[Summary view] [Print] [Text view]

   1  <?php
   2  
   3  /*
   4   * This file is part of the Symfony package.
   5   *
   6   * (c) Fabien Potencier <fabien@symfony.com>
   7   *
   8   * For the full copyright and license information, please view the LICENSE
   9   * file that was distributed with this source code.
  10   */
  11  
  12  namespace Symfony\Component\HttpFoundation\Session\Storage\Handler;
  13  
  14  /**
  15   * Session handler using a PDO connection to read and write data.
  16   *
  17   * It works with MySQL, PostgreSQL, Oracle, SQL Server and SQLite and implements
  18   * different locking strategies to handle concurrent access to the same session.
  19   * Locking is necessary to prevent loss of data due to race conditions and to keep
  20   * the session data consistent between read() and write(). With locking, requests
  21   * for the same session will wait until the other one finished writing. For this
  22   * reason it's best practice to close a session as early as possible to improve
  23   * concurrency. PHPs internal files session handler also implements locking.
  24   *
  25   * Attention: Since SQLite does not support row level locks but locks the whole database,
  26   * it means only one session can be accessed at a time. Even different sessions would wait
  27   * for another to finish. So saving session in SQLite should only be considered for
  28   * development or prototypes.
  29   *
  30   * Session data is a binary string that can contain non-printable characters like the null byte.
  31   * For this reason it must be saved in a binary column in the database like BLOB in MySQL.
  32   * Saving it in a character column could corrupt the data. You can use createTable()
  33   * to initialize a correctly defined table.
  34   *
  35   * @see http://php.net/sessionhandlerinterface
  36   *
  37   * @author Fabien Potencier <fabien@symfony.com>
  38   * @author Michael Williams <michael.williams@funsational.com>
  39   * @author Tobias Schultze <http://tobion.de>
  40   */
  41  class PdoSessionHandler implements \SessionHandlerInterface
  42  {
  43      /**
  44       * No locking is done. This means sessions are prone to loss of data due to
  45       * race conditions of concurrent requests to the same session. The last session
  46       * write will win in this case. It might be useful when you implement your own
  47       * logic to deal with this like an optimistic approach.
  48       */
  49      const LOCK_NONE = 0;
  50  
  51      /**
  52       * Creates an application-level lock on a session. The disadvantage is that the
  53       * lock is not enforced by the database and thus other, unaware parts of the
  54       * application could still concurrently modify the session. The advantage is it
  55       * does not require a transaction.
  56       * This mode is not available for SQLite and not yet implemented for oci and sqlsrv.
  57       */
  58      const LOCK_ADVISORY = 1;
  59  
  60      /**
  61       * Issues a real row lock. Since it uses a transaction between opening and
  62       * closing a session, you have to be careful when you use same database connection
  63       * that you also use for your application logic. This mode is the default because
  64       * it's the only reliable solution across DBMSs.
  65       */
  66      const LOCK_TRANSACTIONAL = 2;
  67  
  68      /**
  69       * @var \PDO|null PDO instance or null when not connected yet
  70       */
  71      private $pdo;
  72  
  73      /**
  74       * @var string|false|null DSN string or null for session.save_path or false when lazy connection disabled
  75       */
  76      private $dsn = false;
  77  
  78      /**
  79       * @var string Database driver
  80       */
  81      private $driver;
  82  
  83      /**
  84       * @var string Table name
  85       */
  86      private $table = 'sessions';
  87  
  88      /**
  89       * @var string Column for session id
  90       */
  91      private $idCol = 'sess_id';
  92  
  93      /**
  94       * @var string Column for session data
  95       */
  96      private $dataCol = 'sess_data';
  97  
  98      /**
  99       * @var string Column for lifetime
 100       */
 101      private $lifetimeCol = 'sess_lifetime';
 102  
 103      /**
 104       * @var string Column for timestamp
 105       */
 106      private $timeCol = 'sess_time';
 107  
 108      /**
 109       * @var string Username when lazy-connect
 110       */
 111      private $username = '';
 112  
 113      /**
 114       * @var string Password when lazy-connect
 115       */
 116      private $password = '';
 117  
 118      /**
 119       * @var array Connection options when lazy-connect
 120       */
 121      private $connectionOptions = array();
 122  
 123      /**
 124       * @var int The strategy for locking, see constants
 125       */
 126      private $lockMode = self::LOCK_TRANSACTIONAL;
 127  
 128      /**
 129       * It's an array to support multiple reads before closing which is manual, non-standard usage.
 130       *
 131       * @var \PDOStatement[] An array of statements to release advisory locks
 132       */
 133      private $unlockStatements = array();
 134  
 135      /**
 136       * @var bool True when the current session exists but expired according to session.gc_maxlifetime
 137       */
 138      private $sessionExpired = false;
 139  
 140      /**
 141       * @var bool Whether a transaction is active
 142       */
 143      private $inTransaction = false;
 144  
 145      /**
 146       * @var bool Whether gc() has been called
 147       */
 148      private $gcCalled = false;
 149  
 150      /**
 151       * You can either pass an existing database connection as PDO instance or
 152       * pass a DSN string that will be used to lazy-connect to the database
 153       * when the session is actually used. Furthermore it's possible to pass null
 154       * which will then use the session.save_path ini setting as PDO DSN parameter.
 155       *
 156       * List of available options:
 157       *  * db_table: The name of the table [default: sessions]
 158       *  * db_id_col: The column where to store the session id [default: sess_id]
 159       *  * db_data_col: The column where to store the session data [default: sess_data]
 160       *  * db_lifetime_col: The column where to store the lifetime [default: sess_lifetime]
 161       *  * db_time_col: The column where to store the timestamp [default: sess_time]
 162       *  * db_username: The username when lazy-connect [default: '']
 163       *  * db_password: The password when lazy-connect [default: '']
 164       *  * db_connection_options: An array of driver-specific connection options [default: array()]
 165       *  * lock_mode: The strategy for locking, see constants [default: LOCK_TRANSACTIONAL]
 166       *
 167       * @param \PDO|string|null $pdoOrDsn A \PDO instance or DSN string or null
 168       * @param array            $options  An associative array of options
 169       *
 170       * @throws \InvalidArgumentException When PDO error mode is not PDO::ERRMODE_EXCEPTION
 171       */
 172      public function __construct($pdoOrDsn = null, array $options = array())
 173      {
 174          if ($pdoOrDsn instanceof \PDO) {
 175              if (\PDO::ERRMODE_EXCEPTION !== $pdoOrDsn->getAttribute(\PDO::ATTR_ERRMODE)) {
 176                  throw new \InvalidArgumentException(sprintf('"%s" requires PDO error mode attribute be set to throw Exceptions (i.e. $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION))', __CLASS__));
 177              }
 178  
 179              $this->pdo = $pdoOrDsn;
 180              $this->driver = $this->pdo->getAttribute(\PDO::ATTR_DRIVER_NAME);
 181          } else {
 182              $this->dsn = $pdoOrDsn;
 183          }
 184  
 185          $this->table = isset($options['db_table']) ? $options['db_table'] : $this->table;
 186          $this->idCol = isset($options['db_id_col']) ? $options['db_id_col'] : $this->idCol;
 187          $this->dataCol = isset($options['db_data_col']) ? $options['db_data_col'] : $this->dataCol;
 188          $this->lifetimeCol = isset($options['db_lifetime_col']) ? $options['db_lifetime_col'] : $this->lifetimeCol;
 189          $this->timeCol = isset($options['db_time_col']) ? $options['db_time_col'] : $this->timeCol;
 190          $this->username = isset($options['db_username']) ? $options['db_username'] : $this->username;
 191          $this->password = isset($options['db_password']) ? $options['db_password'] : $this->password;
 192          $this->connectionOptions = isset($options['db_connection_options']) ? $options['db_connection_options'] : $this->connectionOptions;
 193          $this->lockMode = isset($options['lock_mode']) ? $options['lock_mode'] : $this->lockMode;
 194      }
 195  
 196      /**
 197       * Creates the table to store sessions which can be called once for setup.
 198       *
 199       * Session ID is saved in a column of maximum length 128 because that is enough even
 200       * for a 512 bit configured session.hash_function like Whirlpool. Session data is
 201       * saved in a BLOB. One could also use a shorter inlined varbinary column
 202       * if one was sure the data fits into it.
 203       *
 204       * @throws \PDOException    When the table already exists
 205       * @throws \DomainException When an unsupported PDO driver is used
 206       */
 207      public function createTable()
 208      {
 209          // connect if we are not yet
 210          $this->getConnection();
 211  
 212          switch ($this->driver) {
 213              case 'mysql':
 214                  // We use varbinary for the ID column because it prevents unwanted conversions:
 215                  // - character set conversions between server and client
 216                  // - trailing space removal
 217                  // - case-insensitivity
 218                  // - language processing like é == e
 219                  $sql = "CREATE TABLE $this->table ($this->idCol VARBINARY(128) NOT NULL PRIMARY KEY, $this->dataCol BLOB NOT NULL, $this->lifetimeCol MEDIUMINT NOT NULL, $this->timeCol INTEGER UNSIGNED NOT NULL) COLLATE utf8_bin, ENGINE = InnoDB";
 220                  break;
 221              case 'sqlite':
 222                  $sql = "CREATE TABLE $this->table ($this->idCol TEXT NOT NULL PRIMARY KEY, $this->dataCol BLOB NOT NULL, $this->lifetimeCol INTEGER NOT NULL, $this->timeCol INTEGER NOT NULL)";
 223                  break;
 224              case 'pgsql':
 225                  $sql = "CREATE TABLE $this->table ($this->idCol VARCHAR(128) NOT NULL PRIMARY KEY, $this->dataCol BYTEA NOT NULL, $this->lifetimeCol INTEGER NOT NULL, $this->timeCol INTEGER NOT NULL)";
 226                  break;
 227              case 'oci':
 228                  $sql = "CREATE TABLE $this->table ($this->idCol VARCHAR2(128) NOT NULL PRIMARY KEY, $this->dataCol BLOB NOT NULL, $this->lifetimeCol INTEGER NOT NULL, $this->timeCol INTEGER NOT NULL)";
 229                  break;
 230              case 'sqlsrv':
 231                  $sql = "CREATE TABLE $this->table ($this->idCol VARCHAR(128) NOT NULL PRIMARY KEY, $this->dataCol VARBINARY(MAX) NOT NULL, $this->lifetimeCol INTEGER NOT NULL, $this->timeCol INTEGER NOT NULL)";
 232                  break;
 233              default:
 234                  throw new \DomainException(sprintf('Creating the session table is currently not implemented for PDO driver "%s".', $this->driver));
 235          }
 236  
 237          try {
 238              $this->pdo->exec($sql);
 239          } catch (\PDOException $e) {
 240              $this->rollback();
 241  
 242              throw $e;
 243          }
 244      }
 245  
 246      /**
 247       * Returns true when the current session exists but expired according to session.gc_maxlifetime.
 248       *
 249       * Can be used to distinguish between a new session and one that expired due to inactivity.
 250       *
 251       * @return bool Whether current session expired
 252       */
 253      public function isSessionExpired()
 254      {
 255          return $this->sessionExpired;
 256      }
 257  
 258      /**
 259       * {@inheritdoc}
 260       */
 261      public function open($savePath, $sessionName)
 262      {
 263          if (null === $this->pdo) {
 264              $this->connect($this->dsn ?: $savePath);
 265          }
 266  
 267          return true;
 268      }
 269  
 270      /**
 271       * {@inheritdoc}
 272       */
 273      public function read($sessionId)
 274      {
 275          try {
 276              return $this->doRead($sessionId);
 277          } catch (\PDOException $e) {
 278              $this->rollback();
 279  
 280              throw $e;
 281          }
 282      }
 283  
 284      /**
 285       * {@inheritdoc}
 286       */
 287      public function gc($maxlifetime)
 288      {
 289          // We delay gc() to close() so that it is executed outside the transactional and blocking read-write process.
 290          // This way, pruning expired sessions does not block them from being started while the current session is used.
 291          $this->gcCalled = true;
 292  
 293          return true;
 294      }
 295  
 296      /**
 297       * {@inheritdoc}
 298       */
 299      public function destroy($sessionId)
 300      {
 301          // delete the record associated with this id
 302          $sql = "DELETE FROM $this->table WHERE $this->idCol = :id";
 303  
 304          try {
 305              $stmt = $this->pdo->prepare($sql);
 306              $stmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
 307              $stmt->execute();
 308          } catch (\PDOException $e) {
 309              $this->rollback();
 310  
 311              throw $e;
 312          }
 313  
 314          return true;
 315      }
 316  
 317      /**
 318       * {@inheritdoc}
 319       */
 320      public function write($sessionId, $data)
 321      {
 322          $maxlifetime = (int) ini_get('session.gc_maxlifetime');
 323  
 324          try {
 325              // We use a single MERGE SQL query when supported by the database.
 326              $mergeStmt = $this->getMergeStatement($sessionId, $data, $maxlifetime);
 327              if (null !== $mergeStmt) {
 328                  $mergeStmt->execute();
 329  
 330                  return true;
 331              }
 332  
 333              $updateStmt = $this->getUpdateStatement($sessionId, $data, $maxlifetime);
 334              $updateStmt->execute();
 335  
 336              // When MERGE is not supported, like in Postgres < 9.5, we have to use this approach that can result in
 337              // duplicate key errors when the same session is written simultaneously (given the LOCK_NONE behavior).
 338              // We can just catch such an error and re-execute the update. This is similar to a serializable
 339              // transaction with retry logic on serialization failures but without the overhead and without possible
 340              // false positives due to longer gap locking.
 341              if (!$updateStmt->rowCount()) {
 342                  try {
 343                      $insertStmt = $this->getInsertStatement($sessionId, $data, $maxlifetime);
 344                      $insertStmt->execute();
 345                  } catch (\PDOException $e) {
 346                      // Handle integrity violation SQLSTATE 23000 (or a subclass like 23505 in Postgres) for duplicate keys
 347                      if (0 === strpos($e->getCode(), '23')) {
 348                          $updateStmt->execute();
 349                      } else {
 350                          throw $e;
 351                      }
 352                  }
 353              }
 354          } catch (\PDOException $e) {
 355              $this->rollback();
 356  
 357              throw $e;
 358          }
 359  
 360          return true;
 361      }
 362  
 363      /**
 364       * {@inheritdoc}
 365       */
 366      public function close()
 367      {
 368          $this->commit();
 369  
 370          while ($unlockStmt = array_shift($this->unlockStatements)) {
 371              $unlockStmt->execute();
 372          }
 373  
 374          if ($this->gcCalled) {
 375              $this->gcCalled = false;
 376  
 377              // delete the session records that have expired
 378              if ('mysql' === $this->driver) {
 379                  $sql = "DELETE FROM $this->table WHERE $this->lifetimeCol + $this->timeCol < :time";
 380              } else {
 381                  $sql = "DELETE FROM $this->table WHERE $this->lifetimeCol < :time - $this->timeCol";
 382              }
 383  
 384              $stmt = $this->pdo->prepare($sql);
 385              $stmt->bindValue(':time', time(), \PDO::PARAM_INT);
 386              $stmt->execute();
 387          }
 388  
 389          if (false !== $this->dsn) {
 390              $this->pdo = null; // only close lazy-connection
 391          }
 392  
 393          return true;
 394      }
 395  
 396      /**
 397       * Lazy-connects to the database.
 398       *
 399       * @param string $dsn DSN string
 400       */
 401      private function connect($dsn)
 402      {
 403          $this->pdo = new \PDO($dsn, $this->username, $this->password, $this->connectionOptions);
 404          $this->pdo->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);
 405          $this->driver = $this->pdo->getAttribute(\PDO::ATTR_DRIVER_NAME);
 406      }
 407  
 408      /**
 409       * Helper method to begin a transaction.
 410       *
 411       * Since SQLite does not support row level locks, we have to acquire a reserved lock
 412       * on the database immediately. Because of https://bugs.php.net/42766 we have to create
 413       * such a transaction manually which also means we cannot use PDO::commit or
 414       * PDO::rollback or PDO::inTransaction for SQLite.
 415       *
 416       * Also MySQLs default isolation, REPEATABLE READ, causes deadlock for different sessions
 417       * due to http://www.mysqlperformanceblog.com/2013/12/12/one-more-innodb-gap-lock-to-avoid/ .
 418       * So we change it to READ COMMITTED.
 419       */
 420      private function beginTransaction()
 421      {
 422          if (!$this->inTransaction) {
 423              if ('sqlite' === $this->driver) {
 424                  $this->pdo->exec('BEGIN IMMEDIATE TRANSACTION');
 425              } else {
 426                  if ('mysql' === $this->driver) {
 427                      $this->pdo->exec('SET TRANSACTION ISOLATION LEVEL READ COMMITTED');
 428                  }
 429                  $this->pdo->beginTransaction();
 430              }
 431              $this->inTransaction = true;
 432          }
 433      }
 434  
 435      /**
 436       * Helper method to commit a transaction.
 437       */
 438      private function commit()
 439      {
 440          if ($this->inTransaction) {
 441              try {
 442                  // commit read-write transaction which also releases the lock
 443                  if ('sqlite' === $this->driver) {
 444                      $this->pdo->exec('COMMIT');
 445                  } else {
 446                      $this->pdo->commit();
 447                  }
 448                  $this->inTransaction = false;
 449              } catch (\PDOException $e) {
 450                  $this->rollback();
 451  
 452                  throw $e;
 453              }
 454          }
 455      }
 456  
 457      /**
 458       * Helper method to rollback a transaction.
 459       */
 460      private function rollback()
 461      {
 462          // We only need to rollback if we are in a transaction. Otherwise the resulting
 463          // error would hide the real problem why rollback was called. We might not be
 464          // in a transaction when not using the transactional locking behavior or when
 465          // two callbacks (e.g. destroy and write) are invoked that both fail.
 466          if ($this->inTransaction) {
 467              if ('sqlite' === $this->driver) {
 468                  $this->pdo->exec('ROLLBACK');
 469              } else {
 470                  $this->pdo->rollBack();
 471              }
 472              $this->inTransaction = false;
 473          }
 474      }
 475  
 476      /**
 477       * Reads the session data in respect to the different locking strategies.
 478       *
 479       * We need to make sure we do not return session data that is already considered garbage according
 480       * to the session.gc_maxlifetime setting because gc() is called after read() and only sometimes.
 481       *
 482       * @param string $sessionId Session ID
 483       *
 484       * @return string The session data
 485       */
 486      private function doRead($sessionId)
 487      {
 488          $this->sessionExpired = false;
 489  
 490          if (self::LOCK_ADVISORY === $this->lockMode) {
 491              $this->unlockStatements[] = $this->doAdvisoryLock($sessionId);
 492          }
 493  
 494          $selectSql = $this->getSelectSql();
 495          $selectStmt = $this->pdo->prepare($selectSql);
 496          $selectStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
 497          $insertStmt = null;
 498  
 499          do {
 500              $selectStmt->execute();
 501              $sessionRows = $selectStmt->fetchAll(\PDO::FETCH_NUM);
 502  
 503              if ($sessionRows) {
 504                  if ($sessionRows[0][1] + $sessionRows[0][2] < time()) {
 505                      $this->sessionExpired = true;
 506  
 507                      return '';
 508                  }
 509  
 510                  return \is_resource($sessionRows[0][0]) ? stream_get_contents($sessionRows[0][0]) : $sessionRows[0][0];
 511              }
 512  
 513              if (null !== $insertStmt) {
 514                  $this->rollback();
 515                  throw new \RuntimeException('Failed to read session: INSERT reported a duplicate id but next SELECT did not return any data.');
 516              }
 517  
 518              if (self::LOCK_TRANSACTIONAL === $this->lockMode && 'sqlite' !== $this->driver) {
 519                  // Exclusive-reading of non-existent rows does not block, so we need to do an insert to block
 520                  // until other connections to the session are committed.
 521                  try {
 522                      $insertStmt = $this->getInsertStatement($sessionId, '', 0);
 523                      $insertStmt->execute();
 524                  } catch (\PDOException $e) {
 525                      // Catch duplicate key error because other connection created the session already.
 526                      // It would only not be the case when the other connection destroyed the session.
 527                      if (0 === strpos($e->getCode(), '23')) {
 528                          // Retrieve finished session data written by concurrent connection by restarting the loop.
 529                          // We have to start a new transaction as a failed query will mark the current transaction as
 530                          // aborted in PostgreSQL and disallow further queries within it.
 531                          $this->rollback();
 532                          $this->beginTransaction();
 533                          continue;
 534                      }
 535  
 536                      throw $e;
 537                  }
 538              }
 539  
 540              return '';
 541          } while (true);
 542      }
 543  
 544      /**
 545       * Executes an application-level lock on the database.
 546       *
 547       * @param string $sessionId Session ID
 548       *
 549       * @return \PDOStatement The statement that needs to be executed later to release the lock
 550       *
 551       * @throws \DomainException When an unsupported PDO driver is used
 552       *
 553       * @todo implement missing advisory locks
 554       *       - for oci using DBMS_LOCK.REQUEST
 555       *       - for sqlsrv using sp_getapplock with LockOwner = Session
 556       */
 557      private function doAdvisoryLock($sessionId)
 558      {
 559          switch ($this->driver) {
 560              case 'mysql':
 561                  // MySQL 5.7.5 and later enforces a maximum length on lock names of 64 characters. Previously, no limit was enforced.
 562                  $lockId = \substr($sessionId, 0, 64);
 563                  // should we handle the return value? 0 on timeout, null on error
 564                  // we use a timeout of 50 seconds which is also the default for innodb_lock_wait_timeout
 565                  $stmt = $this->pdo->prepare('SELECT GET_LOCK(:key, 50)');
 566                  $stmt->bindValue(':key', $lockId, \PDO::PARAM_STR);
 567                  $stmt->execute();
 568  
 569                  $releaseStmt = $this->pdo->prepare('DO RELEASE_LOCK(:key)');
 570                  $releaseStmt->bindValue(':key', $lockId, \PDO::PARAM_STR);
 571  
 572                  return $releaseStmt;
 573              case 'pgsql':
 574                  // Obtaining an exclusive session level advisory lock requires an integer key.
 575                  // When session.sid_bits_per_character > 4, the session id can contain non-hex-characters.
 576                  // So we cannot just use hexdec().
 577                  if (4 === \PHP_INT_SIZE) {
 578                      $sessionInt1 = $this->convertStringToInt($sessionId);
 579                      $sessionInt2 = $this->convertStringToInt(substr($sessionId, 4, 4));
 580  
 581                      $stmt = $this->pdo->prepare('SELECT pg_advisory_lock(:key1, :key2)');
 582                      $stmt->bindValue(':key1', $sessionInt1, \PDO::PARAM_INT);
 583                      $stmt->bindValue(':key2', $sessionInt2, \PDO::PARAM_INT);
 584                      $stmt->execute();
 585  
 586                      $releaseStmt = $this->pdo->prepare('SELECT pg_advisory_unlock(:key1, :key2)');
 587                      $releaseStmt->bindValue(':key1', $sessionInt1, \PDO::PARAM_INT);
 588                      $releaseStmt->bindValue(':key2', $sessionInt2, \PDO::PARAM_INT);
 589                  } else {
 590                      $sessionBigInt = $this->convertStringToInt($sessionId);
 591  
 592                      $stmt = $this->pdo->prepare('SELECT pg_advisory_lock(:key)');
 593                      $stmt->bindValue(':key', $sessionBigInt, \PDO::PARAM_INT);
 594                      $stmt->execute();
 595  
 596                      $releaseStmt = $this->pdo->prepare('SELECT pg_advisory_unlock(:key)');
 597                      $releaseStmt->bindValue(':key', $sessionBigInt, \PDO::PARAM_INT);
 598                  }
 599  
 600                  return $releaseStmt;
 601              case 'sqlite':
 602                  throw new \DomainException('SQLite does not support advisory locks.');
 603              default:
 604                  throw new \DomainException(sprintf('Advisory locks are currently not implemented for PDO driver "%s".', $this->driver));
 605          }
 606      }
 607  
 608      /**
 609       * Encodes the first 4 (when PHP_INT_SIZE == 4) or 8 characters of the string as an integer.
 610       *
 611       * Keep in mind, PHP integers are signed.
 612       *
 613       * @param string $string
 614       *
 615       * @return int
 616       */
 617      private function convertStringToInt($string)
 618      {
 619          if (4 === \PHP_INT_SIZE) {
 620              return (\ord($string[3]) << 24) + (\ord($string[2]) << 16) + (\ord($string[1]) << 8) + \ord($string[0]);
 621          }
 622  
 623          $int1 = (\ord($string[7]) << 24) + (\ord($string[6]) << 16) + (\ord($string[5]) << 8) + \ord($string[4]);
 624          $int2 = (\ord($string[3]) << 24) + (\ord($string[2]) << 16) + (\ord($string[1]) << 8) + \ord($string[0]);
 625  
 626          return $int2 + ($int1 << 32);
 627      }
 628  
 629      /**
 630       * Return a locking or nonlocking SQL query to read session information.
 631       *
 632       * @return string The SQL string
 633       *
 634       * @throws \DomainException When an unsupported PDO driver is used
 635       */
 636      private function getSelectSql()
 637      {
 638          if (self::LOCK_TRANSACTIONAL === $this->lockMode) {
 639              $this->beginTransaction();
 640  
 641              switch ($this->driver) {
 642                  case 'mysql':
 643                  case 'oci':
 644                  case 'pgsql':
 645                      return "SELECT $this->dataCol, $this->lifetimeCol, $this->timeCol FROM $this->table WHERE $this->idCol = :id FOR UPDATE";
 646                  case 'sqlsrv':
 647                      return "SELECT $this->dataCol, $this->lifetimeCol, $this->timeCol FROM $this->table WITH (UPDLOCK, ROWLOCK) WHERE $this->idCol = :id";
 648                  case 'sqlite':
 649                      // we already locked when starting transaction
 650                      break;
 651                  default:
 652                      throw new \DomainException(sprintf('Transactional locks are currently not implemented for PDO driver "%s".', $this->driver));
 653              }
 654          }
 655  
 656          return "SELECT $this->dataCol, $this->lifetimeCol, $this->timeCol FROM $this->table WHERE $this->idCol = :id";
 657      }
 658  
 659      /**
 660       * Returns an insert statement supported by the database for writing session data.
 661       *
 662       * @param string $sessionId   Session ID
 663       * @param string $sessionData Encoded session data
 664       * @param int    $maxlifetime session.gc_maxlifetime
 665       *
 666       * @return \PDOStatement The insert statement
 667       */
 668      private function getInsertStatement($sessionId, $sessionData, $maxlifetime)
 669      {
 670          switch ($this->driver) {
 671              case 'oci':
 672                  $data = fopen('php://memory', 'r+');
 673                  fwrite($data, $sessionData);
 674                  rewind($data);
 675                  $sql = "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, EMPTY_BLOB(), :lifetime, :time) RETURNING $this->dataCol into :data";
 676                  break;
 677              default:
 678                  $data = $sessionData;
 679                  $sql = "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, :data, :lifetime, :time)";
 680                  break;
 681          }
 682  
 683          $stmt = $this->pdo->prepare($sql);
 684          $stmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
 685          $stmt->bindParam(':data', $data, \PDO::PARAM_LOB);
 686          $stmt->bindParam(':lifetime', $maxlifetime, \PDO::PARAM_INT);
 687          $stmt->bindValue(':time', time(), \PDO::PARAM_INT);
 688  
 689          return $stmt;
 690      }
 691  
 692      /**
 693       * Returns an update statement supported by the database for writing session data.
 694       *
 695       * @param string $sessionId   Session ID
 696       * @param string $sessionData Encoded session data
 697       * @param int    $maxlifetime session.gc_maxlifetime
 698       *
 699       * @return \PDOStatement The update statement
 700       */
 701      private function getUpdateStatement($sessionId, $sessionData, $maxlifetime)
 702      {
 703          switch ($this->driver) {
 704              case 'oci':
 705                  $data = fopen('php://memory', 'r+');
 706                  fwrite($data, $sessionData);
 707                  rewind($data);
 708                  $sql = "UPDATE $this->table SET $this->dataCol = EMPTY_BLOB(), $this->lifetimeCol = :lifetime, $this->timeCol = :time WHERE $this->idCol = :id RETURNING $this->dataCol into :data";
 709                  break;
 710              default:
 711                  $data = $sessionData;
 712                  $sql = "UPDATE $this->table SET $this->dataCol = :data, $this->lifetimeCol = :lifetime, $this->timeCol = :time WHERE $this->idCol = :id";
 713                  break;
 714          }
 715  
 716          $stmt = $this->pdo->prepare($sql);
 717          $stmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
 718          $stmt->bindParam(':data', $data, \PDO::PARAM_LOB);
 719          $stmt->bindParam(':lifetime', $maxlifetime, \PDO::PARAM_INT);
 720          $stmt->bindValue(':time', time(), \PDO::PARAM_INT);
 721  
 722          return $stmt;
 723      }
 724  
 725      /**
 726       * Returns a merge/upsert (i.e. insert or update) statement when supported by the database for writing session data.
 727       *
 728       * @param string $sessionId   Session ID
 729       * @param string $data        Encoded session data
 730       * @param int    $maxlifetime session.gc_maxlifetime
 731       *
 732       * @return \PDOStatement|null The merge statement or null when not supported
 733       */
 734      private function getMergeStatement($sessionId, $data, $maxlifetime)
 735      {
 736          switch (true) {
 737              case 'mysql' === $this->driver:
 738                  $mergeSql = "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, :data, :lifetime, :time) ".
 739                      "ON DUPLICATE KEY UPDATE $this->dataCol = VALUES($this->dataCol), $this->lifetimeCol = VALUES($this->lifetimeCol), $this->timeCol = VALUES($this->timeCol)";
 740                  break;
 741              case 'sqlsrv' === $this->driver && version_compare($this->pdo->getAttribute(\PDO::ATTR_SERVER_VERSION), '10', '>='):
 742                  // MERGE is only available since SQL Server 2008 and must be terminated by semicolon
 743                  // It also requires HOLDLOCK according to http://weblogs.sqlteam.com/dang/archive/2009/01/31/UPSERT-Race-Condition-With-MERGE.aspx
 744                  $mergeSql = "MERGE INTO $this->table WITH (HOLDLOCK) USING (SELECT 1 AS dummy) AS src ON ($this->idCol = ?) ".
 745                      "WHEN NOT MATCHED THEN INSERT ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (?, ?, ?, ?) ".
 746                      "WHEN MATCHED THEN UPDATE SET $this->dataCol = ?, $this->lifetimeCol = ?, $this->timeCol = ?;";
 747                  break;
 748              case 'sqlite' === $this->driver:
 749                  $mergeSql = "INSERT OR REPLACE INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, :data, :lifetime, :time)";
 750                  break;
 751              case 'pgsql' === $this->driver && version_compare($this->pdo->getAttribute(\PDO::ATTR_SERVER_VERSION), '9.5', '>='):
 752                  $mergeSql = "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, :data, :lifetime, :time) ".
 753                      "ON CONFLICT ($this->idCol) DO UPDATE SET ($this->dataCol, $this->lifetimeCol, $this->timeCol) = (EXCLUDED.$this->dataCol, EXCLUDED.$this->lifetimeCol, EXCLUDED.$this->timeCol)";
 754                  break;
 755              default:
 756                  // MERGE is not supported with LOBs: http://www.oracle.com/technetwork/articles/fuecks-lobs-095315.html
 757                  return null;
 758          }
 759  
 760          $mergeStmt = $this->pdo->prepare($mergeSql);
 761  
 762          if ('sqlsrv' === $this->driver) {
 763              $mergeStmt->bindParam(1, $sessionId, \PDO::PARAM_STR);
 764              $mergeStmt->bindParam(2, $sessionId, \PDO::PARAM_STR);
 765              $mergeStmt->bindParam(3, $data, \PDO::PARAM_LOB);
 766              $mergeStmt->bindParam(4, $maxlifetime, \PDO::PARAM_INT);
 767              $mergeStmt->bindValue(5, time(), \PDO::PARAM_INT);
 768              $mergeStmt->bindParam(6, $data, \PDO::PARAM_LOB);
 769              $mergeStmt->bindParam(7, $maxlifetime, \PDO::PARAM_INT);
 770              $mergeStmt->bindValue(8, time(), \PDO::PARAM_INT);
 771          } else {
 772              $mergeStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
 773              $mergeStmt->bindParam(':data', $data, \PDO::PARAM_LOB);
 774              $mergeStmt->bindParam(':lifetime', $maxlifetime, \PDO::PARAM_INT);
 775              $mergeStmt->bindValue(':time', time(), \PDO::PARAM_INT);
 776          }
 777  
 778          return $mergeStmt;
 779      }
 780  
 781      /**
 782       * Return a PDO instance.
 783       *
 784       * @return \PDO
 785       */
 786      protected function getConnection()
 787      {
 788          if (null === $this->pdo) {
 789              $this->connect($this->dsn ?: ini_get('session.save_path'));
 790          }
 791  
 792          return $this->pdo;
 793      }
 794  }