Laravel 管道流原理

array_reduce(
    ['App\Http\Middleware\AllowOrigin::class','Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::class'],
    function ($stack, $pipe) {        //callback
        return function ($request) use ($stack, $pipe) {//$request http request对象 
            if ($pipe instanceof Closure) {
                return $pipe($request, $stack);
            } elseif (!is_object($pipe)) {
                //解析中间件参数
                list($name, $parameters) = $this->parsePipeString($pipe);
                $pipe = $this->getContainer()->make($name);
                $parameters = array_merge([$request, $stack], $parameters);
            } else {
                $parameters = [$request, $stack];
            }
            return $pipe->handle($request,$stack);//stack变量很关键
        };
    },
    function ($request) {    //init闭包
        $this->app->instance('request', $request);
        return $this->router->dispatch($request);
    }
);Copy

$stack = init闭包;  
$pipe = 'App\Http\Middleware\AllowOrigin::class';Copy

!is_object('App\Http\Middleware\AllowOrigin::class') = true;
$pipe = new App\Http\Middleware\AllowOrigin();
$pipe->handle($request,$stack = 'init闭包');Copy

//注意返回值是个闭包。
function(){
    $pipe = new App\Http\Middleware\AllowOrigin();
    return $pipe->handle($request,$stack = 'init闭包');
}Copy

$stack = function(){
    $pipe = new App\Http\Middleware\AllowOrigin();
    return $pipe->handle($request,$stack = 'init闭包');
};//第一次循环返回的闭包
$pipe = 'Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::class';Copy

!is_object('Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::class') = true;
$pipe = new Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode();
$pipe->handle($request,$stack); //注意这里的$stack。Copy

function(){
    $pipe = Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode();
    return $pipe->handle($request,$stack = '第一次循环返回的闭包');
}Copy

    public function then(Closure $destination)
    {
        $pipeline = array_reduce(
            array_reverse($this->pipes), $this->carry(), $this->prepareDestination($destination)
        );

        return $pipeline($this->passable); //执行array_reduce()返回的闭包。
    }Copy

//执行CheckForMaintenanceMode的handle方法：
//这里把参数值代入handle()方法
public function handle($request, Closure $next = function(){
    $pipe = new App\Http\Middleware\AllowOrigin();
    return $pipe->handle($request,$stack = 'init闭包');
})
    {
        ...  //Middleware的业务逻辑，此处省略。
        return $next($request);
    }
//很明显，下面该执行$next闭包。即该执行App\Http\Middleware\AllowOrigin()->handle()方法，
//再接着，就该执行init闭包，即$this->router->dispatch($request);Copy

$arr = ['MW_A', 'MW_B'];
$arr = array_reverse($arr);

$destination = function ($request) {
    echo 'Destination, request:  ' . $request . PHP_EOL;
};

$middleware = function ($request, $carry, $mw) {
    $request .= '.' . $mw;
    echo 'Middleware: ' . $mw . ', request: ' . $request . PHP_EOL;
    return $carry($request);
};

$res = array_reduce($arr, function ($carry, $item) {
    return function ($request) use ($carry, $item) {
        // IoC
        global $middleware;
        return $middleware($request, $carry, $item);
    };
}, $destination);

var_dump($res('RequestObject'));Copy

Middleware: MW_A, request: RequestObject.MW_A
Middleware: MW_B, request: RequestObject.MW_A.MW_B
Destination, request:  RequestObject.MW_A.MW_B
NULLCopy

// $m* 代表中间件  
$m1 = function ($request, $next) {  
    $request[] = 'm1';  
    $response = $next($request);  
    $response[] = 'm1-end';  

    return $response;  
};  

$m2 = function ($request, $next) {  
    $request[] = 'm2';  
    $response = $next($request);  
    $response[] = 'm2-end';  

    return $response;  
};  

$m3 = function ($request, $next) {  
    $request[] = 'm3';  
    return $next($request);  
};  

// $r 代表路由  
$r = function ($request) {  
    $request[] = 'route';  
    $response = $request;  
    return $response;  
};  

// 简易 Pipeline
$res = array_reduce(  
    array_reverse([$m1, $m2, $m3]),  
    function ($carry, $item) {  
        return function ($request) use ($carry, $item) {  
            return $item($request, $carry);  
        };  
    },  
    (function ($r) {  
        return function ($request) use ($r) {  
            return $r($request);  
        };  
    })($r)  
);  

$request = [];  
$response = $res($request);  
var_dump($response);Copy