dry-run: Verify if the object supports dry-run

For each object, first we verify if they have a dryRun parameter in the
openapi for the patch verb. If we can't find the object, we assume that
CRD will behave like "namespace". So we check if namespace supports
dryRun. If it does, then we verify that the resource is a CRD.

pkg/kubectl/cmd/apply/apply.go

@@ -42,6 +42,7 @@ import (
 	"k8s.io/cli-runtime/pkg/genericclioptions"
 	"k8s.io/cli-runtime/pkg/genericclioptions/printers"
 	"k8s.io/cli-runtime/pkg/genericclioptions/resource"
+	"k8s.io/client-go/discovery"
 	"k8s.io/client-go/dynamic"
 	oapi "k8s.io/kube-openapi/pkg/util/proto"
 	"k8s.io/kubernetes/pkg/kubectl"
@@ -76,11 +77,12 @@ type ApplyOptions struct {
 	PruneWhitelist             []string
 	ShouldIncludeUninitialized bool
 
-	Validator     validation.Schema
-	Builder       *resource.Builder
-	Mapper        meta.RESTMapper
-	DynamicClient dynamic.Interface
-	OpenAPISchema openapi.Resources
+	Validator       validation.Schema
+	Builder         *resource.Builder
+	Mapper          meta.RESTMapper
+	DynamicClient   dynamic.Interface
+	DiscoveryClient discovery.DiscoveryInterface
+	OpenAPISchema   openapi.Resources
 
 	Namespace        string
 	EnforceNamespace bool
@@ -211,6 +213,11 @@ func (o *ApplyOptions) Complete(f cmdutil.Factory, cmd *cobra.Command) error {
 		return err
 	}
 
+	o.DiscoveryClient, err = f.ToDiscoveryClient()
+	if err != nil {
+		return err
+	}
+
 	dynamicClient, err := f.DynamicClient()
 	if err != nil {
 		return err
@@ -403,19 +410,25 @@ func (o *ApplyOptions) Run() error {
 				fmt.Fprintf(o.ErrOut, warningNoLastAppliedConfigAnnotation, o.cmdBaseName)
 			}
 
+			dryRunVerifier := &DryRunVerifier{
+				Finder:        cmdutil.NewCRDFinder(cmdutil.CRDFromDynamic(o.DynamicClient)),
+				OpenAPIGetter: o.DiscoveryClient,
+			}
+
 			helper := resource.NewHelper(info.Client, info.Mapping)
 			patcher := &Patcher{
-				Mapping:       info.Mapping,
-				Helper:        helper,
-				DynamicClient: o.DynamicClient,
-				Overwrite:     o.Overwrite,
-				BackOff:       clockwork.NewRealClock(),
-				Force:         o.DeleteOptions.ForceDeletion,
-				Cascade:       o.DeleteOptions.Cascade,
-				Timeout:       o.DeleteOptions.Timeout,
-				GracePeriod:   o.DeleteOptions.GracePeriod,
-				ServerDryRun:  o.ServerDryRun,
-				OpenapiSchema: openapiSchema,
+				Mapping:        info.Mapping,
+				Helper:         helper,
+				DynamicClient:  o.DynamicClient,
+				DryRunVerifier: dryRunVerifier,
+				Overwrite:      o.Overwrite,
+				BackOff:        clockwork.NewRealClock(),
+				Force:          o.DeleteOptions.ForceDeletion,
+				Cascade:        o.DeleteOptions.Cascade,
+				Timeout:        o.DeleteOptions.Timeout,
+				GracePeriod:    o.DeleteOptions.GracePeriod,
+				ServerDryRun:   o.ServerDryRun,
+				OpenapiSchema:  openapiSchema,
 			}
 
 			patchBytes, patchedObject, err := patcher.Patch(info.Object, modified, info.Source, info.Namespace, info.Name, o.ErrOut)
@@ -668,9 +681,10 @@ func (p *Patcher) delete(namespace, name string) error {
 }
 
 type Patcher struct {
-	Mapping       *meta.RESTMapping
-	Helper        *resource.Helper
-	DynamicClient dynamic.Interface
+	Mapping        *meta.RESTMapping
+	Helper         *resource.Helper
+	DynamicClient  dynamic.Interface
+	DryRunVerifier *DryRunVerifier
 
 	Overwrite bool
 	BackOff   clockwork.Clock
@@ -684,7 +698,52 @@ type Patcher struct {
 	OpenapiSchema openapi.Resources
 }
 
+// DryRunVerifier verifies if a given group-version-kind supports DryRun
+// against the current server. Sending dryRun requests to apiserver that
+// don't support it will result in objects being unwillingly persisted.
+//
+// It reads the OpenAPI to see if the given GVK supports dryRun. If the
+// GVK can not be found, we assume that CRDs will have the same level of
+// support as "namespaces", and non-CRDs will not be supported. We
+// delay the check for CRDs as much as possible though, since it
+// requires an extra round-trip to the server.
+type DryRunVerifier struct {
+	Finder        cmdutil.CRDFinder
+	OpenAPIGetter discovery.OpenAPISchemaInterface
+}
+
+// HasSupport verifies if the given gvk supports DryRun. An error is
+// returned if it doesn't.
+func (v *DryRunVerifier) HasSupport(gvk schema.GroupVersionKind) error {
+	oapi, err := v.OpenAPIGetter.OpenAPISchema()
+	if err != nil {
+		return fmt.Errorf("failed to download openapi: %v", err)
+	}
+	supports, err := openapi.SupportsDryRun(oapi, gvk)
+	if err != nil {
+		// We assume that we couldn't find the type, then check for namespace:
+		supports, _ = openapi.SupportsDryRun(oapi, schema.GroupVersionKind{Group: "", Version: "v1", Kind: "Namespace"})
+		// If namespace supports dryRun, then we will support dryRun for CRDs only.
+		if supports {
+			supports, err = v.Finder.HasCRD(gvk.GroupKind())
+			if err != nil {
+				return fmt.Errorf("failed to check CRD: %v", err)
+			}
+		}
+	}
+	if !supports {
+		return fmt.Errorf("%v doesn't support dry-run", gvk)
+	}
+	return nil
+}
+
 func (p *Patcher) patchSimple(obj runtime.Object, modified []byte, source, namespace, name string, errOut io.Writer) ([]byte, runtime.Object, error) {
+	if p.ServerDryRun {
+		if err := p.DryRunVerifier.HasSupport(p.Mapping.GroupVersionKind); err != nil {
+			return nil, nil, err
+		}
+	}
+
 	// Serialize the current configuration of the object from the server.
 	current, err := runtime.Encode(unstructured.UnstructuredJSONScheme, obj)
 	if err != nil {