Write-through caching of session data

CachedPdoSessionStorage.php

<?php

use PDO;
use Symfony\Component\HttpFoundation\SessionStorage\NativeSessionStorage;

/**
 * CachedPdoSessionStorage.
 *
 * @author Jose Prado <pradador@me.com>
 */
class CachedPdoSessionStorage extends NativeSessionStorage
{
    /**
     * Default refresh time of 300 seconds (5 minutes)
     * 
     * @var int
     */
    const REFRESH_TIME = 3600;
    
    /**
     * @var PDO
     */
    protected $_db;
    
    /**
     * @var CacheInterface
     */
    protected $_cache;
    
    /**
     * @var array
     */
    protected $dbOptions;
    
    /**
     * @var int
     */
    protected $lifetime;
    
    protected $initialSessionId;
    
    /**
     * @var array
     */
    protected $initialSessionData;
    
	/**
     * Constructor.
     * 
     * @param CacheInterface $cache     A CacheInterface instance
     * @param PDO            $db        A PDO instance
     * @param array          $options   Optional options array
     * @param array          $dbOptions Optional DB options array
     */
    public function __construct(CacheInterface $cache, PDO $db, array $options = array(), array $dbOptions = array())
    {
        if (!array_key_exists('db_table', $dbOptions)) {
            throw new \InvalidArgumentException('You must provide the "db_table" option for a PdoSessionStorage.');
        }
        
        $this->_cache = $cache;
        $this->_db = $db;
        $this->lifetime = intval(ini_get("session.gc_maxlifetime"));
        
        $options = array_merge(array(
        	'refresh_time' => self::REFRESH_TIME
        ), $options);
        
        $this->dbOptions = array_merge(array(
            'db_id_col'   => 'sess_id',
            'db_data_col' => 'sess_data',
            'db_time_col' => 'sess_time',
        ), $dbOptions);
        
        parent::__construct($options);
    }

    /**
     * Starts the session.
     */
    public function start()
    {
        if (self::$sessionStarted) {
            return;
        }
        
        // use this object as the session handler
        session_set_save_handler(
            array($this, 'sessionOpen'),
            array($this, 'sessionClose'),
            array($this, 'sessionRead'),
            array($this, 'sessionWrite'),
            array($this, 'sessionDestroy'),
            array($this, 'sessionGC')
        );
        
        return parent::start();
    }
    
    /**
     * Reads initial session data if a session exists and stores it for
     * later comparison.
     */
    public function sessionOpen($path = null, $name = null)
    {
        $id = session_id();
        
        if ($id != '') {
            $this->initialSessionId = $id;
            $this->initialSessionData = $this->sessionRead($id);
        }
        
        return TRUE;
    }
    
    /**
     * Unsets all object data.
     */
    public function sessionClose()
    {
        return TRUE;
    }
    
    /**
     * Destroys a session.
     *
     * @param  string $id  A session ID
     * @return Boolean   true, if the session was destroyed, otherwise an exception is thrown
     * @throws RuntimeException If the session cannot be destroyed
     */
    public function sessionDestroy($id)
    {
        $this->_cache->delete($id);
        $this->_cache->delete('db-'.$id);
        
        // get table/column
        $dbTable = $this->dbOptions['db_table'];
        $dbIdCol = $this->dbOptions['db_id_col'];
        
        // delete the record associated with this id
        $sql = "DELETE FROM $dbTable WHERE $dbIdCol = :id";

        try {
            $stmt = $this->_db->prepare($sql);
            $stmt->bindParam(':id', $id, \PDO::PARAM_STR);
            $stmt->execute();
        } catch (\PDOException $e) {
            throw new \RuntimeException(sprintf('PDOException was thrown when trying to manipulate session data: %s', $e->getMessage()), 0, $e);
        }

        return TRUE;
    }
    
    /**
     * Cached sessions expire automatically so we just need to evict all expired
     * DB sessions.
     * 
     * @param  int $lifetime  The lifetime of a session
     * @return Boolean true, if old sessions have been cleaned, otherwise an exception is thrown
     * @throws RuntimeException If any old sessions cannot be cleaned
     */
    public function sessionGC($lifetime)
    {
        // get table/column
        $dbTable   = $this->dbOptions['db_table'];
        $dbTimeCol = $this->dbOptions['db_time_col'];

        // delete the record associated with this id
        $sql = "DELETE FROM $dbTable WHERE $dbTimeCol < (:time - $lifetime)";

        try {
            $this->_db->query($sql);
            $stmt = $this->_db->prepare($sql);
            $stmt->bindValue(':time', time(), \PDO::PARAM_INT);
            $stmt->execute();
        } catch (\PDOException $e) {
            throw new \RuntimeException(sprintf('PDOException was thrown when trying to manipulate session data: %s', $e->getMessage()), 0, $e);
        }

        return TRUE;
    }
    
    /**
     * Reads the session data from either the cache or the DB in case of
     * a miss. Then updates the database expiration time based on the time
     * since the last DB access.
     *  
     * @see Symfony\Component\HttpFoundation\SessionStorage.PdoSessionStorage::sessionRead()
     */
    public function sessionRead($id)
    {
        $now = time();
        $data = $this->_cache->get($id);
        
        if ($data === FALSE) {
            
            $dbTable   = $this->dbOptions['db_table'];
            $dbDataCol = $this->dbOptions['db_data_col'];
            $dbIdCol   = $this->dbOptions['db_id_col'];
    
            try {
                
                $sql = "SELECT $dbDataCol FROM $dbTable WHERE $dbIdCol = :id";
    
                $stmt = $this->_db->prepare($sql);
                $stmt->bindParam(':id', $id, \PDO::PARAM_STR, 255);
                $stmt->execute();
                
                $sessionRows = $stmt->fetchAll(\PDO::FETCH_NUM);
                
                // If session is found, update the time value, otherwise create
                // a new session.
                if (count($sessionRows) == 1) {
                    $data = $sessionRows[0][0];
                    $this->updateSessionTime($id, $now);
                } else {
                    $data = '';
                    $this->createNewSession($id);
                }
                
            } catch (\PDOException $e) {
                throw new \RuntimeException(sprintf('PDOException was thrown when trying to manipulate session data: %s', $e->getMessage()), 0, $e);
            }
            
        } else {
            
            $expiration = $this->_cache->get('db-'.$id);
            
			if ($expiration === FALSE || $now - $this->options['refresh_time'] > $expiration - $this->lifetime) {
				$this->updateSessionTime($id, $now);
			}
        }
        
        $this->_cache->set($id, $data, $this->lifetime);
        
        return $data;
    }
    
    /**
     * Writes the session data to the cache and the DB and updates the
     * last db update record.
     * 
     * @param  string $id    A session ID
     * @param  string $data  A serialized chunk of session data
     * @return Boolean true, if the session was written, otherwise an exception is thrown
     * @throws \RuntimeException If the session data cannot be written
     */
    public function sessionWrite($id, $data)
    {
        $retVal = $this->_cache->set($id, $data, $this->lifetime);
        
        if ($this->initialSessionId !== $id || $this->initialSessionData !== $data) {
            
            // get table/column
            $dbTable   = $this->dbOptions['db_table'];
            $dbDataCol = $this->dbOptions['db_data_col'];
            $dbIdCol   = $this->dbOptions['db_id_col'];
            $dbTimeCol = $this->dbOptions['db_time_col'];
            
            switch ($this->_db->getAttribute(\PDO::ATTR_DRIVER_NAME)) {
                case 'mysql':
                    $sql  = "INSERT INTO $dbTable ($dbIdCol, $dbDataCol, $dbTimeCol) VALUES (:id, :data, :time)";
                    $sql .= " ON DUPLICATE KEY UPDATE $dbDataCol = VALUES($dbDataCol),";
                    $sql .= " $dbTimeCol = CASE WHEN $dbTimeCol = :time THEN (VALUES($dbTimeCol) + 1)";
                    $sql .= " ELSE VALUES($dbTimeCol) END";
	                break;
	                
                default:
                    $sql = "UPDATE $dbTable SET $dbDataCol = :data, $dbTimeCol = :time WHERE $dbIdCol = :id";
                    break;
            }
            
            try {
                $stmt = $this->_db->prepare($sql);
                $stmt->bindParam(':id', $id, \PDO::PARAM_STR);
                $stmt->bindParam(':data', $data, \PDO::PARAM_STR);
                $stmt->bindValue(':time', time(), \PDO::PARAM_INT);
                $stmt->execute();
    
                if (!$stmt->rowCount()) {
                    // No session exists in the database to update. This happens when we have called
                    // session_regenerate_id()
                    $this->createNewSession($id, $data);
                }
            } catch (\PDOException $e) {
                throw new \RuntimeException(sprintf('PDOException was thrown when trying to manipulate session data: %s', $e->getMessage()), 0, $e);
            }
            
            $expiration = time() + $this->lifetime;
            $this->_cache->set('db-'.$id, $expiration, $this->lifetime);
        }
        
        return $retVal;
    }

    /**
     * Creates a new session with the given $id and $data
     *
     * @param string $id
     * @param string $data
     */
    public function createNewSession($id, $data = '')
    {
        // get table/column
        $dbTable   = $this->dbOptions['db_table'];
        $dbDataCol = $this->dbOptions['db_data_col'];
        $dbIdCol   = $this->dbOptions['db_id_col'];
        $dbTimeCol = $this->dbOptions['db_time_col'];

        $sql = "INSERT INTO $dbTable ($dbIdCol, $dbDataCol, $dbTimeCol) VALUES (:id, :data, :time)";

        $stmt = $this->_db->prepare($sql);
        $stmt->bindParam(':id', $id, \PDO::PARAM_STR);
        $stmt->bindParam(':data', $data, \PDO::PARAM_STR);
        $stmt->bindValue(':time', time(), \PDO::PARAM_INT);
        $stmt->execute();

        return true;
    }
    
    /**
     * Updates the time of the session in the database and refreshes the last
     * DB access value in the cache.
     * 
     * @param integer $id  The session id to update.
     * @param integer $now Optional time to use.
     * @return Boolean true, if the session time was updated or no session was found. Otherwise exception is thrown.
     */
    public function updateSessionTime($id, $now = NULL)
    {
        if ($now === NULL) {
            $now = time();
        }
        
        $dbTable   = $this->dbOptions['db_table'];
        $dbTimeCol = $this->dbOptions['db_time_col'];
        $dbIdCol   = $this->dbOptions['db_id_col'];
        
        try {
            
            $sql = "UPDATE $dbTable SET $dbTimeCol = :time WHERE $dbIdCol = :id";
            
            $stmt = $this->_db->prepare($sql);
            $stmt->bindValue(':time', time(), \PDO::PARAM_INT);
            $stmt->bindParam(':id', $id, \PDO::PARAM_STR);
            $stmt->execute();
            
        } catch (\PDOException $e) {
            throw new \RuntimeException(sprintf('PDOException was thrown when trying to manipulate session data: %s', $e->getMessage()), 0, $e);
        }
        
        $expiration = $now + $this->lifetime;
        $this->_cache->set('db-'.$id, $expiration, $this->lifetime);
        
        return TRUE;
    }
}

CacheInterface.php

<?php

/**
 * Cache interface to provide a uniform interface for the SessionStorage classes.
 *  
 * @author Jose Prado <pradador@me.com>
 */
interface CacheInterface
{
    /**
     * Retrieves an entry from the cache.
     * 
     * @param string $id The id to retrieve
     * @return mixed The data found or FALSE if cache miss
     */
    public function get($id);
    
    /**
     * Stores an entry in the cache using the supplied id and data.
     * 
     * @param string  $id       The cache id
     * @param mixed   $data     The data to store
     * @param integer $lifetime The lifetime of the record.
     * @return Boolean Whether or not the item was stored in the cache.
     */
    public function set($id, $data, $lifetime);
    
    /**
     * Deletes an entry from the cache.
     * 
     * @param string $id The cache id to delete.
     * @return Boolean Whether or not the item was deleted.
     */
    public function delete($id);
}

MemcacheAdapter.php

<?php

/**
 * MemcacheAdapter
 * 
 * @author Jose Prado <pradador@me.com>
 */
class MemcacheAdapter implements CacheInterface
{
    /**
     * @var Memcache
     */
    protected $_cache;
    
    /**
     * Constructor.
     * 
     * @param Memcache $cache A Memcache instance
     */
    public function __construct(\Memcache $cache)
    {
        $this->setCache($cache);
    }
    
    /**
     * @return Memcache
     */
    public function getCache()
    {
        return $this->_cache;
    }
    
    /**
     * @param Memcache $cache
     */
    public function setCache(\Memcache $cache)
    {
        $this->_cache = $cache;
        
        return $this;
    }
    
    /**
     * @see CacheInterface::get()
     */
    public function get($id)
    {
        return $this->_cache->get($id);
    }
    
    /**
     * @see CacheInterface::set()
     */
    public function set($id, $data, $lifetime)
    {
        return $this->_cache->set($id, $data, FALSE, $lifetime);
    }
    
    /**
     * @see CacheInterface::delete()
     */
    public function delete($id)
    {
        return $this->_cache->delete($id);
    }
}

MemcachedAdapter.php

<?php

/**
 * MemcachedAdapter
 * 
 * @author Jose Prado <pradador@me.com>
 */
class MemcachedAdapter implements CacheInterface
{
    /**
     * @var Memcached
     */
    protected $_cache;
    
    /**
     * Constructor.
     * 
     * @param Memcached $cache A Memcached instance
     */
    public function __construct(\Memcached $cache)
    {
        $this->setCache($cache);
    }
    
    /**
     * @return Memcached
     */
    public function getCache()
    {
        return $this->_cache;
    }
    
    /**
     * @param Memcached $cache
     */
    public function setCache(\Memcached $cache)
    {
        $this->_cache = $cache;
        
        return $this;
    }
    
    /**
     * @see CacheInterface::get()
     */
    public function get($id)
    {
        return $this->_cache->get($id);
    }
    
    /**
     * @see CacheInterface::set()
     */
    public function set($id, $data, $lifetime)
    {
        return $this->_cache->set($id, $data, $lifetime);
    }
    
    /**
     * @see CacheInterface::delete()
     */
    public function delete($id)
    {
        return $this->_cache->delete($id);
    }
}