Config UI: visualize Modbusproxy (#24015)

Co-authored-by: Michael Geers <michael@geers.tv>

cmd/setup.go

@@ -951,13 +951,33 @@ func configureDevices(conf globalconfig.All) error {
 	return joinErrors(errs...)
 }
 
+// migrateYamlToJson converts a settings value from yaml to json if needed
+func migrateYamlToJson[T any](key string) error {
+	var err error
+	if settings.IsJson(key) {
+		// already JSON, nothing to do
+		return nil
+	}
+
+	var data T
+	if err := settings.Yaml(key, new(T), &data); err == nil {
+		settings.SetJson(key, data)
+		log.INFO.Printf("migrated %s setting to JSON", key)
+	}
+
+	return err
+}
+
 func configureModbusProxy(conf *[]globalconfig.ModbusProxy) error {
-	// migrate settings
 	if settings.Exists(keys.ModbusProxy) {
-		*conf = []globalconfig.ModbusProxy{}
-		if err := settings.Yaml(keys.ModbusProxy, new([]map[string]any), &conf); err != nil {
+		// TODO: delete if not needed any more
+		if err := migrateYamlToJson[[]globalconfig.ModbusProxy](keys.ModbusProxy); err != nil {
 			return err
 		}
+
+		if err := settings.Json(keys.ModbusProxy, &conf); err != nil {
+			return fmt.Errorf("failed to read modbusproxy setting: %w", err)
+		}
 	}
 
 	for _, cfg := range *conf {