Programming Jabber

Waiting for packets

Once everything is set up, and the script has announced its presence, it really just needs to sit back and listen to the <presence/> elements that come in. If one of these is from the intended notification recipient, and the availability state is right (i.e., not in dnd mode), we know that the circumstances are appropriate for sending the notification.

But the elements being sent over the stream from the server don’t spontaneously get received, parsed, and dispatched; we can control when that happens from the script. This is the nub of the symbiosis between the element events and the procedural routines, and it’s name is process().

Calling process() will check on the stream to see if any XML fragments have arrived and are waiting to be picked up. If there are any, Steps 3 through 5, shown in Figure 8-6 and described in Section 8.3.4, are executed. The numeric value specified in the call to process() is the number of seconds to wait for incoming fragments if none is currently waiting to be picked up. Specifying no value (or 0) means that the method won’t hang around if nothing has arrived. Specifying a value of 30 means that it will wait up to half a minute. We really want something in between, and it turns out that waiting for up to a second for fragments in a finite loop like this:

for i in range(5):
  con.process(1)

will allow for a slightly stuttered arrival of the <presence/> elements that are sent to the script as a result of the server-initiated probes. ...