Friday, July 3, 2009

gen_component project: service discovery with exmpp

The gen_component behavior is growing up and is making more sense to me as the XMPP component project is moving along. I can even see gen_component rivaling gen_server in the nearest future :-). Jokes aside, it will have handle_iq, handle_message, handle_presence and possibly more callbacks with helpers glueing it all together, in a fashion similar to OTP behaviors.
By the way, the component doesn't even have to be a process, depending on what exactly your component does. So far I managed to avoid maintaining conversational state, but will have to introduce it going forward. For instance, to tell the registered user from a new one, having state seems to be a must, doesn't it? Still, should I use Mnesia for it, rather than process state?

The project is now having service discovery written using exmpp. The imaginary weather alert service exposes itself through disco_info/1 and disco_items/1 (which are now part of gen_component).

That's how it looks like in Psi:


As you can see, there are two weather alerts running, each one having few nodes for specific weather alerts. Are you thinking of stock tickers, twits etc. ? Yes, everything is possible with gen_component and XMPP :-)

Check out the source code and instructions.
Next in line is in-band registration.
I'll be doing web interface with Strophe or jsJac as well once I have a chance.
I would be interested in your thoughts and ideas on gen_component.

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