sparkles: 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 <vincepri@vmware.com>

Author: vincepri

pkg/builder/webhook.go

@@ -17,6 +17,7 @@ limitations under the License.
 package builder
 
 import (
+	"errors"
 	"net/http"
 	"net/url"
 	"strings"
@@ -32,10 +33,12 @@ import (
 
 // WebhookBuilder builds a Webhook.
 type WebhookBuilder struct {
-	apiType runtime.Object
-	gvk     schema.GroupVersionKind
-	mgr     manager.Manager
-	config  *rest.Config
+	apiType       runtime.Object
+	withDefaulter admission.CustomDefaulter
+	withValidator admission.CustomValidator
+	gvk           schema.GroupVersionKind
+	mgr           manager.Manager
+	config        *rest.Config
 }
 
 // WebhookManagedBy allows inform its manager.Manager.
@@ -53,6 +56,18 @@ func (blder *WebhookBuilder) For(apiType runtime.Object) *WebhookBuilder {
 	return blder
 }
 
+// WithDefaulter takes a admission.WithDefaulter interface, a MutatingWebhook will be wired for this type.
+func (blder *WebhookBuilder) WithDefaulter(defaulter admission.CustomDefaulter) *WebhookBuilder {
+	blder.withDefaulter = defaulter
+	return blder
+}
+
+// WithValidator takes a admission.WithValidator interface, a ValidatingWebhook will be wired for this type.
+func (blder *WebhookBuilder) WithValidator(validator admission.CustomValidator) *WebhookBuilder {
+	blder.withValidator = validator
+	return blder
+}
+
 // Complete builds the webhook.
 func (blder *WebhookBuilder) Complete() error {
 	// Set the Config
@@ -69,9 +84,13 @@ 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 +107,7 @@ 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)
 
@@ -108,13 +122,21 @@ func (blder *WebhookBuilder) registerDefaultingWebhook() {
 	}
 }
 
-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
+func (blder *WebhookBuilder) getDefaultingWebhook() *admission.Webhook {
+	if defaulter := blder.withDefaulter; defaulter != nil {
+		return admission.WithCustomDefaulter(blder.apiType, defaulter)
+	}
+	if defaulter, ok := blder.apiType.(admission.Defaulter); ok {
+		return admission.DefaultingWebhookFor(defaulter)
 	}
-	vwh := admission.ValidatingWebhookFor(validator)
+	log.Info(
+		"skip registering a mutating webhook, object does not implement admission.Defaulter or WithDefaulter wasn't called",
+		"GVK", blder.gvk)
+	return nil
+}
+
+func (blder *WebhookBuilder) registerValidatingWebhook() {
+	vwh := blder.getValidatingWebhook()
 	if vwh != nil {
 		path := generateValidatePath(blder.gvk)
 
@@ -129,6 +151,19 @@ func (blder *WebhookBuilder) registerValidatingWebhook() {
 	}
 }
 
+func (blder *WebhookBuilder) getValidatingWebhook() *admission.Webhook {
+	if validator := blder.withValidator; validator != nil {
+		return admission.WithCustomValidator(blder.apiType, validator)
+	}
+	if validator, ok := blder.apiType.(admission.Validator); ok {
+		return admission.ValidatingWebhookFor(validator)
+	}
+	log.Info(
+		"skip registering a validating webhook, object does not implement admission.Validator or WithValidator wasn't called",
+		"GVK", blder.gvk)
+	return nil
+}
+
 func (blder *WebhookBuilder) registerConversionWebhook() error {
 	ok, err := conversion.IsConvertible(blder.mgr.GetScheme(), blder.apiType)
 	if err != nil {
@@ -145,6 +180,13 @@ func (blder *WebhookBuilder) registerConversionWebhook() error {
 	return nil
 }
 
+func (blder *WebhookBuilder) getType() (runtime.Object, error) {
+	if blder.apiType != nil {
+		return blder.apiType, nil
+	}
+	return nil, errors.New("For() must be called with a valid object")
+}
+
 func (blder *WebhookBuilder) isAlreadyHandled(path string) bool {
 	if blder.mgr.GetWebhookServer().WebhookMux == nil {
 		return false

pkg/builder/webhook_test.go

@@ -134,6 +134,81 @@ func runTests(admissionReviewVersion string) {
 		ExpectWithOffset(1, w.Code).To(Equal(http.StatusNotFound))
 	})
 
+	It("should scaffold a defaulting webhook with a custom defaulter", func() {
+		By("creating a controller manager")
+		m, err := manager.New(cfg, manager.Options{})
+		ExpectWithOffset(1, err).NotTo(HaveOccurred())
+
+		By("registering the type in the Scheme")
+		builder := scheme.Builder{GroupVersion: testDefaulterGVK.GroupVersion()}
+		builder.Register(&TestDefaulter{}, &TestDefaulterList{})
+		err = builder.AddToScheme(m.GetScheme())
+		ExpectWithOffset(1, err).NotTo(HaveOccurred())
+
+		err = WebhookManagedBy(m).
+			WithDefaulter(&TestCustomDefaulter{}).
+			For(&TestDefaulter{}).
+			Complete()
+		ExpectWithOffset(1, err).NotTo(HaveOccurred())
+		svr := m.GetWebhookServer()
+		ExpectWithOffset(1, svr).NotTo(BeNil())
+
+		reader := strings.NewReader(`{
+  "kind":"AdmissionReview",
+  "apiVersion":"admission.k8s.io/` + admissionReviewVersion + `",
+  "request":{
+    "uid":"07e52e8d-4513-11e9-a716-42010a800270",
+    "kind":{
+      "group":"",
+      "version":"v1",
+      "kind":"TestDefaulter"
+    },
+    "resource":{
+      "group":"",
+      "version":"v1",
+      "resource":"testdefaulter"
+    },
+    "namespace":"default",
+    "operation":"CREATE",
+    "object":{
+      "replica":1
+    },
+    "oldObject":null
+  }
+}`)
+
+		ctx, cancel := context.WithCancel(context.Background())
+		cancel()
+		// TODO: we may want to improve it to make it be able to inject dependencies,
+		// but not always try to load certs and return not found error.
+		err = svr.Start(ctx)
+		if err != nil && !os.IsNotExist(err) {
+			ExpectWithOffset(1, err).NotTo(HaveOccurred())
+		}
+
+		By("sending a request to a mutating webhook path")
+		path := generateMutatePath(testDefaulterGVK)
+		req := httptest.NewRequest("POST", "http://svc-name.svc-ns.svc"+path, reader)
+		req.Header.Add("Content-Type", "application/json")
+		w := httptest.NewRecorder()
+		svr.WebhookMux.ServeHTTP(w, req)
+		ExpectWithOffset(1, w.Code).To(Equal(http.StatusOK))
+		By("sanity checking the response contains reasonable fields")
+		ExpectWithOffset(1, w.Body).To(ContainSubstring(`"allowed":true`))
+		ExpectWithOffset(1, w.Body).To(ContainSubstring(`"patch":`))
+		ExpectWithOffset(1, w.Body).To(ContainSubstring(`"code":200`))
+
+		By("sending a request to a validating webhook path that doesn't exist")
+		path = generateValidatePath(testDefaulterGVK)
+		_, err = reader.Seek(0, 0)
+		ExpectWithOffset(1, err).NotTo(HaveOccurred())
+		req = httptest.NewRequest("POST", "http://svc-name.svc-ns.svc"+path, reader)
+		req.Header.Add("Content-Type", "application/json")
+		w = httptest.NewRecorder()
+		svr.WebhookMux.ServeHTTP(w, req)
+		ExpectWithOffset(1, w.Code).To(Equal(http.StatusNotFound))
+	})
+
 	It("should scaffold a validating webhook if the type implements the Validator interface", func() {
 		By("creating a controller manager")
 		m, err := manager.New(cfg, manager.Options{})
@@ -209,6 +284,82 @@ func runTests(admissionReviewVersion string) {
 		ExpectWithOffset(1, w.Body).To(ContainSubstring(`"code":403`))
 	})
 
+	It("should scaffold a validating webhook with a custom validator", func() {
+		By("creating a controller manager")
+		m, err := manager.New(cfg, manager.Options{})
+		ExpectWithOffset(1, err).NotTo(HaveOccurred())
+
+		By("registering the type in the Scheme")
+		builder := scheme.Builder{GroupVersion: testValidatorGVK.GroupVersion()}
+		builder.Register(&TestValidator{}, &TestValidatorList{})
+		err = builder.AddToScheme(m.GetScheme())
+		ExpectWithOffset(1, err).NotTo(HaveOccurred())
+
+		err = WebhookManagedBy(m).
+			WithValidator(&TestCustomValidator{}).
+			For(&TestValidator{}).
+			Complete()
+		ExpectWithOffset(1, err).NotTo(HaveOccurred())
+		svr := m.GetWebhookServer()
+		ExpectWithOffset(1, svr).NotTo(BeNil())
+
+		reader := strings.NewReader(`{
+  "kind":"AdmissionReview",
+  "apiVersion":"admission.k8s.io/` + admissionReviewVersion + `",
+  "request":{
+    "uid":"07e52e8d-4513-11e9-a716-42010a800270",
+    "kind":{
+      "group":"",
+      "version":"v1",
+      "kind":"TestValidator"
+    },
+    "resource":{
+      "group":"",
+      "version":"v1",
+      "resource":"testvalidator"
+    },
+    "namespace":"default",
+    "operation":"UPDATE",
+    "object":{
+      "replica":1
+    },
+    "oldObject":{
+      "replica":2
+    }
+  }
+}`)
+
+		ctx, cancel := context.WithCancel(context.Background())
+		cancel()
+		// TODO: we may want to improve it to make it be able to inject dependencies,
+		// but not always try to load certs and return not found error.
+		err = svr.Start(ctx)
+		if err != nil && !os.IsNotExist(err) {
+			ExpectWithOffset(1, err).NotTo(HaveOccurred())
+		}
+
+		By("sending a request to a mutating webhook path that doesn't exist")
+		path := generateMutatePath(testValidatorGVK)
+		req := httptest.NewRequest("POST", "http://svc-name.svc-ns.svc"+path, reader)
+		req.Header.Add("Content-Type", "application/json")
+		w := httptest.NewRecorder()
+		svr.WebhookMux.ServeHTTP(w, req)
+		ExpectWithOffset(1, w.Code).To(Equal(http.StatusNotFound))
+
+		By("sending a request to a validating webhook path")
+		path = generateValidatePath(testValidatorGVK)
+		_, err = reader.Seek(0, 0)
+		ExpectWithOffset(1, err).NotTo(HaveOccurred())
+		req = httptest.NewRequest("POST", "http://svc-name.svc-ns.svc"+path, reader)
+		req.Header.Add("Content-Type", "application/json")
+		w = httptest.NewRecorder()
+		svr.WebhookMux.ServeHTTP(w, req)
+		ExpectWithOffset(1, w.Code).To(Equal(http.StatusOK))
+		By("sanity checking the response contains reasonable field")
+		ExpectWithOffset(1, w.Body).To(ContainSubstring(`"allowed":false`))
+		ExpectWithOffset(1, w.Body).To(ContainSubstring(`"code":403`))
+	})
+
 	It("should scaffold defaulting and validating webhooks if the type implements both Defaulter and Validator interfaces", func() {
 		By("creating a controller manager")
 		m, err := manager.New(cfg, manager.Options{})
@@ -537,3 +688,51 @@ func (dv *TestDefaultValidator) ValidateDelete() error {
 	}
 	return nil
 }
+
+// TestCustomDefaulter.
+
+type TestCustomDefaulter struct{}
+
+func (*TestCustomDefaulter) Default(ctx context.Context, obj runtime.Object) error {
+	d := obj.(*TestDefaulter) //nolint:ifshort
+	if d.Replica < 2 {
+		d.Replica = 2
+	}
+	return nil
+}
+
+var _ admission.CustomDefaulter = &TestCustomDefaulter{}
+
+// TestCustomValidator.
+
+type TestCustomValidator struct{}
+
+func (*TestCustomValidator) ValidateCreate(ctx context.Context, obj runtime.Object) error {
+	v := obj.(*TestValidator) //nolint:ifshort
+	if v.Replica < 0 {
+		return errors.New("number of replica should be greater than or equal to 0")
+	}
+	return nil
+}
+
+func (*TestCustomValidator) ValidateUpdate(ctx context.Context, oldObj, newObj runtime.Object) error {
+	v := newObj.(*TestValidator)
+	old := oldObj.(*TestValidator) //nolint:ifshort
+	if v.Replica < 0 {
+		return errors.New("number of replica should be greater than or equal to 0")
+	}
+	if v.Replica < old.Replica {
+		return fmt.Errorf("new replica %v should not be fewer than old replica %v", v.Replica, old.Replica)
+	}
+	return nil
+}
+
+func (*TestCustomValidator) ValidateDelete(ctx context.Context, obj runtime.Object) error {
+	v := obj.(*TestValidator) //nolint:ifshort
+	if v.Replica > 0 {
+		return errors.New("number of replica should be less than or equal to 0 to delete")
+	}
+	return nil
+}
+
+var _ admission.CustomValidator = &TestCustomValidator{}