the process when the snooper received a QUERY message.

def _do_query(self, query, iph, eth, in_port, msg):
        """the process when the snooper received a QUERY message."""
        datapath = msg.datapath
        dpid = datapath.id
        ofproto = datapath.ofproto
        parser = datapath.ofproto_parser

        # learn the querier.
        self._to_querier[dpid] = {
            'port': in_port,
            'ip': iph.src,
            'mac': eth.src
        }

        # set the timeout time.
        timeout = igmp.QUERY_RESPONSE_INTERVAL
        if query.maxresp:
            timeout = query.maxresp / 10

        self._to_hosts.setdefault(dpid, {})
        if query.address == '0.0.0.0':
            # general query. reset all reply status.
            for group in self._to_hosts[dpid].values():
                group['replied'] = False
                group['leave'] = None
        else:
            # specific query. reset the reply status of the specific
            # group.
            group = self._to_hosts[dpid].get(query.address)
            if group:
                group['replied'] = False
                group['leave'] = None

        actions = [parser.OFPActionOutput(ofproto.OFPP_FLOOD)]
        self._do_packet_out(
            datapath, msg.data, in_port, actions)

        # wait for REPORT messages.
        hub.spawn(self._do_timeout_for_query, timeout, datapath)