A tiny application that scrapes flight information from the Christchurch International Airport homepage, and presents it in a format suitable for iPhone.

This is not an official application, and may change or disappear at any time. It was mostly for something to do while my work servers were down following a major earthquake.

The airport's flight information is served using a ghastly ASPX site. The domestic arrivals information is available from the homepage, but everything else has to be fetched with a POST request, which seems to need a bunch of form variables from the homepage, so I make heavy use of a tiny Redis cache with about five keys.

Each time a request is made for the Domestic Arrivals information, we hit the homepage, grab the flight information, and cache the ASPX view state data at the same time. For the other three flight types, we check if we have any relatively fresh view state data in the cache (the expiry is set at a relatively conservative two minutes), and use that to form the POST request to the flights page; if there isn't any, we first perform a quick hit on the homepage to get some new view state parameters.

Redis's automatic key expiry comes in really handy here: we can just set keys with an expiry time of thirty seconds or so and never have to worry about manually expiring stuff. Eventually, we'll get a request for data that has expired from the cache, and it'll be time to scrape it again. Simple!

The scraping of the flight information is relatively simple after that: just find the table and rip the rows out one by one. For now, the JSONified version of the flight information is stored wholesale in Redis as a single string, since we never do anything else with it.

I used a bunch of stuff on this project I hadn't really played with before:

• Sinatra as super-lightweight middleware
• Hpricot for scraping the HTML data
• HAML for markup (I don't really get HAML: tell the truth, it kind of annoyed me)
• Redis for caching
• iScroll for the fixed-pane scrolling and "pull to refresh"

The whole thing runs on Heroku.

In theory, the airport could tell me to take all this down. I'd hope that they'd at least see that if someone could put the guts of this together in an afternoon without access to any kind of API, it would be relatively cost-effective to provide an official mobile site. Hell, I'd give them this one.

For now, this is only an iPhone app. I've downloaded the Android SDK, but haven't dipped my toes in those murky waters just yet. We'll see.

Matt Powell (@fauxparse) March 2011