说说laravel管道pipeline的实现

发表于 更新于
我来过，我战斗过，我不在乎结局。
Laravel中比较优雅的实现了MiddleWare. 主要用来层层递进的处理Request.

Pipeline对象

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(new Pipeline())
     ->send($passable) // 待处理对象，要经过流水线的对象（比如request对象）
     ->through($middlewares) // 流水线上的各个环节（中间件）
     ->via('handle') // 指定每个环节的处理方法，比如 Authenticate::handle
     ->then($handler); // 尽头，最后的处理（返回时，则是源头）

then()方法

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

$this->pipes 是我们的中间件数组:

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[2018-01-24 08:55:58] local.INFO: array (
  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',
  6 => 'Illuminate\\Routing\\Middleware\\SubstituteBindings',
)

carry()方法

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protected function carry()
{
    return function ($stack, $pipe) {
        return function ($passable) use ($stack, $pipe) {
            if ($pipe instanceof Closure) {
                // 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];
            }

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

这里使用了array_reduce和闭包, 在闭包中判断, 如果是迭代就执行这个迭代.
$this->method 这个方法是handle, 也是每次我们需要自定义中间件时需要实现的方法.

简化说明

先看下面这段代码

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$arr = ['AAAA'];

$res = array_reduce($arr, function($carry, $item){
    return function () use ($carry, $item) {
        if (is_null($carry)) {
            return 'Carry IS NULL' . $item;
        }
    };
});

此时的数组长度为1，并且没有指定初始值, 故仅仅会迭代一次,返回一个闭包 use（$carry = null, $item = ‘AAAA’），当我们执行（$res()）这个闭包时，得到的结果为Carry IS NULLAAAA

然后我们再看另外一段代码

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$arr = ['AAAA', 'BBBB'];

$res = array_reduce($arr, function($carry, $item){
    return function () use ($carry, $item) {
        if (is_null($carry)) {
            return 'Carry IS NULL' . $item;
        }
        if ($carry instanceof \Closure) {
            return $carry() . $item;
        }
    };
});

我们新增了一个条件判断，若当前迭代的值是一个闭包，返回该闭包的执行结果。
当我们执行这个闭包时，满足$carry instanceof \Closure，得到结果Carry IS NULLAAAABBBB。

https://laravel-china.org/articles/5206/the-use-of-php-built-in-function-array-reduce-in-laravel