How can I reliably identify a specific error in PHP?

Question

Because of PHP's unlink() not supporting exceptions natively, I'm making a wrapper function for it. It should throw a FileNotFoundException if, well, the given file could not be deleted because it doesn't exist.

For this, I need to determine whether the error thrown by unlink() was caused by a missing file or something else.

This is my test version for a custom delete function:

public function deleteFile($path){ set_error_handler(function($errLevel, $errString){ debug($errLevel); debug($errString); }); unlink($path); restore_error_handler(); }

For $errLevel and $errString I get 2 (E_WARNING) and unlink(/tmp/fooNonExisting): No such file or directory

A rather bold approach would be like this:

if( strpos($errString, 'No such file or directory') !== false ) { throw new FileNotFoundException(); };

Question 1: How much can I rely on the error string being the same across different PHP versions? Question 2: Is there a much better way?

pixelistik · Accepted Answer · 2014-09-25 10:09:27Z

2

I would simplify the code:

public function deleteFile($path){ if (!file_exists($path) { throw new FileNotFoundException(); }else{ unlink($path); } if (file_exists($path) { throw new FileNotDeleted(); } }

Then you don't have to catch the $errstr and do complicated error catching. And it will work down to PHP 4 when exceptions were introduced.

edited Sep 25, 2014 at 10:09

pixelistik

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answered Jun 5, 2012 at 15:18

powtac

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4 Comments

pixelistik Over a year ago

Yes, good solution. But this will bury all other types of problems, too, like wrong file permissions. I'd rather only convert "file not found" into an exception.

pixelistik Over a year ago

I modified your solution (review pending), with unlink() in an else block we can get rid of the bad @ part. I'll probably use this technique, but let's wait what other answers are coming about the initial error handling/identification issue.

pixelistik Over a year ago

Choosing this answer as correct, even though it does not teach me lots of details about PHP error handlers. But it points in a simple direction, which I was also asking for.

powtac Over a year ago

For PHP error "magic" have a look at php.net/manual/function.error-get-last.php and php.net/manual/reserved.variables.phperrormsg.php

Community · Accepted Answer · 2017-05-23 12:27:21Z

While reading trough my old questions I came across the ErrorException, combined with set_error_handler() this would be a automatic Error to Exception transformer for all native PHP errors:

function exception_error_handler($errno, $errstr, $errfile, $errline ) { throw new ErrorException($errstr, 0, $errno, $errfile, $errline); } set_error_handler("exception_error_handler"); /* Trigger exception */ unlink('Does not exitsts');

Can anybody prof this?

It won't work for every error. Beside parser-time and startup errors, some other runtime errors, as fatal errors, are not catch by any error handler.

Emmanuel Okeke · Accepted Answer · 2012-06-05 15:27:47Z

I believe it(i.e. your code) should be portable enough as it is... As regards a better way to achieve the same thing, i would do things differently (although the code is simple, it's also more readable...so bear with me)

function deleteFile($file_path){ if(!is_file($file_path)){ throw new Exception("The path does not seem to point to a valid file"); } if(!file_exists($file_path)){ throw new Exception("File not found!"); } if(unlink($file_path)){ return true; } else { throw new Exception("File deletion failed!"); } }

Of course you can always compress and improve on the code...hop this helps!

goat · Accepted Answer · 2012-06-05 15:37:36Z

I've seen php error messages change quite a bit over the years. Maybe, try to detect a change in the last error over a very granular piece of code, and then result to string parsing in a very loose manor.

$lastErr = error_get_last(); unlink($file); if ($lastErr !== error_get_last()) { // do something //maybe string parsing and/or testing with file_exists, is_writable etc... }

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