Laravel 启动流程

时间 2019-11-08

标签 laravel 启动流程繁體版

原文原文链接

Last-Modified: 2019年5月10日16:19:07php

阶段划分

Laravel 5.5
请求到响应的整个执行阶段概括为 4 个:

程序启动准备阶段html
- 文件自动加载
- 服务容器实例化
- 基础服务提供者的注册
- 核心类的实例化
请求实例化阶段laravel
- 实例化 Request 实例
请求处理阶段web
- 准备请求处理的环境
- 将请求实例经过中间件处理及经过路由和控制器的分发控制
响应发送和程序终止阶段redis
- 将响应内容返回给客户端
- 记录与客户端有关的信息等

1. 程序启动准备

程序入口在 index.php 中bootstrap

require __DIR__.'/../vendor/autoload.php';

$app = require_once __DIR__.'/../bootstrap/app.php';    # 获取服务容器实例

$kernel = $app->make(Illuminate\Contracts\Http\Kernel::class);

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

$response->send();

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

建立服务容器实例api

服务容器的建立在 bootstrap\app.php 中进行.数组

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

1.1 容器基础配置

容器 Application 的构造函数:安全

public function __construct($basePath = null)
{
    if ($basePath) {
        $this->setBasePath($basePath);
    }

    $this->registerBaseBindings();

    $this->registerBaseServiceProviders();

    $this->registerCoreContainerAliases();
}

构造函数主要完成如下基本配置:服务器

目录路径(绑定到容器中, 并提供类方法获取子目录)

public function setBasePath($basePath)
{
    $this->basePath = rtrim($basePath, '\/');

    $this->bindPathsInContainer();

    return $this;
}

protected function bindPathsInContainer()
    {
        $this->instance('path', $this->path());
        $this->instance('path.base', $this->basePath());
        $this->instance('path.lang', $this->langPath());
        $this->instance('path.config', $this->configPath());
        $this->instance('path.public', $this->publicPath());
        $this->instance('path.storage', $this->storagePath());
        $this->instance('path.database', $this->databasePath());
        $this->instance('path.resources', $this->resourcePath());
        $this->instance('path.bootstrap', $this->bootstrapPath());
    }

绑定容器自身

protected function registerBaseBindings()
{
    static::setInstance($this);

    $this->instance('app', $this);

    $this->instance(Container::class, $this);

    $this->instance(PackageManifest::class, new PackageManifest(
        new Filesystem, $this->basePath(), $this->getCachedPackagesPath()
    ));
}

基础服务注册( Event, Log, Route)

protected function registerBaseServiceProviders()
{
    $this->register(new EventServiceProvider($this));

    $this->register(new LogServiceProvider($this));

    $this->register(new RoutingServiceProvider($this));
}

别名注册

多个接口名对应一个简短别名, 后续在注册服务时只需绑定到别名上便可 (而没必要绑定到具体接口名)

public function registerCoreContainerAliases()
{
    foreach ([
        'app'                  => [\Illuminate\Foundation\Application::class, \Illuminate\Contracts\Container\Container::class, \Illuminate\Contracts\Foundation\Application::class,  \Psr\Container\ContainerInterface::class],
        'auth'                 => [\Illuminate\Auth\AuthManager::class, \Illuminate\Contracts\Auth\Factory::class],
        'auth.driver'          => [\Illuminate\Contracts\Auth\Guard::class],
        'blade.compiler'       => [\Illuminate\View\Compilers\BladeCompiler::class],
        'cache'                => [\Illuminate\Cache\CacheManager::class, \Illuminate\Contracts\Cache\Factory::class],
        'cache.store'          => [\Illuminate\Cache\Repository::class, \Illuminate\Contracts\Cache\Repository::class],
        'config'               => [\Illuminate\Config\Repository::class, \Illuminate\Contracts\Config\Repository::class],
        'cookie'               => [\Illuminate\Cookie\CookieJar::class, \Illuminate\Contracts\Cookie\Factory::class, \Illuminate\Contracts\Cookie\QueueingFactory::class],
        'encrypter'            => [\Illuminate\Encryption\Encrypter::class, \Illuminate\Contracts\Encryption\Encrypter::class],
        'db'                   => [\Illuminate\Database\DatabaseManager::class],
        'db.connection'        => [\Illuminate\Database\Connection::class, \Illuminate\Database\ConnectionInterface::class],
        'events'               => [\Illuminate\Events\Dispatcher::class, \Illuminate\Contracts\Events\Dispatcher::class],
        'files'                => [\Illuminate\Filesystem\Filesystem::class],
        'filesystem'           => [\Illuminate\Filesystem\FilesystemManager::class, \Illuminate\Contracts\Filesystem\Factory::class],
        'filesystem.disk'      => [\Illuminate\Contracts\Filesystem\Filesystem::class],
        'filesystem.cloud'     => [\Illuminate\Contracts\Filesystem\Cloud::class],
        'hash'                 => [\Illuminate\Contracts\Hashing\Hasher::class],
        'translator'           => [\Illuminate\Translation\Translator::class, \Illuminate\Contracts\Translation\Translator::class],
        'log'                  => [\Illuminate\Log\Writer::class, \Illuminate\Contracts\Logging\Log::class, \Psr\Log\LoggerInterface::class],
        'mailer'               => [\Illuminate\Mail\Mailer::class, \Illuminate\Contracts\Mail\Mailer::class, \Illuminate\Contracts\Mail\MailQueue::class],
        'auth.password'        => [\Illuminate\Auth\Passwords\PasswordBrokerManager::class, \Illuminate\Contracts\Auth\PasswordBrokerFactory::class],
        'auth.password.broker' => [\Illuminate\Auth\Passwords\PasswordBroker::class, \Illuminate\Contracts\Auth\PasswordBroker::class],
        'queue'                => [\Illuminate\Queue\QueueManager::class, \Illuminate\Contracts\Queue\Factory::class, \Illuminate\Contracts\Queue\Monitor::class],
        'queue.connection'     => [\Illuminate\Contracts\Queue\Queue::class],
        'queue.failer'         => [\Illuminate\Queue\Failed\FailedJobProviderInterface::class],
        'redirect'             => [\Illuminate\Routing\Redirector::class],
        'redis'                => [\Illuminate\Redis\RedisManager::class, \Illuminate\Contracts\Redis\Factory::class],
        'request'              => [\Illuminate\Http\Request::class, \Symfony\Component\HttpFoundation\Request::class],
        'router'               => [\Illuminate\Routing\Router::class, \Illuminate\Contracts\Routing\Registrar::class, \Illuminate\Contracts\Routing\BindingRegistrar::class],
        'session'              => [\Illuminate\Session\SessionManager::class],
        'session.store'        => [\Illuminate\Session\Store::class, \Illuminate\Contracts\Session\Session::class],
        'url'                  => [\Illuminate\Routing\UrlGenerator::class, \Illuminate\Contracts\Routing\UrlGenerator::class],
        'validator'            => [\Illuminate\Validation\Factory::class, \Illuminate\Contracts\Validation\Factory::class],
        'view'                 => [\Illuminate\View\Factory::class, \Illuminate\Contracts\View\Factory::class],
    ] as $key => $aliases) {
        foreach ($aliases as $alias) {
            $this->alias($key, $alias);
        }
    }
}

1.2 核心类绑定

$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
);

绑定重要接口:

Http 核心类
命令行核心类
异常处理类

1.3 实例化 Http 核心类

$kernel = $app->make(Illuminate\Contracts\Http\Kernel::class);

Http 核心类的构造函数

public function __construct(Application $app, Router $router)
{
    $this->app = $app;
    $this->router = $router;

    $router->middlewarePriority = $this->middlewarePriority;

    foreach ($this->middlewareGroups as $key => $middleware) {
        $router->middlewareGroup($key, $middleware);
    }

    foreach ($this->routeMiddleware as $key => $middleware) {
        $router->aliasMiddleware($key, $middleware);
    }
}

上述过程主要作的事是将中间件赋值给路由

中间件顺序优先级列表
中间件组
中间件别名

核心类 app/Http/Kernel.php

<?php

namespace App\Http;

use Illuminate\Foundation\Http\Kernel as HttpKernel;

class Kernel extends HttpKernel
{
    // 全局中间件，最早调用
    protected $middleware = [

        // 检测是否应用是否进入『维护模式』
        // 见：https://d.laravel-china.org/docs/5.5/configuration#maintenance-mode
        \Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::class,

        // 检测请求的数据是否过大
        \Illuminate\Foundation\Http\Middleware\ValidatePostSize::class,

        // 对提交的请求参数进行 PHP 函数 `trim()` 处理
        \App\Http\Middleware\TrimStrings::class,

        // 将提交请求参数中空子串转换为 null
        \Illuminate\Foundation\Http\Middleware\ConvertEmptyStringsToNull::class,

        // 修正代理服务器后的服务器参数
        \App\Http\Middleware\TrustProxies::class,
    ];

    // 定义中间件组
    protected $middlewareGroups = [

        // Web 中间件组，应用于 routes/web.php 路由文件
        'web' => [
            // Cookie 加密解密
            \App\Http\Middleware\EncryptCookies::class,

            // 将 Cookie 添加到响应中
            \Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse::class,

            // 开启会话
            \Illuminate\Session\Middleware\StartSession::class,

            // 认证用户，此中间件之后 Auth 类才能生效
            // 见：https://d.laravel-china.org/docs/5.5/authentication
            \Illuminate\Session\Middleware\AuthenticateSession::class,

            // 将系统的错误数据注入到视图变量 $errors 中
            \Illuminate\View\Middleware\ShareErrorsFromSession::class,

            // 检验 CSRF ，防止跨站请求伪造的安全威胁
            // 见：https://d.laravel-china.org/docs/5.5/csrf
            \App\Http\Middleware\VerifyCsrfToken::class,

            // 处理路由绑定
            // 见：https://d.laravel-china.org/docs/5.5/routing#route-model-binding
            \Illuminate\Routing\Middleware\SubstituteBindings::class,
        ],

        // API 中间件组，应用于 routes/api.php 路由文件
        'api' => [
            // 使用别名来调用中间件
            // 请见：https://d.laravel-china.org/docs/5.5/middleware#为路由分配中间件
            'throttle:60,1',
            'bindings',
        ],
    ];

    // 中间件别名设置，容许你使用别名调用中间件，例如上面的 api 中间件组调用
    protected $routeMiddleware = [

        // 只有登陆用户才能访问，咱们在控制器的构造方法中大量使用
        'auth' => \Illuminate\Auth\Middleware\Authenticate::class,

        // HTTP Basic Auth 认证
        'auth.basic' => \Illuminate\Auth\Middleware\AuthenticateWithBasicAuth::class,

        // 处理路由绑定
        // 见：https://d.laravel-china.org/docs/5.5/routing#route-model-binding
        'bindings' => \Illuminate\Routing\Middleware\SubstituteBindings::class,

        // 用户受权功能
        'can' => \Illuminate\Auth\Middleware\Authorize::class,

        // 只有游客才能访问，在 register 和 login 请求中使用，只有未登陆用户才能访问这些页面
        'guest' => \App\Http\Middleware\RedirectIfAuthenticated::class,

        // 访问节流，相似于 『1 分钟只能请求 10 次』的需求，通常在 API 中使用
        'throttle' => \Illuminate\Routing\Middleware\ThrottleRequests::class,
    ];
}

2. 请求实例化

以处理 Http 请求为例

index.php 入口文件

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

请求是经过 Illuminate\Http\Request::capture() 实例化的, 主要是将请求信息以对象形式表现出来

3. 请求处理

入口文件:

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

$kernel->handle(...) 处理请求过程

Illuminate\Foundation\Http\Kernel

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();        # 核心类初始化

    return (new Pipeline($this->app))
        ->send($request)
        ->through($this->app->shouldSkipMiddleware() ? [] : $this->middleware)
        ->then($this->dispatchToRouter());
}


protected function dispatchToRouter()
{
    return function ($request) {
        $this->app->instance('request', $request);

        return $this->router->dispatch($request);
    };
}

实际处理请求逻辑主要在 sendRequestThroughRouter 方法中, 它主要作了:

核心类的初始化

经由中间件过滤后将请求最终交由 Router 处理

对于 Http 请求处理, 中间件包括:

protected $middleware = [

    \Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::class,

    \Illuminate\Foundation\Http\Middleware\ValidatePostSize::class,

    \App\Http\Middleware\TrimStrings::class,

    \Illuminate\Foundation\Http\Middleware\ConvertEmptyStringsToNull::class,

    \App\Http\Middleware\TrustProxies::class,

];

该中间件数组定义在 Http 核心类中, 同时在核心类的构造函数中传递给 Router 类

3.1 请求处理环境初始化

核心类的初始化 bootstrap()

protected $bootstrappers = [
    \Illuminate\Foundation\Bootstrap\LoadEnvironmentVariables::class,
    \Illuminate\Foundation\Bootstrap\LoadConfiguration::class,
    \Illuminate\Foundation\Bootstrap\HandleExceptions::class,
    \Illuminate\Foundation\Bootstrap\RegisterFacades::class,
    \Illuminate\Foundation\Bootstrap\RegisterProviders::class,
    \Illuminate\Foundation\Bootstrap\BootProviders::class,
];

# 初始化
public function bootstrap()
{
    if (! $this->app->hasBeenBootstrapped()) {
        $this->app->bootstrapWith($this->bootstrappers());
    }
}

protected function bootstrappers()
{
    return $this->bootstrappers;
}

在服务容器 Application 类中

public function bootstrapWith(array $bootstrappers)
{
    $this->hasBeenBootstrapped = true;

    foreach ($bootstrappers as $bootstrapper) {
        $this['events']->fire('bootstrapping: '.$bootstrapper, [$this]);

        $this->make($bootstrapper)->bootstrap($this);

        $this['events']->fire('bootstrapped: '.$bootstrapper, [$this]);
    }
}

该步骤主要是主要是对核心类中定义的 $bootstrappers 数组元素(引导类)初始化.

bootstrap 过程具体是在服务容器来中进行, 由核心类调用并传入待初始化的类

Http 核心类默认包含如下 6 个启动服务:

1. 环境监测 `\Illuminate\Foundation\Bootstrap\LoadEnvironmentVariables::class`

从 .env 文件中解析环境变量到 getevn(), $_ENV, $_SERVER

依赖 vlucas/phpdotenv 扩展包

2. 配置加载 `\Illuminate\Foundation\Bootstrap\LoadConfiguration::class`

载入 config 目录下全部 php 配置文件, 并将生成的配置存储类绑定到服务容器 $app['config']

同时配置时区及多字节格式(utf8)

3. 常处理 `\Illuminate\Foundation\Bootstrap\HandleExceptions::class`

报告全部错误 error_report(E_ALL)

提供对未捕获的异常, 错误的全局处理 set_error_handler, set_exception_handler, register_shutdown_function

4. 外观注册 `\Illuminate\Foundation\Bootstrap\RegisterFacades::class`

从 app.aliases 中读取外观配置数组

'aliases' => [

        'App' => Illuminate\Support\Facades\App::class,
        'Artisan' => Illuminate\Support\Facades\Artisan::class,
        'Auth' => Illuminate\Support\Facades\Auth::class,
        'Blade' => Illuminate\Support\Facades\Blade::class,
        'Broadcast' => Illuminate\Support\Facades\Broadcast::class,
        'Bus' => Illuminate\Support\Facades\Bus::class,
        'Cache' => Illuminate\Support\Facades\Cache::class,
        'Config' => Illuminate\Support\Facades\Config::class,
        'Cookie' => Illuminate\Support\Facades\Cookie::class,
        'Crypt' => Illuminate\Support\Facades\Crypt::class,
        'DB' => Illuminate\Support\Facades\DB::class,
        'Eloquent' => Illuminate\Database\Eloquent\Model::class,
        'Event' => Illuminate\Support\Facades\Event::class,
        'File' => Illuminate\Support\Facades\File::class,
        'Gate' => Illuminate\Support\Facades\Gate::class,
        'Hash' => Illuminate\Support\Facades\Hash::class,
        'Lang' => Illuminate\Support\Facades\Lang::class,
        'Log' => Illuminate\Support\Facades\Log::class,
        'Mail' => Illuminate\Support\Facades\Mail::class,
        'Notification' => Illuminate\Support\Facades\Notification::class,
        'Password' => Illuminate\Support\Facades\Password::class,
        'Queue' => Illuminate\Support\Facades\Queue::class,
        'Redirect' => Illuminate\Support\Facades\Redirect::class,
        'Redis' => Illuminate\Support\Facades\Redis::class,
        'Request' => Illuminate\Support\Facades\Request::class,
        'Response' => Illuminate\Support\Facades\Response::class,
        'Route' => Illuminate\Support\Facades\Route::class,
        'Schema' => Illuminate\Support\Facades\Schema::class,
        'Session' => Illuminate\Support\Facades\Session::class,
        'Storage' => Illuminate\Support\Facades\Storage::class,
        'URL' => Illuminate\Support\Facades\URL::class,
        'Validator' => Illuminate\Support\Facades\Validator::class,
        'View' => Illuminate\Support\Facades\View::class,

    ],

使用 spl_autoload_register(...) 处理类加载, 配合 class_alias() 提供类的别名调用

Facade 外观类基类依赖 __callStatic` 调用方法( 使用服务容器实例化对应类)

5. 服务提供者注册 `\Illuminate\Foundation\Bootstrap\RegisterProviders::class`

从 app.providers 中读取全部服务提供者

'providers' => [

        /*
         * Laravel Framework Service Providers...
         */
        Illuminate\Auth\AuthServiceProvider::class,
        Illuminate\Broadcasting\BroadcastServiceProvider::class,
        Illuminate\Bus\BusServiceProvider::class,
        Illuminate\Cache\CacheServiceProvider::class,
        Illuminate\Foundation\Providers\ConsoleSupportServiceProvider::class,
        Illuminate\Cookie\CookieServiceProvider::class,
        Illuminate\Database\DatabaseServiceProvider::class,
        Illuminate\Encryption\EncryptionServiceProvider::class,
        Illuminate\Filesystem\FilesystemServiceProvider::class,
        Illuminate\Foundation\Providers\FoundationServiceProvider::class,
        Illuminate\Hashing\HashServiceProvider::class,
        Illuminate\Mail\MailServiceProvider::class,
        Illuminate\Notifications\NotificationServiceProvider::class,
        Illuminate\Pagination\PaginationServiceProvider::class,
        Illuminate\Pipeline\PipelineServiceProvider::class,
        Illuminate\Queue\QueueServiceProvider::class,
        Illuminate\Redis\RedisServiceProvider::class,
        Illuminate\Auth\Passwords\PasswordResetServiceProvider::class,
        Illuminate\Session\SessionServiceProvider::class,
        Illuminate\Translation\TranslationServiceProvider::class,
        Illuminate\Validation\ValidationServiceProvider::class,
        Illuminate\View\ViewServiceProvider::class,

        /*
         * Package Service Providers...
         */

        /*
         * Application Service Providers...
         */
        App\Providers\AppServiceProvider::class,
        App\Providers\AuthServiceProvider::class,
        // App\Providers\BroadcastServiceProvider::class,
        App\Providers\EventServiceProvider::class,
        App\Providers\RouteServiceProvider::class,    # 路由表生成
    ],

服务提供者通过解析后分为 3 种类型的服务提供者:

eager 类型
立刻调用 register 注册
deferred 类型
记录下来, 当服务容器解析对应服务时, 才注册对应的服务提供者
when 类型
记录下来, 当对应 event 触发时在注册对应服务提供者

6. 启动提供者 `\Illuminate\Foundation\Bootstrap\BootProviders::class`

调用服务容器的 boot() 方法, 依次调用在服务容器中 register 的全部服务提供者的 boot() 方法

3.2 路由处理请求

在内核处理请求, 将请求实例经过中间件处理后, 将请求的处理交给路由 Router 进行控制器的分发.

Http Kernel

protected function dispatchToRouter()
{
    return function ($request) {
        $this->app->instance('request', $request);

        return $this->router->dispatch($request);
    };
}

路由表存储结构说明

Illuminate\Routing\Route 存储单条路由
Illuminate\Routing\RouteCollection 保存全部 Route 实例, 造成路由表

Illuminate\Routing\Router 类实例持有 RouteCollection 路由表实例.

即, 一个 Router 持有一个 RouteCollection, 而 RouteCollection 拥有 N 个 Route

在 Router 中对请求的处理一样通过一系列的 路由中间件

# 路由处理请求的入库
public function dispatchToRoute(Request $request)
{
    return $this->runRoute($request, $this->findRoute($request));
}

# 根据请求的 url 和 method 查找对应的 route
protected function findRoute($request)
{
    $this->current = $route = $this->routes->match($request);

    $this->container->instance(Route::class, $route);

    return $route;
}

# 根据对应的请求和路由条目, 返回相应的 $response
protected function runRoute(Request $request, Route $route)
{
    $request->setRouteResolver(function () use ($route) {
        return $route;
    });

    $this->events->dispatch(new Events\RouteMatched($route, $request));

    return $this->prepareResponse($request,
                                  $this->runRouteWithinStack($route, $request)
                                 );
}

# 请求通过路由中间件过滤后, 交由 route 的 run() 方法处理
protected function runRouteWithinStack(Route $route, Request $request)
{
    $shouldSkipMiddleware = $this->container->bound('middleware.disable') &&
        $this->container->make('middleware.disable') === true;

    $middleware = $shouldSkipMiddleware ? [] : $this->gatherRouteMiddleware($route);

    return (new Pipeline($this->container))
        ->send($request)
        ->through($middleware)
        ->then(function ($request) use ($route) {
            return $this->prepareResponse(
                $request, $route->run()
            );
        });
}

route 的 run() 方法最终将请求转给 Illuminate\Routing\ControllerDispatcher::dispatch 处理

public function dispatch(Route $route, $controller, $method)
{
    $parameters = $this->resolveClassMethodDependencies(
        $route->parametersWithoutNulls(), $controller, $method
    );

    if (method_exists($controller, 'callAction')) {
            return $controller->callAction($method, $parameters);
    }

    return $controller->{$method}(...array_values($parameters));
}

剩下的事情就是 Controller控制器的事了.

3.3 处理返回的 Response

在 Router 中有一个方法, 用于对返回的 $response 进行处理

public function prepareResponse($request, $response)
{
    return static::toResponse($request, $response);
}

/**
* @return \Illuminate\Http\Response|\Illuminate\Http\JsonResponse
*/
public static function toResponse($request, $response)
{
    if ($response instanceof Responsable) {
        $response = $response->toResponse($request);
    }

    if ($response instanceof PsrResponseInterface) {
        $response = (new HttpFoundationFactory)->createResponse($response);
    } elseif (! $response instanceof SymfonyResponse &&
              ($response instanceof Arrayable ||
               $response instanceof Jsonable ||
               $response instanceof ArrayObject ||
               $response instanceof JsonSerializable ||
               is_array($response))) {
        $response = new JsonResponse($response);
    } elseif (! $response instanceof SymfonyResponse) {
        $response = new Response($response);
    }

    if ($response->getStatusCode() === Response::HTTP_NOT_MODIFIED) {
        $response->setNotModified();
    }

    return $response->prepare($request);    # 最后的处理
}

上述过程当中, 在返回 $response 以前进行了最后的处理 $response->prepare($request)

该过程是在 Symfony\Component\HttpFoundation\Response::prepare() 中进行

对响应的封装是经过 Illuminate\Http\Response 类完成, 该类底层是 Symfony 框架的 Response 类
即, Symfony\Component\HttpFoundation\Response

public function prepare(Request $request)
{
    $headers = $this->headers;

    if ($this->isInformational() || $this->isEmpty()) {
        $this->setContent(null);
        $headers->remove('Content-Type');
        $headers->remove('Content-Length');
    } else {
        // Content-type based on the Request
        if (!$headers->has('Content-Type')) {
            $format = $request->getRequestFormat();
            if (null !== $format && $mimeType = $request->getMimeType($format)) {
                $headers->set('Content-Type', $mimeType);
            }
        }

        // Fix Content-Type
        $charset = $this->charset ?: 'UTF-8';
        if (!$headers->has('Content-Type')) {
            $headers->set('Content-Type', 'text/html; charset='.$charset);
        } elseif (0 === stripos($headers->get('Content-Type'), 'text/') && false === stripos($headers->get('Content-Type'), 'charset')) {
            // add the charset
            $headers->set('Content-Type', $headers->get('Content-Type').'; charset='.$charset);
        }

        // Fix Content-Length
        if ($headers->has('Transfer-Encoding')) {
            $headers->remove('Content-Length');
        }

        if ($request->isMethod('HEAD')) {
            // cf. RFC2616 14.13
            $length = $headers->get('Content-Length');
            $this->setContent(null);
            if ($length) {
                $headers->set('Content-Length', $length);
            }
        }
    }

    // Fix protocol
    if ('HTTP/1.0' != $request->server->get('SERVER_PROTOCOL')) {
        $this->setProtocolVersion('1.1');
    }

    // Check if we need to send extra expire info headers
    if ('1.0' == $this->getProtocolVersion() && false !== strpos($this->headers->get('Cache-Control'), 'no-cache')) {
        $this->headers->set('pragma', 'no-cache');
        $this->headers->set('expires', -1);
    }

    $this->ensureIEOverSSLCompatibility($request);

    return $this;
}

4. 响应发送和程序终止

4.1 响应的发送

在 index.php 入口文件的最后是将响应返回给客户端

$response->send();

Symfony\Component\HttpFoundation\Response

public function send()
{
    $this->sendHeaders();
    $this->sendContent();

    if (function_exists('fastcgi_finish_request')) {
        fastcgi_finish_request();
    } elseif (!\in_array(PHP_SAPI, array('cli', 'phpdbg'), true)) {
        static::closeOutputBuffers(0, true);
    }

    return $this;
}

public function sendHeaders()
{
    // headers have already been sent by the developer
    if (headers_sent()) {
        return $this;
    }

    // headers
    foreach ($this->headers->allPreserveCase() as $name => $values) {
        foreach ($values as $value) {
            header($name.': '.$value, false, $this->statusCode);
        }
    }

    // status
    header(sprintf('HTTP/%s %s %s', $this->version, $this->statusCode, $this->statusText), true, $this->statusCode);

    return $this;
}

public function sendContent()
{
    echo $this->content;

    return $this;
}

4.2 请求停止

在 index.php 入口文件的最后:

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

依旧以 Http Kernel 为例:

public function terminate($request, $response)
{
    $this->terminateMiddleware($request, $response);    # 中间件停止处理

    $this->app->terminate();    # 服务容器的停止处理函数
}

protected function terminateMiddleware($request, $response)
{
    $middlewares = $this->app->shouldSkipMiddleware() ? [] : array_merge(
        $this->gatherRouteMiddleware($request),
        $this->middleware
    );

    foreach ($middlewares as $middleware) {
        if (! is_string($middleware)) {
            continue;
        }

        list($name) = $this->parseMiddleware($middleware);

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

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

此处的中间件指的是定义在 Kernel 中的 $middleware 中间件数组列表, 不包含路由中间件.

Laravel 5.1 注: 默认只有会话中间件包含 terminate() 函数

Application 服务容器的停止处理函数

public function terminate()
{
    foreach ($this->terminatingCallbacks as $terminating) {
        $this->call($terminating);
    }
}