Re: [xmpp] 3921bis: probe + unavailable

[Peter Saint-Andre <stpeter at stpeter.im>]

On 2/1/10 1:34 PM, Jonas Lindberg wrote:
> On Mon, Feb 1, 2010 at 8:56 PM, Ben Schumacher <Ben.Schumacher at webex.com> wrote:
>> On 01/30/2010 03:29 PM, Jonas Lindberg wrote:
>>> While I agree this would simplify the protocol a little, I am not
>>> convinced it is a change worth making.
>>>
>>> First of all, not responding to probe when unavailable is a pretty
>>> good optimization. A large part of Xmpp traffic is presence. This
>>> change would further significantly increase the presence traffic,
>>> making scaling more challenging and adding load to c2s and s2s
>>> connections. For example, a cell phone xmpp client may be better off
>>> not getting potentially thousands of presence unavailable stanzas for
>>> offline friends when connecting over gprs.
>>>
>>> I'm also not convinced this change make it significantly easier to
>>> implement xmpp clients/servers. Especially if we are going to
>>> recommend that clients and servers SHOULD cope with no response for
>>> legacy reasons.
>>>
>>
>> Jonas-
>>
>> I agree with your points -- it would likely result in extra traffic.
>> That being said, I much prefer this to the ambiguity (and potential
>> presence leak) of the prior language. As it happens, servers and clients
>> will *always* have to cope with no response as this is a network'd
>> service and packets can get lost, etc, so I'm not sure the language
>> should be "SHOULD" re: legacy services, but rather maybe a note that
>> indicates that you may not get a response.
>>
>> Ben
>>
> 
> While one can argue it's a little prettier, I don't think it's very practical.
> 
> Making this change at scale requires very significant work and comes
> at a significant cost in traffic increase (consider user with >1000
> mostly offline friends). It will also result in worse user experience
> for users with large rosters on low bandwidth connections, like the
> common scenario of a cell phone.

I would find SHOULD acceptable here. How about the following text?

   2.  Else, if the contact has no available resources, then the server
       SHOULD reply to the presence probe by sending to the user a
       presence stanza of type "unavailable" (although sending
       unavailable presence here is preferable because it results in a
       deterministic answer to the probe, it is not mandatory because it
       can greatly increase the number of presence notifications
       generated by the contact's server); this presence stanza MAY
       include the full XML of the last unavailable presence stanza that
       the server received from the contact, if appropriate in
       accordance with local security policies, otherwise it will
       indicate only that the contact is unavailable.

Peter

-- 
Peter Saint-Andre
https://stpeter.im/

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