Allow resource updates to omit an owner refs UID

agent/grpc-external/services/resource/write.go

@@ -179,6 +179,15 @@ func (s *Server) Write(ctx context.Context, req *pbresource.WriteRequest) (*pbre
 				return storage.ErrCASFailure
 			}
 
+			// Fill in an empty Owner UID with the existing owner's UID. If other parts
+			// of the owner ID like the type or name have changed then the subsequent
+			// EqualID call will still error as you are not allowed to change the owner.
+			// This is a small UX nicety to repeatedly "apply" a resource that should
+			// have an owner without having to care about the current owners incarnation.
+			if input.Owner != nil && existing.Owner != nil && input.Owner.Uid == "" {
+				input.Owner.Uid = existing.Owner.Uid
+			}
+
 			// Owner can only be set on creation. Enforce immutability.
 			if !resource.EqualID(input.Owner, existing.Owner) {
 				return status.Errorf(codes.InvalidArgument, "owner cannot be changed")

agent/grpc-external/services/resource/write_test.go

@@ -571,6 +571,25 @@ func TestWrite_Owner_Uid(t *testing.T) {
 		require.NotEmpty(t, rsp2.Resource.Owner.Uid)
 		require.Equal(t, artist.Id.Uid, rsp2.Resource.Owner.Uid)
 	})
+
+	t.Run("no-uid - update auto resolve", func(t *testing.T) {
+		artist, err := demo.GenerateV2Artist()
+		require.NoError(t, err)
+
+		uid := ulid.Make().String()
+		album, err := demo.GenerateV2Album(artist.Id)
+		require.NoError(t, err)
+		album.Owner.Uid = uid
+
+		_, err = client.Write(testContext(t), &pbresource.WriteRequest{Resource: album})
+		require.NoError(t, err)
+
+		// unset the uid and rewrite the resource
+		album.Owner.Uid = ""
+		rsp, err := client.Write(testContext(t), &pbresource.WriteRequest{Resource: album})
+		require.NoError(t, err)
+		require.Equal(t, uid, rsp.GetResource().GetOwner().GetUid())
+	})
 }
 
 type blockOnceBackend struct {