[xml] DTDs and null SystemID/ExternalID ?

[Stefan Jeglinski <jeglin 4pi com>]

Setup for the question: it appears that there are 3 basic DOCTYPES 
for an xml document:

1:
<!DOCTYPE root_name SYSTEM "local_path_to_dtd">
<
...
(xml content)
...
>

2:
<!DOCTYPE root_name PUBLIC "url_to_dtd">
<
...
(xml content)
...
>

3:
<!DOCTYPE root_name [
...
(element definitions etc)
...
]>
<
...
(xml content)
...
>


I'm trying to do the 3rd one, where the dtd is self-contained within 
the xml file. I am doing it in memory, using 
xmlParserInputBufferCreate etc. I create a doc using xmlNewDoc, then 
the dtd from the buffer using xmlIOParseDTD, and then blow it out to 
disk with xmlSaveFormatFile. Works like a champ, except that...

I've boxed myself into a corner. Snooping the libxml2 source 
(xmlsave.c, xmlDtdDumpOutput), I see that I can create the 3rd type 
only if SystemID and ExternalID are NULL. But this is directly at 
odds with xmlIOParseDTD, which ultimately allocates both and fills 
them in with "none".

You can't naively can't set them to NULL after the fact, because you 
will die in xmlFreeDoc.

Is there a way to create the dtd in memory so that both SystemID and 
ExternalID are NULL, giving me DOCTYPE #3? Or am I out in left field 
here? (I'm working my way through learning this stuff bit by bit, and 
frankly don't know any better...)


Stefan Jeglinski