code: func Dir(root string, listDirectory bool) http.FileSystem {
  	fs := http.Dir(root)
  	if listDirectory {
  		return fs
  	}
  	return &onlyfilesFS{fs}
  }
docs: // Dir returns a http.Filesystem that can be used by http.FileServer(). It is used internally
  // in router.Static().
  // if listDirectory == true, then it works the same as http.Dir() otherwise it returns
  // a filesystem that prevents http.FileServer() to list the directory files.