Re: [xml] Per parser xmlGcMemSetup

[Daniel Veillard <veillard redhat com>]

On Sat, May 05, 2007 at 10:40:22PM +0200, Joachim Zobel wrote:
> Am Samstag, den 05.05.2007, 15:28 -0400 schrieb Daniel Veillard:
> 
> >   if you're calling the callbacks from libxml2 just to build a tree it's
> > bad, either use one of the parsers or build the tree with the tree API.
> > Other uses are not suported, in the sense that I may break randomly 
> > how the callback works. 
> 
> >   I don't know why you are doing this but this sounds extremely fishy,
> > would you care to explain, because I'm trying to guess and mostly I see
> > only bad reasons.
> 
> THis is IMHO necessarily so. Apache has so called filters that can
> modify the outgoing contents. mod_xml2 is such a filter. It runs the
> libxml2 parser to turn a stream of text buffers (called buckets by
> apache) into a stream of sax events (called sax buckets by me). Other
> filters can then modify these sax events. The sax buckets automatically
> turn back into text when they are treated as such, so no filter is
> necessary on the network end.
> 
> One of such filter is mod_i18n. It checks the stream of sax events it
> passes until it detects a certain attribute and then starts building a
> small partial tree, which is modified and then turned back into sax
> events. 

But mod_i18n should know it is operating on top of libxml2 parser,
so why doesn't it use the libxml2 allocation routines ? The SAX interfaces
at the C level are really parser specific, and libxml2 SAX2 have been heavilly
modified to improve performances, so I don't see why it would use a different
allocator then.

> The point with this is that it stays streaming as much as possible and
> it is also possible to do tree manipulation. It is in many cases a
> usable workaround for the sax/dom dilemma and I am already thinking
> about using the same trick for another module.
> 
> It does however require to call the SAX2 callbacks.

That sounds quite complex, though there is certainly good reasons for this :-)

Daniel

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