[xml] [Fwd: Resolving entity references from a DTD using SAX parser]

[Rachael Churchill <rachael churchill linguamatics com>]

Hi

I hope I'm not being rude, but I didn't get any replies to this email 
when I sent it to the mailing list before, so I'm just sending it again 
in case it got missed. If anyone can help answer my questions that'd be 
really good.

Thanks very much,
Rachael

-------- Original Message --------
Subject:        [xml] Resolving entity references from a DTD using SAX parser
Date:   Fri, 17 Apr 2009 13:13:26 +0100
From:   Rachael Churchill <rachael churchill linguamatics com>
To:     xml gnome org



Hi

Please could you help me get libxml2 to resolve entity references such 
as &foo; which are defined in a DTD declared in the XML document?

I am using the SAX parser (I know about the warning on 
http://xmlsoft.org/entities.html, but we really have to use SAX for our 
purposes), declaring element handlers and character handlers and then 
calling XMLParseChunk. I originally assumed the parser would 
automatically read in the DTD when it found the declaration, and then 
resolve the custom-defined entity references as it found them, like it 
does with the predefined ones such as &amp; but this seems not to be the 
case.

I think I have to declare a reference-handling function as 
SAXHandler.reference, and then in that function, which gets called when 
an entity reference is found, call xmlGetEntityFromTable to look up what 
that entity reference resolves to.  But how do I populate the table 
using the entity references defined in the DTD? The functions like 
xmlAddDtdEntity and xmlAddDocEntity seem to require an xmlDocPtr, which 
I thought only existed when doing DOM parsing. So do I need to use 
xmlNewEntity instead, which does the same thing without needing an 
xmlDocPtr? Also, xmlGetEntityFromTable isn't exposed by the API. It's 
called from xmlGetDocEntity, xmlGetDtdEntity and xmlGetParameterEntity, 
but they all require an xmlDocPtr too. May I change the API so that 
xmlGetEntityFromTable is exposed, or is there another way of doing it?

Also, how do I get the filename of the DTD? Is there a function for 
that, or do I need to manually parse the XML document looking for the 
declaration? Then when I have the DTD,  I need to parse it. Calling 
xmlParseDTD with the filename as the SystemID argument seems to work; 
then can I use the "elements" field of the xmlDtdPtr it returns as the 
table I need to refer to in xmlGetEntityFromTable (and so not need 
xmlAdd*Entry)?

Thanks very much,
Rachael
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