What are the best practices for handling POST data and form submissions in PHP to prevent duplicate form submissions?

To prevent duplicate form submissions in PHP, one common approach is to use a token or unique identifier that is generated when the form is loaded and checked when the form is submitted. This token can be stored in a session variable and compared with the token submitted with the form data. If the tokens match, the form submission can be processed; otherwise, the submission can be ignored to prevent duplicates. 

```php
session_start();

if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    if ($_POST['token'] == $_SESSION['token']) {
        // Process form submission
        // Reset token to prevent duplicate submissions
        $_SESSION['token'] = bin2hex(random_bytes(32));
    } else {
        // Duplicate form submission detected
        // Redirect or display an error message
    }
}

// Generate and store a unique token for the form
if (!isset($_SESSION['token'])) {
    $_SESSION['token'] = bin2hex(random_bytes(32));
}
```
This code snippet demonstrates how to prevent duplicate form submissions by using a token stored in a session variable. The token is generated when the form is loaded and compared with the token submitted with the form data. If the tokens match, the form submission is processed, and the token is reset to prevent duplicates. If the tokens do not match, a duplicate form submission is detected, and appropriate action can be taken.

Keywords

POST data form submissions prevent duplicate PHP functions error handling

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