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Differences Between: [Versions 310 and 400] [Versions 39 and 400] [Versions 400 and 401] [Versions 400 and 402] [Versions 400 and 403]

   1  <?php
   2  // This file is part of Moodle - http://moodle.org/
   3  //
   4  // Moodle is free software: you can redistribute it and/or modify
   5  // it under the terms of the GNU General Public License as published by
   6  // the Free Software Foundation, either version 3 of the License, or
   7  // (at your option) any later version.
   8  //
   9  // Moodle is distributed in the hope that it will be useful,
  10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  // GNU General Public License for more details.
  13  //
  14  // You should have received a copy of the GNU General Public License
  15  // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
  16  
  17  /**
  18   * Redis based session handler.
  19   *
  20   * @package    core
  21   * @copyright  2015 Russell Smith <mr-russ@smith2001.net>
  22   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  23   */
  24  
  25  namespace core\session;
  26  
  27  use RedisException;
  28  
  29  defined('MOODLE_INTERNAL') || die();
  30  
  31  /**
  32   * Redis based session handler.
  33   *
  34   * The default Redis session handler does not handle locking in 2.2.7, so we have written a php session handler
  35   * that uses locking.  The places where locking is used was modeled from the memcached code that is used in Moodle
  36   * https://github.com/php-memcached-dev/php-memcached/blob/master/php_memcached_session.c
  37   *
  38   * @package    core
  39   * @copyright  2016 Russell Smith
  40   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  41   */
  42  class redis extends handler {
  43      /**
  44       * Compressor: none.
  45       */
  46      const COMPRESSION_NONE      = 'none';
  47      /**
  48       * Compressor: PHP GZip.
  49       */
  50      const COMPRESSION_GZIP      = 'gzip';
  51      /**
  52       * Compressor: PHP Zstandard.
  53       */
  54      const COMPRESSION_ZSTD      = 'zstd';
  55  
  56      /** @var string $host save_path string  */
  57      protected $host = '';
  58      /** @var int $port The port to connect to */
  59      protected $port = 6379;
  60      /** @var string $auth redis password  */
  61      protected $auth = '';
  62      /** @var int $database the Redis database to store sesions in */
  63      protected $database = 0;
  64      /** @var array $servers list of servers parsed from save_path */
  65      protected $prefix = '';
  66      /** @var int $acquiretimeout how long to wait for session lock in seconds */
  67      protected $acquiretimeout = 120;
  68      /** @var int $lockretry how long to wait between session lock attempts in ms */
  69      protected $lockretry = 100;
  70      /** @var int $serializer The serializer to use */
  71      protected $serializer = \Redis::SERIALIZER_PHP;
  72      /** @var int $compressor The compressor to use */
  73      protected $compressor = self::COMPRESSION_NONE;
  74      /** @var string $lasthash hash of the session data content */
  75      protected $lasthash = null;
  76  
  77      /**
  78       * @var int $lockexpire how long to wait in seconds before expiring the lock automatically
  79       * so that other requests may continue execution, ignored if PECL redis is below version 2.2.0.
  80       */
  81      protected $lockexpire;
  82  
  83      /** @var Redis Connection */
  84      protected $connection = null;
  85  
  86      /** @var array $locks List of currently held locks by this page. */
  87      protected $locks = array();
  88  
  89      /** @var int $timeout How long sessions live before expiring. */
  90      protected $timeout;
  91  
  92      /**
  93       * Create new instance of handler.
  94       */
  95      public function __construct() {
  96          global $CFG;
  97  
  98          if (isset($CFG->session_redis_host)) {
  99              $this->host = $CFG->session_redis_host;
 100          }
 101  
 102          if (isset($CFG->session_redis_port)) {
 103              $this->port = (int)$CFG->session_redis_port;
 104          }
 105  
 106          if (isset($CFG->session_redis_auth)) {
 107              $this->auth = $CFG->session_redis_auth;
 108          }
 109  
 110          if (isset($CFG->session_redis_database)) {
 111              $this->database = (int)$CFG->session_redis_database;
 112          }
 113  
 114          if (isset($CFG->session_redis_prefix)) {
 115              $this->prefix = $CFG->session_redis_prefix;
 116          }
 117  
 118          if (isset($CFG->session_redis_acquire_lock_timeout)) {
 119              $this->acquiretimeout = (int)$CFG->session_redis_acquire_lock_timeout;
 120          }
 121  
 122          if (isset($CFG->session_redis_acquire_lock_retry)) {
 123              $this->lockretry = (int)$CFG->session_redis_acquire_lock_retry;
 124          }
 125  
 126          if (!empty($CFG->session_redis_serializer_use_igbinary) && defined('\Redis::SERIALIZER_IGBINARY')) {
 127              $this->serializer = \Redis::SERIALIZER_IGBINARY; // Set igbinary serializer if phpredis supports it.
 128          }
 129  
 130          // The following configures the session lifetime in redis to allow some
 131          // wriggle room in the user noticing they've been booted off and
 132          // letting them log back in before they lose their session entirely.
 133          $updatefreq = empty($CFG->session_update_timemodified_frequency) ? 20 : $CFG->session_update_timemodified_frequency;
 134          $this->timeout = $CFG->sessiontimeout + $updatefreq + MINSECS;
 135  
 136          $this->lockexpire = $CFG->sessiontimeout;
 137          if (isset($CFG->session_redis_lock_expire)) {
 138              $this->lockexpire = (int)$CFG->session_redis_lock_expire;
 139          }
 140  
 141          if (isset($CFG->session_redis_compressor)) {
 142              $this->compressor = $CFG->session_redis_compressor;
 143          }
 144      }
 145  
 146      /**
 147       * Start the session.
 148       *
 149       * @return bool success
 150       */
 151      public function start() {
 152          $result = parent::start();
 153  
 154          return $result;
 155      }
 156  
 157      /**
 158       * Init session handler.
 159       */
 160      public function init() {
 161          if (!extension_loaded('redis')) {
 162              throw new exception('sessionhandlerproblem', 'error', '', null, 'redis extension is not loaded');
 163          }
 164  
 165          if (empty($this->host)) {
 166              throw new exception('sessionhandlerproblem', 'error', '', null,
 167                      '$CFG->session_redis_host must be specified in config.php');
 168          }
 169  
 170          // The session handler requires a version of Redis with the SETEX command (at least 2.0).
 171          $version = phpversion('Redis');
 172          if (!$version or version_compare($version, '2.0') <= 0) {
 173              throw new exception('sessionhandlerproblem', 'error', '', null, 'redis extension version must be at least 2.0');
 174          }
 175  
 176          $this->connection = new \Redis();
 177  
 178          $result = session_set_save_handler(array($this, 'handler_open'),
 179              array($this, 'handler_close'),
 180              array($this, 'handler_read'),
 181              array($this, 'handler_write'),
 182              array($this, 'handler_destroy'),
 183              array($this, 'handler_gc'));
 184          if (!$result) {
 185              throw new exception('redissessionhandlerproblem', 'error');
 186          }
 187  
 188          // MDL-59866: Add retries for connections (up to 5 times) to make sure it goes through.
 189          $counter = 1;
 190          $maxnumberofretries = 5;
 191  
 192          while ($counter <= $maxnumberofretries) {
 193  
 194              try {
 195  
 196                  $delay = rand(100, 500);
 197  
 198                  // One second timeout was chosen as it is long for connection, but short enough for a user to be patient.
 199                  if (!$this->connection->connect($this->host, $this->port, 1, null, $delay)) {
 200                      throw new RedisException('Unable to connect to host.');
 201                  }
 202  
 203                  if ($this->auth !== '') {
 204                      if (!$this->connection->auth($this->auth)) {
 205                          throw new RedisException('Unable to authenticate.');
 206                      }
 207                  }
 208  
 209                  if (!$this->connection->setOption(\Redis::OPT_SERIALIZER, $this->serializer)) {
 210                      throw new RedisException('Unable to set Redis PHP Serializer option.');
 211                  }
 212  
 213                  if ($this->prefix !== '') {
 214                      // Use custom prefix on sessions.
 215                      if (!$this->connection->setOption(\Redis::OPT_PREFIX, $this->prefix)) {
 216                          throw new RedisException('Unable to set Redis Prefix option.');
 217                      }
 218                  }
 219                  if ($this->database !== 0) {
 220                      if (!$this->connection->select($this->database)) {
 221                          throw new RedisException('Unable to select Redis database '.$this->database.'.');
 222                      }
 223                  }
 224                  $this->connection->ping();
 225                  return true;
 226              } catch (RedisException $e) {
 227                  $logstring = "Failed to connect (try {$counter} out of {$maxnumberofretries}) to redis ";
 228                  $logstring .= "at {$this->host}:{$this->port}, error returned was: {$e->getMessage()}";
 229  
 230                  debugging($logstring);
 231              }
 232  
 233              $counter++;
 234  
 235              // Introduce a random sleep between 100ms and 500ms.
 236              usleep(rand(100000, 500000));
 237          }
 238  
 239          // We have exhausted our retries, time to give up.
 240          if (isset($logstring)) {
 241              throw new RedisException($logstring);
 242          }
 243      }
 244  
 245      /**
 246       * Update our session search path to include session name when opened.
 247       *
 248       * @param string $savepath  unused session save path. (ignored)
 249       * @param string $sessionname Session name for this session. (ignored)
 250       * @return bool true always as we will succeed.
 251       */
 252      public function handler_open($savepath, $sessionname) {
 253          return true;
 254      }
 255  
 256      /**
 257       * Close the session completely. We also remove all locks we may have obtained that aren't expired.
 258       *
 259       * @return bool true on success.  false on unable to unlock sessions.
 260       */
 261      public function handler_close() {
 262          $this->lasthash = null;
 263          try {
 264              foreach ($this->locks as $id => $expirytime) {
 265                  if ($expirytime > $this->time()) {
 266                      $this->unlock_session($id);
 267                  }
 268                  unset($this->locks[$id]);
 269              }
 270          } catch (RedisException $e) {
 271              error_log('Failed talking to redis: '.$e->getMessage());
 272              return false;
 273          }
 274  
 275          return true;
 276      }
 277      /**
 278       * Read the session data from storage
 279       *
 280       * @param string $id The session id to read from storage.
 281       * @return string The session data for PHP to process.
 282       *
 283       * @throws RedisException when we are unable to talk to the Redis server.
 284       */
 285      public function handler_read($id) {
 286          try {
 287              if ($this->requires_write_lock()) {
 288                  $this->lock_session($id);
 289              }
 290              $sessiondata = $this->uncompress($this->connection->get($id));
 291  
 292              if ($sessiondata === false) {
 293                  if ($this->requires_write_lock()) {
 294                      $this->unlock_session($id);
 295                  }
 296                  $this->lasthash = sha1('');
 297                  return '';
 298              }
 299              $this->connection->expire($id, $this->timeout);
 300          } catch (RedisException $e) {
 301              error_log('Failed talking to redis: '.$e->getMessage());
 302              throw $e;
 303          }
 304          $this->lasthash = sha1(base64_encode($sessiondata));
 305          return $sessiondata;
 306      }
 307  
 308      /**
 309       * Compresses session data.
 310       *
 311       * @param mixed $value
 312       * @return string
 313       */
 314      private function compress($value) {
 315          switch ($this->compressor) {
 316              case self::COMPRESSION_NONE:
 317                  return $value;
 318              case self::COMPRESSION_GZIP:
 319                  return gzencode($value);
 320              case self::COMPRESSION_ZSTD:
 321                  return zstd_compress($value);
 322              default:
 323                  debugging("Invalid compressor: {$this->compressor}");
 324                  return $value;
 325          }
 326      }
 327  
 328      /**
 329       * Uncompresses session data.
 330       *
 331       * @param string $value
 332       * @return mixed
 333       */
 334      private function uncompress($value) {
 335          if ($value === false) {
 336              return false;
 337          }
 338  
 339          switch ($this->compressor) {
 340              case self::COMPRESSION_NONE:
 341                  break;
 342              case self::COMPRESSION_GZIP:
 343                  $value = gzdecode($value);
 344                  break;
 345              case self::COMPRESSION_ZSTD:
 346                  $value = zstd_uncompress($value);
 347                  break;
 348              default:
 349                  debugging("Invalid compressor: {$this->compressor}");
 350          }
 351  
 352          return $value;
 353      }
 354  
 355      /**
 356       * Write the serialized session data to our session store.
 357       *
 358       * @param string $id session id to write.
 359       * @param string $data session data
 360       * @return bool true on write success, false on failure
 361       */
 362      public function handler_write($id, $data) {
 363  
 364          $hash = sha1(base64_encode($data));
 365  
 366          // If the content has not changed don't bother writing.
 367          if ($hash === $this->lasthash) {
 368              return true;
 369          }
 370  
 371          if (is_null($this->connection)) {
 372              // The session has already been closed, don't attempt another write.
 373              error_log('Tried to write session: '.$id.' before open or after close.');
 374              return false;
 375          }
 376  
 377          // We do not do locking here because memcached doesn't.  Also
 378          // PHP does open, read, destroy, write, close. When a session doesn't exist.
 379          // There can be race conditions on new sessions racing each other but we can
 380          // address that in the future.
 381          try {
 382              $data = $this->compress($data);
 383  
 384              $this->connection->setex($id, $this->timeout, $data);
 385          } catch (RedisException $e) {
 386              error_log('Failed talking to redis: '.$e->getMessage());
 387              return false;
 388          }
 389          return true;
 390      }
 391  
 392      /**
 393       * Handle destroying a session.
 394       *
 395       * @param string $id the session id to destroy.
 396       * @return bool true if the session was deleted, false otherwise.
 397       */
 398      public function handler_destroy($id) {
 399          $this->lasthash = null;
 400          try {
 401              $this->connection->del($id);
 402              $this->unlock_session($id);
 403          } catch (RedisException $e) {
 404              error_log('Failed talking to redis: '.$e->getMessage());
 405              return false;
 406          }
 407  
 408          return true;
 409      }
 410  
 411      /**
 412       * Garbage collect sessions.  We don't we any as Redis does it for us.
 413       *
 414       * @param integer $maxlifetime All sessions older than this should be removed.
 415       * @return bool true, as Redis handles expiry for us.
 416       */
 417      public function handler_gc($maxlifetime) {
 418          return true;
 419      }
 420  
 421      /**
 422       * Unlock a session.
 423       *
 424       * @param string $id Session id to be unlocked.
 425       */
 426      protected function unlock_session($id) {
 427          if (isset($this->locks[$id])) {
 428              $this->connection->del($id.".lock");
 429              unset($this->locks[$id]);
 430          }
 431      }
 432  
 433      /**
 434       * Obtain a session lock so we are the only one using it at the moment.
 435       *
 436       * @param string $id The session id to lock.
 437       * @return bool true when session was locked, exception otherwise.
 438       * @throws exception When we are unable to obtain a session lock.
 439       */
 440      protected function lock_session($id) {
 441          $lockkey = $id.".lock";
 442  
 443          $haslock = isset($this->locks[$id]) && $this->time() < $this->locks[$id];
 444          $startlocktime = $this->time();
 445  
 446          /* To be able to ensure sessions don't write out of order we must obtain an exclusive lock
 447           * on the session for the entire time it is open.  If another AJAX call, or page is using
 448           * the session then we just wait until it finishes before we can open the session.
 449           */
 450  
 451          // Store the current host, process id and the request URI so it's easy to track who has the lock.
 452          $hostname = gethostname();
 453          if ($hostname === false) {
 454              $hostname = 'UNKNOWN HOST';
 455          }
 456          $pid = getmypid();
 457          if ($pid === false) {
 458              $pid = 'UNKNOWN';
 459          }
 460          $uri = isset($_SERVER['REQUEST_URI']) ? $_SERVER['REQUEST_URI'] : 'unknown uri';
 461  
 462          $whoami = "[pid {$pid}] {$hostname}:$uri";
 463  
 464          while (!$haslock) {
 465  
 466              $haslock = $this->connection->setnx($lockkey, $whoami);
 467  
 468              if ($haslock) {
 469                  $this->locks[$id] = $this->time() + $this->lockexpire;
 470                  $this->connection->expire($lockkey, $this->lockexpire);
 471                  return true;
 472              }
 473  
 474              if ($this->time() > $startlocktime + $this->acquiretimeout) {
 475                  // This is a fatal error, better inform users.
 476                  // It should not happen very often - all pages that need long time to execute
 477                  // should close session immediately after access control checks.
 478                  $whohaslock = $this->connection->get($lockkey);
 479                  // phpcs:ignore
 480                  error_log("Cannot obtain session lock for sid: $id within $this->acquiretimeout seconds. " .
 481                      "It is likely another page ($whohaslock) has a long session lock, or the session lock was never released.");
 482                  throw new exception("Unable to obtain session lock");
 483              }
 484  
 485              if ($this->time() < $startlocktime + 5) {
 486                  // We want a random delay to stagger the polling load. Ideally
 487                  // this delay should be a fraction of the average response
 488                  // time. If it is too small we will poll too much and if it is
 489                  // too large we will waste time waiting for no reason. 100ms is
 490                  // the default starting point.
 491                  $delay = rand($this->lockretry, $this->lockretry * 1.1);
 492              } else {
 493                  // If we don't get a lock within 5 seconds then there must be a
 494                  // very long lived process holding the lock so throttle back to
 495                  // just polling roughly once a second.
 496                  $delay = rand(1000, 1100);
 497              }
 498  
 499              usleep($delay * 1000);
 500          }
 501      }
 502  
 503      /**
 504       * Return the current time.
 505       *
 506       * @return int the current time as a unixtimestamp.
 507       */
 508      protected function time() {
 509          return time();
 510      }
 511  
 512      /**
 513       * Check the backend contains data for this session id.
 514       *
 515       * Note: this is intended to be called from manager::session_exists() only.
 516       *
 517       * @param string $sid
 518       * @return bool true if session found.
 519       */
 520      public function session_exists($sid) {
 521          if (!$this->connection) {
 522              return false;
 523          }
 524  
 525          try {
 526              return !empty($this->connection->exists($sid));
 527          } catch (RedisException $e) {
 528              return false;
 529          }
 530      }
 531  
 532      /**
 533       * Kill all active sessions, the core sessions table is purged afterwards.
 534       */
 535      public function kill_all_sessions() {
 536          global $DB;
 537          if (!$this->connection) {
 538              return;
 539          }
 540  
 541          $rs = $DB->get_recordset('sessions', array(), 'id DESC', 'id, sid');
 542          foreach ($rs as $record) {
 543              $this->handler_destroy($record->sid);
 544          }
 545          $rs->close();
 546      }
 547  
 548      /**
 549       * Kill one session, the session record is removed afterwards.
 550       *
 551       * @param string $sid
 552       */
 553      public function kill_session($sid) {
 554          if (!$this->connection) {
 555              return;
 556          }
 557  
 558          $this->handler_destroy($sid);
 559      }
 560  }