Factor out StrategicMerge into a generic function and add a test

internal/controller/factory/statefulset.go

@@ -18,19 +18,18 @@ package factory
 
 import (
 	"context"
-	"encoding/json"
 	"fmt"
 
 	appsv1 "k8s.io/api/apps/v1"
 	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/util/intstr"
-	"k8s.io/apimachinery/pkg/util/strategicpatch"
 	ctrl "sigs.k8s.io/controller-runtime"
 	"sigs.k8s.io/controller-runtime/pkg/client"
 
 	etcdaenixiov1alpha1 "github.com/aenix-io/etcd-operator/api/v1alpha1"
+	"github.com/aenix-io/etcd-operator/internal/k8sutils"
 )
 
 const (
@@ -75,25 +74,12 @@ func CreateOrUpdateStatefulSet(
 		Containers: []corev1.Container{generateContainer(cluster)},
 		Volumes:    volumes,
 	}
-	basePodSpecBytes, err := json.Marshal(basePodSpec)
-	if err != nil {
-		return fmt.Errorf("cannot marshal generated base pod spec to JSON: %w", err)
-	}
 	if cluster.Spec.PodTemplate.Spec.Containers == nil {
 		cluster.Spec.PodTemplate.Spec.Containers = make([]corev1.Container, 0)
 	}
-	overridePodSpecBytes, err := json.Marshal(cluster.Spec.PodTemplate.Spec)
-	if err != nil {
-		return fmt.Errorf("cannot marshal field podTemplate.spec to JSON: %w", err)
-	}
-	finalPodSpecBytes, err := strategicpatch.StrategicMergePatch(basePodSpecBytes, overridePodSpecBytes, &corev1.PodSpec{})
-	if err != nil {
-		return fmt.Errorf("cannot patch base pod spec with podTemplate.spec: %w", err)
-	}
-	finalPodSpec := corev1.PodSpec{}
-	err = json.Unmarshal(finalPodSpecBytes, &finalPodSpec)
+	finalPodSpec, err := k8sutils.StrategicMerge(basePodSpec, cluster.Spec.PodTemplate.Spec)
 	if err != nil {
-		return fmt.Errorf("cannot unmarshal finalized podspec from JSON: %w", err)
+		return fmt.Errorf("cannot strategic-merge base podspec with podTemplate.spec: %w", err)
 	}
 
 	statefulSet := &appsv1.StatefulSet{

internal/k8sutils/strategicmerge.go

@@ -0,0 +1,32 @@
+package k8sutils
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"k8s.io/apimachinery/pkg/util/strategicpatch"
+)
+
+func StrategicMerge[K any](base, patch K) (merged K, err error) {
+	baseBytes, err := json.Marshal(base)
+	if err != nil {
+		return merged, fmt.Errorf("cannot marshal base object to JSON: %w", err)
+	}
+
+	patchBytes, err := json.Marshal(patch)
+	if err != nil {
+		return merged, fmt.Errorf("cannot marshal patch object to JSON: %w", err)
+	}
+
+	mergedBytes, err := strategicpatch.StrategicMergePatch(baseBytes, patchBytes, &merged)
+	if err != nil {
+		return merged, fmt.Errorf("cannot patch base pod spec with podTemplate.spec: %w", err)
+	}
+
+	err = json.Unmarshal(mergedBytes, &merged)
+	if err != nil {
+		return merged, fmt.Errorf("cannot unmarshal merged object from JSON: %w", err)
+	}
+
+	return merged, nil
+}

internal/k8sutils/strategicmerge_test.go

@@ -0,0 +1,19 @@
+package k8sutils
+
+import (
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+	corev1 "k8s.io/api/core/v1"
+)
+
+var _ = Describe("StrategicMerge handler", func() {
+	When("Merging two podspecs", func() {
+		It("Should merge two empty podspecs into an empty podspec", func() {
+			p1 := corev1.PodSpec{}
+			p2 := corev1.PodSpec{}
+			p, err := StrategicMerge(p1, p2)
+			Expect(err).NotTo(HaveOccurred())
+			Expect(p).To(Equal(p1))
+		})
+	})
+})

internal/k8sutils/suite_test.go

@@ -0,0 +1,13 @@
+package k8sutils
+
+import (
+	"testing"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+func TestK8SUtils(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "K8SUtils Suite")
+}