2 ideas (not verified):
First:
Instead of placing regular links to files (that you want to download) on your page place links like .../dowanload.php which may look sth like this:
<?php
// download.php file
session_start(); // if needed
$filename = $_GET['filename']);
header( 'Content-type: text/plain' ); // use any MIME you want here
header( 'Content-Disposition: attachment; filename="' . htmlspecialchars($filename) . '"' );
header( 'Pragma: no-cache' );
// of course add some error handling
$filename = 'c:/php/php.ini';
$handle = fopen($filename, 'rb');
// do not use file_get_contents as you've said files are up to 4GB - so read in chunks
while($chunk = fread($handle, 1000)) // chunk size may depend on your filesize
{
echo $chunk;
flush();
// write progress info to the DB, or session variable in order to update progress bar
}
fclose($handle);
?>
This way you may keep eye on your download process. In the meantime you may write progress info to the DB/session var and update progress bar reading status from DB/session var using AJAX of course polling a script that reads progress info.
That is very simplified but I think it might work as you want.
Second:
Apache 2.4 has Lua language built in:
I bet you can try to write LUA Apache handler that will monitor your download - send progress to the DB and update progress bar using PHP/AJAX taking progress info from the DB.
Similarly - there are modules for perl and even python (but not for win)