/*
Copyright 2016 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 filters

import (
	"context"
	"fmt"
	"net/http"
	"net/http/httptest"
	"net/url"
	"os"
	"reflect"
	"strings"
	"sync"
	"testing"
	"time"

	flowcontrol "k8s.io/api/flowcontrol/v1beta3"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/types"
	"k8s.io/apimachinery/pkg/util/sets"
	"k8s.io/apimachinery/pkg/util/wait"
	"k8s.io/apiserver/pkg/apis/flowcontrol/bootstrap"
	"k8s.io/apiserver/pkg/authentication/user"
	apifilters "k8s.io/apiserver/pkg/endpoints/filters"
	epmetrics "k8s.io/apiserver/pkg/endpoints/metrics"
	apirequest "k8s.io/apiserver/pkg/endpoints/request"
	"k8s.io/apiserver/pkg/server/mux"
	utilflowcontrol "k8s.io/apiserver/pkg/util/flowcontrol"
	fq "k8s.io/apiserver/pkg/util/flowcontrol/fairqueuing"
	fcmetrics "k8s.io/apiserver/pkg/util/flowcontrol/metrics"
	fcrequest "k8s.io/apiserver/pkg/util/flowcontrol/request"
	"k8s.io/client-go/informers"
	clientset "k8s.io/client-go/kubernetes"
	"k8s.io/client-go/kubernetes/fake"
	"k8s.io/component-base/metrics/legacyregistry"
	"k8s.io/component-base/metrics/testutil"
	"k8s.io/klog/v2"

	"github.com/google/go-cmp/cmp"
)

func TestMain(m *testing.M) {
	klog.InitFlags(nil)
	os.Exit(m.Run())
}

type mockDecision int

const (
	decisionNoQueuingExecute mockDecision = iota
	decisionQueuingExecute
	decisionCancelWait
	decisionReject
	decisionSkipFilter
)

var defaultRequestWorkEstimator = func(req *http.Request, fsName, plName string) fcrequest.WorkEstimate {
	return fcrequest.WorkEstimate{InitialSeats: 1}
}

type fakeApfFilter struct {
	mockDecision mockDecision
	postEnqueue  func()
	postDequeue  func()

	utilflowcontrol.WatchTracker
	utilflowcontrol.MaxSeatsTracker
}

func (t fakeApfFilter) Handle(ctx context.Context,
	requestDigest utilflowcontrol.RequestDigest,
	noteFn func(fs *flowcontrol.FlowSchema, pl *flowcontrol.PriorityLevelConfiguration, flowDistinguisher string),
	workEstimator func() fcrequest.WorkEstimate,
	queueNoteFn fq.QueueNoteFn,
	execFn func(),
) {
	if t.mockDecision == decisionSkipFilter {
		panic("Handle should not be invoked")
	}
	noteFn(bootstrap.SuggestedFlowSchemaGlobalDefault, bootstrap.SuggestedPriorityLevelConfigurationGlobalDefault, requestDigest.User.GetName())
	switch t.mockDecision {
	case decisionNoQueuingExecute:
		execFn()
	case decisionQueuingExecute:
		queueNoteFn(true)
		t.postEnqueue()
		queueNoteFn(false)
		t.postDequeue()
		execFn()
	case decisionCancelWait:
		queueNoteFn(true)
		t.postEnqueue()
		queueNoteFn(false)
		t.postDequeue()
	case decisionReject:
		return
	}
}

func (t fakeApfFilter) Run(stopCh <-chan struct{}) error {
	return nil
}

func (t fakeApfFilter) Install(c *mux.PathRecorderMux) {
}

func newApfServerWithSingleRequest(t *testing.T, decision mockDecision) *httptest.Server {
	onExecuteFunc := func() {
		if decision == decisionCancelWait {
			t.Errorf("execute should not be invoked")
		}
		// atomicReadOnlyExecuting can be either 0 or 1 as we test one request at a time.
		if decision != decisionSkipFilter && atomicReadOnlyExecuting != 1 {
			t.Errorf("Wanted %d requests executing, got %d", 1, atomicReadOnlyExecuting)
		}
	}
	postExecuteFunc := func() {}
	// atomicReadOnlyWaiting can be either 0 or 1 as we test one request at a time.
	postEnqueueFunc := func() {
		if atomicReadOnlyWaiting != 1 {
			t.Errorf("Wanted %d requests in queue, got %d", 1, atomicReadOnlyWaiting)
		}
	}
	postDequeueFunc := func() {
		if atomicReadOnlyWaiting != 0 {
			t.Errorf("Wanted %d requests in queue, got %d", 0, atomicReadOnlyWaiting)
		}
	}
	return newApfServerWithHooks(t, decision, onExecuteFunc, postExecuteFunc, postEnqueueFunc, postDequeueFunc)
}

func newApfServerWithHooks(t *testing.T, decision mockDecision, onExecute, postExecute, postEnqueue, postDequeue func()) *httptest.Server {
	fakeFilter := fakeApfFilter{
		mockDecision:    decision,
		postEnqueue:     postEnqueue,
		postDequeue:     postDequeue,
		WatchTracker:    utilflowcontrol.NewWatchTracker(),
		MaxSeatsTracker: utilflowcontrol.NewMaxSeatsTracker(),
	}
	return newApfServerWithFilter(t, fakeFilter, onExecute, postExecute)
}

func newApfServerWithFilter(t *testing.T, flowControlFilter utilflowcontrol.Interface, onExecute, postExecute func()) *httptest.Server {
	epmetrics.Register()
	fcmetrics.Register()
	apfServer := httptest.NewServer(newApfHandlerWithFilter(t, flowControlFilter, onExecute, postExecute))
	return apfServer
}

func newApfHandlerWithFilter(t *testing.T, flowControlFilter utilflowcontrol.Interface, onExecute, postExecute func()) http.Handler {
	requestInfoFactory := &apirequest.RequestInfoFactory{APIPrefixes: sets.NewString("apis", "api"), GrouplessAPIPrefixes: sets.NewString("api")}
	longRunningRequestCheck := BasicLongRunningRequestCheck(sets.NewString("watch"), sets.NewString("proxy"))

	apfHandler := WithPriorityAndFairness(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		onExecute()
	}), longRunningRequestCheck, flowControlFilter, defaultRequestWorkEstimator)

	handler := apifilters.WithRequestInfo(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		r = r.WithContext(apirequest.WithUser(r.Context(), &user.DefaultInfo{
			Groups: []string{user.AllUnauthenticated},
		}))
		apfHandler.ServeHTTP(w, r)
		postExecute()
		if atomicReadOnlyExecuting != 0 {
			t.Errorf("Wanted %d requests executing, got %d", 0, atomicReadOnlyExecuting)
		}
	}), requestInfoFactory)

	return handler
}

func TestApfSkipLongRunningRequest(t *testing.T) {
	server := newApfServerWithSingleRequest(t, decisionSkipFilter)
	defer server.Close()

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	StartPriorityAndFairnessWatermarkMaintenance(ctx.Done())

	// send a watch request to test skipping long running request
	if err := expectHTTPGet(fmt.Sprintf("%s/api/v1/foos/foo/proxy", server.URL), http.StatusOK); err != nil {
		// request should not be rejected
		t.Error(err)
	}
}

func TestApfRejectRequest(t *testing.T) {
	server := newApfServerWithSingleRequest(t, decisionReject)
	defer server.Close()

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	StartPriorityAndFairnessWatermarkMaintenance(ctx.Done())

	if err := expectHTTPGet(fmt.Sprintf("%s/api/v1/namespaces/default", server.URL), http.StatusTooManyRequests); err != nil {
		t.Error(err)
	}

	checkForExpectedMetrics(t, []string{
		"apiserver_request_terminations_total",
		"apiserver_request_total",
	})
}

func TestApfExemptRequest(t *testing.T) {
	server := newApfServerWithSingleRequest(t, decisionNoQueuingExecute)
	defer server.Close()

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	StartPriorityAndFairnessWatermarkMaintenance(ctx.Done())

	if err := expectHTTPGet(fmt.Sprintf("%s/api/v1/namespaces/default", server.URL), http.StatusOK); err != nil {
		t.Error(err)
	}

	checkForExpectedMetrics(t, []string{
		"apiserver_current_inflight_requests",
		"apiserver_flowcontrol_read_vs_write_current_requests",
	})
}

func TestApfExecuteRequest(t *testing.T) {
	server := newApfServerWithSingleRequest(t, decisionQueuingExecute)
	defer server.Close()

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	StartPriorityAndFairnessWatermarkMaintenance(ctx.Done())

	if err := expectHTTPGet(fmt.Sprintf("%s/api/v1/namespaces/default", server.URL), http.StatusOK); err != nil {
		t.Error(err)
	}

	checkForExpectedMetrics(t, []string{
		"apiserver_current_inflight_requests",
		"apiserver_current_inqueue_requests",
		"apiserver_flowcontrol_read_vs_write_current_requests",
	})
}

func TestApfExecuteMultipleRequests(t *testing.T) {
	concurrentRequests := 5
	preStartExecute, postStartExecute := &sync.WaitGroup{}, &sync.WaitGroup{}
	preEnqueue, postEnqueue := &sync.WaitGroup{}, &sync.WaitGroup{}
	preDequeue, postDequeue := &sync.WaitGroup{}, &sync.WaitGroup{}
	finishExecute := &sync.WaitGroup{}
	for _, wg := range []*sync.WaitGroup{preStartExecute, postStartExecute, preEnqueue, postEnqueue, preDequeue, postDequeue, finishExecute} {
		wg.Add(concurrentRequests)
	}

	onExecuteFunc := func() {
		preStartExecute.Done()
		preStartExecute.Wait()
		if int(atomicReadOnlyExecuting) != concurrentRequests {
			t.Errorf("Wanted %d requests executing, got %d", concurrentRequests, atomicReadOnlyExecuting)
		}
		postStartExecute.Done()
		postStartExecute.Wait()
	}

	postEnqueueFunc := func() {
		preEnqueue.Done()
		preEnqueue.Wait()
		if int(atomicReadOnlyWaiting) != concurrentRequests {
			t.Errorf("Wanted %d requests in queue, got %d", 1, atomicReadOnlyWaiting)

		}
		postEnqueue.Done()
		postEnqueue.Wait()
	}

	postDequeueFunc := func() {
		preDequeue.Done()
		preDequeue.Wait()
		if atomicReadOnlyWaiting != 0 {
			t.Errorf("Wanted %d requests in queue, got %d", 0, atomicReadOnlyWaiting)
		}
		postDequeue.Done()
		postDequeue.Wait()
	}

	postExecuteFunc := func() {
		finishExecute.Done()
		finishExecute.Wait()
	}

	server := newApfServerWithHooks(t, decisionQueuingExecute, onExecuteFunc, postExecuteFunc, postEnqueueFunc, postDequeueFunc)
	defer server.Close()

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	StartPriorityAndFairnessWatermarkMaintenance(ctx.Done())

	var wg sync.WaitGroup
	wg.Add(concurrentRequests)
	for i := 0; i < concurrentRequests; i++ {
		go func() {
			defer wg.Done()
			if err := expectHTTPGet(fmt.Sprintf("%s/api/v1/namespaces/default", server.URL), http.StatusOK); err != nil {
				t.Error(err)
			}
		}()
	}
	wg.Wait()

	checkForExpectedMetrics(t, []string{
		"apiserver_current_inflight_requests",
		"apiserver_current_inqueue_requests",
		"apiserver_flowcontrol_read_vs_write_current_requests",
	})
}

func TestApfCancelWaitRequest(t *testing.T) {
	server := newApfServerWithSingleRequest(t, decisionCancelWait)
	defer server.Close()

	if err := expectHTTPGet(fmt.Sprintf("%s/api/v1/namespaces/default", server.URL), http.StatusTooManyRequests); err != nil {
		t.Error(err)
	}

	checkForExpectedMetrics(t, []string{
		"apiserver_current_inflight_requests",
		"apiserver_request_terminations_total",
		"apiserver_request_total",
	})
}

type fakeWatchApfFilter struct {
	lock     sync.Mutex
	inflight int
	capacity int

	postExecutePanic bool
	preExecutePanic  bool

	utilflowcontrol.WatchTracker
	utilflowcontrol.MaxSeatsTracker
}

func newFakeWatchApfFilter(capacity int) *fakeWatchApfFilter {
	return &fakeWatchApfFilter{
		capacity:        capacity,
		WatchTracker:    utilflowcontrol.NewWatchTracker(),
		MaxSeatsTracker: utilflowcontrol.NewMaxSeatsTracker(),
	}
}

func (f *fakeWatchApfFilter) Handle(ctx context.Context,
	requestDigest utilflowcontrol.RequestDigest,
	noteFn func(fs *flowcontrol.FlowSchema, pl *flowcontrol.PriorityLevelConfiguration, flowDistinguisher string),
	_ func() fcrequest.WorkEstimate,
	_ fq.QueueNoteFn,
	execFn func(),
) {
	noteFn(bootstrap.SuggestedFlowSchemaGlobalDefault, bootstrap.SuggestedPriorityLevelConfigurationGlobalDefault, requestDigest.User.GetName())
	canExecute := false
	func() {
		f.lock.Lock()
		defer f.lock.Unlock()
		if f.inflight < f.capacity {
			f.inflight++
			canExecute = true
		}
	}()
	if !canExecute {
		return
	}

	if f.preExecutePanic {
		panic("pre-exec-panic")
	}
	execFn()
	if f.postExecutePanic {
		panic("post-exec-panic")
	}

	f.lock.Lock()
	defer f.lock.Unlock()
	f.inflight--
}

func (f *fakeWatchApfFilter) Run(stopCh <-chan struct{}) error {
	return nil
}

func (t *fakeWatchApfFilter) Install(c *mux.PathRecorderMux) {
}

func (f *fakeWatchApfFilter) wait() error {
	return wait.Poll(100*time.Millisecond, wait.ForeverTestTimeout, func() (bool, error) {
		f.lock.Lock()
		defer f.lock.Unlock()
		return f.inflight == 0, nil
	})
}

func TestApfExecuteWatchRequestsWithInitializationSignal(t *testing.T) {
	signalsLock := sync.Mutex{}
	signals := []utilflowcontrol.InitializationSignal{}
	sendSignals := func() {
		signalsLock.Lock()
		defer signalsLock.Unlock()
		for i := range signals {
			signals[i].Signal()
		}
		signals = signals[:0]
	}

	newInitializationSignal = func() utilflowcontrol.InitializationSignal {
		signalsLock.Lock()
		defer signalsLock.Unlock()
		signal := utilflowcontrol.NewInitializationSignal()
		signals = append(signals, signal)
		return signal
	}
	defer func() {
		newInitializationSignal = utilflowcontrol.NewInitializationSignal
	}()

	// We test if initialization after receiving initialization signal the
	// new requests will be allowed to run by:
	// - sending N requests that will occupy the whole capacity
	// - sending initialiation signals for them
	// - ensuring that number of inflight requests will get to zero
	concurrentRequests := 5
	firstRunning := sync.WaitGroup{}
	firstRunning.Add(concurrentRequests)
	allRunning := sync.WaitGroup{}
	allRunning.Add(2 * concurrentRequests)

	fakeFilter := newFakeWatchApfFilter(concurrentRequests)

	onExecuteFunc := func() {
		firstRunning.Done()

		fakeFilter.wait()

		allRunning.Done()
		allRunning.Wait()
	}

	postExecuteFunc := func() {}

	server := newApfServerWithFilter(t, fakeFilter, onExecuteFunc, postExecuteFunc)
	defer server.Close()

	var wg sync.WaitGroup
	wg.Add(2 * concurrentRequests)
	for i := 0; i < concurrentRequests; i++ {
		go func() {
			defer wg.Done()
			if err := expectHTTPGet(fmt.Sprintf("%s/api/v1/namespaces/default/pods?watch=true", server.URL), http.StatusOK); err != nil {
				t.Error(err)
			}
		}()
	}

	firstRunning.Wait()
	sendSignals()
	fakeFilter.wait()
	firstRunning.Add(concurrentRequests)

	for i := 0; i < concurrentRequests; i++ {
		go func() {
			defer wg.Done()
			if err := expectHTTPGet(fmt.Sprintf("%s/api/v1/namespaces/default/pods?watch=true", server.URL), http.StatusOK); err != nil {
				t.Error(err)
			}
		}()
	}
	firstRunning.Wait()
	sendSignals()
	wg.Wait()
}

func TestApfRejectWatchRequestsWithInitializationSignal(t *testing.T) {
	fakeFilter := newFakeWatchApfFilter(0)

	onExecuteFunc := func() {
		t.Errorf("Request unexepectedly executing")
	}
	postExecuteFunc := func() {}

	server := newApfServerWithFilter(t, fakeFilter, onExecuteFunc, postExecuteFunc)
	defer server.Close()

	if err := expectHTTPGet(fmt.Sprintf("%s/api/v1/namespaces/default/pods?watch=true", server.URL), http.StatusTooManyRequests); err != nil {
		t.Error(err)
	}
}

func TestApfWatchPanic(t *testing.T) {
	epmetrics.Register()
	fcmetrics.Register()

	fakeFilter := newFakeWatchApfFilter(1)

	onExecuteFunc := func() {
		panic("test panic")
	}
	postExecuteFunc := func() {}

	apfHandler := newApfHandlerWithFilter(t, fakeFilter, onExecuteFunc, postExecuteFunc)
	handler := func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if err := recover(); err == nil {
				t.Errorf("expected panic, got %v", err)
			}
		}()
		apfHandler.ServeHTTP(w, r)
	}
	server := httptest.NewServer(http.HandlerFunc(handler))
	defer server.Close()

	if err := expectHTTPGet(fmt.Sprintf("%s/api/v1/namespaces/default/pods?watch=true", server.URL), http.StatusOK); err != nil {
		t.Errorf("unexpected error: %v", err)
	}
}

func TestApfWatchHandlePanic(t *testing.T) {
	epmetrics.Register()
	fcmetrics.Register()
	preExecutePanicingFilter := newFakeWatchApfFilter(1)
	preExecutePanicingFilter.preExecutePanic = true

	postExecutePanicingFilter := newFakeWatchApfFilter(1)
	postExecutePanicingFilter.postExecutePanic = true

	testCases := []struct {
		name   string
		filter *fakeWatchApfFilter
	}{
		{
			name:   "pre-execute panic",
			filter: preExecutePanicingFilter,
		},
		{
			name:   "post-execute panic",
			filter: postExecutePanicingFilter,
		},
	}

	onExecuteFunc := func() {
		time.Sleep(5 * time.Second)
	}
	postExecuteFunc := func() {}

	for _, test := range testCases {
		t.Run(test.name, func(t *testing.T) {
			apfHandler := newApfHandlerWithFilter(t, test.filter, onExecuteFunc, postExecuteFunc)
			handler := func(w http.ResponseWriter, r *http.Request) {
				defer func() {
					if err := recover(); err == nil {
						t.Errorf("expected panic, got %v", err)
					}
				}()
				apfHandler.ServeHTTP(w, r)
			}
			server := httptest.NewServer(http.HandlerFunc(handler))
			defer server.Close()

			if err := expectHTTPGet(fmt.Sprintf("%s/api/v1/namespaces/default/pods?watch=true", server.URL), http.StatusOK); err != nil {
				t.Errorf("unexpected error: %v", err)
			}
		})
	}
}

// TestContextClosesOnRequestProcessed ensures that the request context is cancelled
// automatically even if the server doesn't cancel is explicitly.
// This is required to ensure we won't be leaking goroutines that wait for context
// cancelling (e.g. in queueset::StartRequest method).
// Even though in production we are not using httptest.Server, this logic is shared
// across these two.
func TestContextClosesOnRequestProcessed(t *testing.T) {
	epmetrics.Register()
	fcmetrics.Register()
	wg := sync.WaitGroup{}
	wg.Add(1)
	handler := func(w http.ResponseWriter, r *http.Request) {
		ctx := r.Context()
		// asynchronously wait for context being closed
		go func() {
			<-ctx.Done()
			wg.Done()
		}()
	}
	server := httptest.NewServer(http.HandlerFunc(handler))
	defer server.Close()

	if err := expectHTTPGet(fmt.Sprintf("%s/api/v1/namespaces/default/pods?watch=true", server.URL), http.StatusOK); err != nil {
		t.Errorf("unexpected error: %v", err)
	}

	wg.Wait()
}

type fakeFilterRequestDigest struct {
	*fakeApfFilter
	requestDigestGot *utilflowcontrol.RequestDigest
	workEstimateGot  fcrequest.WorkEstimate
}

func (f *fakeFilterRequestDigest) Handle(ctx context.Context,
	requestDigest utilflowcontrol.RequestDigest,
	noteFn func(fs *flowcontrol.FlowSchema, pl *flowcontrol.PriorityLevelConfiguration, flowDistinguisher string),
	workEstimator func() fcrequest.WorkEstimate,
	_ fq.QueueNoteFn, _ func(),
) {
	f.requestDigestGot = &requestDigest
	noteFn(bootstrap.MandatoryFlowSchemaCatchAll, bootstrap.MandatoryPriorityLevelConfigurationCatchAll, "")
	f.workEstimateGot = workEstimator()
}

func TestApfWithRequestDigest(t *testing.T) {
	epmetrics.Register()
	fcmetrics.Register()
	longRunningFunc := func(_ *http.Request, _ *apirequest.RequestInfo) bool { return false }
	fakeFilter := &fakeFilterRequestDigest{}

	reqDigestExpected := &utilflowcontrol.RequestDigest{
		RequestInfo: &apirequest.RequestInfo{Verb: "get"},
		User:        &user.DefaultInfo{Name: "foo"},
	}
	workExpected := fcrequest.WorkEstimate{
		InitialSeats:      5,
		FinalSeats:        7,
		AdditionalLatency: 3 * time.Second,
	}

	handler := WithPriorityAndFairness(http.HandlerFunc(func(_ http.ResponseWriter, req *http.Request) {}),
		longRunningFunc,
		fakeFilter,
		func(_ *http.Request, _, _ string) fcrequest.WorkEstimate { return workExpected },
	)

	w := httptest.NewRecorder()
	req, err := http.NewRequest(http.MethodGet, "/bar", nil)
	if err != nil {
		t.Fatalf("Failed to create new http request - %v", err)
	}
	req = req.WithContext(apirequest.WithRequestInfo(req.Context(), reqDigestExpected.RequestInfo))
	req = req.WithContext(apirequest.WithUser(req.Context(), reqDigestExpected.User))

	handler.ServeHTTP(w, req)

	if !reflect.DeepEqual(reqDigestExpected, fakeFilter.requestDigestGot) {
		t.Errorf("Expected RequestDigest to match, diff: %s", cmp.Diff(reqDigestExpected, fakeFilter.requestDigestGot))
	}
	if !reflect.DeepEqual(workExpected, fakeFilter.workEstimateGot) {
		t.Errorf("Expected WorkEstimate to match, diff: %s", cmp.Diff(workExpected, fakeFilter.workEstimateGot))
	}
}

func TestPriorityAndFairnessWithPanicRecoveryAndTimeoutFilter(t *testing.T) {
	epmetrics.Register()
	fcmetrics.Register()
	timeFmt := "15:04:05.999"

	t.Run("priority level concurrency is set to 1, request handler panics, next request should not be rejected", func(t *testing.T) {
		const (
			requestTimeout                                        = 1 * time.Minute
			userName                                              = "alice"
			fsName                                                = "test-fs"
			plName                                                = "test-pl"
			serverConcurrency, plConcurrencyShares, plConcurrency = 1, 1, 1
		)

		apfConfiguration := newConfiguration(fsName, plName, userName, plConcurrencyShares, 0)
		stopCh := make(chan struct{})
		controller, controllerCompletedCh := startAPFController(t, stopCh, apfConfiguration, serverConcurrency, requestTimeout/4, plName, plConcurrency)

		headerMatcher := headerMatcher{}
		var executed bool
		// we will raise a panic for the first request.
		firstRequestPathPanic := "/request/panic-as-designed"
		requestHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			executed = true
			headerMatcher.inspect(w, fsName, plName)

			if r.URL.Path == firstRequestPathPanic {
				panic(fmt.Errorf("request handler panic'd as designed - %#v", r.RequestURI))
			}
		})
		handler := newHandlerChain(t, requestHandler, controller, userName, requestTimeout)

		server, requestGetter := newHTTP2ServerWithClient(handler, requestTimeout*2)
		defer server.Close()

		// we send two requests synchronously, one at a time
		//  - first request is expected to panic as designed
		//  - second request is expected to success
		_, err := requestGetter(firstRequestPathPanic)
		if !executed {
			t.Errorf("Expected inner handler to be executed for request: %q", firstRequestPathPanic)
		}
		if isClientTimeout(err) {
			t.Fatalf("the client has unexpectedly timed out - request: %q error: %s", firstRequestPathPanic, err.Error())
		}
		expectResetStreamError(t, err)

		executed = false
		// the second request should be served successfully.
		secondRequestPathShouldWork := "/request/should-succeed-as-expected"
		response, err := requestGetter(secondRequestPathShouldWork)
		if !executed {
			t.Errorf("Expected inner handler to be executed for request: %s", secondRequestPathShouldWork)
		}
		if err != nil {
			t.Fatalf("Expected request: %q to get a response, but got error: %#v", secondRequestPathShouldWork, err)
		}
		if response.StatusCode != http.StatusOK {
			t.Errorf("Expected HTTP status code: %d for request: %q, but got: %#v", http.StatusOK, secondRequestPathShouldWork, response)
		}

		for _, err := range headerMatcher.errors() {
			t.Errorf("Expected APF headers to match, but got: %v", err)
		}

		close(stopCh)
		t.Log("Waiting for the controller to shutdown")

		controllerErr := <-controllerCompletedCh
		if controllerErr != nil {
			t.Errorf("Expected no error from the controller, but got: %#v", controllerErr)
		}
	})

	t.Run("priority level concurrency is set to 1, request times out and inner handler hasn't written to the response yet", func(t *testing.T) {
		t.Parallel()
		const (
			requestTimeout                                        = 5 * time.Second
			userName                                              = "alice"
			fsName                                                = "test-fs"
			plName                                                = "test-pl"
			serverConcurrency, plConcurrencyShares, plConcurrency = 1, 1, 1
		)

		apfConfiguration := newConfiguration(fsName, plName, userName, plConcurrencyShares, 0)
		stopCh := make(chan struct{})
		controller, controllerCompletedCh := startAPFController(t, stopCh, apfConfiguration, serverConcurrency, requestTimeout/4, plName, plConcurrency)

		headerMatcher := headerMatcher{}
		var executed bool
		rquestTimesOutPath := "/request/time-out-as-designed"
		reqHandlerCompletedCh, callerRoundTripDoneCh := make(chan struct{}), make(chan struct{})
		requestHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			executed = true
			headerMatcher.inspect(w, fsName, plName)

			if r.URL.Path == rquestTimesOutPath {
				defer close(reqHandlerCompletedCh)

				// this will force the request to time out.
				<-callerRoundTripDoneCh
			}
		})
		handler := newHandlerChain(t, requestHandler, controller, userName, requestTimeout)

		server, requestGetter := newHTTP2ServerWithClient(handler, requestTimeout*2)
		defer server.Close()

		// send a request synchronously with a client timeout of requestTimeout*2 seconds
		// this ensures the test does not block indefinitely if the server does not respond.
		var (
			response *http.Response
			err      error
		)
		func() {
			defer close(callerRoundTripDoneCh)

			t.Logf("Waiting for the request: %q to time out", rquestTimesOutPath)
			response, err = requestGetter(rquestTimesOutPath)
			if isClientTimeout(err) {
				t.Fatalf("the client has unexpectedly timed out - request: %q error: %s", rquestTimesOutPath, err.Error())
			}
		}()

		if !executed {
			t.Errorf("Expected inner handler to be executed for request: %q", rquestTimesOutPath)
		}
		t.Logf("Waiting for the inner handler of the request: %q to complete", rquestTimesOutPath)
		<-reqHandlerCompletedCh

		if err != nil {
			t.Fatalf("Expected request: %q to get a response, but got error: %#v", rquestTimesOutPath, err)
		}
		if response.StatusCode != http.StatusGatewayTimeout {
			t.Errorf("Expected HTTP status code: %d for request: %q, but got: %#v", http.StatusGatewayTimeout, rquestTimesOutPath, response)
		}

		for _, err := range headerMatcher.errors() {
			t.Errorf("Expected APF headers to match, but got: %v", err)
		}

		close(stopCh)
		t.Log("Waiting for the controller to shutdown")

		controllerErr := <-controllerCompletedCh
		if controllerErr != nil {
			t.Errorf("Expected no error from the controller, but got: %#v", controllerErr)
		}
	})

	t.Run("priority level concurrency is set to 1, inner handler panics after the request times out", func(t *testing.T) {
		t.Parallel()
		const (
			requestTimeout                                        = 5 * time.Second
			userName                                              = "alice"
			fsName                                                = "test-fs"
			plName                                                = "test-pl"
			serverConcurrency, plConcurrencyShares, plConcurrency = 1, 1, 1
		)

		apfConfiguration := newConfiguration(fsName, plName, userName, plConcurrencyShares, 0)
		stopCh := make(chan struct{})
		controller, controllerCompletedCh := startAPFController(t, stopCh, apfConfiguration, serverConcurrency, requestTimeout/4, plName, plConcurrency)

		headerMatcher := headerMatcher{}
		var innerHandlerWriteErr error
		reqHandlerCompletedCh, callerRoundTripDoneCh := make(chan struct{}), make(chan struct{})
		rquestTimesOutPath := "/request/time-out-as-designed"
		requestHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			headerMatcher.inspect(w, fsName, plName)

			if r.URL.Path == rquestTimesOutPath {
				defer close(reqHandlerCompletedCh)
				<-callerRoundTripDoneCh

				// we expect the timeout handler to have timed out this request by now and any attempt
				// to write to the response should return a http.ErrHandlerTimeout error.
				_, innerHandlerWriteErr = w.Write([]byte("foo"))

				panic(http.ErrAbortHandler)
			}
		})
		handler := newHandlerChain(t, requestHandler, controller, userName, requestTimeout)

		server, requestGetter := newHTTP2ServerWithClient(handler, requestTimeout*2)
		defer server.Close()

		// send a request synchronously with a client timeout of requestTimeout*2 seconds
		// this ensures the test does not block indefinitely if the server does not respond.
		var (
			response *http.Response
			err      error
		)
		func() {
			defer close(callerRoundTripDoneCh)
			t.Logf("Waiting for the request: %q to time out", rquestTimesOutPath)
			response, err = requestGetter(rquestTimesOutPath)
			if isClientTimeout(err) {
				t.Fatalf("the client has unexpectedly timed out - request: %q error: %s", rquestTimesOutPath, err.Error())
			}
		}()

		t.Logf("Waiting for the inner handler of the request: %q to complete", rquestTimesOutPath)
		<-reqHandlerCompletedCh

		if innerHandlerWriteErr != http.ErrHandlerTimeout {
			t.Fatalf("Expected error: %#v, but got: %#v", http.ErrHandlerTimeout, err)
		}
		if err != nil {
			t.Fatalf("Expected request: %q to get a response, but got error: %#v", rquestTimesOutPath, err)
		}
		if response.StatusCode != http.StatusGatewayTimeout {
			t.Errorf("Expected HTTP status code: %d for request: %q, but got: %#v", http.StatusGatewayTimeout, rquestTimesOutPath, response)
		}

		for _, err := range headerMatcher.errors() {
			t.Errorf("Expected APF headers to match, but got: %v", err)
		}

		close(stopCh)
		t.Log("Waiting for the controller to shutdown")

		controllerErr := <-controllerCompletedCh
		if controllerErr != nil {
			t.Errorf("Expected no error from the controller, but got: %#v", controllerErr)
		}
	})

	t.Run("priority level concurrency is set to 1, inner handler writes to the response before request times out", func(t *testing.T) {
		t.Parallel()
		const (
			requestTimeout                                        = 5 * time.Second
			userName                                              = "alice"
			fsName                                                = "test-fs"
			plName                                                = "test-pl"
			serverConcurrency, plConcurrencyShares, plConcurrency = 1, 1, 1
		)

		apfConfiguration := newConfiguration(fsName, plName, userName, plConcurrencyShares, 0)
		stopCh := make(chan struct{})
		controller, controllerCompletedCh := startAPFController(t, stopCh, apfConfiguration, serverConcurrency, requestTimeout/4, plName, plConcurrency)

		headerMatcher := headerMatcher{}
		var innerHandlerWriteErr error
		rquestTimesOutPath := "/request/time-out-as-designed"
		reqHandlerCompletedCh, callerRoundTripDoneCh := make(chan struct{}), make(chan struct{})
		requestHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			headerMatcher.inspect(w, fsName, plName)

			if r.URL.Path == rquestTimesOutPath {
				defer close(reqHandlerCompletedCh)

				// inner handler writes header and then let the request time out.
				w.WriteHeader(http.StatusBadRequest)
				<-callerRoundTripDoneCh

				// we expect the timeout handler to have timed out this request by now and any attempt
				// to write to the response should return a http.ErrHandlerTimeout error.
				_, innerHandlerWriteErr = w.Write([]byte("foo"))
			}
		})
		handler := newHandlerChain(t, requestHandler, controller, userName, requestTimeout)

		server, requestGetter := newHTTP2ServerWithClient(handler, requestTimeout*2)
		defer server.Close()

		var err error
		func() {
			defer close(callerRoundTripDoneCh)
			t.Logf("Waiting for the request: %q to time out", rquestTimesOutPath)
			_, err = requestGetter(rquestTimesOutPath)
			if isClientTimeout(err) {
				t.Fatalf("the client has unexpectedly timed out - request: %q error: %s", rquestTimesOutPath, err.Error())
			}
		}()

		t.Logf("Waiting for the inner handler of the request: %q to complete", rquestTimesOutPath)
		<-reqHandlerCompletedCh

		if innerHandlerWriteErr != http.ErrHandlerTimeout {
			t.Fatalf("Expected error: %#v, but got: %#v", http.ErrHandlerTimeout, err)
		}
		expectResetStreamError(t, err)

		for _, err := range headerMatcher.errors() {
			t.Errorf("Expected APF headers to match, but got: %v", err)
		}

		close(stopCh)
		t.Log("Waiting for the controller to shutdown")

		controllerErr := <-controllerCompletedCh
		if controllerErr != nil {
			t.Errorf("Expected no error from the controller, but got: %#v", controllerErr)
		}
	})

	t.Run("priority level concurrency is set to 1, queue length is 1, first request should time out and second (enqueued) request should time out as well", func(t *testing.T) {
		t.Parallel()

		type result struct {
			err      error
			response *http.Response
		}

		const (
			requestTimeout                                                     = 5 * time.Second
			userName                                                           = "alice"
			fsName                                                             = "test-fs"
			plName                                                             = "test-pl"
			serverConcurrency, plConcurrencyShares, plConcurrency, queueLength = 1, 1, 1, 1
		)

		apfConfiguration := newConfiguration(fsName, plName, userName, plConcurrencyShares, queueLength)
		stopCh := make(chan struct{})
		controller, controllerCompletedCh := startAPFController(t, stopCh, apfConfiguration, serverConcurrency, requestTimeout/4, plName, plConcurrency)

		headerMatcher := headerMatcher{}
		var firstRequestInnerHandlerWriteErr error
		var secondRequestExecuted bool
		firstRequestTimesOutPath := "/request/first/time-out-as-designed"
		secondRequestEnqueuedPath := "/request/second/enqueued-as-designed"
		firstReqHandlerCompletedCh, firstReqInProgressCh := make(chan struct{}), make(chan struct{})
		firstReqRoundTripDoneCh, secondReqRoundTripDoneCh := make(chan struct{}), make(chan struct{})
		requestHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			headerMatcher.inspect(w, fsName, plName)

			if r.URL.Path == firstRequestTimesOutPath {
				defer close(firstReqHandlerCompletedCh)

				close(firstReqInProgressCh)
				<-firstReqRoundTripDoneCh

				// make sure we wait until the caller of the second request returns, this is to
				// ensure that second request never has a chance to be executed (to avoid flakes)
				<-secondReqRoundTripDoneCh

				// we expect the timeout handler to have timed out this request by now and any attempt
				// to write to the response should return a http.ErrHandlerTimeout error.
				_, firstRequestInnerHandlerWriteErr = w.Write([]byte("foo"))
				return
			}

			if r.URL.Path == secondRequestEnqueuedPath {
				// we expect the concurrency to be set to 1 and so this request should never be executed.
				secondRequestExecuted = true
			}
		})
		handler := newHandlerChain(t, requestHandler, controller, userName, requestTimeout)

		server, requestGetter := newHTTP2ServerWithClient(handler, requestTimeout*2)
		defer server.Close()

		// This test involves two requests sent to the same priority level, which has 1 queue and
		// a concurrency limit of 1.  The handler chain include the timeout filter.
		// Each request is sent from a separate goroutine, with a client-side timeout that is
		// double the timeout filter's limit.
		// The first request should get dispatched immediately; execution (a) starts with closing
		// the channel that triggers the second client goroutine to send its request and then (b)
		// waits for both client goroutines to have gotten a response (expected to be timeouts).
		// The second request sits in the queue until the timeout filter does its thing, which
		// it does concurrently to both requests.  For the first request this should make the client
		// get a timeout response without directly affecting execution.  For the second request, the
		// fact that the timeout filter closes the request's Context.Done() causes the request to be
		// promptly ejected from its queue.  The goroutine doing the APF handling writes an HTTP
		// response message with status 429.
		// The timeout handler invokes its inner handler in one goroutine while reacting to the
		// passage of time in its original goroutine.  That reaction to a time out consists of either
		// (a) writing an HTTP response message with status 504 to indicate the timeout or (b) doing an
		// HTTP/2 stream close; the latter is done if either the connection has been "hijacked" or some
		// other goroutine (e.g., the one running the inner handler) has started to write a response.
		// In the scenario tested here, there is thus a race between two goroutines to respond to
		// the second request and any of their responses is allowed by the test.
		firstReqResultCh, secondReqResultCh := make(chan result, 1), make(chan result, 1)
		go func() {
			defer close(firstReqRoundTripDoneCh)
			t.Logf("At %s, Sending request: %q", time.Now().Format(timeFmt), firstRequestTimesOutPath)
			resp, err := requestGetter(firstRequestTimesOutPath)
			t.Logf("At %s, RoundTrip of request: %q has completed", time.Now().Format(timeFmt), firstRequestTimesOutPath)
			firstReqResultCh <- result{err: err, response: resp}
		}()
		go func() {
			// we must wait for the "first" request to start executing before
			// we can initiate the "second".
			defer close(secondReqRoundTripDoneCh)

			<-firstReqInProgressCh
			t.Logf("At %s, Sending request: %q", time.Now().Format(timeFmt), secondRequestEnqueuedPath)
			resp, err := requestGetter(secondRequestEnqueuedPath)
			t.Logf("At %s, RoundTrip of request: %q has completed", time.Now().Format(timeFmt), secondRequestEnqueuedPath)
			secondReqResultCh <- result{err: err, response: resp}
		}()

		firstReqResult := <-firstReqResultCh
		if isClientTimeout(firstReqResult.err) {
			t.Fatalf("the client has unexpectedly timed out - request: %q error: %s", firstRequestTimesOutPath, fmtError(firstReqResult.err))
		}
		t.Logf("Waiting for the inner handler of the request: %q to complete", firstRequestTimesOutPath)
		<-firstReqHandlerCompletedCh

		// first request is expected to time out.
		if firstRequestInnerHandlerWriteErr != http.ErrHandlerTimeout {
			t.Fatalf("Expected error: %#v, but got: %s", http.ErrHandlerTimeout, fmtError(firstRequestInnerHandlerWriteErr))
		}
		if isStreamReset(firstReqResult.err) || firstReqResult.response.StatusCode != http.StatusGatewayTimeout {
			// got what was expected
		} else if firstReqResult.err != nil {
			t.Fatalf("Expected request: %q to get a response or stream reset, but got error: %s", firstRequestTimesOutPath, fmtError(firstReqResult.err))
		} else if firstReqResult.response.StatusCode != http.StatusGatewayTimeout {
			t.Errorf("Expected HTTP status code: %d for request: %q, but got: %#+v", http.StatusGatewayTimeout, firstRequestTimesOutPath, firstReqResult.response)
		}

		// second request is expected to either be rejected (ideal behavior) or time out (current approximation of the ideal behavior)
		secondReqResult := <-secondReqResultCh
		if isClientTimeout(secondReqResult.err) {
			t.Fatalf("the client has unexpectedly timed out - request: %q error: %s", secondRequestEnqueuedPath, fmtError(secondReqResult.err))
		}
		if secondRequestExecuted {
			t.Errorf("Expected second request to be enqueued: %q", secondRequestEnqueuedPath)
		}
		if isStreamReset(secondReqResult.err) || secondReqResult.response.StatusCode == http.StatusTooManyRequests || secondReqResult.response.StatusCode == http.StatusGatewayTimeout {
			// got what was expected
		} else if secondReqResult.err != nil {
			t.Fatalf("Expected request: %q to get a response or stream reset, but got error: %s", secondRequestEnqueuedPath, fmtError(secondReqResult.err))
		} else if !(secondReqResult.response.StatusCode == http.StatusTooManyRequests || secondReqResult.response.StatusCode == http.StatusGatewayTimeout) {
			t.Errorf("Expected HTTP status code: %d or %d for request: %q, but got: %#+v", http.StatusTooManyRequests, http.StatusGatewayTimeout, secondRequestEnqueuedPath, secondReqResult.response)
		}

		for _, err := range headerMatcher.errors() {
			t.Errorf("Expected APF headers to match, but got: %v", err)
		}

		close(stopCh)
		t.Log("Waiting for the controller to shutdown")

		controllerErr := <-controllerCompletedCh
		if controllerErr != nil {
			t.Errorf("Expected no error from the controller, but got: %s", fmtError(controllerErr))
		}
	})
}

func fmtError(err error) string {
	return fmt.Sprintf("%#+v=%q", err, err.Error())
}

func startAPFController(t *testing.T, stopCh <-chan struct{}, apfConfiguration []runtime.Object, serverConcurrency int,
	requestWaitLimit time.Duration, plName string, plConcurrency int) (utilflowcontrol.Interface, <-chan error) {
	clientset := newClientset(t, apfConfiguration...)
	// this test does not rely on resync, so resync period is set to zero
	factory := informers.NewSharedInformerFactory(clientset, 0)
	controller := utilflowcontrol.New(factory, clientset.FlowcontrolV1beta3(), serverConcurrency, requestWaitLimit)

	factory.Start(stopCh)

	// wait for the informer cache to sync.
	timeout, cancel := context.WithTimeout(context.TODO(), 5*time.Second)
	defer cancel()
	cacheSyncDone := factory.WaitForCacheSync(timeout.Done())
	if names := unsyncedInformers(cacheSyncDone); len(names) > 0 {
		t.Fatalf("WaitForCacheSync did not successfully complete, resources=%#v", names)
	}

	controllerCompletedCh := make(chan error)
	var controllerErr error
	go func() {
		controllerErr = controller.Run(stopCh)
		controllerCompletedCh <- controllerErr
	}()

	// make sure that apf controller syncs the priority level configuration object we are using in this test.
	// read the metrics and ensure the concurrency limit for our priority level is set to the expected value.
	pollErr := wait.PollImmediate(100*time.Millisecond, 5*time.Second, func() (done bool, err error) {
		if err := gaugeValueMatch("apiserver_flowcontrol_nominal_limit_seats", map[string]string{"priority_level": plName}, plConcurrency); err != nil {
			t.Logf("polling retry - error: %s", err)
			return false, nil
		}
		return true, nil
	})
	if pollErr != nil {
		t.Fatalf("expected the apf controller to sync the priotity level configuration object: %s", plName)
	}

	return controller, controllerCompletedCh
}

// returns a started http2 server, with a client function to send request to the server.
func newHTTP2ServerWithClient(handler http.Handler, clientTimeout time.Duration) (*httptest.Server, func(path string) (*http.Response, error)) {
	server := httptest.NewUnstartedServer(handler)
	server.EnableHTTP2 = true
	server.StartTLS()
	cli := server.Client()
	cli.Timeout = clientTimeout
	return server, func(path string) (*http.Response, error) {
		return cli.Get(server.URL + path)
	}
}

type headerMatcher struct {
	lock    sync.Mutex
	errsGot []error
}

// verifies that the expected flow schema and priority level UIDs are attached to the header.
func (m *headerMatcher) inspect(w http.ResponseWriter, expectedFS, expectedPL string) {
	err := func() error {
		if w == nil {
			return fmt.Errorf("expected a non nil HTTP response")
		}

		key := flowcontrol.ResponseHeaderMatchedFlowSchemaUID
		if value := w.Header().Get(key); expectedFS != value {
			return fmt.Errorf("expected HTTP header %s to have value %q, but got: %q", key, expectedFS, value)
		}

		key = flowcontrol.ResponseHeaderMatchedPriorityLevelConfigurationUID
		if value := w.Header().Get(key); expectedPL != value {
			return fmt.Errorf("expected HTTP header %s to have value %q, but got %q", key, expectedPL, value)
		}
		return nil
	}()
	if err == nil {
		return
	}

	m.lock.Lock()
	defer m.lock.Unlock()
	m.errsGot = append(m.errsGot, err)
}

func (m *headerMatcher) errors() []error {
	m.lock.Lock()
	defer m.lock.Unlock()
	return m.errsGot[:]
}

// when a request panics, http2 resets the stream with an INTERNAL_ERROR message
func expectResetStreamError(t *testing.T, err error) {
	if err == nil {
		t.Fatalf("expected the server to send an error, but got nil")
	}
	if isStreamReset(err) {
		return
	}
	t.Fatalf("expected a stream reset error, but got %#+v=%s", err, err.Error())
}

func newClientset(t *testing.T, objects ...runtime.Object) clientset.Interface {
	clientset := fake.NewSimpleClientset(objects...)
	if clientset == nil {
		t.Fatal("unable to create fake client set")
	}
	return clientset
}

// builds a chain of handlers that include the panic recovery and timeout filter, so we can simulate the behavior of
// a real apiserver.
// the specified user is added as the authenticated user to the request context.
func newHandlerChain(t *testing.T, handler http.Handler, filter utilflowcontrol.Interface, userName string, requestTimeout time.Duration) http.Handler {
	requestInfoFactory := &apirequest.RequestInfoFactory{APIPrefixes: sets.NewString("apis", "api"), GrouplessAPIPrefixes: sets.NewString("api")}
	longRunningRequestCheck := BasicLongRunningRequestCheck(sets.NewString("watch"), sets.NewString("proxy"))

	apfHandler := WithPriorityAndFairness(handler, longRunningRequestCheck, filter, defaultRequestWorkEstimator)

	// add the handler in the chain that adds the specified user to the request context
	handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		r = r.WithContext(apirequest.WithUser(r.Context(), &user.DefaultInfo{
			Name:   userName,
			Groups: []string{user.AllAuthenticated},
		}))

		apfHandler.ServeHTTP(w, r)
	})

	handler = WithTimeoutForNonLongRunningRequests(handler, longRunningRequestCheck)
	// we don't have any request with invalid timeout, so leaving audit policy and sink nil.
	handler = apifilters.WithRequestDeadline(handler, nil, nil, longRunningRequestCheck, nil, requestTimeout)
	handler = apifilters.WithRequestInfo(handler, requestInfoFactory)
	handler = WithPanicRecovery(handler, requestInfoFactory)
	handler = apifilters.WithAuditInit(handler)
	return handler
}

func unsyncedInformers(status map[reflect.Type]bool) []string {
	names := make([]string, 0)

	for objType, synced := range status {
		if !synced {
			names = append(names, objType.Name())
		}
	}

	return names
}

func newConfiguration(fsName, plName, user string, concurrency int32, queueLength int32) []runtime.Object {
	fs := &flowcontrol.FlowSchema{
		ObjectMeta: metav1.ObjectMeta{
			Name: fsName,
			UID:  types.UID(fsName),
		},
		Spec: flowcontrol.FlowSchemaSpec{
			MatchingPrecedence: 1,
			PriorityLevelConfiguration: flowcontrol.PriorityLevelConfigurationReference{
				Name: plName,
			},
			DistinguisherMethod: &flowcontrol.FlowDistinguisherMethod{
				Type: flowcontrol.FlowDistinguisherMethodByUserType,
			},
			Rules: []flowcontrol.PolicyRulesWithSubjects{
				{
					Subjects: []flowcontrol.Subject{
						{
							Kind: flowcontrol.SubjectKindUser,
							User: &flowcontrol.UserSubject{
								Name: user,
							},
						},
					},
					NonResourceRules: []flowcontrol.NonResourcePolicyRule{
						{
							Verbs:           []string{flowcontrol.VerbAll},
							NonResourceURLs: []string{flowcontrol.NonResourceAll},
						},
					},
				},
			},
		},
	}

	var (
		responseType flowcontrol.LimitResponseType = flowcontrol.LimitResponseTypeReject
		qcfg         *flowcontrol.QueuingConfiguration
	)
	if queueLength > 0 {
		responseType = flowcontrol.LimitResponseTypeQueue
		qcfg = &flowcontrol.QueuingConfiguration{
			Queues:           1,
			QueueLengthLimit: queueLength,
			HandSize:         1,
		}
	}
	pl := &flowcontrol.PriorityLevelConfiguration{
		ObjectMeta: metav1.ObjectMeta{
			Name: plName,
			UID:  types.UID(plName),
		},
		Spec: flowcontrol.PriorityLevelConfigurationSpec{
			Type: flowcontrol.PriorityLevelEnablementLimited,
			Limited: &flowcontrol.LimitedPriorityLevelConfiguration{
				NominalConcurrencyShares: concurrency,
				LimitResponse: flowcontrol.LimitResponse{
					Type:    responseType,
					Queuing: qcfg,
				},
			},
		},
	}

	return []runtime.Object{fs, pl}
}

// gathers and checks the metrics.
func checkForExpectedMetrics(t *testing.T, expectedMetrics []string) {
	metricsFamily, err := legacyregistry.DefaultGatherer.Gather()
	if err != nil {
		t.Fatalf("Failed to gather metrics %v", err)
	}

	metrics := map[string]interface{}{}
	for _, mf := range metricsFamily {
		metrics[*mf.Name] = mf
	}

	for _, metricName := range expectedMetrics {
		if _, ok := metrics[metricName]; !ok {
			if !ok {
				t.Errorf("Scraped metrics did not include expected metric %s", metricName)
			}
		}
	}
}

// gaugeValueMatch ensures that the value of gauge metrics matching the labelFilter is as expected.
func gaugeValueMatch(name string, labelFilter map[string]string, wantValue int) error {
	metrics, err := legacyregistry.DefaultGatherer.Gather()
	if err != nil {
		return fmt.Errorf("failed to gather metrics: %s", err)
	}

	sum := 0
	familyMatch, labelMatch := false, false
	for _, mf := range metrics {
		if mf.GetName() != name {
			continue
		}

		familyMatch = true
		for _, metric := range mf.GetMetric() {
			if !testutil.LabelsMatch(metric, labelFilter) {
				continue
			}

			labelMatch = true
			sum += int(metric.GetGauge().GetValue())
		}
	}
	if !familyMatch {
		return fmt.Errorf("expected to find the metric family: %s in the gathered result", name)
	}
	if !labelMatch {
		return fmt.Errorf("expected to find metrics with matching labels: %#+v", labelFilter)
	}
	if wantValue != sum {
		return fmt.Errorf("expected the sum to be: %d, but got: %d for gauge metric: %s with labels %#+v", wantValue, sum, name, labelFilter)
	}

	return nil
}

func isClientTimeout(err error) bool {
	if urlErr, ok := err.(*url.Error); ok {
		return urlErr.Timeout()
	}
	return false
}

func isStreamReset(err error) bool {
	if err == nil {
		return false
	}
	if urlErr, ok := err.(*url.Error); ok {
		// Sadly, the client does not receive a more specific indication
		// of stream reset.
		return strings.Contains(urlErr.Err.Error(), "INTERNAL_ERROR")
	}
	return false
}
