Function extract_header_fly_client_ip 

pub fn extract_header_fly_client_ip(
    headers: &HeaderMap,
) -> Result<Option<IpAddr>, Error>

Extract the raw, untrusted IP asserted by Fly-Client-IP.

This reads only the HeaderMap. A missing field returns None; duplicate, non-text, empty, or non-IP values return an error without including the value. Surrounding whitespace is ignored. This vendor field is not an IETF standard, and the function does not authenticate Fly.io or the sender.