✨ Add namespace enforcing wrapper for client.Client (#1088)

* This commit adds a namespace enforcing wrapper for client.Client.
This helps while dealing with namespace-scoped objects, where the
namespace value need not be specified in every operation.

* Modify namespaced client to use RestMapper for finding the scope of object.

* Address review comments

pkg/client/namespaced_client.go

@@ -0,0 +1,253 @@
+/*
+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"
+	"errors"
+	"fmt"
+
+	"k8s.io/apimachinery/pkg/api/meta"
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	"sigs.k8s.io/controller-runtime/pkg/client/apiutil"
+)
+
+// NewNamespacedClient wraps an existing client enforcing the namespace value.
+// All functions using this client will have the same namespace declared here.
+func NewNamespacedClient(c Client, ns string) Client {
+	return &namespacedClient{
+		client:    c,
+		namespace: ns,
+	}
+}
+
+var _ Client = &namespacedClient{}
+
+// namespacedClient is a Client that wraps another Client in order to enforce the specified namespace value.
+type namespacedClient struct {
+	namespace string
+	client    Client
+}
+
+// Scheme returns the scheme this client is using.
+func (n *namespacedClient) Scheme() *runtime.Scheme {
+	return n.client.Scheme()
+}
+
+// RESTMapper returns the scheme this client is using.
+func (n *namespacedClient) RESTMapper() meta.RESTMapper {
+	return n.client.RESTMapper()
+}
+
+// isNamespaced returns true if the object is namespace scoped.
+// For unstructured objects the gvk is found from the object itself.
+func isNamespaced(c Client, obj runtime.Object) (bool, error) {
+	var gvk schema.GroupVersionKind
+	var err error
+
+	_, isUnstructured := obj.(*unstructured.Unstructured)
+	_, isUnstructuredList := obj.(*unstructured.UnstructuredList)
+
+	isUnstructured = isUnstructured || isUnstructuredList
+	if isUnstructured {
+		gvk = obj.GetObjectKind().GroupVersionKind()
+	} else {
+		gvk, err = apiutil.GVKForObject(obj, c.Scheme())
+		if err != nil {
+			return false, err
+		}
+	}
+
+	gk := schema.GroupKind{
+		Group: gvk.Group,
+		Kind:  gvk.Kind,
+	}
+	restmapping, err := c.RESTMapper().RESTMapping(gk)
+	if err != nil {
+		return false, fmt.Errorf("failed to get restmapping: %w", err)
+	}
+	scope := restmapping.Scope.Name()
+
+	if scope == "" {
+		return false, errors.New("Scope cannot be identified. Empty scope returned")
+	}
+
+	if scope != meta.RESTScopeNameRoot {
+		return true, nil
+	}
+	return false, nil
+}
+
+// Create implements clinet.Client
+func (n *namespacedClient) Create(ctx context.Context, obj Object, opts ...CreateOption) error {
+	isNamespaceScoped, err := isNamespaced(n.client, obj)
+	if err != nil {
+		return fmt.Errorf("error finding the scope of the object: %v", err)
+	}
+
+	objectNamespace := obj.GetNamespace()
+	if objectNamespace != n.namespace && objectNamespace != "" {
+		return fmt.Errorf("Namespace %s of the object %s does not match the namespace %s on the client", objectNamespace, obj.GetName(), n.namespace)
+	}
+
+	if isNamespaceScoped && objectNamespace == "" {
+		obj.SetNamespace(n.namespace)
+	}
+	return n.client.Create(ctx, obj, opts...)
+}
+
+// Update implements client.Client
+func (n *namespacedClient) Update(ctx context.Context, obj Object, opts ...UpdateOption) error {
+	isNamespaceScoped, err := isNamespaced(n.client, obj)
+	if err != nil {
+		return fmt.Errorf("error finding the scope of the object: %v", err)
+	}
+
+	objectNamespace := obj.GetNamespace()
+	if objectNamespace != n.namespace && objectNamespace != "" {
+		return fmt.Errorf("Namespace %s of the object %s does not match the namespace %s on the client", objectNamespace, obj.GetName(), n.namespace)
+	}
+
+	if isNamespaceScoped && objectNamespace == "" {
+		obj.SetNamespace(n.namespace)
+	}
+	return n.client.Update(ctx, obj, opts...)
+}
+
+// Delete implements client.Client
+func (n *namespacedClient) Delete(ctx context.Context, obj Object, opts ...DeleteOption) error {
+	isNamespaceScoped, err := isNamespaced(n.client, obj)
+	if err != nil {
+		return fmt.Errorf("error finding the scope of the object: %v", err)
+	}
+
+	objectNamespace := obj.GetNamespace()
+	if objectNamespace != n.namespace && objectNamespace != "" {
+		return fmt.Errorf("Namespace %s of the object %s does not match the namespace %s on the client", objectNamespace, obj.GetName(), n.namespace)
+	}
+
+	if isNamespaceScoped && objectNamespace == "" {
+		obj.SetNamespace(n.namespace)
+	}
+	return n.client.Delete(ctx, obj, opts...)
+}
+
+// DeleteAllOf implements client.Client
+func (n *namespacedClient) DeleteAllOf(ctx context.Context, obj Object, opts ...DeleteAllOfOption) error {
+	isNamespaceScoped, err := isNamespaced(n.client, obj)
+	if err != nil {
+		return fmt.Errorf("error finding the scope of the object: %v", err)
+	}
+
+	if isNamespaceScoped {
+		opts = append(opts, InNamespace(n.namespace))
+	}
+	return n.client.DeleteAllOf(ctx, obj, opts...)
+}
+
+// Patch implements client.Client
+func (n *namespacedClient) Patch(ctx context.Context, obj Object, patch Patch, opts ...PatchOption) error {
+	isNamespaceScoped, err := isNamespaced(n.client, obj)
+	if err != nil {
+		return fmt.Errorf("error finding the scope of the object: %v", err)
+	}
+
+	objectNamespace := obj.GetNamespace()
+	if objectNamespace != n.namespace && objectNamespace != "" {
+		return fmt.Errorf("Namespace %s of the object %s does not match the namespace %s on the client", objectNamespace, obj.GetName(), n.namespace)
+	}
+
+	if isNamespaceScoped && objectNamespace == "" {
+		obj.SetNamespace(n.namespace)
+	}
+	return n.client.Patch(ctx, obj, patch, opts...)
+}
+
+// Get implements client.Client
+func (n *namespacedClient) Get(ctx context.Context, key ObjectKey, obj Object) error {
+	isNamespaceScoped, err := isNamespaced(n.client, obj)
+	if err != nil {
+		return fmt.Errorf("error finding the scope of the object: %v", err)
+	}
+	if isNamespaceScoped {
+		if key.Namespace != "" && key.Namespace != n.namespace {
+			return fmt.Errorf("Namespace %s provided for the object %s does not match the namesapce %s on the client", key.Namespace, obj.GetName(), n.namespace)
+		}
+		key.Namespace = n.namespace
+	}
+	return n.client.Get(ctx, key, obj)
+}
+
+// List implements client.Client
+func (n *namespacedClient) List(ctx context.Context, obj ObjectList, opts ...ListOption) error {
+	if n.namespace != "" {
+		opts = append(opts, InNamespace(n.namespace))
+	}
+	return n.client.List(ctx, obj, opts...)
+}
+
+// Status implements client.StatusClient
+func (n *namespacedClient) Status() StatusWriter {
+	return &namespacedClientStatusWriter{StatusClient: n.client.Status(), namespace: n.namespace, namespacedclient: n}
+}
+
+// ensure namespacedClientStatusWriter implements client.StatusWriter
+var _ StatusWriter = &namespacedClientStatusWriter{}
+
+type namespacedClientStatusWriter struct {
+	StatusClient     StatusWriter
+	namespace        string
+	namespacedclient Client
+}
+
+// Update implements client.StatusWriter
+func (nsw *namespacedClientStatusWriter) Update(ctx context.Context, obj Object, opts ...UpdateOption) error {
+	isNamespaceScoped, err := isNamespaced(nsw.namespacedclient, obj)
+	if err != nil {
+		return fmt.Errorf("error finding the scope of the object: %v", err)
+	}
+
+	objectNamespace := obj.GetNamespace()
+	if objectNamespace != nsw.namespace && objectNamespace != "" {
+		return fmt.Errorf("Namespace %s of the object %s does not match the namespace %s on the client", objectNamespace, obj.GetName(), nsw.namespace)
+	}
+
+	if isNamespaceScoped && objectNamespace == "" {
+		obj.SetNamespace(nsw.namespace)
+	}
+	return nsw.StatusClient.Update(ctx, obj, opts...)
+}
+
+// Patch implements client.StatusWriter
+func (nsw *namespacedClientStatusWriter) Patch(ctx context.Context, obj Object, patch Patch, opts ...PatchOption) error {
+	isNamespaceScoped, err := isNamespaced(nsw.namespacedclient, obj)
+	if err != nil {
+		return fmt.Errorf("error finding the scope of the object: %v", err)
+	}
+
+	objectNamespace := obj.GetNamespace()
+	if objectNamespace != nsw.namespace && objectNamespace != "" {
+		return fmt.Errorf("Namespace %s of the object %s does not match the namespace %s on the client", objectNamespace, obj.GetName(), nsw.namespace)
+	}
+
+	if isNamespaceScoped && objectNamespace == "" {
+		obj.SetNamespace(nsw.namespace)
+	}
+	return nsw.StatusClient.Patch(ctx, obj, patch, opts...)
+}