CloudWatch/Logs: Fix query error when results are sparse (#24702)

pkg/tsdb/cloudwatch/log_query.go

@@ -8,13 +8,33 @@ import (
 )
 
 func logsResultsToDataframes(response *cloudwatchlogs.GetQueryResultsOutput) (*data.Frame, error) {
+	nonEmptyRows := make([][]*cloudwatchlogs.ResultField, 0)
+	// Sometimes CloudWatch can send empty rows
+	for _, row := range response.Results {
+		if len(row) == 0 {
+			continue
+		}
+		if len(row) == 1 {
+			if row[0].Value == nil {
+				continue
+			}
+			// Sometimes it sends row with only timestamp
+			if _, err := time.Parse(cloudWatchTSFormat, *row[0].Value); err == nil {
+				continue
+			}
+		}
+		nonEmptyRows = append(nonEmptyRows, row)
+	}
+
+	rowCount := len(nonEmptyRows)
+
 	fieldValues := make(map[string]interface{})
 
 	// Maintaining a list of field names in the order returned from CloudWatch
 	// as just iterating over fieldValues would not give a consistent order
 	fieldNames := make([]*string, 0)
 
-	for _, row := range response.Results {
+	for i, row := range nonEmptyRows {
 		for _, resultField := range row {
 			// Strip @ptr field from results as it's not needed
 			if *resultField.Field == "@ptr" {
@@ -26,9 +46,9 @@ func logsResultsToDataframes(response *cloudwatchlogs.GetQueryResultsOutput) (*d
 
 				// Check if field is time field
 				if _, err := time.Parse(cloudWatchTSFormat, *resultField.Value); err == nil {
-					fieldValues[*resultField.Field] = make([]*time.Time, 0)
+					fieldValues[*resultField.Field] = make([]*time.Time, rowCount)
 				} else {
-					fieldValues[*resultField.Field] = make([]*string, 0)
+					fieldValues[*resultField.Field] = make([]*string, rowCount)
 				}
 			}
 
@@ -38,9 +58,9 @@ func logsResultsToDataframes(response *cloudwatchlogs.GetQueryResultsOutput) (*d
 					return nil, err
 				}
 
-				fieldValues[*resultField.Field] = append(timeField, &parsedTime)
+				timeField[i] = &parsedTime
 			} else {
-				fieldValues[*resultField.Field] = append(fieldValues[*resultField.Field].([]*string), resultField.Value)
+				fieldValues[*resultField.Field].([]*string)[i] = resultField.Value
 			}
 		}
 	}
@@ -112,7 +132,11 @@ func groupResults(results *data.Frame, groupingFieldNames []string) ([]*data.Fra
 func generateGroupKey(fields []*data.Field, row int) string {
 	groupKey := ""
 	for _, field := range fields {
-		groupKey += *field.At(row).(*string)
+		if strField, ok := field.At(row).(*string); ok {
+			if strField != nil {
+				groupKey += *strField
+			}
+		}
 	}
 
 	return groupKey

pkg/tsdb/cloudwatch/log_query_test.go

@@ -80,6 +80,13 @@ func TestLogsResultsToDataframes(t *testing.T) {
 			},
 			// Sometimes cloudwatch returns empty row
 			{},
+			// or rows with only timestamp
+			{
+				&cloudwatchlogs.ResultField{
+					Field: aws.String("@timestamp"),
+					Value: aws.String("2020-03-02 17:04:05.000"),
+				},
+			},
 			{
 				&cloudwatchlogs.ResultField{
 					Field: aws.String("@ptr"),
@@ -205,20 +212,23 @@ func TestGroupKeyGeneration(t *testing.T) {
 		aws.String("fakelog-a"),
 		aws.String("fakelog-b"),
 		aws.String("fakelog-c"),
+		nil,
 	})
 
 	streamField := data.NewField("stream", data.Labels{}, []*string{
 		aws.String("stream-a"),
 		aws.String("stream-b"),
 		aws.String("stream-c"),
+		aws.String("stream-d"),
 	})
 
 	fakeFields := []*data.Field{logField, streamField}
-	expectedKeys := []string{"fakelog-astream-a", "fakelog-bstream-b", "fakelog-cstream-c"}
+	expectedKeys := []string{"fakelog-astream-a", "fakelog-bstream-b", "fakelog-cstream-c", "stream-d"}
 
 	assert.Equal(t, expectedKeys[0], generateGroupKey(fakeFields, 0))
 	assert.Equal(t, expectedKeys[1], generateGroupKey(fakeFields, 1))
 	assert.Equal(t, expectedKeys[2], generateGroupKey(fakeFields, 2))
+	assert.Equal(t, expectedKeys[3], generateGroupKey(fakeFields, 3))
 }
 
 func TestGroupingResults(t *testing.T) {