说明：本文主要通过学习Laravel的session源码学习Laravel是如何设计session的，将自己的学习心得分享出来，希望对别人有所帮助。Laravel在web middleware中定义了session中间件IlluminateSessionMiddlewareStartSession::class，并通过该中间件来设计session，这个中间件的主要工作分为三步：
(1)启动session，通过session handler从一些存储介质如redis中读取session值;
(2)操作session，对session数据CRUD增删改查操作;
(3)关闭session，把session_id写入到response header中，默认是laravel_session。
开发环境：Laravel5.3 PHP7
启动Session
首先看下IlluminateSessionMiddlewareStartSession::class中间件源码中handle()方法：
public function handle($request, Closure $next)
{
// 前置操作
$this->sessionHandled = true;
if ($this->sessionConfigured()) {
// Start session.
/** * @var IlluminateSessionStore $session */
$session = $this->startSession($request);
$request->setSession($session);
$this->collectGarbage($session);
}
$response = $next($request);
// 后置操作
if ($this->sessionConfigured()) {
$this->storeCurrentUrl($request, $session);
$this->addCookieToResponse($response, $session);
}
return $response;
}从Laravel5.2之Middleware源码解析这篇文章中知道，该中间件有前置操作和后置操作。看下sessionConfigured()的源码：
/** * Determine if a session driver has been configured. * * @return bool */
protected function sessionConfigured()
{
// 检查session.php中driver选项是否设置
return ! is_null(Arr::get($this->manager->getSessionConfig(), 'driver'));
}
// IlluminateSessionSessionManager
/** * Get the session configuration. * * @return array */
public function getSessionConfig()
{
return $this->app['config']['session'];
}首先中间件检查session.php中driver选项是否设置，这里假设设置为经常使用的redis作为session的存储介质，并且需要在database.php中设置下redis的链接，本地需要装好redis，通过redis-cli命令查看redis是否已经安装好。OK,然后中间件使用startSession()方法来启动session:
protected function startSession(Request $request)
{
/** * @var IlluminateSessionStore $session */
$session = $this->getSession($request); // 获取session实例，Laravel使用Store类来管理session
$session->setRequestOnHandler($request);
// Load the session data from the store repository by the handler.
$session->start();
return $session;
}
public function getSession(Request $request)
{
/** * Get the session store instance via the driver. * * @var IlluminateSessionStore $session */
$session = $this->manager->driver();
/** * $session->getName() === 'laravel_session' === config('session.cookie') */
$session->setId($request->cookies->get($session->getName()));
return $session;
}startSession()主要分为两步：获取session实例IlluminateSessionStore，主要步骤是session = this->manager->driver();通过该实例从存储介质中读取该次请求所需要的session数据，主要步骤是
代码语言：javascript复制 // IlluminateSupportManager
public function driver($driver = null)
{
// $driver = 'redis'
$driver = $driver ?: $this->getDefaultDriver();
if (! isset($this->drivers[$driver])) {
$this->drivers[$driver] = $this->createDriver($driver);
}
return $this->drivers[$driver];
}
protected function createDriver($driver)
{
$method = 'create'.Str::studly($driver).'Driver';
if (isset($this->customCreators[$driver])) {
return $this->callCustomCreator($driver);
} elseif (method_exists($this, $method)) { // 判断IlluminateSessionSessionManager中是否存在createRedisDriver()方法
// 存在，call这个createRedisDriver()方法
return $this->$method();
}
throw new InvalidArgumentException("Driver [$driver] not supported.");
}
// IlluminateSessionSessionManager
public function getDefaultDriver()
{
// 返回 'redis'
return $this->app['config']['session.driver'];
}从以上源码中很容易知道，选择的driver是redis，最后还是要调用IlluminateSessionSessionManager中的createRedisDriver()方法:
代码语言：javascript复制 protected function createRedisDriver()
{
/** * @var IlluminateSessionCacheBasedSessionHandler $handler */
$handler = $this->createCacheHandler('redis');
// 设置redis连接
$handler->getCache()->getStore()->setConnection($this->app['config']['session.connection']);
return $this->buildSession($handler);
}
protected function createCacheHandler($driver)
{
// $store = 'redis'
$store = $this->app['config']->get('session.store') ?: $driver;
$minutes = $this->app['config']['session.lifetime'];
// $this->app['cache']->store($store)返回IlluminateCacheRepository实例
return new CacheBasedSessionHandler(clone $this->app['cache']->store($store), $minutes);
}
// IlluminateSessionCacheBasedSessionHandler
/** * Get the underlying cache repository. * * @return IlluminateContractsCacheRepository|IlluminateCacheRepository */
public function getCache()
{
return $this->cache;
}
// IlluminateCacheRepository
/** * Get the cache store implementation. * * @return IlluminateContractsCacheStore|RedisStore */
public function getStore()
{
return $this->store;
}
// IlluminateCacheRedisStore
/** * Set the connection name to be used. * * @param string $connection * @return void */
public function setConnection($connection)
{
$this->connection = $connection;
}从以上源码知道获取到IlluminateSessionCacheBasedSessionHandler这个handler后，就可以buildSession()了:
protected function buildSession($handler)
{
// 设置加密的则返回EncryptedStore实例，这里假设没有加密
if ($this->app['config']['session.encrypt']) {
return new EncryptedStore(
$this->app['config']['session.cookie'], $handler, $this->app['encrypter']
);
} else {
// 默认$this->app['config']['session.cookie'] === 'laravel_session'
return new Store($this->app['config']['session.cookie'], $handler);
}
}从源码中可看出session实例就是IlluminateSessionStore实例，并且构造Store类还需要一个重要的部件handler，构造好了session实例后，就可以通过这个handler来从session存储的介质中如redis获取session数据了，这里设置的session driver是redis,所以handler就会是IlluminateSessionCacheBasedSessionHandler。总的来说，现在已经构造好了session实例即IlluminateSessionStore。
然后第二步就是$session->start()从存储介质中加载session数据:
public function start()
{
// 从存储介质中加载session数据
$this->loadSession();
// session存储介质中没有'_token'这个key就生成一个
if (! $this->has('_token')) {
$this->regenerateToken();
}
return $this->started = true;
}关键是loadSession()的源码：
代码语言：javascript复制 // Illuminate/Session/Store
protected function loadSession()
{
// 从redis中读取key为'laravel_session'的数据后存入session实例即Store的$attributes属性中
$this->attributes = array_merge($this->attributes, $this->readFromHandler());
foreach (array_merge($this->bags, [$this->metaBag]) as $bag) {
/** * @var SymfonyComponentHttpFoundationSessionStorageMetadataBag $bag */
$this->initializeLocalBag($bag);
$bag->initialize($this->bagData[$bag->getStorageKey()]);
}
}
protected function readFromHandler()
{
// 主要是这句，通过handler从存储介质redis中读取session数据
// $this->getId() === 'laravel_session'
$data = $this->handler->read($this->getId());
if ($data) {
$data = @unserialize($this->prepareForUnserialize($data));
if ($data !== false && ! is_null($data) && is_array($data)) {
return $data;
}
}
return [];
}这里的handler是IlluminateSessionCacheBasedSessionHandler，看下该handler的read()源码：
// $sessionId === 'laravel_session'
public function read($sessionId)
{
// 这里的cache是IlluminateCacheRepository
return $this->cache->get($sessionId, '');
}
// IlluminateCacheRepository
public function get($key, $default = null)
{
if (is_array($key)) {
return $this->many($key);
}
// 这里的store是IlluminateCacheRedisStore
$value = $this->store->get($this->itemKey($key));
if (is_null($value)) {
$this->fireCacheEvent('missed', [$key]);
$value = value($default);
} else {
$this->fireCacheEvent('hit', [$key, $value]);
}
return $value;
}
// IlluminateCacheRedisStore
public function get($key)
{
if (! is_null($value = $this->connection()->get($this->prefix.$key))) {
return $this->unserialize($value);
}
}通过以上代码，很容易了解从redis存储介质中加载key为'laravel_session'的数据，最后还是调用了RedisStore::get(key, default)方法。
但不管咋样，通过handle()第一步session = this->startSession(
然后就是this->collectGarbage(
总结：本文主要学习了session机制的启动工作中第一步session的实例化，主要包括两步骤：Store的实例化；从redis中读取key为laravel_session的数据。中篇再聊下session垃圾回收，和session的增删改查操作，到时见。
