refactor: properly run the function exactly once

Author: faiq

common/pkg/capi/clustertopology/handlers/mutation/meta.go

@@ -62,25 +62,32 @@ func (mgp metaGeneratePatches) Name() string {
 	return mgp.name
 }
 
-func (mgp metaGeneratePatches) GeneratePatches(
-	ctx context.Context,
-	req *runtimehooksv1.GeneratePatchesRequest,
-	resp *runtimehooksv1.GeneratePatchesResponse,
-) {
-	clusterKey := handlers.ClusterKeyFromReq(req)
-	getCluster := func(ctx context.Context) (*clusterv1.Cluster, error) {
-		cluster := &clusterv1.Cluster{}
-		var err error
-		fn := sync.OnceFunc(func() {
-			err = mgp.cl.Get(ctx, clusterKey, cluster)
+func (mgp metaGeneratePatches) CreateClusterGetter(
+	clusterKey client.ObjectKey,
+) func(context.Context) (*clusterv1.Cluster, error) {
+	return func(ctx context.Context) (*clusterv1.Cluster, error) {
+		var (
+			cluster clusterv1.Cluster
+			err     error
+			once    sync.Once
+		)
+		once.Do(func() {
+			err = mgp.cl.Get(ctx, clusterKey, &cluster)
 		})
-		fn()
 		if err != nil {
 			return nil, fmt.Errorf("failed to fetch cluster %w", err)
 		}
-		return cluster, nil
+		return &cluster, nil
 	}
+}
 
+func (mgp metaGeneratePatches) GeneratePatches(
+	ctx context.Context,
+	req *runtimehooksv1.GeneratePatchesRequest,
+	resp *runtimehooksv1.GeneratePatchesResponse,
+) {
+	clusterKey := handlers.ClusterKeyFromReq(req)
+	clusterGetter := mgp.CreateClusterGetter(clusterKey)
 	topologymutation.WalkTemplates(
 		ctx,
 		unstructured.UnstructuredJSONScheme,
@@ -93,7 +100,7 @@ func (mgp metaGeneratePatches) GeneratePatches(
 			holderRef runtimehooksv1.HolderReference,
 		) error {
 			for _, h := range mgp.mutators {
-				if err := h.Mutate(ctx, obj.(*unstructured.Unstructured), vars, holderRef, clusterKey, getCluster); err != nil {
+				if err := h.Mutate(ctx, obj.(*unstructured.Unstructured), vars, holderRef, clusterKey, clusterGetter); err != nil {
 					return err
 				}
 			}