docs: def Update(self, attribute=None):
      """Update an attribute from the client."""
      # List the directory on the client
      currently_running = self.Get(self.Schema.CONTENT_LOCK)
  
      # Is this flow still active?
      if currently_running:
        flow_obj = aff4.FACTORY.Open(currently_running, token=self.token)
        if flow_obj and flow_obj.GetRunner().IsRunning():
          return
  
      # The client_id is the first element of the URN
      client_id = self.urn.Path().split("/", 2)[1]
  
      # Get the pathspec for this object
      pathspec = self.Get(self.Schema.STAT).pathspec
      flow_urn = flow.StartAFF4Flow(
          client_id=client_id,
          # TODO(user): dependency loop between aff4_grr.py and transfer.py
          # flow_name=transfer.MultiGetFile.__name__,
          flow_name="MultiGetFile",
          token=self.token,
          pathspecs=[pathspec])
      self.Set(self.Schema.CONTENT_LOCK(flow_urn))
      self.Close()
  
      return flow_urn