retrieval: Fix "up" reporting for failed scrapes

retrieval/scrape.go

@@ -579,7 +579,6 @@ mainLoop:
 		}
 
 		var (
-			total, added      int
 			start             = time.Now()
 			scrapeCtx, cancel = context.WithTimeout(sl.ctx, timeout)
 		)
@@ -591,18 +590,20 @@ mainLoop:
 			)
 		}
 
-		err := sl.scraper.scrape(scrapeCtx, buf)
+		scrapeErr := sl.scraper.scrape(scrapeCtx, buf)
 		cancel()
 		var b []byte
-		if err == nil {
+		if scrapeErr == nil {
 			b = buf.Bytes()
 		} else if errc != nil {
-			errc <- err
+			errc <- scrapeErr
 		}
+
 		// A failed scrape is the same as an empty scrape,
 		// we still call sl.append to trigger stale markers.
-		if total, added, err = sl.append(b, start); err != nil {
+		total, added, appErr := sl.append(b, start)
-			sl.l.With("err", err).Warn("append failed")
+		if appErr != nil {
+			sl.l.With("err", appErr).Warn("append failed")
 			// The append failed, probably due to a parse error or sample limit.
 			// Call sl.append again with an empty scrape to trigger stale markers.
 			if _, _, err := sl.append([]byte{}, start); err != nil {
@@ -610,7 +611,11 @@ mainLoop:
 			}
 		}
 
-		sl.report(start, time.Since(start), total, added, err)
+		if scrapeErr == nil {
+			scrapeErr = appErr
+		}
+
+		sl.report(start, time.Since(start), total, added, scrapeErr)
 		last = start
 
 		select {

retrieval/scrape_test.go

@@ -821,6 +821,28 @@ func TestScrapeLoopRunAppliesScrapeLimit(t *testing.T) {
 	}
 }
 
+func TestScrapeLoopRunReportsTargetDownOnScrapeError(t *testing.T) {
+	var (
+		scraper        = &testScraper{}
+		reportAppender = &collectResultAppender{}
+		reportApp      = func() storage.Appender { return reportAppender }
+	)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	sl := newScrapeLoop(ctx, scraper, func() storage.Appender { return nopAppender{} }, reportApp, nil)
+
+	scraper.scrapeFunc = func(ctx context.Context, w io.Writer) error {
+		cancel()
+		return fmt.Errorf("scrape failed")
+	}
+
+	sl.run(10*time.Millisecond, time.Hour, nil)
+
+	if reportAppender.result[0].v != 0 {
+		t.Fatalf("bad 'up' value; want 0, got %v", reportAppender.result[0].v)
+	}
+}
+
 type errorAppender struct {
 	collectResultAppender
 }