Validate values length for prometheus scaler (#2264)

Signed-off-by: Magdalena Andruszak <[email protected]>

CHANGELOG.md

@@ -54,6 +54,7 @@
 - Improve error message if `IdleReplicaCount` are equal to `MinReplicaCount` to be the same as the check ([#2212](https://github.com/kedacore/keda/pull/2212))
 - Improve Cloudwatch Scaler metric exporting logic ([#2243](https://github.com/kedacore/keda/pull/2243))
 - Refactor aws related scalers to reuse the aws clients instead of creating a new one for every GetMetrics call([#2255](https://github.com/kedacore/keda/pull/2255))
+- Validating values length in prometheus query response ([#2264](https://github.com/kedacore/keda/pull/2264))
 
 ### Breaking Changes
 

pkg/scalers/prometheus_scaler.go

@@ -263,6 +263,13 @@ func (s *prometheusScaler) ExecutePromQuery(ctx context.Context) (float64, error
 		return -1, fmt.Errorf("prometheus query %s returned multiple elements", s.metadata.query)
 	}
 
+	valueLen := len(result.Data.Result[0].Value)
+	if valueLen == 0 {
+		return 0, nil
+	} else if valueLen < 2 {
+		return -1, fmt.Errorf("prometheus query %s didn't return enough values", s.metadata.query)
+	}
+
 	val := result.Data.Result[0].Value[1]
 	if val != nil {
 		s := val.(string)

pkg/scalers/prometheus_scaler_test.go

@@ -3,8 +3,11 @@ package scalers
 import (
 	"context"
 	"net/http"
+	"net/http/httptest"
 	"strings"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )
 
 type parsePrometheusMetadataTestData struct {
@@ -119,3 +122,87 @@ func TestPrometheusScalerAuthParams(t *testing.T) {
 		}
 	}
 }
+
+type prometheusQromQueryResultTestData struct {
+	name           string
+	bodyStr        string
+	responseStatus int
+	expectedValue  float64
+	isError        bool
+}
+
+var testPromQueryResult = []prometheusQromQueryResultTestData{
+	{
+		name:           "no results",
+		bodyStr:        `{}`,
+		responseStatus: http.StatusOK,
+		expectedValue:  0,
+		isError:        false,
+	},
+	{
+		name:           "no values",
+		bodyStr:        `{"data":{"result":[]}}`,
+		responseStatus: http.StatusOK,
+		expectedValue:  0,
+		isError:        false,
+	},
+	{
+		name:           "valid value",
+		bodyStr:        `{"data":{"result":[{"value": ["1", "2"]}]}}`,
+		responseStatus: http.StatusOK,
+		expectedValue:  2,
+		isError:        false,
+	},
+	{
+		name:           "not enough values",
+		bodyStr:        `{"data":{"result":[{"value": ["1"]}]}}`,
+		responseStatus: http.StatusOK,
+		expectedValue:  -1,
+		isError:        true,
+	},
+	{
+		name:           "multiple results",
+		bodyStr:        `{"data":{"result":[{},{}]}}`,
+		responseStatus: http.StatusOK,
+		expectedValue:  -1,
+		isError:        true,
+	},
+	{
+		name:           "error status response",
+		bodyStr:        `{}`,
+		responseStatus: http.StatusBadRequest,
+		expectedValue:  -1,
+		isError:        true,
+	},
+}
+
+func TestPrometheusScalerExecutePromQuery(t *testing.T) {
+	for _, testData := range testPromQueryResult {
+		t.Run(testData.name, func(t *testing.T) {
+			server := httptest.NewServer(http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
+				writer.WriteHeader(testData.responseStatus)
+
+				if _, err := writer.Write([]byte(testData.bodyStr)); err != nil {
+					t.Fatal(err)
+				}
+			}))
+
+			scaler := prometheusScaler{
+				metadata: &prometheusMetadata{
+					serverAddress: server.URL,
+				},
+				httpClient: http.DefaultClient,
+			}
+
+			value, err := scaler.ExecutePromQuery(context.TODO())
+
+			assert.Equal(t, testData.expectedValue, value)
+
+			if testData.isError {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+			}
+		})
+	}
+}