def client_connected(
        self, reader: asyncio.StreamReader, writer: asyncio.StreamWriter
    ) -> None:
        """
        Callback when the TCP connection is established.

        Record references to the stream reader and the stream writer to avoid
        using private attributes ``_stream_reader`` and ``_stream_writer`` of
        :class:`~asyncio.StreamReaderProtocol`.

        """
        self.reader = reader
        self.writer = writer