bug #27250 [Session] limiting :key for GET_LOCK to 64 chars (oleg-andreyev)

This PR was merged into the 2.7 branch.

Discussion
----------

[Session] limiting :key for GET_LOCK to 64 chars

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT

> MySQL 5.7.5 and later enforces a maximum length on lock names of 64 characters. Previously, no limit was enforced.

Cases:
- `session_id` is set by developers manually
- `session.sid_length` is configured

Ref.:
- https://dev.mysql.com/doc/refman/5.7/en/miscellaneous-functions.html#function_get-lock
- http://php.net/manual/en/session.configuration.php#ini.session.sid-length

Other issues:
- https://github.com/go-sql-driver/mysql/issues/385
- https://github.com/stefangabos/Zebra_Session/issues/16

Commits
-------

9cda96b8b5 #27250 limiting GET_LOCK key up to 64 char due to changes in MySQL 5.7.5 and later

src/Symfony/Component/HttpFoundation/Session/Storage/Handler/PdoSessionHandler.php

@@ -552,14 +552,16 @@ class PdoSessionHandler implements \SessionHandlerInterface
     {
         switch ($this->driver) {
             case 'mysql':
+                // MySQL 5.7.5 and later enforces a maximum length on lock names of 64 characters. Previously, no limit was enforced.
+                $lockId = \substr($sessionId, 0, 64);
                 // should we handle the return value? 0 on timeout, null on error
                 // we use a timeout of 50 seconds which is also the default for innodb_lock_wait_timeout
                 $stmt = $this->pdo->prepare('SELECT GET_LOCK(:key, 50)');
-                $stmt->bindValue(':key', $sessionId, \PDO::PARAM_STR);
+                $stmt->bindValue(':key', $lockId, \PDO::PARAM_STR);
                 $stmt->execute();
 
                 $releaseStmt = $this->pdo->prepare('DO RELEASE_LOCK(:key)');
-                $releaseStmt->bindValue(':key', $sessionId, \PDO::PARAM_STR);
+                $releaseStmt->bindValue(':key', $lockId, \PDO::PARAM_STR);
 
                 return $releaseStmt;
             case 'pgsql':