Webbased chat in php without using database or file

Question

I am trying to implement a realtime chat application using PHP . Is it possible to do it without using a persistent data storage like database or file . Basically what I need is

Answer 1

If you have a business need for PHP, then adding another language to the mix just means you then have two problems.

It is perfectly possible to run a permanent, constantly-running daemonised PHP IRCd server: I know, because I've done it, to make an online game which ran for years.

The IRC server part I used is a modified version of WaveIRCd: http://sourceforge.net/projects/waveircd/

I daemonised it using code I made available here: http://www.thudgame.com/node/254

That code might be overkill: I wrote it to be as rugged as I could, so it tries to daemonise using PHP's pcntl_fork(), then falls back to calling itself recursively in the background, then falls back to perl, and so on: it also handles the security restrictions of PHP's safe mode in case someone turns that on, and the security restrictions imposed by being called through cron.

You could probably strip it down to just a few lines: the bits with the comments "Daemon Rule..." - follow those rules, and you'll daemonize your process just fine.

In order to handle any unexpected daemon deaths, etc, I then ran that daemoniser every minute through cron, where it checked to see if the daemon was already running, and if so either quietly died, or if the daemon was nonresponsive, killed it and took its place.

Because of the whole distributed nature of IRC, it was nicely rugged, and gave me a multiplayer browser game with no downtime for a good few years until bit-rot ate the site a few months back. I should try to rewrite the front end in Flash and get it back up again someday, when I have time...

(I then ran another daemonizer for a PHP bot to manage the game itself, then had my game connect to it as a java applet, and talk to the bot to play the game, but that's irrelevant here).

Since WaveIRCd is no longer maintained, it's probably worth having a hunt around to find if anyone else has forked the project and is supporting it.

[2012 edit: that said, if you want your front end to be HTML5/Javascript, or if you want to connect through the same port that HTTP connects through, then your options are more limited than when using Flash or Java. In that case, take the advice of others, and use "WebSockets" (poor support in most current browsers) or the "Socket.io" project (which uses WebSockets, but falls back to Flash, or various other methods, depending what the browser has available).

The above is for situations where your host allows you to run a service on another port. In particular, many have explicit rules in their ToS against running an IRCd.]

[2019 edit: WebSockets are now widely supported, you should be fine using them. As a relevant case study, Slack is written in PHP (per https://slack.engineering/taking-php-seriously-cf7a60065329), and for some time supported the IRC protocol, though I believe that that has since been retired. As its main protocol, it uses an API based on JSON over WebSockets (https://api.slack.com/rtm). This all shows that a PHP IRCd can deliver enterprise-level performance and quality, even where the IRC protocol is translated to/from another one, which you'd expect to give poorer performance.]