Horton

Re: PostgreSQL vs SQL/XML Standards

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Pavel Stehule <pavel.stehule@gmail.com>
Cc: Chapman Flack <chap@anastigmatix.net>, Markus Winand <markus.winand@winand.at>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-03-08T12:20:30Z
Lists: pgsql-hackers 
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?

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

Commits

  1. Improve documentation about our XML functionality

  2. Improve documentation about our XML functionality.

  3. Add volatile qualifier missed in commit 2e616dee9.

  4. Fix crash with old libxml2

  5. Fix minor deficiencies in XMLTABLE, xpath(), xmlexists()

  6. Fix the BY {REF,VALUE} clause of XMLEXISTS/XMLTABLE

  7. doc: Update README.links

  8. XPath fixes: