unknown file size while downloading via php script

if your browser doesn't appear to be obeying the headers generated by your PHP script—especially Content-Length—it is fairly likely that Apache's mod_deflate extension is enabled.

You can easily disable it for a single script using the following line in an applicable .htaccess file: 

 

SetEnvIfNoCase Request_URI ^/download\.php no-gzip dont-vary

 

 

 

thanks to http://paul.luminos.nl/show_post.php?p=471