Why Doesn\'t My Custom PHP Error Message Appear When mysqli_connect Fails?

Why Doesn't PHP Display My Custom Error Message When mysqli_connect Fails?

Understanding the Error Detection Mechanism

In the past, PHP's mysql extension required manual error handling. However, the mysqli extension introduced in PHP 8.1 now automatically triggers exceptions upon encountering errors, eliminating the need for manual error detection.

Custom Error Message Confusion

Your code includes an if (!$conn) block that attempts to output a custom error message. This approach is outdated. mysqli inherently throws errors, which should be handled automatically.

Hiding Error Messages from Users

To hide error messages from site visitors, you should use the display_errors configuration option. Setting it to 0 will prevent PHP from displaying any errors. You can set this option in php.ini or in PHP code using ini_set('display_errors', 0).

Displaying a User-Friendly Error Page

While it's essential to hide system errors from users, you may want to display a user-friendly error page. This can be achieved using an error handler like:

<code class="php">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>
              An internal server error has occurred.<br>
              Please try again later.";
    }
});</code>

This handler logs the error, sets an HTTP 500 status code, and displays a generic error message if display_errors is set to 0.

Handling Connection Errors

In certain scenarios, you may need to explicitly handle connection errors. This can be done using a try-catch block. However, such handling should be limited to cases where specific error scenarios require alternative actions.

Hiding Sensitive Information

If you're concerned about sensitive information appearing in the stack trace, consider upgrading to PHP 8.2 or later, which hides database passwords from the stack trace.

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