Back in my original Save the Bits article, I noted that a foreign currency application on the iPhone, which I'll refer to as AppX, uploaded 16K of data and downloaded 136K just to render a graph.
I said I'd get back when I'd run a packet sniffer. I've just done that, and the results aren't pretty. It uses HTTP, to talk to the server, which is as you'd expect. Writing a custom protocol is always painful. But instead of the logical thing to do, which is a short sweet transaction to get the data, and any associated metadata like an ad, like this.
- Client: Hi, can I have some data
- Server: Here's your data, and an ad to go with it
- Client: (Draws graph)
What's actually going on is an extended chat, whereby AppX does something like this
- Client: Hi
- Server: Hi, have a cookie
- Client: Here's my cookie
- Server: Here's an ad for you to display
OK, not too many complaints so far, apart from the amount of to-ing and fro-ing which makes the most of all those round trip high latency transaction, but now it gets really fun:
- Client: Hi again
- Client: Can I have some more?
- Server: Sure
- Client: And an image to represent my graph? I don't fancy drawing all that data myself.
- Server: No problem
- Server: You got it
No wonder it's slow. I've heard of Whale Song, but this is ridiculous...