How Can the Post-Redirect-Get (PRG) Pattern Prevent Form Resubmission in PHP?

Post-Redirect-Get (PRG) Pattern in PHP: Achieving Form Resubmission Protection

When designing web applications, preventing the resubmission of forms after page reloads or back button actions can enhance user experience and maintain data integrity. The Post-Redirect-Get (PRG) pattern is a widely recognized approach to address this issue, but finding straightforward PHP implementations can be challenging.

Here's a simplified example that demonstrates the PRG pattern in PHP:

<?php if ($_POST) {
    // Validate input

    if (/* Input is valid */) {
        // Execute code (such as database updates) here.
        // Redirect to this page.
        header("Location: {$_SERVER['REQUEST_URI']}", true, 303);
        exit();
    }
}
?>

<!-- Your HTML page with a form -->

In this example, when the form is submitted via POST, the input is validated. If the input is valid, code such as database updates is executed. Subsequently, the script redirects the user to the same page using the Location header. The 303 See Other status code indicates that the request should be repeated via GET, effectively preventing form resubmission.

By using $_SERVER['REQUEST_URI'], this example avoids potential issues with PHP_SELF in CMS systems and frameworks. The exit() function is called to prevent the execution of the HTML code below the redirect.

This PRG implementation offers protection against form resubmission while minimizing code complexity. By employing this pattern, you can enhance the robustness and user experience of your web applications.

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