Crow：路由局部插件2 调用before_handle

Crow：http请求到Rule绑定的handler_的调用链-CSDN博客

中介绍了当找到对应的路由后Router::handle

template<typename App>
typename std::enable_if<std::tuple_size<typename App::mw_container_t>::value != 0, void>::type
  handle_rule(BaseRule* rule, crow::request& req, crow::response& res, const crow::routing_params& rp)
{
    if (!rule->mw_indices_.empty())
    {
        ...
    }
}

template<typename... Middlewares>
class Crow
{
    using mw_container_t = std::tuple<Middlewares...>;
};

struct middleware_indices
{
    bool empty() const
    {
        return indices_.empty();
    }
private:
    std::vector<int> indices_;
}

当Crow类中有插件时，会调用这个版本的handle_rule

而改handle_rule会先判断mw_indices_是否为空

也就是