Add example of using resource builder to load a manifest file

Author: liggitt

staging/src/k8s.io/cli-runtime/pkg/resource/BUILD

@@ -56,6 +56,7 @@ go_library(
 go_test(
     name = "go_default_test",
     srcs = [
+        "builder_example_test.go",
         "builder_test.go",
         "crd_finder_test.go",
         "dry_run_verifier_test.go",

staging/src/k8s.io/cli-runtime/pkg/resource/builder.go

@@ -35,6 +35,8 @@ import (
 	"k8s.io/apimachinery/pkg/runtime/serializer"
 	utilerrors "k8s.io/apimachinery/pkg/util/errors"
 	"k8s.io/apimachinery/pkg/util/sets"
+	"k8s.io/client-go/discovery"
+	"k8s.io/client-go/rest"
 	"k8s.io/client-go/restmapper"
 )
 
@@ -176,6 +178,25 @@ func newBuilder(clientConfigFn ClientConfigFunc, restMapper RESTMapperFunc, cate
 	}
 }
 
+// noopClientGetter implements RESTClientGetter returning only errors.
+// used as a dummy getter in a local-only builder.
+type noopClientGetter struct{}
+
+func (noopClientGetter) ToRESTConfig() (*rest.Config, error) {
+	return nil, fmt.Errorf("local operation only")
+}
+func (noopClientGetter) ToDiscoveryClient() (discovery.CachedDiscoveryInterface, error) {
+	return nil, fmt.Errorf("local operation only")
+}
+func (noopClientGetter) ToRESTMapper() (meta.RESTMapper, error) {
+	return nil, fmt.Errorf("local operation only")
+}
+
+// NewLocalBuilder returns a builder that is configured not to create REST clients and avoids asking the server for results.
+func NewLocalBuilder() *Builder {
+	return NewBuilder(noopClientGetter{}).Local()
+}
+
 func NewBuilder(restClientGetter RESTClientGetter) *Builder {
 	categoryExpanderFn := func() (restmapper.CategoryExpander, error) {
 		discoveryClient, err := restClientGetter.ToDiscoveryClient()

staging/src/k8s.io/cli-runtime/pkg/resource/builder_example_test.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 resource_test
+
+import (
+	"bytes"
+	"fmt"
+
+	"k8s.io/cli-runtime/pkg/resource"
+	"k8s.io/client-go/kubernetes/scheme"
+)
+
+var exampleManifest = `
+apiVersion: admissionregistration.k8s.io/v1
+kind: MutatingWebhookConfiguration
+metadata:
+  name: mutating1
+---
+apiVersion: admissionregistration.k8s.io/v1
+kind: MutatingWebhookConfigurationList
+items:
+- apiVersion: admissionregistration.k8s.io/v1
+  kind: MutatingWebhookConfiguration
+  metadata:
+    name: mutating2
+- apiVersion: admissionregistration.k8s.io/v1
+  kind: MutatingWebhookConfiguration
+  metadata:
+    name: mutating3
+---
+apiVersion: admissionregistration.k8s.io/v1
+kind: ValidatingWebhookConfiguration
+metadata:
+  name: validating1
+---
+apiVersion: admissionregistration.k8s.io/v1
+kind: ValidatingWebhookConfigurationList
+items:
+- apiVersion: admissionregistration.k8s.io/v1
+  kind: ValidatingWebhookConfiguration
+  metadata:
+    name: validating2
+- apiVersion: admissionregistration.k8s.io/v1
+  kind: ValidatingWebhookConfiguration
+  metadata:
+    name: validating3
+---
+apiVersion: v1
+kind: List
+items:
+- apiVersion: admissionregistration.k8s.io/v1
+  kind: MutatingWebhookConfiguration
+  metadata:
+    name: mutating4
+- apiVersion: admissionregistration.k8s.io/v1
+  kind: ValidatingWebhookConfiguration
+  metadata:
+    name: validating4
+---
+`
+
+// ExampleLocalBuilderLoad demonstrates using a local resource builder to read typed resources from a manifest
+func ExampleLocalBuilder() {
+	// Create a local builder...
+	builder := resource.NewLocalBuilder().
+		// Configure with a scheme to get typed objects in the versions registered with the scheme.
+		// As an alternative, could call Unstructured() to get unstructured objects.
+		WithScheme(scheme.Scheme, scheme.Scheme.PrioritizedVersionsAllGroups()...).
+		// Provide input via a Reader.
+		// As an alternative, could call Path(false, "/path/to/file") to read from a file.
+		Stream(bytes.NewBufferString(exampleManifest), "input").
+		// Flatten items contained in List objects
+		Flatten().
+		// Accumulate as many items as possible
+		ContinueOnError()
+
+	// Run the builder
+	result := builder.Do()
+
+	if err := result.Err(); err != nil {
+		fmt.Println("builder error:", err)
+		return
+	}
+
+	items, err := result.Infos()
+	if err != nil {
+		fmt.Println("infos error:", err)
+		return
+	}
+
+	for _, item := range items {
+		fmt.Printf("%s (%T)\n", item.String(), item.Object)
+	}
+
+	// Output:
+	// Name: "mutating1", Namespace: "" (*v1.MutatingWebhookConfiguration)
+	// Name: "mutating2", Namespace: "" (*v1.MutatingWebhookConfiguration)
+	// Name: "mutating3", Namespace: "" (*v1.MutatingWebhookConfiguration)
+	// Name: "validating1", Namespace: "" (*v1.ValidatingWebhookConfiguration)
+	// Name: "validating2", Namespace: "" (*v1.ValidatingWebhookConfiguration)
+	// Name: "validating3", Namespace: "" (*v1.ValidatingWebhookConfiguration)
+	// Name: "mutating4", Namespace: "" (*v1.MutatingWebhookConfiguration)
+	// Name: "validating4", Namespace: "" (*v1.ValidatingWebhookConfiguration)
+}