From 43371527129d819b141b957b83d8dab485040c1b Mon Sep 17 00:00:00 2001
From: KonH <konh@yandex.ru>
Date: Tue, 18 Oct 2022 20:25:04 +0200
Subject: [PATCH] Change signature - return non-reference from
 ReadPrometheusStyleResult

Related to https://github.com/grafana/grafana/issues/52430
---
 pkg/tsdb/loki/api.go                      | 8 --------
 pkg/tsdb/prometheus/querydata/response.go | 9 +++------
 pkg/util/converter/prom.go                | 6 +++---
 pkg/util/converter/prom_test.go           | 2 +-
 4 files changed, 7 insertions(+), 18 deletions(-)

diff --git a/pkg/tsdb/loki/api.go b/pkg/tsdb/loki/api.go
index 553cc9bdf4d..d94ecf6b714 100644
--- a/pkg/tsdb/loki/api.go
+++ b/pkg/tsdb/loki/api.go
@@ -163,14 +163,6 @@ func (api *LokiAPI) DataQuery(ctx context.Context, query lokiQuery) (data.Frames
 	iter := jsoniter.Parse(jsoniter.ConfigDefault, resp.Body, 1024)
 	res := converter.ReadPrometheusStyleResult(iter, converter.Options{MatrixWideSeries: false, VectorWideSeries: false})
 
-	if res == nil {
-		// it's hard to say if this is an error-case or not.
-		// we know the http-response was a success-response
-		// (otherwise we wouldn't be here in the code),
-		// so we will go with a success, with no data.
-		return data.Frames{}, nil
-	}
-
 	if res.Error != nil {
 		return nil, res.Error
 	}
diff --git a/pkg/tsdb/prometheus/querydata/response.go b/pkg/tsdb/prometheus/querydata/response.go
index 64b0ffe48fb..aecf5a11cbc 100644
--- a/pkg/tsdb/prometheus/querydata/response.go
+++ b/pkg/tsdb/prometheus/querydata/response.go
@@ -27,9 +27,6 @@ func (s *QueryData) parseResponse(ctx context.Context, q *models.Query, res *htt
 		MatrixWideSeries: s.enableWideSeries,
 		VectorWideSeries: s.enableWideSeries,
 	})
-	if r == nil {
-		return nil, fmt.Errorf("received empty response from prometheus")
-	}
 
 	// The ExecutedQueryString can be viewed in QueryInspector in UI
 	for _, frame := range r.Frames {
@@ -41,7 +38,7 @@ func (s *QueryData) parseResponse(ctx context.Context, q *models.Query, res *htt
 	}
 
 	r = processExemplars(q, r)
-	return r, nil
+	return &r, nil
 }
 
 func addMetadataToMultiFrame(q *models.Query, frame *data.Frame) {
@@ -135,7 +132,7 @@ func getName(q *models.Query, field *data.Field) string {
 	return legend
 }
 
-func processExemplars(q *models.Query, dr *backend.DataResponse) *backend.DataResponse {
+func processExemplars(q *models.Query, dr backend.DataResponse) backend.DataResponse {
 	sampler := newExemplarSampler()
 
 	// we are moving from a multi-frame response returned
@@ -203,7 +200,7 @@ func processExemplars(q *models.Query, dr *backend.DataResponse) *backend.DataRe
 
 	frames = append(frames, exemplarFrame)
 
-	return &backend.DataResponse{
+	return backend.DataResponse{
 		Frames: frames,
 		Error:  dr.Error,
 	}
diff --git a/pkg/util/converter/prom.go b/pkg/util/converter/prom.go
index 5a51b33f2f1..ca6377885dc 100644
--- a/pkg/util/converter/prom.go
+++ b/pkg/util/converter/prom.go
@@ -24,7 +24,7 @@ type Options struct {
 }
 
 // ReadPrometheusStyleResult will read results from a prometheus or loki server and return data frames
-func ReadPrometheusStyleResult(iter *jsoniter.Iterator, opt Options) *backend.DataResponse {
+func ReadPrometheusStyleResult(iter *jsoniter.Iterator, opt Options) backend.DataResponse {
 	var rsp *backend.DataResponse
 	status := "unknown"
 	errorType := ""
@@ -55,7 +55,7 @@ func ReadPrometheusStyleResult(iter *jsoniter.Iterator, opt Options) *backend.Da
 	}
 
 	if status == "error" {
-		return &backend.DataResponse{
+		return backend.DataResponse{
 			Error: fmt.Errorf("%s: %s", errorType, err),
 		}
 	}
@@ -69,7 +69,7 @@ func ReadPrometheusStyleResult(iter *jsoniter.Iterator, opt Options) *backend.Da
 		}
 	}
 
-	return rsp
+	return *rsp
 }
 
 func readWarnings(iter *jsoniter.Iterator) []data.Notice {
diff --git a/pkg/util/converter/prom_test.go b/pkg/util/converter/prom_test.go
index 97620675d6a..29649c6a68c 100644
--- a/pkg/util/converter/prom_test.go
+++ b/pkg/util/converter/prom_test.go
@@ -68,7 +68,7 @@ func runScenario(name string, opts Options) func(t *testing.T) {
 		}
 
 		fname := name + "-frame"
-		experimental.CheckGoldenJSONResponse(t, "testdata", fname, rsp, update)
+		experimental.CheckGoldenJSONResponse(t, "testdata", fname, &rsp, update)
 	}
 }