05. Pipeline 和 Middleware

[xiaohuilam]

Laravel 的管道机制，是其中间件 (middleware) 得以被序列执行的基础

管道机制

在开始之前我们先帖一段管理的应用代码，位于 02. HTTP Kernel Handle解析

laravel/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php

Lines 148 to 151 in d081c91

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

语义化得出的分析为
携带 send 请求对象，经过中间件的处理，然后进入路由。

代码解析

1. send 携带方法
   

   laravel/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php

   Lines 53 to 64 in d081c91

   	/**
   	* Set the object being sent through the pipeline.
   	*
   	* @param mixed $passable
   	* @return $this
   	*/
   	public function send($passable)
   	{
   	$this->passable = $passable;
   	return $this;
   	}

   
   好像没啥出奇的，就是传入并储存一个对象，返回 $this

2. through 经过方法
   

   laravel/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php

   Lines 66 to 77 in d081c91

   	/**
   	* Set the array of pipes.
   	*
   	* @param array|mixed $pipes
   	* @return $this
   	*/
   	public function through($pipes)
   	{
   	$this->pipes = is_array($pipes) ? $pipes : func_get_args();
   	return $this;
   	}

   
   好像也没啥关键的实现，传入“被管道”的集合，返回 $this

3. then 异步方法
   

   laravel/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php

   Lines 92 to 105 in d081c91

   	/**
   	* Run the pipeline with a final destination callback.
   	*
   	* @param \Closure $destination
   	* @return mixed
   	*/
   	public function then(Closure $destination)
   	{
   	$pipeline = array_reduce(
   	array_reverse($this->pipes), $this->carry(), $this->prepareDestination($destination)
   	);
   	return $pipeline($this->passable);
   	}

之前的都只是做登记一下就GG的作用，这个 then 才是根本大法，
使用 array_reduce 处理得到 $pipeline。这个 array_reduce 是何方神圣呢？我们查文档得到:
Iteratively reduce the array to a single value using a callback function（中文意思就是 使用回调函数，迭代地将数组减少为单个值）。

但在走到 array_reduce 之前，调用了 carry 方法 (在 5.3 及以前版本，carry 方法其实为 getSlice 方法，而过程几乎一样 来源)，其内部逻辑为：

laravel/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php

Lines 120 to 159 in d081c91

	/**
	* Get a Closure that represents a slice of the application onion.
	*
	* @return \Closure
	*/
	protected function carry()
	{
	return function ($stack, $pipe) {
	return function ($passable) use ($stack, $pipe) {
	if (is_callable($pipe)) {
	// If the pipe is an instance of a Closure, we will just call it directly but
	// otherwise we'll resolve the pipes out of the container and call it with
	// the appropriate method and arguments, returning the results back out.
	return $pipe($passable, $stack);
	} elseif (! is_object($pipe)) {
	list($name, $parameters) = $this->parsePipeString($pipe);
	// If the pipe is a string we will parse the string and resolve the class out
	// of the dependency injection container. We can then build a callable and
	// execute the pipe function giving in the parameters that are required.
	$pipe = $this->getContainer()->make($name);
	$parameters = array_merge([$passable, $stack], $parameters);
	} else {
	// If the pipe is already an object we'll just make a callable and pass it to
	// the pipe as-is. There is no need to do any extra parsing and formatting
	// since the object we're given was already a fully instantiated object.
	$parameters = [$passable, $stack];
	}
	$response = method_exists($pipe, $this->method)
	? $pipe->{$this->method}(...$parameters)
	: $pipe(...$parameters);
	return $response instanceof Responsable
	? $response->toResponse($this->container->make(Request::class))
	: $response;
	};
	};
	}

Laravel 的这个 carry 方法返回的是一个闭包，执行返回的闭包所返回的又是一个闭包，只不过前一个返回是 array_reduce 批量执行时拿到的，后面是处理原始对象（请求）时，处理中间件时候拿到的。

• 闭包（前一个）的第一个参数 $stack 为 null 或者闭包对象，第二个参数 $pipe 为从1开始的调用顺序。
• 闭包（前一个）的返回值，为管道中被执行的逻辑，也就是 middleware 的 handle。

具体 handle 代码我们举一个例子:

laravel/vendor/laravel/framework/src/Illuminate/Foundation/Http/Middleware/VerifyCsrfToken.php

Lines 58 to 83 in d081c91

	/**
	* Handle an incoming request.
	*
	* @param \Illuminate\Http\Request $request
	* @param \Closure $next
	* @return mixed
	*
	* @throws \Illuminate\Session\TokenMismatchException
	*/
	public function handle($request, Closure $next)
	{
	if (
	$this->isReading($request) ||
	$this->runningUnitTests() ||
	$this->inExceptArray($request) ||
	$this->tokensMatch($request)
	) {
	return tap($next($request), function ($response) use ($request) {
	if ($this->addHttpCookie) {
	$this->addCookieToResponse($request, $response);
	}
	});
	}
	throw new TokenMismatchException;
	}

其中的 $next($request) 表示执行下一个中间件, $next 指的就是下面这个闭包

laravel/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php

Lines 128 to 157 in d081c91

	return function ($passable) use ($stack, $pipe) {
	if (is_callable($pipe)) {
	// If the pipe is an instance of a Closure, we will just call it directly but
	// otherwise we'll resolve the pipes out of the container and call it with
	// the appropriate method and arguments, returning the results back out.
	return $pipe($passable, $stack);
	} elseif (! is_object($pipe)) {
	list($name, $parameters) = $this->parsePipeString($pipe);
	// If the pipe is a string we will parse the string and resolve the class out
	// of the dependency injection container. We can then build a callable and
	// execute the pipe function giving in the parameters that are required.
	$pipe = $this->getContainer()->make($name);
	$parameters = array_merge([$passable, $stack], $parameters);
	} else {
	// If the pipe is already an object we'll just make a callable and pass it to
	// the pipe as-is. There is no need to do any extra parsing and formatting
	// since the object we're given was already a fully instantiated object.
	$parameters = [$passable, $stack];
	}
	$response = method_exists($pipe, $this->method)
	? $pipe->{$this->method}(...$parameters)
	: $pipe(...$parameters);
	return $response instanceof Responsable
	? $response->toResponse($this->container->make(Request::class))
	: $response;
	};

关于中间件执行的流程，是不是有眉目了？

等上面执行完成，Laravel 就要执行这个闭包了

laravel/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php

Lines 166 to 178 in d081c91

	/**
	* Get the route dispatcher callback.
	*
	* @return \Closure
	*/
	protected function dispatchToRouter()
	{
	return function ($request) {
	$this->app->instance('request', $request);
	return $this->router->dispatch($request);
	};
	}

也就是执行路由的 dispatch 逻辑（包含被调用的逻辑一共 82 行代码）。

laravel/vendor/laravel/framework/src/Illuminate/Routing/Router.php

Lines 601 to 682 in d081c91

	/**
	* Dispatch the request to the application.
	*
	* @param \Illuminate\Http\Request $request
	* @return \Illuminate\Http\Response|\Illuminate\Http\JsonResponse
	*/
	public function dispatch(Request $request)
	{
	$this->currentRequest = $request;
	return $this->dispatchToRoute($request);
	}
	/**
	* Dispatch the request to a route and return the response.
	*
	* @param \Illuminate\Http\Request $request
	* @return mixed
	*/
	public function dispatchToRoute(Request $request)
	{
	return $this->runRoute($request, $this->findRoute($request));
	}
	/**
	* Find the route matching a given request.
	*
	* @param \Illuminate\Http\Request $request
	* @return \Illuminate\Routing\Route
	*/
	protected function findRoute($request)
	{
	$this->current = $route = $this->routes->match($request);
	$this->container->instance(Route::class, $route);
	return $route;
	}
	/**
	* Return the response for the given route.
	*
	* @param \Illuminate\Http\Request $request
	* @param \Illuminate\Routing\Route $route
	* @return mixed
	*/
	protected function runRoute(Request $request, Route $route)
	{
	$request->setRouteResolver(function () use ($route) {
	return $route;
	});
	$this->events->dispatch(new Events\RouteMatched($route, $request));
	return $this->prepareResponse($request,
	$this->runRouteWithinStack($route, $request)
	);
	}
	/**
	* Run the given route within a Stack "onion" instance.
	*
	* @param \Illuminate\Routing\Route $route
	* @param \Illuminate\Http\Request $request
	* @return mixed
	*/
	protected function runRouteWithinStack(Route $route, Request $request)
	{
	$shouldSkipMiddleware = $this->container->bound('middleware.disable') &&
	$this->container->make('middleware.disable') === true;
	$middleware = $shouldSkipMiddleware ? [] : $this->gatherRouteMiddleware($route);
	return (new Pipeline($this->container))
	->send($request)
	->through($middleware)
	->then(function ($request) use ($route) {
	return $this->prepareResponse(
	$request, $route->run()
	);
	});
	}

你可能会因为这里又有中间件而诧异

laravel/vendor/laravel/framework/src/Illuminate/Routing/Router.php

Lines 674 to 681 in d081c91

	return (new Pipeline($this->container))
	->send($request)
	->through($middleware)
	->then(function ($request) use ($route) {
	return $this->prepareResponse(
	$request, $route->run()
	);
	});

其实这里的中间件和前面的不一样，前面的是在kernel 中注册的中间件。这里的中间件是在路由绑定中注册的中间件。是两部分。

于是乎，Laravel 鬼使神差的实现了中间件的管道执行机制。

接下来，请查看 09. 容器的依赖注入机制 了解 $route->run() 背后的故事。