Provide a truly lazy restmapper

This commit adds a rest mapper that will lazily query the provided
client for discovery information to do REST mappings.

pkg/client/apiutil/lazyrestmapper/lazyrestmapper.go

@@ -0,0 +1,261 @@
+/*
+Copyright 2023 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 lazyrestmapper
+
+import (
+	"sync"
+
+	"k8s.io/apimachinery/pkg/api/meta"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
+	"k8s.io/client-go/discovery"
+	"k8s.io/client-go/rest"
+	"k8s.io/client-go/restmapper"
+)
+
+// LazyRESTMapper is a RESTMapper that will lazily query the provided
+// client for discovery information to do REST mappings.
+type LazyRESTMapper struct {
+	mapper      meta.RESTMapper
+	client      *discovery.DiscoveryClient
+	knownGroups map[string]*restmapper.APIGroupResources
+
+	// mutex to provide thread-safe mapper reloading
+	mu sync.Mutex
+}
+
+// NewLazyRESTMapper initializes a LazyRESTMapper
+func NewLazyRESTMapper(c *rest.Config) (meta.RESTMapper, error) {
+	dc, err := discovery.NewDiscoveryClientForConfig(c)
+	if err != nil {
+		return nil, err
+	}
+
+	return &LazyRESTMapper{
+		mapper:      restmapper.NewDiscoveryRESTMapper([]*restmapper.APIGroupResources{}),
+		client:      dc,
+		knownGroups: map[string]*restmapper.APIGroupResources{},
+	}, nil
+}
+
+// NewLazyRESTMapperWithClient initializes a LazyRESTMapper
+func NewLazyRESTMapperWithClient(dc *discovery.DiscoveryClient) meta.RESTMapper {
+	return &LazyRESTMapper{
+		mapper:      restmapper.NewDiscoveryRESTMapper([]*restmapper.APIGroupResources{}),
+		client:      dc,
+		knownGroups: map[string]*restmapper.APIGroupResources{},
+	}
+}
+
+func (m *LazyRESTMapper) addKnownGroupAndReload(groupName string) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	groupResources, err := getFilteredAPIGroupResources(m.client, groupName)
+	if err != nil || groupResources == nil {
+		return err
+	}
+
+	m.knownGroups[groupName] = groupResources
+
+	updatedGroupResources := make([]*restmapper.APIGroupResources, 0, len(m.knownGroups))
+	for _, v := range m.knownGroups {
+		updatedGroupResources = append(updatedGroupResources, v)
+	}
+
+	m.mapper = restmapper.NewDiscoveryRESTMapper(updatedGroupResources)
+
+	return nil
+}
+
+// KindFor implements Mapper.KindFor
+func (m *LazyRESTMapper) KindFor(resource schema.GroupVersionResource) (schema.GroupVersionKind, error) {
+	res, err := m.mapper.KindFor(resource)
+	if meta.IsNoMatchError(err) {
+		if err = m.addKnownGroupAndReload(resource.Group); err != nil {
+			return res, err
+		}
+		res, err = m.mapper.KindFor(resource)
+	}
+	return res, err
+}
+
+// KindsFor implements Mapper.KindsFor
+func (m *LazyRESTMapper) KindsFor(resource schema.GroupVersionResource) ([]schema.GroupVersionKind, error) {
+	res, err := m.mapper.KindsFor(resource)
+	if meta.IsNoMatchError(err) {
+		if err = m.addKnownGroupAndReload(resource.Group); err != nil {
+			return res, err
+		}
+		res, err = m.mapper.KindsFor(resource)
+	}
+	return res, err
+}
+
+// ResourceFor implements Mapper.ResourceFor
+func (m *LazyRESTMapper) ResourceFor(input schema.GroupVersionResource) (schema.GroupVersionResource, error) {
+	res, err := m.mapper.ResourceFor(input)
+	if meta.IsNoMatchError(err) {
+		if err = m.addKnownGroupAndReload(input.Group); err != nil {
+			return res, err
+		}
+		res, err = m.mapper.ResourceFor(input)
+	}
+	return res, err
+}
+
+// ResourcesFor implements Mapper.ResourcesFor
+func (m *LazyRESTMapper) ResourcesFor(input schema.GroupVersionResource) ([]schema.GroupVersionResource, error) {
+	res, err := m.mapper.ResourcesFor(input)
+	if meta.IsNoMatchError(err) {
+		if err = m.addKnownGroupAndReload(input.Group); err != nil {
+			return res, err
+		}
+		res, err = m.mapper.ResourcesFor(input)
+	}
+	return res, err
+}
+
+// RESTMapping implements Mapper.RESTMapping
+func (m *LazyRESTMapper) RESTMapping(gk schema.GroupKind, versions ...string) (*meta.RESTMapping, error) {
+	res, err := m.mapper.RESTMapping(gk, versions...)
+	if meta.IsNoMatchError(err) {
+		if err = m.addKnownGroupAndReload(gk.Group); err != nil {
+			return res, err
+		}
+		res, err = m.mapper.RESTMapping(gk, versions...)
+	}
+	return res, err
+}
+
+// RESTMappings implements Mapper.RESTMappings
+func (m *LazyRESTMapper) RESTMappings(gk schema.GroupKind, versions ...string) ([]*meta.RESTMapping, error) {
+	res, err := m.mapper.RESTMappings(gk, versions...)
+	if meta.IsNoMatchError(err) {
+		if err = m.addKnownGroupAndReload(gk.Group); err != nil {
+			return res, err
+		}
+		res, err = m.mapper.RESTMappings(gk, versions...)
+	}
+	return res, err
+}
+
+// ResourceSingularizer implements Mapper.ResourceSingularizer
+func (m *LazyRESTMapper) ResourceSingularizer(resource string) (string, error) {
+	return m.mapper.ResourceSingularizer(resource)
+}
+
+// fetchGroupVersionResources uses the discovery client to fetch the resources for the specified group in parallel.
+// Mainly replicates the same named function from the client-go internals aside from the changed `apiGroups` argument type (uses slice instead of a single group).
+// ref: https://github.com/kubernetes/kubernetes/blob/a84d877310ba5cf9237c8e8e3218229c202d3a1e/staging/src/k8s.io/client-go/discovery/discovery_client.go#L506
+func fetchGroupVersionResources(d discovery.DiscoveryInterface, apiGroup metav1.APIGroup) (map[schema.GroupVersion]*metav1.APIResourceList, map[schema.GroupVersion]error) {
+	groupVersionResources := make(map[schema.GroupVersion]*metav1.APIResourceList)
+	failedGroups := make(map[schema.GroupVersion]error)
+
+	wg := &sync.WaitGroup{}
+	resultLock := &sync.Mutex{}
+	for _, version := range apiGroup.Versions {
+		groupVersion := schema.GroupVersion{Group: apiGroup.Name, Version: version.Version}
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			defer utilruntime.HandleCrash()
+
+			apiResourceList, err := d.ServerResourcesForGroupVersion(groupVersion.String())
+
+			// lock to record results
+			resultLock.Lock()
+			defer resultLock.Unlock()
+
+			if err != nil {
+				// TODO: maybe restrict this to NotFound errors
+				failedGroups[groupVersion] = err
+			}
+			if apiResourceList != nil {
+				// even in case of error, some fallback might have been returned
+				groupVersionResources[groupVersion] = apiResourceList
+			}
+		}()
+	}
+	wg.Wait()
+
+	return groupVersionResources, failedGroups
+}
+
+// filteredServerGroupsAndResources returns the supported resources for groups filtered by passed predicate and versions.
+// Mainly replicate ServerGroupsAndResources function from the client-go. The difference is that this function takes
+// a group name as an argument for filtering out unwanted groups.
+// ref: https://github.com/kubernetes/kubernetes/blob/a84d877310ba5cf9237c8e8e3218229c202d3a1e/staging/src/k8s.io/client-go/discovery/discovery_client.go#L383
+func filteredServerGroupsAndResources(d discovery.DiscoveryInterface, groupName string) (*metav1.APIGroup, []*metav1.APIResourceList, error) {
+	sgs, err := d.ServerGroups()
+	if sgs == nil {
+		return nil, nil, err
+	}
+
+	apiGroup := metav1.APIGroup{}
+	for i := range sgs.Groups {
+		if groupName == (&sgs.Groups[i]).Name {
+			apiGroup = sgs.Groups[i]
+		}
+	}
+
+	groupVersionResources, failedGroups := fetchGroupVersionResources(d, apiGroup)
+
+	// order results by group/version discovery order
+	result := []*metav1.APIResourceList{}
+	for _, version := range apiGroup.Versions {
+		gv := schema.GroupVersion{Group: apiGroup.Name, Version: version.Version}
+		if resources, ok := groupVersionResources[gv]; ok {
+			result = append(result, resources)
+		}
+	}
+
+	if len(failedGroups) == 0 {
+		return &apiGroup, result, nil
+	}
+
+	return &apiGroup, result, &discovery.ErrGroupDiscoveryFailed{Groups: failedGroups}
+}
+
+// getFilteredAPIGroupResources uses the provided discovery client to gather
+// discovery information and populate a slice of APIGroupResources.
+func getFilteredAPIGroupResources(cl discovery.DiscoveryInterface, groupName string) (*restmapper.APIGroupResources, error) {
+	group, rs, err := filteredServerGroupsAndResources(cl, groupName)
+	if rs == nil || group == nil {
+		return nil, err
+		// TODO track the errors and update callers to handle partial errors.
+	}
+	rsm := map[string]*metav1.APIResourceList{}
+	for _, r := range rs {
+		rsm[r.GroupVersion] = r
+	}
+
+	groupResources := &restmapper.APIGroupResources{
+		Group:              *group,
+		VersionedResources: make(map[string][]metav1.APIResource),
+	}
+	for _, version := range group.Versions {
+		resources, ok := rsm[version.GroupVersion]
+		if !ok {
+			continue
+		}
+		groupResources.VersionedResources[version.Version] = resources.APIResources
+	}
+
+	return groupResources, nil
+}