如何清除表单数据，以便刷新不重复数据而不转发？

Question

I created a guestbook, in which users can add entries via an HTML form. After submitting data to the guestbook, some users refresh the page. All browsers I know resubmit the data. afterwards. Is there a way to tell the browser, that the data should not be resubmitted?

I used to have a redirect after sucessfully storig the data to the database. But, now I want to promt some additional information to the user, e.g. "Thanks for your entry entitled '...'.", or "A coy of the entry was sent to your e-Mail-Adress...". I really like to avoid adding all the values to GET-Parameters to be able to use the information after the forwarding.

Is there another way (without a forward!) to prevnt the browser from submitting the data again after the user click on the "refresh" button?

Answer 1

Maybe you could set a session variable with a hash of the data posted and check it each time the page is loaded. If the hash is the same, the data has already been submitted:

<?php
session_start(); //Start the session

$dataHash = md5($_POST['name'].$_POST['comment'].$_POST['whatever']); //Get a hash of the submitted data

if(isset($_SESSION['gbHash']) && $_SESSION['gbHash'] == $dataHash) { //Check if the data has been submitted before
    //Do not save the data/show a warning message
} else {
    //Save the data/show a thank you message
}


$_SESSION['gbHash'] = $dataHash;
?>