Analysis of middleware source code based on laravel5.2

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

    Facade::clearResolvedInstance('request');

    $this->bootstrap();

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

public function then(Closure $destination)
{
    $firstSlice = $this->getInitialSlice($destination);

    $pipes = array_reverse($this->pipes);

    return call_user_func(
        array_reduce($pipes, $this->getSlice(), $firstSlice), $this->passable
    );
}

//将数组中的元素，依次执行$func函数，且上一次的$func的返回值作为下一次调用$func的第一个参数输入
function array_reduce_back($arr, callable $func, $firstResult = null)
{
    $result = $firstResult;
    
    foreach ($arr as $v) {
        $result = $func($result, $v);
    }
    
    return $result;
}

call_user_func(
        array_reduce([1, 2, 3], $this->getSlice(), $firstSlice), $this->passable
    );

// 把具体的参数带进来
return (new Pipeline($this->app))
                ->send($request)
                ->through(['\Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode'])
                ->then($this->dispatchToRouter());

function($requset) use (\Illuminate\Foundation\Http\Kernel::dispatchToRouter(), '\Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode') {

            if ($pipe instanceof Closure) {
                return call_user_func($pipe, $passable, $stack);
            }
            
            // $name和$parameters很容易得到
            // $name = '\Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode';
            // $parameters = [];
            list($name, $parameters) = $this->parsePipeString($pipe);


            // 执行的就是\Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::handle($request, \Illuminate\Foundation\Http\Kernel::dispatchToRouter())
            return call_user_func_array([$this->container->make($name), $this->method],
                        array_merge([$passable, $stack], $parameters));
}

public function handle($request, Closure $next)
{
    if ($this->app->isDownForMaintenance()) {
        throw new HttpException(503);
    }

    return $next($request);
}

// 使用管道，发送$request,使之通过middleware ，再到$func
(new Pipeline($this->app))->send($request)->through($this->middleware)->then($func);

public function dispatchToRoute(Request $request)
{
    // 找到具体的路由对象，过程略
    $route = $this->findRoute($request);

    $request->setRouteResolver(function () use ($route) {
        return $route;
    });

    // 执行Request匹配到Route的事件，具体的代码在这里：\Illuminate\Foundation\Providers\FoundationServiceProvider::configureFormRequests
    $this->events->fire(new Events\RouteMatched($route, $request));
    
    // 这里就运行路由中间件了
    $response = $this->runRouteWithinStack($route, $request);

    return $this->prepareResponse($request, $response);
}


protected function runRouteWithinStack(Route $route, Request $request)
{
    // 获取该路由上的中间件
    // 简单就点可这样写：
    // $middleware = App::shouldSkipMiddleware() ? [] : $this->gatherRouteMiddlewares($route);
    $shouldSkipMiddleware = $this->container->bound('middleware.disable') &&
                         $this->container->make('middleware.disable') === true;

    $middleware = $shouldSkipMiddleware ? [] : $this->gatherRouteMiddlewares($route);
    
    // 了解Pipeline后，这里就好理解了，应该是通过管道，发送$request,经过$middleware，再到then中的回调
    return (new Pipeline($this->container))
                    ->send($request)
                    ->through($middleware)
                    ->then(function ($request) use ($route) {
                        return $this->prepareResponse(
                            $request,
                            $route->run($request)
                        );
                    });
}