Laravel 的 Session机制简介

前些天，为了解答一个问题，就去研究了Laravel的源码，讲讲我的收获：
这个是问题源：
http://segmentfault.com/q/1010000003776645?_ea=365137

本文讲的Laravel全部使用5.1版本。

我们首先看Laravel是如何创建Session组件的。
首先我们可以看见在Kernerl.php中注册了StartSession这个类（这里不去讨论Laravel的DI和IoC），看下这个类是如何使用的。

Session Start

我们在这个类中的handle方法看到如下代码

public function handle($request, Closure $next){    $this->sessionHandled = true;    // If a session driver has been configured, we will need to start the session here    // so that the data is ready for an application. Note that the Laravel sessions    // do not make use of PHP "native" sessions in any way since they are crappy.    if ($this->sessionConfigured()) {        $session = $this->startSession($request);        $request->setSession($session);    }    $response = $next($request);    // Again, if the session has been configured we will need to close out the session    // so that the attributes may be persisted to some storage medium. We will also    // add the session identifier cookie to the application response headers now.    if ($this->sessionConfigured()) {        $this->storeCurrentUrl($request, $session);        $this->collectGarbage($session);        $this->addCookieToResponse($response, $session);    }    return $response;}

OK，一个典型的过滤器，在这个StartSession中获取Session的方法是getSession。

Get Session

它使用了Laravel注入的SessionManager 这个类的完整限定名是：\Illuminate\Session\SessionManager

/** * Start the session for the given request. * * @param  \Illuminate\Http\Request  $request * @return \Illuminate\Session\SessionInterface */protected function startSession(Request $request){    with($session = $this->getSession($request))->setRequestOnHandler($request);    $session->start();    return $session;}/** * Get the session implementation from the manager. * * @param  \Illuminate\Http\Request  $request * @return \Illuminate\Session\SessionInterface */public function getSession(Request $request){    $session = $this->manager->driver();    $session->setId($request->cookies->get($session->getName()));    return $session;}

我们在这个函数中看到，它调用了SessionManager的drive方法，drive方法是SessionManager的父类Manager中定义的，看到它的实现是这样的

/** * Get a driver instance. * * @param  string  $driver * @return mixed */public function driver($driver = null){    $driver = $driver ?: $this->getDefaultDriver();    // If the given driver has not been created before, we will create the instances    // here and cache it so we can return it next time very quickly. If there is    // already a driver created by this name, we'll just return that instance.    if (! isset($this->drivers[$driver])) {        $this->drivers[$driver] = $this->createDriver($driver);    }    return $this->drivers[$driver];}/** * Create a new driver instance. * * @param  string  $driver * @return mixed * * @throws \InvalidArgumentException */protected function createDriver($driver){    $method = 'create'.ucfirst($driver).'Driver';    // We'll check to see if a creator method exists for the given driver. If not we    // will check for a custom driver creator, which allows developers to create    // drivers using their own customized driver creator Closure to create it.    if (isset($this->customCreators[$driver])) {        return $this->callCustomCreator($driver);    } elseif (method_exists($this, $method)) {        return $this->$method();    }    throw new InvalidArgumentException("Driver [$driver] not supported.");}

也就是调用getDefaultDriver方法

/** * Get the default session driver name. * * @return string */public function getDefaultDriver(){    return $this->app['config']['session.driver'];}

这里就是我们在app/config/session.php中定义的driver字段，获取这个字段后，我们可以从createDriver的源码看到，它实际上是调用createXXXXDriver的方式获取到driver的。

OK，我们看下最简单的File，也就是createFileDriver

/** * Create an instance of the file session driver. * * @return \Illuminate\Session\Store */protected function createFileDriver(){    return $this->createNativeDriver();}/** * Create an instance of the file session driver. * * @return \Illuminate\Session\Store */protected function createNativeDriver(){    $path = $this->app['config']['session.files'];    return $this->buildSession(new FileSessionHandler($this->app['files'], $path));}/** * Build the session instance. * * @param  \SessionHandlerInterface  $handler * @return \Illuminate\Session\Store */protected function buildSession($handler){    if ($this->app['config']['session.encrypt']) {        return new EncryptedStore(            $this->app['config']['session.cookie'], $handler, $this->app['encrypter']        );    } else {        return new Store($this->app['config']['session.cookie'], $handler);    }}

这个Store就是我们Session的实体了，它的具体读写调用使用抽象的Handler进行，也就是说如果是读文件，就new FileHandler如果是Redis就是new RedisHandler实现read和write即可。

Session ID

回到StartSession 这个类，我们再看getSession这个方法

 $session->setId($request->cookies->get($session->getName()));

了解Web的人都应该知道，session是根据cookie中存的key来区分不同的会话的，所以sessionId尤为重要，这里我们先不关心Cookie是如何读取，我们知道在这里读取了cookie中存放的SessionId就够了。

接下去看怎么加载数据

Data

依然是StartSession这个类，
我们看startSession这个方法，下一句调用的就是$session->start();，这句话是干嘛呢？经过前面的分析，我们知道$session已经是Store对象了，那么它的start方法如下：

public function start(){    $this->loadSession();    if (! $this->has('_token')) {        $this->regenerateToken();    }    return $this->started = true;}/** * Load the session data from the handler. * * @return void */protected function loadSession(){    $this->attributes = array_merge($this->attributes, $this->readFromHandler());    foreach (array_merge($this->bags, [$this->metaBag]) as $bag) {        $this->initializeLocalBag($bag);        $bag->initialize($this->bagData[$bag->getStorageKey()]);    }} /** * Read the session data from the handler. * * @return array */protected function readFromHandler(){    $data = $this->handler->read($this->getId());    if ($data) {        $data = @unserialize($this->prepareForUnserialize($data));        if ($data !== false && $data !== null && is_array($data)) {            return $data;        }    }    return [];}

依次调用了loadSession和readFromHandler 好，可以看到从handler中调用了read方法，这个方法就是从我们之前定义的各种handler中读取数据了，它是个抽象方法，在子类中具体实现，然后返回给Store（存入到Store中的attributes数组中去了，到此为止，Session的初始化方法都结束了，

public function get($name, $default = null){    return Arr::get($this->attributes, $name, $default);}

这个函数去读取Session中的数据了。

Summary

OK，Session整个初始化的过程总结下：

StartSession#handle -> StartSession#startSession -> StartSession#getSession -> SessionManager#getDefaultDriver -> SessionManager#createXXXHandler -> Store -> Store#setId -> Store#startSession

Laravel巧妙的使用了面向对象的接口方式，为我们提供了各种各样不同的存储方式，一旦我们了解了存储方式和加密规则，让不同的web容器进行Session共享的目的也可以达到~