Re: PostgreSQL vs SQL/XML Standards

pá 8. 3. 2019 v 13:20 odesílatel Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
napsal:

> On 2019-Mar-08, Pavel Stehule wrote:
>
> > looks like error in xmlXPathCompiledEval function, that produce little
> bit
> > broken result for XML_DOCUMENT_NODE type. I hadn't this problem with
> > libxml2 2.7.6 64bit, but I seen this issue on same version on 32bit.
> >
> > Currently I had not fresh 32 bit system to check it.
> >
> > I found a workaround - in this case copy (and release xmlNode) is not
> > necessary.
> >
> > please, apply attached patch.
>
> Wow :-( At this point I'm wondering if this should be put in back
> branches as well ... I mean, distill part of commit 251cf2e27bec that
> doesn't affect the behavior of text nodes, and put it on all branches
> together with your fix?
>

The problem is just for case result: XML_DOCUMENT_TYPE, target XML. For
this case the previously used transformation doesn't work.

Is not problem to detect this situation. The content field has -1 instead
0.

Originally there was inverted logic, so xmlCopyNode and xmlFreeNode was not
used for XML_DOCUMENT_TYPE, and then we didn't hit this bug.

> Another thought: should we refuse to work on known-broken libxml2
> versions? Seems like this bug could affect other parts of code too -- I
> see that xmlXPathCompiledEval() is called in file places (including two
> in contrib/xml2).
>
> Third thought: an alternative might be to create a wrapper for
> xmlXPathCompiledEval that detects NULL content and fills in a pointer
> that xmlFreeNode can free.
>

>
> --
> Álvaro Herrera https://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>