I'm trying to handle static file with our sendfile, but I realized it's impossible to call it in the handler of run-server. Although sanitize-response supports procedure as body, it never let me use sendfile at any chance, because the final writing operation should be delayed to server-impl-write. If I do it in advanced (in sanitize-response), the body will appear before the http header, which is wrong way.
My suggestion is to support thunk as body, the thunk included body writing operation, and sanitize-response will pass it to the next step without any cooking. When server-impl-write detected it's a thunk, it'll call it directly to write the body rather than calling write-response-body. Of course, in this way, users have to pass Content-Length manually in build-response. Consider the size of file will be confirmed when calling sendfile, it's easy to do that. In short, my approach is some kind of lazy evaluation for body handling. I can format a patch if it's agreed. Comments?
