Back button re-submit form data ($_POST)

Solution 1:

If you are submitting a form with search parameters, you are trying to get some data, not modify some.

So, you should use the HTTP GET method, and not POST : POST should be used when you intend to create/modify data, and GET should be used when you intend to fetch some data.

Or, if you have some create/modify operation that has to be done :

The form first POSTs to a first page
- That page does some operations (like writing something to a database)
- And then redirects to another page, using a Location HTTP header.
It's that last page, that's queries by the browser using a GET requests, that displays the data fetched from the parameters received in the URL.

See the Post/Redirect/Get page on wikipedia, about this.

Solution 2:

Use the Post/Redirect/Get (PRG) Pattern.

PRG Pattern

Solution 3:

Send a Location header in the script you POSTed to, pointing to the page that comes after.

Solution 4:

Don't use POST for search. Search can safely be done with GET since it won't alter anything.

Solution 5:

This applies to PHP and IE8.

Not only must you set cacheing to private, but you must remove the 4 cacheing headers and this can only be done with PHP 5.3. In PHP 5.2 you can only set the 4 headers to blank values if using the Zend Framework's setHeader() method. For some reason is not sufficient on IE8 to set the 4 header values to empty values. Here's the code for PHP 5.3:

    header_remove("Expires");
    header_remove("Cache-Control");
    header_remove("Pragma");
    header_remove("Last-Modified");