Response

前面两节我们分别讲了Laravel的控制器和Request对象，在讲Request对象的那一节我们看了Request对象是如何被创建出来的以及它支持的方法都定义在哪里，讲控制器时我们详细地描述了如何找到Request对应的控制器方法然后执行处理程序的，本节我们就来说剩下的那一部分，控制器方法的执行结果是如何被转换成响应对象Response然后返回给客户端的。

创建Response

让我们回到Laravel执行路由处理程序返回响应的代码块:

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;//收集路由和控制器里应用的中间件$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());});}
}

在讲控制器的那一节里我们已经提到过runRouteWithinStack方法里是最终执行路由处理程序(控制器方法或者闭包处理程序)的地方，通过上面的代码我们也可以看到执行的结果会传递给Router的prepareResponse方法，当程序流返回到runRoute里后又执行了一次prepareResponse方法得到了要返回给客户端的Response对象， 下面我们就来详细看一下prepareResponse方法。

class Router implements RegistrarContract, BindingRegistrar
{/*** 通过给定值创建Response对象** @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);}
}

在上面的代码中我们看到有三种Response:

通过prepareResponse中的逻辑可以看到，无论路由执行结果返回的是什么值最终都会被Laravel转换为成一个Response对象，而这些对象都是SymfonyComponentHttpFoundationResponse类或者其子类的对象。从这里也就能看出来跟Request一样Laravel的Response也是依赖Symfony框架的HttpFoundation组件来实现的。

nodejs redis，我们来看一下SymfonyComponentHttpFoundationResponse的构造方法：

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');}//设置响应的Contentpublic 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;}
}

所以路由处理程序的返回值在创业Response对象时会设置到对象的content属性里，该属性的值就是返回给客户端的响应的响应内容。

设置Response headers

生成Response对象后就要执行对象的prepare方法了，该方法定义在Symfony\Component\HttpFoundation\Resposne类中，其主要目的是对Response进行微调使其能够遵从HTTP/1.1协议（RFC 2616）。

namespace Symfony\Component\HttpFoundation;
class Response
{//在响应被发送给客户端之前对其进行修订使其能遵从HTTP/1.1协议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 Requestif (!$headers->has('Content-Type')) {$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-Lengthif ($headers->has('Transfer-Encoding')) {$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 protocolif ('HTTP/1.0' != $request->server->get('SERVER_PROTOCOL')) {$this->setProtocolVersion('1.1');}// Check if we need to send extra expire info headersif ('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;}
}

prepare里针对各种情况设置了相应的response header 比如Content-Type、Content-Length等等这些我们常见的首部字段。

发送Response

创建并设置完Response后它会流经路由和框架中间件的后置操作，在中间件的后置操作里一般都是对Response进行进一步加工，最后程序流回到Http Kernel那里， Http Kernel会把Response发送给客户端，我们来看一下这部分的代码。

//入口文件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);

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;}//发送headers到客户端public function sendHeaders(){// headers have already been sent by the developerif (headers_sent()) {return $this;}// headersforeach ($this->headers->allPreserveCaseWithoutCookies() as $name => $values) {foreach ($values as $value) {header($name.': '.$value, false, $this->statusCode);}}// statusheader(sprintf('HTTP/%s %s %s', $this->version, $this->statusCode, $this->statusText), true, $this->statusCode);// cookiesforeach ($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;}//发送响应内容到客户端public function sendContent(){echo $this->content;return $this;}
}

send的逻辑就非常好理解了，把之前设置好的那些headers设置到HTTP响应的首部字段里，Content会echo后被设置到HTTP响应的主体实体中。最后PHP会把完整的HTTP响应发送给客户端。

laravel 前端、send响应后Http Kernel会执行terminate方法调用terminate中间件里的terminate方法，最后执行应用的termiate方法来结束整个应用生命周期(从接收请求开始到返回响应结束)。

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