24 hour expire url with random url creation for cloaked file downloads

You can't hide the location, but if your clients have signed up, store the signup time anywhere (DB, flatfile). Before the user can download that file make a check if the user can still downloadthat file..

To output a file in PHP you can use the following:

if (downloadIsValid()) {
header("Content-type: $mimetype");
header("Content-Disposition: attachment; filename=\"".$filename."\"");
readfile($absolutePathOfFile);
} else {
echo "no longer able to download file";
}

Add a datetime field to your user database, called something like 'downloadexpires', then update it when they have signed up:

$downloadexpires = date('Y-m-d H:i:s', strtotime('now + 24 hours'));
mysql_query("UPDATE users SET downloadexpires = '$downloadexpires' WHERE id = '$user_id'");

Then when you want to check the download time (called from hernst42's code above):

function downloadIsValid($user_id) {
  $result = mysql_query("SELECT id FROM users WHERE downloadexpires > NOW() AND id = '$user_id'");
  return (mysql_num_rows($result) > 0);
}

Only other thing is that it's a good idea to add a content-length header, especially if you're downloading large files:

header('Content-length: '.filesize($absolutePathOfFile));

Make sure that you do use the correct MIME type for the file you're downloading - there is no such type as 'application/force-download', so don't use it.

For your unique URLs, generate them at the time you register the user, md5() is good for this. You might find that it's useful to map them back to a script parameter using mod_rewrite on Apache.

I don't think you'll find a download script as such, it's really a very loose association of several small parts, and everyone will want to do it differently

Thanks for the points :)