✨ Allow webhooks to register custom validators/defaulter types

This changeset allows our webhook builder to take in a handler any other
struct other than a runtime.Object.

Today having an object as the primary source of truth for both
Defaulting and Validators makes API types carry a lot of information and
business logic alongside their definitions.

Moreover, lots of folks in the past have asked for ways to have an
external type to handle these operations and use a controller runtime
client for validations.

This change brings a new way to register webhooks, which admission.For
handler any type (struct) can be a defaulting or validating handler for
a runtime Object.

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

Author: vincepri

pkg/builder/webhook.go

@@ -17,6 +17,7 @@ limitations under the License.
 package builder
 
 import (
+	"errors"
 	"net/http"
 	"net/url"
 	"strings"
@@ -33,6 +34,7 @@ import (
 // WebhookBuilder builds a Webhook.
 type WebhookBuilder struct {
 	apiType runtime.Object
+	forType admission.For
 	gvk     schema.GroupVersionKind
 	mgr     manager.Manager
 	config  *rest.Config
@@ -53,6 +55,15 @@ func (blder *WebhookBuilder) For(apiType runtime.Object) *WebhookBuilder {
 	return blder
 }
 
+// HandlerFor takes a admission.admissionFor interface.
+//
+// If the given object implements the admission.DefaulterFor interface, a MutatingWebhook will be wired for this type.
+// If the given object implements the admission.ValidatorFor interface, a ValidatingWebhook will be wired for this type.
+func (blder *WebhookBuilder) HandlerFor(forType admission.For) *WebhookBuilder {
+	blder.forType = forType
+	return blder
+}
+
 // Complete builds the webhook.
 func (blder *WebhookBuilder) Complete() error {
 	// Set the Config
@@ -69,9 +80,13 @@ func (blder *WebhookBuilder) loadRestConfig() {
 }
 
 func (blder *WebhookBuilder) registerWebhooks() error {
+	typ, err := blder.getType()
+	if err != nil {
+		return err
+	}
+
 	// Create webhook(s) for each type
-	var err error
-	blder.gvk, err = apiutil.GVKForObject(blder.apiType, blder.mgr.GetScheme())
+	blder.gvk, err = apiutil.GVKForObject(typ, blder.mgr.GetScheme())
 	if err != nil {
 		return err
 	}
@@ -88,12 +103,7 @@ func (blder *WebhookBuilder) registerWebhooks() error {
 
 // registerDefaultingWebhook registers a defaulting webhook if th.
 func (blder *WebhookBuilder) registerDefaultingWebhook() {
-	defaulter, isDefaulter := blder.apiType.(admission.Defaulter)
-	if !isDefaulter {
-		log.Info("skip registering a mutating webhook, admission.Defaulter interface is not implemented", "GVK", blder.gvk)
-		return
-	}
-	mwh := admission.DefaultingWebhookFor(defaulter)
+	mwh := blder.getDefaultingWebhook()
 	if mwh != nil {
 		path := generateMutatePath(blder.gvk)
 
@@ -108,10 +118,22 @@ func (blder *WebhookBuilder) registerDefaultingWebhook() {
 	}
 }
 
+func (blder *WebhookBuilder) getDefaultingWebhook() *admission.Webhook {
+	if defaulter, ok := blder.apiType.(admission.Defaulter); ok {
+		return admission.DefaultingWebhookFor(defaulter)
+	}
+	if defaulter, ok := blder.forType.(admission.DefaulterFor); ok {
+		return admission.DefaulterForToWebhook(defaulter)
+	}
+	log.Info(
+		"skip registering a mutating webhook, admission.Defaulter or admission.DefaulterFor interface is not implemented",
+		"GVK", blder.gvk)
+	return nil
+}
+
 func (blder *WebhookBuilder) registerValidatingWebhook() {
 	validator, isValidator := blder.apiType.(admission.Validator)
 	if !isValidator {
-		log.Info("skip registering a validating webhook, admission.Validator interface is not implemented", "GVK", blder.gvk)
 		return
 	}
 	vwh := admission.ValidatingWebhookFor(validator)
@@ -129,6 +151,19 @@ func (blder *WebhookBuilder) registerValidatingWebhook() {
 	}
 }
 
+func (blder *WebhookBuilder) getValidatingWebhook() *admission.Webhook {
+	if validator, ok := blder.apiType.(admission.Validator); ok {
+		return admission.ValidatingWebhookFor(validator)
+	}
+	if validator, ok := blder.forType.(admission.ValidatorFor); ok {
+		return admission.ValidatorForToWebhook(validator)
+	}
+	log.Info(
+		"skip registering a validating webhook, admission.Validator or admission.ValidatorFor interface is not implemented",
+		"GVK", blder.gvk)
+	return nil
+}
+
 func (blder *WebhookBuilder) registerConversionWebhook() error {
 	ok, err := conversion.IsConvertible(blder.mgr.GetScheme(), blder.apiType)
 	if err != nil {
@@ -145,6 +180,16 @@ func (blder *WebhookBuilder) registerConversionWebhook() error {
 	return nil
 }
 
+func (blder *WebhookBuilder) getType() (runtime.Object, error) {
+	if blder.apiType != nil {
+		return blder.apiType, nil
+	}
+	if blder.forType != nil {
+		return blder.forType.For(), nil
+	}
+	return nil, errors.New("one of For() or HandlerFor() should be called")
+}
+
 func (blder *WebhookBuilder) isAlreadyHandled(path string) bool {
 	if blder.mgr.GetWebhookServer().WebhookMux == nil {
 		return false

pkg/webhook/admission/admission_for.go

@@ -0,0 +1,8 @@
+package admission
+
+import "k8s.io/apimachinery/pkg/runtime"
+
+// For registers a type as an admission handler.
+type For interface {
+	For() runtime.Object
+}

pkg/webhook/admission/defaulter_handler.go

@@ -0,0 +1,74 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package admission
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+
+	"k8s.io/apimachinery/pkg/runtime"
+)
+
+// DefaulterFor defines functions for setting defaults on resources.
+type DefaulterFor interface {
+	For
+	Default(ctx context.Context, obj runtime.Object)
+}
+
+// DefaulterForToWebhook creates a new Webhook for a DefaulterFor interface.
+func DefaulterForToWebhook(defaulter DefaulterFor) *Webhook {
+	return &Webhook{
+		Handler: &defaulterForType{handler: defaulter},
+	}
+}
+
+type defaulterForType struct {
+	handler DefaulterFor
+	decoder *Decoder
+	scheme  *runtime.Scheme
+}
+
+var _ DecoderInjector = &defaulterForType{}
+
+func (h *defaulterForType) InjectDecoder(d *Decoder) error {
+	h.decoder = d
+	return nil
+}
+
+// Handle handles admission requests.
+func (h *defaulterForType) Handle(ctx context.Context, req Request) Response {
+	if h.handler == nil {
+		panic("defaulter should never be nil")
+	}
+
+	// Get the object in the request
+	obj := h.handler.For().DeepCopyObject()
+	if err := h.decoder.Decode(req, obj); err != nil {
+		return Errored(http.StatusBadRequest, err)
+	}
+
+	// Default the object
+	h.handler.Default(ctx, obj)
+	marshalled, err := json.Marshal(obj)
+	if err != nil {
+		return Errored(http.StatusInternalServerError, err)
+	}
+
+	// Create the patch
+	return PatchResponseFromRaw(req.Object.Raw, marshalled)
+}

pkg/webhook/admission/validator_handler.go

@@ -0,0 +1,122 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package admission
+
+import (
+	"context"
+	goerrors "errors"
+	"net/http"
+
+	v1 "k8s.io/api/admission/v1"
+	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/runtime"
+)
+
+// Validator defines functions for validating an operation.
+type ValidatorFor interface {
+	For
+	ValidateCreate(ctx context.Context, obj runtime.Object) error
+	ValidateUpdate(ctx context.Context, old runtime.Object, new runtime.Object) error
+	ValidateDelete(ctx context.Context, obj runtime.Object) error
+}
+
+// ValidatingWebhookFor creates a new Webhook for validating the provided type.
+func ValidatorForToWebhook(validator ValidatorFor) *Webhook {
+	return &Webhook{
+		Handler: &validatorForType{handler: validator},
+	}
+}
+
+type validatorForType struct {
+	handler ValidatorFor
+	decoder *Decoder
+}
+
+var _ DecoderInjector = &validatorForType{}
+
+// InjectDecoder injects the decoder into a validatingHandler.
+func (h *validatorForType) InjectDecoder(d *Decoder) error {
+	h.decoder = d
+	return nil
+}
+
+// Handle handles admission requests.
+func (h *validatorForType) Handle(ctx context.Context, req Request) Response {
+	if h.handler == nil {
+		panic("handler should never be nil")
+	}
+
+	// Get the object in the request
+	obj := h.handler.For().DeepCopyObject()
+	if req.Operation == v1.Create {
+		err := h.decoder.Decode(req, obj)
+		if err != nil {
+			return Errored(http.StatusBadRequest, err)
+		}
+
+		err = h.handler.ValidateCreate(ctx, obj)
+		if err != nil {
+			var apiStatus apierrors.APIStatus
+			if goerrors.As(err, &apiStatus) {
+				return validationResponseFromStatus(false, apiStatus.Status())
+			}
+			return Denied(err.Error())
+		}
+	}
+
+	if req.Operation == v1.Update {
+		oldObj := obj.DeepCopyObject()
+
+		err := h.decoder.DecodeRaw(req.Object, obj)
+		if err != nil {
+			return Errored(http.StatusBadRequest, err)
+		}
+		err = h.decoder.DecodeRaw(req.OldObject, oldObj)
+		if err != nil {
+			return Errored(http.StatusBadRequest, err)
+		}
+
+		err = h.handler.ValidateUpdate(ctx, oldObj, obj)
+		if err != nil {
+			var apiStatus apierrors.APIStatus
+			if goerrors.As(err, &apiStatus) {
+				return validationResponseFromStatus(false, apiStatus.Status())
+			}
+			return Denied(err.Error())
+		}
+	}
+
+	if req.Operation == v1.Delete {
+		// In reference to PR: https://github.com/kubernetes/kubernetes/pull/76346
+		// OldObject contains the object being deleted
+		err := h.decoder.DecodeRaw(req.OldObject, obj)
+		if err != nil {
+			return Errored(http.StatusBadRequest, err)
+		}
+
+		err = h.handler.ValidateDelete(ctx, obj)
+		if err != nil {
+			var apiStatus apierrors.APIStatus
+			if goerrors.As(err, &apiStatus) {
+				return validationResponseFromStatus(false, apiStatus.Status())
+			}
+			return Denied(err.Error())
+		}
+	}
+
+	return Allowed("")
+}