How Can I Prevent Unintended Form Resubmission in Web Applications?

Preventing Unintended Form Resubmission

Form resubmission due to page refresh is a common annoyance in web applications. To handle this issue effectively, it's crucial to employ the following strategies:

Redirect After Submission

Instead of displaying the response on the same page, redirect the user to a separate page once the form is submitted. This ensures that when the refreshed page loads, it's a new GET request and not a repeat of the POST request that has already been processed.

Example:

// submit
// set success flash message (you are using a framework, right?)
header('Location: /path/to/record');
exit;

Disable Browser Caching

To prevent the browser from caching your form, add the following headers to your PHP script:

header('Cache-Control: no-cache, no-store, must-revalidate');
header('Pragma: no-cache');

Unique Page Token

Generate a unique token on the server for each form submission. Include this token as a hidden field in the form and verify it before processing. If the token doesn't match or is missing, discard the request as a duplicate submission.

Example (with session token):

<?php session_start();

// Generate a unique token and store it in the session
$token = md5(uniqid(mt_rand(), true));
$_SESSION['token'] = $token;

?>

<?php session_start();

// Get the submitted token
$token = $_POST['token'];

// Check if the token matches the session token
if ($token != $_SESSION['token']) {
  // Discard the request
} else {
  // Process the form data
}

Conclusion

By implementing these techniques, you can effectively prevent unwanted form resubmissions due to page refresh and ensure that your web application behaves as intended.

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