[Devel] ETag in Presence module

[Anca-Maria Vamanu]

Hello,

RFC3903 :

8.3.  Server Usage

   Entity-tags are generated and maintained by the ESC.  They are part
   of the state maintained by the ESC that also includes the actual
   event state and its remaining expiration interval.  An entity-tag is
   generated and stored for each successful event state publication, and
   returned to the EPA in a 200 (OK) response.  Each event state
   publication from the EPA that updates a previous publication will
   include an entity-tag that the ESC can use as a search key in the set
   of active publications.

This is exacly what presence module does. 
When a new Publish is received, it generates a Etag and includes in the 200ok reply. If a publish with a SIP-If-Match header is received, that is an updating Publish, it searches if
it has a matching etag stored in database. 

It does not reuse it for other publications and it respects the unicity propriety described in: 


6. The ESC returns a 200 (OK) response. The response MUST contain an

      Expires header field indicating the expiration interval chosen by
      the ESC.  The response MUST also contain a SIP-ETag header field
      that contains a single entity-tag identifying the publication.
      The ESC MUST generate a new entity-tag for each successful
      publication, replacing any previous entity-tag associated with
      that event state. The generated entity-tag MUST be unique from any
      other entity-tags currently assigned to event state associated
      with that Request-URI, and MUST be different from any entity-tag
      assigned previously to event state for that Request-URI.  See
      Section 8.3 for more information on the ESC handling of entity-
      tags.


Klaus Darilion wrote:

> Hi!
>
> Is the ETag constant for a certain client "session"?
>
> RFC3903 mandates that the Etag should be changed with every PUBLISH:
>
> 6.6: ...The ESC MUST generate a new entity-tag for each successful
>       publication, replacing any previous entity-tag associated with
>       that event state.
>
> I think currently openser reuses the Etag from the received PUBLISH in 
> the 200 Ok. Nevertheless, if "changing" Etag will be introduced IMO a 
> constant Etag should be chooseable with module parameters.
>
> regards
> klaus
>
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