Re: Default attribute values

[Kjell Ahlstedt <kjell ahlstedt bredband net>]

I got this message only today, more than a week after it was sent. If 
you don't subscribe to libxmlplusplus-list, that's probably the reason 
why it took so long.

I can see that you've already filed the bug report 
https://bugzilla.gnome.org/show_bug.cgi?id=701674. I'll discuss the 
issue there, when I've studied it a bit.

Kjell

2013-05-28 06:38, xmlpp otpproductions com skrev:
> Hi all --
>
> I'm porting a python server to C++.  I auditioned a lot of XML
> frameworks, and for me libxml++ was hands down the most usable.  It
> lets me think like a C++ programmer instead of like a standards
> author.  So thanks for that!
>
> However, we have been relying on default values of attributes defined
> in a DTD.  We've written a lot of python client programs that send XML
> to the server, and they don't specify all the attributes.  The python
> XML framework we used (amara) would add them in when it validated.
>
> That is not happening when I use libxml++.  I take the XML sent in to
> the server by a client, and combine it in memory with a DTD the server
> knows about.  I construct a DOMParser and call set_validate() on it,
> and then call DOMParser.parse_memory().  It does correctly flag
> invalid XML, but it does not add in attributes with default values.
>
> I don't know anything about libxml2, but I've read a lot of source
> tonight.  It appears to me that DOMParser::parse_memory() calls the C
> function xmlCreateParserMemoryCtxt(), which creates some in-memory
> data structures but does not set any options.  Then the C++
> DomParser::parse_context() is called.  This calls the C++ function
> Parser::initialize_context; if set_validate() has been called
> previously then initialize_context() adds the XML_PARSE_DTDVALID
> option to the context.  After initialize_context() returns,
> parse_context() calls the C function xmlParseDocument().
>
> I know libxml2 can insert default parameters, because if I call the
> xmllint program (part of the libxml2 distribution) with the command
> line options '--valid --dtdattrs', the output has the default
> attributes inserted.  From reading the source for xmllint, it appears
> the key step is EITHER setting the XML_PARSE_DTDATTR option on the
> parser before calling the parse function; OR setting the
> XML_COMPLETE_ATTRS bit in the global C variable
> xmlLoadExtDtdDefaultValue before calling the parse function.  I didn't
> see any way to do either of those as a user of libxml++.
>
> Have I missed something?  Is there acurrently a way to get this
> behavior?
>
> If not, should I file a bug?  It seems to me that this should be the
> default behavior -- if a DTD writer goes to the trouble of adding
> attributes with default values, they want the parser to implement
> them.  Of course, doing that in libxml++ would be a
> non-backward-compatible change; although I think it would be a fairly
> benign change -- for most programs the appearance of additional
> attributes won't have any effect.  But probably that's a bad idea; how
> about adding a set_dtdattrs() function to the Parser class, which one
> could call before calling Parser::parse_* function?
>
> Thanks for your attention!
>
> Bob Nolty
> _______________________________________________