docs: function rpcToSpecifiedServer(client, msg, serverType, routeParam, cb) {
      if (typeof routeParam !== 'string') {
          logger.error('[dreamix-rpc] server id is not a string, server id: %j', routeParam);
          return;
      }
      if (routeParam === '*') {
          const servers = client._station.servers;
          async.each(Object.keys(servers), (serverId, next) => {
              const server = servers[serverId];
              if (server.serverType === serverType) {
                  client.rpcInvoke(serverId, msg, (err) => {
                      next(err);
                  });
              }
          }, cb);
      }
      client.rpcInvoke(routeParam, msg, cb);
  }