[Standards] Proposed XMPP Extension: Roster Versioning

Peter Saint-Andre stpeter at stpeter.im
Tue Mar 11 03:56:42 UTC 2008

Dave Cridland wrote:
> On Mon Mar 10 23:45:28 2008, Peter Saint-Andre wrote:
>> One potential problem: this is not a nice, small, incremental change.
>> Now servers and clients must support:
>> 1. The 'sequence' attribute.
>> 2. Roster pushes via message, not IQ.
>> 3. Multiple items in a roster push.
>> 4. Multiple items in a roster set.
>> The more we change, the less likely it is that clients and servers will
>> add this feature. Then we're back where we started.
>> "If it ain't broke, don't fix it."
>> So what's broken?
>> 1. Huge roster gets every time you log in. The 'sequence' stuff fixes
>> this.
>> What's not broken?
>> 2. Roster pushes via IQ.
>> 3. One item per roster push.
>> 4. One item per roster set.
>> Why are we fixing 2, 3, and 4? Just because we can? Because it is more
>> elegant? Or because it really solves a big problem on the network?
>> Unless there is a compelling need, I'd vote for changing as little as
>> possible.
> The problem is that if you go for Joe's concept - which is certainly
> elegant - of having the roster "diff" simply sent as a bunch of pushes,
> then these - being sent as <iq/> - need to be acknowledged. Now, I
> appreciate that clients don't always do this, but the fact is that they
> should be doing so. I'm unhappy with suggesting that clients quietly
> ignore RFC 3920 because nobody cares.
> So we can fix that simply by using <message/> instead of <iq/> - it's a
> pretty trivial change, and it eliminates the type='result' reply for
> clients on all pushes, so it's inarguably a performance improvement.
> Next up, Joe introduces a problem in as much as the client can't tell
> when it's finished receiving updates, and is now receiving bona-fide
> pushes. Joe says this isn't a problem, but I'm unconvinced - client
> authors have said this is a niggle, at least, for the initial presence
> push, after all.
> We can easily avoid this by having multiple items in a push - again,
> this cuts down on overhead, and so is a performance improvement.
> These two are simply taking Joe's concept - the update-as-push - and
> cleaning it up, getting the protocol better.
> Now... On to point 4. This isn't really needed, and it's not solving a
> big problem. But it's not a huge addition, and it does gain us a bit,
> and - perhaps most importantly - it fits neatly into this spec, and is
> too small to be independent.

The way you present things, it all sounds very reasonable. But in the
end we have strayed somewhat far from RFC 3921. Will client and server
developers come along for the ride? Are the costs worth the benefits? I
think we need some input from someone other than you, me, and Joe in
order to know. I volunteer Rachel Blackman for the job. ;-)


Peter Saint-Andre

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