def fetch_room_ids(self, names):
        """ Fetches the ids of the rooms with the given names """
        ret = {}
        names_set = set(names)
        try:
            for d in msgpack.unpack(urllib2.urlopen(
                    "%s/list/locations?format=msgpack" % self.url)):
                name = d['name'].upper() # normalize: Hg -> HG
                if name in names_set:
                    ret[name] = d['id']
        except urllib2.HTTPError, e:
            raise RuusterError(e)
        return ret