Laravel5.5源码详解 -- 中间件MiddleWare分析

傷城~ 2022-06-03 10:39 155阅读 0赞

# Laravel5.5源码详解 – 中间件MiddleWare分析 #

## 启动流程 ##

首先，我们从/public/index.php开始，程序正是从这里启动的。Middleware正是在这里启动，如下

$response = $kernel->handle(
        $request = Illuminate\Http\Request::capture()
    );

注意到这个Kernel，本质上是/app/Http/Kernel.php，其handle函数在其父类Illuminate\\Foundation\\Http\\Kernel中，

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);
            }
    
            $this->app['events']->dispatch(
                new Events\RequestHandled($request, $response)
            );
    
            return $response;
        }
    
        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());
        }

这里有必要解释最后这几句：

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

这三句等价于：

$this->container = $this->app;
    $this->passable = $request;
    $this->pipes =$pipes[middleWares array];

其中中间件名（路径）是以数组的形式传递给pipes\[\]的。

这里，最关键、也是最难理解是的，是看then函数。要理解这个函数，必须理解laravel的Pipeline。下面先列出来，然后再重点逐步讲解。

先看Pipeline（Illuminate\\Routing\\Pipeline）里面的carry 和 prepareDestination

…
    use Illuminate\Pipeline\Pipeline as BasePipeline;
    
    class Pipeline extends BasePipeline { 
        protected function prepareDestination(Closure $destination) { 
            return function ($passable) use ($destination) { 
                try {
                    return $destination($passable);
                } catch (Exception $e) {
                    return $this->handleException($passable, $e);
                } catch (Throwable $e) {
                    return $this->handleException($passable, new FatalThrowableError($e));
                }
            };
        }
    
        protected function carry() { 
            return function ($stack, $pipe) { 
                return function ($passable) use ($stack, $pipe) { 
                    try {
                        $slice = parent::carry();
    
                        $callable = $slice($stack, $pipe);
    
                        return $callable($passable);
                    } catch (Exception $e) {
                        return $this->handleException($passable, $e);
                    } catch (Throwable $e) {
                        return $this->handleException($passable, new FatalThrowableError($e));
                    }
                };
            };
    }
    …
    }

上面这段代码中，其父类basePipeline（Illuminate\\Pipeline\\Pipeline）的源代码如下，其中就有大名鼎鼎的流程函数send，via， through，then

use Illuminate\Contracts\Pipeline\Pipeline as PipelineContract;
    class Pipeline implements PipelineContract { 
        protected $container; 
        protected $passable;
        protected $pipes = [];
        protected $method = 'handle';
    
        public function __construct(Container $container = null) { 
            $this->container = $container;
        }
    
        public function send($passable) { 
            $this->passable = $passable;
            return $this;
        }
    
        public function through($pipes) { 
            $this->pipes = is_array($pipes) ? $pipes : func_get_args();
            return $this;
        }
    
        public function via($method) { 
            $this->method = $method;
            return $this;
        }
    
        public function then(Closure $destination) { 
            // 所有中间件作为decorator函数，如同一系列按顺序排列的多段管道（多个中间件），
            // request必须经过这些管道，每段管道都有一个handle函数，对request进行处理。
            // 下面这一句，完成了管道的铺设工作 $pipeline
            $pipeline = array_reduce(
                array_reverse($this->pipes), $this->carry(), $this->prepareDestination($destination)
            );
    
            // 事务处理，完工后返回response
            return $pipeline($this->passable);
        }
    
        protected function prepareDestination(Closure $destination) { 
            return function ($passable) use ($destination) { 
                return $destination($passable);
            };
        }
    
        protected function carry() { 
            return function ($stack, $pipe) { 
                return function ($passable) use ($stack, $pipe) { 
                    if (is_callable($pipe)) {                    
                        return $pipe($passable, $stack);
                    } elseif (! is_object($pipe)) {
    
                        list($name, $parameters) = $this->parsePipeString($pipe);
    
                        $pipe = $this->getContainer()->make($name);
    
                        $parameters = array_merge([$passable, $stack], $parameters);
                    } else {
                        $parameters = [$passable, $stack];
                    }
                    return method_exists($pipe, $this->method)
                                    ? $pipe->{
       $this->method}(...$parameters)
                                    : $pipe(...$parameters);
                };
            };
        }
    
        protected function parsePipeString($pipe) { 
            list($name, $parameters) = array_pad(explode(':', $pipe, 2), 2, []);
            if (is_string($parameters)) {
                $parameters = explode(',', $parameters);
            }
            return [$name, $parameters];
        }
    
        protected function getContainer() { 
            if (! $this->container) {
                throw new RuntimeException('A container instance has not been passed to the Pipeline.');
            }
            return $this->container;
        }
    }

在carry()函数中，中间件被实例化，得到的这个$pipe，就是中间件对象，

$pipe = $this->getContainer()->make($name);

所以，在carry()函数最后的return中，

$pipe->{$this->method}(...$parameters)

实际上相当于调用了中间件的handle函数，来处理我们的目标函数（标的函数或对象）。标的函数（也就是要经过中间件的那些目标函数，比如Login会经过Auth中间件检查授权，那么Login就是标的函数）。

现在回来看，在then中传入进来的都是什么？

$destination是个闭包，如下

Closure { #23 ▼
      class: "Illuminate\Foundation\Http\Kernel"
      this: Kernel { #29 …}
      parameters: { ▼
        $request: { } } file: "D:\wamp64\www\laravel\larablog\vendor\laravel\framework\src\Illuminate\Foundation\Http\Kernel.php" line: "173 to 177" }

也就是下面这个闭包，他负责把request的实例绑定到app的intannces数组中去。

return function ($request) {
                $this->app->instance('request', $request);
                return $this->router->dispatch($request);
            };

$this->pipes就是那些中间件，前面提到过的，当然后面还有更多，不再一一列举。

array:6 [▼
      0 => "Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode"
      1 => "Illuminate\Foundation\Http\Middleware\ValidatePostSize"
      2 => "App\Http\Middleware\TrimStrings"
      3 => "Illuminate\Foundation\Http\Middleware\ConvertEmptyStringsToNull"
      4 => "App\Http\Middleware\TrustProxies"
      5 => "Barryvdh\Debugbar\Middleware\InjectDebugbar"
    ]

函数then()之中最后return回去的那个Pipeline，是下面这个东东，

Closure { #166 ▼
      class: "Illuminate\Routing\Pipeline"
      this: Pipeline { #34 …}
      parameters: { ▼
        $passable: { } } use: { ▼ $stack: Closure { #171 …}
        $pipe: "Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode" } file: "D:\wamp64\www\laravel\larablog\vendor\laravel\framework\src\Illuminate\Routing\Pipeline.php" line: "47 to 59" }

这个闭包也就是下面这段代码

return function ($passable) use ($stack, $pipe) { 
                    try {
                        $slice = parent::carry();
                        $callable = $slice($stack, $pipe);
                        return $callable($passable);
                    } catch (Exception $e) {
                        return $this->handleException($passable, $e);
                    } catch (Throwable $e) {
                        return $this->handleException($passable, new FatalThrowableError($e));
                    }
                };

$this->passable($passable)又是什么呢？也是一个闭包，结合前面提到的sendRequestThroughRouter和下面的代码，

public function send($passable)
    {
        $this->passable = $passable;
        return $this;
    }

可以看到，这个$passable就是我们要发送的request。

另外，我们注意到，那个through什么也没干，和前面那个send一样，就是完成一次赋值的操作（$pipes通常都是不为空的数组，在这种情况下，最后执行的结果，就相当于$this->pipes = $pipes），

public function through($pipes)
    {
        $this->pipes = is_array($pipes) ? $pipes : func_get_args();
        return $this;
    }

加入以下调试代码，可以看到输出结果，

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

整个过程传进来的参数如下  
`$destination;`

Closure { #23 ▼
      class: "Illuminate\Foundation\Http\Kernel"
      this: Kernel { #29 …}
      parameters: { ▶}
      file: "D:\wamp64\www\laravel\larablog\vendor\laravel\framework\src\Illuminate\Foundation\Http\Kernel.php"
      line: "173 to 177"
    }

`$this->pipes;`

array:6 [▼
    
      0 => "Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode"
      1 => "Illuminate\Foundation\Http\Middleware\ValidatePostSize"
      2 => "App\Http\Middleware\TrimStrings"
      3 => "Illuminate\Foundation\Http\Middleware\ConvertEmptyStringsToNull"
      4 => "App\Http\Middleware\TrustProxies"
      5 => "Barryvdh\Debugbar\Middleware\InjectDebugbar"
    ]

`最后得到的$pipeline;`

Closure { #166 ▼
      class: "Illuminate\Routing\Pipeline"
      this: Pipeline { #34 …}
      parameters: { ▶}
      use: { ▶}
      file: "D:\wamp64\www\laravel\larablog\vendor\laravel\framework\src\Illuminate\Routing\Pipeline.php"
      line: "47 to 59"
    }

`$destination;`

Closure { #289 ▼
      class: "Illuminate\Routing\Router"
      this: Router { #25 …}
      parameters: { ▶}
      use: { ▶}
      file: "D:\wamp64\www\laravel\larablog\vendor\laravel\framework\src\Illuminate\Routing\Router.php"
      line: "656 to 660"
    }

`$this->pipes;`

array:7 [▼
      0 => "App\Http\Middleware\EncryptCookies"
      1 => "Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse"
      2 => "Illuminate\Session\Middleware\StartSession"
      3 => "Illuminate\View\Middleware\ShareErrorsFromSession"
      4 => "App\Http\Middleware\VerifyCsrfToken"
      5 => "Illuminate\Auth\Middleware\Authenticate:admin"
      6 => "Illuminate\Routing\Middleware\SubstituteBindings"
    ]

`最后得到的$pipeline;`

Closure { #319 ▼
      class: "Illuminate\Routing\Pipeline"
      this: Pipeline { #284 …}
      parameters: { ▶}
      use: { ▶}
      file: "D:\wamp64\www\laravel\larablog\vendor\laravel\framework\src\Illuminate\Routing\Pipeline.php"
      line: "47 to 59"
    }

可以看到，这些middleWare分两波传进来。

## array\_reduce（） ##

array\_reduce在这里起到了最重要的作用，从原理上来说，  
假设

$pipes = [0 => ‘middleWare1’, 1 => ‘middleWare2’, 2 => ‘middleWare3’];

array\_reverse(pipes)之后，

$pipes = [0 => ‘middleWare3’, 1 => ‘middleWare2’, 2 => ‘middleWare1’];

那么，下面这个array\_reduce函数中

$pipeline = array_reduce(
        array_reverse($this->pipes), $this->carry(), $this->prepareDestination($destination)
    );

`prepareDestination(Closure $destination)`相当于执行`$destination($passable);`并再次形成一个闭包。

还记得`$destionation`是什么吗？为方便，我再次贴出来，就是这段代码，

return function ($request) {
            $this->app->instance('request', $request);
            return $this->router->dispatch($request);
        };

这里没有任何奇特的地方，就是必须不断构造闭包，否则array\_reduce他老人家不认识（你不能把普通函数当参数传进去）。Laravel的这种写法确实简洁，但不好理解。另外说一句，在`$destination`已经是闭包的前提下，这里`prepareDestination`再来构造一次就有些多余；但这一段是必须的，万一你什么地方传进来的不是闭包呢？  
当然，我们可以停下来看一眼这个carry是怎样进一步构造闭包的，我把子类函数和父类函数的代码分别贴上来。特别注意的是，我特意加上了两个dump来辅助调试。

protected function carry()
    {
        return function ($stack, $pipe) {
            return function ($passable) use ($stack, $pipe) {
                try {
                    dump($stack);
                    dump($pipe);
                    $slice = parent::carry();
                    $callable = $slice($stack, $pipe);
                    return $callable($passable);
                } catch (Exception $e) {
                    return $this->handleException($passable, $e);
                } catch (Throwable $e) {
                    return $this->handleException($passable, new FatalThrowableError($e));
                }
            };
        };
    }
    
    protected function carry()
    {
        return function ($stack, $pipe) {
            return function ($passable) use ($stack, $pipe) {
                if (is_callable($pipe)) {
                    return $pipe($passable, $stack);
                } elseif (! is_object($pipe)) {
                    list($name, $parameters) = $this->parsePipeString($pipe);
                    $pipe = $this->getContainer()->make($name);
                    $parameters = array_merge([$passable, $stack], $parameters);
                } else {                    
                    $parameters = [$passable, $stack];
                }
                return method_exists($pipe, $this->method)
                                ? $pipe->{$this->method}(...$parameters)
                                : $pipe(...$parameters);
            };
        };
    }

输出的代码如下面所示，很长，注意到两点，第一，最先出现的闭包use的是下面要出现的闭包。第二，pipes出现的顺序，和在then中参数传送进来的顺序是完全一样的，第一个就是

`"Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode"`。

Closure { #170 ▼
      class:"Illuminate\Routing\Pipeline"
      this: Pipeline { #34 …}
      parameters: { ▼
        $passable: { } } use: { ▼ $stack: Closure { #169 …}
        $pipe:"Illuminate\Foundation\Http\Middleware\ValidatePostSize" } file:"D:\wamp64\www\laravel\larablog\vendor\laravel\framework\src\Illuminate\Routing\Pipeline.php" line: "47 to 61" } "Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode" Closure { #169 ▼ class:"Illuminate\Routing\Pipeline" this: Pipeline { #34 …} parameters: { ▶} use: { ▼ $stack: Closure { #168 …}
        $pipe:"App\Http\Middleware\TrimStrings" } file: "D:\wamp64\www\laravel\larablog\vendor\laravel\framework\src\Illuminate\Routing\Pipeline.php" line: "47 to 61" } "Illuminate\Foundation\Http\Middleware\ValidatePostSize"

下面都是一样的，原理上就是这个样子，后面省略不少，不然打出来太长了

Closure { #168 ▼ use: {▼ $stack: Closure { #167 …}
    
    
    Closure { #167 ▼ use: {▼ $stack: Closure { #166 …}
    
    
    Closure { #166 ▼ use: {▼ $stack: Closure { #119 …} 
    
    。。。。。。

## array\_reverse($this->pipes) ##

关于array\_reverse($this->pipes)的原因，我写了个可以直接运行的例程，参考下面的代码。在此之前，如果你想知道些decorator的模型，可以参考这篇文章：[Decorator函数][Decorator]

<?php interface IMiddleware { public function handle(); } //definition of middle ware classes class CheckForMaintenanceMode implements IMiddleware { private $middleware; public function __construct(IMiddleware $middleware) { $this->middleware = $middleware; } public function handle() { //$this->middleware->handle(); echo 'CheckForMaintenanceMode' . "<br>"; echo "<hr>"; $this->middleware->handle(); } } class ValidatePostSize implements IMiddleware { private $middleware; public function __construct(IMiddleware $middleware) { $this->middleware = $middleware; } public function handle() { //$this->middleware->handle(); echo 'ValidatePostSize' . "<br>"; echo "<hr>"; $this->middleware->handle(); } } class TrimStrings implements IMiddleware { private $middleware; public function __construct(IMiddleware $middleware) { $this->middleware = $middleware; } public function handle() { //$this->middleware->handle(); echo 'TrimStrings' . "<br>"; echo "<hr>"; $this->middleware->handle(); } } //define a passable request interface IPassable extends IMiddleware { public function getRequest(); } class Request implements IPassable { public function handle() { echo 'Handle request from the client, and it has passed through all the 3 middlewares.'. "<br>"; echo "<hr>"; } public function getRequest() { return $this; } } class Client { protected $request; protected $response; public function __construct() { $this->request = new Request(); $this->response = $this->wrapDecorator($this->request); } public function wrapDecorator(IMiddleware $decorator) { $decorator = new TrimStrings($decorator); //2 = func(1) $decorator = new ValidatePostSize($decorator); //3= func(2) $response = new CheckForMaintenanceMode($decorator); //4= func(3) return $response; } /** * @return \MyRightCapital\Development\DecoratorPattern\IMiddleware */ public function getResponse() { return $this->response->handle(); } } $client = new Client; $client->getResponse();

运行上面这段代码(或者，在命令窗口输入 php index.php > index.html，然后用浏览器打开index.html)，你会得到下面的结果，

CheckForMaintenanceMode
    ValidatePostSize
    TrimStrings
    Handle requestfrom the client, and it has passed through all the 3 middlewares.

如果你把那些echo语句调到$this->middleware->handle()这句的前面，你会得到一个相反的输出顺序，如下，

Handle requestfrom the client, and it has passed through all the 3 middlewares.
    TrimStrings
    ValidatePostSize
    CheckForMaintenanceMode

这些反序一般并不是我们所希望的，因为在laravel中，大多数情况下是希望middleWare 能在response被handle之前，做一些具体的把关工作（相当于这里的echo），所以，这里echo语句都应该在handle语句之前。因此，也不难理解，为什么在laravel的then逻辑中，array\_reduce的第一个参数是array\_reverse($this->pipes)！

[Decorator]: http://blog.csdn.net/tanmx219/article/details/78806787