

I suggest ajax-pulling is the best way to go - you are distributing computation to the client and keeping it simple (KIS principle :)

Of course you can get around it, the question is, is it worth it?

Hope this helps :)

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RFC 6202 might be a good read.