server http response to trigger browser download

 https://stackoverflow.com/questions/386845/http-headers-for-file-downloads

Content-Disposition: attachment; filename="MyFileName.ext"

https://stackoverflow.com/questions/6520231/how-to-force-browser-to-download-file

or many more :

header("Content-Disposition: attachment; filename=\"".$fname_local."\"");
header("Content-Type: application/force-download");
header("Content-Transfer-Encoding: binary");
header("Content-Length: ".filesize($fname));