How to catch undefined functions with set_error_handler in PHP

Question

I'm taking the leap: my PHP scripts will ALL fail gracefully!

At least, that's what I'm hoping for...`

I don't want to wrap (practically) every single line in try...catch statements, so I think my best bet is to make a custom error handler for the beginning of my files.

I'm testing it out on a practice page:

function customError($level,$message,$file,$line,$context) {
    echo "Sorry, an error has occured on line $line.<br />";
    echo "The function that caused the error says $message.<br />";
    die();
}

set_error_handler("customError");

echo($imAFakeVariable);

This works fine, returning:

Sorry, an error has occurred on line 17. The function that caused the error says Undefined variable: imAFakeVariable.

However, this setup doesn't work for undefined functions.

function customError($level,$message,$file,$line,$context) {
    echo "Sorry, an error has occured on line $line.<br />";
    echo "The function that caused the error says $message.<br />";
    die();
}

set_error_handler("customError");

imAFakeFunction();

This returns:

Fatal error: Call to undefined function: imafakefunction() in /Library/WebServer/Documents/experimental/errorhandle.php on line 17

Why isn't my custom error handler catching undefined functions? Are there other problems that this will cause?

Answer 1

set_error_handler is designed to handle errors with codes of: E_USER_ERROR | E_USER_WARNING | E_USER_NOTICE. This is because set_error_handler is meant to be a method of reporting errors thrown by the user error function trigger_error.

However, I did find this comment in the manual that may help you:

"The following error types cannot be handled with a user defined function: E_ERROR, E_PARSE, E_CORE_ERROR, E_CORE_WARNING, E_COMPILE_ERROR, E_COMPILE_WARNING, and most of E_STRICT raised in the file where set_error_handler() is called."

This is not exactly true. set_error_handler() can't handle them, but ob_start() can handle at least E_ERROR.

<?php

function error_handler($output)
{
    $error = error_get_last();
    $output = "";
    foreach ($error as $info => $string)
        $output .= "{$info}: {$string}\n";
    return $output;
}

ob_start('error_handler');

will_this_undefined_function_raise_an_error();

?>

Really though these errors should be silently reported in a file, for example. Hopefully you won't have many E_PARSE errors in your project! :-)

As for general error reporting, stick with Exceptions (I find it helpful to make them tie in with my MVC system). You can build a pretty versatile Exception to provide options via buttons and add plenty of description to let the user know what's wrong.

Answer 2

I guess you needs to use register_shutdown_function also

For example:

 register_shutdown_function( array( $this, 'customError' ));.

   function customError() 
   {

     $arrStrErrorInfo = error_get_last();

     print_r( $arrStrErrorInfo );

   }

Answer 3

From the documentation (emphasis added):

The following error types cannot be handled with a user defined function: E_ERROR, E_PARSE, E_CORE_ERROR, E_CORE_WARNING, E_COMPILE_ERROR, E_COMPILE_WARNING, and most of E_STRICT raised in the file where set_error_handler() is called.

Calling undefined functions triggers an E_ERROR, thus it can not be handled by the error callback (or by exception handlers for that matter). All that you can do is set error_reporting to 0.

PS, if you are rolling your own error handler, you should take care to handle correctly the @ operator. From the documentation (emphasis added):

It is important to remember that the standard PHP error handler is completely bypassed. error_reporting() settings will have no effect and your error handler will be called regardless - however you are still able to read the current value of error_reporting and act appropriately. Of particular note is that this value will be 0 if the statement that caused the error was prepended by the @ error-control operator.

Answer 4

Why isn't my custom error handler catching undefinedd functions? Are there other problems that this will cause?

At a guess, I'd say that undefined function errors travel through a different execution path than other error types. Perhaps the PHP designers could tell you more, except I doubt PHP is in any way designed.

If you'd like your scripts to fail gracefully while still writing them PHP-style, try putting the entire page in a function and then call it within a try..catch block.

Answer 5

I've been playing around with error handling for some time and it seems like it works for the most part.

function fatalHandler() {
    global $fatalHandlerError, $fatalHandlerTitle;

    $fatalHandlerError = error_get_last();

    if( $fatalHandlerError !== null ) {

        print($fatalHandlerTitle="{$fatalHandlerTitle} | ".join(" | ", $fatalHandlerError).
                (preg_match("/memory/i", $fatalHandlerError["message"]) ? " | Mem: limit ".ini_get('memory_limit')." / peak ".round(memory_get_peak_usage(true)/(1024*1024))."M" : "")."\n".
                        "GET: ".var_export($_GET,1)."\n".
                        "POST: ".var_export($_POST,1)."\n".
                        "SESSION: ".var_export($_SESSION,1)."\n".
                        "HEADERS: ".var_export(getallheaders(),1));
    }

    return $fatalHandlerTitle;
}

function fatalHandlerInit($title="phpError") {
    global $fatalHandlerError, $fatalHandlerTitle;

    $fatalHandlerTitle = $title;
    $fatalHandlerError = error_get_last();

    set_error_handler( "fatalHandler" );
}

Now I have an issue where if the memory is exhausted, it doesn't report it every time. It seems like it depends on how much memory is being used. I did a script to load a large file (takes ~6.6M of memory) in an infinite loop. Setup1:

ini_set('memory_limit', '296M');

fatalHandlerInit("testing");

$file[] = file("large file"); // copy paste a bunch of times

In this case I get the error to be reports and it dies on 45 file load.

Setup2 - same but change: ini_set('memory_limit', '299M');

This time I don't get an error and it doesn't even call my custom error function. The script dies on the same line.

Does anyone have a clue why and how to go around that?

Answer 6

Very interesting thing that I've discovered today as I was facing the similar problem. If you use the following - it will catch the error with your custom error handler function / method:

ini_set('display_errors', 'Off');
error_reporting(-1);

set_error_handler(array("Cmd\Exception\Handler", "getError"), -1 & ~E_NOTICE & ~E_USER_NOTICE);

By setting 'display_errors' to 'Off' you can catch still catch them with the handler.

Answer 7

At a guess, I'd say that undefined function errors travel through a different execution path than other error types. Perhaps the PHP designers could tell you more, except I doubt PHP is in any way designed.