Lighttpd

When a script running from behind a FastCGI server uses the X-LIGHTTPD-send-file header, and your script also issues a "Connection: Keep-Alive" header, X-LIGHTTPD-send-file header makes Lighty disregard the Keep-Alive header and add its own "Connection: Close" header.

Thus, the client will receive both headers, close and Keep-Alive.

When the script DOES NOT use the X-LIGHTTPD-send-file header, Keep-Alive works OK, that is, it will be there.

On the other hand, if the script DOES NOT generate the Keep-Alive header and uses the X-LIGHTTPD-send-file header, Lighty will genereate a "Connection: Close" header.