adds an admission plugin to the sample apiserver.

staging/src/k8s.io/sample-apiserver/pkg/admission/plugin/banflunder/BUILD

+package(default_visibility = ["//visibility:public"])
+
+licenses(["notice"])
+
+load(
+    "@io_bazel_rules_go//go:def.bzl",
+    "go_library",
+    "go_test",
+)
+
+go_library(
+    name = "go_default_library",
+    srcs = ["admission.go"],
+    tags = ["automanaged"],
+    deps = [
+        "//vendor/k8s.io/apimachinery/pkg/api/errors:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/labels:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/admission:go_default_library",
+        "//vendor/k8s.io/sample-apiserver/pkg/admission/wardleinitializer:go_default_library",
+        "//vendor/k8s.io/sample-apiserver/pkg/apis/wardle:go_default_library",
+        "//vendor/k8s.io/sample-apiserver/pkg/client/informers_generated/internalversion:go_default_library",
+        "//vendor/k8s.io/sample-apiserver/pkg/client/listers_generated/wardle/internalversion:go_default_library",
+    ],
+)
+
+go_test(
+    name = "go_default_xtest",
+    srcs = ["admission_test.go"],
+    tags = ["automanaged"],
+    deps = [
+        "//vendor/k8s.io/apimachinery/pkg/apis/meta/v1:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/runtime:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/runtime/schema:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/admission:go_default_library",
+        "//vendor/k8s.io/client-go/testing:go_default_library",
+        "//vendor/k8s.io/sample-apiserver/pkg/admission/plugin/banflunder:go_default_library",
+        "//vendor/k8s.io/sample-apiserver/pkg/admission/wardleinitializer:go_default_library",
+        "//vendor/k8s.io/sample-apiserver/pkg/apis/wardle:go_default_library",
+        "//vendor/k8s.io/sample-apiserver/pkg/client/clientset_generated/internalclientset/fake:go_default_library",
+        "//vendor/k8s.io/sample-apiserver/pkg/client/informers_generated/internalversion:go_default_library",
+    ],
+)

staging/src/k8s.io/sample-apiserver/pkg/admission/plugin/banflunder/admission.go

+/*
+Copyright 2017 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 banflunder
+
+import (
+	"fmt"
+
+	"k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/labels"
+	"k8s.io/apiserver/pkg/admission"
+	"k8s.io/sample-apiserver/pkg/admission/wardleinitializer"
+	"k8s.io/sample-apiserver/pkg/apis/wardle"
+	informers "k8s.io/sample-apiserver/pkg/client/informers_generated/internalversion"
+	listers "k8s.io/sample-apiserver/pkg/client/listers_generated/wardle/internalversion"
+)
+
+type disallowFlunder struct {
+	*admission.Handler
+	lister listers.FischerLister
+}
+
+var _ = wardleinitializer.WantsInternalWardleInformerFactory(&disallowFlunder{})
+
+// Admit ensures that the object in-flight is of kind Flunder.
+// In addition checks that the Name is not on the banned list.
+// The list is stored in Fischers API objects.
+func (d *disallowFlunder) Admit(a admission.Attributes) error {
+	// we are only interested in flunders
+	if a.GetKind().GroupKind() != wardle.Kind("Flunder") {
+		return nil
+	}
+
+	flunderName := a.GetName()
+	fischers, err := d.lister.List(labels.Everything())
+	if err != nil {
+		return err
+	}
+
+	for _, fischer := range fischers {
+		for _, disallowedFlunder := range fischer.DisallowedFlunders {
+			if flunderName == disallowedFlunder {
+				return errors.NewForbidden(
+					a.GetResource().GroupResource(),
+					a.GetName(),
+					fmt.Errorf("this name may not be used, please change the resource name"),
+				)
+			}
+		}
+	}
+	return nil
+}
+
+// SetInternalWardleInformerFactory gets Lister from SharedInformerFactory.
+// The lister knows how to lists Fischers.
+func (d *disallowFlunder) SetInternalWardleInformerFactory(f informers.SharedInformerFactory) {
+	d.lister = f.Wardle().InternalVersion().Fischers().Lister()
+}
+
+// Validate checks whether the plugin was correctly initialized.
+func (d *disallowFlunder) Validate() error {
+	if d.lister == nil {
+		return fmt.Errorf("missing fischer lister")
+	}
+	return nil
+}
+
+// New creates a new ban flunder admission plugin
+func New() (admission.Interface, error) {
+	return &disallowFlunder{}, nil
+}

staging/src/k8s.io/sample-apiserver/pkg/admission/plugin/banflunder/admission_test.go

+/*
+Copyright 2017 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 banflunder_test
+
+import (
+	"testing"
+	"time"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	"k8s.io/apiserver/pkg/admission"
+	clienttesting "k8s.io/client-go/testing"
+	"k8s.io/sample-apiserver/pkg/admission/plugin/banflunder"
+	"k8s.io/sample-apiserver/pkg/admission/wardleinitializer"
+	"k8s.io/sample-apiserver/pkg/apis/wardle"
+	"k8s.io/sample-apiserver/pkg/client/clientset_generated/internalclientset/fake"
+	informers "k8s.io/sample-apiserver/pkg/client/informers_generated/internalversion"
+)
+
+// TestBanfluderAdmissionPlugin tests various test cases against
+// ban flunder admission plugin
+func TestBanflunderAdmissionPlugin(t *testing.T) {
+	var scenarios = []struct {
+		informersOutput        wardle.FischerList
+		admissionInput         wardle.Flunder
+		admissionInputKind     schema.GroupVersionKind
+		admissionInputResource schema.GroupVersionResource
+		admissionMustFail      bool
+	}{
+		// scenario 1:
+		// a flunder with a name that appears on a list of disallowed flunders must be banned
+		{
+			informersOutput: wardle.FischerList{
+				Items: []wardle.Fischer{
+					{DisallowedFlunders: []string{"badname"}},
+				},
+			},
+			admissionInput: wardle.Flunder{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "badname",
+					Namespace: "",
+				},
+			},
+			admissionInputKind:     wardle.Kind("Flunder").WithVersion("version"),
+			admissionInputResource: wardle.Resource("flunders").WithVersion("version"),
+			admissionMustFail:      true,
+		},
+		// scenario 2:
+		// a flunder with a name that does not appear on a list of disallowed flunders must be admitted
+		{
+			informersOutput: wardle.FischerList{
+				Items: []wardle.Fischer{
+					{DisallowedFlunders: []string{"badname"}},
+				},
+			},
+			admissionInput: wardle.Flunder{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "goodname",
+					Namespace: "",
+				},
+			},
+			admissionInputKind:     wardle.Kind("Flunder").WithVersion("version"),
+			admissionInputResource: wardle.Resource("flunders").WithVersion("version"),
+			admissionMustFail:      false,
+		},
+		// scenario 3:
+		// a flunder with a name that appears on a list of disallowed flunders would be banned
+		// but the kind passed in is not a flunder thus the whole request is accepted
+		{
+			informersOutput: wardle.FischerList{
+				Items: []wardle.Fischer{
+					{DisallowedFlunders: []string{"badname"}},
+				},
+			},
+			admissionInput: wardle.Flunder{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      "badname",
+					Namespace: "",
+				},
+			},
+			admissionInputKind:     wardle.Kind("NotFlunder").WithVersion("version"),
+			admissionInputResource: wardle.Resource("notflunders").WithVersion("version"),
+			admissionMustFail:      false,
+		},
+	}
+
+	for index, scenario := range scenarios {
+		func() {
+			// prepare
+			cs := &fake.Clientset{}
+			cs.AddReactor("list", "fischers", func(action clienttesting.Action) (bool, runtime.Object, error) {
+				return true, &scenario.informersOutput, nil
+			})
+			informersFactory := informers.NewSharedInformerFactory(cs, 5*time.Minute)
+
+			target, err := banflunder.New()
+			if err != nil {
+				t.Fatalf("scenario %d: failed to create banflunder admission plugin due to = %v", index, err)
+			}
+
+			targetInitializer, err := wardleinitializer.New(informersFactory)
+			if err != nil {
+				t.Fatalf("scenario %d: failed to crate wardle plugin initializer due to = %v", index, err)
+			}
+			targetInitializer.Initialize(target)
+
+			err = admission.Validate(target)
+			if err != nil {
+				t.Fatalf("scenario %d: failed to initialize banflunder admission plugin due to =%v", index, err)
+			}
+
+			stop := make(chan struct{})
+			defer close(stop)
+			informersFactory.Start(stop)
+			informersFactory.WaitForCacheSync(stop)
+
+			// act
+			err = target.Admit(admission.NewAttributesRecord(
+				&scenario.admissionInput,
+				nil,
+				scenario.admissionInputKind,
+				scenario.admissionInput.ObjectMeta.Namespace,
+				scenario.admissionInput.ObjectMeta.Name,
+				scenario.admissionInputResource,
+				"",
+				admission.Create,
+				nil),
+			)
+
+			// validate
+			if scenario.admissionMustFail && err == nil {
+				t.Errorf("scenario %d: expected an error but got nothing", index)
+			}
+
+			if !scenario.admissionMustFail && err != nil {
+				t.Errorf("scenario %d: banflunder admission plugin returned unexpected error = %v", index, err)
+			}
+		}()
+	}
+}