async def AddCharm(self, channel, url):
        '''
        channel : str
        url : str
        Returns -> None
        '''
        # map input types to rpc msg
        _params = dict()
        msg = dict(type='Client',
                   request='AddCharm',
                   version=1,
                   params=_params)
        _params['channel'] = channel
        _params['url'] = url
        reply = await self.rpc(msg)
        return reply
channel : str
        url : str
        Returns -> None