1: <?php
  2: 
  3: /*
  4:  * This file is part of the Symfony package.
  5:  *
  6:  * (c) Fabien Potencier <[email protected]>
  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 <[email protected]>
 38:  * @author Michael Williams <[email protected]>
 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|null|false 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:      * Constructor.
152:      *
153:      * You can either pass an existing database connection as PDO instance or
154:      * pass a DSN string that will be used to lazy-connect to the database
155:      * when the session is actually used. Furthermore it's possible to pass null
156:      * which will then use the session.save_path ini setting as PDO DSN parameter.
157:      *
158:      * List of available options:
159:      *  * db_table: The name of the table [default: sessions]
160:      *  * db_id_col: The column where to store the session id [default: sess_id]
161:      *  * db_data_col: The column where to store the session data [default: sess_data]
162:      *  * db_lifetime_col: The column where to store the lifetime [default: sess_lifetime]
163:      *  * db_time_col: The column where to store the timestamp [default: sess_time]
164:      *  * db_username: The username when lazy-connect [default: '']
165:      *  * db_password: The password when lazy-connect [default: '']
166:      *  * db_connection_options: An array of driver-specific connection options [default: array()]
167:      *  * lock_mode: The strategy for locking, see constants [default: LOCK_TRANSACTIONAL]
168:      *
169:      * @param \PDO|string|null $pdoOrDsn A \PDO instance or DSN string or null
170:      * @param array            $options  An associative array of options
171:      *
172:      * @throws \InvalidArgumentException When PDO error mode is not PDO::ERRMODE_EXCEPTION
173:      */
174:     public function __construct($pdoOrDsn = null, array $options = array())
175:     {
176:         if ($pdoOrDsn instanceof \PDO) {
177:             if (\PDO::ERRMODE_EXCEPTION !== $pdoOrDsn->getAttribute(\PDO::ATTR_ERRMODE)) {
178:                 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__));
179:             }
180: 
181:             $this->pdo = $pdoOrDsn;
182:             $this->driver = $this->pdo->getAttribute(\PDO::ATTR_DRIVER_NAME);
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 MEDIUMINT NOT NULL, $this->timeCol INTEGER UNSIGNED NOT NULL) COLLATE utf8_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:         if (null === $this->pdo) {
266:             $this->connect($this->dsn ?: $savePath);
267:         }
268: 
269:         return true;
270:     }
271: 
272:     /**
273:      * {@inheritdoc}
274:      */
275:     public function read($sessionId)
276:     {
277:         try {
278:             return $this->doRead($sessionId);
279:         } catch (\PDOException $e) {
280:             $this->rollback();
281: 
282:             throw $e;
283:         }
284:     }
285: 
286:     /**
287:      * {@inheritdoc}
288:      */
289:     public function gc($maxlifetime)
290:     {
291:         // We delay gc() to close() so that it is executed outside the transactional and blocking read-write process.
292:         // This way, pruning expired sessions does not block them from being started while the current session is used.
293:         $this->gcCalled = true;
294: 
295:         return true;
296:     }
297: 
298:     /**
299:      * {@inheritdoc}
300:      */
301:     public function destroy($sessionId)
302:     {
303:         // delete the record associated with this id
304:         $sql = "DELETE FROM $this->table WHERE $this->idCol = :id";
305: 
306:         try {
307:             $stmt = $this->pdo->prepare($sql);
308:             $stmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
309:             $stmt->execute();
310:         } catch (\PDOException $e) {
311:             $this->rollback();
312: 
313:             throw $e;
314:         }
315: 
316:         return true;
317:     }
318: 
319:     /**
320:      * {@inheritdoc}
321:      */
322:     public function write($sessionId, $data)
323:     {
324:         $maxlifetime = (int) ini_get('session.gc_maxlifetime');
325: 
326:         try {
327:             // We use a single MERGE SQL query when supported by the database.
328:             $mergeStmt = $this->getMergeStatement($sessionId, $data, $maxlifetime);
329:             if (null !== $mergeStmt) {
330:                 $mergeStmt->execute();
331: 
332:                 return true;
333:             }
334: 
335:             $updateStmt = $this->pdo->prepare(
336:                 "UPDATE $this->table SET $this->dataCol = :data, $this->lifetimeCol = :lifetime, $this->timeCol = :time WHERE $this->idCol = :id"
337:             );
338:             $updateStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
339:             $updateStmt->bindParam(':data', $data, \PDO::PARAM_LOB);
340:             $updateStmt->bindParam(':lifetime', $maxlifetime, \PDO::PARAM_INT);
341:             $updateStmt->bindValue(':time', time(), \PDO::PARAM_INT);
342:             $updateStmt->execute();
343: 
344:             // When MERGE is not supported, like in Postgres < 9.5, we have to use this approach that can result in
345:             // duplicate key errors when the same session is written simultaneously (given the LOCK_NONE behavior).
346:             // We can just catch such an error and re-execute the update. This is similar to a serializable
347:             // transaction with retry logic on serialization failures but without the overhead and without possible
348:             // false positives due to longer gap locking.
349:             if (!$updateStmt->rowCount()) {
350:                 try {
351:                     $insertStmt = $this->pdo->prepare(
352:                         "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, :data, :lifetime, :time)"
353:                     );
354:                     $insertStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
355:                     $insertStmt->bindParam(':data', $data, \PDO::PARAM_LOB);
356:                     $insertStmt->bindParam(':lifetime', $maxlifetime, \PDO::PARAM_INT);
357:                     $insertStmt->bindValue(':time', time(), \PDO::PARAM_INT);
358:                     $insertStmt->execute();
359:                 } catch (\PDOException $e) {
360:                     // Handle integrity violation SQLSTATE 23000 (or a subclass like 23505 in Postgres) for duplicate keys
361:                     if (0 === strpos($e->getCode(), '23')) {
362:                         $updateStmt->execute();
363:                     } else {
364:                         throw $e;
365:                     }
366:                 }
367:             }
368:         } catch (\PDOException $e) {
369:             $this->rollback();
370: 
371:             throw $e;
372:         }
373: 
374:         return true;
375:     }
376: 
377:     /**
378:      * {@inheritdoc}
379:      */
380:     public function close()
381:     {
382:         $this->commit();
383: 
384:         while ($unlockStmt = array_shift($this->unlockStatements)) {
385:             $unlockStmt->execute();
386:         }
387: 
388:         if ($this->gcCalled) {
389:             $this->gcCalled = false;
390: 
391:             // delete the session records that have expired
392:             $sql = "DELETE FROM $this->table WHERE $this->lifetimeCol + $this->timeCol < :time";
393: 
394:             $stmt = $this->pdo->prepare($sql);
395:             $stmt->bindValue(':time', time(), \PDO::PARAM_INT);
396:             $stmt->execute();
397:         }
398: 
399:         if (false !== $this->dsn) {
400:             $this->pdo = null; // only close lazy-connection
401:         }
402: 
403:         return true;
404:     }
405: 
406:     /**
407:      * Lazy-connects to the database.
408:      *
409:      * @param string $dsn DSN string
410:      */
411:     private function connect($dsn)
412:     {
413:         $this->pdo = new \PDO($dsn, $this->username, $this->password, $this->connectionOptions);
414:         $this->pdo->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);
415:         $this->driver = $this->pdo->getAttribute(\PDO::ATTR_DRIVER_NAME);
416:     }
417: 
418:     /**
419:      * Helper method to begin a transaction.
420:      *
421:      * Since SQLite does not support row level locks, we have to acquire a reserved lock
422:      * on the database immediately. Because of https://bugs.php.net/42766 we have to create
423:      * such a transaction manually which also means we cannot use PDO::commit or
424:      * PDO::rollback or PDO::inTransaction for SQLite.
425:      *
426:      * Also MySQLs default isolation, REPEATABLE READ, causes deadlock for different sessions
427:      * due to http://www.mysqlperformanceblog.com/2013/12/12/one-more-innodb-gap-lock-to-avoid/ .
428:      * So we change it to READ COMMITTED.
429:      */
430:     private function beginTransaction()
431:     {
432:         if (!$this->inTransaction) {
433:             if ('sqlite' === $this->driver) {
434:                 $this->pdo->exec('BEGIN IMMEDIATE TRANSACTION');
435:             } else {
436:                 if ('mysql' === $this->driver) {
437:                     $this->pdo->exec('SET TRANSACTION ISOLATION LEVEL READ COMMITTED');
438:                 }
439:                 $this->pdo->beginTransaction();
440:             }
441:             $this->inTransaction = true;
442:         }
443:     }
444: 
445:     /**
446:      * Helper method to commit a transaction.
447:      */
448:     private function commit()
449:     {
450:         if ($this->inTransaction) {
451:             try {
452:                 // commit read-write transaction which also releases the lock
453:                 if ('sqlite' === $this->driver) {
454:                     $this->pdo->exec('COMMIT');
455:                 } else {
456:                     $this->pdo->commit();
457:                 }
458:                 $this->inTransaction = false;
459:             } catch (\PDOException $e) {
460:                 $this->rollback();
461: 
462:                 throw $e;
463:             }
464:         }
465:     }
466: 
467:     /**
468:      * Helper method to rollback a transaction.
469:      */
470:     private function rollback()
471:     {
472:         // We only need to rollback if we are in a transaction. Otherwise the resulting
473:         // error would hide the real problem why rollback was called. We might not be
474:         // in a transaction when not using the transactional locking behavior or when
475:         // two callbacks (e.g. destroy and write) are invoked that both fail.
476:         if ($this->inTransaction) {
477:             if ('sqlite' === $this->driver) {
478:                 $this->pdo->exec('ROLLBACK');
479:             } else {
480:                 $this->pdo->rollBack();
481:             }
482:             $this->inTransaction = false;
483:         }
484:     }
485: 
486:     /**
487:      * Reads the session data in respect to the different locking strategies.
488:      *
489:      * We need to make sure we do not return session data that is already considered garbage according
490:      * to the session.gc_maxlifetime setting because gc() is called after read() and only sometimes.
491:      *
492:      * @param string $sessionId Session ID
493:      *
494:      * @return string The session data
495:      */
496:     private function doRead($sessionId)
497:     {
498:         $this->sessionExpired = false;
499: 
500:         if (self::LOCK_ADVISORY === $this->lockMode) {
501:             $this->unlockStatements[] = $this->doAdvisoryLock($sessionId);
502:         }
503: 
504:         $selectSql = $this->getSelectSql();
505:         $selectStmt = $this->pdo->prepare($selectSql);
506:         $selectStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
507: 
508:         do {
509:             $selectStmt->execute();
510:             $sessionRows = $selectStmt->fetchAll(\PDO::FETCH_NUM);
511: 
512:             if ($sessionRows) {
513:                 if ($sessionRows[0][1] + $sessionRows[0][2] < time()) {
514:                     $this->sessionExpired = true;
515: 
516:                     return '';
517:                 }
518: 
519:                 return is_resource($sessionRows[0][0]) ? stream_get_contents($sessionRows[0][0]) : $sessionRows[0][0];
520:             }
521: 
522:             if (self::LOCK_TRANSACTIONAL === $this->lockMode && 'sqlite' !== $this->driver) {
523:                 // Exclusive-reading of non-existent rows does not block, so we need to do an insert to block
524:                 // until other connections to the session are committed.
525:                 try {
526:                     $insertStmt = $this->pdo->prepare(
527:                         "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, :data, :lifetime, :time)"
528:                     );
529:                     $insertStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
530:                     $insertStmt->bindValue(':data', '', \PDO::PARAM_LOB);
531:                     $insertStmt->bindValue(':lifetime', 0, \PDO::PARAM_INT);
532:                     $insertStmt->bindValue(':time', time(), \PDO::PARAM_INT);
533:                     $insertStmt->execute();
534:                 } catch (\PDOException $e) {
535:                     // Catch duplicate key error because other connection created the session already.
536:                     // It would only not be the case when the other connection destroyed the session.
537:                     if (0 === strpos($e->getCode(), '23')) {
538:                         // Retrieve finished session data written by concurrent connection by restarting the loop.
539:                         // We have to start a new transaction as a failed query will mark the current transaction as
540:                         // aborted in PostgreSQL and disallow further queries within it.
541:                         $this->rollback();
542:                         $this->beginTransaction();
543:                         continue;
544:                     }
545: 
546:                     throw $e;
547:                 }
548:             }
549: 
550:             return '';
551:         } while (true);
552:     }
553: 
554:     /**
555:      * Executes an application-level lock on the database.
556:      *
557:      * @param string $sessionId Session ID
558:      *
559:      * @return \PDOStatement The statement that needs to be executed later to release the lock
560:      *
561:      * @throws \DomainException When an unsupported PDO driver is used
562:      *
563:      * @todo implement missing advisory locks
564:      *       - for oci using DBMS_LOCK.REQUEST
565:      *       - for sqlsrv using sp_getapplock with LockOwner = Session
566:      */
567:     private function doAdvisoryLock($sessionId)
568:     {
569:         switch ($this->driver) {
570:             case 'mysql':
571:                 // should we handle the return value? 0 on timeout, null on error
572:                 // we use a timeout of 50 seconds which is also the default for innodb_lock_wait_timeout
573:                 $stmt = $this->pdo->prepare('SELECT GET_LOCK(:key, 50)');
574:                 $stmt->bindValue(':key', $sessionId, \PDO::PARAM_STR);
575:                 $stmt->execute();
576: 
577:                 $releaseStmt = $this->pdo->prepare('DO RELEASE_LOCK(:key)');
578:                 $releaseStmt->bindValue(':key', $sessionId, \PDO::PARAM_STR);
579: 
580:                 return $releaseStmt;
581:             case 'pgsql':
582:                 // Obtaining an exclusive session level advisory lock requires an integer key.
583:                 // So we convert the HEX representation of the session id to an integer.
584:                 // Since integers are signed, we have to skip one hex char to fit in the range.
585:                 if (4 === PHP_INT_SIZE) {
586:                     $sessionInt1 = hexdec(substr($sessionId, 0, 7));
587:                     $sessionInt2 = hexdec(substr($sessionId, 7, 7));
588: 
589:                     $stmt = $this->pdo->prepare('SELECT pg_advisory_lock(:key1, :key2)');
590:                     $stmt->bindValue(':key1', $sessionInt1, \PDO::PARAM_INT);
591:                     $stmt->bindValue(':key2', $sessionInt2, \PDO::PARAM_INT);
592:                     $stmt->execute();
593: 
594:                     $releaseStmt = $this->pdo->prepare('SELECT pg_advisory_unlock(:key1, :key2)');
595:                     $releaseStmt->bindValue(':key1', $sessionInt1, \PDO::PARAM_INT);
596:                     $releaseStmt->bindValue(':key2', $sessionInt2, \PDO::PARAM_INT);
597:                 } else {
598:                     $sessionBigInt = hexdec(substr($sessionId, 0, 15));
599: 
600:                     $stmt = $this->pdo->prepare('SELECT pg_advisory_lock(:key)');
601:                     $stmt->bindValue(':key', $sessionBigInt, \PDO::PARAM_INT);
602:                     $stmt->execute();
603: 
604:                     $releaseStmt = $this->pdo->prepare('SELECT pg_advisory_unlock(:key)');
605:                     $releaseStmt->bindValue(':key', $sessionBigInt, \PDO::PARAM_INT);
606:                 }
607: 
608:                 return $releaseStmt;
609:             case 'sqlite':
610:                 throw new \DomainException('SQLite does not support advisory locks.');
611:             default:
612:                 throw new \DomainException(sprintf('Advisory locks are currently not implemented for PDO driver "%s".', $this->driver));
613:         }
614:     }
615: 
616:     /**
617:      * Return a locking or nonlocking SQL query to read session information.
618:      *
619:      * @return string The SQL string
620:      *
621:      * @throws \DomainException When an unsupported PDO driver is used
622:      */
623:     private function getSelectSql()
624:     {
625:         if (self::LOCK_TRANSACTIONAL === $this->lockMode) {
626:             $this->beginTransaction();
627: 
628:             switch ($this->driver) {
629:                 case 'mysql':
630:                 case 'oci':
631:                 case 'pgsql':
632:                     return "SELECT $this->dataCol, $this->lifetimeCol, $this->timeCol FROM $this->table WHERE $this->idCol = :id FOR UPDATE";
633:                 case 'sqlsrv':
634:                     return "SELECT $this->dataCol, $this->lifetimeCol, $this->timeCol FROM $this->table WITH (UPDLOCK, ROWLOCK) WHERE $this->idCol = :id";
635:                 case 'sqlite':
636:                     // we already locked when starting transaction
637:                     break;
638:                 default:
639:                     throw new \DomainException(sprintf('Transactional locks are currently not implemented for PDO driver "%s".', $this->driver));
640:             }
641:         }
642: 
643:         return "SELECT $this->dataCol, $this->lifetimeCol, $this->timeCol FROM $this->table WHERE $this->idCol = :id";
644:     }
645: 
646:     /**
647:      * Returns a merge/upsert (i.e. insert or update) statement when supported by the database for writing session data.
648:      *
649:      * @param string $sessionId   Session ID
650:      * @param string $data        Encoded session data
651:      * @param int    $maxlifetime session.gc_maxlifetime
652:      *
653:      * @return \PDOStatement|null The merge statement or null when not supported
654:      */
655:     private function getMergeStatement($sessionId, $data, $maxlifetime)
656:     {
657:         $mergeSql = null;
658:         switch (true) {
659:             case 'mysql' === $this->driver:
660:                 $mergeSql = "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, :data, :lifetime, :time) ".
661:                     "ON DUPLICATE KEY UPDATE $this->dataCol = VALUES($this->dataCol), $this->lifetimeCol = VALUES($this->lifetimeCol), $this->timeCol = VALUES($this->timeCol)";
662:                 break;
663:             case 'oci' === $this->driver:
664:                 // DUAL is Oracle specific dummy table
665:                 $mergeSql = "MERGE INTO $this->table USING DUAL ON ($this->idCol = ?) ".
666:                     "WHEN NOT MATCHED THEN INSERT ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (?, ?, ?, ?) ".
667:                     "WHEN MATCHED THEN UPDATE SET $this->dataCol = ?, $this->lifetimeCol = ?, $this->timeCol = ?";
668:                 break;
669:             case 'sqlsrv' === $this->driver && version_compare($this->pdo->getAttribute(\PDO::ATTR_SERVER_VERSION), '10', '>='):
670:                 // MERGE is only available since SQL Server 2008 and must be terminated by semicolon
671:                 // It also requires HOLDLOCK according to http://weblogs.sqlteam.com/dang/archive/2009/01/31/UPSERT-Race-Condition-With-MERGE.aspx
672:                 $mergeSql = "MERGE INTO $this->table WITH (HOLDLOCK) USING (SELECT 1 AS dummy) AS src ON ($this->idCol = ?) ".
673:                     "WHEN NOT MATCHED THEN INSERT ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (?, ?, ?, ?) ".
674:                     "WHEN MATCHED THEN UPDATE SET $this->dataCol = ?, $this->lifetimeCol = ?, $this->timeCol = ?;";
675:                 break;
676:             case 'sqlite' === $this->driver:
677:                 $mergeSql = "INSERT OR REPLACE INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, :data, :lifetime, :time)";
678:                 break;
679:             case 'pgsql' === $this->driver && version_compare($this->pdo->getAttribute(\PDO::ATTR_SERVER_VERSION), '9.5', '>='):
680:                 $mergeSql = "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->lifetimeCol, $this->timeCol) VALUES (:id, :data, :lifetime, :time) ".
681:                     "ON CONFLICT ($this->idCol) DO UPDATE SET ($this->dataCol, $this->lifetimeCol, $this->timeCol) = (EXCLUDED.$this->dataCol, EXCLUDED.$this->lifetimeCol, EXCLUDED.$this->timeCol)";
682:                 break;
683:         }
684: 
685:         if (null !== $mergeSql) {
686:             $mergeStmt = $this->pdo->prepare($mergeSql);
687: 
688:             if ('sqlsrv' === $this->driver || 'oci' === $this->driver) {
689:                 $mergeStmt->bindParam(1, $sessionId, \PDO::PARAM_STR);
690:                 $mergeStmt->bindParam(2, $sessionId, \PDO::PARAM_STR);
691:                 $mergeStmt->bindParam(3, $data, \PDO::PARAM_LOB);
692:                 $mergeStmt->bindParam(4, $maxlifetime, \PDO::PARAM_INT);
693:                 $mergeStmt->bindValue(5, time(), \PDO::PARAM_INT);
694:                 $mergeStmt->bindParam(6, $data, \PDO::PARAM_LOB);
695:                 $mergeStmt->bindParam(7, $maxlifetime, \PDO::PARAM_INT);
696:                 $mergeStmt->bindValue(8, time(), \PDO::PARAM_INT);
697:             } else {
698:                 $mergeStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
699:                 $mergeStmt->bindParam(':data', $data, \PDO::PARAM_LOB);
700:                 $mergeStmt->bindParam(':lifetime', $maxlifetime, \PDO::PARAM_INT);
701:                 $mergeStmt->bindValue(':time', time(), \PDO::PARAM_INT);
702:             }
703: 
704:             return $mergeStmt;
705:         }
706:     }
707: 
708:     /**
709:      * Return a PDO instance.
710:      *
711:      * @return \PDO
712:      */
713:     protected function getConnection()
714:     {
715:         if (null === $this->pdo) {
716:             $this->connect($this->dsn ?: ini_get('session.save_path'));
717:         }
718: 
719:         return $this->pdo;
720:     }
721: }
722: