fn encode(&mut self, message: Self::Item, buf: &mut BytesMut) -> Result<(), Self::Error> {
        let mut msg_buf = BytesMut::with_capacity(20);
        try!(message
                 .write_to_buf(&mut msg_buf)
                 .map_err(MessageError::from));
        buf.reserve(8 + msg_buf.len());
        buf.put_u64::<LittleEndian>(msg_buf.len() as u64);
        buf.put(msg_buf);
        Ok(())
    }