请教一些问题

[sirodeneko]

1.本例子中是网关是只有一个服务的，但是如果我有多个服务，网关的代码应该如何编写，grpc是如何确定要选择那个路由的。

2.这行代码中的第二个参数为什么是"://authority/",有什么含义吗

conn, err := grpc.DialContext(ctx, r.Scheme()+"://authority/"+*svc, grpc.WithInsecure(), grpc.WithBalancerName(roundrobin.Name), grpc.WithBlock())

[wwcd]

问题1，多个grpc服务后端话，每个后端是一个conn，然后通过注册其支持的接口，

grpc-lb/cmd/gw/gw.go

Line 42 in 9238d81

err = pb.RegisterGreeterHandler(ctx, mux, conn)

问题2，参见代码注释的链接https://github.com/grpc/grpc/blob/master/doc/naming.md#name-syntax

[sirodeneko]

我大概知道是怎么回事了，
调用 grpc.DialContext(ctx, r.Scheme()+"://authority/"+"serviceName",...)时
会根据第二个参数解析出一个resolver.Target{}
Scheme=r.Scheme()
Authority="authority"
Endpoint="serviceName"
根据Scheme将拿到我们注册的Builder.

还有一个问题,grpc每次调用我们的Build方法，就会进行watch一个服务，但是我看grpc是根据schema来区分不同的Resolver，但是我要求可以查询每个不同的服务，请问如果schema相同，Endpoint（即服务）不同会重复调用Build方法吗。
这是我的代码，进行了一些修改，服务名从resolver.Target中拿

const schema = "wethedevelop/resolver"

// resolver is the implementaion of grpc.resolve.Builder
type Resolver struct {
	endpoints  string
	cli     *clientv3.Client
	cc      resolver.ClientConn
}

// NewResolver return resolver builder
// target example: "http://127.0.0.1:2379,http://127.0.0.1:12379,http://127.0.0.1:22379"
// service is service name
func NewResolver(endpoints string) resolver.Builder {
	return &Resolver{endpoints: endpoints}
}

// Scheme return etcdv3 schema
func (r *Resolver) Scheme() string {
	return schema
}

// ResolveNow
func (r *Resolver) ResolveNow(rn resolver.ResolveNowOptions) {
}

// Close
func (r *Resolver) Close() {
}

// Build to resolver.Resolver
func (r *Resolver) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOptions) (resolver.Resolver, error) {
	var err error

	r.cli, err = clientv3.New(clientv3.Config{
		Endpoints: strings.Split(r.endpoints, ","),
	})
	if err != nil {
		return nil, fmt.Errorf("gateway: create clientv3 client failed: %v", err)
	}

	r.cc = cc

	go r.watch(fmt.Sprintf("/%s/%s/", schema, target.Endpoint))

	return r, nil
}

func (r *Resolver) watch(prefix string) {
	addrDict := make(map[string]resolver.Address)

	update := func() {
		addrList := make([]resolver.Address, 0, len(addrDict))
		for _, v := range addrDict {
			addrList = append(addrList, v)
		}
		r.cc.UpdateState(resolver.State{Addresses: addrList})
	}

	resp, err := r.cli.Get(context.Background(), prefix, clientv3.WithPrefix())
	if err == nil {
		for i := range resp.Kvs {
			addrDict[string(resp.Kvs[i].Value)] = resolver.Address{Addr: string(resp.Kvs[i].Value)}
		}
	}

	update()

	rch := r.cli.Watch(context.Background(), prefix, clientv3.WithPrefix(), clientv3.WithPrevKV())
	for n := range rch {
		for _, ev := range n.Events {
			switch ev.Type {
			case mvccpb.PUT:
				addrDict[string(ev.Kv.Key)] = resolver.Address{Addr: string(ev.Kv.Value)}
			case mvccpb.DELETE:
				delete(addrDict, string(ev.PrevKv.Key))
			}
		}
		update()
	}
}