def transform(request, data, finishing=False):
    """Transform in-coming message entity. request will be updated in
        place. Returns the transformed request data.

        ``request``,
            :class:`IHTTPRequest` plugin whose `request.response` attribute
            is being transformed.

        ``data``,
            Either request body or chunk data (in case of chunked encoding)
            in byte-string.

        ``finishing``,
            In case of chunked encoding, this denotes whether this is the last
            chunk to be received.
        """
