[client-go] Polymorphic Scale Client

This introduces a polymorphic scale client capable of operating against
scale subresources which return different group-versions of Scale.  The
scale subresources may be in group-versions different than the scale
itself, so that we no longer need a copy of every scalable resource in
the extensions API group.

To discovery which Scale group-versions go to which subresources,
discovery is used.

The scale client maintains its own internal versions and conversions to
several external versions, with a "hub" version that's a copy of the
autoscaling internal version.

It currently supports the following group-versions for Scale subresources:

- extensions/v1beta1.Scale
- autoscaling/v1.Scale

Kubernetes-commit: d61a2d90372c301dd11088df8941acf2bb01c38c

scale/client.go

@@ -0,0 +1,197 @@
+/*
+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 scale
+
+import (
+	"fmt"
+
+	autoscaling "k8s.io/api/autoscaling/v1"
+	"k8s.io/apimachinery/pkg/api/meta"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	serializer "k8s.io/apimachinery/pkg/runtime/serializer"
+	"k8s.io/client-go/dynamic"
+	restclient "k8s.io/client-go/rest"
+)
+
+var scaleConverter = NewScaleConverter()
+var codecs = serializer.NewCodecFactory(scaleConverter.Scheme())
+
+// restInterfaceProvider turns a restclient.Config into a restclient.Interface.
+// It's overridable for the purposes of testing.
+type restInterfaceProvider func(*restclient.Config) (restclient.Interface, error)
+
+// scaleClient is an implementation of ScalesGetter
+// which makes use of a RESTMapper and a generic REST
+// client to support an discoverable resource.
+// It behaves somewhat similarly to the dynamic ClientPool,
+// but is more specifically scoped to Scale.
+type scaleClient struct {
+	mapper meta.RESTMapper
+
+	apiPathResolverFunc dynamic.APIPathResolverFunc
+	scaleKindResolver   ScaleKindResolver
+	clientBase          restclient.Interface
+}
+
+// NewForConfig creates a new ScalesGetter which resolves kinds
+// to resources using the given RESTMapper, and API paths using
+// the given dynamic.APIPathResolverFunc.
+func NewForConfig(cfg *restclient.Config, mapper meta.RESTMapper, resolver dynamic.APIPathResolverFunc, scaleKindResolver ScaleKindResolver) (ScalesGetter, error) {
+	// so that the RESTClientFor doesn't complain
+	cfg.GroupVersion = &schema.GroupVersion{}
+
+	cfg.NegotiatedSerializer = serializer.DirectCodecFactory{
+		CodecFactory: codecs,
+	}
+	if len(cfg.UserAgent) == 0 {
+		cfg.UserAgent = restclient.DefaultKubernetesUserAgent()
+	}
+
+	client, err := restclient.RESTClientFor(cfg)
+	if err != nil {
+		return nil, err
+	}
+
+	return New(client, mapper, resolver, scaleKindResolver), nil
+}
+
+// New creates a new ScalesGetter using the given client to make requests.
+// The GroupVersion on the client is ignored.
+func New(baseClient restclient.Interface, mapper meta.RESTMapper, resolver dynamic.APIPathResolverFunc, scaleKindResolver ScaleKindResolver) ScalesGetter {
+	return &scaleClient{
+		mapper: mapper,
+
+		apiPathResolverFunc: resolver,
+		scaleKindResolver:   scaleKindResolver,
+		clientBase:          baseClient,
+	}
+}
+
+// pathAndVersionFor returns the appropriate base path and the associated full GroupVersionResource
+// for the given GroupResource
+func (c *scaleClient) pathAndVersionFor(resource schema.GroupResource) (string, schema.GroupVersionResource, error) {
+	gvr, err := c.mapper.ResourceFor(resource.WithVersion(""))
+	if err != nil {
+		return "", gvr, fmt.Errorf("unable to get full preferred group-version-resource for %s: %v", resource.String(), err)
+	}
+
+	groupVer := gvr.GroupVersion()
+
+	// we need to set the API path based on GroupVersion (defaulting to the legacy path if none is set)
+	// TODO: we "cheat" here since the API path really only depends on group ATM, but this should
+	// *probably* take GroupVersionResource and not GroupVersionKind.
+	apiPath := c.apiPathResolverFunc(groupVer.WithKind(""))
+	if apiPath == "" {
+		apiPath = "/api"
+	}
+
+	path := restclient.DefaultVersionedAPIPath(apiPath, groupVer)
+
+	return path, gvr, nil
+}
+
+// namespacedScaleClient is an ScaleInterface for fetching
+// Scales in a given namespace.
+type namespacedScaleClient struct {
+	client    *scaleClient
+	namespace string
+}
+
+func (c *scaleClient) Scales(namespace string) ScaleInterface {
+	return &namespacedScaleClient{
+		client:    c,
+		namespace: namespace,
+	}
+}
+
+func (c *namespacedScaleClient) Get(resource schema.GroupResource, name string) (*autoscaling.Scale, error) {
+	// Currently, a /scale endpoint can return different scale types.
+	// Until we have support for the alternative API representations proposal,
+	// we need to deal with accepting different API versions.
+	// In practice, this is autoscaling/v1.Scale and extensions/v1beta1.Scale
+
+	path, gvr, err := c.client.pathAndVersionFor(resource)
+	if err != nil {
+		return nil, fmt.Errorf("unable to get client for %s: %v", resource.String(), err)
+	}
+
+	rawObj, err := c.client.clientBase.Get().
+		AbsPath(path).
+		Namespace(c.namespace).
+		Resource(gvr.Resource).
+		Name(name).
+		SubResource("scale").
+		Do().
+		Get()
+
+	if err != nil {
+		return nil, err
+	}
+
+	// convert whatever this is to autoscaling/v1.Scale
+	scaleObj, err := scaleConverter.ConvertToVersion(rawObj, autoscaling.SchemeGroupVersion)
+	if err != nil {
+		return nil, fmt.Errorf("received an object from a /scale endpoint which was not convertible to autoscaling Scale: %v", err)
+	}
+
+	return scaleObj.(*autoscaling.Scale), nil
+}
+
+func (c *namespacedScaleClient) Update(resource schema.GroupResource, scale *autoscaling.Scale) (*autoscaling.Scale, error) {
+	path, gvr, err := c.client.pathAndVersionFor(resource)
+	if err != nil {
+		return nil, fmt.Errorf("unable to get client for %s: %v", resource.String(), err)
+	}
+
+	// Currently, a /scale endpoint can receive and return different scale types.
+	// Until we hvae support for the alternative API representations proposal,
+	// we need to deal with sending and accepting differnet API versions.
+
+	// figure out what scale we actually need here
+	desiredGVK, err := c.client.scaleKindResolver.ScaleForResource(gvr)
+	if err != nil {
+		return nil, fmt.Errorf("could not find proper group-version for scale subresource of %s: %v", gvr.String(), err)
+	}
+
+	// convert this to whatever this endpoint wants
+	scaleUpdate, err := scaleConverter.ConvertToVersion(scale, desiredGVK.GroupVersion())
+	if err != nil {
+		return nil, fmt.Errorf("could not convert scale update to internal Scale: %v", err)
+	}
+
+	rawObj, err := c.client.clientBase.Put().
+		AbsPath(path).
+		Namespace(c.namespace).
+		Resource(gvr.Resource).
+		Name(scale.Name).
+		SubResource("scale").
+		Body(scaleUpdate).
+		Do().
+		Get()
+
+	if err != nil {
+		return nil, fmt.Errorf("could not fetch the scale for %s %s: %v", resource.String(), scale.Name, err)
+	}
+
+	// convert whatever this is back to autoscaling/v1.Scale
+	scaleObj, err := scaleConverter.ConvertToVersion(rawObj, autoscaling.SchemeGroupVersion)
+	if err != nil {
+		return nil, fmt.Errorf("received an object from a /scale endpoint which was not convertible to autoscaling Scale: %v", err)
+	}
+
+	return scaleObj.(*autoscaling.Scale), err
+}