User-friendly error handling

[wilku]

Hi there.

I'm trying to face error handling in my application (production server). Thus far I have managed to add mysql errors to my error_log.txt using trigger_error(). Db abstraction class echoes prepared html page with general 'error happend and admins are being informed right now' and issues the error to stop execution.
I also wrote a script that checks error_log.txt and emails me if thera are errors there (with a lock mechanism to avoid getting emails about the same error every 5 minutes if I am away).

What I would like to ask is if there is a way to do similar error page for standard errors (fatal). I'm working with IIS and PHP5.
Obviously setting error handler inside php won't work. Is there any elegant solution instead of displaying blank page when fatal error occurs?

[zingbats]

Simply put: No.

The issue is that a fatal error is (AFAIK) a compiler error. IE: The code isn't valid, and hence none of it is run.

The best way to get round this would be to eval() each page from another, and see the response given.

[bpat1434]

With Fatal errors, you can't catch them at all. Typically, to use your own error handler (for general errors) you use [man]set_error_handler[/man] to set your own error handler class or function. Unfortunately this is limited as:

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.

If errors occur before the script is executed (e.g. on file uploads) the custom error handler cannot be called since it is not registered at that time.

The only thing you could do is use the php binary and do a quick syntax check on it. Something like:

<?php

$output = shell_exec('php -l ' . escapeshellcmd(realpath(dirname(__FILE__).'/index.php')));

if(strpos($output, 'No syntax errors detected') === false)
{
	// There was a syntax error.... better do something!!
	echo 'Syntax Errors found!!';
	echo '<br />';
	echo $output;
}
else
{
	// No syntax error.... continue...
	echo 'No syntax errors found.... continuing...';
}

?>

might be better for you to use rather than eval. Much safer to just use a syntax check rather than possibly executing arbitrary code 😉

[wilku]

Thank you for your reply.
I'm pretty sure about syntax errors - I use PDT within Eclipse, and it complains about syntax errors "on the fly". It's fatal errors I'm worried about. Let's say something brakes in my application - some required file is missing, script takes too long to execute etc. - it would be more elegant to serve some page, even static, about a general inability to display anything (preferably in the site colors) than in fact display an empty, white page. I was thinking that maybe on error php sends some information that iis can interpret and serve this static page. But I didn't find anything like that. Do you know of anything similar? I'am not such an expert on C to try to hardcode such behaviour in php engine.

EDIT: ASP error results in 500 header and there is a possibility to configure custom error pages for that. Is there anything similar for PHP. After hours of searching I'm beginning to think that it's not possible.

[bpat1434]

Missing files during include could be wrapped in a try{}catch(e){} statement I believe. It should catch like normal.

Scripts timing out is another issue that I don't think you can catch.

[wilku]

I think I might have found something at last:

Travis Raybold wrote:

the way i can handle fatal errors is to first thing on every page send a
Location header that redirects to the error page, and if i get a fatal
error it goes to the error page. if i finish the page normally, the last
bit of code i have resets the Location header. this necessitates turning
off buffering, obviously.

I think he means turning buffering on. Second thing - header calls aren't buffered, but maybe a meta refresh. Proof of concept:

<?php
ob_start();
echo "<meta http-equiv=\"refresh\" content=\"0;url=http://wikipedia.org\" />";

echo "Page content";

//undefinedFunction(); //fatal error - works
//require('foobar.php'); //fatal error - works

//trying to timeout
while (true)
{
	$i = 1;
}//works as well


//if everything is allright
$page = str_replace("<meta http-equiv=\"refresh\" content=\"0;url=http://wikipedia.org\" />","",ob_get_contents());
ob_end_clean();
echo $page;
?>

What do you think about this? Would output buffering make user wait considerably longer for the page to load? I have a template system anyway (Smarty), so the application does everything before displaying anything.

[bpat1434]

That seems to work; however, if you have a page that does a lot of processing, and it's standard output (meaning not running through a template) it might just screw things up and make load times longer, but that's something you'll have to test on your individual server.