code: func FileServer(dir http.Dir) http.Handler {
  	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
  		p := path.Join(string(dir), r.URL.Path)
  		if f, err := os.Stat(p); err == nil && !f.IsDir() {
  			http.ServeFile(w, r, p)
  			return
  		}
  
  		http.NotFound(w, r)
  	})
  }
docs: // FileServer file server that disabled file listing