關於Laravel的二、三事（1）一次請求的生命週期

最初，一次請求將會到達public/index.php,這個檔案的內容非常簡單：

require __DIR__.'/../bootstrap/autoload.php';
$app = require_once __DIR__.'/../bootstrap/app.php';
$kernel = $app->make(Illuminate\Contracts\Http\Kernel::class);

$response = $kernel->handle(
    $request = Illuminate\Http\Request::capture()
);

$response->send();

$kernel->terminate($request, $response);

首先載入了兩個檔案bootstrap/autoload.php和bootstrap/app.php，首先來看autoload.php的內容：

define('LARAVEL_START', microtime(true));
require __DIR__.'/../vendor/autoload.php';
$compiledPath = __DIR__.'/cache/compiled.php';

if (file_exists($compiledPath)) {
    require $compiledPath;
}

/vendor/autoload.php檔案是composer提供的一個載入檔案，引入這個檔案之後我們就可以方便的使用其他類了。

之後是/cache/compile.php檔案，包含了常用的類，以提升處理請求的效能。

再來看bootstrap/app.php：

$app = new Illuminate\Foundation\Application(
    realpath(__DIR__.'/../')
);

$app->singleton(
    Illuminate\Contracts\Http\Kernel::class,
    App\Http\Kernel::class
);


$app->singleton(
    Illuminate\Contracts\Console\Kernel::class,
    App\Console\Kernel::class
);


$app->singleton(
    Illuminate\Contracts\Debug\ExceptionHandler::class,
    App\Exceptions\Handler::class
);

return $app;

主要是返回一些環境配置資訊和各種中介軟體和簡寫的資訊。

之後index.php建立了一個Kernel例項，開啟Illuminate\Contracts\Http\Kernel::class，程式碼如下：

class Kernel extends HttpKernel
{
    protected $middleware = [
        \Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::class,
    ];

    protected $middlewareGroups = [
        'web' => [
            \App\Http\Middleware\EncryptCookies::class,
            \Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse::class,
            \Illuminate\Session\Middleware\StartSession::class,
            \Illuminate\View\Middleware\ShareErrorsFromSession::class,
            \App\Http\Middleware\VerifyCsrfToken::class,
        ],

        'api' => [
            'throttle:60,1',
        ],
    ];

    protected $routeMiddleware = [
        'auth' => \App\Http\Middleware\Authenticate::class,
        'auth.basic' => \Illuminate\Auth\Middleware\AuthenticateWithBasicAuth::class,
        'can' => \Illuminate\Foundation\Http\Middleware\Authorize::class,
        'guest' => \App\Http\Middleware\RedirectIfAuthenticated::class,
        'throttle' => \Illuminate\Routing\Middleware\ThrottleRequests::class,
    ];
}

定義了一系列中介軟體的陣列，這些中介軟體將會在處理請求時被執行

EncryptCookies::class用於處理對於cookies的加密解密；

AddQueuedCookiesToResponse::class用於給Response的header新增cookies資訊；

StartSession::class用於首次請求時建立session資訊，處理請求時驗證session的有效性，在請求結束時儲存session資訊；

ShareErrorsFromSession::class返回session的錯誤資訊；

VerifyCsrfToken::class驗證CSRF令牌；

路由中介軟體：

Illuminate\Support\Facades\Auth\Authenticate::class用於驗證發出的請求型別；

Illuminate\Auth\Middleware\AuthenticateWithBasicAuth::class用基本的Auth進行驗證；

Illuminate\Foundation\Http\Middleware\Authorize::class將請求與模型繫結；

App\Http\Middleware\RedirectIfAuthenticated::class驗證後重定向；

Illuminate\Routing\Middleware\ThrottleRequests::class用於請求頻率的限制。

然後是對請求的捕捉，捕捉之後交給kernel::handle()：

 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);
        }

        $this->app['events']->fire('kernel.handled', [$request, $response]);

        return $response;
    }

首先是接收引數，然後通過路由轉發請求。

最後執行kernel::terminate()：

public function terminate($request, $response)
    {
        $middlewares = $this->app->shouldSkipMiddleware() ? [] : array_merge(
            $this->gatherRouteMiddlewares($request),
            $this->middleware
        );

        foreach ($middlewares as $middleware) {
            list($name, $parameters) = $this->parseMiddleware($middleware);

            $instance = $this->app->make($name);

            if (method_exists($instance, 'terminate')) {
                $instance->terminate($request, $response);
            }
        }

        $this->app->terminate();
    }

通過kernel::gatherRouteMiddlewares()獲取獲取所有路由，並且對應要使用的中介軟體，然後對所有的中介軟體進行解析並進行處理，執行完之後終結請求。