Re: [xmpp] Use of namespace in RFC 3920

[Dave Cridland <dave at cridland.net>]

On Wed Sep 23 17:01:40 2009, Jehan Pagès wrote:
> The RFC is clearly trying to make an excuse for badly programmed XML
> parsers, not able to expand prefixes into namespaces (or keep track  
> of
> declared prefix in parent elements).

It's also opening the door for heavily optimized pathways which elide  
reserialization and all sorts.

>  So you MUST absolutely have a
> default namespace in the root <stream>, and this one MUST be the one
> for the stanza ("jabber:client" or "jabber:server", most typically)

Right, this allows us to detirmine whether it's a client, server, or  
component. We actually do this - so if you want to, you can point  
clients, components, and servers alike at a single port and it'll all  
just work.

If we didn't do this, we'd need some additional signalling to  
distinguish, or else we'd have to use distinct TCP ports for all  
three, which seems suboptimal, especially when we're already using  
this quite happily.

>  +
> you MUST have a prefix declared, for the stream related first level
> elements,

Well if you've already got a default namespace, it stands to reason  
you can't have the stream top-level elements in it.

>  and this prefix MUST be "stream".

I don't care about this, and FWIW, we do not rely on it. Also, it's a  
SHOULD not a MUST, and a MAY rely on. The latter, I think, needs  
changing - this should be SHOULD (because of legacy systems) and MUST  
NOT rely on.


> So for instance, the current RFC asks me to reject and consider this
> stream start as an error, though it is perfectly valid XML and
> conforming to XMPP:
>
> <toto:stream
>           from='juliet at im.example.com'
>           to='im.example.com'
>           version='1.0'
>           xml:lang='en'
>           xmlns='jabber:client'
>           xmlns:toto='http://etherx.jabber.org/streams'>
No, the RFC says you MAY reject it. Section 11.2.1 says so.


> And many other examples: for instance, if I prefer to use a declared
> namespace for "jabber:client" instead of a default namespace, why
> couldn't I?

See above. Various other things, like XEP-0220, get triggered by the  
default namespace choice of the initiator of the stream.

> For historical reasons, some older implementations may accept only a
> stream element qualification through a prefix named "stream" (and  
> not
> for instance through a default namespace, nor a prefix named other
> than "stream"), declared in the initial <stream/> element. For
> backwards compatibility, it may therefore be a good idea, though not
> mandatory, to declare a prefix named "stream" and with value
> "http://etherx.jabber.org/streams"; in the <stream/> header. However  
> an
> implementation MUST NOT send any error, hence reject a stream doing
> differently, as long as the qualified names for the <stream/>,
> <features/> and <error/> element are correct with this alternative
> method.

"it may therefore be a good idea, though not mandatory" = SHOULD.

Dave.
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