Fix KCPRequestInfoResolver for kind: Cluster

The cache server preprocesses the path to remove the cluster prefix
in https://github.com/kcp-dev/kcp/blob/88d6071b2aaf47bcd5e854f8209e4c3bd8035b35/pkg/cache/server/config.go#L172-L186.

When a resource of type "cluster" is created and the first cluster
prefix is dropped, the path would be a k8s request info path (/apis/...)
but will still have the `clusters` keyword in the path.

Due to this, the regex in the kcp request info resolver does not work
well.

This commit updates the resolver:

1. If a path is a k8s request info path (begins with `/api` or `/apis`),
then the path is not checked against the regex.

2. The regex is updated to preserve the forward slash in the
strippedURL.

pkg/server/requestinfo/kcp_request_info_resolver.go

@@ -19,6 +19,7 @@ package requestinfo
 import (
 	"net/http"
 	"regexp"
+	"strings"
 
 	"k8s.io/apiserver/pkg/endpoints/request"
 )
@@ -33,16 +34,28 @@ func NewKCPRequestInfoResolver() *KCPRequestInfoResolver {
 	}
 }
 
-var clustersRE = regexp.MustCompile(`/clusters/[^/]+/(.*)$`)
+var clustersRE = regexp.MustCompile(`/clusters/[^/]+(/.*)$`)
 
 func (k *KCPRequestInfoResolver) NewRequestInfo(req *http.Request) (*request.RequestInfo, error) {
-	matches := clustersRE.FindStringSubmatch(req.URL.Path)
-	if len(matches) == 2 {
-		// matches[0] is the leftmost pattern that matches (which includes /clusters/...) - skip over that
-		strippedURL := matches[1]
-		t := req.Clone(req.Context())
-		t.URL.Path = strippedURL
-		return k.delegate.NewRequestInfo(t)
+	if !containsPrefix([]string{"/apis/", "/api/"}, req.URL.Path) {
+		matches := clustersRE.FindStringSubmatch(req.URL.Path)
+		if len(matches) == 2 {
+			// matches[0] is the leftmost pattern that matches (which includes /clusters/...) - skip over that
+			strippedURL := matches[1]
+			t := req.Clone(req.Context())
+			t.URL.Path = strippedURL
+			return k.delegate.NewRequestInfo(t)
+		}
 	}
 	return k.delegate.NewRequestInfo(req)
 }
+
+// containsPrefix returns true if the specified path has a prefix that contained in given prefix Set
+func containsPrefix(prefixSet []string, path string) bool {
+	for _, prefix := range prefixSet {
+		if strings.HasPrefix(path, prefix) {
+			return true
+		}
+	}
+	return false
+}

pkg/server/requestinfo/kcp_request_info_resolver_test.go

@@ -0,0 +1,115 @@
+/*
+Copyright 2023 The KCP 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 requestinfo
+
+import (
+	"net/http"
+	"net/url"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestRequestInfoResolver(t *testing.T) {
+	tests := map[string]struct {
+		path                string
+		expectedPath        string
+		expectedResource    string
+		expectedSubresource string
+	}{
+		"path with /api prefix": {
+			path:             "/api/v1/namespaces/default/pods",
+			expectedPath:     "/api/v1/namespaces/default/pods",
+			expectedResource: "pods",
+		},
+		"path with /apis prefix": {
+			path:             "/apis/wildwest.dev/v1alpha1/namespaces/default/cowboys/woody",
+			expectedPath:     "/apis/wildwest.dev/v1alpha1/namespaces/default/cowboys/woody",
+			expectedResource: "cowboys",
+		},
+		"path with /apis prefix -- status subresource": {
+			path:                "/apis/wildwest.dev/v1alpha1/namespaces/default/cowboys/woody/status",
+			expectedPath:        "/apis/wildwest.dev/v1alpha1/namespaces/default/cowboys/woody/status",
+			expectedResource:    "cowboys",
+			expectedSubresource: "status",
+		},
+		"path with /apis prefix -- clusters resource": {
+			path:             "/apis/wildwest.dev/v1alpha1/namespaces/default/clusters/woody",
+			expectedPath:     "/apis/wildwest.dev/v1alpha1/namespaces/default/clusters/woody",
+			expectedResource: "clusters",
+		},
+		"path with /apis prefix -- clusters resource, status subresource": {
+			path:                "/apis/wildwest.dev/v1alpha1/namespaces/default/clusters/woody/status",
+			expectedPath:        "/apis/wildwest.dev/v1alpha1/namespaces/default/clusters/woody/status",
+			expectedResource:    "clusters",
+			expectedSubresource: "status",
+		},
+		"path with /clusters prefix": {
+			path:             "/clusters/root/apis/wildwest.dev/v1alpha1/namespaces/default/cowboys/woody",
+			expectedPath:     "/apis/wildwest.dev/v1alpha1/namespaces/default/cowboys/woody",
+			expectedResource: "cowboys",
+		},
+		"path with /clusters prefix -- status subresource": {
+			path:                "/clusters/root/apis/wildwest.dev/v1alpha1/namespaces/default/cowboys/woody/status",
+			expectedPath:        "/apis/wildwest.dev/v1alpha1/namespaces/default/cowboys/woody/status",
+			expectedResource:    "cowboys",
+			expectedSubresource: "status",
+		},
+		"path with /clusters prefix -- clusters resource": {
+			path:             "/clusters/root/apis/wildwest.dev/v1alpha1/namespaces/default/clusters/woody",
+			expectedPath:     "/apis/wildwest.dev/v1alpha1/namespaces/default/clusters/woody",
+			expectedResource: "clusters",
+		},
+		"path with /clusters prefix -- clusters resource, status subresource": {
+			path:                "/clusters/root:my-ws/apis/wildwest.dev/v1alpha1/namespaces/default/clusters/woody/status",
+			expectedPath:        "/apis/wildwest.dev/v1alpha1/namespaces/default/clusters/woody/status",
+			expectedResource:    "clusters",
+			expectedSubresource: "status",
+		},
+		"path with /services prefix": {
+			path:             "/services/apiexport/root:my-ws/my-service/clusters/*/api/v1/configmaps",
+			expectedPath:     "/api/v1/configmaps",
+			expectedResource: "configmaps",
+		},
+		"path with /services prefix -- clusters resource, status subresource": {
+			path:                "/services/apiexport/root:my-ws/my-service/clusters/*/apis/wildwest.dev/v1alpha1/namespaces/default/clusters/woody/status",
+			expectedPath:        "/apis/wildwest.dev/v1alpha1/namespaces/default/clusters/woody/status",
+			expectedResource:    "clusters",
+			expectedSubresource: "status",
+		},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			url, err := url.Parse(test.path)
+			require.NoError(t, err, "error parsing path %q to URL", test.path)
+
+			req := &http.Request{
+				URL:    url,
+				Method: http.MethodGet,
+			}
+
+			requestInfo, err := NewKCPRequestInfoResolver().NewRequestInfo(req)
+			require.NoError(t, err, "unexpected error")
+
+			require.Equal(t, test.expectedPath, requestInfo.Path, "unexpected requestInfo.Path")
+			require.Equal(t, test.expectedResource, requestInfo.Resource, "unexpected requestInfo.Resource")
+			require.Equal(t, test.expectedSubresource, requestInfo.Subresource, "unexpected requestInfo.Subresource")
+
+		})
+	}
+}