Update Marshal func to use VT

pkg/cache/types/types.go

@@ -9,6 +9,10 @@ import (
 // Resource is the base interface for the xDS payload.
 type Resource interface {
 	proto.Message
+}
+
+type VtResource interface {
+	Resource
 	MarshalVTStrict() ([]byte, error)
 }
 

pkg/cache/v3/resource.go

@@ -18,16 +18,14 @@ import (
 	"crypto/sha256"
 	"encoding/hex"
 	"fmt"
-	"google.golang.org/protobuf/proto"
-	"reflect"
-
 	cluster "github.com/envoyproxy/go-control-plane/envoy/config/cluster/v3"
 	endpoint "github.com/envoyproxy/go-control-plane/envoy/config/endpoint/v3"
 	listener "github.com/envoyproxy/go-control-plane/envoy/config/listener/v3"
 	route "github.com/envoyproxy/go-control-plane/envoy/config/route/v3"
 	runtime "github.com/envoyproxy/go-control-plane/envoy/service/runtime/v3"
 	"github.com/envoyproxy/go-control-plane/pkg/cache/types"
 	"github.com/envoyproxy/go-control-plane/pkg/resource/v3"
+	"google.golang.org/protobuf/proto"
 )
 
 // GetResponseType returns the enumeration for a valid xDS type URL.
@@ -126,12 +124,14 @@ func GetResourceWithTTLNames(resources []types.ResourceWithTTL) []string {
 
 // MarshalResource converts the Resource to MarshaledResource.
 func MarshalResource(resource types.Resource) (types.MarshaledResource, error) {
-	t := reflect.TypeOf(resource)
-	_, ok := t.MethodByName("MarshalVTStrict")
-	if !ok {
-		return proto.MarshalOptions{Deterministic: true}.Marshal(resource)
+	switch v := resource.(type) {
+	case types.VtResource:
+		return v.MarshalVTStrict()
+	case types.Resource:
+		return proto.MarshalOptions{Deterministic: true}.Marshal(v)
+	default:
+		return nil, fmt.Errorf("failed to marshal, message is %T, must satisfy the vtprotoMessage interface or want proto.Message", v)
 	}
-	return resource.MarshalVTStrict()
 }
 
 // GetResourceReferences returns a map of dependent resources keyed by resource type, given a map of resources.