Determining successful download using php readfile - php

Question

I need to know if a user selected download then clicked the cancel button, which is not the same as readfile having an error. I have inspected the count returned by the readfile function, but it shows the bytes in the file even if the user canceled the download from the Save As dialog.
The reason this is needed is because my site has a one-time download, where a member gives permission for another use to download their file one time, then the permission goes away. But if a member clicks the download button then decides not to download it right then, I dont' want my database to get updated to show they got the file.
This deals with intellectual property protection since the files are the property of the member who uploaded them, and I need to keep an audit trail of exactly what other members downloaded the file in case they start floating around the internet. But if the readfile function always reflects the filesize (meaning those bytes were transferred in some way), I have no way to know if the file was actually downloaded.
I have seen a number of posts about this subject, but no real solutions to what has to be a frequent need - did they download it or not? Just knowing that they clicked the download button doesn't really say whether they decided to go through with it since the Save As dialog box allows someone to cancel the actual completion of the download.
For completeness, here is my download code up until the readfile function:
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header("Content-Disposition: attachment; filename=$download_name");
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: public');
header('Content-Length: ' . filesize("sub/$doc_file"));
ob_clean();
flush();
$wasdownloaded = readfile("sub/$doc_file");

Answer 1

I fear the correct answer is "Impossible" - let me explain: You might be able to correctly figure out, when the file has crossed the wire, but you can't figure out reliably, whether the client threw it away or not.
Example (chronological sequence):
A user on MSIE clicks download and is presented with the "Save where" Dialog.
While this dialog is open, the download is started in the background.
The user navigates around in the dialog or simply does nothing (phone rang, he talks)
The background download is finished, your script sees the download as complete
The user clicks on "cancel"
MSIE deletes the tempfile, the download is never stored in a user-accessible form
Result:
The user sees the file as "not downloaded" - and he is correct
Your app sees the file as "correctly downloaded" - and it is correct

Answer 2

You would first need ignore_user_abort().
This would allow your script to continue on after the user has hit cancel, or escape.
You would then have to print out the file and continuously check with connection_aborted().
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header("Content-Disposition: attachment; filename=$download_name");
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: public');
header('Content-Length: ' . filesize("sub/$doc_file"));
ob_clean();
flush();
$fp=fopen("sub/$doc_file","rb");
while(!feof($fp))
{
print(fread($fp,1024*8));
flush();
ob_flush();
if( connection_aborted() )
{
//do code for handling aborts
}
}

Answer 3

Use this comment on php.net : http://www.php.net/manual/en/function.fread.php#72716
On fclose you would be able to determine if file has been downloaded successful, because your are checking if user aborted connection with connection_status()