From 88256cdfed637f633a33626aeac7f956a71f75fa Mon Sep 17 00:00:00 2001
From: Norwin Schnyder <norwin.schnyder+github@gmail.com>
Date: Tue, 19 Dec 2023 10:12:03 +0000
Subject: [PATCH] fix: nil pointer exception due to failed injection

Signed-off-by: Norwin Schnyder <norwin.schnyder+github@gmail.com>
---
 pkg/webhook/injection.go    | 20 ++++++++++++++++++--
 pkg/webhook/webhook.go      |  4 ++--
 pkg/webhook/webhook_test.go | 10 ++++++++++
 3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/pkg/webhook/injection.go b/pkg/webhook/injection.go
index 052f5d9..219acfd 100644
--- a/pkg/webhook/injection.go
+++ b/pkg/webhook/injection.go
@@ -5,23 +5,39 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/webhook/admission"
 )
 
+// ClientInjector is used to inject a client.Client into webhook handlers.
+type ClientInjector interface {
+	InjectClient(client.Client) error
+}
+
+// ensure InjectedClient implements ClientInjector
+var _ ClientInjector = &InjectedClient{}
+
 // InjectedClient holds an injected client.Client
 type InjectedClient struct {
 	Client client.Client
 }
 
-// InjectClient implements the inject.Client interface.
+// InjectClient implements the ClientInjector interface.
 func (i *InjectedClient) InjectClient(client client.Client) error {
 	i.Client = client
 	return nil
 }
 
+// DecoderInjector is used to inject an admission.Decoder into webhook handlers.
+type DecoderInjector interface {
+	InjectDecoder(*admission.Decoder) error
+}
+
+// ensure InjectedDecoder implements DecoderInjector
+var _ DecoderInjector = &InjectedDecoder{}
+
 // InjectedDecoder holds an injected admission.Decoder
 type InjectedDecoder struct {
 	Decoder *admission.Decoder
 }
 
-// InjectDecoder implements the admission.DecoderInjector interface.
+// InjectDecoder implements the DecoderInjector interface.
 func (i *InjectedDecoder) InjectDecoder(decoder *admission.Decoder) error {
 	i.Decoder = decoder
 	return nil
diff --git a/pkg/webhook/webhook.go b/pkg/webhook/webhook.go
index 3e9296a..2dd9ad9 100644
--- a/pkg/webhook/webhook.go
+++ b/pkg/webhook/webhook.go
@@ -108,13 +108,13 @@ func (blder *Builder) Complete(i interface{}) error {
 		return fmt.Errorf("webhook instance %v does implement neither Mutator nor Validator interface", i)
 	}
 
-	if injector, ok := i.(InjectedClient); ok {
+	if injector, ok := i.(ClientInjector); ok {
 		if err := injector.InjectClient(blder.mgr.GetClient()); err != nil {
 			return err
 		}
 	}
 
-	if injector, ok := i.(InjectedDecoder); ok {
+	if injector, ok := i.(DecoderInjector); ok {
 		if err := injector.InjectDecoder(decoder); err != nil {
 			return err
 		}
diff --git a/pkg/webhook/webhook_test.go b/pkg/webhook/webhook_test.go
index 1447818..a974d61 100644
--- a/pkg/webhook/webhook_test.go
+++ b/pkg/webhook/webhook_test.go
@@ -70,6 +70,16 @@ var _ = Describe("Webhook", func() {
 				Complete(&webhook.ValidatingWebhook{})
 			Ω(err).ShouldNot(HaveOccurred())
 		})
+		It("should inject client and decoder", func() {
+			wh := &webhook.ValidatingWebhook{}
+			err := webhook.NewGenericWebhookManagedBy(mgr).
+				For(&corev1.Pod{}).
+				Complete(wh)
+			Ω(err).ShouldNot(HaveOccurred())
+
+			Ω(wh.Client).ShouldNot(BeNil())
+			Ω(wh.Decoder).ShouldNot(BeNil())
+		})
 		It("should not fail if mutating webhook is already registered", func() {
 			err := webhook.NewGenericWebhookManagedBy(mgr).
 				For(&corev1.Pod{}).