PHP : Custom error handler - handling parse & fatal errors

How can i handle parse & fatal errors using a custom error handler?

Answers


Simple Answer: You can't. See the manual:

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.

For every other error, you can use set_error_handler()

EDIT:

Since it seems, that there are some discussions on this topic, with regards to using register_shutdown_function, we should take a look at the definition of handling: To me, handling an error means catching the error and reacting in a way that is "nice" for the user and the underlying data (databases, files, web services, etc.).

Using register_shutdown_function you cannot handle an error from within the code where it was called, meaning the code would still stop working at the point where the error occurs. You can, however, present the user with an error message instead of a white page, but you cannot, for example, roll back anything that your code did prior to failing.


Actually you can handle parse and fatal errors. It is true that the error handler function you defined with set_error_handler() will not be called. The way to do it is by defining a shutdown function with register_shutdown_function(). Here is what I have working in my website:

File prepend.php (this file will be prepended to all php scripts automatically). See below for tips on prepending files to PHP.

set_error_handler("errorHandler");
register_shutdown_function("shutdownHandler");

function errorHandler($error_level, $error_message, $error_file, $error_line, $error_context)
{
$error = "lvl: " . $error_level . " | msg:" . $error_message . " | file:" . $error_file . " | ln:" . $error_line;
switch ($error_level) {
    case E_ERROR:
    case E_CORE_ERROR:
    case E_COMPILE_ERROR:
    case E_PARSE:
        mylog($error, "fatal");
        break;
    case E_USER_ERROR:
    case E_RECOVERABLE_ERROR:
        mylog($error, "error");
        break;
    case E_WARNING:
    case E_CORE_WARNING:
    case E_COMPILE_WARNING:
    case E_USER_WARNING:
        mylog($error, "warn");
        break;
    case E_NOTICE:
    case E_USER_NOTICE:
        mylog($error, "info");
        break;
    case E_STRICT:
        mylog($error, "debug");
        break;
    default:
        mylog($error, "warn");
}
}

function shutdownHandler() //will be called when php script ends.
{
$lasterror = error_get_last();
switch ($lasterror['type'])
{
    case E_ERROR:
    case E_CORE_ERROR:
    case E_COMPILE_ERROR:
    case E_USER_ERROR:
    case E_RECOVERABLE_ERROR:
    case E_CORE_WARNING:
    case E_COMPILE_WARNING:
    case E_PARSE:
        $error = "[SHUTDOWN] lvl:" . $lasterror['type'] . " | msg:" . $lasterror['message'] . " | file:" . $lasterror['file'] . " | ln:" . $lasterror['line'];
        mylog($error, "fatal");
}
}

function mylog($error, $errlvl)
{
...do whatever you want...
}

PHP will call function errorHandler() if he catches an error in any of the scripts. If the error forces the script to shutdown immediately, the error is handled by function shutdownHandler().

This is working on the site I have under development. I haven't yet tested it in production. But it is currently catching all errors I find while developing it.

I believe there is a risk of catching the same error twice, once by each function. This could happen if an error that I am handling in the function shutdownHandler() was also caught by function errorHandler().

TODO's:

1 - I need to work on a better log() function to handle errors gracefully. Because I am still in development, I am basically logging the error to a database and echoing it to the screen.

2 - Implement error handling for all MySQL calls.

3 - Implement error handling for my javascript code.

IMPORTANT NOTES:

1 - I am using the following line in my php.ini to automatically prepend the above script to all php scripts:

auto_prepend_file = "/homepages/45/d301354504/htdocs/hmsee/cgi-bin/errorhandling.php"

it works well.

2 - I am logging and resolving all errors, including E_STRICT errors. I believe in developing a clean code. During development, my php.ini file has the following lines:

track_errors = 1
display_errors = 1
error_reporting = 2147483647
html_errors = 0

When I go live, I will change display_errors to 0 to reduce the risk of my users seeing ugly PHP error messages.

I hope this helps someone.


You can track these errors using code like this:

(Parse errors can only be caught if they occur in other script files via include() or require(), or by putting this code into an auto_prepend_file as other answers have mentioned.)

function shutdown() {
    $isError = false;

    if ($error = error_get_last()){
    switch($error['type']){
        case E_ERROR:
        case E_CORE_ERROR:
        case E_COMPILE_ERROR:
        case E_USER_ERROR:
            $isError = true;
            break;
        }
    }

    if ($isError){
        var_dump ($error);//do whatever you need with it
    }
}

register_shutdown_function('shutdown');

From the PHP.net comments on the page http://www.php.net/manual/en/function.set-error-handler.php

I have realized that a few people here mentioned that you cannot capture parse errors (type 4, E_PARSE). This is not true. Here is how I do. I hope this helps someone.

1) Create a "auto_prepend.php" file in the web root and add this:

<?php 
register_shutdown_function('error_alert'); 

function error_alert() 
{ 
        if(is_null($e = error_get_last()) === false) 
        { 
                mail('your.email@example.com', 'Error from auto_prepend', print_r($e, true)); 
        } 
} 
?> 

2) Then add this "php_value auto_prepend_file /www/auto_prepend.php" to your .htaccess file in the web root.

  • make sure you change the email address and the path to the file.

From my experience you can catch all type of errors, hide the default error message and display an error message of your own (if you like). Below are listed the things you need.

1) An initial/top level script, let us call it index.php where you store you custom error handler functions. Custom error function handlers must stay at the top so they catch errors below them, by "below" I mean in inclued files.

2) The assumption that this top script is error free must be true! this is very important, you cannot catch fatal errors in index.php when your custom error handler function is found in index.php.

3) Php directives (must also be found in index.php) set_error_handler("myNonFatalErrorHandler"); #in order to catch non fatal errors register_shutdown_function('myShutdown'); #in order to catch fatal errors ini_set('display_errors', false); #in order to hide errors shown to user by php ini_set('log_errors',FALSE); #assuming we log the errors our selves ini_set('error_reporting', E_ALL); #We like to report all errors

while in production (if I am not wrong) we can leave ini_set('error_reporting', E_ALL); as is in order to be able to log error, in the same time ini_set('display_errors', false); will make sure that no errors are displayed to the user.

As for the actual content of the two functions I am talking, myNonFatalErrorHandler and myShutdown, I don't put detailed content here in order to keep things simple. In addition the other visitors have given alot of examples. I just show a very plain idea.

function myNonFatalErrorHandler($v, $m, $f, $l, $c){
 $some_logging_var_arr1[]="format $v, $m, $f, ".$err_lvl[$l].", $c the way you like";
 //You can display the content of $some_logging_var_arr1 at the end of execution too.
}

function myShutdown()
{
  if( ($e=error_get_last())!==null ){
      $some_logging_var_arr2= "Format the way you like:". $err_level[$e['type']].$e['message'].$e['file'].$e['line'];
  }
//display $some_logging_var_arr2 now or later, e.g. from a custom session close function
}

as for $err_lvl it can be:

$err_lvl = array(E_ERROR=>'E_ERROR', E_CORE_ERROR=>'E_CORE_ERROR', E_COMPILE_ERROR=>'E_COMPILE_ERROR', E_USER_ERROR=>'E_USER_ERROR', E_PARSE=>'E_PARSE', E_RECOVERABLE_ERROR=>'E_RECOVERABLE_ERROR', E_WARNING=>'E_WARNING', E_CORE_WARNING=>'E_CORE_WARNING', E_COMPILE_WARNING=>'E_COMPILE_WARNING',
E_USER_WARNING=>'E_USER_WARNING', E_NOTICE=>'E_NOTICE', E_USER_NOTICE=>'E_USER_NOTICE',E_STRICT=>'E_STRICT');

The script with parse error is always interrupted and it can not be handled. So if the script is called directly or by include/require, there is nothing you can do. But if it is called by AJAX, flash or any other way, there is a workaround how to detect parse errors.

I needed this to handle swfupload script. Swfupload is a flash that handles file uploads and everytime file is uploaded, it calls PHP handling script to handle filedata - but there is no browser output, so the PHP handling script needs these settings for debugging purposes:

  • warnings and notices ob_start(); at the beginning and store content into session by ob_get_contents(); at the end of the handling script: This can be displayed into browser by another script
  • fatal errors register_shutdown_function() to set the session with the same trick as above
  • parse errors if the ob_get_contents() is located at the end of the handling script and parse error occured before, the session is not filled (it is null). The debugging script can handle it this way: if(!isset($_SESSION["swfupload"])) echo "parse error";

Note 1 null means is not set to isset()


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