Make scrape time unambigious.

This commit changes the scraper interface to accept a timestamp
so the reported timestamp by the caller and the timestamp
attached to samples does not differ.

retrieval/scrape.go

@@ -66,13 +66,6 @@ func init() {
 	prometheus.MustRegister(targetSkippedScrapes)
 }
 
-// A scraper retrieves samples and accepts a status report at the end.
-type scraper interface {
-	scrape(context.Context) (model.Samples, error)
-	report(start time.Time, dur time.Duration, err error)
-	offset(interval time.Duration) time.Duration
-}
-
 // scrapePool manages scrapes for sets of targets.
 type scrapePool struct {
 	appender storage.SampleAppender
@@ -178,6 +171,13 @@ func (sp *scrapePool) sync(tgroups map[string]map[model.Fingerprint]*Target) {
 	sp.mtx.Unlock()
 }
 
+// A scraper retrieves samples and accepts a status report at the end.
+type scraper interface {
+	scrape(ctx context.Context, ts time.Time) (model.Samples, error)
+	report(start time.Time, dur time.Duration, err error)
+	offset(interval time.Duration) time.Duration
+}
+
 type loop interface {
 	run(interval, timeout time.Duration, errc chan<- error)
 	stop()
@@ -239,7 +239,7 @@ func (sl *scrapeLoop) run(interval, timeout time.Duration, errc chan<- error) {
 				float64(time.Since(last)) / float64(time.Second), // Sub-second precision.
 			)
 
-			samples, err := sl.scraper.scrape(scrapeCtx)
+			samples, err := sl.scraper.scrape(scrapeCtx, start)
 			if err == nil {
 				sl.append(samples)
 			} else if errc != nil {

retrieval/scrape_test.go

@@ -63,7 +63,7 @@ func TestScrapeLoopRun(t *testing.T) {
 	scraper.offsetDur = 0
 
 	block := make(chan struct{})
-	scraper.scrapeFunc = func(ctx context.Context) (model.Samples, error) {
+	scraper.scrapeFunc = func(ctx context.Context, ts time.Time) (model.Samples, error) {
 		select {
 		case <-block:
 		case <-ctx.Done():
@@ -116,7 +116,7 @@ type testScraper struct {
 
 	samples    model.Samples
 	scrapeErr  error
-	scrapeFunc func(context.Context) (model.Samples, error)
+	scrapeFunc func(context.Context, time.Time) (model.Samples, error)
 }
 
 func (ts *testScraper) offset(interval time.Duration) time.Duration {
@@ -129,9 +129,9 @@ func (ts *testScraper) report(start time.Time, duration time.Duration, err error
 	ts.lastError = err
 }
 
-func (ts *testScraper) scrape(ctx context.Context) (model.Samples, error) {
+func (ts *testScraper) scrape(ctx context.Context, t time.Time) (model.Samples, error) {
 	if ts.scrapeFunc != nil {
-		return ts.scrapeFunc(ctx)
+		return ts.scrapeFunc(ctx, t)
 	}
 	return ts.samples, ts.scrapeErr
 }

retrieval/target.go

@@ -340,13 +340,11 @@ func (t *Target) InstanceIdentifier() string {
 
 const acceptHeader = `application/vnd.google.protobuf;proto=io.prometheus.client.MetricFamily;encoding=delimited;q=0.7,text/plain;version=0.0.4;q=0.3,application/json;schema="prometheus/telemetry";version=0.0.2;q=0.2,*/*;q=0.1`
 
-func (t *Target) scrape(ctx context.Context) (model.Samples, error) {
+func (t *Target) scrape(ctx context.Context, ts time.Time) (model.Samples, error) {
 	t.RLock()
 	client := t.httpClient
 	t.RUnlock()
 
-	start := time.Now()
-
 	req, err := http.NewRequest("GET", t.URL().String(), nil)
 	if err != nil {
 		return nil, err
@@ -370,7 +368,7 @@ func (t *Target) scrape(ctx context.Context) (model.Samples, error) {
 	sdec := expfmt.SampleDecoder{
 		Dec: expfmt.NewDecoder(resp.Body, expfmt.ResponseFormat(resp.Header)),
 		Opts: &expfmt.DecodeOptions{
-			Timestamp: model.TimeFromUnixNano(start.UnixNano()),
+			Timestamp: model.TimeFromUnixNano(ts.UnixNano()),
 		},
 	}
 

retrieval/target_test.go

@@ -181,7 +181,7 @@ func TestTargetScrape404(t *testing.T) {
 	testTarget := newTestTarget(server.URL, time.Second, model.LabelSet{})
 
 	want := errors.New("server returned HTTP status 404 Not Found")
-	_, got := testTarget.scrape(context.Background())
+	_, got := testTarget.scrape(context.Background(), time.Now())
 	if got == nil || want.Error() != got.Error() {
 		t.Fatalf("want err %q, got %q", want, got)
 	}
@@ -229,7 +229,7 @@ func TestURLParams(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if _, err = target.scrape(context.Background()); err != nil {
+	if _, err = target.scrape(context.Background(), time.Now()); err != nil {
 		t.Fatal(err)
 	}
 }