add fetching into discovery client for OpenAPI v3

reflect latest struct changes

use correct discovery openapi test data layout

make the OpenAPIv3 interface less blue

field grouping

add copyrights

implement cached discovery client

add cached discovery tests

address review feedback

Kubernetes-commit: 075866b3e3ea029c243d82d8d6eb99e96d9c49d3

util/testing/fake_openapi_handler.go

@@ -0,0 +1,174 @@
+/*
+Copyright 2021 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 testing
+
+import (
+	"encoding/json"
+	"io/fs"
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+
+	openapi_v3 "github.com/google/gnostic/openapiv3"
+	"k8s.io/kube-openapi/pkg/handler3"
+	"k8s.io/kube-openapi/pkg/spec3"
+)
+
+type FakeOpenAPIServer struct {
+	HttpServer      *httptest.Server
+	ServedDocuments map[string]*openapi_v3.Document
+	RequestCounters map[string]int
+}
+
+// Creates a mock OpenAPIV3 server as it would be on a standing kubernetes
+// API server.
+//
+// specsPath - Give a path to some test data organized so that each GroupVersion
+// 	has its own OpenAPI V3 JSON file.
+// 		i.e. apps/v1beta1 is stored in <specsPath>/apps/v1beta1.json
+func NewFakeOpenAPIV3Server(specsPath string) (*FakeOpenAPIServer, error) {
+	mux := &testMux{
+		counts: map[string]int{},
+	}
+	server := httptest.NewServer(mux)
+
+	openAPIVersionedService, err := handler3.NewOpenAPIService(nil)
+	if err != nil {
+		return nil, err
+	}
+
+	err = openAPIVersionedService.RegisterOpenAPIV3VersionedService("/openapi/v3", mux)
+	if err != nil {
+		return nil, err
+	}
+
+	grouped := make(map[string][]byte)
+	var testV3Specs = make(map[string]*openapi_v3.Document)
+
+	addSpec := func(path string) {
+		file, err := os.Open(path)
+		if err != nil {
+			panic(err)
+		}
+
+		defer file.Close()
+		vals, err := ioutil.ReadAll(file)
+		if err != nil {
+			panic(err)
+		}
+
+		rel, err := filepath.Rel(specsPath, path)
+		if err == nil {
+			grouped[rel[:(len(rel)-len(filepath.Ext(rel)))]] = vals
+		}
+	}
+
+	filepath.WalkDir(specsPath, func(path string, d fs.DirEntry, err error) error {
+		if filepath.Ext(path) != ".json" || d.IsDir() {
+			return nil
+		}
+
+		addSpec(path)
+		return nil
+	})
+
+	for gv, jsonSpec := range grouped {
+		spec := &spec3.OpenAPI{}
+		err = json.Unmarshal(jsonSpec, spec)
+		if err != nil {
+			return nil, err
+		}
+		gnosticSpec, err := openapi_v3.ParseDocument(jsonSpec)
+		if err != nil {
+			return nil, err
+		}
+		testV3Specs[gv] = gnosticSpec
+		openAPIVersionedService.UpdateGroupVersion(gv, spec)
+	}
+
+	return &FakeOpenAPIServer{
+		HttpServer:      server,
+		ServedDocuments: testV3Specs,
+		RequestCounters: mux.counts,
+	}, nil
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Tiny Test HTTP Mux
+////////////////////////////////////////////////////////////////////////////////
+// Implements the mux interface used by handler3 for registering the OpenAPI
+//	handlers
+
+type testMux struct {
+	lock      sync.Mutex
+	prefixMap map[string]http.Handler
+	pathMap   map[string]http.Handler
+	counts    map[string]int
+}
+
+func (t *testMux) Handle(path string, handler http.Handler) {
+	t.lock.Lock()
+	defer t.lock.Unlock()
+
+	if t.pathMap == nil {
+		t.pathMap = make(map[string]http.Handler)
+	}
+	t.pathMap[path] = handler
+}
+
+func (t *testMux) HandlePrefix(path string, handler http.Handler) {
+	t.lock.Lock()
+	defer t.lock.Unlock()
+
+	if t.prefixMap == nil {
+		t.prefixMap = make(map[string]http.Handler)
+	}
+	t.prefixMap[path] = handler
+}
+
+func (t *testMux) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	t.lock.Lock()
+	defer t.lock.Unlock()
+
+	if t.counts == nil {
+		t.counts = make(map[string]int)
+	}
+
+	if val, exists := t.counts[req.URL.Path]; exists {
+		t.counts[req.URL.Path] = val + 1
+	} else {
+		t.counts[req.URL.Path] = 1
+	}
+
+	if handler, ok := t.pathMap[req.URL.Path]; ok {
+		handler.ServeHTTP(w, req)
+		return
+	}
+
+	for k, v := range t.prefixMap {
+		if strings.HasPrefix(req.URL.Path, k) {
+			v.ServeHTTP(w, req)
+			return
+		}
+	}
+
+	w.WriteHeader(http.StatusNotFound)
+}