InfluxDB: Return default retention policy from backend as first element (#69818)

* Reformatting and restructuring

* Update unit test

* Always send the default retention policy as first element

* Fix typo

* Update test

* Update test once more

pkg/tsdb/influxdb/response_parser.go

@@ -74,6 +74,9 @@ func transformRows(rows []Row, query Query) data.Frames {
 	// It's sized for a reasonably-large name, but will grow if needed.
 	frameName := make([]byte, 0, 128)
 
+	retentionPolicyQuery := isRetentionPolicyQuery(query)
+	tagValuesQuery := isTagValuesQuery(query)
+
 	for _, row := range rows {
 		var hasTimeCol = false
 
@@ -86,11 +89,32 @@ func transformRows(rows []Row, query Query) data.Frames {
 		if !hasTimeCol {
 			var values []string
 
+			if retentionPolicyQuery {
+				values = make([]string, 1, len(row.Values))
+			} else {
+				values = make([]string, 0, len(row.Values))
+			}
+
 			for _, valuePair := range row.Values {
-				if strings.Contains(strings.ToLower(query.RawQuery), strings.ToLower("SHOW TAG VALUES")) {
+				if tagValuesQuery {
 					if len(valuePair) >= 2 {
 						values = append(values, valuePair[1].(string))
 					}
+				} else if retentionPolicyQuery {
+					// We want to know whether the given retention policy is the default one or not.
+					// If it is default policy then we should add it to the beginning.
+					// The index 4 gives us if that policy is default or not.
+					// https://docs.influxdata.com/influxdb/v1.8/query_language/explore-schema/#show-retention-policies
+					// Only difference is v0.9. In that version we don't receive shardGroupDuration value.
+					// https://archive.docs.influxdata.com/influxdb/v0.9/query_language/schema_exploration/#show-retention-policies
+					// Since it is always the last value we will check that last value always.
+					if len(valuePair) >= 1 {
+						if valuePair[len(row.Columns)-1].(bool) {
+							values[0] = valuePair[0].(string)
+						} else {
+							values = append(values, valuePair[0].(string))
+						}
+					}
 				} else {
 					if len(valuePair) >= 1 {
 						values = append(values, valuePair[0].(string))
@@ -294,3 +318,11 @@ func parseNumber(value interface{}) *float64 {
 
 	return &fvalue
 }
+
+func isTagValuesQuery(query Query) bool {
+	return strings.Contains(strings.ToLower(query.RawQuery), strings.ToLower("SHOW TAG VALUES"))
+}
+
+func isRetentionPolicyQuery(query Query) bool {
+	return strings.Contains(strings.ToLower(query.RawQuery), strings.ToLower("SHOW RETENTION POLICIES"))
+}

pkg/tsdb/influxdb/response_parser_test.go

@@ -10,9 +10,10 @@ import (
 	"github.com/google/go-cmp/cmp"
 	"github.com/grafana/grafana-plugin-sdk-go/backend"
 	"github.com/grafana/grafana-plugin-sdk-go/data"
-	"github.com/grafana/grafana/pkg/util"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
+	"github.com/grafana/grafana/pkg/util"
 )
 
 func prepare(text string) io.ReadCloser {
@@ -733,6 +734,78 @@ func TestInfluxdbResponseParser(t *testing.T) {
 	})
 }
 
+func TestResponseParser_Parse_RetentionPolicy(t *testing.T) {
+	t.Run("Influxdb response parser should parse metricFindQueries->SHOW RETENTION POLICIES normally", func(t *testing.T) {
+		parser := &ResponseParser{}
+
+		response := `
+		{
+		  "results": [
+		    {
+		      "statement_id": 0,
+		      "series": [
+		        {
+		          "columns": [
+		            "name",
+		            "duration",
+		            "shardGroupDuration",
+		            "replicaN",
+		            "default"
+		          ],
+		          "values": [
+		            [
+		              "autogen",
+		              "0s",
+		              "168h0m0s",
+		              1,
+		              false
+		            ],
+		            [
+		              "bar",
+		              "24h0m0s",
+		              "1h0m0s",
+		              1,
+		              true
+		            ],
+		            [
+		              "5m_avg",
+		              "2400h0m0s",
+		              "24h0m0s",
+		              1,
+		              false
+		            ],
+		            [
+		              "1m_avg",
+		              "240h0m0s",
+		              "24h0m0s",
+		              1,
+		              false
+		            ]
+		          ]
+		        }
+		      ]
+		    }
+		  ]
+		}
+		`
+
+		var queries []Query
+		queries = append(queries, Query{RefID: "metricFindQuery", RawQuery: "SHOW RETENTION POLICIES"})
+		policyFrame := data.NewFrame("",
+			data.NewField("value", nil, []string{
+				"bar", "autogen", "5m_avg", "1m_avg",
+			}),
+		)
+
+		result := parser.Parse(prepare(response), queries)
+
+		frame := result.Responses["metricFindQuery"]
+		if diff := cmp.Diff(policyFrame, frame.Frames[0], data.FrameTestCompareOptions()...); diff != "" {
+			t.Errorf("Result mismatch (-want +got):\n%s", diff)
+		}
+	})
+}
+
 func TestResponseParser_Parse(t *testing.T) {
 	tests := []struct {
 		name  string