Avoiding form resubmit in php when pressing f5

Question

I have the following code on my site (using php and smarty) to try and avoid a form resubmitting when I hit f5:

if ($this->bln_added == false) {
    if (isset($_POST['submit'])) {
        $this->obj_site->obj_smarty->assign('title', $_POST['tas_heading']);
        $this->obj_site->obj_smarty->assign('desc', $_POST['tas_description']);
    }
} else {
    $this->obj_site->obj_smarty->assign('title', '');
    $this->obj_site->obj_smarty->assign('desc', '');
    unset($_POST);
}

bln_added is false by default, but changes to true once the form is successfully submitted. The smarty variables title and desc are used in the template to keep the form content there in case there is a user error and they need to change what they entered.

If the form is submitted successfully it sets bln_added = true, so the second bit of code should not only clear the form fields, but also empty $_POST. But if I press f5 the post data is still there.

Any ideas?

Answer 1

I solved this (in php) by:

1. in the form add a unique identifier (id+counter) not based on time() (!!!)

2. post to a separate file (postform.php) that checked for a session with that unique identifier

3. a) if session with unique identifier was NOT found: post to the database and fill session with unique identifier

   b) if session with unique identifier was found: do nothing

4. after either 3a/3b redirect to result page with header('Location: http://mydomain.com/mypage')

Result is:
no resubmit actions on either refresh/backbutton and only resubmit warning on double click backbutton (but no resubmit action)

Answer 2

Header redirect after post is necessary, but insufficient.

In PHP side after submitting the form successfully, perform a redirect. Eg. header('Location: http://www.example.com/form.php');

But it is not enough. Some users press links twice (doubleclick). A JavaScript is required that would disable submit button after first click.

Answer 3

Your method could work in theory, but there's a much easier way.

After submitting the form successfully, perform a redirect. It doesn't matter where to, but it'll clear the $_POST.

header('Location: http://www.example.com/form.php');

In your case, it sounds like you want to redirect to the page you're already on. Append a $_GET parameter to the URL if you want to display a confirmation message.

Hope this helps,

Tom

Answer 4

The best method I found is using javascript and css. Common php redirection method header('Location: http://www.yourdomain.com/url); will work but It cause warning " Warning: Cannot modify header information - headers already sent" in different frameworks and cms like wordpress, drupal etc. So my suggestion is to follow the below code

echo '<style>body{display:none;}</style>'; 
echo '<script>window.location.href = "http://www.siteurl.com/mysuccesspage";</script>'; 
exit;

The style tag is important otherwise the user may feel like page loaded twice. If we use style tag with body display none and then refresh the page , then the user experience will be like same as php header('Location: ....);

I hope this will help :)

Answer 5

You can rewrite your form-submit into AJAX-way. If you need to show HTML-content, return it in JSON-format and insert with JavaScript(jQuery for example.)

Answer 6

Use Header location after successful post action

header('Location: '.$_SERVER['HTTP_REFERER']);