support direct scheme on rpc resolver

rpcx/internal/resolver/discovbuilder.go

@@ -0,0 +1,39 @@
+package resolver
+
+import (
+	"strings"
+
+	"github.com/tal-tech/go-zero/core/discov"
+	"google.golang.org/grpc/resolver"
+)
+
+type discovBuilder struct{}
+
+func (d *discovBuilder) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOptions) (
+	resolver.Resolver, error) {
+	hosts := strings.Split(target.Authority, EndpointSep)
+	sub, err := discov.NewSubscriber(hosts, target.Endpoint)
+	if err != nil {
+		return nil, err
+	}
+
+	update := func() {
+		var addrs []resolver.Address
+		for _, val := range subset(sub.Values(), subsetSize) {
+			addrs = append(addrs, resolver.Address{
+				Addr: val,
+			})
+		}
+		cc.UpdateState(resolver.State{
+			Addresses: addrs,
+		})
+	}
+	sub.AddListener(update)
+	update()
+
+	return &nopResolver{cc: cc}, nil
+}
+
+func (d *discovBuilder) Scheme() string {
+	return DiscovScheme
+}