fix(pubsublite): return an error if no topic or subscription fields w…

…ere updated (#3502)

For consistency with pubsub implementation.

pubsublite/admin.go

@@ -15,6 +15,7 @@ package pubsublite
 
 import (
 	"context"
+	"errors"
 
 	"cloud.google.com/go/pubsublite/internal/wire"
 	"google.golang.org/api/option"
@@ -23,6 +24,11 @@ import (
 	pb "google.golang.org/genproto/googleapis/cloud/pubsublite/v1"
 )
 
+var (
+	errNoTopicFieldsUpdated        = errors.New("pubsublite: no fields updated for topic")
+	errNoSubscriptionFieldsUpdated = errors.New("pubsublite: no fields updated for subscription")
+)
+
 // AdminClient provides admin operations for Cloud Pub/Sub Lite resources
 // within a Google Cloud region. An AdminClient may be shared by multiple
 // goroutines.
@@ -45,7 +51,8 @@ func NewAdminClient(ctx context.Context, region string, opts ...option.ClientOpt
 	return &AdminClient{admin: admin}, nil
 }
 
-// CreateTopic creates a new topic from the given config.
+// CreateTopic creates a new topic from the given config. If the topic already
+// exists an error will be returned.
 func (ac *AdminClient) CreateTopic(ctx context.Context, config TopicConfig) (*TopicConfig, error) {
 	req := &pb.CreateTopicRequest{
 		Parent:  config.Name.location().String(),
@@ -60,9 +67,13 @@ func (ac *AdminClient) CreateTopic(ctx context.Context, config TopicConfig) (*To
 }
 
 // UpdateTopic updates an existing topic from the given config and returns the
-// new topic config.
+// new topic config. UpdateTopic returns an error if no fields were modified.
 func (ac *AdminClient) UpdateTopic(ctx context.Context, config TopicConfigToUpdate) (*TopicConfig, error) {
-	topicpb, err := ac.admin.UpdateTopic(ctx, config.toUpdateRequest())
+	req := config.toUpdateRequest()
+	if len(req.GetUpdateMask().GetPaths()) == 0 {
+		return nil, errNoTopicFieldsUpdated
+	}
+	topicpb, err := ac.admin.UpdateTopic(ctx, req)
 	if err != nil {
 		return nil, err
 	}
@@ -106,7 +117,8 @@ func (ac *AdminClient) Topics(ctx context.Context, location LocationPath) *Topic
 	}
 }
 
-// CreateSubscription creates a new subscription from the given config.
+// CreateSubscription creates a new subscription from the given config. If the
+// subscription already exists an error will be returned.
 func (ac *AdminClient) CreateSubscription(ctx context.Context, config SubscriptionConfig) (*SubscriptionConfig, error) {
 	req := &pb.CreateSubscriptionRequest{
 		Parent:         config.Name.location().String(),
@@ -121,9 +133,14 @@ func (ac *AdminClient) CreateSubscription(ctx context.Context, config Subscripti
 }
 
 // UpdateSubscription updates an existing subscription from the given config and
-// returns the new subscription config.
+// returns the new subscription config. UpdateSubscription returns an error if
+// no fields were modified.
 func (ac *AdminClient) UpdateSubscription(ctx context.Context, config SubscriptionConfigToUpdate) (*SubscriptionConfig, error) {
-	subspb, err := ac.admin.UpdateSubscription(ctx, config.toUpdateRequest())
+	req := config.toUpdateRequest()
+	if len(req.GetUpdateMask().GetPaths()) == 0 {
+		return nil, errNoSubscriptionFieldsUpdated
+	}
+	subspb, err := ac.admin.UpdateSubscription(ctx, req)
 	if err != nil {
 		return nil, err
 	}

pubsublite/admin_test.go

@@ -95,6 +95,10 @@ func TestAdminTopicCRUD(t *testing.T) {
 		t.Errorf("UpdateTopic() got: %v\nwant: %v", gotConfig, topicConfig)
 	}
 
+	if _, err := admin.UpdateTopic(ctx, TopicConfigToUpdate{}); !test.ErrorEqual(err, errNoTopicFieldsUpdated) {
+		t.Errorf("UpdateTopic() got err: (%v), want err: (%v)", err, errNoTopicFieldsUpdated)
+	}
+
 	if gotConfig, err := admin.Topic(ctx, topicPath); err != nil {
 		t.Errorf("Topic() got err: %v", err)
 	} else if !testutil.Equal(gotConfig, &topicConfig) {
@@ -296,6 +300,10 @@ func TestAdminSubscriptionCRUD(t *testing.T) {
 		t.Errorf("UpdateSubscription() got: %v\nwant: %v", gotConfig, subscriptionConfig)
 	}
 
+	if _, err := admin.UpdateSubscription(ctx, SubscriptionConfigToUpdate{}); !test.ErrorEqual(err, errNoSubscriptionFieldsUpdated) {
+		t.Errorf("UpdateSubscription() got err: (%v), want err: (%v)", err, errNoSubscriptionFieldsUpdated)
+	}
+
 	if gotConfig, err := admin.Subscription(ctx, subscriptionPath); err != nil {
 		t.Errorf("Subscription() got err: %v", err)
 	} else if !testutil.Equal(gotConfig, &subscriptionConfig) {