PHP: Determine how many bytes sent over http

functions.php

<?php
// Determine how many bytes sent over http
ignore_user_abort(true);

$handle = fopen($file_path, 'r');
while ( ! feof($handle)) {
    echo fread($handle, 4096);
    if (connection_aborted()) {
    	$transfer_success = false;
    	$bytes_transferred = ftell($handle);
    	break;
    }
}
fclose($handle);