Correctly handle error unwrapping in rules and remote write receiver

errors.Unwrap() actually dangerously returns nil if the error does not have an
Unwrap() method, which is the case in at least one of these places where I
noticed that no error was being logged at all when it should have.

Signed-off-by: Julius Volz <julius.volz@gmail.com>

rules/manager.go

@@ -673,6 +673,9 @@ func (g *Group) Eval(ctx context.Context, ts time.Time) {
 					rule.SetLastError(err)
 					sp.SetStatus(codes.Error, err.Error())
 					unwrappedErr := errors.Unwrap(err)
+					if unwrappedErr == nil {
+						unwrappedErr = err
+					}
 					switch {
 					case errors.Is(unwrappedErr, storage.ErrOutOfOrderSample):
 						numOutOfOrder++
@@ -700,6 +703,9 @@ func (g *Group) Eval(ctx context.Context, ts time.Time) {
 					// Series no longer exposed, mark it stale.
 					_, err = app.Append(0, lset, timestamp.FromTime(ts), math.Float64frombits(value.StaleNaN))
 					unwrappedErr := errors.Unwrap(err)
+					if unwrappedErr == nil {
+						unwrappedErr = err
+					}
 					switch {
 					case unwrappedErr == nil:
 					case errors.Is(unwrappedErr, storage.ErrOutOfOrderSample), errors.Is(unwrappedErr, storage.ErrDuplicateSampleForTimestamp):
@@ -727,6 +733,9 @@ func (g *Group) cleanupStaleSeries(ctx context.Context, ts time.Time) {
 		// Rule that produced series no longer configured, mark it stale.
 		_, err := app.Append(0, s, timestamp.FromTime(ts), math.Float64frombits(value.StaleNaN))
 		unwrappedErr := errors.Unwrap(err)
+		if unwrappedErr == nil {
+			unwrappedErr = err
+		}
 		switch {
 		case unwrappedErr == nil:
 		case errors.Is(unwrappedErr, storage.ErrOutOfOrderSample), errors.Is(unwrappedErr, storage.ErrDuplicateSampleForTimestamp):

storage/remote/write_handler.go

@@ -67,11 +67,14 @@ func (h *writeHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 // checkAppendExemplarError modifies the AppendExamplar's returned error based on the error cause.
 func (h *writeHandler) checkAppendExemplarError(err error, e exemplar.Exemplar, outOfOrderErrs *int) error {
-	unwrapedErr := errors.Unwrap(err)
+	unwrappedErr := errors.Unwrap(err)
+	if unwrappedErr == nil {
+		unwrappedErr = err
+	}
 	switch {
-	case errors.Is(unwrapedErr, storage.ErrNotFound):
+	case errors.Is(unwrappedErr, storage.ErrNotFound):
 		return storage.ErrNotFound
-	case errors.Is(unwrapedErr, storage.ErrOutOfOrderExemplar):
+	case errors.Is(unwrappedErr, storage.ErrOutOfOrderExemplar):
 		*outOfOrderErrs++
 		level.Debug(h.logger).Log("msg", "Out of order exemplar", "exemplar", fmt.Sprintf("%+v", e))
 		return nil
@@ -98,8 +101,11 @@ func (h *writeHandler) write(ctx context.Context, req *prompb.WriteRequest) (err
 		for _, s := range ts.Samples {
 			_, err = app.Append(0, labels, s.Timestamp, s.Value)
 			if err != nil {
-				unwrapedErr := errors.Unwrap(err)
+				unwrappedErr := errors.Unwrap(err)
-				if errors.Is(unwrapedErr, storage.ErrOutOfOrderSample) || errors.Is(unwrapedErr, storage.ErrOutOfBounds) || errors.Is(unwrapedErr, storage.ErrDuplicateSampleForTimestamp) {
+				if unwrappedErr == nil {
+					unwrappedErr = err
+				}
+				if errors.Is(err, storage.ErrOutOfOrderSample) || errors.Is(unwrappedErr, storage.ErrOutOfBounds) || errors.Is(unwrappedErr, storage.ErrDuplicateSampleForTimestamp) {
 					level.Error(h.logger).Log("msg", "Out of order sample from remote write", "err", err.Error(), "series", labels.String(), "timestamp", s.Timestamp)
 				}
 				return err
@@ -123,6 +129,9 @@ func (h *writeHandler) write(ctx context.Context, req *prompb.WriteRequest) (err
 			_, err = app.AppendHistogram(0, labels, hp.Timestamp, hs)
 			if err != nil {
 				unwrappedErr := errors.Unwrap(err)
+				if unwrappedErr == nil {
+					unwrappedErr = err
+				}
 				// Althogh AppendHistogram does not currently return ErrDuplicateSampleForTimestamp there is
 				// a note indicating its inclusion in the future.
 				if errors.Is(unwrappedErr, storage.ErrOutOfOrderSample) || errors.Is(unwrappedErr, storage.ErrOutOfBounds) || errors.Is(unwrappedErr, storage.ErrDuplicateSampleForTimestamp) {