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.

Kubernetes-commit: d94c733ee2bfaedd9a1c45d58fbd56c99403c94d

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
 }