[MTOS-dev] XML parsing

[Mark Paschal]

Hi, mtos-dev folks,

I told Tim a while ago I would start a thread about XML parsing in MT, 
so I'll take the current quietude as an opportunity to do so.

While we don't parse XML in any of the core functions, we do in:

* the Atompub server(s)
* profile exchange for OpenID commenters

Given our general product requirements and that the larger Perl 
community applies TMTOWTDI doubly to XML, parsing XML presents some 
challenges. XML::Atom, the CPAN module we use in our Atompub 
endpoints, will use the preferred XML::LibXML if available, but we 
ship XML::XPath in extlib to have known minimal XML support.

However, XML::XPath uses XML::Parser, which requires the expat library 
for the heavy lifting. While most servers have expat (removing it on 
my dev machine through the package manager would remove 185 dependent 
packages--essentially everything), it is a dependency, and completely 
fresh servers using some UNIX distributions may not have expat 
installed. When neither libxml nor expat are installed, it's not 
obvious what the problem is; mt-wizard reports that XML::Atom is 
missing, which isn't precisely the case.

It would seem we could further use the same fallback technique we 
already use, eventually falling back to a pure-perl XML module such as 
XML::SAX::PurePerl. To keep developing MT and plugins simple, though, 
we would want to build a sort of "XML::Any" module that encapsulates 
the selection of an XML library and provides a common API. That's a 
non-trivial undertaking, so other solutions are welcome.

Does anyone have other thoughts, problems, or solutions about XML 
parsing in MT?

This isn't a pressing issue and isn't a performance focus, but I see 
us doing much more in the future with Atompub and XML APIs (I 
certainly am in my hack-day time), so we should plan for it. Thanks in 
advance for your input!


Mark Paschal
Software developer, Movable Type
mark at sixapart.com