Create a method to check dryRun is supported

We don't want to run dryRun requests against servers that don't support
dry-run, since they might ignore the flag and just persist the unwanted
changes.

This creates a new method that checks in the OpenAPI if the dryRun
parameter can be used.

pkg/kubectl/cmd/util/openapi/dryrun.go

@@ -0,0 +1,65 @@
+/*
+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 openapi
+
+import (
+	"errors"
+
+	openapi_v2 "github.com/googleapis/gnostic/OpenAPIv2"
+	yaml "gopkg.in/yaml.v2"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+)
+
+func hasGVKExtension(extensions []*openapi_v2.NamedAny, gvk schema.GroupVersionKind) bool {
+	for _, extension := range extensions {
+		if extension.GetValue().GetYaml() == "" ||
+			extension.GetName() != "x-kubernetes-group-version-kind" {
+			continue
+		}
+		var value map[string]string
+		err := yaml.Unmarshal([]byte(extension.GetValue().GetYaml()), &value)
+		if err != nil {
+			continue
+		}
+
+		if value["group"] == gvk.Group && value["kind"] == gvk.Kind && value["version"] == gvk.Version {
+			return true
+		}
+		return false
+	}
+	return false
+}
+
+// SupportsDryRun is a method that let's us look in the OpenAPI if the
+// specific group-version-kind supports the dryRun query parameter for
+// the PATCH end-point.
+func SupportsDryRun(doc *openapi_v2.Document, gvk schema.GroupVersionKind) (bool, error) {
+	for _, path := range doc.GetPaths().GetPath() {
+		// Is this describing the gvk we're looking for?
+		if !hasGVKExtension(path.GetValue().GetPatch().GetVendorExtension(), gvk) {
+			continue
+		}
+		for _, param := range path.GetValue().GetPatch().GetParameters() {
+			if param.GetParameter().GetNonBodyParameter().GetQueryParameterSubSchema().GetName() == "dryRun" {
+				return true, nil
+			}
+		}
+		return false, nil
+	}
+
+	return false, errors.New("couldn't find GVK in openapi")
+}