Re: [xml] using xmlSetExternalEntityLoader to return internally generated XML documents

[Rush Manbert <rush manbert com>]

Nathan Day wrote:
> I have a lot of XML documents that are generated using the tree API  or 
> the XSLT API and I want to be able to refer to them in other XML  
> document within LIBXML2 through URL's (xincludes, xslt imports,  
> includes, document(), etc.). Looking at the documentation  
> xmlSetExternalEntityLoader is what I want but I am not sure what I am  
> supposed to do next. I guess I am supposed to create a  
> xmlParserInputPtr but how do I create one for an XML document, is  that 
> what xmlNewEntityInputStream is for, in which case how do I  create a 
> xmlEntity.

The xsltproc utility does this, so get its source and see what it does. 
I actually hacked its init code to use in my app, and hacked the entity 
loader to call my own code.

> Another question I have,
> I have some XSL transformations that take a long time, up to 6  seconds 
> in some cases, fortunately large parts of these  transformations produce 
> the same result. So what I want to do is  create a mechanism so that 
> when a XML document is being serialised  into a string I can have my own 
> call back function called at  particular points so that I can insert 
> previously serialised text. I  suppose I could just insert a big text 
> element into the xml document  another possibility is to serialise the 
> document my self, this is for  generating HTML, would this be difficult.

It's not too hard to walk the DOM tree and make callbacks for each node, 
or for some filtered subset. Then you can insert nodes (and entire 
subtrees) into the DOM tree before you serialize the content. However, 
that means that you need to know the DOM representation of the stuff 
you're trying to insert, so you would need to try to generate it then 
save off the representation (I'm assuming you want to cache a 
transformation result, then use it in subsequent documents.), so it 
might not be useful for you. And you might not even be creating a DOM 
tree. Maybe the SAX interface would be useful? (I haven't used it.)

Hope it helps,
Rush