apiserver: refactor WithRetryAfter server filter

staging/src/k8s.io/apiserver/pkg/server/config.go

@@ -800,7 +800,8 @@ func DefaultBuildHandlerChain(apiHandler http.Handler, c *Config) http.Handler {
 	handler = genericapifilters.WithCacheControl(handler)
 	handler = genericfilters.WithHSTS(handler, c.HSTSDirectives)
 	if c.ShutdownSendRetryAfter {
-		handler = genericfilters.WithRetryAfter(handler, c.lifecycleSignals.AfterShutdownDelayDuration.Signaled())
+		shouldRetryAfterFn := genericfilters.NewShouldRespondWithRetryAfterFunc(c.ShutdownSendRetryAfter, c.lifecycleSignals.AfterShutdownDelayDuration.Signaled())
+		handler = genericfilters.WithRetryAfter(handler, shouldRetryAfterFn)
 	}
 	handler = genericfilters.WithHTTPLogging(handler)
 	if utilfeature.DefaultFeatureGate.Enabled(genericfeatures.APIServerTracing) {

staging/src/k8s.io/apiserver/pkg/server/filters/with_retry_after.go

@@ -46,11 +46,11 @@ type retryAfterParams struct {
 	Message string
 }
 
-// shouldRespondWithRetryAfterFunc returns true if the requests should
+// ShouldRespondWithRetryAfterFunc returns true if the requests should
 // be rejected with a Retry-After response once certain conditions are met.
 // The retryAfterParams returned contains instructions on how to
 // construct the Retry-After response.
-type shouldRespondWithRetryAfterFunc func() (*retryAfterParams, bool)
+type ShouldRespondWithRetryAfterFunc func() (*retryAfterParams, bool)
 
 // WithRetryAfter rejects any incoming new request(s) with a 429
 // if the specified shutdownDelayDurationElapsedFn channel is closed
@@ -62,25 +62,40 @@ type shouldRespondWithRetryAfterFunc func() (*retryAfterParams, bool)
 //   - 'Connection: close': tear down the TCP connection
 //
 // TODO: is there a way to merge WithWaitGroup and this filter?
-func WithRetryAfter(handler http.Handler, shutdownDelayDurationElapsedCh <-chan struct{}) http.Handler {
+func WithRetryAfter(handler http.Handler, when ShouldRespondWithRetryAfterFunc) http.Handler {
+	// NOTE: both WithRetryAfter and WithWaitGroup must use the same exact isRequestExemptFunc 'isRequestExemptFromRetryAfter,
+	// otherwise SafeWaitGroup might wait indefinitely and will prevent the server from shutting down gracefully.
+	return withRetryAfter(handler, isRequestExemptFromRetryAfter, when)
+}
+
+// NewShouldRespondWithRetryAfterFunc returns a ShouldRespondWithRetryAfterFunc
+func NewShouldRespondWithRetryAfterFunc(shutdownSendRetryAfter bool, shutdownCh <-chan struct{}) ShouldRespondWithRetryAfterFunc {
+	if !shutdownSendRetryAfter {
+		return func() (*retryAfterParams, bool) {
+			return nil, false
+		}
+	}
+
+	return newShutdownRetryAfterFunc(shutdownCh)
+}
+
+func newShutdownRetryAfterFunc(shutdownCh <-chan struct{}) ShouldRespondWithRetryAfterFunc {
 	shutdownRetryAfterParams := &retryAfterParams{
 		TearDownConnection: true,
 		Message:            "The apiserver is shutting down, please try again later.",
 	}
 
-	// NOTE: both WithRetryAfter and WithWaitGroup must use the same exact isRequestExemptFunc 'isRequestExemptFromRetryAfter,
-	// otherwise SafeWaitGroup might wait indefinitely and will prevent the server from shutting down gracefully.
-	return withRetryAfter(handler, isRequestExemptFromRetryAfter, func() (*retryAfterParams, bool) {
+	return func() (*retryAfterParams, bool) {
 		select {
-		case <-shutdownDelayDurationElapsedCh:
+		case <-shutdownCh:
 			return shutdownRetryAfterParams, true
 		default:
 			return nil, false
 		}
-	})
+	}
 }
 
-func withRetryAfter(handler http.Handler, isRequestExemptFn isRequestExemptFunc, shouldRespondWithRetryAfterFn shouldRespondWithRetryAfterFunc) http.Handler {
+func withRetryAfter(handler http.Handler, isRequestExemptFn isRequestExemptFunc, shouldRespondWithRetryAfterFn ShouldRespondWithRetryAfterFunc) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
 		params, send := shouldRespondWithRetryAfterFn()
 		if !send || isRequestExemptFn(req) {

staging/src/k8s.io/apiserver/pkg/server/filters/with_retry_after_test.go

@@ -17,8 +17,10 @@ limitations under the License.
 package filters
 
 import (
+	"github.com/google/go-cmp/cmp"
 	"net/http"
 	"net/http/httptest"
+	"reflect"
 	"testing"
 
 	utilwaitgroup "k8s.io/apimachinery/pkg/util/waitgroup"
@@ -28,7 +30,7 @@ import (
 func TestWithRetryAfter(t *testing.T) {
 	tests := []struct {
 		name                   string
-		shutdownDelayDurationElapsedFn func() <-chan struct{}
+		when                   ShouldRespondWithRetryAfterFunc
 		requestURL             string
 		userAgent              string
 		safeWaitGroupIsWaiting bool
@@ -39,8 +41,8 @@ func TestWithRetryAfter(t *testing.T) {
 	}{
 		{
 			name: "retry-after disabled",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(false)
+			when: func() (*retryAfterParams, bool) {
+				return nil, false
 			},
 			requestURL:         "/api/v1/namespaces",
 			userAgent:          "foo",
@@ -51,8 +53,11 @@ func TestWithRetryAfter(t *testing.T) {
 		},
 		{
 			name: "retry-after enabled, request is not exempt",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*retryAfterParams, bool) {
+				return &retryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:         "/api/v1/namespaces",
 			userAgent:          "foo",
@@ -61,10 +66,28 @@ func TestWithRetryAfter(t *testing.T) {
 			retryAfterExpected: "5",
 			statusCodeExpected: http.StatusTooManyRequests,
 		},
+		{
+			name: "retry-after enabled, request is not exempt, no connection tear down",
+			when: func() (*retryAfterParams, bool) {
+				return &retryAfterParams{
+					TearDownConnection: false,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
+			},
+			requestURL:         "/api/v1/namespaces",
+			userAgent:          "foo",
+			handlerInvoked:     0,
+			closeExpected:      "",
+			retryAfterExpected: "5",
+			statusCodeExpected: http.StatusTooManyRequests,
+		},
 		{
 			name: "retry-after enabled, request is exempt(/metrics)",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*retryAfterParams, bool) {
+				return &retryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:         "/metrics?foo=bar",
 			userAgent:          "foo",
@@ -75,8 +98,11 @@ func TestWithRetryAfter(t *testing.T) {
 		},
 		{
 			name: "retry-after enabled, request is exempt(/livez)",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*retryAfterParams, bool) {
+				return &retryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:         "/livez?verbose",
 			userAgent:          "foo",
@@ -87,8 +113,11 @@ func TestWithRetryAfter(t *testing.T) {
 		},
 		{
 			name: "retry-after enabled, request is exempt(/readyz)",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*retryAfterParams, bool) {
+				return &retryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:         "/readyz?verbose",
 			userAgent:          "foo",
@@ -99,8 +128,11 @@ func TestWithRetryAfter(t *testing.T) {
 		},
 		{
 			name: "retry-after enabled, request is exempt(/healthz)",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*retryAfterParams, bool) {
+				return &retryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:         "/healthz?verbose",
 			userAgent:          "foo",
@@ -111,8 +143,11 @@ func TestWithRetryAfter(t *testing.T) {
 		},
 		{
 			name: "retry-after enabled, request is exempt(local loopback)",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*retryAfterParams, bool) {
+				return &retryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:         "/api/v1/namespaces",
 			userAgent:          "kube-apiserver/",
@@ -121,22 +156,13 @@ func TestWithRetryAfter(t *testing.T) {
 			retryAfterExpected: "",
 			statusCodeExpected: http.StatusOK,
 		},
-		{
-			name: "nil channel",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return nil
-			},
-			requestURL:         "/api/v1/namespaces",
-			userAgent:          "foo",
-			handlerInvoked:     1,
-			closeExpected:      "",
-			retryAfterExpected: "",
-			statusCodeExpected: http.StatusOK,
-		},
 		{
 			name: "retry-after enabled, request is exempt(/readyz), SafeWaitGroup is in waiting mode",
-			shutdownDelayDurationElapsedFn: func() <-chan struct{} {
-				return newChannel(true)
+			when: func() (*retryAfterParams, bool) {
+				return &retryAfterParams{
+					TearDownConnection: true,
+					Message:            "The apiserver is shutting down, please try again later.",
+				}, true
 			},
 			requestURL:             "/readyz?verbose",
 			userAgent:              "foo",
@@ -165,7 +191,7 @@ func TestWithRetryAfter(t *testing.T) {
 			wrapped := WithWaitGroup(handler, func(*http.Request, *apirequest.RequestInfo) bool {
 				return false
 			}, safeWG)
-			wrapped = WithRetryAfter(wrapped, test.shutdownDelayDurationElapsedFn())
+			wrapped = WithRetryAfter(wrapped, test.when)
 
 			req, err := http.NewRequest(http.MethodGet, test.requestURL, nil)
 			if err != nil {
@@ -198,6 +224,58 @@ func TestWithRetryAfter(t *testing.T) {
 	}
 }
 
+func TestNewShouldRespondWithRetryAfterFunc(t *testing.T) {
+	tests := []struct {
+		name                     string
+		shutdownSendRetryAfter   bool
+		shutdownCh               <-chan struct{}
+		sendRetryAfterExpected   bool
+		retryAfterParamsExpected *retryAfterParams
+	}{
+		{
+			name:                     "shutdown-send-retry-after is disabled",
+			shutdownSendRetryAfter:   false,
+			shutdownCh:               newChannel(true),
+			sendRetryAfterExpected:   false,
+			retryAfterParamsExpected: nil,
+		},
+		{
+			name:                   "shutdown-send-retry-after is enabled, shutting down",
+			shutdownSendRetryAfter: true,
+			shutdownCh:             newChannel(true),
+			sendRetryAfterExpected: true,
+			retryAfterParamsExpected: &retryAfterParams{
+				TearDownConnection: true,
+				Message:            "The apiserver is shutting down, please try again later.",
+			},
+		},
+		{
+			name:                     "shutdown-send-retry-after is enabled, not shutting down",
+			shutdownSendRetryAfter:   true,
+			shutdownCh:               newChannel(false),
+			sendRetryAfterExpected:   false,
+			retryAfterParamsExpected: nil,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			fn := NewShouldRespondWithRetryAfterFunc(test.shutdownSendRetryAfter, test.shutdownCh)
+			if fn == nil {
+				t.Fatal("Expected a non nil ShouldRespondWithRetryAfterFunc")
+			}
+
+			retryAfterParamsGot, sendRetryAfterGot := fn()
+			if test.sendRetryAfterExpected != sendRetryAfterGot {
+				t.Errorf("Expected send retry-after: %t, but got: %t", test.sendRetryAfterExpected, sendRetryAfterGot)
+			}
+			if !reflect.DeepEqual(test.retryAfterParamsExpected, retryAfterParamsGot) {
+				t.Errorf("Expected retry-after params to match, diff: %s", cmp.Diff(test.retryAfterParamsExpected, retryAfterParamsGot))
+			}
+		})
+	}
+}
+
 func newChannel(closed bool) <-chan struct{} {
 	ch := make(chan struct{})
 	if closed {

staging/src/k8s.io/apiserver/pkg/server/genericapiserver_graceful_termination_test.go

@@ -519,7 +519,8 @@ func newGenericAPIServer(t *testing.T, keepListening bool) *GenericAPIServer {
 	config.BuildHandlerChainFunc = func(apiHandler http.Handler, c *Config) http.Handler {
 		handler := genericfilters.WithWaitGroup(apiHandler, c.LongRunningFunc, c.HandlerChainWaitGroup)
 		if c.ShutdownSendRetryAfter {
-			handler = genericfilters.WithRetryAfter(handler, c.lifecycleSignals.AfterShutdownDelayDuration.Signaled())
+			shouldRetryAfterFn := genericfilters.NewShouldRespondWithRetryAfterFunc(c.ShutdownSendRetryAfter, c.lifecycleSignals.AfterShutdownDelayDuration.Signaled())
+			handler = genericfilters.WithRetryAfter(handler, shouldRetryAfterFn)
 		}
 		handler = genericapifilters.WithRequestInfo(handler, c.RequestInfoResolver)
 		return handler