code: def dump_begin(self, selector_id):
          
  
          if self.dump_walker is not None:
              self.storage.destroy_walker(self.dump_walker)
  
          selector = DataStreamSelector.FromEncoded(selector_id)
          self.dump_walker = self.storage.create_walker(selector, skip_all=False)
  
          return Error.NO_ERROR, Error.NO_ERROR, self.dump_walker.count()
docs: Start dumping a stream.
  
          Args:
              selector_id (int): The buffered stream we want to dump.
  
          Returns:
              (int, int, int): Error code, second error code, number of available readings