code: func (fs FileServer) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
  	// r.URL.Path has already been cleaned by Caddy.
  	if r.URL.Path == "" {
  		r.URL.Path = "/"
  	}
  	return fs.serveFile(w, r, r.URL.Path)
  }
docs: // ServeHTTP serves static files for r according to fs's configuration.