code: def expectedBody(self, data):
          
          bodyLen = None
          if data.len == 1:
              bodyLen = UInt8()
          elif data.len == 2:
              bodyLen = UInt16Be()
          elif data.len == 4:
              bodyLen = UInt32Be()
          else:
              log.error("invalid header length")
              return
          data.readType(bodyLen)
          self.expect(bodyLen.value, self._callbackBody)
docs: Read header and wait header value to call next state
          @param data: Stream that length are to header length (1|2|4 bytes)
          set next state to callBack body when length read from header
          are received