pipeline in laravel

Reference: https://segmentfault.com/a/1190000010092899?utm_medium=hao.caibaojian.com&utm_source=hao.caibaojian.com&share_user=1030000000178452

The concept is easy to understand,but the code is so confused. Every pipe will be run in order . Also they will get the data given by the previous pipe.

let’s see how Laravel get the job done .

Illuminate\Foundation\Http\Kernel
 
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());
}

Illuminate\Foundation\Http\Kernel

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());

}

Before dispatching the request to router , Laravel will go through all the middleware first. The request object will be passed through all the middleware. middleware array is in the App\Http\Kernel

Illuminate\Pipeline\Pipeline

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

    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];
                }

                return method_exists($pipe, $this->method)
                                ? $pipe->{$this->method}(...$parameters)
                                : $pipe(...$parameters);
            };
        };
    }



}

Illuminate\Pipeline\Pipeline

class Pipeline {

//...

public function then(Closure $destination)

{

$pipeline = array_reduce(

array_reverse($this->pipes), $this->carry(), $this->prepareDestination($destination)

);

return $pipeline($this->passable);

}

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];

}

return method_exists($pipe, $this->method)

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

: $pipe(...$parameters);

};

}

reference: array_reduce
array_reduce( $pipes,callable$ callable, $initial)$ this->carry() will return a closure . two parameters ( $stack,$ pipe) will be provided into this closure function . $stack is the return value of the previous pipe.$ item is the current pipe. And $initial will be the first$ stack, it’s a closure function too.

=====>

$callable = return function($passable) use($stack,$pipe) {
 //...
}

$callable = return function($passable) use($stack,$pipe) {

//...

}

The following is how the pipe iterations work.
——————————————————–
let’s say $pipe = [middleware1, middleware2] array_reverse will reverse the$ pipe array,so $pipe = [middleware2,middleware1] ====================first iteration===================$ stack = dispatchToRouter
$pipe = middleware2 so the return value = return function ($ passable) use (dispatchToRouter ,middleware2) { //….}
Let’s look into detail. u can see the $passable and$ stack will pass into the middleware as parameters.
it’s time to find out how a middleware looks like.

<?php

namespace Illuminate\Foundation\Http\Middleware;

use Closure;
use Illuminate\Contracts\Foundation\Application;
use Illuminate\Foundation\Http\Exceptions\MaintenanceModeException;

class CheckForMaintenanceMode
{
    /**
     * The application implementation.
     *
     * @var \Illuminate\Contracts\Foundation\Application
     */
    protected $app;

    /**
     * Create a new middleware instance.
     *
     * @param  \Illuminate\Contracts\Foundation\Application  $app
     * @return void
     */
    public function __construct(Application $app)
    {
        $this->app = $app;
    }

    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     *
     * @throws \Symfony\Component\HttpKernel\Exception\HttpException
     */
    public function handle($request, Closure $next)
    {
        if ($this->app->isDownForMaintenance()) {
            $data = json_decode(file_get_contents($this->app->storagePath().'/framework/down'), true);

            throw new MaintenanceModeException($data['time'], $data['retry'], $data['message']);
        }

        return $next($request);
    }
}

<?php

namespace Illuminate\Foundation\Http\Middleware;

use Closure;

use Illuminate\Contracts\Foundation\Application;

use Illuminate\Foundation\Http\Exceptions\MaintenanceModeException;

class CheckForMaintenanceMode

{

/**

* The application implementation.

* @var \Illuminate\Contracts\Foundation\Application

protected $app;

/**

* Create a new middleware instance.

* @param \Illuminate\Contracts\Foundation\Application $app

* @return void

public function __construct(Application $app)

{

$this->app = $app;

}

/**

* Handle an incoming request.

* @param \Illuminate\Http\Request $request

* @param \Closure $next

* @return mixed

* @throws \Symfony\Component\HttpKernel\Exception\HttpException

public function handle($request, Closure $next)

{

if ($this->app->isDownForMaintenance()) {

$data = json_decode(file_get_contents($this->app->storagePath().'/framework/down'), true);

throw new MaintenanceModeException($data['time'], $data['retry'], $data['message']);

}

return $next($request);

}

it will run the $next function at the end of the handle function, and the$ next is equal to $stack.so it means it will call the$ stack at the end.
so the execute order looks like this :
dispatchToRouter <- -call– middleware2
=================second iteration=====================
$stack = a closure return by first iteration$ pipe = middleware1
the same as first iteration, the return value will be a closure.
and the execute order will be ：
dispatchToRouter <–call–middleware2 <–call– middleware1
========================done=======================
u may be confuse ,they are all closure. when will all these closure get called?
look carefully into the then() function.
the last iteration will return a closure. and the then() function invoke the closure and pass the request object as a parameter.

that’s it!