php - 如何在另一个中间件中使用 'Clousre $next' 调用 Laravel 中间件的 handle() 方法？

Question

这是 Laravel 的 ValidatePostSize 中的 handle() 方法:

public function handle($request, Closure $next)
{
    $max = $this->getPostMaxSize();

    if ($max > 0 && $request->server('CONTENT_LENGTH') > $max) {
        throw new PostTooLargeException;
    }

    return $next($request);
}

现在，使用 $next($request) 为另一个中间件调用此方法。我的理解是 handle() 方法被转换为 $next。我想知道这是如何发生在引擎盖下的。

Answer 1

To pass the request deeper into the application (allowing the middleware to "pass"), simply call the $next callback with the $request. https://laravel.com/docs/5.4/middleware#defining-middleware

当 Laravel 处理请求时，它会运行堆栈中所有适用的中间件。中间件可以设置为在路由/ Controller 方法之前和/或之后运行。

为了能够做到这一点，Laravel 使用 Illuminate\Pipeline\Pipeline .本质上，它使用 array_reduce遍历中间件堆栈，然后返回 Closure执行该中间件。美妙之处在于使用 array_reverse允许将下一个中间件执行传递给前一个。

再详细说明一点:

当 Illuminate\Foundation\Http\Kernel@handle被称为它用 sendRequestThroughRouter 建立响应其中包含以下内容:

return (new Pipeline($this->app))
            ->send($request)
            ->through($this->app->shouldSkipMiddleware() ? [] : $this->middleware)
            ->then($this->dispatchToRouter());

Pipeline是 Illuminate\Routing\Pipeline扩展 Illuminate\Pipeline\Pipeline .
then()上面的方法本质上是:

->then(function ($request) {
    $this->app->instance('request', $request);

    return $this->router->dispatch($request);
})

那么意味着我们从一个接受最终结果的闭包开始(记住此时不会调用闭包)。

然后，在 then()方法， array_reduce和 array_reverse如上所述的部分发生。

下面是一个简化的例子，说明什么时候实际发生在 then()方法(假设您知道 array_reduce 的工作原理):

function then(Closure $destination)
{
    $pipeline = array_reduce(

        array_reverse($this->middlewares),

        //Remember $nextClosure is going to be the closure returned 
        //from the previous iteration

        function ($nextClosure, $middlewareClass) {

            //This is the $next closure you see in your middleware
            return function ($request) use ($nextClosure, $middlewareClass) {

                //Resolve the middleware
                $middleware = app($middlewareClass);

                //Call the middleware
                return $middleware->{$this->method}($request, $nextClosure);
            };
        },

        //The finial closure that will be called that resolves the destination

        function ($request) use ($destination) {
            return $destination($request);
        }
    );

    return $pipeline($this->request);
}

假设我们有 3 个中间件:

[
    One::class,
    Two::class,
    Three::class,
];

$pipeline上面的变量基本上是:

function ($request) {

    return app(One::class)->handle($request, function ($request) {

        return app(Two::class)->handle($request, function ($request) {

            return app(Three::class)->handle($request, function ($request) {

                return $destination($request);

            });
        };);
    };);
};

希望这可以帮助!