Programming Jabber

Presence callback

Having dealt with the incoming <message/> elements, we turn to the <presence/> elements. Most of those we receive in this conference room will be notifications from people entering and leaving the room, as shown in Example 9-2. We want to perform housekeeping on our keywords dictionary so the entries don’t become stale. We also want to deal with the potential problem of conflicting nicknames. Let’s look at that first.

We want to check for the possibility of nickname conflict problems that may occur when we enter the room, and the chosen nickname (flash) is already taken.

Remembering that a conflict notification will look something like this:

<presence to='[e-mail]/jarltk'
        from='[e-mail]/flash'
        type='error'>
  <error code='409'>Conflict</error>
</presence>

we test for the receipt of a <presence/> element with the following:

def presenceCB(con, prs):

    # Deal with nickname conflict in room
    if str(prs.getFrom()) == roomjid and prs.getType() == 'error':
        prsnode = prs.asNode()
        error = prsnode.getTag('error')
        if error:
          if (error.getAttr('code') == '409'):
              print "Cannot join room - conflicting nickname"
              con.disconnect()
              sys.exit(0)

The <presence/> element will appear to be sent from the JID that we constructed for the initial room entry negotiation (in the roomjid variable further down in the script); for example:

[e-mail]/kassist

We compare this value to the value of the incoming <presence/>’s from attribute, and also ...