[xmpp] 3921bis: probe + unavailable

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

Regarding the server response to an inbound presence probe, Section
4.3.2 of 3921bis currently reads as follows:

******

   2.  Else, if the contact has no available resources, then the server
       SHOULD reply to the presence probe by sending to the user the
       full XML of the last presence stanza of type "unavailable"
       received by the server from the contact (however, the server MAY
       opt to not reply at all).

******

There are two issues I'd like to bring up:

a. My sense of existing implementations is that people would prefer a
definitive answer to the probe (i.e., <presence type='unavailable'/>).
Therefore I would like to change "SHOULD reply with unavailable but MAY
opt to not reply at all" to "MUST reply with unavailable".

b. Someone poked me offlist about a potential security issue here: what
if the probing user was blocked from receiving the contact's presence at
that time (e.g. via privacy lists)?

Therefore I suggest that the spec shall be modified to read as follows:

******

   2.  Else, if the contact has no available resources, then the server
       MUST reply to the presence probe by sending to the user a
       presence stanza of type "unavailable"; this presence stanza
       SHOULD be empty but (subject to local security policies) MAY
       include the full XML of the last unavailable presence stanza that
       the server received from the contact.

   CS: <presence from='mercutio at example.com'
                 to='juliet at example.com'
                 type='unavailable'/>

******

Objections?

Peter

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

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