[OpenSIPS-Devel] presentity expiration and etag handling

[Kennard_White at logitech.com]

Hi,

While looking at another feature (see patch upload 3058434) I came across a
strange behavior and traced it down to a section of  presence code.

Given an subscription (via SUBSCRIBE) and an existing presentity (via
PUBLISH) for event "presence", opensips send different NOTIFY PIDFs
documents depending upon if the presentity is expired via timeout vs an
explicit PUBLISH with Expires=0 header. In the first case (timeout), the
NOTIFY PIDF is completely missing the original presentity (and the body may
be empty if no other tuples). In the second case (unpublish), the NOTIFY
PIDF has an edited copy of the original presentity (with basic status set
closed). This occurs when the presentity hash tables are enabled and
fallback2db is disabled.

I doubt this is a really a bug (the behavior when presentities go away is
not defined by the RFCs as far as I can tell). But I suspect this is a
change in behavior introduced by the hash table code. Since some clients
react very differently to no-body NOTIFY messages compared to ones
containing 'closed' status, this can (and did) lead to strange system
behavior.

The root cause of the different behavior is that during message cleaning,
the presentity is deleted from the hash tables before the notification is
generated. In more detail, the call sequence is:

	publish.c msg_presentity_clean() calls
    	notify.c: publ_notify() calls
      notify.c: get_p_notify_body() calls
	notify_body.c: pres_agg_nbody()

The etag of the expiring presentity (or its body index) is passed down the
above call chain. The last function attempts to "edit" the expiring
presentity, setting the basic status to 'closed' prior to sending out the
NOTIFY.

But the stale presentity is deleted from the hash table before the above
call sequence, thus it never shows up in the list of presentities queried
by get_p_notify_body() and is not edited to indicate closed.

Probably msg_presentity_clean() calling publ_notify() with the expiring
etag doesn't serve any purpose, at least with fallback2db disabled, and is
potentially misleading since it doesn't do what one would expect.

Regards,
Kennard
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