Programming Jabber

The InPresence() subroutine

Our presence handler, the callback subroutine InPresence(), honors requests for subscription and unsubscription to the script user’s (and therefore the coffee’s) presence. This callback is designed to work in the same way as the presenceCB() callback in the Python recipe described in Section 8.3.

However, while the Python Jabberpy library hands to the callbacks a jabber.Client object and the element to be handled, the Perl Net::Jabber library hands over a session ID and the element to be handled. Don’t worry about the session ID here; it’s related to functionality for building Jabber servers, not clients, and we can and should ignore it for the purposes of this recipe. What is important is the element to be handled, which appears as the second argument passed to the subroutine collected by the $presence variable from $_[1].

What is common between the two libraries is that the element that is passed to be handled as the subject of the callback is an instance of the class that the callback represents. In other words, a callback is used to handle <presence/> elements, and the element received is an instance of the Net::Jabber::Presence class (just as the element received by a Jabberpy presence callback is an instance of the jabber.Presence class).

# Handle presence messages sub InPresence { my $presence = $_[1]; my $from = $presence->GetFrom(); my $type = $presence->GetType(); if ($type eq "subscribe") { print "Subscribe request ($from) ...\n"; $jabber->Send($presence->Reply(type ...