prometheus/scrape/scrape_test.go

// Copyright 2016 The Prometheus 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 scrape

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"io/ioutil"
	"math"
	"net/http"
	"net/http/httptest"
	"net/url"
	"strings"
	"sync"
	"testing"
	"time"

	"github.com/pkg/errors"
	dto "github.com/prometheus/client_model/go"
	config_util "github.com/prometheus/common/config"
	"github.com/prometheus/common/model"

	"github.com/prometheus/prometheus/config"
	"github.com/prometheus/prometheus/discovery/targetgroup"
	"github.com/prometheus/prometheus/pkg/labels"
	"github.com/prometheus/prometheus/pkg/relabel"
	"github.com/prometheus/prometheus/pkg/textparse"
	"github.com/prometheus/prometheus/pkg/timestamp"
	"github.com/prometheus/prometheus/pkg/value"
	"github.com/prometheus/prometheus/storage"
	"github.com/prometheus/prometheus/util/teststorage"
	"github.com/prometheus/prometheus/util/testutil"
)

func TestNewScrapePool(t *testing.T) {
	var (
		app   = &nopAppendable{}
		cfg   = &config.ScrapeConfig{}
		sp, _ = newScrapePool(cfg, app, 0, nil)
	)

	if a, ok := sp.appendable.(*nopAppendable); !ok || a != app {
		t.Fatalf("Wrong sample appender")
	}
	if sp.config != cfg {
		t.Fatalf("Wrong scrape config")
	}
	if sp.newLoop == nil {
		t.Fatalf("newLoop function not initialized")
	}
}

func TestDroppedTargetsList(t *testing.T) {
	var (
		app = &nopAppendable{}
		cfg = &config.ScrapeConfig{
			JobName:        "dropMe",
			ScrapeInterval: model.Duration(1),
			RelabelConfigs: []*relabel.Config{
				{
					Action:       relabel.Drop,
					Regex:        relabel.MustNewRegexp("dropMe"),
					SourceLabels: model.LabelNames{"job"},
				},
			},
		}
		tgs = []*targetgroup.Group{
			{
				Targets: []model.LabelSet{
					{model.AddressLabel: "127.0.0.1:9090"},
				},
			},
		}
		sp, _                  = newScrapePool(cfg, app, 0, nil)
		expectedLabelSetString = "{__address__=\"127.0.0.1:9090\", job=\"dropMe\"}"
		expectedLength         = 1
	)
	sp.Sync(tgs)
	sp.Sync(tgs)
	if len(sp.droppedTargets) != expectedLength {
		t.Fatalf("Length of dropped targets exceeded expected length, expected %v, got %v", expectedLength, len(sp.droppedTargets))
	}
	if sp.droppedTargets[0].DiscoveredLabels().String() != expectedLabelSetString {
		t.Fatalf("Got %v, expected %v", sp.droppedTargets[0].DiscoveredLabels().String(), expectedLabelSetString)
	}
}

// TestDiscoveredLabelsUpdate checks that DiscoveredLabels are updated
// even when new labels don't affect the target `hash`.
func TestDiscoveredLabelsUpdate(t *testing.T) {

	sp := &scrapePool{}
	// These are used when syncing so need this to avoid a panic.
	sp.config = &config.ScrapeConfig{
		ScrapeInterval: model.Duration(1),
		ScrapeTimeout:  model.Duration(1),
	}
	sp.activeTargets = make(map[uint64]*Target)
	t1 := &Target{
		discoveredLabels: labels.Labels{
			labels.Label{
				Name:  "label",
				Value: "name",
			},
		},
	}
	sp.activeTargets[t1.hash()] = t1

	t2 := &Target{
		discoveredLabels: labels.Labels{
			labels.Label{
				Name:  "labelNew",
				Value: "nameNew",
			},
		},
	}
	sp.sync([]*Target{t2})

	testutil.Equals(t, t2.DiscoveredLabels(), sp.activeTargets[t1.hash()].DiscoveredLabels())
}

type testLoop struct {
	startFunc func(interval, timeout time.Duration, errc chan<- error)
	stopFunc  func()
}

func (l *testLoop) run(interval, timeout time.Duration, errc chan<- error) {
	l.startFunc(interval, timeout, errc)
}

func (l *testLoop) stop() {
	l.stopFunc()
}

func (l *testLoop) getCache() *scrapeCache {
	return nil
}

func TestScrapePoolStop(t *testing.T) {
	sp := &scrapePool{
		activeTargets: map[uint64]*Target{},
		loops:         map[uint64]loop{},
		cancel:        func() {},
		client:        http.DefaultClient,
	}
	var mtx sync.Mutex
	stopped := map[uint64]bool{}
	numTargets := 20

	// Stopping the scrape pool must call stop() on all scrape loops,
	// clean them and the respective targets up. It must wait until each loop's
	// stop function returned before returning itself.

	for i := 0; i < numTargets; i++ {
		t := &Target{
			labels: labels.FromStrings(model.AddressLabel, fmt.Sprintf("example.com:%d", i)),
		}
		l := &testLoop{}
		l.stopFunc = func() {
			time.Sleep(time.Duration(i*20) * time.Millisecond)

			mtx.Lock()
			stopped[t.hash()] = true
			mtx.Unlock()
		}

		sp.activeTargets[t.hash()] = t
		sp.loops[t.hash()] = l
	}

	done := make(chan struct{})
	stopTime := time.Now()

	go func() {
		sp.stop()
		close(done)
	}()

	select {
	case <-time.After(5 * time.Second):
		t.Fatalf("scrapeLoop.stop() did not return as expected")
	case <-done:
		// This should have taken at least as long as the last target slept.
		if time.Since(stopTime) < time.Duration(numTargets*20)*time.Millisecond {
			t.Fatalf("scrapeLoop.stop() exited before all targets stopped")
		}
	}

	mtx.Lock()
	testutil.Equals(t, numTargets, len(stopped), "Unexpected number of stopped loops")
	mtx.Unlock()

	testutil.Assert(t, len(sp.activeTargets) == 0, "Targets were not cleared on stopping: %d left", len(sp.activeTargets))
	testutil.Assert(t, len(sp.loops) == 0, "Loops were not cleared on stopping: %d left", len(sp.loops))
}

func TestScrapePoolReload(t *testing.T) {
	var mtx sync.Mutex
	numTargets := 20

	stopped := map[uint64]bool{}

	reloadCfg := &config.ScrapeConfig{
		ScrapeInterval: model.Duration(3 * time.Second),
		ScrapeTimeout:  model.Duration(2 * time.Second),
	}
	// On starting to run, new loops created on reload check whether their preceding
	// equivalents have been stopped.
	newLoop := func(opts scrapeLoopOptions) loop {
		l := &testLoop{}
		l.startFunc = func(interval, timeout time.Duration, errc chan<- error) {
			testutil.Equals(t, 3*time.Second, interval, "Unexpected scrape interval")
			testutil.Equals(t, 2*time.Second, timeout, "Unexpected scrape timeout")

			mtx.Lock()
			targetScraper := opts.scraper.(*targetScraper)
			testutil.Assert(t, stopped[targetScraper.hash()], "Scrape loop for %v not stopped yet", targetScraper)
			mtx.Unlock()
		}
		return l
	}
	sp := &scrapePool{
		appendable:    &nopAppendable{},
		activeTargets: map[uint64]*Target{},
		loops:         map[uint64]loop{},
		newLoop:       newLoop,
		logger:        nil,
		client:        http.DefaultClient,
	}

	// Reloading a scrape pool with a new scrape configuration must stop all scrape
	// loops and start new ones. A new loop must not be started before the preceding
	// one terminated.

	for i := 0; i < numTargets; i++ {
		t := &Target{
			labels: labels.FromStrings(model.AddressLabel, fmt.Sprintf("example.com:%d", i)),
		}
		l := &testLoop{}
		l.stopFunc = func() {
			time.Sleep(time.Duration(i*20) * time.Millisecond)

			mtx.Lock()
			stopped[t.hash()] = true
			mtx.Unlock()
		}

		sp.activeTargets[t.hash()] = t
		sp.loops[t.hash()] = l
	}
	done := make(chan struct{})

	beforeTargets := map[uint64]*Target{}
	for h, t := range sp.activeTargets {
		beforeTargets[h] = t
	}

	reloadTime := time.Now()

	go func() {
		sp.reload(reloadCfg)
		close(done)
	}()

	select {
	case <-time.After(5 * time.Second):
		t.Fatalf("scrapeLoop.reload() did not return as expected")
	case <-done:
		// This should have taken at least as long as the last target slept.
		if time.Since(reloadTime) < time.Duration(numTargets*20)*time.Millisecond {
			t.Fatalf("scrapeLoop.stop() exited before all targets stopped")
		}
	}

	mtx.Lock()
	testutil.Equals(t, numTargets, len(stopped), "Unexpected number of stopped loops")
	mtx.Unlock()

	testutil.Equals(t, sp.activeTargets, beforeTargets, "Reloading affected target states unexpectedly")
	testutil.Equals(t, numTargets, len(sp.loops), "Unexpected number of stopped loops after reload")
}

func TestScrapePoolAppender(t *testing.T) {
	cfg := &config.ScrapeConfig{}
	app := &nopAppendable{}
	sp, _ := newScrapePool(cfg, app, 0, nil)

	loop := sp.newLoop(scrapeLoopOptions{
		target: &Target{},
	})
	appl, ok := loop.(*scrapeLoop)
	testutil.Assert(t, ok, "Expected scrapeLoop but got %T", loop)

	wrapped := appl.appender()

	tl, ok := wrapped.(*timeLimitAppender)
	testutil.Assert(t, ok, "Expected timeLimitAppender but got %T", wrapped)

	_, ok = tl.Appender.(nopAppender)
	testutil.Assert(t, ok, "Expected base appender but got %T", tl.Appender)

	loop = sp.newLoop(scrapeLoopOptions{
		target: &Target{},
		limit:  100,
	})
	appl, ok = loop.(*scrapeLoop)
	testutil.Assert(t, ok, "Expected scrapeLoop but got %T", loop)

	wrapped = appl.appender()

	sl, ok := wrapped.(*limitAppender)
	testutil.Assert(t, ok, "Expected limitAppender but got %T", wrapped)

	tl, ok = sl.Appender.(*timeLimitAppender)
	testutil.Assert(t, ok, "Expected limitAppender but got %T", sl.Appender)

	_, ok = tl.Appender.(nopAppender)
	testutil.Assert(t, ok, "Expected base appender but got %T", tl.Appender)
}

func TestScrapePoolRaces(t *testing.T) {
	interval, _ := model.ParseDuration("500ms")
	timeout, _ := model.ParseDuration("1s")
	newConfig := func() *config.ScrapeConfig {
		return &config.ScrapeConfig{ScrapeInterval: interval, ScrapeTimeout: timeout}
	}
	sp, _ := newScrapePool(newConfig(), &nopAppendable{}, 0, nil)
	tgts := []*targetgroup.Group{
		{
			Targets: []model.LabelSet{
				{model.AddressLabel: "127.0.0.1:9090"},
				{model.AddressLabel: "127.0.0.2:9090"},
				{model.AddressLabel: "127.0.0.3:9090"},
				{model.AddressLabel: "127.0.0.4:9090"},
				{model.AddressLabel: "127.0.0.5:9090"},
				{model.AddressLabel: "127.0.0.6:9090"},
				{model.AddressLabel: "127.0.0.7:9090"},
				{model.AddressLabel: "127.0.0.8:9090"},
			},
		},
	}

	sp.Sync(tgts)
	active := sp.ActiveTargets()
	dropped := sp.DroppedTargets()
	expectedActive, expectedDropped := len(tgts[0].Targets), 0

	testutil.Equals(t, expectedActive, len(active), "Invalid number of active targets")
	testutil.Equals(t, expectedDropped, len(dropped), "Invalid number of dropped targets")

	for i := 0; i < 20; i++ {
		time.Sleep(time.Duration(10 * time.Millisecond))
		sp.reload(newConfig())
	}
	sp.stop()
}

func TestScrapeLoopStopBeforeRun(t *testing.T) {
	scraper := &testScraper{}

	sl := newScrapeLoop(context.Background(),
		scraper,
		nil, nil,
		nopMutator,
		nopMutator,
		nil, nil, 0,
		true,
	)

	// The scrape pool synchronizes on stopping scrape loops. However, new scrape
	// loops are started asynchronously. Thus it's possible, that a loop is stopped
	// again before having started properly.
	// Stopping not-yet-started loops must block until the run method was called and exited.
	// The run method must exit immediately.

	stopDone := make(chan struct{})
	go func() {
		sl.stop()
		close(stopDone)
	}()

	select {
	case <-stopDone:
		t.Fatalf("Stopping terminated before run exited successfully")
	case <-time.After(500 * time.Millisecond):
	}

	// Running the scrape loop must exit before calling the scraper even once.
	scraper.scrapeFunc = func(context.Context, io.Writer) error {
		t.Fatalf("scraper was called for terminated scrape loop")
		return nil
	}

	runDone := make(chan struct{})
	go func() {
		sl.run(1, 0, nil)
		close(runDone)
	}()

	select {
	case <-runDone:
	case <-time.After(1 * time.Second):
		t.Fatalf("Running terminated scrape loop did not exit")
	}

	select {
	case <-stopDone:
	case <-time.After(1 * time.Second):
		t.Fatalf("Stopping did not terminate after running exited")
	}
}

func nopMutator(l labels.Labels) labels.Labels { return l }

func TestScrapeLoopStop(t *testing.T) {
	var (
		signal   = make(chan struct{})
		appender = &collectResultAppender{}
		scraper  = &testScraper{}
		app      = func() storage.Appender { return appender }
	)
	defer close(signal)

	sl := newScrapeLoop(context.Background(),
		scraper,
		nil, nil,
		nopMutator,
		nopMutator,
		app,
		nil,
		0,
		true,
	)

	// Terminate loop after 2 scrapes.
	numScrapes := 0

	scraper.scrapeFunc = func(ctx context.Context, w io.Writer) error {
		numScrapes++
		if numScrapes == 2 {
			go sl.stop()
		}
		w.Write([]byte("metric_a 42\n"))
		return nil
	}

	go func() {
		sl.run(10*time.Millisecond, time.Hour, nil)
		signal <- struct{}{}
	}()

	select {
	case <-signal:
	case <-time.After(5 * time.Second):
		t.Fatalf("Scrape wasn't stopped.")
	}

	// We expected 1 actual sample for each scrape plus 5 for report samples.
	// At least 2 scrapes were made, plus the final stale markers.
	if len(appender.result) < 6*3 || len(appender.result)%6 != 0 {
		t.Fatalf("Expected at least 3 scrapes with 6 samples each, got %d samples", len(appender.result))
	}
	// All samples in a scrape must have the same timestamp.
	var ts int64
	for i, s := range appender.result {
		if i%6 == 0 {
			ts = s.t
		} else if s.t != ts {
			t.Fatalf("Unexpected multiple timestamps within single scrape")
		}
	}
	// All samples from the last scrape must be stale markers.
	for _, s := range appender.result[len(appender.result)-5:] {
		if !value.IsStaleNaN(s.v) {
			t.Fatalf("Appended last sample not as expected. Wanted: stale NaN Got: %x", math.Float64bits(s.v))
		}
	}
}

func TestScrapeLoopRun(t *testing.T) {
	var (
		signal = make(chan struct{})
		errc   = make(chan error)

		scraper = &testScraper{}
		app     = func() storage.Appender { return &nopAppender{} }
	)
	defer close(signal)

	ctx, cancel := context.WithCancel(context.Background())
	sl := newScrapeLoop(ctx,
		scraper,
		nil, nil,
		nopMutator,
		nopMutator,
		app,
		nil,
		0,
		true,
	)

	// The loop must terminate during the initial offset if the context
	// is canceled.
	scraper.offsetDur = time.Hour

	go func() {
		sl.run(time.Second, time.Hour, errc)
		signal <- struct{}{}
	}()

	// Wait to make sure we are actually waiting on the offset.
	time.Sleep(1 * time.Second)

	cancel()
	select {
	case <-signal:
	case <-time.After(5 * time.Second):
		t.Fatalf("Cancellation during initial offset failed")
	case err := <-errc:
		t.Fatalf("Unexpected error: %s", err)
	}

	// The provided timeout must cause cancellation of the context passed down to the
	// scraper. The scraper has to respect the context.
	scraper.offsetDur = 0

	block := make(chan struct{})
	scraper.scrapeFunc = func(ctx context.Context, _ io.Writer) error {
		select {
		case <-block:
		case <-ctx.Done():
			return ctx.Err()
		}
		return nil
	}

	ctx, cancel = context.WithCancel(context.Background())
	sl = newScrapeLoop(ctx,
		scraper,
		nil, nil,
		nopMutator,
		nopMutator,
		app,
		nil,
		0,
		true,
	)

	go func() {
		sl.run(time.Second, 100*time.Millisecond, errc)
		signal <- struct{}{}
	}()

	select {
	case err := <-errc:
		if err != context.DeadlineExceeded {
			t.Fatalf("Expected timeout error but got: %s", err)
		}
	case <-time.After(3 * time.Second):
		t.Fatalf("Expected timeout error but got none")
	}

	// We already caught the timeout error and are certainly in the loop.
	// Let the scrapes returns immediately to cause no further timeout errors
	// and check whether canceling the parent context terminates the loop.
	close(block)
	cancel()

	select {
	case <-signal:
		// Loop terminated as expected.
	case err := <-errc:
		t.Fatalf("Unexpected error: %s", err)
	case <-time.After(3 * time.Second):
		t.Fatalf("Loop did not terminate on context cancellation")
	}
}

func TestScrapeLoopMetadata(t *testing.T) {
	var (
		signal  = make(chan struct{})
		scraper = &testScraper{}
		cache   = newScrapeCache()
	)
	defer close(signal)

	ctx, cancel := context.WithCancel(context.Background())
	sl := newScrapeLoop(ctx,
		scraper,
		nil, nil,
		nopMutator,
		nopMutator,
		func() storage.Appender { return nopAppender{} },
		cache,
		0,
		true,
	)
	defer cancel()

	total, _, _, err := sl.append([]byte(`# TYPE test_metric counter
# HELP test_metric some help text
# UNIT test_metric metric
test_metric 1
# TYPE test_metric_no_help gauge
# HELP test_metric_no_type other help text
# EOF`), "application/openmetrics-text", time.Now())
	testutil.Ok(t, err)
	testutil.Equals(t, 1, total)

	md, ok := cache.GetMetadata("test_metric")
	testutil.Assert(t, ok, "expected metadata to be present")
	testutil.Assert(t, textparse.MetricTypeCounter == md.Type, "unexpected metric type")
	testutil.Equals(t, "some help text", md.Help)
	testutil.Equals(t, "metric", md.Unit)

	md, ok = cache.GetMetadata("test_metric_no_help")
	testutil.Assert(t, ok, "expected metadata to be present")
	testutil.Assert(t, textparse.MetricTypeGauge == md.Type, "unexpected metric type")
	testutil.Equals(t, "", md.Help)
	testutil.Equals(t, "", md.Unit)

	md, ok = cache.GetMetadata("test_metric_no_type")
	testutil.Assert(t, ok, "expected metadata to be present")
	testutil.Assert(t, textparse.MetricTypeUnknown == md.Type, "unexpected metric type")
	testutil.Equals(t, "other help text", md.Help)
	testutil.Equals(t, "", md.Unit)
}

func TestScrapeLoopSeriesAdded(t *testing.T) {
	// Need a full storage for correct Add/AddFast semantics.
	s := teststorage.New(t)
	defer s.Close()

	app, err := s.Appender()
	testutil.Ok(t, err)

	ctx, cancel := context.WithCancel(context.Background())
	sl := newScrapeLoop(ctx,
		&testScraper{},
		nil, nil,
		nopMutator,
		nopMutator,
		func() storage.Appender { return app },
		nil,
		0,
		true,
	)
	defer cancel()

	total, added, seriesAdded, err := sl.append([]byte("test_metric 1\n"), "", time.Time{})
	testutil.Ok(t, err)
	testutil.Equals(t, 1, total)
	testutil.Equals(t, 1, added)
	testutil.Equals(t, 1, seriesAdded)

	total, added, seriesAdded, err = sl.append([]byte("test_metric 1\n"), "", time.Time{})
	testutil.Ok(t, err)
	testutil.Equals(t, 1, total)
	testutil.Equals(t, 1, added)
	testutil.Equals(t, 0, seriesAdded)
}

func TestScrapeLoopRunCreatesStaleMarkersOnFailedScrape(t *testing.T) {
	appender := &collectResultAppender{}
	var (
		signal  = make(chan struct{})
		scraper = &testScraper{}
		app     = func() storage.Appender { return appender }
	)
	defer close(signal)

	ctx, cancel := context.WithCancel(context.Background())
	sl := newScrapeLoop(ctx,
		scraper,
		nil, nil,
		nopMutator,
		nopMutator,
		app,
		nil,
		0,
		true,
	)
	// Succeed once, several failures, then stop.
	numScrapes := 0

	scraper.scrapeFunc = func(ctx context.Context, w io.Writer) error {
		numScrapes++

		if numScrapes == 1 {
			w.Write([]byte("metric_a 42\n"))
			return nil
		} else if numScrapes == 5 {
			cancel()
		}
		return errors.New("scrape failed")
	}

	go func() {
		sl.run(10*time.Millisecond, time.Hour, nil)
		signal <- struct{}{}
	}()

	select {
	case <-signal:
	case <-time.After(5 * time.Second):
		t.Fatalf("Scrape wasn't stopped.")
	}

	// 1 successfully scraped sample, 1 stale marker after first fail, 5 report samples for
	// each scrape successful or not.
	testutil.Equals(t, 27, len(appender.result), "Appended samples not as expected")
	testutil.Equals(t, 42.0, appender.result[0].v, "Appended first sample not as expected")
	testutil.Assert(t, value.IsStaleNaN(appender.result[6].v),
		"Appended second sample not as expected. Wanted: stale NaN Got: %x", math.Float64bits(appender.result[6].v))
}

func TestScrapeLoopRunCreatesStaleMarkersOnParseFailure(t *testing.T) {
	appender := &collectResultAppender{}
	var (
		signal     = make(chan struct{})
		scraper    = &testScraper{}
		app        = func() storage.Appender { return appender }
		numScrapes = 0
	)
	defer close(signal)

	ctx, cancel := context.WithCancel(context.Background())
	sl := newScrapeLoop(ctx,
		scraper,
		nil, nil,
		nopMutator,
		nopMutator,
		app,
		nil,
		0,
		true,
	)

	// Succeed once, several failures, then stop.
	scraper.scrapeFunc = func(ctx context.Context, w io.Writer) error {
		numScrapes++

		if numScrapes == 1 {
			w.Write([]byte("metric_a 42\n"))
			return nil
		} else if numScrapes == 2 {
			w.Write([]byte("7&-\n"))
			return nil
		} else if numScrapes == 3 {
			cancel()
		}
		return errors.New("scrape failed")
	}

	go func() {
		sl.run(10*time.Millisecond, time.Hour, nil)
		signal <- struct{}{}
	}()

	select {
	case <-signal:
	case <-time.After(5 * time.Second):
		t.Fatalf("Scrape wasn't stopped.")
	}

	// 1 successfully scraped sample, 1 stale marker after first fail, 5 report samples for
	// each scrape successful or not.
	testutil.Equals(t, 17, len(appender.result), "Appended samples not as expected")
	testutil.Equals(t, 42.0, appender.result[0].v, "Appended first sample not as expected")
	testutil.Assert(t, value.IsStaleNaN(appender.result[6].v),
		"Appended second sample not as expected. Wanted: stale NaN Got: %x", math.Float64bits(appender.result[6].v))
}

func TestScrapeLoopCache(t *testing.T) {
	s := teststorage.New(t)
	defer s.Close()

	sapp, err := s.Appender()
	testutil.Ok(t, err)

	appender := &collectResultAppender{next: sapp}
	var (
		signal  = make(chan struct{})
		scraper = &testScraper{}
		app     = func() storage.Appender { return appender }
	)
	defer close(signal)

	ctx, cancel := context.WithCancel(context.Background())
	sl := newScrapeLoop(ctx,
		scraper,
		nil, nil,
		nopMutator,
		nopMutator,
		app,
		nil,
		0,
		true,
	)

	numScrapes := 0

	scraper.scrapeFunc = func(ctx context.Context, w io.Writer) error {
		if numScrapes == 1 || numScrapes == 2 {
			if _, ok := sl.cache.series["metric_a"]; !ok {
				t.Errorf("metric_a missing from cache after scrape %d", numScrapes)
			}
			if _, ok := sl.cache.series["metric_b"]; !ok {
				t.Errorf("metric_b missing from cache after scrape %d", numScrapes)
			}
		} else if numScrapes == 3 {
			if _, ok := sl.cache.series["metric_a"]; !ok {
				t.Errorf("metric_a missing from cache after scrape %d", numScrapes)
			}
			if _, ok := sl.cache.series["metric_b"]; ok {
				t.Errorf("metric_b present in cache after scrape %d", numScrapes)
			}
		}

		numScrapes++

		if numScrapes == 1 {
			w.Write([]byte("metric_a 42\nmetric_b 43\n"))
			return nil
		} else if numScrapes == 3 {
			w.Write([]byte("metric_a 44\n"))
			return nil
		} else if numScrapes == 4 {
			cancel()
		}
		return fmt.Errorf("scrape failed")
	}

	go func() {
		sl.run(10*time.Millisecond, time.Hour, nil)
		signal <- struct{}{}
	}()

	select {
	case <-signal:
	case <-time.After(5 * time.Second):
		t.Fatalf("Scrape wasn't stopped.")
	}

	// 1 successfully scraped sample, 1 stale marker after first fail, 5 report samples for
	// each scrape successful or not.
	if len(appender.result) != 26 {
		t.Fatalf("Appended samples not as expected. Wanted: %d samples Got: %d", 26, len(appender.result))
	}
}

func TestScrapeLoopCacheMemoryExhaustionProtection(t *testing.T) {
	s := teststorage.New(t)
	defer s.Close()

	sapp, err := s.Appender()
	testutil.Ok(t, err)

	appender := &collectResultAppender{next: sapp}
	var (
		signal  = make(chan struct{})
		scraper = &testScraper{}
		app     = func() storage.Appender { return appender }
	)
	defer close(signal)

	ctx, cancel := context.WithCancel(context.Background())
	sl := newScrapeLoop(ctx,
		scraper,
		nil, nil,
		nopMutator,
		nopMutator,
		app,
		nil,
		0,
		true,
	)

	numScrapes := 0

	scraper.scrapeFunc = func(ctx context.Context, w io.Writer) error {
		numScrapes++
		if numScrapes < 5 {
			s := ""
			for i := 0; i < 500; i++ {
				s = fmt.Sprintf("%smetric_%d_%d 42\n", s, i, numScrapes)
			}
			w.Write([]byte(fmt.Sprintf(s + "&")))
		} else {
			cancel()
		}
		return nil
	}

	go func() {
		sl.run(10*time.Millisecond, time.Hour, nil)
		signal <- struct{}{}
	}()

	select {
	case <-signal:
	case <-time.After(5 * time.Second):
		t.Fatalf("Scrape wasn't stopped.")
	}

	if len(sl.cache.series) > 2000 {
		t.Fatalf("More than 2000 series cached. Got: %d", len(sl.cache.series))
	}
}

func TestScrapeLoopAppend(t *testing.T) {
	tests := []struct {
		title           string
		honorLabels     bool
		scrapeLabels    string
		discoveryLabels []string
		expLset         labels.Labels
		expValue        float64
	}{
		{
			// When "honor_labels" is not set
			// label name collision is handler by adding a prefix.
			title:           "Label name collision",
			honorLabels:     false,
			scrapeLabels:    `metric{n="1"} 0`,
			discoveryLabels: []string{"n", "2"},
			expLset:         labels.FromStrings("__name__", "metric", "exported_n", "1", "n", "2"),
			expValue:        0,
		}, {
			// When "honor_labels" is not set
			// exported label from discovery don't get overwritten
			title:           "Label name collision",
			honorLabels:     false,
			scrapeLabels:    `metric 0`,
			discoveryLabels: []string{"n", "2", "exported_n", "2"},
			expLset:         labels.FromStrings("__name__", "metric", "n", "2", "exported_n", "2"),
			expValue:        0,
		}, {
			// Labels with no value need to be removed as these should not be ingested.
			title:           "Delete Empty labels",
			honorLabels:     false,
			scrapeLabels:    `metric{n=""} 0`,
			discoveryLabels: nil,
			expLset:         labels.FromStrings("__name__", "metric"),
			expValue:        0,
		}, {
			// Honor Labels should ignore labels with the same name.
			title:           "Honor Labels",
			honorLabels:     true,
			scrapeLabels:    `metric{n1="1" n2="2"} 0`,
			discoveryLabels: []string{"n1", "0"},
			expLset:         labels.FromStrings("__name__", "metric", "n1", "1", "n2", "2"),
			expValue:        0,
		}, {
			title:           "Stale - NaN",
			honorLabels:     false,
			scrapeLabels:    `metric NaN`,
			discoveryLabels: nil,
			expLset:         labels.FromStrings("__name__", "metric"),
			expValue:        float64(value.NormalNaN),
		},
	}

	for _, test := range tests {
		app := &collectResultAppender{}

		discoveryLabels := &Target{
			labels: labels.FromStrings(test.discoveryLabels...),
		}

		sl := newScrapeLoop(context.Background(),
			nil, nil, nil,
			func(l labels.Labels) labels.Labels {
				return mutateSampleLabels(l, discoveryLabels, test.honorLabels, nil)
			},
			func(l labels.Labels) labels.Labels {
				return mutateReportSampleLabels(l, discoveryLabels)
			},
			func() storage.Appender { return app },
			nil,
			0,
			true,
		)

		now := time.Now()

		_, _, _, err := sl.append([]byte(test.scrapeLabels), "", now)
		testutil.Ok(t, err)

		expected := []sample{
			{
				metric: test.expLset,
				t:      timestamp.FromTime(now),
				v:      test.expValue,
			},
		}

		// When the expected value is NaN
		// DeepEqual will report NaNs as being different,
		// so replace it with the expected one.
		if test.expValue == float64(value.NormalNaN) {
			app.result[0].v = expected[0].v
		}

		t.Logf("Test:%s", test.title)
		testutil.Equals(t, expected, app.result)
	}
}

func TestScrapeLoopAppendSampleLimit(t *testing.T) {
	resApp := &collectResultAppender{}
	app := &limitAppender{Appender: resApp, limit: 1}

	sl := newScrapeLoop(context.Background(),
		nil, nil, nil,
		nopMutator,
		nopMutator,
		func() storage.Appender { return app },
		nil,
		0,
		true,
	)

	// Get the value of the Counter before performing the append.
	beforeMetric := dto.Metric{}
	err := targetScrapeSampleLimit.Write(&beforeMetric)
	testutil.Ok(t, err)

	beforeMetricValue := beforeMetric.GetCounter().GetValue()

	now := time.Now()
	_, _, _, err = sl.append([]byte("metric_a 1\nmetric_b 1\nmetric_c 1\n"), "", now)
	if err != errSampleLimit {
		t.Fatalf("Did not see expected sample limit error: %s", err)
	}

	// Check that the Counter has been incremented a single time for the scrape,
	// not multiple times for each sample.
	metric := dto.Metric{}
	err = targetScrapeSampleLimit.Write(&metric)
	testutil.Ok(t, err)

	value := metric.GetCounter().GetValue()
	change := value - beforeMetricValue
	testutil.Assert(t, change == 1, "Unexpected change of sample limit metric: %f", change)

	// And verify that we got the samples that fit under the limit.
	want := []sample{
		{
			metric: labels.FromStrings(model.MetricNameLabel, "metric_a"),
			t:      timestamp.FromTime(now),
			v:      1,
		},
	}
	testutil.Equals(t, want, resApp.result, "Appended samples not as expected")
}

func TestScrapeLoop_ChangingMetricString(t *testing.T) {
	// This is a regression test for the scrape loop cache not properly maintaining
	// IDs when the string representation of a metric changes across a scrape. Thus
	// we use a real storage appender here.
	s := teststorage.New(t)
	defer s.Close()

	app, err := s.Appender()
	testutil.Ok(t, err)

	capp := &collectResultAppender{next: app}

	sl := newScrapeLoop(context.Background(),
		nil, nil, nil,
		nopMutator,
		nopMutator,
		func() storage.Appender { return capp },
		nil,
		0,
		true,
	)

	now := time.Now()
	_, _, _, err = sl.append([]byte(`metric_a{a="1",b="1"} 1`), "", now)
	testutil.Ok(t, err)

	_, _, _, err = sl.append([]byte(`metric_a{b="1",a="1"} 2`), "", now.Add(time.Minute))
	testutil.Ok(t, err)

	// DeepEqual will report NaNs as being different, so replace with a different value.
	want := []sample{
		{
			metric: labels.FromStrings("__name__", "metric_a", "a", "1", "b", "1"),
			t:      timestamp.FromTime(now),
			v:      1,
		},
		{
			metric: labels.FromStrings("__name__", "metric_a", "a", "1", "b", "1"),
			t:      timestamp.FromTime(now.Add(time.Minute)),
			v:      2,
		},
	}
	testutil.Equals(t, want, capp.result, "Appended samples not as expected")
}

func TestScrapeLoopAppendStaleness(t *testing.T) {
	app := &collectResultAppender{}

	sl := newScrapeLoop(context.Background(),
		nil, nil, nil,
		nopMutator,
		nopMutator,
		func() storage.Appender { return app },
		nil,
		0,
		true,
	)

	now := time.Now()
	_, _, _, err := sl.append([]byte("metric_a 1\n"), "", now)
	testutil.Ok(t, err)

	_, _, _, err = sl.append([]byte(""), "", now.Add(time.Second))
	testutil.Ok(t, err)

	ingestedNaN := math.Float64bits(app.result[1].v)
	testutil.Equals(t, value.StaleNaN, ingestedNaN, "Appended stale sample wasn't as expected")

	// DeepEqual will report NaNs as being different, so replace with a different value.
	app.result[1].v = 42
	want := []sample{
		{
			metric: labels.FromStrings(model.MetricNameLabel, "metric_a"),
			t:      timestamp.FromTime(now),
			v:      1,
		},
		{
			metric: labels.FromStrings(model.MetricNameLabel, "metric_a"),
			t:      timestamp.FromTime(now.Add(time.Second)),
			v:      42,
		},
	}
	testutil.Equals(t, want, app.result, "Appended samples not as expected")
}

func TestScrapeLoopAppendNoStalenessIfTimestamp(t *testing.T) {
	app := &collectResultAppender{}
	sl := newScrapeLoop(context.Background(),
		nil, nil, nil,
		nopMutator,
		nopMutator,
		func() storage.Appender { return app },
		nil,
		0,
		true,
	)

	now := time.Now()
	_, _, _, err := sl.append([]byte("metric_a 1 1000\n"), "", now)
	testutil.Ok(t, err)

	_, _, _, err = sl.append([]byte(""), "", now.Add(time.Second))
	testutil.Ok(t, err)

	want := []sample{
		{
			metric: labels.FromStrings(model.MetricNameLabel, "metric_a"),
			t:      1000,
			v:      1,
		},
	}
	testutil.Equals(t, want, app.result, "Appended samples not as expected")
}

func TestScrapeLoopRunReportsTargetDownOnScrapeError(t *testing.T) {
	var (
		scraper  = &testScraper{}
		appender = &collectResultAppender{}
		app      = func() storage.Appender { return appender }
	)

	ctx, cancel := context.WithCancel(context.Background())
	sl := newScrapeLoop(ctx,
		scraper,
		nil, nil,
		nopMutator,
		nopMutator,
		app,
		nil,
		0,
		true,
	)

	scraper.scrapeFunc = func(ctx context.Context, w io.Writer) error {
		cancel()
		return errors.New("scrape failed")
	}

	sl.run(10*time.Millisecond, time.Hour, nil)
	testutil.Equals(t, 0.0, appender.result[0].v, "bad 'up' value")
}

func TestScrapeLoopRunReportsTargetDownOnInvalidUTF8(t *testing.T) {
	var (
		scraper  = &testScraper{}
		appender = &collectResultAppender{}
		app      = func() storage.Appender { return appender }
	)

	ctx, cancel := context.WithCancel(context.Background())
	sl := newScrapeLoop(ctx,
		scraper,
		nil, nil,
		nopMutator,
		nopMutator,
		app,
		nil,
		0,
		true,
	)

	scraper.scrapeFunc = func(ctx context.Context, w io.Writer) error {
		cancel()
		w.Write([]byte("a{l=\"\xff\"} 1\n"))
		return nil
	}

	sl.run(10*time.Millisecond, time.Hour, nil)
	testutil.Equals(t, 0.0, appender.result[0].v, "bad 'up' value")
}

type errorAppender struct {
	collectResultAppender
}

func (app *errorAppender) Add(lset labels.Labels, t int64, v float64) (uint64, error) {
	switch lset.Get(model.MetricNameLabel) {
	case "out_of_order":
		return 0, storage.ErrOutOfOrderSample
	case "amend":
		return 0, storage.ErrDuplicateSampleForTimestamp
	case "out_of_bounds":
		return 0, storage.ErrOutOfBounds
	default:
		return app.collectResultAppender.Add(lset, t, v)
	}
}

func (app *errorAppender) AddFast(lset labels.Labels, ref uint64, t int64, v float64) error {
	return app.collectResultAppender.AddFast(lset, ref, t, v)
}

func TestScrapeLoopAppendGracefullyIfAmendOrOutOfOrderOrOutOfBounds(t *testing.T) {
	app := &errorAppender{}

	sl := newScrapeLoop(context.Background(),
		nil,
		nil, nil,
		nopMutator,
		nopMutator,
		func() storage.Appender { return app },
		nil,
		0,
		true,
	)

	now := time.Unix(1, 0)
	total, added, seriesAdded, err := sl.append([]byte("out_of_order 1\namend 1\nnormal 1\nout_of_bounds 1\n"), "", now)
	testutil.Ok(t, err)

	want := []sample{
		{
			metric: labels.FromStrings(model.MetricNameLabel, "normal"),
			t:      timestamp.FromTime(now),
			v:      1,
		},
	}
	testutil.Equals(t, want, app.result, "Appended samples not as expected")
	testutil.Equals(t, 4, total)
	testutil.Equals(t, 1, added)
	testutil.Equals(t, 1, seriesAdded)
}

func TestScrapeLoopOutOfBoundsTimeError(t *testing.T) {
	app := &collectResultAppender{}
	sl := newScrapeLoop(context.Background(),
		nil,
		nil, nil,
		nopMutator,
		nopMutator,
		func() storage.Appender {
			return &timeLimitAppender{
				Appender: app,
				maxTime:  timestamp.FromTime(time.Now().Add(10 * time.Minute)),
			}
		},
		nil,
		0,
		true,
	)

	now := time.Now().Add(20 * time.Minute)
	total, added, seriesAdded, err := sl.append([]byte("normal 1\n"), "", now)
	testutil.Equals(t, 1, total)
	testutil.Equals(t, 0, added)
	testutil.Equals(t, 0, seriesAdded)

	testutil.Ok(t, err)
}

func TestTargetScraperScrapeOK(t *testing.T) {
	const (
		configTimeout   = 1500 * time.Millisecond
		expectedTimeout = "1.500000"
	)

	server := httptest.NewServer(
		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			accept := r.Header.Get("Accept")
			if !strings.HasPrefix(accept, "application/openmetrics-text;") {
				t.Errorf("Expected Accept header to prefer application/openmetrics-text, got %q", accept)
			}

			timeout := r.Header.Get("X-Prometheus-Scrape-Timeout-Seconds")
			if timeout != expectedTimeout {
				t.Errorf("Expected scrape timeout header %q, got %q", expectedTimeout, timeout)
			}

			w.Header().Set("Content-Type", `text/plain; version=0.0.4`)
			w.Write([]byte("metric_a 1\nmetric_b 2\n"))
		}),
	)
	defer server.Close()

	serverURL, err := url.Parse(server.URL)
	if err != nil {
		panic(err)
	}

	ts := &targetScraper{
		Target: &Target{
			labels: labels.FromStrings(
				model.SchemeLabel, serverURL.Scheme,
				model.AddressLabel, serverURL.Host,
			),
		},
		client:  http.DefaultClient,
		timeout: configTimeout,
	}
	var buf bytes.Buffer

	contentType, err := ts.scrape(context.Background(), &buf)
	testutil.Ok(t, err)
	testutil.Equals(t, "text/plain; version=0.0.4", contentType)
	testutil.Equals(t, "metric_a 1\nmetric_b 2\n", buf.String())
}

func TestTargetScrapeScrapeCancel(t *testing.T) {
	block := make(chan struct{})

	server := httptest.NewServer(
		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			<-block
		}),
	)
	defer server.Close()

	serverURL, err := url.Parse(server.URL)
	if err != nil {
		panic(err)
	}

	ts := &targetScraper{
		Target: &Target{
			labels: labels.FromStrings(
				model.SchemeLabel, serverURL.Scheme,
				model.AddressLabel, serverURL.Host,
			),
		},
		client: http.DefaultClient,
	}
	ctx, cancel := context.WithCancel(context.Background())

	errc := make(chan error)

	go func() {
		time.Sleep(1 * time.Second)
		cancel()
	}()

	go func() {
		_, err := ts.scrape(ctx, ioutil.Discard)
		if err == nil {
			errc <- errors.New("Expected error but got nil")
		} else if ctx.Err() != context.Canceled {
			errc <- errors.Errorf("Expected context cancellation error but got: %s", ctx.Err())
		}
		close(errc)
	}()

	select {
	case <-time.After(5 * time.Second):
		t.Fatalf("Scrape function did not return unexpectedly")
	case err := <-errc:
		testutil.Ok(t, err)
	}
	// If this is closed in a defer above the function the test server
	// doesn't terminate and the test doesn't complete.
	close(block)
}

func TestTargetScrapeScrapeNotFound(t *testing.T) {
	server := httptest.NewServer(
		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			w.WriteHeader(http.StatusNotFound)
		}),
	)
	defer server.Close()

	serverURL, err := url.Parse(server.URL)
	if err != nil {
		panic(err)
	}

	ts := &targetScraper{
		Target: &Target{
			labels: labels.FromStrings(
				model.SchemeLabel, serverURL.Scheme,
				model.AddressLabel, serverURL.Host,
			),
		},
		client: http.DefaultClient,
	}

	_, err = ts.scrape(context.Background(), ioutil.Discard)
	testutil.Assert(t, strings.Contains(err.Error(), "404"), "Expected \"404 NotFound\" error but got: %s", err)
}

// testScraper implements the scraper interface and allows setting values
// returned by its methods. It also allows setting a custom scrape function.
type testScraper struct {
	offsetDur time.Duration

	lastStart    time.Time
	lastDuration time.Duration
	lastError    error

	scrapeErr  error
	scrapeFunc func(context.Context, io.Writer) error
}

func (ts *testScraper) offset(interval time.Duration, jitterSeed uint64) time.Duration {
	return ts.offsetDur
}

func (ts *testScraper) Report(start time.Time, duration time.Duration, err error) {
	ts.lastStart = start
	ts.lastDuration = duration
	ts.lastError = err
}

func (ts *testScraper) scrape(ctx context.Context, w io.Writer) (string, error) {
	if ts.scrapeFunc != nil {
		return "", ts.scrapeFunc(ctx, w)
	}
	return "", ts.scrapeErr
}

func TestScrapeLoop_RespectTimestamps(t *testing.T) {
	s := teststorage.New(t)
	defer s.Close()

	app, err := s.Appender()
	testutil.Ok(t, err)

	capp := &collectResultAppender{next: app}

	sl := newScrapeLoop(context.Background(),
		nil, nil, nil,
		nopMutator,
		nopMutator,
		func() storage.Appender { return capp },
		nil, 0,
		true,
	)

	now := time.Now()
	_, _, _, err = sl.append([]byte(`metric_a{a="1",b="1"} 1 0`), "", now)
	testutil.Ok(t, err)

	want := []sample{
		{
			metric: labels.FromStrings("__name__", "metric_a", "a", "1", "b", "1"),
			t:      0,
			v:      1,
		},
	}
	testutil.Equals(t, want, capp.result, "Appended samples not as expected")
}

func TestScrapeLoop_DiscardTimestamps(t *testing.T) {
	s := teststorage.New(t)
	defer s.Close()

	app, err := s.Appender()
	testutil.Ok(t, err)

	capp := &collectResultAppender{next: app}

	sl := newScrapeLoop(context.Background(),
		nil, nil, nil,
		nopMutator,
		nopMutator,
		func() storage.Appender { return capp },
		nil, 0,
		false,
	)

	now := time.Now()
	_, _, _, err = sl.append([]byte(`metric_a{a="1",b="1"} 1 0`), "", now)
	testutil.Ok(t, err)

	want := []sample{
		{
			metric: labels.FromStrings("__name__", "metric_a", "a", "1", "b", "1"),
			t:      timestamp.FromTime(now),
			v:      1,
		},
	}
	testutil.Equals(t, want, capp.result, "Appended samples not as expected")
}

func TestScrapeLoopDiscardDuplicateLabels(t *testing.T) {
	s := teststorage.New(t)
	defer s.Close()

	app, err := s.Appender()
	testutil.Ok(t, err)

	ctx, cancel := context.WithCancel(context.Background())
	sl := newScrapeLoop(ctx,
		&testScraper{},
		nil, nil,
		nopMutator,
		nopMutator,
		func() storage.Appender { return app },
		nil,
		0,
		true,
	)
	defer cancel()

	// We add a good and a bad metric to check that both are discarded.
	_, _, _, err = sl.append([]byte("test_metric{le=\"500\"} 1\ntest_metric{le=\"600\",le=\"700\"} 1\n"), "", time.Time{})
	testutil.NotOk(t, err)

	q, err := s.Querier(ctx, time.Time{}.UnixNano(), 0)
	testutil.Ok(t, err)
	series, _, err := q.Select(&storage.SelectParams{}, labels.MustNewMatcher(labels.MatchRegexp, "__name__", ".*"))
	testutil.Ok(t, err)
	testutil.Equals(t, false, series.Next(), "series found in tsdb")

	// We add a good metric to check that it is recorded.
	_, _, _, err = sl.append([]byte("test_metric{le=\"500\"} 1\n"), "", time.Time{})
	testutil.Ok(t, err)

	q, err = s.Querier(ctx, time.Time{}.UnixNano(), 0)
	testutil.Ok(t, err)
	series, _, err = q.Select(&storage.SelectParams{}, labels.MustNewMatcher(labels.MatchEqual, "le", "500"))
	testutil.Ok(t, err)
	testutil.Equals(t, true, series.Next(), "series not found in tsdb")
	testutil.Equals(t, false, series.Next(), "more than one series found in tsdb")
}

func TestReusableConfig(t *testing.T) {
	variants := []*config.ScrapeConfig{
		&config.ScrapeConfig{
			JobName:       "prometheus",
			ScrapeTimeout: model.Duration(15 * time.Second),
		},
		&config.ScrapeConfig{
			JobName:       "httpd",
			ScrapeTimeout: model.Duration(15 * time.Second),
		},
		&config.ScrapeConfig{
			JobName:       "prometheus",
			ScrapeTimeout: model.Duration(5 * time.Second),
		},
		&config.ScrapeConfig{
			JobName:     "prometheus",
			MetricsPath: "/metrics",
		},
		&config.ScrapeConfig{
			JobName:     "prometheus",
			MetricsPath: "/metrics2",
		},
		&config.ScrapeConfig{
			JobName:       "prometheus",
			ScrapeTimeout: model.Duration(5 * time.Second),
			MetricsPath:   "/metrics2",
		},
		&config.ScrapeConfig{
			JobName:        "prometheus",
			ScrapeInterval: model.Duration(5 * time.Second),
			MetricsPath:    "/metrics2",
		},
		&config.ScrapeConfig{
			JobName:        "prometheus",
			ScrapeInterval: model.Duration(5 * time.Second),
			SampleLimit:    1000,
			MetricsPath:    "/metrics2",
		},
	}

	match := [][]int{
		[]int{0, 2},
		[]int{4, 5},
		[]int{4, 6},
		[]int{4, 7},
		[]int{5, 6},
		[]int{5, 7},
		[]int{6, 7},
	}
	noMatch := [][]int{
		[]int{1, 2},
		[]int{0, 4},
		[]int{3, 4},
	}

	for i, m := range match {
		testutil.Equals(t, true, reusableCache(variants[m[0]], variants[m[1]]), "match test %d", i)
		testutil.Equals(t, true, reusableCache(variants[m[1]], variants[m[0]]), "match test %d", i)
		testutil.Equals(t, true, reusableCache(variants[m[1]], variants[m[1]]), "match test %d", i)
		testutil.Equals(t, true, reusableCache(variants[m[0]], variants[m[0]]), "match test %d", i)
	}
	for i, m := range noMatch {
		testutil.Equals(t, false, reusableCache(variants[m[0]], variants[m[1]]), "not match test %d", i)
		testutil.Equals(t, false, reusableCache(variants[m[1]], variants[m[0]]), "not match test %d", i)
	}
}

func TestReuseScrapeCache(t *testing.T) {
	var (
		app = &nopAppendable{}
		cfg = &config.ScrapeConfig{
			JobName:        "Prometheus",
			ScrapeTimeout:  model.Duration(5 * time.Second),
			ScrapeInterval: model.Duration(5 * time.Second),
			MetricsPath:    "/metrics",
		}
		sp, _ = newScrapePool(cfg, app, 0, nil)
		t1    = &Target{
			discoveredLabels: labels.Labels{
				labels.Label{
					Name:  "labelNew",
					Value: "nameNew",
				},
			},
		}
		proxyURL, _ = url.Parse("http://localhost:2128")
	)
	sp.sync([]*Target{t1})

	steps := []struct {
		keep      bool
		newConfig *config.ScrapeConfig
	}{
		{
			keep: true,
			newConfig: &config.ScrapeConfig{
				JobName:        "Prometheus",
				ScrapeInterval: model.Duration(5 * time.Second),
				ScrapeTimeout:  model.Duration(5 * time.Second),
				MetricsPath:    "/metrics",
			},
		},
		{
			keep: false,
			newConfig: &config.ScrapeConfig{
				JobName:        "Prometheus",
				ScrapeInterval: model.Duration(5 * time.Second),
				ScrapeTimeout:  model.Duration(15 * time.Second),
				MetricsPath:    "/metrics2",
			},
		},
		{
			keep: true,
			newConfig: &config.ScrapeConfig{
				JobName:        "Prometheus",
				SampleLimit:    400,
				ScrapeInterval: model.Duration(5 * time.Second),
				ScrapeTimeout:  model.Duration(15 * time.Second),
				MetricsPath:    "/metrics2",
			},
		},
		{
			keep: false,
			newConfig: &config.ScrapeConfig{
				JobName:         "Prometheus",
				HonorTimestamps: true,
				SampleLimit:     400,
				ScrapeInterval:  model.Duration(5 * time.Second),
				ScrapeTimeout:   model.Duration(15 * time.Second),
				MetricsPath:     "/metrics2",
			},
		},
		{
			keep: true,
			newConfig: &config.ScrapeConfig{
				JobName:         "Prometheus",
				HonorTimestamps: true,
				SampleLimit:     400,
				HTTPClientConfig: config_util.HTTPClientConfig{
					ProxyURL: config_util.URL{URL: proxyURL},
				},
				ScrapeInterval: model.Duration(5 * time.Second),
				ScrapeTimeout:  model.Duration(15 * time.Second),
				MetricsPath:    "/metrics2",
			},
		},
		{
			keep: false,
			newConfig: &config.ScrapeConfig{
				JobName:         "Prometheus",
				HonorTimestamps: true,
				HonorLabels:     true,
				SampleLimit:     400,
				ScrapeInterval:  model.Duration(5 * time.Second),
				ScrapeTimeout:   model.Duration(15 * time.Second),
				MetricsPath:     "/metrics2",
			},
		},
	}

	cacheAddr := func(sp *scrapePool) map[uint64]string {
		r := make(map[uint64]string)
		for fp, l := range sp.loops {
			r[fp] = fmt.Sprintf("%p", l.getCache())
		}
		return r
	}

	for i, s := range steps {
		initCacheAddr := cacheAddr(sp)
		sp.reload(s.newConfig)
		for fp, newCacheAddr := range cacheAddr(sp) {
			if s.keep {
				testutil.Assert(t, initCacheAddr[fp] == newCacheAddr, "step %d: old cache and new cache are not the same", i)
			} else {
				testutil.Assert(t, initCacheAddr[fp] != newCacheAddr, "step %d: old cache and new cache are the same", i)
			}
		}
		initCacheAddr = cacheAddr(sp)
		sp.reload(s.newConfig)
		for fp, newCacheAddr := range cacheAddr(sp) {
			testutil.Assert(t, initCacheAddr[fp] == newCacheAddr, "step %d: reloading the exact config invalidates the cache", i)
		}
	}
}