PROBLEM
- PHP function
simplexml_load_file is throwing parsing error parser
error : xmlParseEntityRef while trying to load the XML file from a URL.
CAUSE
- XML returned by the URL is not a valid XML. It contains
& value
instead of &. It is quite possible that there are other errors which aren't obvious at this point of time.
THINGS OUT OF OUR CONTROL
- Ideally, we should make sure that a valid XML is feed into PHP
simplexml_load_file function, but it looks like we don't have any control over how the XML is created.
- It is also not possible to force
simplexml_load_file to process an
invalid XML file. It does not leave us with many options, other than
fixing the XML file itself.
POSSIBLE SOLUTION
Convert Invalid XML to Valid XML. It can be done using PHP tidy extension. Further instructions can be found from http://php.net/manual/en/book.tidy.php
Once you are sure that the extension exists or is installed, please do the following.
/**
* As per the question asked, the URL is loaded into a variable first,
* which we can assume to be $xml
*/
$xml = <<<XML
<?xml version="1.0" encoding="UTF-8"?>
<project orderno="6" campaign_name="International Relief & Development for under developed nations">
<invalid-data>Some other data containing & in it</invalid-data>
<unclosed-tag>
</project>
XML;
/**
* Whenever we use tidy it is best to pass some configuration options
* similar to $tidyConfig. In this particular case we are making sure that
* tidy understands that our input and output is XML.
*/
$tidyConfig = array (
'indent' => true,
'input-xml' => true,
'output-xml' => true,
'wrap' => 200
);
/**
* Now we can use tidy to parse the string and then repair it.
*/
$tidy = new tidy;
$tidy->parseString($xml, $tidyConfig, 'utf8');
$tidy->cleanRepair();
/**
* If we try to output the repaired XML string by echoing $tidy it should look like.
<?xml version="1.0" encoding="utf-8"?>
<project orderno="6" campaign_name="International Relief & Development for under developed nations">
<invalid-data>Some other data containing & in it</invalid-data>
<unclosed-tag></unclosed-tag>
</project>
* As you can see that & is now fixed in campaign_name attribute
* and also with-in invalid-data element. You can also see that the
* <unclosed-tag> which didn't had a close tag, has been fixed too.
*/
echo $tidy;
/**
* Now when we try to use simplexml_load_string to load the clean XML. When we
* try to print_r it should look something like below.
SimpleXMLElement Object
(
[@attributes] => Array
(
[orderno] => 6
[campaign_name] => International Relief & Development for under developed nations
)
[invalid-data] => Some other data containing & in it
[unclosed-tag] => SimpleXMLElement Object
(
)
)
*/
$simpleXmlElement = simplexml_load_string($tidy);
print_r($simpleXmlElement);
CAUTION
The developer should try to compare the invalid XML with a valid XML (generated by tidy), to see there are no adverse side effects after using tidy. Tidy does an extremely good job of doing it correctly, but it never hurts to see it visually and to be 100% sure. In our case it should be as simple as comparing $xml with $tidy.
