[xslt] Few questions

[Carlo Contavalli <ccontavalli libero it>]

Hi! 
  I'm almost done writing a module using libxml/libxslt (mainly 
2.5.7 and 1.0.30), and I have a few question marks still to answer:  

  - (libxslt) the module provides some extension tags (registered 
    with xsltRegisterExtElement). The function handling one of the 
    extension tags needs to retrieve all the text that would
    be expanded by the xslt processor in the corresponding ``subtree''. 
    To do this, I've used:

    	xsltEvalTemplateString(...)

    is this correct? If my tag contains a <fallback handler, however,
    althought working correctly, I keep getting the non-fatal error:

      xsltApplyOneTemplate: fallback was not compiled

    is there another function I should use? What can I do to avoid
    the error (something smarter than removing the fallback node 
    from the tree)?

  - (libxml) Some xml documents that get parsed use external entityes 
    fetched from http urls. I get an uncoherent behavior due to the fact 
    that if the dtd does not exist on the local file system, I get a sort
    of warning telling me the dtd does not exist, but parsing goes on. 
    However, when it is fetched from a remote url, the http status of 
    the request is not checked and if the document does not exist 
    libxml tryes to parse the error page as if it was the DTD, leading 
    to a fatal error (it is quite uncommon to have a 404 page
    containing a valid DTD).
    So, if the dtd does not exist on the local file system -> ignorable
    warning, if it does not exist on a remote url -> parsing stops with
    an error not always easy to understand (Extra content at the end
    of the document... but where did it get the document?). Is this
    an expected behavior? Is there something I can do to avoid the 
    problem?

  - (libxslt) The application changes the error handlers, calling 
    xsltSetGenericErrorFunc with its own handler and its own
    context. However, I sometimes get segfault due to transform.c
    calling xsltGenericError(xsltGenericDebugContext, where
    xsltGenericDebugContext is a different (unknown) data 
    type than the one expected by my handler as GenericErrorContext. 
    Is this behavior expected? How can I make sure 
    xsltGenericError gets called only with its own context
    (without enabling debugging - still there in 1.0.32)?

  - (libxml) The application I'm talking about is _not_ multithreaded
    (at least by default). However, it is made
    of a list of modules being called in a big loop, where 
    more than a module may make use of the libxml library in 
    the same thread of execution. libxml makes use of many global 
    variables, some of which may be changed to customize its 
    behavior. Actually, to avoid one module influencing the
    parsing of another module, I compile libxml with multithreading
    support and save the ``state'' of the library by copying
    the memory area returned by xmlGetGlobalState with memcpy
    and by restoring it after the module has executed, leading
    to something like:
      At module initialization
        - create new global state (malloc and InitializeGlobalState)
 	- save global state (GetGlobalState and memcpy)	
	- overwrite the global state with the one created above
	- (change libxml defaults)
	- save my own global state
	- restore previous global state

      At module execution (in the big loop)
        - save global state
	- overwrite the global state with my own
	- (work with libxml)
	- restore global state

    Is there a better way to do this? Is there any other
    solution than copying every single global variable
    when multithreading is disabled? I've looked at the
    source code, and I believe it would be nice to let 
    the applications access the statics NewGlobalState
    and FreeGlobalState, and to have a SetGlobalState
    that acts directly on the tsd variables being used
    (if you believe it worth, I could easily provide the
    needed code).

  - (libxslt) What's the status for libxslt? I haven't seen 
    any threading support and the only globals I've seen 
    are those for error handling.
    Am I on the safe side (with regard to the problem
    highlited above) if I save and restore just them
    before and after running the module? 

Sorry for the long mail and sorry for the OT about libxml, but 
I really didn't know how to best split the mail.  Feel free to
answer me on any of the two lists.

Thanks in advance,
Cheers,
Carlo

-- 
  GPG Fingerprint: 2383 7B14 4D08 53A4 2C1A CA29 9E98 5431 1A68 6975
                        -------------
A computer lets you make more mistakes faster than any other invention,
with the possible exceptions of handguns and Tequilla.
	-- Mitch Ratcliffe