Extract delegator.Helper interface to allow making delegate decision based on cache state

staging/src/k8s.io/apiserver/pkg/storage/cacher/cacher_whitebox_test.go

@@ -48,6 +48,7 @@ import (
 	examplev1 "k8s.io/apiserver/pkg/apis/example/v1"
 	"k8s.io/apiserver/pkg/features"
 	"k8s.io/apiserver/pkg/storage"
+	"k8s.io/apiserver/pkg/storage/cacher/delegator"
 	"k8s.io/apiserver/pkg/storage/cacher/metrics"
 	etcd3testing "k8s.io/apiserver/pkg/storage/etcd3/testing"
 	etcdfeature "k8s.io/apiserver/pkg/storage/feature"
@@ -334,9 +335,12 @@ func TestShouldDelegateList(t *testing.T) {
 					expectBypass = bypass
 				}
 			}
-			gotBypass, _ := shouldDelegateList(toStorageOpts(opt))
+			result, err := shouldDelegateList(toStorageOpts(opt), delegator.CacheWithoutSnapshots{})
-			if gotBypass != expectBypass {
+			if err != nil {
-				t.Errorf("Unexpected bypass result for List request with options %+v, bypass expected: %v, got: %v", opt, expectBypass, gotBypass)
+				t.Fatal(err)
+			}
+			if result.ShouldDelegate != expectBypass {
+				t.Errorf("Unexpected bypass result for List request with options %+v, bypass expected: %v, got: %v", opt, expectBypass, result.ShouldDelegate)
 			}
 		}
 	}

staging/src/k8s.io/apiserver/pkg/storage/cacher/delegator.go

@@ -36,8 +36,8 @@ import (
 	"k8s.io/apiserver/pkg/audit"
 	"k8s.io/apiserver/pkg/features"
 	"k8s.io/apiserver/pkg/storage"
+	"k8s.io/apiserver/pkg/storage/cacher/delegator"
 	"k8s.io/apiserver/pkg/storage/cacher/metrics"
-	etcdfeature "k8s.io/apiserver/pkg/storage/feature"
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	"k8s.io/component-base/tracing"
 	"k8s.io/klog/v2"
@@ -180,8 +180,11 @@ func (c *CacheDelegator) GetList(ctx context.Context, key string, opts storage.L
 	if err != nil {
 		return err
 	}
-	shouldDelegate, consistentRead := shouldDelegateList(opts)
+	result, err := shouldDelegateList(opts, delegator.CacheWithoutSnapshots{})
-	if shouldDelegate {
+	if err != nil {
+		return err
+	}
+	if result.ShouldDelegate {
 		return c.storage.GetList(ctx, key, opts, listObj)
 	}
 
@@ -203,7 +206,7 @@ func (c *CacheDelegator) GetList(ctx context.Context, key string, opts storage.L
 			return c.storage.GetList(ctx, key, opts, listObj)
 		}
 	}
-	if consistentRead {
+	if result.ConsistentRead {
 		listRV, err = c.storage.GetCurrentResourceVersion(ctx)
 		if err != nil {
 			return err
@@ -215,7 +218,7 @@ func (c *CacheDelegator) GetList(ctx context.Context, key string, opts storage.L
 	success := "true"
 	fallback := "false"
 	if err != nil {
-		if consistentRead {
+		if result.ConsistentRead {
 			if storage.IsTooLargeResourceVersion(err) {
 				fallback = "true"
 				// Reset resourceVersion during fallback from consistent read.
@@ -229,7 +232,7 @@ func (c *CacheDelegator) GetList(ctx context.Context, key string, opts storage.L
 		}
 		return err
 	}
-	if consistentRead {
+	if result.ConsistentRead {
 		metrics.ConsistentReadTotal.WithLabelValues(c.cacher.resourcePrefix, success, fallback).Add(1)
 	}
 	return nil
@@ -243,36 +246,32 @@ func shouldDelegateListOnNotReadyCache(opts storage.ListOptions) bool {
 	return noLabelSelector && noFieldSelector && hasLimit
 }
 
-// NOTICE: Keep in sync with shouldListFromStorage function in
+// NOTICE: Keep in sync with shouldDelegateList function in
 //
 //	staging/src/k8s.io/apiserver/pkg/util/flowcontrol/request/list_work_estimator.go
-func shouldDelegateList(opts storage.ListOptions) (shouldDeletage, consistentRead bool) {
+func shouldDelegateList(opts storage.ListOptions, cache delegator.Helper) (delegator.Result, error) {
 	// see https://kubernetes.io/docs/reference/using-api/api-concepts/#semantics-for-get-and-list
-	consistentRead = false
 	switch opts.ResourceVersionMatch {
 	case metav1.ResourceVersionMatchExact:
-		return true, consistentRead
+		return cache.ShouldDelegateExactRV(opts.ResourceVersion, opts.Recursive)
 	case metav1.ResourceVersionMatchNotOlderThan:
-		return false, consistentRead
+		return delegator.Result{ShouldDelegate: false}, nil
 	case "":
 		// Legacy exact match
 		if opts.Predicate.Limit > 0 && len(opts.ResourceVersion) > 0 && opts.ResourceVersion != "0" {
-			return true, consistentRead
+			return cache.ShouldDelegateExactRV(opts.ResourceVersion, opts.Recursive)
 		}
 		// Continue
 		if len(opts.Predicate.Continue) > 0 {
-			return true, consistentRead
+			return cache.ShouldDelegateContinue(opts.Predicate.Continue, opts.Recursive)
 		}
 		// Consistent Read
 		if opts.ResourceVersion == "" {
-			consistentRead = true
+			return cache.ShouldDelegateConsistentRead()
-			consistentListFromCacheEnabled := utilfeature.DefaultFeatureGate.Enabled(features.ConsistentListFromCache)
-			requestWatchProgressSupported := etcdfeature.DefaultFeatureSupportChecker.Supports(storage.RequestWatchProgress)
-			return !consistentListFromCacheEnabled || !requestWatchProgressSupported, consistentRead
 		}
-		return false, consistentRead
+		return delegator.Result{ShouldDelegate: false}, nil
 	default:
-		return true, consistentRead
+		return delegator.Result{ShouldDelegate: true}, nil
 	}
 }
 

staging/src/k8s.io/apiserver/pkg/storage/cacher/delegator/interface.go

@@ -0,0 +1,73 @@
+/*
+Copyright 2025 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 delegator
+
+import (
+	"k8s.io/apiserver/pkg/features"
+	"k8s.io/apiserver/pkg/storage"
+	etcdfeature "k8s.io/apiserver/pkg/storage/feature"
+	utilfeature "k8s.io/apiserver/pkg/util/feature"
+)
+
+type Helper interface {
+	ShouldDelegateExactRV(rv string, recursive bool) (Result, error)
+	ShouldDelegateContinue(continueToken string, recursive bool) (Result, error)
+	ShouldDelegateConsistentRead() (Result, error)
+}
+
+// Result of delegator decision.
+type Result struct {
+	// Whether a request cannot be served by cache and should be delegated to etcd.
+	ShouldDelegate bool
+	// Whether a request is a consistent read, used by delegator to decide if it should call GetCurrentResourceVersion to get RV.
+	// Included in interface as only cacher has keyPrefix needed to parse continue token.
+	ConsistentRead bool
+}
+
+type CacheWithoutSnapshots struct{}
+
+var _ Helper = CacheWithoutSnapshots{}
+
+func (c CacheWithoutSnapshots) ShouldDelegateContinue(continueToken string, recursive bool) (Result, error) {
+	return Result{
+		ShouldDelegate: true,
+		// Continue with negative RV is considered a consistent read, however token cannot be parsed without keyPrefix unavailable in staging/src/k8s.io/apiserver/pkg/util/flow_control/request/list_work_estimator.go.
+		ConsistentRead: false,
+	}, nil
+}
+
+func (c CacheWithoutSnapshots) ShouldDelegateExactRV(rv string, recursive bool) (Result, error) {
+	return Result{
+		ShouldDelegate: true,
+		ConsistentRead: false,
+	}, nil
+}
+
+func (c CacheWithoutSnapshots) ShouldDelegateConsistentRead() (Result, error) {
+	return Result{
+		ShouldDelegate: !ConsistentReadSupported(),
+		ConsistentRead: true,
+	}, nil
+}
+
+// ConsistentReadSupported returns whether cache can be used to serve reads with RV not yet observed by cache, including both consistent reads.
+// Function is located here to avoid import cycles between staging/src/k8s.io/apiserver/pkg/storage/cacher/delegator.go and staging/src/k8s.io/apiserver/pkg/util/flow_control/request/list_work_estimator.go.
+func ConsistentReadSupported() bool {
+	consistentListFromCacheEnabled := utilfeature.DefaultFeatureGate.Enabled(features.ConsistentListFromCache)
+	requestWatchProgressSupported := etcdfeature.DefaultFeatureSupportChecker.Supports(storage.RequestWatchProgress)
+	return consistentListFromCacheEnabled && requestWatchProgressSupported
+}

staging/src/k8s.io/apiserver/pkg/storage/cacher/delegator_test.go

@@ -20,8 +20,6 @@ import (
 	"context"
 	"testing"
 
-	"k8s.io/apimachinery/pkg/apis/meta/internalversion"
-	"k8s.io/apimachinery/pkg/apis/meta/internalversion/validation"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apiserver/pkg/apis/example"
@@ -194,56 +192,3 @@ func TestCalculateDigest(t *testing.T) {
 		})
 	}
 }
-
-func TestValidateUndelegatedListOptions(t *testing.T) {
-	opts := []storage.ListOptions{}
-	keyPrefix := "/pods/"
-	continueOnRV1, err := storage.EncodeContinue("/pods/a", keyPrefix, 1)
-	if err != nil {
-		t.Fatalf("Unexpected error: %v", err)
-	}
-	continueOnNegativeRV, err := storage.EncodeContinue("/pods/a", keyPrefix, -1)
-	if err != nil {
-		t.Fatalf("Unexpected error: %v", err)
-	}
-	for _, rv := range []string{"", "0", "1"} {
-		for _, match := range []metav1.ResourceVersionMatch{"", metav1.ResourceVersionMatchExact, metav1.ResourceVersionMatchNotOlderThan} {
-			for _, c := range []string{"", continueOnRV1, continueOnNegativeRV} {
-				for _, limit := range []int64{0, 100} {
-					for _, recursive := range []bool{true, false} {
-						opt := storage.ListOptions{
-							ResourceVersion:      rv,
-							ResourceVersionMatch: match,
-							Predicate: storage.SelectionPredicate{
-								Limit:    limit,
-								Continue: c,
-							},
-							Recursive: recursive,
-						}
-						// Skip requests that will not pass apiserver validation
-						if errs := validation.ValidateListOptions(&internalversion.ListOptions{
-							ResourceVersion:      opt.ResourceVersion,
-							ResourceVersionMatch: opt.ResourceVersionMatch,
-							Limit:                opt.Predicate.Limit,
-							Continue:             opt.Predicate.Continue,
-						}, false); len(errs) != 0 {
-							continue
-						}
-						// Skip requests sent directly to etcd
-						if delegateList, _ := shouldDelegateList(opt); delegateList {
-							continue
-						}
-						opts = append(opts, opt)
-					}
-
-				}
-			}
-		}
-	}
-	for _, opt := range opts {
-		_, _, err := storage.ValidateListOptions(keyPrefix, storage.APIObjectVersioner{}, opt)
-		if err != nil {
-			t.Errorf("Expected List requests %+v to pass validation, got: %v", opt, err)
-		}
-	}
-}

staging/src/k8s.io/apiserver/pkg/storage/cacher/watch_cache.go

@@ -32,9 +32,9 @@ import (
 	"k8s.io/apimachinery/pkg/watch"
 	"k8s.io/apiserver/pkg/features"
 	"k8s.io/apiserver/pkg/storage"
+	"k8s.io/apiserver/pkg/storage/cacher/delegator"
 	"k8s.io/apiserver/pkg/storage/cacher/metrics"
 	"k8s.io/apiserver/pkg/storage/cacher/progress"
-	etcdfeature "k8s.io/apiserver/pkg/storage/feature"
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	"k8s.io/client-go/tools/cache"
 	"k8s.io/component-base/tracing"
@@ -496,8 +496,7 @@ func (s sortableStoreElements) Swap(i, j int) {
 // WaitUntilFreshAndList returns list of pointers to `storeElement` objects along
 // with their ResourceVersion and the name of the index, if any, that was used.
 func (w *watchCache) WaitUntilFreshAndList(ctx context.Context, resourceVersion uint64, key string, opts storage.ListOptions) (resp listResp, index string, err error) {
-	requestWatchProgressSupported := etcdfeature.DefaultFeatureSupportChecker.Supports(storage.RequestWatchProgress)
+	if delegator.ConsistentReadSupported() && w.notFresh(resourceVersion) {
-	if utilfeature.DefaultFeatureGate.Enabled(features.ConsistentListFromCache) && requestWatchProgressSupported && w.notFresh(resourceVersion) {
 		w.waitingUntilFresh.Add()
 		err = w.waitUntilFreshAndBlock(ctx, resourceVersion)
 		w.waitingUntilFresh.Remove()
@@ -562,8 +561,7 @@ func (w *watchCache) notFresh(resourceVersion uint64) bool {
 // WaitUntilFreshAndGet returns a pointers to <storeElement> object.
 func (w *watchCache) WaitUntilFreshAndGet(ctx context.Context, resourceVersion uint64, key string) (interface{}, bool, uint64, error) {
 	var err error
-	requestWatchProgressSupported := etcdfeature.DefaultFeatureSupportChecker.Supports(storage.RequestWatchProgress)
+	if delegator.ConsistentReadSupported() && w.notFresh(resourceVersion) {
-	if utilfeature.DefaultFeatureGate.Enabled(features.ConsistentListFromCache) && requestWatchProgressSupported && w.notFresh(resourceVersion) {
 		w.waitingUntilFresh.Add()
 		err = w.waitUntilFreshAndBlock(ctx, resourceVersion)
 		w.waitingUntilFresh.Remove()

staging/src/k8s.io/apiserver/pkg/util/flowcontrol/request/list_work_estimator.go

@@ -23,10 +23,7 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	apirequest "k8s.io/apiserver/pkg/endpoints/request"
-	"k8s.io/apiserver/pkg/features"
+	"k8s.io/apiserver/pkg/storage/cacher/delegator"
-	"k8s.io/apiserver/pkg/storage"
-	etcdfeature "k8s.io/apiserver/pkg/storage/feature"
-	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	"k8s.io/klog/v2"
 )
 
@@ -85,7 +82,12 @@ func (e *listWorkEstimator) estimate(r *http.Request, flowSchemaName, priorityLe
 			return WorkEstimate{InitialSeats: e.config.MinimumSeats}
 		}
 	}
-	listFromStorage, _ := shouldListFromStorage(&listOptions)
+	// TODO: Check whether watchcache is enabled.
+	result, err := shouldDelegateList(&listOptions, delegator.CacheWithoutSnapshots{})
+	if err != nil {
+		return WorkEstimate{InitialSeats: maxSeats}
+	}
+	listFromStorage := result.ShouldDelegate
 	isListFromCache := requestInfo.Verb == "watch" || !listFromStorage
 
 	numStored, err := e.countGetterFn(key(requestInfo))
@@ -162,32 +164,30 @@ func key(requestInfo *apirequest.RequestInfo) string {
 // NOTICE: Keep in sync with shouldDelegateList function in
 //
 //	staging/src/k8s.io/apiserver/pkg/storage/cacher/delegator.go
-func shouldListFromStorage(opts *metav1.ListOptions) (shouldDeletage, consistentRead bool) {
+func shouldDelegateList(opts *metav1.ListOptions, cache delegator.Helper) (delegator.Result, error) {
 	// see https://kubernetes.io/docs/reference/using-api/api-concepts/#semantics-for-get-and-list
-	consistentRead = false
 	switch opts.ResourceVersionMatch {
 	case metav1.ResourceVersionMatchExact:
-		return true, consistentRead
+		return cache.ShouldDelegateExactRV(opts.ResourceVersion, defaultRecursive)
 	case metav1.ResourceVersionMatchNotOlderThan:
-		return false, consistentRead
+		return delegator.Result{ShouldDelegate: false}, nil
 	case "":
 		// Legacy exact match
 		if opts.Limit > 0 && len(opts.ResourceVersion) > 0 && opts.ResourceVersion != "0" {
-			return true, consistentRead
+			return cache.ShouldDelegateExactRV(opts.ResourceVersion, defaultRecursive)
 		}
 		// Continue
 		if len(opts.Continue) > 0 {
-			return true, consistentRead
+			return cache.ShouldDelegateContinue(opts.Continue, defaultRecursive)
 		}
 		// Consistent Read
 		if opts.ResourceVersion == "" {
-			consistentRead = true
+			return cache.ShouldDelegateConsistentRead()
-			consistentListFromCacheEnabled := utilfeature.DefaultFeatureGate.Enabled(features.ConsistentListFromCache)
-			requestWatchProgressSupported := etcdfeature.DefaultFeatureSupportChecker.Supports(storage.RequestWatchProgress)
-			return !consistentListFromCacheEnabled || !requestWatchProgressSupported, consistentRead
 		}
-		return false, consistentRead
+		return delegator.Result{ShouldDelegate: false}, nil
 	default:
-		return true, consistentRead
+		return delegator.Result{ShouldDelegate: true}, nil
 	}
 }
+
+var defaultRecursive = true