Investigating the Hidden Custom Error Message in mysqli_connect Failures

In an attempt to establish a database connection, you encountered an issue where the custom error message you defined was not being displayed when the connection failed. You are also seeking a method to suppress error messages from the user's view.

The Nature of the Error Message

Starting with PHP 8.1, the mysqli extension now automatically throws exceptions in the event of an error, eliminating the need for manual error handling as was done in earlier versions of PHP.

The Rationale Behind Error Suppression

Custom error messages, like the one you defined, are no longer recommended for error handling. Both PDO and mysqli have the ability to raise errors automatically, just like any other PHP command. Therefore, manually checking for errors, as you attempted to do with the if (!$conn) segment, is obsolete.

Avoiding Error Exposure to Users

To prevent error messages from reaching the user, you should utilize the display_errors configuration option, which can be set to 0 to suppress all error output. This can be configured in the php.ini file or directly in your PHP code:

ini_set('display_errors', 0);

Providing a User-Friendly Error Page

Instead of displaying cryptic error messages, it is advisable to present a user-friendly error page to site visitors. This can be achieved by setting up an error handler, such as the one below, which will catch all irrecoverable errors:

set_exception_handler(function ($e)
{
    error_log($e);
    http_response_code(500);
    if (ini_get('display_errors')) {
        echo $e;
    } else {
        echo "<h1>500 Internal Server Error</h1>\nAn internal server error has been occurred.<br>\nPlease try again later.";
    }
});

Handling Database Connection Errors Separately

If you need to specifically handle database connection errors, you can use a separate connection test script wrapped in a try-catch block, separate from your regular connection code.

Protecting Connection Credentials

For enhanced security, update your PHP version to 8.2 or later, which obscures database passwords from appearing in the stack trace.