I'm not sure I understand why anyone would ever want to send a 100
response anyway.

If I were to add support for this, I'd probably refactor send_response()
so that there's a lower-level function send_response_only() that *only*
sends the response header and change send_response() to call that
followed by sending the headers. I'm not sure where the request logging
code should go but I suspect it should be in send_response(), not in
send_response_only().

Speaking of send_response(), I wonder if it is correct to send the
Server: and Date: headers when the request version is HTTP/0.9?

I don't think we should add the paranoid version to the code; in general
this code is not sufficiently aware of all the quirks of HTTP to prevent
nonsensical things from happening.