PHP: How to manage errors gracefully?

Question

When failed to access something on the web (api, database), how would I stop executing the rest of the script and log the error in the log file? Well, and so that the visito

Answer 1

I generally like using Exceptions, in that kind of situation : it allows me to have all error-handling code at one place.

For instance, I'd use something a bit like this :

try {
    // Some code

    // Some code that throws an exception

    // Some other code -- will not be executed when there's been an Exception

} catch (Exception $e) {
    // Log the technical error to file / database

    // Display a nice error message
}

With that, all error-handling code is in the catch block -- and not scatterred accros my whole application.

Note, though, that many PHP functions don't throw exceptions, and only raise a warning or an error...

For those, you could use set_error_handler to define your own error handler -- which could throw an Exception ;-)
For instance, see the example on the manual page of ErrorException.

Although this will work real fine for many errors/warnings, you should note that it will not work for Parse Error nor Fatal Error :

• The first kind are actually raised before the PHP code is actually executed
• And the second kind are... well... Fatal.

And I would never place any die nor exit in the middle of my code : that's, in my opinion, one of the worst possible way of dealing with errors.

I would also configure my server / application so :

• Error messages are not displayed in the output, setting display_errors to Off.
• Errors are logged to a file, using log_errors and error_log.

Answer 2

and so that the visitor wouldn't see the exact cause but rather they would see my custom message

I would suggest you to go through this excellent article by David Walsh on custom error handling in PHP.

You can use set_error_handler() function for that.

how would I stop executing the rest of the script and log the error in the log file?

There is a default function of PHP to log errors; error_log

Example from PHP.net:

<?php
// Send notification through the server log if we can not
// connect to the database.
if (!Ora_Logon($username, $password)) {
    error_log("Oracle database not available!", 0);
    exit; //exit
}

// Notify administrator by email if we run out of FOO
if (!($foo = allocate_new_foo())) {
    error_log("Big trouble, we're all out of FOOs!", 1,
               "operator@example.com");
}

// another way to call error_log():
error_log("You messed up!", 3, "/var/tmp/my-errors.log");
?>

.

More Resources:

This is also good article covering most of it related to error handling.