说明：本文主要学习Laravel的学习笔Middleware的源码设计思想，并将学习心得分享出来，记之解析希望对别人有所帮助。源码Laravel学习笔记之Decorator Pattern已经聊过Laravel使用了Decorator Pattern来设计Middleware，学习笔看Laravel源码发现其巧妙用了Closure和PHP的记之解析一些数组函数来设计Middleware。
开发环境：Laravel5.3 + PHP7 + OS X 10.11
PHP内置函数array_reverse、源码array_reduce、学习笔call_user_func和call_user_func_array
看Laravel源码之前，记之解析先看下这几个PHP内置函数的源码使用。首先array_reverse()函数比较简单，学习笔倒置数组，记之解析看测试代码：
$pipes = [ Pipe1,源码 Pipe2, Pipe3, Pipe4, Pipe5, Pipe6, ]; $pipes = array_reverse($pipes); var_dump($pipes); // output array(6) { [0] => string(5) "Pipe6" [1] => string(5) "Pipe5" [2] => string(5) "Pipe4" [3] => string(5) "Pipe3" [4] => string(5) "Pipe2" [5] => string(5) "Pipe1" } array_reduce内置函数主要是用回调函数去迭代数组中每一个值，并且每一次回调得到的学习笔结果值作为下一次回调的初始值，***返回最终迭代的记之解析值：
/** * @link http://php.net/manual/zh/function.array-reduce.php * @param int $v * @param int $w * * @return int */ function rsum($v, $w) { $v += $w; return $v; } $a = [1, 2, 3, 4, 5]; // 10为初始值 $b = array_reduce($a, "rsum", 10); // ***输出 (((((10 + 1) + 2) + 3) + 4) + 5) = 25 echo $b . PHP_EOL; call_user_func()是执行回调函数，并可输入参数作为回调函数的源码参数，看测试代码：
class TestCallUserFunc { public function index($request) { echo $request . PHP_EOL; } } /** * @param $test */ function testCallUserFunc($test) { echo $test . PHP_EOL; } // [$class, $method] call_user_func([TestCallUserFunc, index], pipes); // 输出pipes // Closure call_user_func(function ($passable) { echo $passable . PHP_EOL; }, pipes); // 输出pipes // function call_user_func(testCallUserFunc , pipes); // 输出pipes call_user_func_array与call_user_func基本一样，只不过传入的参数是数组：
class TestCallUserFuncArray { public function index($request) { echo $request . PHP_EOL; } } /** * @param $test */ function testCallUserFuncArray($test) { echo $test . PHP_EOL; } // [$class, $method] call_user_func_array([TestCallUserFuncArray, index], [pipes]); // 输出pipes // Closure call_user_func_array(function ($passable) { echo $passable . PHP_EOL; }, [pipes]); // 输出pipes // function call_user_func_array(testCallUserFuncArray , [pipes]); // 输出pipes Middleware源码解析
了解了几个PHP内置函数后再去看下Middleware源码就比较简单了。Laravel学习笔记之IoC Container实例化源码解析已经聊过Application的实例化，得到index.php中的$app变量，即\Illuminate\Foundation\Application的香港云服务器实例化对象。然后继续看下index.php的源码：
/** * @var \App\Http\Kernel $kernel */ $kernel = $app->make(Illuminate\Contracts\Http\Kernel::class); $response = $kernel->handle( $request = Illuminate\Http\Request::capture() ); $response->send(); $kernel->terminate($request, $response); 首先从容器中解析出Kernel对象，对于\App\Http\Kernel对象的依赖:\Illuminate\Foundation\Application和\Illuminate\Routing\Router，容器会自动解析。看下Kernel的构造函数：
/** * Create a new HTTP kernel instance. * * @param \Illuminate\Contracts\Foundation\Application $app * @param \Illuminate\Routing\Router $router */ public function __construct(Application $app, Router $router) { $this->app = $app; $this->router = $router; foreach ($this->middlewareGroups as $key => $middleware) { $router->middlewareGroup($key, $middleware); } foreach ($this->routeMiddleware as $key => $middleware) { $router->middleware($key, $middleware); } } // \Illuminate\Routing\Router内的方法 public function middlewareGroup($name, array $middleware) { $this->middlewareGroups[$name] = $middleware; return $this; } public function middleware($name, $class) { $this->middleware[$name] = $class; return $this; } 构造函数初始化了几个中间件数组，$middleware[ ], $middlewareGroups[ ]和$routeMiddleware[ ]，Laravel5.0的时候记得中间件数组还没有分的这么细。然后就是Request的实例化：
$request = Illuminate\Http\Request::capture() 这个过程以后再聊吧，不管咋样，得到了Illuminate\Http\Request对象，然后传入Kernel中：
/** * Handle an incoming HTTP request. * * @param \Illuminate\Http\Request $request * @return \Illuminate\Http\Response */ public function handle($request) { try { $request->enableHttpMethodParameterOverride(); $response = $this->sendRequestThroughRouter($request); } catch (Exception $e) { $this->reportException($e); $response = $this->renderException($request, $e); } catch (Throwable $e) { $this->reportException($e = new FatalThrowableError($e)); $response = $this->renderException($request, $e); } $this->app[events]->fire(kernel.handled, [$request, $response]); return $response; } 主要是sendRequestThroughRouter($request)函数执行了转换操作：把\Illuminate\Http\Request对象转换成了\Illuminate\Http\Response，然后通过Kernel的send()方法发送给客户端。同时，顺便触发了kernel.handled内核已处理请求事件。OK，重点关注下sendRequestThroughRouter($request)方法：
/** * Send the given request through the middleware / router. * * @param \Illuminate\Http\Request $request * @return \Illuminate\Http\Response */ protected function sendRequestThroughRouter($request) { $this->app->instance(request, $request); Facade::clearResolvedInstance(request); /* 依次执行$bootstrappers中每一个bootstrapper的bootstrap()函数,做了几件准备事情: 1. 环境检测 2. 配置加载 3. 日志配置 4. 异常处理 5. 注册Facades 6. 注册Providers 7. 启动服务 protected $bootstrappers = [ Illuminate\Foundation\Bootstrap\DetectEnvironment, Illuminate\Foundation\Bootstrap\LoadConfiguration, Illuminate\Foundation\Bootstrap\ConfigureLogging, Illuminate\Foundation\Bootstrap\HandleExceptions, Illuminate\Foundation\Bootstrap\RegisterFacades, Illuminate\Foundation\Bootstrap\RegisterProviders, Illuminate\Foundation\Bootstrap\BootProviders, ];*/ $this->bootstrap(); return (new Pipeline($this->app)) ->send($request) ->through($this->app->shouldSkipMiddleware() ? [] : $this->middleware) ->then($this->dispatchToRouter()); } $this->bootstrap()主要是做了程序初始化工作，以后再聊具体细节。然后是Pipeline来传输Request，Laravel中把Pipeline管道单独拿出来作为一个service(可看Illuminate/Pipeline文件夹)，说明Pipeline做的亿华云事情还是很重要的：主要就是作为Request的传输管道，依次通过$middlewares[ ], 或middlewareGroups[ ], 或$routeMiddleware[ ]这些中间件的前置操作，和控制器的某个action或者直接闭包处理得到Response，然后又带着Reponse依次通过$middlewares[ ], 或middlewareGroups[ ], 或$routeMiddleware[ ]这些中间件的后置操作得到准备就绪的Response，然后通过send()发送给客户端。
这个过程有点像汽车工厂的生产一样，Pipeline是传送带，起初Request可能就是个汽车空壳子，经过传送带旁边的一个个机械手middleware@before的过滤和操作(如检查零件刚度是不是合格，壳子尺寸是不是符合要求，给壳子喷个漆或抹个油啥的)，然后进入中央控制区加个发动机(Controller@action，或Closure)，然后又继续经过检查和附加操作middleware@after(如添加个挡风镜啥的)，服务器托管然后通过门外等着的火车直接运送到消费者手里send()。在每一步装配过程中，都需要Service来支持，Service是通过Container来解析{ make()}提供的，并且Service是通过ServiceProvider注册绑定{ bind(),singleton(),instance()}到Container中的。
看下Pipeline的send()和through()源码：
public function send($passable) { $this->passable = $passable; return $this; } public function through($pipes) { $this->pipes = is_array($pipes) ? $pipes : func_get_args(); return $this; } send()传送的对象是Request，through()所要通过的对象是$middleware[ ]，OK，再看下dispatchToRouter()的源码直接返回一个Closure：
protected function dispatchToRouter() { return function ($request) { $this->app->instance(request, $request); return $this->router->dispatch($request); }; } 然后重点看下then()函数源码：
public function then(Closure $destination) { $firstSlice = $this->getInitialSlice($destination); $pipes = array_reverse($this->pipes); // $this->passable = Request对象 return call_user_func( array_reduce($pipes, $this->getSlice(), $firstSlice), $this->passable ); } protected function getInitialSlice(Closure $destination) { return function ($passable) use ($destination) { return call_user_func($destination, $passable); }; } 这里假设$middlewares为(尽管源码中$middlewares只有一个CheckForMaintenanceMode::class)：
$middlewares = [ CheckForMaintenanceMode::class, AddQueuedCookiesToResponse::class, StartSession::class, ShareErrorsFromSession::class, VerifyCsrfToken::class, ]; 先获得***个slice(这里作者是比作洋葱，一层层的穿过，从一侧穿过到另一侧，比喻倒也形象)并作为array_reduce()的初始值，就像上文中array_reduce()测试例子中的10这个初始值，这个初始值现在是个闭包：
$destination = function ($request) { $this->app->instance(request, $request); return $this->router->dispatch($request); }; $firstSlice = function ($passable) use ($destination) { return call_user_func($destination, $passable); }; OK,然后要对$middlewares[ ]进行翻转，为啥要翻转呢?
看过这篇Laravel学习笔记之Decorator Pattern文章就会发现，在Client类利用Decorator Pattern进行依次装饰的时候，是按照$middlewares[ ]数组中值倒着new的：
public function wrapDecorator(IMiddleware $decorator) { $decorator = new VerifyCsrfToken($decorator); $decorator = new ShareErrorsFromSession($decorator); $decorator = new StartSession($decorator); $decorator = new AddQueuedCookiesToResponse($decorator); $response = new CheckForMaintenanceMode($decorator); return $response; } 这样才能得到一个符合$middlewares[ ]顺序的$response对象：
$response = new CheckForMaintenanceMode( new AddQueuedCookiesToResponse( new StartSession( new ShareErrorsFromSession( new VerifyCsrfToken( new Request() ) ) ) ) ); 看下array_reduce()中的迭代回调函数getSlice(){ 这个迭代回调函数比作剥洋葱时获取每一层洋葱slice，初始值是$firstSlice}：
protected function getSlice() { return function ($stack, $pipe) { return function ($passable) use ($stack, $pipe) { if ($pipe instanceof Closure) { return call_user_func($pipe, $passable, $stack); } elseif (! is_object($pipe)) { list($name, $parameters) = $this->parsePipeString($pipe); $pipe = $this->container->make($name); $parameters = array_merge([$passable, $stack], $parameters); } else{ $parameters = [$passable, $stack]; } return call_user_func_array([$pipe, $this->method], $parameters); }; }; } 返回的是个闭包，仔细看下第二层闭包里的逻辑，这里$middlewares[ ]传入的是每一个中间件的名字，然后通过容器解析出每一个中间件对象：
$pipe = $this->container->make($name); 并***用call_user_func_array([$class, $method], array $parameters)来调用这个$class里的$method方法，参数是$parameters。
Demo
接下来写个demo看下整个流程。先简化下getSlice()函数，这里就默认$pipe传入的是类名称(整个demo中所有class都在同一个文件内)：
// PipelineTest.php // Get the slice in every step. function getSlice() { return function ($stack, $pipe) { return function ($passable) use ($stack, $pipe) { /** * @var Middleware $pipe */ return call_user_func_array([$pipe, handle], [$passable, $stack]); }; }; } 再把$middlewares[ ]中五个中间件类写上，对于前置操作和后置操作做个简化，直接echo字符串：
// PipelineTest.php <?php interface Middleware { public static function handle($request, Closure $closure); } class CheckForMaintenanceMode implements Middleware { public static function handle($request, Closure $next) { echo $request . : Check if the application is in the maintenance status. . PHP_EOL; $next($request); } } class AddQueuedCookiesToResponse implements Middleware { public static function handle($request, Closure $next) { $next($request); echo $request . : Add queued cookies to the response. . PHP_EOL; } } class StartSession implements Middleware { public static function handle($request, Closure $next) { echo $request . : Start session of this request. . PHP_EOL; $next($request); echo $request . : Close session of this response. . PHP_EOL; } } class ShareErrorsFromSession implements Middleware { public static function handle($request, Closure $next) { $next($request); echo $request . : Share the errors variable from response to the views. . PHP_EOL; } } class VerifyCsrfToken implements Middleware { public static function handle($request, Closure $next) { echo $request . : Verify csrf token when post request. . PHP_EOL; $next($request); } } 给上完整的一个Pipeline类，这里的Pipeline对Laravel中的Pipeline做了稍微简化，只选了几个重要的函数：
// PipelineTest.php class Pipeline { /** * @var array */ protected $middlewares = []; /** * @var int */ protected $request; // Get the initial slice function getInitialSlice(Closure $destination) { return function ($passable) use ($destination) { return call_user_func($destination, $passable); }; } // Get the slice in every step. function getSlice() { return function ($stack, $pipe) { return function ($passable) use ($stack, $pipe) { /** * @var Middleware $pipe */ return call_user_func_array([$pipe, handle], [$passable, $stack]); }; }; } // When process the Closure, send it as parameters. Here, input an int number. function send(int $request) { $this->request = $request; return $this; } // Get the middlewares array. function through(array $middlewares) { $this->middlewares = $middlewares; return $this; } // Run the Filters. function then(Closure $destination) { $firstSlice = $this->getInitialSlice($destination); $pipes = array_reverse($this->middlewares); $run = array_reduce($pipes, $this->getSlice(), $firstSlice); return call_user_func($run, $this->request); } } OK,现在开始传入Request,这里简化为一个整数而不是Request对象了：
// PipelineTest.php /** * @return \Closure */ function dispatchToRouter() { return function ($request) { echo $request . : Send Request to the Kernel, and Return Response. . PHP_EOL; }; } $request = 10; $middlewares = [ CheckForMaintenanceMode::class, AddQueuedCookiesToResponse::class, StartSession::class, ShareErrorsFromSession::class, VerifyCsrfToken::class, ]; (new Pipeline())->send($request)->through($middlewares)->then(dispatchToRouter()); 执行php PipelineTest.php得到Response：
10: Check if the application is in the maintenance status. 10: Start session of this request. 10: Verify csrf token when post request. 10: Send Request to the Kernel, and Return Response. 10: Share the errors variable from response to the views. 10: Close session of this response. 10: Add queued cookies to the response. 一步一步分析下执行过程：
1.首先获取$firstSlice
$destination = function ($request) { echo $request . : Send Request to the Kernel, and Return Response. . PHP_EOL; }; $firstSlice = function ($passable) use ($destination) { return call_user_func($destination, $passable); }; 这时经过初始化后：
$this->request = 10; $pipes = [ VerifyCsrfToken::class, ShareErrorsFromSession::class, StartSession::class, AddQueuedCookiesToResponse::class, CheckForMaintenanceMode::class, ]; 2.执行***次getSlice()后的结果作为新的$stack，其值为：
$stack = $firstSlice; $pipe = VerifyCsrfToken::class; $stack_1 = function ($passable) use ($stack, $pipe) { /** * @var Middleware $pipe */ return call_user_func_array([$pipe, handle], [$passable, $stack]); }; 3.执行第二次getSlice()后的结果作为新的$stack，其值为：
$stack = $stack_1; $pipe = ShareErrorsFromSession::class; $stack_2 = function ($passable) use ($stack, $pipe) { /** * @var Middleware $pipe */ return call_user_func_array([$pipe, handle], [$passable, $stack]); }; 4.执行第三次getSlice()后的结果作为新的$stack，其值为：
$stack = $stack_2; $pipe = StartSession::class; $stack_3 = function ($passable) use ($stack, $pipe) { /** * @var Middleware $pipe */ return call_user_func_array([$pipe, handle], [$passable, $stack]); }; 5.执行第四次getSlice()后的结果作为新的$stack，其值为：
$stack = $stack_3; $pipe = AddQueuedCookiesToResponse::class; $stack_4 = function ($passable) use ($stack, $pipe) { /** * @var Middleware $pipe */ return call_user_func_array([$pipe, handle], [$passable, $stack]); }; 6.执行第五次getSlice()后的结果作为新的$stack，其值为：
$stack = $stack_4; $pipe = CheckForMaintenanceMode::class; $stack_5 = function ($passable) use ($stack, $pipe) { /** * @var Middleware $pipe */ return call_user_func_array([$pipe, handle], [$passable, $stack]); }; 这时，$stack_5也就是then()里的$run,然后执行call_user_func($run, 10),看执行过程:
1.$stack_5(10) = CheckForMaintenanceMode::handle(10, $stack_4)
echo 10: Check if the application is in the maintenance status. . PHP_EOL; stack_4(10); 2.$stack_4(10) = AddQueuedCookiesToResponse::handle(10, $stack_3)
$stack_3(10); echo 10: Add queued cookies to the response. . PHP_EOL; 3.$stack_3(10) = StartSession::handle(10, $stack_2)
echo 10: Start session of this request. . PHP_EOL; $stack_2(10); echo 10: Close session of this response. . PHP_EOL; 4.$stack_2(10) = ShareErrorsFromSession::handle(10, $stack_1)
$stack_1(10); echo 10: Share the errors variable from response to the views. . PHP_EOL; 5.$stack_1(10) = VerifyCsrfToken::handle(10, $firstSlice)
echo 10: Verify csrf token when post request. . PHP_EOL; $firstSlice(10); 6.$firstSlice(10) =
$firstSlice(10) = call_user_func($destination, 10) = echo 10: Send Request to the Kernel, and Return Response. . PHP_EOL; OK,再把上面执行顺序整理一下：
1. echo 10: Check if the application is in the maintenance status. . PHP_EOL; // ***个step 3_1. echo 10: Start session of this request. . PHP_EOL; // 第三个step 5. echo 10: Verify csrf token when post request. . PHP_EOL; // 第五个step 6.echo 10: Send Request to the Kernel, and Return Response. . PHP_EOL; //第六个step 4. echo 10: Share the errors variable from response to the views. . PHP_EOL; // 第四个step 3_2. echo 10: Close session of this response. . PHP_EOL; // 第三个step 2. echo 10: Add queued cookies to the response. . PHP_EOL; // 第二个step 经过上面的一步步分析，就能很清楚Laravel源码中Middleware的执行步骤了。再复杂的步骤只要一步步拆解，就很清晰每一步的逻辑，然后把步骤组装，就能知道全貌了。
总结：本文主要学习了Laravel的Middleware的源码，学习完后就知道没有什么神秘之处，只需要动手一步步拆解就行。后面再学习下Container的源码，到时见。