Programming Jabber

Sending of availability information

OK. We’ve connected, authenticated, defined, and registered the callback to handle <presence/> elements, and requested the roster, so mod_roster will send us any presence subscription (or unsubscription) requests. Now we need to make an availability announcement in the form of a simple <presence/> element:

<presence/>

We can do this by calling the sendInitPresence() method on the connection object:

con.sendInitPresence()

This availability information will be distributed to all the entities that are subscribed to the script’s presence and are online at that moment. It will also signify to the Jabber server that we are properly online—in which case it can forward to us any messages that had been stored up in our absence.

We’re not really expecting any <message/> elements; indeed, we haven’t set up any subroutine to handle them, so they’d just be thrown away by the library anyway. The real reason for sending presence is so that the server will actively go and probe those in a presence subscription relationship with the script and report back on those who are available (who have themselves sent their presence during their current session). This causes <presence/> elements to arrive on the stream and make their way to the presenceCB() handler.