code: def body_storage_pair(self):
          
          future = Future()
  
          def send_body():
              nonlocal future
              data = yield
              future.set_result(data)
              yield
  
          sender = send_body()
          next(sender)
          return future, sender
docs: Return reader/writer pair for storing receiving body data.
          These are event-loop specific objects.
  
          The reader should be an awaitable object that returns the
          body data once created.