What is the correct way of handling errors and warnings on filesystem functions in PHP?

Question

When using filesystem functions, what would be the correct way of handling errors such as:

Warning: symlink(): No such file or directory in /path-to-script/symlink.php on line XXX

My usual approach is to check for any condition that could produce an error before calling the filesystem function. But if the command fails for a reason I haven't foreseen, how can I catch the error to show the user a more helpful message?

This is a simplification of the code that creates the symbolic link:

$filename = 'some-file.ext';
$source_path = '/full/path/to/source/dir/';
$dest_path = '/full/path/to/destination/dir/';

if(file_exists($source_path . $filename)) {
    if(is_dir($dest_path)) {
        if( ! file_exists($dest_path . $filename)) {
            if (symlink($source_path . $filename, $dest_path . $filename)) {
                echo 'Success';
            } else {
                echo 'Error';
            }
        }
        else {
            if (is_link($dest_path . $filename)) {
                $current_source_path = readlink($dest_path . $filename);
                if ( $current_source_path == $source_path . $filename) {
                    echo 'Link exists';
                } else {
                    echo "Link exists but points to: {$current_source_path}";
                }
            } else {
                echo "{$source_path}{$filename} exists but it is not a link";
            }
        }
    } else {
        echo "{$source_path} is not a dir or doesn't exist";
    }
} else {
    echo "{$source_path}{$filename} doesn't exist";
}

Followup / Solutions

As sugested by Sander, using set_error_handler() to turn errors and warnings into exceptions.

function exception_error_handler($errno, $errstr, $errfile, $errline ) {
    throw new ErrorException($errstr, $errno, 0, $errfile, $errline);
}

set_error_handler("exception_error_handler");

try {
    symlink($source_path . $filename, $dest_path . $filename);
    echo 'Success';
}
catch (ErrorException $ex) {
    echo "There was an error linking {$source_path}{$filename} to {$dest_path}{$filename}: {$ex->getMessage()}";
}

restore_error_handler();

Using the @ operator is another solution (although some suggest avoiding it whenever possible):

if (@symlink($source_path . $filename, $dest_path . $filename)) {
    echo 'Success';
} else {
    $symlink_error = error_get_last();        
    echo "There was an error linking {$source_path}{$filename} to {$dest_path}{$filename}: {$symlink_error['message']}";
}

score 4 · Accepted Answer · answered Nov 13 '12 at 18:25

4

I think you want to want to set an errorhandler which throws exceptions:

function exception_error_handler($errno, $errstr, $errfile, $errline ) {
    // see http://php.net/manual/en/class.errorexception.php
    throw new ErrorException($errstr, $errno, 0, $errfile, $errline);
}

set_error_handler("exception_error_handler");

Then your code would be:

try {
    symlink(); // when an error occured, it jumps to the catch
} catch (ErrorException $ex) {
    // do stuff with $ex
}

answered Nov 13 '12 at 18:25

sroes

14,663
1
53
72

This would get called for every error? What if i wanted to use is only on certain functions? – Lando Nov 13 '12 at 19:58
The catch will only be called on the first error that occurred. You can read up on the subject at http://php.net/manual/en/language.exceptions.php – sroes Nov 13 '12 at 20:30
What I meant was how could I target this to a specific function, later I found `restore_error_handler()` [here](http://stackoverflow.com/a/1241751/1132838) :). – Lando Nov 20 '12 at 15:04

score 1 · Answer 2 · answered Nov 13 '12 at 18:29

1

I suggest using Fileysystem component that is widely used and tested solution for filesystem operations https://github.com/symfony/Filesystem/blob/master/Filesystem.php#L248

answered Nov 13 '12 at 18:29

Ziumin

4,800
1
27
34

I am not currently using any framework as this is a simple script. It does give me some ideas on how to solve the problem, thanks for the link. – Lando Nov 13 '12 at 19:33
You can use it as standalone component without using a framework – Ziumin Nov 13 '12 at 21:02

What is the correct way of handling errors and warnings on filesystem functions in PHP?

2 Answers2