File resource persistence in PHP

Question

I'm developing a simple chat web application based on the MSN protocol. The server communicates with the MSN server through a file resource returned from fsockopen (). The client accesses the server via XMLHttpRequest. The server initially logs in, and prints out the contact list (formatted in an HTML table) which the client receives through the responseText () of the XMLHttpRequest object.

Here's the problem. The file resource that is responsible for communication with the MSN server must be kept alive in order for all chat related functions to work (creating conversations, keeping track of offline/online state changes, etc). However in order for the XMLHttpRequest to complete, the PHP script must finish execution. Which means the client will get no response from the XMLHttpRequest while the chat session is in progress.

Whats worse is a file resource cannot be serialized, meaning I cannot simply store the chat session in a $_SESSION [] placeholder.

So, my question is, is there any possible way for me to 'transfer' a file resource from one file to another?

Answer 1

A possible solution would be to have a PHP script on the server-side that just doesn't end ; this way, the resource corresponding to the fsockopen call would never be deleted, and the connection wouldn't be closed.

About this, you might want to search for the term "comet" ; the basic idea is to have a script that runs forever on the server-side, that sends updates to the client whenever it's necessary.

Instead of having the browser send an Ajax request every X seconds, you'd keep an openened connection between the client and the server -- just note that, unfortunatly, PHP is often said not to be the best tool for that job...

On stackoverflow : [php] comet

Answer 2

The resource can't survive the end of the request unless you create PHP extension that does it (like persistent MySQL connections do with mysql_pconnect() for example). However, you could use Comet technology and for example Bayeux protocol supported by Dojo toolkit among others, to talk to the server. That would require either standalone server or long-running request, in latter case ensure that PHP and webserver time limits would not kill that request for running too long.

Answer 3

In most languages its not possible to pass file handles between applications - AFAIK most operating systems don't allow it either.

The solution is to keep the server process running as daemon - which means it needs to run outside of the webserver.

See

http://symcbean.blogspot.com/2010/02/php-and-long-running-processes.html

and

http://www.phpclasses.org/browse/package/5758.html

C.

Answer 4

Thanks everyone for the suggestions. Before I started this project I had considered using comet technology, but decided against (PHP/Apache don't seem to implement well). I've come up with a hacked together solution, not the most elegant but workable.

One PHP script is responsible for the MSN server communication, it will run as long as the user is active. It writes data to a file (email_out), as well as reads data from a file (email_in). Whenever the client sends a AJAX request a separate PHP script will write any POST data to the file (email_in) and will return any data from (email_out). Both scripts will not read/write data until they finally have access to the file (as there will be fighting for the file resource).

I don't know, suggestions? This is certainty not the most efficient means of doing things but it's really the only PHP/apache solution I could think of.