Warning: DOMXPath::evaluate(): Invalid expression

[oach]

Hello All,

 

I have searched these forums and the net but haven't found an exact answer.  I have a "path" (could be paths) that is/are causing warnings as it/they is/are poorly formed.  This is bloating our logs, therefore I need to alleviate the issue.

There are thousands of paths in the database so I do not know which are causing issues.

I know I can add the "@" to the call to quiet the warning.  First question: does that keep the warning from going into the logs?

 

I would prefer not to use the method above as it bypasses the real issue. 

Looking at the SimpleXMLElement documentation along with DOMDocument and DOMXPAth, I can't find a way to validate the actual path.  All of the below throw a warning or notice:

$xpath->evaluate($path);
$xpath->query($path);
$node->xpath($path);

Final question: Is there a "simple" way to validate the $path prior to actually making the call to one of the methods of the various XML PHP classes?

 

Thank you for your time and assistance.

Edited November 5, 2020 by oach

[gw1500se]

What is the actual warning?

[oach]

There are back-to-back warnings on the $node->xpath($path) call.

• Warning: SimpleXMLElement::xpath(): Invalid expression in /var/www/html/test/xml.php on line...
• arning: SimpleXMLElement::xpath(): xmlXPathEval: evaluation failed in /var/www/html/test/xml.php on line...

The test file is trying to mimic what is happening in production in an easy to reproduce situation.

[gw1500se]

It is the line # I am looking for which you didn't post. And post that line with the code around it. Also post any code that produces variables used. I suspect the first warning may have produced the 2nd.

[kicken]

The functions you list all say they return false on an error such as a bad path, so check for that and log the details you need to determine which path is invalid so you can fix it.

$result = $xpath->evaluate($path);
if ($result === false){
    trigger_error('Invalid XPath: '.$path, E_USER_WARNING);
}

If you want to prevent the built-in warning, then use libxml_use_internal_errors.

libxml_use_internal_errors(true);
$result = $xpath->evaluate($path);
if ($result === false){
    $errors = libxml_get_errors();
    $errors = array_reduce($errors, function($carry, $error){
        return sprintf("%s[%s:%d] %s\r\n", $carry, $error->file, $error->line, $error->message);
    }, '');
    trigger_error(sprintf("Invalid XPath: %s\r\nErrors: %s", $path, $errors), E_USER_WARNING);
}
libxml_use_internal_errors(false);

 

[requinix]

4 hours ago, oach said:

I know I can add the "@" to the call to quiet the warning.  First question: does that keep the warning from going into the logs?

Depends on your setup. With normal PHP yes, silencing the error keeps it suppressed.
If you have a logging system set up to intercept and log errors then it depends. PHP will invoke the system's custom error logger even with @s, but in such a way that smart code will be able to recognize that happened and not log it. A naive logger will see "omg error, gotta log it".

For the record. You're right in that you shouldn't do it: hiding errors doesn't make them go away, just like how stopping Covid-19 testing doesn't mean there are no more cases.