Laravel核心程式碼學習 -- 響應 Response

kevinyan發表於2018-05-28
Laravel

Response

前面兩節我們分別講了Laravel的控制器和Request物件，在講Request物件的那一節我們看了Request物件是如何被建立出來的以及它支援的方法都定義在哪裡，講控制器時我們詳細地描述瞭如何找到Request對應的控制器方法然後執行處理程式的，本節我們就來說剩下的那一部分，控制器方法的執行結果是如何被轉換成響應物件Response然後返回給客戶端的。

建立Response

讓我們回到Laravel執行路由處理程式返回響應的程式碼塊:

namespace Illuminate\Routing;
class Router implements RegistrarContract, BindingRegistrar
{	 
    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)
        );
    }
    
    protected function runRouteWithinStack(Route $route, Request $request)
    {
        $shouldSkipMiddleware = $this->container->bound('middleware.disable') &&
                            $this->container->make('middleware.disable') === true;
        //收集路由和控制器裡應用的中介軟體
        $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()
                        );
                    });
    
    }
}
複製程式碼

在講控制器的那一節裡我們已經提到過runRouteWithinStack方法裡是最終執行路由處理程式(控制器方法或者閉包處理程式)的地方，通過上面的程式碼我們也可以看到執行的結果會傳遞給Router的prepareResponse方法，當程式流返回到runRoute裡後又執行了一次prepareResponse方法得到了要返回給客戶端的Response物件， 下面我們就來詳細看一下prepareResponse方法。

class Router implements RegistrarContract, BindingRegistrar
{
    /**
     * 通過給定值建立Response物件
     *
     * @param  \Symfony\Component\HttpFoundation\Request  $request
     * @param  mixed  $response
     * @return \Illuminate\Http\Response|\Illuminate\Http\JsonResponse
     */
    public function prepareResponse($request, $response)
    {
        return static::toResponse($request, $response);
    }
    
    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);
    }
}
複製程式碼

在上面的程式碼中我們看到有三種Response:

Class Name Representation
PsrResponseInterface(Psr\Http\Message\ResponseInterface的別名) Psr規範中對服務端響應的定義
Illuminate\Http\JsonResponse (Symfony\Component\HttpFoundation\Response的子類) Laravel中對服務端JSON響應的定義
Illuminate\Http\Response (Symfony\Component\HttpFoundation\Response的子類) Laravel中對普通的非JSON響應的定義

通過prepareResponse中的邏輯可以看到，無論路由執行結果返回的是什麼值最終都會被Laravel轉換為成一個Response物件，而這些物件都是Symfony\Component\HttpFoundation\Response類或者其子類的物件。從這裡也就能看出來跟Request一樣Laravel的Response也是依賴Symfony框架的HttpFoundation元件來實現的。

我們來看一下Symfony\Component\HttpFoundation\Response的構造方法：

namespace Symfony\Component\HttpFoundation;
class Response
{
    public function __construct($content = '', $status = 200, $headers = array())
    {
        $this->headers = new ResponseHeaderBag($headers);
        $this->setContent($content);
        $this->setStatusCode($status);
        $this->setProtocolVersion('1.0');
    }
    //設定響應的Content
    public function setContent($content)
    {
        if (null !== $content && !is_string($content) && !is_numeric($content) && !is_callable(array($content, '__toString'))) {
            throw new \UnexpectedValueException(sprintf('The Response content must be a string or object implementing __toString(), "%s" given.', gettype($content)));
        }

        $this->content = (string) $content;

        return $this;
    }
}
複製程式碼

所以路由處理程式的返回值在創業Response物件時會設定到物件的content屬性裡，該屬性的值就是返回給客戶端的響應的響應內容。

設定Response headers

生成Response物件後就要執行物件的prepare方法了，該方法定義在Symfony\Component\HttpFoundation\Resposne類中，其主要目的是對Response進行微調使其能夠遵從HTTP/1.1協議（RFC 2616）。

namespace Symfony\Component\HttpFoundation;
class Response
{
    //在響應被髮送給客戶端之前對其進行修訂使其能遵從HTTP/1.1協議
    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;
    }
}
複製程式碼

prepare裡針對各種情況設定了相應的response header 比如Content-Type、Content-Length等等這些我們常見的首部欄位。

傳送Response

建立並設定完Response後它會流經路由和框架中介軟體的後置操作，在中介軟體的後置操作裡一般都是對Response進行進一步加工，最後程式流回到Http Kernel那裡， Http Kernel會把Response傳送給客戶端，我們來看一下這部分的程式碼。

//入口檔案public/index.php
$kernel = $app->make(Illuminate\Contracts\Http\Kernel::class);

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

$response->send();

$kernel->terminate($request, $response);
複製程式碼
namespace Symfony\Component\HttpFoundation;
class Response
{
    public function send()
    {
        $this->sendHeaders();
        $this->sendContent();

        if (function_exists('fastcgi_finish_request')) {
            fastcgi_finish_request();
        } elseif ('cli' !== PHP_SAPI) {
            static::closeOutputBuffers(0, true);
        }

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

        // headers
        foreach ($this->headers->allPreserveCaseWithoutCookies() 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);

        // cookies
        foreach ($this->headers->getCookies() as $cookie) {
            if ($cookie->isRaw()) {
                setrawcookie($cookie->getName(), $cookie->getValue(), $cookie->getExpiresTime(), $cookie->getPath(), $cookie->getDomain(), $cookie->isSecure(), $cookie->isHttpOnly());
            } else {
                setcookie($cookie->getName(), $cookie->getValue(), $cookie->getExpiresTime(), $cookie->getPath(), $cookie->getDomain(), $cookie->isSecure(), $cookie->isHttpOnly());
            }
        }

        return $this;
    }
    
    //傳送響應內容到客戶端
    public function sendContent()
    {
        echo $this->content;

        return $this;
    }
}
複製程式碼

send的邏輯就非常好理解了，把之前設定好的那些headers設定到HTTP響應的首部欄位裡，Content會echo後被設定到HTTP響應的主體實體中。最後PHP會把完整的HTTP響應傳送給客戶端。

send響應後Http Kernel會執行terminate方法呼叫terminate中介軟體裡的terminate方法，最後執行應用的termiate方法來結束整個應用生命週期(從接收請求開始到返回響應結束)。

本文已經收錄在系列文章Laravel核心學習指南裡，歡迎訪問閱讀。

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