Laravel 的 Session机制简介

2018-05-28 后端
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Kernel.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 
publicfunctionhandle($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：IlluminateSessionSessionManager 
/**  
 * Get the session implementation from the manager.  
 *  * @param  IlluminateHttpRequest $request 
 * @return IlluminateSessionSessionInterface 
 */publicfunctiongetSession(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 $driver 
     * @return mixed 
     */publicfunctiondriver($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 $driver * @return mixed  * 
     * * @throws InvalidArgumentException 
     */protectedfunctioncreateDriver($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->$method();
        }thrownew InvalidArgumentException("Driver [$driver] not supported.");
    }
也就是调用getDefaultDriver方法 
/**  * Get the default session driver name.  *  * @return string */publicfunctiongetDefaultDriver(){return$this->app['config']['session.driver'];
    }
这里就是我们在app/config/session.php中定义的driver字段，获取这个字段后，我们可以从createDriver的源码看到
，它实际上是调用createXXXXDriver的方式获取到driver的。 OK，我们看下最简单的File，也就是createFileDriver 
/**  * Create an instance of the file session driver.  
     *  * @return IlluminateSessionStore
     * */protectedfunctioncreateFileDriver(){return$this->createNativeDriver();
    }/**  * Create an instance of the file session driver.  
     *  * @return IlluminateSessionStore 
     */protectedfunctioncreateNativeDriver(){$path = $this->app['config']['session.files'];return$this->buildSession(new FileSessionHandler($this->app['files'], $path));
    }/**  * Build the session instance.  
     *  * @param  SessionHandlerInterface $handler * @return IlluminateSessionStore 
     */protectedfunctionbuildSession($handler){if ( $this->app['config']['session.encrypt'] ) {returnnew EncryptedStore($this->app['config']['session.cookie'], $handler, $this->app['encrypter']);
        } else {returnnew Store($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$session->start();，这句话是干嘛呢？经过前面的分析，我们知道`$sessi
on已经是Store对象了，那么它的start`方法如下： 
publicfunctionstart(){$this->loadSession();if ( !$this->has('_token') ) {$this->regenerateToken();
        }return$this->started = true;
    }/**  * Load the session data from the handler.  *  * @return void */protectedfunctionloadSession(){$this->attributes = array_merge($this->attributes, $this->readFromHandler());foreach ( array_merge($this->bags, [$this->metaBag]) as$bag ) {$this->initializeLocalBag($bag);$bag->initialize($this->bagData[ $bag->getStorageKey() ]);
        }
    }/**  * Read the session data from the handler.  *  * @return array */protectedfunctionreadFromHandler(){$data = $this->handler->read($this->getId());if ( $data ) {$data = @unserialize($this->prepareForUnserialize($data));if ( $data !== false&& $data !== null&& is_array($data) ) {return$data;
            }
        }return [];
    }
依次调用了loadSession和readFromHandler好，可以看到从handler中调用了read方法，这个方法就是从我们之前定
义的各种handler中读取数据了，它是个抽象方法，在子类中具体实现，然后返回给Store（存入到Store中的attributes数组中去了，
到此为止，Session的初始化方法都结束了， 
publicfunctionget($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`Sess
ion`共享的目的也可以达到~