Re: [xml] Invalid namespace definitions after namespace change

[Kasimier Buchcik <kbuchcik 4commerce de>]

Hi,

Jacek Konieczny wrote:
> On Mon, Feb 28, 2005 at 11:45:34AM +0100, Kasimier Buchcik wrote:
>
> > Jacek Konieczny wrote:
> >
> > > Hello,
> > >
> > > I have a big problem with libxml2 python bindings. The problem also
> > > occurs in the C API, but it is easily fixable there (so it can be just
> > > called a 'feature').
> > >
> > > Here is the test case (python code):
> > >
> > > import libxml2
> > > doc=libxml2.parseDoc("<a xmlns='http://a/'><b xmlns='http://b/'/></a>")
> > > a = doc.getRootElement()
> > > b = a.children
> > > print `doc.serialize()`
> > > print "Ns of <b/>: %r" % (b.ns().content,)
> > > b.setNs(a.ns())
> > > print `doc.serialize()`
> > > print "Ns of <b/>: %r" % (b.ns().content,)
> > >
> > > The output is:
> > > '<?xml version="1.0"?>\n<a xmlns="http://a/";><b xmlns="http://b/"/></a>\n'
> > > Ns of <b/>: 'http://b/'
> > > '<?xml version="1.0"?>\n<a xmlns="http://a/";><b xmlns="http://b/"/></a>\n'
> > > Ns of <b/>: 'http://a/'
>
>
> [...]
>
>
> > > The biggest problem is, that I cannot fix that using only the Python
> > > API. xmlNode.reconciliateNs() does nothing about that.
> >
> > There was a bug in xmlSearchNsByHref, which caused xmlReconciliateNs
> > to fail in this scenario. Fixed in CVS (tree.c 1.339).
>
>
> After applying the patch on libxml2-2.6.17 the output is:
>
> '<?xml version="1.0"?>\n<a xmlns="http://a/";><b xmlns="http://b/"/></a>\n'
> Ns of <b/>: 'http://b/'
> '<?xml version="1.0"?>\n<a xmlns="http://a/";><default:b xmlns="http://b/"; xmlns:default="http://a/"/></a>\n'
> Ns of <b/>: 'http://a/'
>
> That is a correct XML, but still does not satisfy me. A prefix has been
> added to <b/> and the unneccessary namespace declaration is still there.

Yes, xmlReconciliateNs does not remove unreferenced namespace
declarations, since it cannot know if those declarations are needed
for following processing or not; it goes the save way in preserving
them. I recommend implementing a "xmlCleanupNsDecl" function, removing
unreferenced namespaces from a given branch.
Adding generated prefixes is OK - take a look at the namespace
normalization algorithm of the W3C [1]; preserving prefixes is not
always possible if serializing, so you should not rely on it.

> For my needs that is still unacceptable. I implement an XMPP
> implementation and for backward-compatibility with many Jabber clients
> I need to use default namespaces (no prefixes) in some places.

I see, OK so you need total control of the declarations.

> I think a function to remove (or override) namespace declaration from
> a node is what I need and I will request it via Bugzilla.

Exactly.

[1] 
http://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407/namespaces-algorithms.html

Regards,

Kasimier