Bug #48601 [Csd->ReO]: xpath() returns FALSE for legitimate query

Edit report at https://bugs.php.net/bug.php?id=48601&edit=1 ID: 48601 Updated by: stas@php.net Reported by: theultramage at gmail dot com Summary: xpath() returns FALSE for legitimate query -Status: Closed +Status: Re-Opened Type: Bug Package: SimpleXML related Operating System: Windows Vista -PHP Version: 6CVS-2009-06-19 (snap) +PHP Version: 5.4SVN Assigned To: rrichards Block user comment: N Private report: N New Comment: Looks like it still happens for me - the unit test fails and the function returns false. Previous Comments: ------------------------------------------------------------------------ [2010-05-05 13:42:16] rrichards@php.net This bug has been fixed in SVN. Snapshots of the sources are packaged every three hours; this change will be in the next snapshot. You can grab the snapshot at http://snaps.php.net/. Thank you for the report, and for helping us make PHP better. ------------------------------------------------------------------------ [2010-05-05 13:40:13] rrichards@php.net Automatic comment from SVN on behalf of rrichards Revision: http://svn.php.net/viewvc/?view=revision&amp;revision=299016 Log: fix bug #48601 (xpath() returns FALSE for legitimate query) add test ------------------------------------------------------------------------ [2009-06-24 16:13:21] theultramage at gmail dot com From the mail of the main libxml developer (http://mail.gnome.org/archives/xml/2009-June/msg00040.html): > A NULL object or an empty node set should be treated in the same way. Also >There is no iterator API. So for one part, the current SimpleXML code has a bug because it does not handle the NULL value correctly (should return empty array, not FALSE). And second, there's currently no other solution. ------------------------------------------------------------------------ [2009-06-19 10:57:16] theultramage at gmail dot com Description: ------------ SimpleXML's xpath() implementation contains code that returns FALSE for some queries where it should be returning an empty container object. In revision 1.79 of simplexml.c (http://cvs.php.net/viewvc.cgi/php-src/ext/simplexml/simplexml.c?r1=1.78&r2=1.79) the call to xmlXPathEval() was hotfixed to avoid crashing if the query errored. However, the author also added a check against "retval->nodesetval", treating NULL as an error situation. I believe this was an incorrect decision. There is a scenario where 'nodesetval' will be NULL - when querying for the attribute of a non-matching element ('/foo/@attr' when there are no 'foo' nodes); in all other 'bad' queries that I tried, 'nodesetval' came initialized and containing zero nodes. So, we can see that for certain queries, simplexml will give an incorrect result. This was already pointed out on 18-dec-2005 by an user comment on the php simplexml::xpath documentation page. I have sent an inquiry to the xml mailing list (http://mail.gnome.org/archives/xml/2009-June/msg00019.html) asking for clarification, however I believe that the current logic is incorrect. I checked php's DOM module src and libxml's xpath1.c code example, and they do not consider it a problem (DOM initializes empty DOMNodeList, example sets count to 0). Alternatively, the code should not be messing with what is apparently internal structures, and instead use the API for processing, if one is available. Reproduce code: --------------- <?php $xml = '<?xml version="1.0" encoding="utf-8"?><dummy/>'; $db = new SimpleXMLElement($xml); if( FALSE !== $db->xpath("/foo/@attr") ) echo "OK"; else echo "Error!"; ?> Expected result: ---------------- xpath() should return an empty array. Actual result: -------------- xpath() returns FALSE. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=48601&edit=1