Strophe Tutorial: Pubsub Weather Alert Demo

August 27, 2009

Strophe has been getting more popular lately, and I keep finding it in new places. Boris Okner has just written an interesting demo application showing off the power of the real-time Web and Strophe. He didn’t just stop with the demo, either; he has provided a detailed walk-through of how it all works as well.

The demo is an imaginary system for weather alerting that allows users to subscribe to various weather stations and receive updates in real-time. It uses Strophe and JavaScript for the front end and ejabberd and some custom Erlang modules for the back end. The XMPP API exposed by the server is similar to standard XMPP pubsub, which can be browsed via service discovery.

I also really like Boris’s description of XMPP’s advantages to tackling this problem:

Another important thing is ability to reuse XMPP server features. For instance, there is no need to have separate database of registered users and their subscriptions, as this is already maintained by XMPP server. All changes in user’s presence (i.e. logged in/out, disconnected) and component presence (restart, disconnection etc.) are also taken care of. It is possible to easily implement IM features, such as live support or chat between users.

I’d add that if he had used standard pubsub, there is very little protocol design work that needs to be done for this type of application. Pubsub and service discovery already have all the standard usage models covered as well as many error cases. It’s a lot easier to implement a well thought out protocol than to design your own and re-discover all the non-obvious issues.

Give Boris’s demo application a spin if you’re interested in what is possible with the real-time Web and how it works.