def chk_body(self):
        if hasattr(self, '_m_chk_body'):
            return self._m_chk_body if hasattr(self, '_m_chk_body') else None

        _pos = self._io.pos()
        self._io.seek(0)
        self._m_chk_body = self._io.read_bytes((self.framesize - 2))
        self._io.seek(_pos)
        return self._m_chk_body if hasattr(self, '_m_chk_body') else None