code: def listdir(self, path):
          
          bucket, obj = self._path_to_bucket_and_key(path)
  
          obj_prefix = self._add_path_delimiter(obj)
          if self._is_root(obj_prefix):
              obj_prefix = ''
  
          obj_prefix_len = len(obj_prefix)
          for it in self._list_iter(bucket, obj_prefix):
              yield self._add_path_delimiter(path) + it['name'][obj_prefix_len:]
docs: Get an iterable with GCS folder contents.
          Iterable contains paths relative to queried path.