Use absolute path instead requestURI in openapiv3 discovery (#117495)

Currently, openapiv3 discovery uses requestURI to discover resources.
However, that does not work when the rest endpoint contains prefixes
(e.g. `http://localhost/test-endpoint/`).
Because requestURI overwrites prefixes also in rest endpoint
(e.g. `http://localhost/openapiv3/apis/apps/v1`).

Since `absPath` keeps the prefixes in the rest endpoint,
this PR changes to absPath instead requestURI.

staging/src/k8s.io/client-go/openapi/client.go

@@ -19,6 +19,7 @@ package openapi
 import (
 	"context"
 	"encoding/json"
+	"strings"
 
 	"k8s.io/client-go/rest"
 	"k8s.io/kube-openapi/pkg/handler3"
@@ -58,7 +59,11 @@ func (c *client) Paths() (map[string]GroupVersion, error) {
 	// Create GroupVersions for each element of the result
 	result := map[string]GroupVersion{}
 	for k, v := range discoMap.Paths {
-		result[k] = newGroupVersion(c, v)
+		// If the server returned a URL rooted at /openapi/v3, preserve any additional client-side prefix.
+		// If the server returned a URL not rooted at /openapi/v3, treat it as an actual server-relative URL.
+		// See https://github.com/kubernetes/kubernetes/issues/117463 for details
+		useClientPrefix := strings.HasPrefix(v.ServerRelativeURL, "/openapi/v3")
+		result[k] = newGroupVersion(c, v, useClientPrefix)
 	}
 	return result, nil
 }

staging/src/k8s.io/client-go/openapi/groupversion.go

@@ -18,6 +18,7 @@ package openapi
 
 import (
 	"context"
+	"net/url"
 
 	"k8s.io/kube-openapi/pkg/handler3"
 )
@@ -29,18 +30,41 @@ type GroupVersion interface {
 }
 
 type groupversion struct {
-	client *client
-	item   handler3.OpenAPIV3DiscoveryGroupVersion
+	client          *client
+	item            handler3.OpenAPIV3DiscoveryGroupVersion
+	useClientPrefix bool
 }
 
-func newGroupVersion(client *client, item handler3.OpenAPIV3DiscoveryGroupVersion) *groupversion {
-	return &groupversion{client: client, item: item}
+func newGroupVersion(client *client, item handler3.OpenAPIV3DiscoveryGroupVersion, useClientPrefix bool) *groupversion {
+	return &groupversion{client: client, item: item, useClientPrefix: useClientPrefix}
 }
 
 func (g *groupversion) Schema(contentType string) ([]byte, error) {
-	return g.client.restClient.Get().
-		RequestURI(g.item.ServerRelativeURL).
-		SetHeader("Accept", contentType).
-		Do(context.TODO()).
-		Raw()
+	if !g.useClientPrefix {
+		return g.client.restClient.Get().
+			RequestURI(g.item.ServerRelativeURL).
+			SetHeader("Accept", contentType).
+			Do(context.TODO()).
+			Raw()
+	}
+
+	locator, err := url.Parse(g.item.ServerRelativeURL)
+	if err != nil {
+		return nil, err
+	}
+
+	path := g.client.restClient.Get().
+		AbsPath(locator.Path).
+		SetHeader("Accept", contentType)
+
+	// Other than root endpoints(openapiv3/apis), resources have hash query parameter to support etags.
+	// However, absPath does not support handling query parameters internally,
+	// so that hash query parameter is added manually
+	for k, value := range locator.Query() {
+		for _, v := range value {
+			path.Param(k, v)
+		}
+	}
+
+	return path.Do(context.TODO()).Raw()
 }

staging/src/k8s.io/client-go/openapi/groupversion_test.go

@@ -0,0 +1,106 @@
+/*
+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 openapi
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	appsv1 "k8s.io/api/apps/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/client-go/kubernetes/scheme"
+	"k8s.io/client-go/rest"
+)
+
+func TestGroupVersion(t *testing.T) {
+	tests := []struct {
+		name                string
+		prefix              string
+		serverReturnsPrefix bool
+	}{
+		{
+			name:                "no prefix",
+			prefix:              "",
+			serverReturnsPrefix: false,
+		},
+		{
+			name:                "prefix not in discovery",
+			prefix:              "/test-endpoint",
+			serverReturnsPrefix: false,
+		},
+		{
+			name:                "prefix in discovery",
+			prefix:              "/test-endpoint",
+			serverReturnsPrefix: true,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				switch {
+				case r.URL.Path == test.prefix+"/openapi/v3/apis/apps/v1" && r.URL.RawQuery == "hash=014fbff9a07c":
+					w.Header().Set("Content-Type", "application/json")
+					w.WriteHeader(http.StatusOK)
+					w.Write([]byte(`{"openapi":"3.0.0","info":{"title":"Kubernetes","version":"unversioned"}}`))
+				case r.URL.Path == test.prefix+"/openapi/v3":
+					// return root content
+					w.Header().Set("Content-Type", "application/json")
+					w.WriteHeader(http.StatusOK)
+					if test.serverReturnsPrefix {
+						w.Write([]byte(fmt.Sprintf(`{"paths":{"apis/apps/v1":{"serverRelativeURL":"%s/openapi/v3/apis/apps/v1?hash=014fbff9a07c"}}}`, test.prefix)))
+					} else {
+						w.Write([]byte(`{"paths":{"apis/apps/v1":{"serverRelativeURL":"/openapi/v3/apis/apps/v1?hash=014fbff9a07c"}}}`))
+					}
+				default:
+					t.Errorf("unexpected request: %s", r.URL.String())
+					w.WriteHeader(http.StatusNotFound)
+					return
+				}
+			}))
+			defer server.Close()
+
+			c, err := rest.RESTClientFor(&rest.Config{
+				Host: server.URL + test.prefix,
+				ContentConfig: rest.ContentConfig{
+					NegotiatedSerializer: scheme.Codecs,
+					GroupVersion:         &appsv1.SchemeGroupVersion,
+				},
+			})
+
+			if err != nil {
+				t.Fatalf("unexpected error occurred: %v", err)
+			}
+
+			openapiClient := NewClient(c)
+			paths, err := openapiClient.Paths()
+			if err != nil {
+				t.Fatalf("unexpected error occurred: %v", err)
+			}
+			schema, err := paths["apis/apps/v1"].Schema(runtime.ContentTypeJSON)
+			if err != nil {
+				t.Fatalf("unexpected error occurred: %v", err)
+			}
+			expectedResult := `{"openapi":"3.0.0","info":{"title":"Kubernetes","version":"unversioned"}}`
+			if string(schema) != expectedResult {
+				t.Fatalf("unexpected result actual: %s expected: %s", string(schema), expectedResult)
+			}
+		})
+	}
+}