Shake your Rump!

This time it's not about Rx for Javascript or even Javascript. Well, that's at least partly because I got hooked on Haskell and have spent most of my free time (not much though) on Haskell projects.
But lately, I've been working on a mobile (Android/iOS) app called Karma. The app will answer the ever-crucial question "who's turn is it to buy the next round?". To make it fun and easy to use, it needed an easy way of telling the system that two guys, say Bob and Mike, have just met for some beers. Thanks to location and acceleration info, it's possible to make this pairing happen just by shaking phones together.
The topic of this post is the "shake to pair" technology included. We started by trying the Bump API. However, we found it quite unreliable, even though the actual Bump application seemed solid. I guess they don't give their best performance for API users?
Now, what would a proper nerd do? What the heck, let's write it from scratch. And POW, here it is:
As you see, it's open-source. And, it's actually very simple:
  1. When user shakes the phone, the RUMP Client sends a message to the server. Like this:
      { "userId" : "john", "displayName" : "John Kennedy", "location": { "latitude": 51.0, "longitude": -0.1 } }
  1. Server matches incoming requests by time (3 second time window to match) and location (1 kilometer max distance).
  2. After 3 seconds from the first received request, the server sends match info to all clients that were matched with the first one. The response is just an array of all the matching requests.
  3. Rump Client delivers the match info to the client application.
  4. Client application does something cool. For instance, the Karma application joins the matched users into the same table and calculates the next buyer.
Well, that's it. On the Github pages, you'll find instructions for building, running and integrating the Android Client into your app.
I think this would provide a nice basis for matching users in a multiplayer game, for instance. Shake your phones to start multi-player, anyone?
What else? We have an iPhone version of Karma in the works. Mayhaps we'll also extract the Rump client part from there and open-source that too? Would it make sense?
The server-side piece is written in Haskell. I'm on a horse.