Function send_http_error 

pub(crate) async fn send_http_error(
    client_stream: &mut Box<dyn ClientStream>,
    status: &str,
    body: &str,
)

Writes an HTTP error response to a client and closes the connection.

The proxied connections are raw TCP streams, so the HTTP framing has to be written by hand. Errors are ignored: the connection is going away regardless.