prevent from removing function with subscriptions. Closes #208

function/errors.go

@@ -57,3 +57,10 @@ type ErrFunctionError struct {
 func (e ErrFunctionError) Error() string {
 	return fmt.Sprintf("Function call failed because of runtime error. Error: %q", e.Original)
 }
+
+// ErrFunctionHasSubscriptionsError occurs when function with subscription is being deleted.
+type ErrFunctionHasSubscriptionsError struct{}
+
+func (e ErrFunctionHasSubscriptionsError) Error() string {
+	return fmt.Sprintf("Function cannot be deleted because it's subscribed to a least one event.")
+}

httpapi/httpapi.go

@@ -146,6 +146,8 @@ func (h HTTPAPI) deleteFunction(w http.ResponseWriter, r *http.Request, params h
 	if err != nil {
 		if _, ok := err.(*function.ErrFunctionNotFound); ok {
 			w.WriteHeader(http.StatusNotFound)
+		} else if _, ok := err.(*function.ErrFunctionHasSubscriptionsError); ok {
+			w.WriteHeader(http.StatusBadRequest)
 		} else {
 			w.WriteHeader(http.StatusInternalServerError)
 		}

httpapi/httpapi_test.go

@@ -202,6 +202,23 @@ func TestRegisterFunction_InternalError(t *testing.T) {
 	assert.Equal(t, `processing error`, httpresp.Errors[0].Message)
 }
 
+func TestDeleteFunction_BadRequest(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+	router, functions, _ := setup(ctrl)
+
+	functions.EXPECT().DeleteFunction("default", function.ID("func1")).Return(&function.ErrFunctionHasSubscriptionsError{})
+
+	resp := httptest.NewRecorder()
+	req, _ := http.NewRequest(http.MethodDelete, "/v1/spaces/default/functions/func1", nil)
+	router.ServeHTTP(resp, req)
+
+	httpresp := &httpapi.Response{}
+	json.Unmarshal(resp.Body.Bytes(), httpresp)
+	assert.Equal(t, http.StatusBadRequest, resp.Code)
+	assert.Equal(t, "Function cannot be deleted because it's subscribed to a least one event.", httpresp.Errors[0].Message)
+}
+
 func setup(ctrl *gomock.Controller) (
 	*httprouter.Router,
 	*mock.MockFunctionService,

libkv/function.go

@@ -124,7 +124,17 @@ func (service Service) GetFunctions(space string) (function.Functions, error) {
 
 // DeleteFunction deletes function from the registry.
 func (service Service) DeleteFunction(space string, id function.ID) error {
-	err := service.FunctionStore.Delete(FunctionKey{space, id}.String())
+	subs, err := service.GetSubscriptions(space)
+	if err != nil {
+		return err
+	}
+	for _, sub := range subs {
+		if id == sub.FunctionID {
+			return &function.ErrFunctionHasSubscriptionsError{}
+		}
+	}
+
+	err = service.FunctionStore.Delete(FunctionKey{space, id}.String())
 	if err != nil {
 		return &function.ErrFunctionNotFound{ID: id}
 	}

libkv/function_test.go

@@ -239,9 +239,12 @@ func TestDeleteFunction(t *testing.T) {
 	ctrl := gomock.NewController(t)
 	defer ctrl.Finish()
 
-	db := mock.NewMockStore(ctrl)
-	db.EXPECT().Delete("default/testid").Return(nil)
-	service := &Service{FunctionStore: db, Log: zap.NewNop()}
+	kvs := []*store.KVPair{}
+	subscriptionsDB := mock.NewMockStore(ctrl)
+	subscriptionsDB.EXPECT().List("default/", &store.ReadOptions{Consistent: true}).Return(kvs, nil)
+	functionsDB := mock.NewMockStore(ctrl)
+	functionsDB.EXPECT().Delete("default/testid").Return(nil)
+	service := &Service{FunctionStore: functionsDB, SubscriptionStore: subscriptionsDB, Log: zap.NewNop()}
 
 	err := service.DeleteFunction("default", function.ID("testid"))
 
@@ -252,15 +255,34 @@ func TestDeleteFunction_NotFound(t *testing.T) {
 	ctrl := gomock.NewController(t)
 	defer ctrl.Finish()
 
-	db := mock.NewMockStore(ctrl)
-	db.EXPECT().Delete("default/testid").Return(errors.New("KV func not found"))
-	service := &Service{FunctionStore: db, Log: zap.NewNop()}
+	kvs := []*store.KVPair{}
+	subscriptionsDB := mock.NewMockStore(ctrl)
+	subscriptionsDB.EXPECT().List("default/", &store.ReadOptions{Consistent: true}).Return(kvs, nil)
+	functionsDB := mock.NewMockStore(ctrl)
+	functionsDB.EXPECT().Delete("default/testid").Return(errors.New("KV func not found"))
+	service := &Service{FunctionStore: functionsDB, SubscriptionStore: subscriptionsDB, Log: zap.NewNop()}
 
 	err := service.DeleteFunction("default", function.ID("testid"))
 
 	assert.EqualError(t, err, `Function "testid" not found.`)
 }
 
+func TestDeleteFunction_SubscriptionExists(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+
+	kvs := []*store.KVPair{
+		{Value: []byte(`{"subscriptionId":"s1","default":"default","event":"test","functionId":"testid"}`)}}
+	subscriptionsDB := mock.NewMockStore(ctrl)
+	subscriptionsDB.EXPECT().List("default/", &store.ReadOptions{Consistent: true}).Return(kvs, nil)
+	functionsDB := mock.NewMockStore(ctrl)
+	service := &Service{FunctionStore: functionsDB, SubscriptionStore: subscriptionsDB, Log: zap.NewNop()}
+
+	err := service.DeleteFunction("default", function.ID("testid"))
+
+	assert.Equal(t, err, &function.ErrFunctionHasSubscriptionsError{})
+}
+
 func TestValidateFunction_AWSLambdaMissingRegion(t *testing.T) {
 	service := &Service{Log: zap.NewNop()}