Is there a way to run some script before the upload starts in php?

Question

Can you run some script before the uploading of a file starts in php? Example, I'm POSTing to upload.php, and in that file I want to check their $_SESSION first before I start wasting bandwidth on them and the file stats uploading to my server. I'm using php 5.2.11 on nginx.

<?php
  if ($_SESSION['admin'] == 'YES') {
    // do upload here
  } else {
    exit;
  }
?>

Answer 1

No. The request doesn't get to the PHP engine until after the file has been uploaded.

Answer 2

No, because the upload is part of the request and is done before PHP even comes into play.

There may be a way around this using the technique of those PHP-/Perl-based uploaders that somehow hook into the uploading process, but then, there also may not. Especially when you're using a different web server.

I would do a quick Ajax-based check for the right session, and bind that to the submit event of the form you are uploading the file with. It may take half a second, but is completely unobtrusive for the user.

Answer 3

You could make an ajax call on the page the form is submitted to check their session state before allowing the form to submit.