Re: xmlconcat (was 9.0 release notes done)

Peter Eisentraut wrote:
> On mån, 2010-03-22 at 19:38 -0400, Andrew Dunstan wrote:
>
>>> But if we are not comfortable about being able to do that safely, I
>>> would be OK with just raising an error if a concatenation is
>>>
>> attempted
>>
>>> where one value contains a DTD. The impact in practice should be
>>>
>> low.
>>
>>>
>>>
>> Right. Can you find a way to do that using the libxml API? I haven't
>> managed to, and I'm pretty sure I can construct XML that fails every
>> simple string search test I can think of, either with a false negative
>> or a false positive.
>>
>
> The documentation on that is terse as usual. In any case, you will need
> to XML parse the input values, and so you might as well resort to
> parsing the output value to see if it is well-formed, which should catch
> this mistake and possibly others.
>
>

Actually, I have come to the conclusion that the biggest problem in this
area is that we accept XML documents with a leading DOCTYPE node at all.
Our docs state:

The xml type can store well-formed "documents", as defined by the
XML standard, as well as "content" fragments, which are defined by
the production XMLDecl? content in the XML standard.

A document with a leading DOCTYPE node matches neither of these rules,
and when we strip the XMLDecl from a piece of XML where it's followed by
a DOCTYPE node we turn something that is legal XML into something that
isn't, even by our own (or possibly the standard's) relaxed definition.
A doctypedecl can only follow an XMLDecl, see
<http://www.w3.org/TR/2006/REC-xml11-20060816/#sec-prolog-dtd>.

So I think we need to go back to the drawing board a bit, rather than
patch a particular reported error case. But these problems are not at
all new to 9.0, and coming up to beta as I hope we are is not the time
for it. I think it will have to wait to 9.1.

cheers

andrew