Convert admission.Decoder in an interface

The current implementation allows to create a decoder without
a scheme/codecs by just referencing the struct `&admission.Decoder{}`
given that codecs is private. The field was filled in before with the
inject package which has been removed. This change retains the Decoder
definition and makes it an interface, `admission.NewDecoder(scheme)` is
now the only way to instantiate our default decoder.

Signed-off-by: Vince Prignano <[email protected]>

pkg/webhook/admission/decode.go

@@ -26,22 +26,35 @@ import (
 
 // Decoder knows how to decode the contents of an admission
 // request into a concrete object.
-type Decoder struct {
+type Decoder interface {
+	// Decode decodes the inlined object in the AdmissionRequest into the passed-in runtime.Object.
+	// If you want decode the OldObject in the AdmissionRequest, use DecodeRaw.
+	// It errors out if req.Object.Raw is empty i.e. containing 0 raw bytes.
+	Decode(req Request, into runtime.Object) error
+
+	// DecodeRaw decodes a RawExtension object into the passed-in runtime.Object.
+	// It errors out if rawObj is empty i.e. containing 0 raw bytes.
+	DecodeRaw(rawObj runtime.RawExtension, into runtime.Object) error
+}
+
+// decoder knows how to decode the contents of an admission
+// request into a concrete object.
+type decoder struct {
 	codecs serializer.CodecFactory
 }
 
-// NewDecoder creates a Decoder given the runtime.Scheme.
-func NewDecoder(scheme *runtime.Scheme) *Decoder {
+// NewDecoder creates a decoder given the runtime.Scheme.
+func NewDecoder(scheme *runtime.Scheme) Decoder {
 	if scheme == nil {
 		panic("scheme should never be nil")
 	}
-	return &Decoder{codecs: serializer.NewCodecFactory(scheme)}
+	return &decoder{codecs: serializer.NewCodecFactory(scheme)}
 }
 
 // Decode decodes the inlined object in the AdmissionRequest into the passed-in runtime.Object.
 // If you want decode the OldObject in the AdmissionRequest, use DecodeRaw.
 // It errors out if req.Object.Raw is empty i.e. containing 0 raw bytes.
-func (d *Decoder) Decode(req Request, into runtime.Object) error {
+func (d *decoder) Decode(req Request, into runtime.Object) error {
 	// we error out if rawObj is an empty object.
 	if len(req.Object.Raw) == 0 {
 		return fmt.Errorf("there is no content to decode")
@@ -51,7 +64,7 @@ func (d *Decoder) Decode(req Request, into runtime.Object) error {
 
 // DecodeRaw decodes a RawExtension object into the passed-in runtime.Object.
 // It errors out if rawObj is empty i.e. containing 0 raw bytes.
-func (d *Decoder) DecodeRaw(rawObj runtime.RawExtension, into runtime.Object) error {
+func (d *decoder) DecodeRaw(rawObj runtime.RawExtension, into runtime.Object) error {
 	// NB(directxman12): there's a bug/weird interaction between decoders and
 	// the API server where the API server doesn't send a GVK on the embedded
 	// objects, which means the unstructured decoder refuses to decode.  It

pkg/webhook/admission/decode_test.go

@@ -29,7 +29,7 @@ import (
 )
 
 var _ = Describe("Admission Webhook Decoder", func() {
-	var decoder *Decoder
+	var decoder Decoder
 	BeforeEach(func() {
 		By("creating a new decoder for a scheme")
 		decoder = NewDecoder(scheme.Scheme)

pkg/webhook/admission/defaulter.go

@@ -43,7 +43,7 @@ func DefaultingWebhookFor(scheme *runtime.Scheme, defaulter Defaulter) *Webhook
 
 type mutatingHandler struct {
 	defaulter Defaulter
-	decoder   *Decoder
+	decoder   Decoder
 }
 
 // Handle handles admission requests.

pkg/webhook/admission/defaulter_custom.go

@@ -43,7 +43,7 @@ func WithCustomDefaulter(scheme *runtime.Scheme, obj runtime.Object, defaulter C
 type defaulterForType struct {
 	defaulter CustomDefaulter
 	object    runtime.Object
-	decoder   *Decoder
+	decoder   Decoder
 }
 
 // Handle handles admission requests.

pkg/webhook/admission/validator.go

@@ -63,7 +63,7 @@ func ValidatingWebhookFor(scheme *runtime.Scheme, validator Validator) *Webhook
 
 type validatingHandler struct {
 	validator Validator
-	decoder   *Decoder
+	decoder   Decoder
 }
 
 // Handle handles admission requests.

pkg/webhook/admission/validator_custom.go

@@ -56,7 +56,7 @@ func WithCustomValidator(scheme *runtime.Scheme, obj runtime.Object, validator C
 type validatorForType struct {
 	validator CustomValidator
 	object    runtime.Object
-	decoder   *Decoder
+	decoder   Decoder
 }
 
 // Handle handles admission requests.

pkg/webhook/webhook_integration_test.go

@@ -153,7 +153,7 @@ var _ = Describe("Webhook", func() {
 })
 
 type rejectingValidator struct {
-	d *admission.Decoder
+	d admission.Decoder
 }
 
 func (v *rejectingValidator) Handle(ctx context.Context, req admission.Request) admission.Response {