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PHP & JavaScript World Domination Series: Storing data in the client.

Luis Argerich, Alejandro Mitrou

One of the things that all programmers love is to write a program which writes another program. On the web we have two different programming environments: the client (browser) and the server. Due to the HTTP protocol definition we can write a program on the server which writes another program to be executed on the client. Let's pick PHP (of course) for the server and JavaScript for the client. We'll show you in this article how you can use this scheme to store data in the client and then minimize the data transfered between the server and the browser for interactive applications like a chat room, a news system or whatever you want.

Ingredients:

• PHP4
• JavaScript
• Frames

The Idea:

We have been trying to develop an HTTP chat room in PHP for a while. HTTP is not a good protocol for chatting but it is firewall/proxy immune, can use the potential of PHP and there's no need for Java Applets. We have had two main problems with the chat room: first since IE doesn't support the PUSH method, we needed to make it a "pull" application, (the client refreshes itself) which is unnatural for a chat application. We decided to make the client refresh time variable, the server will generate the refresh time as a function of the number of messages received in the server in the last x minutes. The second problem was deeper: since the idea is to refresh the client we would need the server to send all the messages each time, we observed that this implied heavy transfers and our benchmarks in a simulated simplified chat room model showed that this was the main cause of delays in the chat. This article deals with that second and deeper problem.

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