On 16/08/10 12:11, Alban Crequy wrote:
Le Sun, 15 Aug 2010 23:05:49 +0100,
Martin Morrison<[email protected]> a écrit :
I've recently been implementing XEP-0115 Entity Capabilities, both the
latest and the legacy versions, and have a few issues that I feel
should be clarified in the latest version of the spec:
1. The legacy version of the spec explicitly says (in 4.2, below
example 8):
[...]
2. The spec only uses the word "SHOULD" when specifying how the Disco
'node' attribute is formed. A receiving entity that supports both
Entity Capabilities and has multiple disco#items nodes thus has
somewhat of a dilemma in deciding how to respond to a disco#info
request for an unknown node. Should it return an<item-not-found/>
error, or assume that the remote entity has used some other mechanism
to construct the 'node' attribute in the request, and return the base
capabilities as if the node was empty?
I think<item-not-found/> is best: sending an empty capability in this
case is bad because the hash will not match and the client will discard
the reply.
3. Related to item 2, the following race condition can occur:
- [email protected] sends Presence to [email protected] with
an Entity Capabilities hash
- In response, juliet sends a disco#info request with the "node#hash"
as the 'node' attribute
- Meanwhile, romeo changes the feature set of his client (e.g. turns
on his camera)
- Upon receiving the disco#info request, what does romeo do?
As the 'node' attribute has been formed using the recommended method,
Romeo can establish that the hash doesn't match his current
capabilities. Should he return an error, or ignore the contents of the
'node' attribute completely and just return his current capabilities
(which will be accepted, since he will already have pushed an updated
hash via Presence)? Either way, I think it would help if the spec
specified what was expected.
For this race, it was suggested to just send<item-not-found/> in this
thread: http://mail.jabber.org/pipermail/standards/2008-May/018713.html
Sending<item-not-found/> will work: Juliet will receive the new hash
a bit later and she will send a new disco request with the new hash.
Alternatively, Telepathy-Gabble keeps a cache mapping
hash->capabilities. So with this implementation, Romeo will send the
*previous* capabilities corresponding with the requested hash.
This was added to work around a bug in iChat: if you send back
item-not-found, it will just ask you again, immediately, forever.
So while sending <item-not-found/> should work, it only works if you
don't know anyone using iChat. :)
--
Will
