说明：本文主要学习Laravel的Middleware的源码设计思想，并将学习心得分享出来，希望对别人有所帮助。Laravel学习笔记之Decorator Pattern已经聊过Laravel使用了Decorator Pattern来设计Middleware，看Laravel源码发现其巧妙用了Closure和PHP的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、array_reduce、call_user_func和call_user_func_array
看Laravel源码之前，先看下这几个PHP内置函数的使用。首先array_reverse()函数比较简单，倒置数组，看测试代码：
$pipes = [
'Pipe1',
'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结果值作为下一次回调的初始值，最后返回最终迭代的值：
/**
* @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);
// 最后输出 (((((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$routeMiddleware[ ]这些中间件的后置操作得到准备就绪的Response，然后通过send()发送给客户端。
这个过程有点像汽车工厂的生产一样，Pipeline是传送带，起初Request可能就是个汽车空壳子，经过传送带旁边的一个个机械手middleware@before的过滤和操作(如检查零件刚度是不是合格，壳子尺寸是不是符合要求，给壳子喷个漆或抹个油啥的)，然后进入中央控制区加个发动机(Controller@action ，或Closure)，然后又继续经过检查和附加操作middleware@after(如添加个挡风镜啥的)，然后通过门外等着的火车直接运送到消费者手里send()。在每一步装配过程中，都需要Service来支持，Service是通过Container来解析{make()}提供的，并且Service是通过ServiceProvider注册绑定{bind(),singleton(),instance()}到Container中的。
看下Pipeline的send()和through()源码：
public function send($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,
];先获得第一个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);并最后用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;
$pipes = [
VerifyCsrfToken::class,
ShareErrorsFromSession::class,
StartSession::class,
AddQueuedCookiesToResponse::class,
CheckForMaintenanceMode::class,
];2.执行第一次getSlice()后的结果作为新的$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; // 第一个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。
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