Re: PostgreSQL vs SQL/XML Standards

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: Chapman Flack <chap(at)anastigmatix(dot)net>, Markus Winand <markus(dot)winand(at)winand(dot)at>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: PostgreSQL vs SQL/XML Standards
Date: 2019-03-08 12:20:30
Message-ID: 20190308122030.GA8440@alvherre.pgsql
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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
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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