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Bug #79344 XmlWriter::writeAttributeNS produces bad XML with null prefix
Submitted: 2020-03-04 16:38 UTC Modified: 2020-03-05 08:30 UTC
From: jtojnar at gmail dot com Assigned:
Status: Open Package: XML Writer
PHP Version: 7.4.3 OS: NixOS
Private report: No CVE-ID: None
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 [2020-03-04 16:38 UTC] jtojnar at gmail dot com
Description:
------------
When passing a `$prefix = null` to `XMLWriter::writeAttributeNs`, it behaves as if empty string was passed, producing a non-well-formed XML document. Same issue happens with `startAttributeNS` method but it works fine for methods for creating elements.

Test script:
---------------
<?php

$writer = new XMLWriter;
$writer->openMemory();
$writer->setIndent(true);
$writer->startElement('foo');

$writer->writeAttributeNS(null, 'test', null, 'test');
// $writer->startAttributeNS(null, 'test', null);
// $writer->text('test');
// $writer->endAttribute();

$writer->endElement();
echo $writer->outputMemory();


Expected result:
----------------
<foo test="test"/>


Actual result:
--------------
<foo :test="test"/>


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 [2020-03-05 08:05 UTC] cmb@php.net
The difference between passing NULL and an empty string to
XMLWriter::writeAttributeNS() is that either NULL or an empty
string is passed to xmlTextWriterWriteAttributeNS() (which does
the actual work).  The documentation of that function[1] is
unfortunately not clear about whether there is a difference or
not.  So we can only observe the current libxml2 behavior, and it
seems there is no difference.

So I don't think there is anything we could do (except for calling
xmlTextWriterWriteAttribute() if both prefix and uri are NULL, but
that would constitute a BC break), besides documenting the
behavior.

http://xmlsoft.org/html/libxml-xmlwriter.html#xmlTextWriterWriteAttributeNS
 [2020-03-05 08:30 UTC] nikic@php.net
@cmb: Are you sure that's the reason? Looking at the implementation, $prefix is accepted as s, not s!, so we will cast NULL to "".
 
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