Programming Jabber

The set_presence() function

This function is used by setup_Jabber() to send the script’s (and therefore the coffee’s) initial presence. It’s also used within the main sensor poll/presence push loop to send further presence packets if the coffee’s state changes.

sub set_presence {
  my ($connection, $s) = @_;
  my $presence = Net::Jabber::Presence->new();
  my ($show, $status) = split("/", $status[$s], 2);
  $presence->SetPresence( show   => $show,
                          status => $status );
  print $status, "\n";
  $connection->Send($presence);
}

On receipt of the Jabber connection object and the coffee status, which will be 0 (NOCOFFEE) or 1 (COFFEE), set_presence() constructs a new Net::Jabber::Presence object. This object represents a <presence/> element, upon which we can make method calls to hone the element as we wish. SetPresence() is one of these methods, with which we can set values for each of the <show/> and <status/> tags. We retrieve the values for each of these tags by pulling the strings from the appropriate member of the @status array, as described earlier in Section 9.2.3.1.

We print the coffee’s status (remember, this function is called only when the status changes, not every time the sensor is polled) and send the newly built <presence/> element down the XML stream to the Jabber server. This is accomplished by passing the presence object as an argument to the Send() method of the connection object in $connection. This works in the same way as the send() function in Jabberpy and the send() function ...