LEOYANG'S BLOG

Laravel HTTP——Pipeline中间件处理源码分析

前言

当所有的路由都加载完毕后,就会根据请求的 url 来将请求分发到对应的路由上去。然而,在分发到路由之前还要经过各种中间件的计算。laravel 利用装饰者模式来实现中间件的功能。

从原始装饰者模式到闭包装饰者

装饰者模式是设计模式的一种,主要进行对象的多次处理与过滤,是在开放-关闭原则下实现动态添加或减少功能的一种方式。下面先看一个装饰者模式的例子:

总共有两种咖啡:Decaf、Espresso,另有两种调味品:Mocha、Whip(3种设计的主要差别在于抽象方式不同)

装饰模式分为3个部分:

1,抽象组件 – 对应Coffee类

2,具体组件 – 对应具体的咖啡,如:Decaf,Espresso

3,装饰者 – 对应调味品,如:Mocha,Whip

原始装饰者模式

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public interface Coffee
{
public double cost();
}
public class Espresso implements Coffee
{
public double cost()
{
return 2.5;
}
}
public class Dressing implements Coffee
{
private Coffee coffee;
public Dressing(Coffee coffee)
{
this.coffee = coffee;
}
public double cost()
{
return coffee.cost();
}
}
public class Whip extends Dressing {
public Whip(Coffee coffee)
{
super(coffee);
}
public double cost()
{
return super.cost() + 0.1;
}
}
public class Mocha extends Dressing
{
public Mocha(Coffee coffee)
{
super(coffee);
}
public double cost()
{
return super.cost() + 0.5;
}
}

当我们使用装饰者模式的时候:

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public class Test {
public static void main(String[] args) {
Coffee coffee = new Espresso();
coffee = new Mocha(coffee);
coffee = new Mocha(coffee);
coffee = new Whip(coffee);
//3.6(2.5 + 0.5 + 0.5 + 0.1)
System.out.println(coffee.cost());
}
}

我们可以看出来,装饰者模式就是利用装饰者类来对具体类不断的进行多层次的处理,首先我们创建了 Espresso 类,然后第一次利用 Mocha 装饰者对 Espresso 咖啡加了摩卡,第二次重复加了摩卡,第三次利用装饰者 WhipEspresso 咖啡加了奶油。每次加入新的调料,装饰者都会对价格 cost 做一些处理(+0.1、+0.5)。

无构造函数的装饰者

我们对这个装饰者进行一些改造:

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public class Espresso
{
double cost;
public double cost()
{
$this-> cost = 2.5;
}
}
public class Dressing
{
public double cost(Espresso $espresso)
{
return ($espresso);
}
}
public class Whip extends Dressing
{
public double cost(Espresso $espresso)
{
$espresso->cost = espresso->cost() + 0.1;
return ($espresso);
}
}
public class Mocha extends Dressing
{
public double cost(Espresso $espresso)
{
$espresso->cost = espresso->cost() + 0.5;
return ($espresso);
}
}
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public class Test {
public static void main(String[] args) {
Coffee $coffee = new Espresso();
$coffee = (new Mocha())->cost($coffee);
$coffee = (new Mocha())->cost($coffee);
$coffee = (new Whip())->cost($coffee);
//3.6(2.5 + 0.5 + 0.5 + 0.1)
System.out.println(coffee.cost());
}
}

改造后,装饰者类通过函数 cost 来注入具体类 caffee,而不是通过构造函数,这样做有助于自动化进行装饰处理。我们改造后发现,想要对具体类通过装饰类进行处理,需要不断的调用 cost 函数,如果有10个装饰操作,就要手动写10个语句,因此我们继续进行改造:

闭包装饰者模式

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public class Espresso
{
double cost;
public double cost()
{
$this-> cost = 2.5;
}
}
public class Dressing
{
public double cost(Espresso $espresso, Closure $closure)
{
return ($espresso);
}
}
public class Whip extends Dressing
{
public double cost(Espresso $espresso, Closure $closure)
{
$espresso->cost = espresso->cost() + 0.1;
return $closure($espresso);
}
}
public class Mocha extends Dressing
{
public double cost(Espresso $espresso, Closure $closure)
{
$espresso->cost = espresso->cost() + 0.5;
return $closure($espresso);
}
}
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public class Test {
public static void main(String[] args) {
Coffee $coffee = new Espresso();
$fun = function($coffee,$fuc,$dressing) {
$dressing->cost($coffee, $fuc);
}
$fuc0 = function($coffee) {
return $coffee;
};
$fuc1 = function($coffee) use ($fuc0, $dressing = (new Mocha(),$fuc) {
return $fun($coffee, $fuc0, $dressing);
}
$fuc2 = function($coffee) use ($fuc1, $dressing = (new Mocha(),$fun) {
return $fuc($coffee, $fun1, $dressing);
}
$fuc3 = function($coffee) use ($fuc2, $dressing = (new Whip(),$fun) {
return $fuc($coffee, $fun2, $dressing);
}
$coffee = $fun3($coffee);
//3.6(2.5 + 0.5 + 0.5 + 0.1)
System.out.println(coffee.cost());
}
}

在这次改造中,我们使用了闭包函数,这样做的目的在于,我们只需要最后一句 $fun3($coffee),就可以启动整个装饰链条。

闭包装饰者的抽象化

然而这种改造还不够深入,因为我们还可以把 $fuc1$fuc2$fuc3 继续抽象化为一个闭包函数,这个闭包函数仅仅是参数 $fuc$dressing 每次不同,$coffee 相同,因此改造如下:

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public class Test {
public static void main(String[] args) {
Coffee $coffee = new Espresso();
$fun = function($coffee) use ($fuc,$dressing) {
$dressing->cost($coffee, $fuc);
}
$fuc = function($fuc,$dressing) use ($fun) {
return $fun;
};
$fuc0 = function($coffee) {
return $coffee;
};
$fuc1 = $fuc($fuc0, (new Mocha());
$fuc2 = $fuc($fuc1, (new Mocha());
$fuc3 = $fuc($fuc2, (new Whip());
$coffee = $fun3($coffee);
//3.6(2.5 + 0.5 + 0.5 + 0.1)
System.out.println(coffee.cost());
}
}

这次,我们把之前的闭包分为两个部分,$fun 负责具体类的参数传递,$fuc负责装饰者和闭包函数的参数传递。在最后一句 $fun3,只需要传递一个具体类,就可以启动整个装饰链条。

闭包装饰者的自动化

到这里,我们还有一件事没有完成,那就是 $fuc1$fuc2$fuc3 这些闭包的构建还是手动的,我们需要将这个过程改为自动的:

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public class Test {
public static void main(String[] args) {
Coffee $coffee = new Espresso();
$fun = function($coffee) use ($fuc,$dressing) {
$dressing->cost($coffee, $fuc);
}
$fuc = function($fuc,$dressing) use ($fun) {
return $fun;
};
$fuc0 = function($coffee) {
return $coffee;
};
$fucn = array_reduce(
[(new Mocha(),(new Mocha(),(new Whip()], $fuc, $fuc0
);
$coffee = $fucn($coffee);
//3.6(2.5 + 0.5 + 0.5 + 0.1)
System.out.println(coffee.cost());
}
}

laravel的闭包装饰者——Pipeline

上一章我们说到了路由的注册启动与加载过程,这个过程由 bootstrap() 完成。当所有的路由加载完毕后,就要进行各种中间件的处理了:

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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());
}
public function shouldSkipMiddleware()
{
return $this->bound('middleware.disable') &&
$this->make('middleware.disable') === true;
}

laravel 的中间件处理由 Pipeline 来完成,它是一个闭包装饰者模式,其中

  • request 是具体类,相当于我们上面的 caffee 类;
  • middleware 中间件是装饰者类,相当于上面的 dressing 类;

我们先看看这个类内部的代码:

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class Pipeline implements PipelineContract
{
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 then(Closure $destination)
{
$pipeline = array_reduce(
array_reverse($this->pipes), $this->carry(), $this->prepareDestination($destination)
);
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, $pipe) {
if ($pipe instanceof Closure) {
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 $pipe->{$this->method}(...$parameters);
};
};
}
}

pipeline 的构造和我们上面所讲的闭包装饰者相同,我们着重来看 carry() 函数的代码:

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function ($stack, $pipe) {
...
}

最外层的闭包相当于上个章节的 $fuc,

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function ($passable) use ($stack, $pipe) {
...
}

里面的这一层比闭包型党与上个章节的 $fun

prepareDestination 这个函数相当于上面的 $fuc0,

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if ($pipe instanceof Closure) {
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 $pipe->{$this->method}(...$parameters);

这一部分相当于上个章节的 $dressing->cost($coffee, $fuc);,这部分主要解析中间件 handle() 函数的参数:

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public function via($method)
{
$this->method = $method;
return $this;
}
protected function parsePipeString($pipe)
{
list($name, $parameters) = array_pad(explode(':', $pipe, 2), 2, []);
if (is_string($parameters)) {
$parameters = explode(',', $parameters);
}
return [$name, $parameters];
}

这样,laravel 就实现了中间件对 request 的层层处理。