code: func autohead(h http.Handler) http.Handler {
  	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
  		if r.Method == "HEAD" {
  			w = &headResponseWriter{w}
  		}
  		h.ServeHTTP(w, r)
  	})
  }
docs: // autohead automatically discards the body of responses to HEAD requests