Trigger action when file download actually completes - php

Question

Nowdays there are a lot of websites for files hosting (uploading websites) and it count for example point per complete download of certain file.
My question
I want to understand what is the idea they are using !
How does it only count on complete downloading of the file ?!
i mean if i canceled downloading of the file after it started , it won't count point!
how does it knew ! is there any php function that able to know if i canceled downloading certain exact file or not !
that question was all time in my mind and thinking about it but i can't understand how does it works or what is the idea behind it. ~ thanks

Answer 1

This can be done by using my other answer as base How can I give download access to files outside public_html directory? and replacing readfile( $filename )
with readfileWhileConnected( $filename ):
Read file until EOF or disconnect:
/** Read $filename until EOF or disconnect,
* if disconnect then error_log() count of bytes read already
*/
function readfileWhileConnected( $filename ) {
// Save and set ini values:
$user_abort = ignore_user_abort();
ignore_user_abort(false);
// Get file size and set bytes_sent to zero:
$fsize = filesize($filename);
$bytes_sent = 0;
// Open file:
$f = fopen($filename, 'r');
// Read file:
while($chunk = fread($f, 1024)) {
// Check if connection is still open:
if(!connection_aborted()) {
// Send $chunk to buffer (if any), then flush() buffers:
echo $chunk;
flush();
// Add $chunk length to $bytes_sent
$bytes_sent += strlen($chunk);
} else {
// Close file:
fclose($f);
error_log("Connection closed at $bytes_sent/$fsize");
exit();
}
// Close file:
fclose($f);
// Reset ini values:
ignore_user_abort($user_abort);
return $bytes_sent;
}
}
After you have your new shiny class myNewSuperDownloadHandlerClass { ... } ready, then make sure you only serve downloads through filedownload.php described here or if have done good myNewSuperDownloadHandlerClass(), then use that, just make sure that readfileWhileConnected() is used for every download requiring connection status polling.
You can easily add callback to be triggered if user closes connection, only 2 exit points here. (seen many functions that have every often return false; return true; return null; return false; return true; and so on..)