Re: [xml] XPathObject and user/user2

[Daniel Veillard <veillard redhat com>]

On Fri, Nov 29, 2002 at 12:50:17PM +0100, Christian Stocker wrote:
> Hi
>
> I'm trying to debug (once again) PHPs domxml extension.
>
> The XPath part of domxml uses obj->user (obj is a xmlXPathObjectPtr) for

  that's bad !

> storing a PHP/Zend internal pointer. But when I look into the source of
> xpath.c, then I see that obj->user is also used internally there. 

  yes, user is needed for XSLT extensions and XPointer entensions. 
user2 is used solely for XPointer, so this might be safer to use.

> Is my assumption right, that obj->user (and user2 for that matter),
> shouldn't be used for application side storage of pointers like _private
> in other structs? 

  right

> Is there an alternative for that (interpreting
> http://mail.gnome.org/archives/xml/2002-June/msg00131.html there
> isn't..) ?

   there isn't in general, user2 seems safer.

> If so, I wonder why it never crashed on me, but it could explain some
> memory leaks on my side.

   Seems unlikely unless it also uses XSLT with the same objects,
but having a crash sounds more probable, code like:
   xmlFreeNodeList((xmlNodePtr) obj->user);
with a pointer to PHP objects is likely to make a lot of damages !
And this is part of xmlXPathFreeObject(), so this hack looks really really
dangerous.

Daniel

-- 
Daniel Veillard      | Red Hat Network https://rhn.redhat.com/
veillard redhat com  | libxml GNOME XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | Rpmfind RPM search engine http://rpmfind.net/