Dave McDermid

We discovered an interesting little problem last week. Interesting, that is, if you enjoy Maths a little more than is healthy. I was interested because what seemed to be a random problem when it should have been consistent, turned out just to be a random problem.

So here is what was happening. Our Sitewatcher was randomly showing a few sites returning 404 (page not found) errors. This was curious, because it was requesting the home page, and this page was certainly not missing. As it happens, there is a tiny weeny glitch with a couple of sites in that they will return a 404 code on the home page if the number 404 features in the query-string. This doesn’t happen in normal circumstances, but as cache:false was being used with jQuery, it was appending a random number to the request.

So here is the question. What is the probability of the number 404 occurring in a random 10 digit sequence? Not so trivial. Particularly because the number is itself is a palindrome. It can overlap itself, causing the number to appear as often as 4 times, making the calculation a little tricky.

We reckoned, by rough estimations, for it to be 1 in ~125, but no doubt a serious mathematician can enlighten us.

Christmas eve. Work was off to a slow start, hindered first by the office Wii, then by table football, and it was only 9.30am. While the rest of the company was at home winding down and preparing for Christmas, Craig & I decided to spend our last few hours on a side project, an Adobe AIR app. We’re the life and soul of Headscape, there’s no doubt.

Although I’d delved into the world of AIR before, I hadn’t really had a proper reason to create something. Our idea was simple, a site watcher. All it had to do was fire off requests to various sites and check the response code. Easy. We could build this with HTML and Javascript no problem. Throw in JQuery and you’re laughing.

The great thing about writing for AIr is that you’re coding for one rendering engine, and it’s webkit. This means writing webkit specific CSS rules completely guilt free. Rounded corners and RGBA can make your design pretty without many images. JQuery’s AJAX library is fantastic, it takes the pain out of requests and helps the code stay clean and readable. Within an hour we had a simple app running.

So we kept going. Using a plugin for JQuery the list became sortable, and the list of sites to watch was imported from an XML file. We created a private twitter account to keep a history of changes, and allow notifications via any standard twitter client. We also added a notification window so the app could be run in the background.

The experience was quite enjoyable, and relatively pain free. The only minor annoyances are having to develop CSS / JS without Firebug, but we managed. Aptana studio made for a competent IDE, and it’s code assistance is handy. Would definitely recommend giving it a whirl if you’re at all interested.

The AIR app is now available to download form Boagworld.com: Download site watcher AIR application