[Standards] mobile optimizations

[Alexander Gnauck]

Dave Cridland wrote:
> 2) Client says "I have the roster as of this point in time". Server says 
> "Here's all the changes since then.".
> 
> This is obviously the best option in terms of efficiency, but it, too, 
> has problems. The key issue is that roster entries won't die - instead, 
> they'll be maintained along with a timestamp when deleted, in order that 
> the server can tell a client it's gone.

yes I think the logic on the server will get very complicated. Util I 
have a mutual subscription to a contact the server updates the roster 
item several times(subscription=none,from or to,both +ask). This will be 
~5 versions until the subscription is mutual.

> I also have a fondness for modified strictly increasing timestamps, but 
> implementors need to appreciate that computer clocks go backwards, so 
> they need to remember to handle odd cases like that by "letting time 
> catch up" - just using a few ms later than the last timestamp until the 
> real time is greater than the last timestamp.

for this reason I would prefer a versioning of the roster, so I client 
can just tell the server I have version 235241 of the roster, let me 
know if this is the current roster or send me the changes otherwise.

Regards,
Alex