sessionwrapper.php

require_once("databasehelper.php");

class SessionException extends Exception
{
    const UNKNOWN = 0;
    const DB_FAIL = 1;
    const NOT_FOUND = 2;

    public function __construct($message, $code = 0, Exception $previous = null)
    {
        parent::__construct($message, $code, $previous);
    }
}

class SessionWrapper
{
    private static $global_session = null;

    public static function startGlobalSession()
    {
        if (SessionWrapper::$global_session == null)
        {
            SessionWrapper::$global_session = new SessionWrapper();
        }
    }

    function __construct()
    {
        $this->startSession();
    }

    function __destruct()
    {

    }

    public function startSession()
    {
        session_set_save_handler(
            array($this, 'open'),
            array($this, 'close'),
            array($this, 'read'),
            array($this, 'write'),
            array($this, 'destroy'),
            array($this, 'gc')
            );

        register_shutdown_function('session_write_close');

        session_start();
    }

    public function open($save_path, $session_name)
    {
        // currently nothing to do for open
        return TRUE;
    }

    public function close()
    {
        // currently nothing to do for close
        return TRUE;
    }

    public function read($session_id)
    {
        try
        {
            $dbh = DatabaseHelper::getInstance();
            $conn = $dbh->getConnection();

            $query = "SELECT us.session_data FROM user_session us WHERE us.session_id = :session_id";

            $pstmt = $conn->prepare($query);
            $pstmt->bindParam(":session_id", $session_id);

            if ($pstmt->execute() == TRUE)
            {
                if ($pstmt->rowCount() == 0)
                {
                    $error_str = "Returned 0 rows. Session doesn't seem to exist.";

                    throw new SessionException($error_str, SessionException::NOT_FOUND);
                }

                else if ($pstmt->rowCount() > 1)
                {
                    $error_str = "Returned more than 1 row. Session ID should be unique.";

                    throw new SessionException($error_str, SessionException::UNKNOWN);
                }

                $row = $pstmt->fetch(PDO::FETCH_ASSOC);

                if ($row === FALSE)
                {
                    $error_arr = $pstmt->errorInfo();
                    $error_str = "Could not fetch row. "
                        . "SQLSTATE code: " . $error_arr[0]
                        . ", Driver code: " . $error_arr[1]
                        . ", Message: " . $error_arr[2];

                    throw new SessionException($error_str, SessionException::QUERY_FAIL);
                }

                $data = $row["session_data"];

                return $data;
            }

            else
            {
                $error_arr = $pstmt->errorInfo();
                $error_str = "Database query execution failed, but didn't throw exception. "
                    . "SQLSTATE code: " . $error_arr[0]
                    . ", Driver code: " . $error_arr[1]
                    . ", Message: " . $error_arr[2];

                throw new SessionException($error_str, SessionException::DB_FAIL);
            }
        }
        catch (DatabaseException $e)
        {
            $error_str = "Database error. Exception received. "
                . "Message: " . $e->getMessage();

            throw new SessionException($error_str, SessionException::DB_FAIL, $e);
        }
        catch (PDOException $e)
        {
            $error_arr = $e->errorInfo;
            $error_str = "Database error. Exception received. "
                . "SQLSTATE code: " . $error_arr[0]
                . ", Driver code: " . $error_arr[1]
                . ", Message: " . $error_arr[2];

            throw new SessionException($error_str, SessionException::DB_FAIL, $e);
        }

        return '';
    }

    public function write($session_id, $data)
    {
        try
        {
            $dbh = DatabaseHelper::getInstance();
            $conn = $dbh->getConnection();

            $exists = FALSE;

            $query = "SELECT us.session_data FROM user_session us WHERE us.session_id = :session_id";

            $pstmt = $conn->prepare($query);
            $pstmt->bindParam(":session_id", $session_id);

            if ($pstmt->execute() == TRUE)
            {
                if ($pstmt->rowCount() == 0)
                {
                    $exists = FALSE;
                }

                else if ($pstmt->rowCount() > 1)
                {
                    $error_str = "Returned more than 1 row. Session ID should be unique.";

                    throw new SessionException($error_str, SessionException::UNKNOWN);
                }

                else
                {
                    $exists = TRUE;
                }
            }
            else
            {
                $error_arr = $pstmt->errorInfo();
                $error_str = "Database query execution failed, but didn't throw exception. "
                    . "SQLSTATE code: " . $error_arr[0]
                    . ", Driver code: " . $error_arr[1]
                    . ", Message: " . $error_arr[2];

                throw new SessionException($error_str, SessionException::DB_FAIL);
            }

            if ($exists == TRUE)
            {
                $query = "UPDATE user_session SET session_id=:session_id, last_request_time=:last_request_time, session_data=:session_data";
            }
            else
            {
                $query = "INSERT INTO user_session (session_id, last_request_time, session_data) "
                    . "VALUES (:session_id, :last_request_time, :session_data)";
            }

            $last_request_time = time();

            $pstmt = $conn->prepare($query);
            $pstmt->bindParam(":session_id", $session_id);
            $pstmt->bindParam(":last_request_time", $last_request_time);
            $pstmt->bindParam(":session_data", $data);

            if ($pstmt->execute() == TRUE)
            {
                return TRUE;
            }
            else
            {
                $error_arr = $pstmt->errorInfo();
                $error_str = "Database query execution failed, but didn't throw exception. "
                    . "SQLSTATE code: " . $error_arr[0]
                    . ", Driver code: " . $error_arr[1]
                    . ", Message: " . $error_arr[2];

                throw new SessionException($error_str, SessionException::DB_FAIL);
            }
        }
        catch (DatabaseException $e)
        {
            $error_str = "Database error. Exception received. "
                . "Message: " . $e->getMessage();

            throw new SessionException($error_str, SessionException::DB_FAIL, $e);
        }
        catch (PDOException $e)
        {
            $error_arr = $e->errorInfo;
            $error_str = "Database error. Exception received. "
                . "SQLSTATE code: " . $error_arr[0]
                . ", Driver code: " . $error_arr[1]
                . ", Message: " . $error_arr[2];

            throw new SessionException($error_str, SessionException::DB_FAIL, $e);
        }

        return FALSE;
    }

    public function destroy($session_id)
    {
        try
        {
            $dbh = DatabaseHelper::getInstance();
            $conn = $dbh->getConnection();

            $query = "DELETE FROM user_session WHERE session_id=:session_id";

            $pstmt = $conn->prepare($query);
            $pstmt->bindParam(":session_id", $session_id);

            if ($pstmt->execute() == TRUE)
            {
                return TRUE;
            }
            else
            {
                $error_arr = $pstmt->errorInfo();
                $error_str = "Database query execution failed, but didn't throw exception. "
                    . "SQLSTATE code: " . $error_arr[0]
                    . ", Driver code: " . $error_arr[1]
                    . ", Message: " . $error_arr[2];

                throw new SessionException($error_str, SessionException::DB_FAIL);
            }
        }
        catch (DatabaseException $e)
        {
            $error_str = "Database error. Exception received. "
                . "Message: " . $e->getMessage();

            throw new SessionException($error_str, SessionException::DB_FAIL, $e);
        }
        catch (PDOException $e)
        {
            $error_arr = $e->errorInfo;
            $error_str = "Database error. Exception received. "
                . "SQLSTATE code: " . $error_arr[0]
                . ", Driver code: " . $error_arr[1]
                . ", Message: " . $error_arr[2];

            throw new SessionException($error_str, SessionException::DB_FAIL, $e);
        }

        return FALSE;
    }

    public function gc($lifetime)
    {
        try
        {
            $dbh = DatabaseHelper::getInstance();
            $conn = $dbh->getConnection();

            $old = time() - $lifetime;

            $query = "DELETE FROM user_session WHERE last_request_time < :old";

            $pstmt = $conn->prepare($query);
            $pstmt->bindParam(":old", $old);

            if ($pstmt->execute() == TRUE)
            {
                return TRUE;
            }
            else
            {
                $error_arr = $pstmt->errorInfo();
                $error_str = "Database query execution failed, but didn't throw exception. "
                    . "SQLSTATE code: " . $error_arr[0]
                    . ", Driver code: " . $error_arr[1]
                    . ", Message: " . $error_arr[2];

                throw new SessionException($error_str, SessionException::DB_FAIL);
            }
        }
        catch (DatabaseException $e)
        {
            $error_str = "Database error. Exception received. "
                . "Message: " . $e->getMessage();

            throw new SessionException($error_str, SessionException::DB_FAIL, $e);
        }
        catch (PDOException $e)
        {
            $error_arr = $e->errorInfo;
            $error_str = "Database error. Exception received. "
                . "SQLSTATE code: " . $error_arr[0]
                . ", Driver code: " . $error_arr[1]
                . ", Message: " . $error_arr[2];

            throw new SessionException($error_str, SessionException::DB_FAIL, $e);
        }

        return FALSE;
    }
}