fix: JSON unmarshaling error handling and nil return (#18700)

* fix: JSON unmarshaling error handling and nil return in ExecuteHealthLua function

Signed-off-by: Yonatan Sasson <yonatanxd7@gmail.com>

* Update util/lua/lua.go

Co-authored-by: Alexandre Gaudreault <alexandre_gaudreault@intuit.com>
Signed-off-by: Michael Crenshaw <350466+crenshaw-dev@users.noreply.github.com>

---------

Signed-off-by: Yonatan Sasson <yonatanxd7@gmail.com>
Signed-off-by: Michael Crenshaw <350466+crenshaw-dev@users.noreply.github.com>
Co-authored-by: Michael Crenshaw <350466+crenshaw-dev@users.noreply.github.com>
Co-authored-by: Alexandre Gaudreault <alexandre_gaudreault@intuit.com>

util/lua/lua.go

@@ -4,9 +4,11 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
+	"reflect"
 	"time"
 
 	"github.com/argoproj/gitops-engine/pkg/health"
@@ -109,6 +111,11 @@ func (vm VM) ExecuteHealthLua(obj *unstructured.Unstructured, script string) (*h
 		healthStatus := &health.HealthStatus{}
 		err = json.Unmarshal(jsonBytes, healthStatus)
 		if err != nil {
+			// Validate if the error is caused by an empty object
+			typeError := &json.UnmarshalTypeError{Value: "array", Type: reflect.TypeOf(healthStatus)}
+			if errors.As(err, &typeError) {
+				return &health.HealthStatus{}, nil
+			}
 			return nil, err
 		}
 		if !isValidHealthStatusCode(healthStatus.Status) {
@@ -119,6 +126,8 @@ func (vm VM) ExecuteHealthLua(obj *unstructured.Unstructured, script string) (*h
 		}
 
 		return healthStatus, nil
+	} else if returnValue.Type() == lua.LTNil {
+		return &health.HealthStatus{}, nil
 	}
 	return nil, fmt.Errorf(incorrectReturnType, "table", returnValue.Type().String())
 }

util/lua/lua_test.go

@@ -137,6 +137,45 @@ func TestInvalidHealthStatusStatus(t *testing.T) {
 	assert.Equal(t, expectedStatus, status)
 }
 
+const validReturnNothingHealthStatusStatus = `local healthStatus = {}
+return
+`
+
+func TestNoReturnHealthStatusStatus(t *testing.T) {
+	testObj := StrToUnstructured(objJSON)
+	vm := VM{}
+	status, err := vm.ExecuteHealthLua(testObj, validReturnNothingHealthStatusStatus)
+	require.NoError(t, err)
+	expectedStatus := &health.HealthStatus{}
+	assert.Equal(t, expectedStatus, status)
+}
+
+const validNilHealthStatusStatus = `local healthStatus = {}
+return nil
+`
+
+func TestNilHealthStatusStatus(t *testing.T) {
+	testObj := StrToUnstructured(objJSON)
+	vm := VM{}
+	status, err := vm.ExecuteHealthLua(testObj, validNilHealthStatusStatus)
+	require.NoError(t, err)
+	expectedStatus := &health.HealthStatus{}
+	assert.Equal(t, expectedStatus, status)
+}
+
+const validEmptyArrayHealthStatusStatus = `local healthStatus = {}
+return healthStatus
+`
+
+func TestEmptyHealthStatusStatus(t *testing.T) {
+	testObj := StrToUnstructured(objJSON)
+	vm := VM{}
+	status, err := vm.ExecuteHealthLua(testObj, validEmptyArrayHealthStatusStatus)
+	require.NoError(t, err)
+	expectedStatus := &health.HealthStatus{}
+	assert.Equal(t, expectedStatus, status)
+}
+
 const infiniteLoop = `while true do ; end`
 
 func TestHandleInfiniteLoop(t *testing.T) {