PHP Download Page

Question

How do these PHP download pages (e.g. somesite.com/download.php?id=somefile) often found work?

I originally thought of a page that does the counter stuff, and then simpl

Answer 1

Most often it is done by using php function readfile:

if(is_allowed_to_download()){
    header("Content-Disposition: attachment; filename=".basename( $file ));
    header("Content-Type: application/octet-stream");
    header("Content-Length: ". filesize( $file ) );
    header("Content-Transfer-Encoding: binary");

    @readfile($file);
    exit;
}

Less often server specific solutions is used - sending header X-SendFile: file-location.exe for lighttpd and apache with mod_xsendfile (nginx also have some equivalent). These are slight better, because http servers are optimized to serve content and allow for advanced usage like Range headers (for download accelerators).