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:
| Class Name | Representation |
|---|---|
| PsrResponseInterface(PsrHttpMessageResponseInterface的别名) | Psr规范中对服务端响应的定义 |
| IlluminateHttpJsonResponse (SymfonyComponentHttpFoundationResponse的子类) | Laravel中对服务端JSON响应的定义 |
| IlluminateHttpResponse (SymfonyComponentHttpFoundationResponse的子类) | Laravel中对普通的非JSON响应的定义 |
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。
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;
}
}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');
$headers->remove('Content-Length');
} else {
// Content-type based on the Request
if (!$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;
}
}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 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;
}
//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。
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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