RogerBW's Blog

When I'm playing play-by-forum games, there's often a deadline. Because players are scattered across the world and many people are bad at time zones, it's helpful to have a countdown to remind people how much time is left. So I made one.

"But Roger", you say, "aren't there lots of those out there already?" Well, up to a point. For a start, most of them need some sort of registration, have restrictions on use, and/or dump advertisements round the edge of the timer. That's not a great start. But more seriously, they all seem to require an embedded object (iframe). Most boards don't allow embedded objects, because those are a Terrible Idea from a security perspective.

So I wrote mine to be a pure image, a non-looping animated GIF with one minute's worth of countdown. That's generated with the Imager library for Perl, which is the best bitmap-mangling library I've ever used; it simply generates sixty images and stuffs them into the GIF container with one-second delays between them. (Actually a few more, to account for reloading delays.)

The HTTP response is stuffed with no-cacheing headers (though I'm sure there will still be a cache out there that ignores them), and includes a Refresh to cause the browser where it's displayed to reload it after the minute has expired.

The trick to all this is that the URL to generate the image includes a unixtime (seconds since the epoch). So there's no need for me to store any sort of database of countdowns people have started; just send a valid time and you get the image generated for you.

How do I avoid having to give a cgi-bin URL? Did I use some terribly trendy web framework? Not a chance. The URL is (hostname)/(unixtime).gif; that's a nice short link with no room for tracking garbage. Apache configuration rewrites it to call the CGI script that generates the image data.

ScriptAliasMatch /([0-9]+).gif /var/www/timer_firedrake_org/cgi-bin/countdown.cgi

The script then looks at the REQUEST_URI environment variable to see what expiry date it should use.

"But Roger, I don't think in seconds since the epoch", you say with your puny human brain. That's why the front page of the site lets you enter the expiry date in a variety of formats and generates the unixtime for you.

All this is available at timer.firedrake.org.