Prometheus: Fix handling errors in streaming client (#61643)

* Return errors from data parsing

* Better error handling

* Fix the tests

* When there is no frame add empty frame to get metadata attached to it

* Fix tests

* Update testdata

pkg/tsdb/prometheus/querydata/request.go

@@ -125,23 +125,17 @@ func (s *QueryData) fetch(ctx context.Context, client *client.Client, q *models.
 
 	if q.InstantQuery {
 		res, err := s.instantQuery(traceCtx, client, q, headers)
-		if err != nil {
-			return nil, err
-		}
-		response.Error = res.Error
+		response.Error = err
 		response.Frames = res.Frames
 	}
 
 	if q.RangeQuery {
 		res, err := s.rangeQuery(traceCtx, client, q, headers)
 		if err != nil {
-			return nil, err
-		}
-		if res.Error != nil {
 			if response.Error == nil {
-				response.Error = res.Error
+				response.Error = err
 			} else {
-				response.Error = fmt.Errorf("%v %w", response.Error, res.Error) // lovely
+				response.Error = fmt.Errorf("%v %w", response.Error, err)
 			}
 		}
 		response.Frames = append(response.Frames, res.Frames...)

pkg/tsdb/prometheus/querydata/response.go

@@ -29,11 +29,13 @@ func (s *QueryData) parseResponse(ctx context.Context, q *models.Query, res *htt
 		MatrixWideSeries: s.enableWideSeries,
 		VectorWideSeries: s.enableWideSeries,
 	})
-	if r.Frames == nil {
-		return r, fmt.Errorf("received empty response from prometheus")
-	}
 
 	// The ExecutedQueryString can be viewed in QueryInspector in UI
+	// Add frame to attach metadata to it
+	if len(r.Frames) == 0 {
+		r.Frames = append(r.Frames, data.NewFrame(""))
+	}
+
 	for _, frame := range r.Frames {
 		if s.enableWideSeries {
 			addMetadataToWideFrame(q, frame)
@@ -42,6 +44,10 @@ func (s *QueryData) parseResponse(ctx context.Context, q *models.Query, res *htt
 		}
 	}
 
+	if r.Error != nil {
+		return r, r.Error
+	}
+
 	r = s.processExemplars(q, r)
 	return r, nil
 }