conn, err := grpc.Dial(  "",  grpc.WithInsecure(),  // 負載均衡，使用 consul 作服務發現  grpc.WithBalancer(grpc.RoundRobin(grpclb.NewConsulResolver(    "127.0.0.1:8500", "grpc.health.v1.add",  ))),)

func NewConsulResolver(address string, service string) naming.Resolver {  return &consulResolver{    address: address,    service: service,  }}type consulResolver struct {  address string  service string}func (r *consulResolver) Resolve(target string) (naming.Watcher, error) {  config := api.DefaultConfig()  config.Address = r.address  client, err := api.NewClient(config)  if err != nil {    return nil, err  }  return &consulWatcher{    client: client,    service: r.service,    addrs:  map[string]struct{}{},  }, nil}type consulWatcher struct {  client  *api.Client  service  string  addrs   map[string]struct{}  lastIndex uint64}func (w *consulWatcher) Next() ([]*naming.Update, error) {  for {    services, metainfo, err := w.client.Health().Service(w.service, "", true, &api.QueryOptions{      WaitIndex: w.lastIndex, // 同步點，這個調用將一直阻塞，直到有新的更新    })    if err != nil {      logrus.Warn("error retrieving instances from Consul: %v", err)    }    w.lastIndex = metainfo.LastIndex    addrs := map[string]struct{}{}    for _, service := range services {      addrs[net.JoinHostPort(service.Service.Address, strconv.Itoa(service.Service.Port))] = struct{}{}    }    var updates []*naming.Update    for addr := range w.addrs {      if _, ok := addrs[addr]; !ok {        updates = append(updates, &naming.Update{Op: naming.Delete, Addr: addr})      }    }    for addr := range addrs {      if _, ok := w.addrs[addr]; !ok {        updates = append(updates, &naming.Update{Op: naming.Add, Addr: addr})      }    }    if len(updates) != 0 {      w.addrs = addrs      return updates, nil    }  }}func (w *consulWatcher) Close() {  // nothing to do}