Does this protect me against page reload and the back button?

Further to my previous question, here's what I decided to implement; it may not be pure P-R-G, but it seems ok. Care to comment?

The form.php has an action; let's call it validate.php.

validate.php is never seen by the user; if validates all $_GET and, if valid writes it to database and generates the HTML of a confirmation page / if not valid, it generates the HTML of an error page explaining what is wrong.

Whichever HTML is generated get stored in a $_SESSION variable and then validate.php does a header('Location: <as开发者_Python百科 appropriate>);

Finally a page called submitted.php of invalid_input.php (in case the user reads the URL) consists only of echo $_SESSION['form_html'];

That seems to me like is proff against both page reload and back button problems.

Or did I goof by trying to reinvent the wheel?

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Firstly, you're better off storing the form data, which means you can perform the validation again. It will also be less html. The problem with the method you're employing now is that it doesn't protect against multiple tabs, since $_SESSION is universal to a browser session.

One way I've used to prevent against duplicate submission (without PRG) is to generate a unique id for every page load (where a form is involved). When I generate that unique id, I add it to a $_SESSION['form_unique_ids'] array, and I include it as a hidden field in every form I generate. Then before I take action on a form submission, I check to see if that unique id is in the session. If it is, this is the first time that form has been submitted, and I remove it from the session. That way if I try to resubmit that page, I will know because that id is not in the session not to process the results.

This could be extended so that instead of storing a single id, you use the id as the key in the array, and let the value be the result of the transaction. Then:

1. If there are errors, you store the $_POST data as well. Then, redirect to original_form.php?id=unique_id and display the validation results. You can either store them or recalculate them there.
2. If there is success, store the success message and redirect to success_page.php?id=unique_id. Display the success message prominently there. If you like, you can remove it from the page.

You have the option of removing the session data when you display it, but that would mean if they refreshed the edit page they'd lose the validation messages and saved form data. I'd rather find a way to get rid of data that is old enough that they're not likely to need it anymore.

Anyway, some of those ideas might be useful. Then again, maybe it's way too much effort for the problem. Your call :)

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As long as you use a php redirect at the end of your validate you cannot reload or back button into the validate.php