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   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 https://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 extends AbstractSessionHandler
  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 = [];
 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 = [];
 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: []]
 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 URL 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 $options = [])
 173      {
 174          if ($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 = $this->pdo->getAttribute(\PDO::ATTR_DRIVER_NAME);
 181          } elseif (\is_string($pdoOrDsn) && false !== strpos($pdoOrDsn, '://')) {
 182              $this->dsn = $this->buildDsnFromUrl($pdoOrDsn);
 183          } else {
 184              $this->dsn = $pdoOrDsn;
 185          }
 186  
 187          $this->table = isset($options['db_table']) ? $options['db_table'] : $this->table;
 188          $this->idCol = isset($options['db_id_col']) ? $options['db_id_col'] : $this->idCol;
 189          $this->dataCol = isset($options['db_data_col']) ? $options['db_data_col'] : $this->dataCol;
 190          $this->lifetimeCol = isset($options['db_lifetime_col']) ? $options['db_lifetime_col'] : $this->lifetimeCol;
 191          $this->timeCol = isset($options['db_time_col']) ? $options['db_time_col'] : $this->timeCol;
 192          $this->username = isset($options['db_username']) ? $options['db_username'] : $this->username;
 193          $this->password = isset($options['db_password']) ? $options['db_password'] : $this->password;
 194          $this->connectionOptions = isset($options['db_connection_options']) ? $options['db_connection_options'] : $this->connectionOptions;
 195          $this->lockMode = isset($options['lock_mode']) ? $options['lock_mode'] : $this->lockMode;
 196      }
 197  
 198      /**
 199       * Creates the table to store sessions which can be called once for setup.
 200       *
 201       * Session ID is saved in a column of maximum length 128 because that is enough even
 202       * for a 512 bit configured session.hash_function like Whirlpool. Session data is
 203       * saved in a BLOB. One could also use a shorter inlined varbinary column
 204       * if one was sure the data fits into it.
 205       *
 206       * @throws \PDOException    When the table already exists
 207       * @throws \DomainException When an unsupported PDO driver is used
 208       */
 209      public function createTable()
 210      {
 211          // connect if we are not yet
 212          $this->getConnection();
 213  
 214          switch ($this->driver) {
 215              case 'mysql':
 216                  // We use varbinary for the ID column because it prevents unwanted conversions:
 217                  // - character set conversions between server and client
 218                  // - trailing space removal
 219                  // - case-insensitivity
 220                  // - language processing like é == e
 221                  $sql = "CREATE TABLE $this->table ($this->idCol VARBINARY(128) NOT NULL PRIMARY KEY, $this->dataCol BLOB NOT NULL, $this->lifetimeCol INTEGER UNSIGNED NOT NULL, $this->timeCol INTEGER UNSIGNED NOT NULL) COLLATE utf8mb4_bin, ENGINE = InnoDB";
 222                  break;
 223              case 'sqlite':
 224                  $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)";
 225                  break;
 226              case 'pgsql':
 227                  $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)";
 228                  break;
 229              case 'oci':
 230                  $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)";
 231                  break;
 232              case 'sqlsrv':
 233                  $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)";
 234                  break;
 235              default:
 236                  throw new \DomainException(sprintf('Creating the session table is currently not implemented for PDO driver "%s".', $this->driver));
 237          }
 238  
 239          try {
 240              $this->pdo->exec($sql);
 241          } catch (\PDOException $e) {
 242              $this->rollback();
 243  
 244              throw $e;
 245          }
 246      }
 247  
 248      /**
 249       * Returns true when the current session exists but expired according to session.gc_maxlifetime.
 250       *
 251       * Can be used to distinguish between a new session and one that expired due to inactivity.
 252       *
 253       * @return bool Whether current session expired
 254       */
 255      public function isSessionExpired()
 256      {
 257          return $this->sessionExpired;
 258      }
 259  
 260      /**
 261       * {@inheritdoc}
 262       */
 263      public function open($savePath, $sessionName)
 264      {
 265          $this->sessionExpired = false;
 266  
 267          if (null === $this->pdo) {
 268              $this->connect($this->dsn ?: $savePath);
 269          }
 270  
 271          return parent::open($savePath, $sessionName);
 272      }
 273  
 274      /**
 275       * {@inheritdoc}
 276       */
 277      public function read($sessionId)
 278      {
 279          try {
 280              return parent::read($sessionId);
 281          } catch (\PDOException $e) {
 282              $this->rollback();
 283  
 284              throw $e;
 285          }
 286      }
 287  
 288      /**
 289       * @return bool
 290       */
 291      public function gc($maxlifetime)
 292      {
 293          // We delay gc() to close() so that it is executed outside the transactional and blocking read-write process.
 294          // This way, pruning expired sessions does not block them from being started while the current session is used.
 295          $this->gcCalled = true;
 296  
 297          return true;
 298      }
 299  
 300      /**
 301       * {@inheritdoc}
 302       */
 303      protected function doDestroy($sessionId)
 304      {
 305          // delete the record associated with this id
 306          $sql = "DELETE FROM $this->table WHERE $this->idCol = :id";
 307  
 308          try {
 309              $stmt = $this->pdo->prepare($sql);
 310              $stmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
 311              $stmt->execute();
 312          } catch (\PDOException $e) {
 313              $this->rollback();
 314  
 315              throw $e;
 316          }
 317  
 318          return true;
 319      }
 320  
 321      /**
 322       * {@inheritdoc}
 323       */
 324      protected function doWrite($sessionId, $data)
 325      {
 326          $maxlifetime = (int) ini_get('session.gc_maxlifetime');
 327  
 328          try {
 329              // We use a single MERGE SQL query when supported by the database.
 330              $mergeStmt = $this->getMergeStatement($sessionId, $data, $maxlifetime);
 331              if (null !== $mergeStmt) {
 332                  $mergeStmt->execute();
 333  
 334                  return true;
 335              }
 336  
 337              $updateStmt = $this->getUpdateStatement($sessionId, $data, $maxlifetime);
 338              $updateStmt->execute();
 339  
 340              // When MERGE is not supported, like in Postgres < 9.5, we have to use this approach that can result in
 341              // duplicate key errors when the same session is written simultaneously (given the LOCK_NONE behavior).
 342              // We can just catch such an error and re-execute the update. This is similar to a serializable
 343              // transaction with retry logic on serialization failures but without the overhead and without possible
 344              // false positives due to longer gap locking.
 345              if (!$updateStmt->rowCount()) {
 346                  try {
 347                      $insertStmt = $this->getInsertStatement($sessionId, $data, $maxlifetime);
 348                      $insertStmt->execute();
 349                  } catch (\PDOException $e) {
 350                      // Handle integrity violation SQLSTATE 23000 (or a subclass like 23505 in Postgres) for duplicate keys
 351                      if (0 === strpos($e->getCode(), '23')) {
 352                          $updateStmt->execute();
 353                      } else {
 354                          throw $e;
 355                      }
 356                  }
 357              }
 358          } catch (\PDOException $e) {
 359              $this->rollback();
 360  
 361              throw $e;
 362          }
 363  
 364          return true;
 365      }
 366  
 367      /**
 368       * {@inheritdoc}
 369       */
 370      public function updateTimestamp($sessionId, $data)
 371      {
 372          $maxlifetime = (int) ini_get('session.gc_maxlifetime');
 373  
 374          try {
 375              $updateStmt = $this->pdo->prepare(
 376                  "UPDATE $this->table SET $this->lifetimeCol = :lifetime, $this->timeCol = :time WHERE $this->idCol = :id"
 377              );
 378              $updateStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
 379              $updateStmt->bindParam(':lifetime', $maxlifetime, \PDO::PARAM_INT);
 380              $updateStmt->bindValue(':time', time(), \PDO::PARAM_INT);
 381              $updateStmt->execute();
 382          } catch (\PDOException $e) {
 383              $this->rollback();
 384  
 385              throw $e;
 386          }
 387  
 388          return true;
 389      }
 390  
 391      /**
 392       * {@inheritdoc}
 393       */
 394      public function close()
 395      {
 396          $this->commit();
 397  
 398          while ($unlockStmt = array_shift($this->unlockStatements)) {
 399              $unlockStmt->execute();
 400          }
 401  
 402          if ($this->gcCalled) {
 403              $this->gcCalled = false;
 404  
 405              // delete the session records that have expired
 406              if ('mysql' === $this->driver) {
 407                  $sql = "DELETE FROM $this->table WHERE $this->lifetimeCol + $this->timeCol < :time";
 408              } else {
 409                  $sql = "DELETE FROM $this->table WHERE $this->lifetimeCol < :time - $this->timeCol";
 410              }
 411  
 412              $stmt = $this->pdo->prepare($sql);
 413              $stmt->bindValue(':time', time(), \PDO::PARAM_INT);
 414              $stmt->execute();
 415          }
 416  
 417          if (false !== $this->dsn) {
 418              $this->pdo = null; // only close lazy-connection
 419          }
 420  
 421          return true;
 422      }
 423  
 424      /**
 425       * Lazy-connects to the database.
 426       *
 427       * @param string $dsn DSN string
 428       */
 429      private function connect($dsn)
 430      {
 431          $this->pdo = new \PDO($dsn, $this->username, $this->password, $this->connectionOptions);
 432          $this->pdo->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);
 433          $this->driver = $this->pdo->getAttribute(\PDO::ATTR_DRIVER_NAME);
 434      }
 435  
 436      /**
 437       * Builds a PDO DSN from a URL-like connection string.
 438       *
 439       * @param string $dsnOrUrl
 440       *
 441       * @return string
 442       *
 443       * @todo implement missing support for oci DSN (which look totally different from other PDO ones)
 444       */
 445      private function buildDsnFromUrl($dsnOrUrl)
 446      {
 447          // (pdo_)?sqlite3?:///... => (pdo_)?sqlite3?://localhost/... or else the URL will be invalid
 448          $url = preg_replace('#^((?:pdo_)?sqlite3?):///#', '$1://localhost/', $dsnOrUrl);
 449  
 450          $params = parse_url($url);
 451  
 452          if (false === $params) {
 453              return $dsnOrUrl; // If the URL is not valid, let's assume it might be a DSN already.
 454          }
 455  
 456          $params = array_map('rawurldecode', $params);
 457  
 458          // Override the default username and password. Values passed through options will still win over these in the constructor.
 459          if (isset($params['user'])) {
 460              $this->username = $params['user'];
 461          }
 462  
 463          if (isset($params['pass'])) {
 464              $this->password = $params['pass'];
 465          }
 466  
 467          if (!isset($params['scheme'])) {
 468              throw new \InvalidArgumentException('URLs without scheme are not supported to configure the PdoSessionHandler.');
 469          }
 470  
 471          $driverAliasMap = [
 472              'mssql' => 'sqlsrv',
 473              'mysql2' => 'mysql', // Amazon RDS, for some weird reason
 474              'postgres' => 'pgsql',
 475              'postgresql' => 'pgsql',
 476              'sqlite3' => 'sqlite',
 477          ];
 478  
 479          $driver = isset($driverAliasMap[$params['scheme']]) ? $driverAliasMap[$params['scheme']] : $params['scheme'];
 480  
 481          // Doctrine DBAL supports passing its internal pdo_* driver names directly too (allowing both dashes and underscores). This allows supporting the same here.
 482          if (0 === strpos($driver, 'pdo_') || 0 === strpos($driver, 'pdo-')) {
 483              $driver = substr($driver, 4);
 484          }
 485  
 486          switch ($driver) {
 487              case 'mysql':
 488              case 'pgsql':
 489                  $dsn = $driver.':';
 490  
 491                  if (isset($params['host']) && '' !== $params['host']) {
 492                      $dsn .= 'host='.$params['host'].';';
 493                  }
 494  
 495                  if (isset($params['port']) && '' !== $params['port']) {
 496                      $dsn .= 'port='.$params['port'].';';
 497                  }
 498  
 499                  if (isset($params['path'])) {
 500                      $dbName = substr($params['path'], 1); // Remove the leading slash
 501                      $dsn .= 'dbname='.$dbName.';';
 502                  }
 503  
 504                  return $dsn;
 505  
 506              case 'sqlite':
 507                  return 'sqlite:'.substr($params['path'], 1);
 508  
 509              case 'sqlsrv':
 510                  $dsn = 'sqlsrv:server=';
 511  
 512                  if (isset($params['host'])) {
 513                      $dsn .= $params['host'];
 514                  }
 515  
 516                  if (isset($params['port']) && '' !== $params['port']) {
 517                      $dsn .= ','.$params['port'];
 518                  }
 519  
 520                  if (isset($params['path'])) {
 521                      $dbName = substr($params['path'], 1); // Remove the leading slash
 522                      $dsn .= ';Database='.$dbName;
 523                  }
 524  
 525                  return $dsn;
 526  
 527              default:
 528                  throw new \InvalidArgumentException(sprintf('The scheme "%s" is not supported by the PdoSessionHandler URL configuration. Pass a PDO DSN directly.', $params['scheme']));
 529          }
 530      }
 531  
 532      /**
 533       * Helper method to begin a transaction.
 534       *
 535       * Since SQLite does not support row level locks, we have to acquire a reserved lock
 536       * on the database immediately. Because of https://bugs.php.net/42766 we have to create
 537       * such a transaction manually which also means we cannot use PDO::commit or
 538       * PDO::rollback or PDO::inTransaction for SQLite.
 539       *
 540       * Also MySQLs default isolation, REPEATABLE READ, causes deadlock for different sessions
 541       * due to https://percona.com/blog/2013/12/12/one-more-innodb-gap-lock-to-avoid/ .
 542       * So we change it to READ COMMITTED.
 543       */
 544      private function beginTransaction()
 545      {
 546          if (!$this->inTransaction) {
 547              if ('sqlite' === $this->driver) {
 548                  $this->pdo->exec('BEGIN IMMEDIATE TRANSACTION');
 549              } else {
 550                  if ('mysql' === $this->driver) {
 551                      $this->pdo->exec('SET TRANSACTION ISOLATION LEVEL READ COMMITTED');
 552                  }
 553                  $this->pdo->beginTransaction();
 554              }
 555              $this->inTransaction = true;
 556          }
 557      }
 558  
 559      /**
 560       * Helper method to commit a transaction.
 561       */
 562      private function commit()
 563      {
 564          if ($this->inTransaction) {
 565              try {
 566                  // commit read-write transaction which also releases the lock
 567                  if ('sqlite' === $this->driver) {
 568                      $this->pdo->exec('COMMIT');
 569                  } else {
 570                      $this->pdo->commit();
 571                  }
 572                  $this->inTransaction = false;
 573              } catch (\PDOException $e) {
 574                  $this->rollback();
 575  
 576                  throw $e;
 577              }
 578          }
 579      }
 580  
 581      /**
 582       * Helper method to rollback a transaction.
 583       */
 584      private function rollback()
 585      {
 586          // We only need to rollback if we are in a transaction. Otherwise the resulting
 587          // error would hide the real problem why rollback was called. We might not be
 588          // in a transaction when not using the transactional locking behavior or when
 589          // two callbacks (e.g. destroy and write) are invoked that both fail.
 590          if ($this->inTransaction) {
 591              if ('sqlite' === $this->driver) {
 592                  $this->pdo->exec('ROLLBACK');
 593              } else {
 594                  $this->pdo->rollBack();
 595              }
 596              $this->inTransaction = false;
 597          }
 598      }
 599  
 600      /**
 601       * Reads the session data in respect to the different locking strategies.
 602       *
 603       * We need to make sure we do not return session data that is already considered garbage according
 604       * to the session.gc_maxlifetime setting because gc() is called after read() and only sometimes.
 605       *
 606       * @param string $sessionId Session ID
 607       *
 608       * @return string The session data
 609       */
 610      protected function doRead($sessionId)
 611      {
 612          if (self::LOCK_ADVISORY === $this->lockMode) {
 613              $this->unlockStatements[] = $this->doAdvisoryLock($sessionId);
 614          }
 615  
 616          $selectSql = $this->getSelectSql();
 617          $selectStmt = $this->pdo->prepare($selectSql);
 618          $selectStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
 619          $insertStmt = null;
 620  
 621          do {
 622              $selectStmt->execute();
 623              $sessionRows = $selectStmt->fetchAll(\PDO::FETCH_NUM);
 624  
 625              if ($sessionRows) {
 626                  if ($sessionRows[0][1] + $sessionRows[0][2] < time()) {
 627                      $this->sessionExpired = true;
 628  
 629                      return '';
 630                  }
 631  
 632                  return \is_resource($sessionRows[0][0]) ? stream_get_contents($sessionRows[0][0]) : $sessionRows[0][0];
 633              }
 634  
 635              if (null !== $insertStmt) {
 636                  $this->rollback();
 637                  throw new \RuntimeException('Failed to read session: INSERT reported a duplicate id but next SELECT did not return any data.');
 638              }
 639  
 640              if (!filter_var(ini_get('session.use_strict_mode'), \FILTER_VALIDATE_BOOLEAN) && self::LOCK_TRANSACTIONAL === $this->lockMode && 'sqlite' !== $this->driver) {
 641                  // In strict mode, session fixation is not possible: new sessions always start with a unique
 642                  // random id, so that concurrency is not possible and this code path can be skipped.
 643                  // Exclusive-reading of non-existent rows does not block, so we need to do an insert to block
 644                  // until other connections to the session are committed.
 645                  try {
 646                      $insertStmt = $this->getInsertStatement($sessionId, '', 0);
 647                      $insertStmt->execute();
 648                  } catch (\PDOException $e) {
 649                      // Catch duplicate key error because other connection created the session already.
 650                      // It would only not be the case when the other connection destroyed the session.
 651                      if (0 === strpos($e->getCode(), '23')) {
 652                          // Retrieve finished session data written by concurrent connection by restarting the loop.
 653                          // We have to start a new transaction as a failed query will mark the current transaction as
 654                          // aborted in PostgreSQL and disallow further queries within it.
 655                          $this->rollback();
 656                          $this->beginTransaction();
 657                          continue;
 658                      }
 659  
 660                      throw $e;
 661                  }
 662              }
 663  
 664              return '';
 665          } while (true);
 666      }
 667  
 668      /**
 669       * Executes an application-level lock on the database.
 670       *
 671       * @param string $sessionId Session ID
 672       *
 673       * @return \PDOStatement The statement that needs to be executed later to release the lock
 674       *
 675       * @throws \DomainException When an unsupported PDO driver is used
 676       *
 677       * @todo implement missing advisory locks
 678       *       - for oci using DBMS_LOCK.REQUEST
 679       *       - for sqlsrv using sp_getapplock with LockOwner = Session
 680       */
 681      private function doAdvisoryLock($sessionId)
 682      {
 683          switch ($this->driver) {
 684              case 'mysql':
 685                  // MySQL 5.7.5 and later enforces a maximum length on lock names of 64 characters. Previously, no limit was enforced.
 686                  $lockId = substr($sessionId, 0, 64);
 687                  // should we handle the return value? 0 on timeout, null on error
 688                  // we use a timeout of 50 seconds which is also the default for innodb_lock_wait_timeout
 689                  $stmt = $this->pdo->prepare('SELECT GET_LOCK(:key, 50)');
 690                  $stmt->bindValue(':key', $lockId, \PDO::PARAM_STR);
 691                  $stmt->execute();
 692  
 693                  $releaseStmt = $this->pdo->prepare('DO RELEASE_LOCK(:key)');
 694                  $releaseStmt->bindValue(':key', $lockId, \PDO::PARAM_STR);
 695  
 696                  return $releaseStmt;
 697              case 'pgsql':
 698                  // Obtaining an exclusive session level advisory lock requires an integer key.
 699                  // When session.sid_bits_per_character > 4, the session id can contain non-hex-characters.
 700                  // So we cannot just use hexdec().
 701                  if (4 === \PHP_INT_SIZE) {
 702                      $sessionInt1 = $this->convertStringToInt($sessionId);
 703                      $sessionInt2 = $this->convertStringToInt(substr($sessionId, 4, 4));
 704  
 705                      $stmt = $this->pdo->prepare('SELECT pg_advisory_lock(:key1, :key2)');
 706                      $stmt->bindValue(':key1', $sessionInt1, \PDO::PARAM_INT);
 707                      $stmt->bindValue(':key2', $sessionInt2, \PDO::PARAM_INT);
 708                      $stmt->execute();
 709  
 710                      $releaseStmt = $this->pdo->prepare('SELECT pg_advisory_unlock(:key1, :key2)');
 711                      $releaseStmt->bindValue(':key1', $sessionInt1, \PDO::PARAM_INT);
 712                      $releaseStmt->bindValue(':key2', $sessionInt2, \PDO::PARAM_INT);
 713                  } else {
 714                      $sessionBigInt = $this->convertStringToInt($sessionId);
 715  
 716                      $stmt = $this->pdo->prepare('SELECT pg_advisory_lock(:key)');
 717                      $stmt->bindValue(':key', $sessionBigInt, \PDO::PARAM_INT);
 718                      $stmt->execute();
 719  
 720                      $releaseStmt = $this->pdo->prepare('SELECT pg_advisory_unlock(:key)');
 721                      $releaseStmt->bindValue(':key', $sessionBigInt, \PDO::PARAM_INT);
 722                  }
 723  
 724                  return $releaseStmt;
 725              case 'sqlite':
 726                  throw new \DomainException('SQLite does not support advisory locks.');
 727              default:
 728                  throw new \DomainException(sprintf('Advisory locks are currently not implemented for PDO driver "%s".', $this->driver));
 729          }
 730      }
 731  
 732      /**
 733       * Encodes the first 4 (when PHP_INT_SIZE == 4) or 8 characters of the string as an integer.
 734       *
 735       * Keep in mind, PHP integers are signed.
 736       *
 737       * @param string $string
 738       *
 739       * @return int
 740       */
 741      private function convertStringToInt($string)
 742      {
 743          if (4 === \PHP_INT_SIZE) {
 744              return (\ord($string[3]) << 24) + (\ord($string[2]) << 16) + (\ord($string[1]) << 8) + \ord($string[0]);
 745          }
 746  
 747          $int1 = (\ord($string[7]) << 24) + (\ord($string[6]) << 16) + (\ord($string[5]) << 8) + \ord($string[4]);
 748          $int2 = (\ord($string[3]) << 24) + (\ord($string[2]) << 16) + (\ord($string[1]) << 8) + \ord($string[0]);
 749  
 750          return $int2 + ($int1 << 32);
 751      }
 752  
 753      /**
 754       * Return a locking or nonlocking SQL query to read session information.
 755       *
 756       * @return string The SQL string
 757       *
 758       * @throws \DomainException When an unsupported PDO driver is used
 759       */
 760      private function getSelectSql()
 761      {
 762          if (self::LOCK_TRANSACTIONAL === $this->lockMode) {
 763              $this->beginTransaction();
 764  
 765              switch ($this->driver) {
 766                  case 'mysql':
 767                  case 'oci':
 768                  case 'pgsql':
 769                      return "SELECT $this->dataCol, $this->lifetimeCol, $this->timeCol FROM $this->table WHERE $this->idCol = :id FOR UPDATE";
 770                  case 'sqlsrv':
 771                      return "SELECT $this->dataCol, $this->lifetimeCol, $this->timeCol FROM $this->table WITH (UPDLOCK, ROWLOCK) WHERE $this->idCol = :id";
 772                  case 'sqlite':
 773                      // we already locked when starting transaction
 774                      break;
 775                  default:
 776                      throw new \DomainException(sprintf('Transactional locks are currently not implemented for PDO driver "%s".', $this->driver));
 777              }
 778          }
 779  
 780          return "SELECT $this->dataCol, $this->lifetimeCol, $this->timeCol FROM $this->table WHERE $this->idCol = :id";
 781      }
 782  
 783      /**
 784       * Returns an insert statement supported by the database for writing session data.
 785       *
 786       * @param string $sessionId   Session ID
 787       * @param string $sessionData Encoded session data
 788       * @param int    $maxlifetime session.gc_maxlifetime
 789       *
 790       * @return \PDOStatement The insert statement
 791       */
 792      private function getInsertStatement($sessionId, $sessionData, $maxlifetime)
 793      {
 794          switch ($this->driver) {
 795              case 'oci':
 796                  $data = fopen('php://memory', 'r+');
 797                  fwrite($data, $sessionData);
 798                  rewind($data);
 799                  $sql = "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, EMPTY_BLOB(), :lifetime, :time) RETURNING $this->dataCol into :data";
 800                  break;
 801              default:
 802                  $data = $sessionData;
 803                  $sql = "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, :data, :lifetime, :time)";
 804                  break;
 805          }
 806  
 807          $stmt = $this->pdo->prepare($sql);
 808          $stmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
 809          $stmt->bindParam(':data', $data, \PDO::PARAM_LOB);
 810          $stmt->bindParam(':lifetime', $maxlifetime, \PDO::PARAM_INT);
 811          $stmt->bindValue(':time', time(), \PDO::PARAM_INT);
 812  
 813          return $stmt;
 814      }
 815  
 816      /**
 817       * Returns an update statement supported by the database for writing session data.
 818       *
 819       * @param string $sessionId   Session ID
 820       * @param string $sessionData Encoded session data
 821       * @param int    $maxlifetime session.gc_maxlifetime
 822       *
 823       * @return \PDOStatement The update statement
 824       */
 825      private function getUpdateStatement($sessionId, $sessionData, $maxlifetime)
 826      {
 827          switch ($this->driver) {
 828              case 'oci':
 829                  $data = fopen('php://memory', 'r+');
 830                  fwrite($data, $sessionData);
 831                  rewind($data);
 832                  $sql = "UPDATE $this->table SET $this->dataCol = EMPTY_BLOB(), $this->lifetimeCol = :lifetime, $this->timeCol = :time WHERE $this->idCol = :id RETURNING $this->dataCol into :data";
 833                  break;
 834              default:
 835                  $data = $sessionData;
 836                  $sql = "UPDATE $this->table SET $this->dataCol = :data, $this->lifetimeCol = :lifetime, $this->timeCol = :time WHERE $this->idCol = :id";
 837                  break;
 838          }
 839  
 840          $stmt = $this->pdo->prepare($sql);
 841          $stmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
 842          $stmt->bindParam(':data', $data, \PDO::PARAM_LOB);
 843          $stmt->bindParam(':lifetime', $maxlifetime, \PDO::PARAM_INT);
 844          $stmt->bindValue(':time', time(), \PDO::PARAM_INT);
 845  
 846          return $stmt;
 847      }
 848  
 849      /**
 850       * Returns a merge/upsert (i.e. insert or update) statement when supported by the database for writing session data.
 851       *
 852       * @param string $sessionId   Session ID
 853       * @param string $data        Encoded session data
 854       * @param int    $maxlifetime session.gc_maxlifetime
 855       *
 856       * @return \PDOStatement|null The merge statement or null when not supported
 857       */
 858      private function getMergeStatement($sessionId, $data, $maxlifetime)
 859      {
 860          switch (true) {
 861              case 'mysql' === $this->driver:
 862                  $mergeSql = "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, :data, :lifetime, :time) ".
 863                      "ON DUPLICATE KEY UPDATE $this->dataCol = VALUES($this->dataCol), $this->lifetimeCol = VALUES($this->lifetimeCol), $this->timeCol = VALUES($this->timeCol)";
 864                  break;
 865              case 'sqlsrv' === $this->driver && version_compare($this->pdo->getAttribute(\PDO::ATTR_SERVER_VERSION), '10', '>='):
 866                  // MERGE is only available since SQL Server 2008 and must be terminated by semicolon
 867                  // It also requires HOLDLOCK according to https://weblogs.sqlteam.com/dang/2009/01/31/upsert-race-condition-with-merge/
 868                  $mergeSql = "MERGE INTO $this->table WITH (HOLDLOCK) USING (SELECT 1 AS dummy) AS src ON ($this->idCol = ?) ".
 869                      "WHEN NOT MATCHED THEN INSERT ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (?, ?, ?, ?) ".
 870                      "WHEN MATCHED THEN UPDATE SET $this->dataCol = ?, $this->lifetimeCol = ?, $this->timeCol = ?;";
 871                  break;
 872              case 'sqlite' === $this->driver:
 873                  $mergeSql = "INSERT OR REPLACE INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, :data, :lifetime, :time)";
 874                  break;
 875              case 'pgsql' === $this->driver && version_compare($this->pdo->getAttribute(\PDO::ATTR_SERVER_VERSION), '9.5', '>='):
 876                  $mergeSql = "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, :data, :lifetime, :time) ".
 877                      "ON CONFLICT ($this->idCol) DO UPDATE SET ($this->dataCol, $this->lifetimeCol, $this->timeCol) = (EXCLUDED.$this->dataCol, EXCLUDED.$this->lifetimeCol, EXCLUDED.$this->timeCol)";
 878                  break;
 879              default:
 880                  // MERGE is not supported with LOBs: https://oracle.com/technetwork/articles/fuecks-lobs-095315.html
 881                  return null;
 882          }
 883  
 884          $mergeStmt = $this->pdo->prepare($mergeSql);
 885  
 886          if ('sqlsrv' === $this->driver) {
 887              $mergeStmt->bindParam(1, $sessionId, \PDO::PARAM_STR);
 888              $mergeStmt->bindParam(2, $sessionId, \PDO::PARAM_STR);
 889              $mergeStmt->bindParam(3, $data, \PDO::PARAM_LOB);
 890              $mergeStmt->bindParam(4, $maxlifetime, \PDO::PARAM_INT);
 891              $mergeStmt->bindValue(5, time(), \PDO::PARAM_INT);
 892              $mergeStmt->bindParam(6, $data, \PDO::PARAM_LOB);
 893              $mergeStmt->bindParam(7, $maxlifetime, \PDO::PARAM_INT);
 894              $mergeStmt->bindValue(8, time(), \PDO::PARAM_INT);
 895          } else {
 896              $mergeStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
 897              $mergeStmt->bindParam(':data', $data, \PDO::PARAM_LOB);
 898              $mergeStmt->bindParam(':lifetime', $maxlifetime, \PDO::PARAM_INT);
 899              $mergeStmt->bindValue(':time', time(), \PDO::PARAM_INT);
 900          }
 901  
 902          return $mergeStmt;
 903      }
 904  
 905      /**
 906       * Return a PDO instance.
 907       *
 908       * @return \PDO
 909       */
 910      protected function getConnection()
 911      {
 912          if (null === $this->pdo) {
 913              $this->connect($this->dsn ?: ini_get('session.save_path'));
 914          }
 915  
 916          return $this->pdo;
 917      }
 918  }