def __init__(
        self,
        msg: HTTPMessage,
        output_options: OutputOptions,
        on_body_chunk_downloaded: Callable[[bytes], None] = None,
        **kwargs
    ):
        """
        :param msg: a :class:`models.HTTPMessage` subclass
        :param output_options: a :class:`OutputOptions` instance to represent
                               which parts of the message is printed.
        """
        assert output_options.any()
        self.msg = msg
        self.output_options = output_options
        self.on_body_chunk_downloaded = on_body_chunk_downloaded
        self.extra_options = kwargs

        :param msg: a :class:`models.HTTPMessage` subclass
        :param output_options: a :class:`OutputOptions` instance to represent
                               which parts of the message is printed.
        
httpie/output/streams.py