[JDEV] Avatar images are per-resource

[Jens Alfke]

One more note on the avatar spec. I realized while in the shower this 
morning that it's important that the image be stored in the public XML 
associated with the resource, not in the XML for the user itself. 
Otherwise multiple logins trying to set different images will stomp over 
the image stored on the server.

I was unsure at the time (this was about while I was lathering my 
armpits) whether the public-XML thingy supported per-resource storage, 
but on looking at the very vague description 
<http://docs.jabber.org/draft-proto/html/xml.html> it appears that it 
does. The trick is to include your resource when sending the IQ 'set' to 
yourself.

So to use an example, the provider of the image would store it on the 
server as follows:

<iq id="1" type="set" to="me at myserver/myresource">
	<query xmlns="jabber-storage:iq:avatar>
		<data mimetype="image/jpeg"> ...Base64 image data goes here.. </data>
	</query>
</iq>

The important thing to note is that the "to" address contains the 
sender's resource. The requester would also need to include the resource 
(as is already shown in the current avatar proposal.)

An additional thing I've done in the example is include a "mimetype" 
attribute on the <data> element. I know I said earlier that the common 
graphics formats are self-describing, but I think it's still safer to 
tag the data. Not all OS's may have support for auto-detecting the image 
type, and future image types may be harder to detect, and also this way 
we could in the future include multiple <data> elements with different 
MIME types and let the receiver easily pick out the best one.

--Jens