code: def recv(self, buf=None, flags=0):
          
          if buf is None:
              rtn, out_buf = wrapper.nn_recv(self.fd, flags)
          else:
              rtn, out_buf = wrapper.nn_recv(self.fd, buf, flags)
          _nn_check_positive_rtn(rtn)
          return bytes(buffer(out_buf))[:rtn]
docs: Recieve a message.