"presenceability" (was Re: [Standards-JIG] PubSub leased subscriptions)

Peter Saint-Andre stpeter at jabber.org
Tue Feb 7 17:15:33 UTC 2006


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Nolan Eakins wrote:
> Peter Saint-Andre wrote:
>>> This isn't really an answer to Jean-Louis's question, but are pub/sub
>>> nodes presencable? Yeah, I made up a word :-) so I'll define it, do
>>> nodes send presence stanzas? Such that when I send a presence to a
>>> pub/sub service, I get a presence stanza with my subscriptions? That
>>> might kill a couple birds with one stanza.
>>
>>
>> No.
>>
>> Presence is sent by entities that are JID addressable, but pubsub nodes
>> are not necessarily JID-addressable. That is, we don't have a protocol
>> for doing this:
>>
>> <presence from='pubsub.shakespeare.lit'>
>>   <foo node='blogs/princely_musings'/>
>> </presence>
> 
> I know pub/sub nodes can't be addressed by JID, but pub/sub services CAN
> be. What I suggested was that you would send a presence to a pub/sub
> service, and it would include a list of nodes that you are subscribed to.
> 
> The pub/sub service's presence would include a list of nodes much like
> the little snippet you included. This would allow me to know what nodes
> that I've subscribed to w/o resorting to private XML storage, and it
> would address Jean-Louis's problem with leased subscriptions.
> 
> The addition of a list of nodes in the presence from pub/sub services
> would solve those two problems.

Aha, I see, that has possibilities. :-) I think I'd prefer it if the
service sends a message rather than including all the subscribed nodes
in a presence packet. Also it probably makes sense for the service to
send the subscriptions (affiliations) only if the client requests them
(what if I'm on a mobile client that doesn't want to receive all these
pubsub affiliations). So perhaps something like this (where we assume
"publisher at domain.tld" is a virtual pubsub service a la PEP):

<presence from='subscriber at domain.tld/foo'
          to='publisher at domain.tld'>
  <affiliations xmlns='http://jabber.org/protocol/pubsub'/>
</presence>

<message from='publisher at domain.tld'
         to='subscriber at domain.tld/foo'>
  <pubsub xmlns='http://jabber.org/protocol/pubsub'>
    <affiliations>
      <entity node='some-node-id'
              jid='subscriber at domain.tld'
              affiliation='none'
              subscription='subscribed'/>
      <entity node='another-node-id'
              jid='subscriber at domain.tld'
              affiliation='none'
              subscription='pending'/>
    </affiliations>
  </pubsub>
</message>

And so on.

For non-PEP services, the subscriber would need to have the service in
its roster with a subscription of 'from' or 'both' but that doesn't seem
onerous.

/me ponders

Peter

- --
Peter Saint-Andre
Jabber Software Foundation
http://www.jabber.org/people/stpeter.shtml

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