✨ Add ClientWithWatch for use in CLIs

This change adds a new WithWatch interface and implementation to the
Client package. It is a superset of the existing Client interface that
additionally contains a Watch method. It is intended to be used by CLI
apps that need to wait for a condition to arise.

Because this is not intended to be used with controllers and might cause
confusion there, the existing interface and all references to it are
kept as-is.

pkg/client/client.go

@@ -53,6 +53,10 @@ type Options struct {
 // case of unstructured types, the group, version, and kind will be extracted
 // from the corresponding fields on the object.
 func New(config *rest.Config, options Options) (Client, error) {
+	return newClient(config, options)
+}
+
+func newClient(config *rest.Config, options Options) (*client, error) {
 	if config == nil {
 		return nil, fmt.Errorf("must provide non-nil rest.Config to client.New")
 	}

pkg/client/interfaces.go

@@ -24,6 +24,7 @@ import (
 	"k8s.io/apimachinery/pkg/api/meta"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/apimachinery/pkg/watch"
 )
 
 // ObjectKey identifies a Kubernetes Object.
@@ -108,6 +109,14 @@ type Client interface {
 	RESTMapper() meta.RESTMapper
 }
 
+// WithWatch supports Watch on top of the CRUD operations supported by
+// the normal Client. Its intended use-case are CLI apps that need to wait for
+// events.
+type WithWatch interface {
+	Client
+	Watch(ctx context.Context, obj ObjectList, opts ...ListOption) (watch.Interface, error)
+}
+
 // IndexerFunc knows how to take an object and turn it into a series
 // of non-namespaced keys. Namespaced objects are automatically given
 // namespaced and non-spaced variants, so keys do not need to include namespace.

pkg/client/watch.go

@@ -0,0 +1,118 @@
+/*
+Copyright 2020 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 client
+
+import (
+	"context"
+	"strings"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+	"k8s.io/apimachinery/pkg/watch"
+	"k8s.io/client-go/dynamic"
+	"k8s.io/client-go/rest"
+)
+
+// NewWithWatch returns a new WithWatch.
+func NewWithWatch(config *rest.Config, options Options) (WithWatch, error) {
+	client, err := newClient(config, options)
+	if err != nil {
+		return nil, err
+	}
+	dynamicClient, err := dynamic.NewForConfig(config)
+	if err != nil {
+		return nil, err
+	}
+	return &watchingClient{client: client, dynamic: dynamicClient}, nil
+}
+
+type watchingClient struct {
+	*client
+	dynamic dynamic.Interface
+}
+
+func (w *watchingClient) Watch(ctx context.Context, list ObjectList, opts ...ListOption) (watch.Interface, error) {
+	switch l := list.(type) {
+	case *unstructured.UnstructuredList:
+		return w.unstructuredWatch(ctx, l, opts...)
+	case *metav1.PartialObjectMetadataList:
+		return w.metadataWatch(ctx, l, opts...)
+	default:
+		return w.typedWatch(ctx, l, opts...)
+	}
+}
+
+func (w *watchingClient) listOpts(opts ...ListOption) ListOptions {
+	listOpts := ListOptions{}
+	listOpts.ApplyOptions(opts)
+	if listOpts.Raw == nil {
+		listOpts.Raw = &metav1.ListOptions{}
+	}
+	listOpts.Raw.Watch = true
+
+	return listOpts
+}
+
+func (w *watchingClient) metadataWatch(ctx context.Context, obj *metav1.PartialObjectMetadataList, opts ...ListOption) (watch.Interface, error) {
+	gvk := obj.GroupVersionKind()
+	if strings.HasSuffix(gvk.Kind, "List") {
+		gvk.Kind = gvk.Kind[:len(gvk.Kind)-4]
+	}
+
+	listOpts := w.listOpts(opts...)
+
+	resInt, err := w.client.metadataClient.getResourceInterface(gvk, listOpts.Namespace)
+	if err != nil {
+		return nil, err
+	}
+
+	return resInt.Watch(ctx, *listOpts.AsListOptions())
+}
+
+func (w *watchingClient) unstructuredWatch(ctx context.Context, obj *unstructured.UnstructuredList, opts ...ListOption) (watch.Interface, error) {
+	gvk := obj.GroupVersionKind()
+	if strings.HasSuffix(gvk.Kind, "List") {
+		gvk.Kind = gvk.Kind[:len(gvk.Kind)-4]
+	}
+
+	r, err := w.client.unstructuredClient.cache.getResource(obj)
+	if err != nil {
+		return nil, err
+	}
+
+	listOpts := w.listOpts(opts...)
+
+	if listOpts.Namespace != "" && r.isNamespaced() {
+		return w.dynamic.Resource(r.mapping.Resource).Namespace(listOpts.Namespace).Watch(ctx, *listOpts.AsListOptions())
+	}
+	return w.dynamic.Resource(r.mapping.Resource).Watch(ctx, *listOpts.AsListOptions())
+}
+
+func (w *watchingClient) typedWatch(ctx context.Context, obj ObjectList, opts ...ListOption) (watch.Interface, error) {
+	r, err := w.client.typedClient.cache.getResource(obj)
+	if err != nil {
+		return nil, err
+	}
+
+	listOpts := w.listOpts(opts...)
+
+	return r.Get().
+		NamespaceIfScoped(listOpts.Namespace, r.isNamespaced()).
+		Resource(r.resource()).
+		VersionedParams(listOpts.AsListOptions(), w.client.typedClient.paramCodec).
+		Watch(ctx)
+}

pkg/client/watch_test.go

@@ -0,0 +1,131 @@
+/*
+Copyright 2020 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 client_test
+
+import (
+	"context"
+	"fmt"
+	"sync/atomic"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+	appsv1 "k8s.io/api/apps/v1"
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+	"k8s.io/apimachinery/pkg/fields"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	"k8s.io/apimachinery/pkg/watch"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+)
+
+var _ = Describe("ClientWithWatch", func() {
+	var dep *appsv1.Deployment
+	var count uint64 = 0
+	var replicaCount int32 = 2
+	var ns = "kube-public"
+	ctx := context.TODO()
+
+	BeforeEach(func(done Done) {
+		atomic.AddUint64(&count, 1)
+		dep = &appsv1.Deployment{
+			ObjectMeta: metav1.ObjectMeta{Name: fmt.Sprintf("watch-deployment-name-%v", count), Namespace: ns, Labels: map[string]string{"app": fmt.Sprintf("bar-%v", count)}},
+			Spec: appsv1.DeploymentSpec{
+				Replicas: &replicaCount,
+				Selector: &metav1.LabelSelector{
+					MatchLabels: map[string]string{"foo": "bar"},
+				},
+				Template: corev1.PodTemplateSpec{
+					ObjectMeta: metav1.ObjectMeta{Labels: map[string]string{"foo": "bar"}},
+					Spec:       corev1.PodSpec{Containers: []corev1.Container{{Name: "nginx", Image: "nginx"}}},
+				},
+			},
+		}
+
+		var err error
+		dep, err = clientset.AppsV1().Deployments(ns).Create(ctx, dep, metav1.CreateOptions{})
+		Expect(err).NotTo(HaveOccurred())
+		close(done)
+	}, serverSideTimeoutSeconds)
+
+	AfterEach(func(done Done) {
+		deleteDeployment(ctx, dep, ns)
+		close(done)
+	}, serverSideTimeoutSeconds)
+
+	Describe("NewWithWatch", func() {
+		It("should return a new Client", func(done Done) {
+			cl, err := client.NewWithWatch(cfg, client.Options{})
+			Expect(err).NotTo(HaveOccurred())
+			Expect(cl).NotTo(BeNil())
+
+			close(done)
+		})
+
+		watchSuite := func(through client.ObjectList, expectedType client.Object) {
+			cl, err := client.NewWithWatch(cfg, client.Options{})
+			Expect(err).NotTo(HaveOccurred())
+			Expect(cl).NotTo(BeNil())
+
+			watchInterface, err := cl.Watch(ctx, through, &client.ListOptions{
+				FieldSelector: fields.OneTermEqualSelector("metadata.name", dep.Name),
+				Namespace:     dep.Namespace,
+			})
+			Expect(err).NotTo(HaveOccurred())
+			Expect(watchInterface).NotTo(BeNil())
+
+			defer watchInterface.Stop()
+
+			event, ok := <-watchInterface.ResultChan()
+			Expect(ok).To(BeTrue())
+			Expect(event.Type).To(BeIdenticalTo(watch.Added))
+			Expect(event.Object).To(BeAssignableToTypeOf(expectedType))
+
+			// The metadata client doesn't set GVK so we just use the
+			// name and UID as a proxy to confirm that we got the right
+			// object.
+			metaObject, ok := event.Object.(metav1.Object)
+			Expect(ok).To(BeTrue())
+			Expect(metaObject.GetName()).To(Equal(dep.Name))
+			Expect(metaObject.GetUID()).To(Equal(dep.UID))
+
+		}
+
+		It("should receive a create event when watching the typed object", func(done Done) {
+			watchSuite(&appsv1.DeploymentList{}, &appsv1.Deployment{})
+			close(done)
+		}, 15)
+
+		It("should receive a create event when watching the unstructured object", func(done Done) {
+			u := &unstructured.UnstructuredList{}
+			u.SetGroupVersionKind(schema.GroupVersionKind{
+				Group:   "apps",
+				Kind:    "Deployment",
+				Version: "v1",
+			})
+			watchSuite(u, &unstructured.Unstructured{})
+			close(done)
+		}, 15)
+
+		It("should receive a create event when watching the metadata object", func(done Done) {
+			m := &metav1.PartialObjectMetadataList{TypeMeta: metav1.TypeMeta{Kind: "Deployment", APIVersion: "apps/v1"}}
+			watchSuite(m, &metav1.PartialObjectMetadata{})
+			close(done)
+		}, 15)
+	})
+
+})