Laravel5.5源码详解 -- 中间件MiddleWare分析

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
1577a
\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

<?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)！