fn parse_request(mut parts: std::str::SplitWhitespace<'_>) -> RequestParserResult<'_> {

        let uri = match parts.next() {

            Some(s) => s,

            None => return Err(RequestParserError::UnexpectedEOF),

        let position = match parts.next() {

            Some(s) => Some(

                s.parse::<SongPosition>()

                    .map_err(|_| RequestParserError::SyntaxError(1, s.to_owned()))?,

            None => None,

        debug_assert!(parts.next().is_none());

        Ok((Request::Add(uri.to_string(), position), ""))

    }

    fn parse_response(

        parts: ResponseAttributes<'_>,

    ) -> Result<Self::Response, ResponseParserError> {

        debug_assert!(parts.is_empty());

        Ok(())

    }