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Differences Between: [Versions 310 and 402] [Versions 311 and 402] [Versions 39 and 402] [Versions 400 and 402] [Versions 401 and 402] [Versions 402 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 $acquirewarn how long before warning when waiting for a lock in seconds */
  69      protected $acquirewarn = null;
  70      /** @var int $lockretry how long to wait between session lock attempts in ms */
  71      protected $lockretry = 100;
  72      /** @var int $serializer The serializer to use */
  73      protected $serializer = \Redis::SERIALIZER_PHP;
  74      /** @var int $compressor The compressor to use */
  75      protected $compressor = self::COMPRESSION_NONE;
  76      /** @var string $lasthash hash of the session data content */
  77      protected $lasthash = null;
  78  
  79      /**
  80       * @var int $lockexpire how long to wait in seconds before expiring the lock automatically
  81       * so that other requests may continue execution, ignored if PECL redis is below version 2.2.0.
  82       */
  83      protected $lockexpire;
  84  
  85      /** @var Redis Connection */
  86      protected $connection = null;
  87  
  88      /** @var array $locks List of currently held locks by this page. */
  89      protected $locks = array();
  90  
  91      /** @var int $timeout How long sessions live before expiring. */
  92      protected $timeout;
  93  
  94      /**
  95       * Create new instance of handler.
  96       */
  97      public function __construct() {
  98          global $CFG;
  99  
 100          if (isset($CFG->session_redis_host)) {
 101              $this->host = $CFG->session_redis_host;
 102          }
 103  
 104          if (isset($CFG->session_redis_port)) {
 105              $this->port = (int)$CFG->session_redis_port;
 106          }
 107  
 108          if (isset($CFG->session_redis_auth)) {
 109              $this->auth = $CFG->session_redis_auth;
 110          }
 111  
 112          if (isset($CFG->session_redis_database)) {
 113              $this->database = (int)$CFG->session_redis_database;
 114          }
 115  
 116          if (isset($CFG->session_redis_prefix)) {
 117              $this->prefix = $CFG->session_redis_prefix;
 118          }
 119  
 120          if (isset($CFG->session_redis_acquire_lock_timeout)) {
 121              $this->acquiretimeout = (int)$CFG->session_redis_acquire_lock_timeout;
 122          }
 123  
 124          if (isset($CFG->session_redis_acquire_lock_warn)) {
 125              $this->acquirewarn = (int)$CFG->session_redis_acquire_lock_warn;
 126          }
 127  
 128          if (isset($CFG->session_redis_acquire_lock_retry)) {
 129              $this->lockretry = (int)$CFG->session_redis_acquire_lock_retry;
 130          }
 131  
 132          if (!empty($CFG->session_redis_serializer_use_igbinary) && defined('\Redis::SERIALIZER_IGBINARY')) {
 133              $this->serializer = \Redis::SERIALIZER_IGBINARY; // Set igbinary serializer if phpredis supports it.
 134          }
 135  
 136          // The following configures the session lifetime in redis to allow some
 137          // wriggle room in the user noticing they've been booted off and
 138          // letting them log back in before they lose their session entirely.
 139          $updatefreq = empty($CFG->session_update_timemodified_frequency) ? 20 : $CFG->session_update_timemodified_frequency;
 140          $this->timeout = $CFG->sessiontimeout + $updatefreq + MINSECS;
 141  
 142          // This sets the Redis session lock expiry time to whatever is lower, either
 143          // the PHP execution time `max_execution_time`, if the value was defined in
 144          // the `php.ini` or the globally configured `sessiontimeout`. Setting it to
 145          // the lower of the two will not make things worse it if the execution timeout
 146          // is longer than the session timeout.
 147          // For the PHP execution time, once the PHP execution time is over, we can be sure
 148          // that the lock is no longer actively held so that the lock can expire safely.
 149          // Although at `lib/classes/php_time_limit.php::raise(int)`, Moodle can
 150          // progressively increase the maximum PHP execution time, this is limited to the
 151          // `max_execution_time` value defined in the `php.ini`.
 152          // For the session timeout, we assume it is safe to consider the lock to expire
 153          // once the session itself expires.
 154          // If we unnecessarily hold the lock any longer, it blocks other session requests.
 155          $this->lockexpire = ini_get('max_execution_time');
 156          if (empty($this->lockexpire) || ($this->lockexpire > (int)$CFG->sessiontimeout)) {
 157              $this->lockexpire = (int)$CFG->sessiontimeout;
 158          }
 159          if (isset($CFG->session_redis_lock_expire)) {
 160              $this->lockexpire = (int)$CFG->session_redis_lock_expire;
 161          }
 162  
 163          if (isset($CFG->session_redis_compressor)) {
 164              $this->compressor = $CFG->session_redis_compressor;
 165          }
 166      }
 167  
 168      /**
 169       * Start the session.
 170       *
 171       * @return bool success
 172       */
 173      public function start() {
 174          $result = parent::start();
 175  
 176          return $result;
 177      }
 178  
 179      /**
 180       * Init session handler.
 181       */
 182      public function init() {
 183          if (!extension_loaded('redis')) {
 184              throw new exception('sessionhandlerproblem', 'error', '', null, 'redis extension is not loaded');
 185          }
 186  
 187          if (empty($this->host)) {
 188              throw new exception('sessionhandlerproblem', 'error', '', null,
 189                      '$CFG->session_redis_host must be specified in config.php');
 190          }
 191  
 192          // The session handler requires a version of Redis with the SETEX command (at least 2.0).
 193          $version = phpversion('Redis');
 194          if (!$version or version_compare($version, '2.0') <= 0) {
 195              throw new exception('sessionhandlerproblem', 'error', '', null, 'redis extension version must be at least 2.0');
 196          }
 197  
 198          $this->connection = new \Redis();
 199  
 200          $result = session_set_save_handler(array($this, 'handler_open'),
 201              array($this, 'handler_close'),
 202              array($this, 'handler_read'),
 203              array($this, 'handler_write'),
 204              array($this, 'handler_destroy'),
 205              array($this, 'handler_gc'));
 206          if (!$result) {
 207              throw new exception('redissessionhandlerproblem', 'error');
 208          }
 209  
 210          // MDL-59866: Add retries for connections (up to 5 times) to make sure it goes through.
 211          $counter = 1;
 212          $maxnumberofretries = 5;
 213  
 214          while ($counter <= $maxnumberofretries) {
 215  
 216              try {
 217  
 218                  $delay = rand(100, 500);
 219  
 220                  // One second timeout was chosen as it is long for connection, but short enough for a user to be patient.
 221                  if (!$this->connection->connect($this->host, $this->port, 1, null, $delay)) {
 222                      throw new RedisException('Unable to connect to host.');
 223                  }
 224  
 225                  if ($this->auth !== '') {
 226                      if (!$this->connection->auth($this->auth)) {
 227                          throw new RedisException('Unable to authenticate.');
 228                      }
 229                  }
 230  
 231                  if (!$this->connection->setOption(\Redis::OPT_SERIALIZER, $this->serializer)) {
 232                      throw new RedisException('Unable to set Redis PHP Serializer option.');
 233                  }
 234  
 235                  if ($this->prefix !== '') {
 236                      // Use custom prefix on sessions.
 237                      if (!$this->connection->setOption(\Redis::OPT_PREFIX, $this->prefix)) {
 238                          throw new RedisException('Unable to set Redis Prefix option.');
 239                      }
 240                  }
 241                  if ($this->database !== 0) {
 242                      if (!$this->connection->select($this->database)) {
 243                          throw new RedisException('Unable to select Redis database '.$this->database.'.');
 244                      }
 245                  }
 246                  return true;
 247              } catch (RedisException $e) {
 248                  $logstring = "Failed to connect (try {$counter} out of {$maxnumberofretries}) to redis ";
 249                  $logstring .= "at {$this->host}:{$this->port}, error returned was: {$e->getMessage()}";
 250  
 251                  debugging($logstring);
 252              }
 253  
 254              $counter++;
 255  
 256              // Introduce a random sleep between 100ms and 500ms.
 257              usleep(rand(100000, 500000));
 258          }
 259  
 260          // We have exhausted our retries, time to give up.
 261          if (isset($logstring)) {
 262              throw new RedisException($logstring);
 263          }
 264      }
 265  
 266      /**
 267       * Update our session search path to include session name when opened.
 268       *
 269       * @param string $savepath  unused session save path. (ignored)
 270       * @param string $sessionname Session name for this session. (ignored)
 271       * @return bool true always as we will succeed.
 272       */
 273      public function handler_open($savepath, $sessionname) {
 274          return true;
 275      }
 276  
 277      /**
 278       * Close the session completely. We also remove all locks we may have obtained that aren't expired.
 279       *
 280       * @return bool true on success.  false on unable to unlock sessions.
 281       */
 282      public function handler_close() {
 283          $this->lasthash = null;
 284          try {
 285              foreach ($this->locks as $id => $expirytime) {
 286                  if ($expirytime > $this->time()) {
 287                      $this->unlock_session($id);
 288                  }
 289                  unset($this->locks[$id]);
 290              }
 291          } catch (RedisException $e) {
 292              error_log('Failed talking to redis: '.$e->getMessage());
 293              return false;
 294          }
 295  
 296          return true;
 297      }
 298      /**
 299       * Read the session data from storage
 300       *
 301       * @param string $id The session id to read from storage.
 302       * @return string The session data for PHP to process.
 303       *
 304       * @throws RedisException when we are unable to talk to the Redis server.
 305       */
 306      public function handler_read($id) {
 307          try {
 308              if ($this->requires_write_lock()) {
 309                  $this->lock_session($id);
 310              }
 311              $sessiondata = $this->uncompress($this->connection->get($id));
 312  
 313              if ($sessiondata === false) {
 314                  if ($this->requires_write_lock()) {
 315                      $this->unlock_session($id);
 316                  }
 317                  $this->lasthash = sha1('');
 318                  return '';
 319              }
 320              $this->connection->expire($id, $this->timeout);
 321          } catch (RedisException $e) {
 322              error_log('Failed talking to redis: '.$e->getMessage());
 323              throw $e;
 324          }
 325          $this->lasthash = sha1(base64_encode($sessiondata));
 326          return $sessiondata;
 327      }
 328  
 329      /**
 330       * Compresses session data.
 331       *
 332       * @param mixed $value
 333       * @return string
 334       */
 335      private function compress($value) {
 336          switch ($this->compressor) {
 337              case self::COMPRESSION_NONE:
 338                  return $value;
 339              case self::COMPRESSION_GZIP:
 340                  return gzencode($value);
 341              case self::COMPRESSION_ZSTD:
 342                  return zstd_compress($value);
 343              default:
 344                  debugging("Invalid compressor: {$this->compressor}");
 345                  return $value;
 346          }
 347      }
 348  
 349      /**
 350       * Uncompresses session data.
 351       *
 352       * @param string $value
 353       * @return mixed
 354       */
 355      private function uncompress($value) {
 356          if ($value === false) {
 357              return false;
 358          }
 359  
 360          switch ($this->compressor) {
 361              case self::COMPRESSION_NONE:
 362                  break;
 363              case self::COMPRESSION_GZIP:
 364                  $value = gzdecode($value);
 365                  break;
 366              case self::COMPRESSION_ZSTD:
 367                  $value = zstd_uncompress($value);
 368                  break;
 369              default:
 370                  debugging("Invalid compressor: {$this->compressor}");
 371          }
 372  
 373          return $value;
 374      }
 375  
 376      /**
 377       * Write the serialized session data to our session store.
 378       *
 379       * @param string $id session id to write.
 380       * @param string $data session data
 381       * @return bool true on write success, false on failure
 382       */
 383      public function handler_write($id, $data) {
 384  
 385          $hash = sha1(base64_encode($data));
 386  
 387          // If the content has not changed don't bother writing.
 388          if ($hash === $this->lasthash) {
 389              return true;
 390          }
 391  
 392          if (is_null($this->connection)) {
 393              // The session has already been closed, don't attempt another write.
 394              error_log('Tried to write session: '.$id.' before open or after close.');
 395              return false;
 396          }
 397  
 398          // We do not do locking here because memcached doesn't.  Also
 399          // PHP does open, read, destroy, write, close. When a session doesn't exist.
 400          // There can be race conditions on new sessions racing each other but we can
 401          // address that in the future.
 402          try {
 403              $data = $this->compress($data);
 404  
 405              $this->connection->setex($id, $this->timeout, $data);
 406          } catch (RedisException $e) {
 407              error_log('Failed talking to redis: '.$e->getMessage());
 408              return false;
 409          }
 410          return true;
 411      }
 412  
 413      /**
 414       * Handle destroying a session.
 415       *
 416       * @param string $id the session id to destroy.
 417       * @return bool true if the session was deleted, false otherwise.
 418       */
 419      public function handler_destroy($id) {
 420          $this->lasthash = null;
 421          try {
 422              $this->connection->del($id);
 423              $this->unlock_session($id);
 424          } catch (RedisException $e) {
 425              error_log('Failed talking to redis: '.$e->getMessage());
 426              return false;
 427          }
 428  
 429          return true;
 430      }
 431  
 432      /**
 433       * Garbage collect sessions.  We don't we any as Redis does it for us.
 434       *
 435       * @param integer $maxlifetime All sessions older than this should be removed.
 436       * @return bool true, as Redis handles expiry for us.
 437       */
 438      public function handler_gc($maxlifetime) {
 439          return true;
 440      }
 441  
 442      /**
 443       * Unlock a session.
 444       *
 445       * @param string $id Session id to be unlocked.
 446       */
 447      protected function unlock_session($id) {
 448          if (isset($this->locks[$id])) {
 449              $this->connection->del($id.".lock");
 450              unset($this->locks[$id]);
 451          }
 452      }
 453  
 454      /**
 455       * Obtain a session lock so we are the only one using it at the moment.
 456       *
 457       * @param string $id The session id to lock.
 458       * @return bool true when session was locked, exception otherwise.
 459       * @throws exception When we are unable to obtain a session lock.
 460       */
 461      protected function lock_session($id) {
 462          $lockkey = $id.".lock";
 463  
 464          $haslock = isset($this->locks[$id]) && $this->time() < $this->locks[$id];
 465          $startlocktime = $this->time();
 466  
 467          /* To be able to ensure sessions don't write out of order we must obtain an exclusive lock
 468           * on the session for the entire time it is open.  If another AJAX call, or page is using
 469           * the session then we just wait until it finishes before we can open the session.
 470           */
 471  
 472          // Store the current host, process id and the request URI so it's easy to track who has the lock.
 473          $hostname = gethostname();
 474          if ($hostname === false) {
 475              $hostname = 'UNKNOWN HOST';
 476          }
 477          $pid = getmypid();
 478          if ($pid === false) {
 479              $pid = 'UNKNOWN';
 480          }
 481          $uri = isset($_SERVER['REQUEST_URI']) ? $_SERVER['REQUEST_URI'] : 'unknown uri';
 482  
 483          $whoami = "[pid {$pid}] {$hostname}:$uri";
 484  
 485          $haswarned = false; // Have we logged a lock warning?
 486  
 487          while (!$haslock) {
 488  
 489              $haslock = $this->connection->setnx($lockkey, $whoami);
 490  
 491              if ($haslock) {
 492                  $this->locks[$id] = $this->time() + $this->lockexpire;
 493                  $this->connection->expire($lockkey, $this->lockexpire);
 494                  return true;
 495              }
 496  
 497              if (!empty($this->acquirewarn) && !$haswarned && $this->time() > $startlocktime + $this->acquirewarn) {
 498                  // This is a warning to better inform users.
 499                  $whohaslock = $this->connection->get($lockkey);
 500                  // phpcs:ignore
 501                  error_log("Warning: Cannot obtain session lock for sid: $id within $this->acquirewarn seconds but will keep trying. " .
 502                      "It is likely another page ($whohaslock) has a long session lock, or the session lock was never released.");
 503                  $haswarned = true;
 504              }
 505  
 506              if ($this->time() > $startlocktime + $this->acquiretimeout) {
 507                  // This is a fatal error, better inform users.
 508                  // It should not happen very often - all pages that need long time to execute
 509                  // should close session immediately after access control checks.
 510                  $whohaslock = $this->connection->get($lockkey);
 511                  // phpcs:ignore
 512                  error_log("Error: Cannot obtain session lock for sid: $id within $this->acquiretimeout seconds. " .
 513                      "It is likely another page ($whohaslock) has a long session lock, or the session lock was never released.");
 514                  $acquiretimeout = format_time($this->acquiretimeout);
 515                  $lockexpire = format_time($this->lockexpire);
 516                  $a = (object)[
 517                      'id' => substr($id, 0, 10),
 518                      'acquiretimeout' => $acquiretimeout,
 519                      'whohaslock' => $whohaslock,
 520                      'lockexpire' => $lockexpire];
 521                  throw new exception("sessioncannotobtainlock", 'error', '', $a);
 522              }
 523  
 524              if ($this->time() < $startlocktime + 5) {
 525                  // We want a random delay to stagger the polling load. Ideally
 526                  // this delay should be a fraction of the average response
 527                  // time. If it is too small we will poll too much and if it is
 528                  // too large we will waste time waiting for no reason. 100ms is
 529                  // the default starting point.
 530                  $delay = rand($this->lockretry, (int)($this->lockretry * 1.1));
 531              } else {
 532                  // If we don't get a lock within 5 seconds then there must be a
 533                  // very long lived process holding the lock so throttle back to
 534                  // just polling roughly once a second.
 535                  $delay = rand(1000, 1100);
 536              }
 537  
 538              usleep($delay * 1000);
 539          }
 540      }
 541  
 542      /**
 543       * Return the current time.
 544       *
 545       * @return int the current time as a unixtimestamp.
 546       */
 547      protected function time() {
 548          return time();
 549      }
 550  
 551      /**
 552       * Check the backend contains data for this session id.
 553       *
 554       * Note: this is intended to be called from manager::session_exists() only.
 555       *
 556       * @param string $sid
 557       * @return bool true if session found.
 558       */
 559      public function session_exists($sid) {
 560          if (!$this->connection) {
 561              return false;
 562          }
 563  
 564          try {
 565              return !empty($this->connection->exists($sid));
 566          } catch (RedisException $e) {
 567              return false;
 568          }
 569      }
 570  
 571      /**
 572       * Kill all active sessions, the core sessions table is purged afterwards.
 573       */
 574      public function kill_all_sessions() {
 575          global $DB;
 576          if (!$this->connection) {
 577              return;
 578          }
 579  
 580          $rs = $DB->get_recordset('sessions', array(), 'id DESC', 'id, sid');
 581          foreach ($rs as $record) {
 582              $this->handler_destroy($record->sid);
 583          }
 584          $rs->close();
 585      }
 586  
 587      /**
 588       * Kill one session, the session record is removed afterwards.
 589       *
 590       * @param string $sid
 591       */
 592      public function kill_session($sid) {
 593          if (!$this->connection) {
 594              return;
 595          }
 596  
 597          $this->handler_destroy($sid);
 598      }
 599  }