Treat non-200 HTTP response as error.

Change-Id: I2a9f3b47012b3c4839be53aa44c66d16dd41a24a

retrieval/target.go

@@ -224,6 +224,9 @@ func (t *target) scrape(timestamp clientmodel.Timestamp, ingester extraction.Ing
 	if err != nil {
 		return err
 	}
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("server returned HTTP status %s", resp.Status)
+	}
 	defer resp.Body.Close()
 
 	processor, err := extraction.ProcessorForRequestHeader(resp.Header)

retrieval/target_test.go

@@ -14,6 +14,7 @@
 package retrieval
 
 import (
+	"errors"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -127,3 +128,20 @@ func TestTargetScrapeTimeout(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestTargetScrape404(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusNotFound)
+	}))
+
+	defer server.Close()
+
+	testTarget := NewTarget(server.URL, 10*time.Millisecond, clientmodel.LabelSet{})
+	ingester := nopIngester{}
+
+	want := errors.New("server returned HTTP status 404 Not Found")
+	got := testTarget.Scrape(time.Now(), ingester)
+	if got == nil || want.Error() != got.Error() {
+		t.Fatalf("want err %q, got %q", want, got)
+	}
+}