feat: support third party orm to interact with go-zero (#1286)

* fixes #987

* chore: fix test failure

* chore: add comments

* feat: support third party orm to interact with go-zero

* chore: refactor

zrpc/resolver/internal/resolver.go

@@ -0,0 +1,50 @@
+package internal
+
+import (
+	"fmt"
+
+	"google.golang.org/grpc/resolver"
+)
+
+const (
+	// DirectScheme stands for direct scheme.
+	DirectScheme = "direct"
+	// DiscovScheme stands for discov scheme.
+	DiscovScheme = "discov"
+	// EtcdScheme stands for etcd scheme.
+	EtcdScheme = "etcd"
+	// KubernetesScheme stands for k8s scheme.
+	KubernetesScheme = "k8s"
+	// EndpointSepChar is the separator cha in endpoints.
+	EndpointSepChar = ','
+
+	subsetSize = 32
+)
+
+var (
+	// EndpointSep is the separator string in endpoints.
+	EndpointSep = fmt.Sprintf("%c", EndpointSepChar)
+
+	directResolverBuilder directBuilder
+	discovResolverBuilder discovBuilder
+	etcdResolverBuilder   etcdBuilder
+	k8sResolverBuilder    kubeBuilder
+)
+
+// RegisterResolver registers the direct and discov schemes to the resolver.
+func RegisterResolver() {
+	resolver.Register(&directResolverBuilder)
+	resolver.Register(&discovResolverBuilder)
+	resolver.Register(&etcdResolverBuilder)
+	resolver.Register(&k8sResolverBuilder)
+}
+
+type nopResolver struct {
+	cc resolver.ClientConn
+}
+
+func (r *nopResolver) Close() {
+}
+
+func (r *nopResolver) ResolveNow(options resolver.ResolveNowOptions) {
+}