code: private void doInstalled(final Message<JsonObject> message) {
      String moduleName = message.body().getString("module");
      if (moduleName == null) {
        message.reply(new JsonObject().putString("status", "error").putString("message", "No module specified."));
        return;
      }
  
      platform.getModuleInfo(moduleName, new Handler<AsyncResult<ModuleInfo>>() {
        @Override
        public void handle(AsyncResult<ModuleInfo> result) {
          if (result.failed() || result.result() == null) {
            message.reply(new JsonObject().putString("status", "ok").putBoolean("result", false));
          } else {
            message.reply(new JsonObject().putString("status", "ok").putBoolean("result", true));
          }
        }
      });
    }
docs: Checks if a module is installed.