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   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   * Memcached based session handler.
  19   *
  20   * @package    core
  21   * @copyright  2013 Petr Skoda {@link http://skodak.org}
  22   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  23   */
  24  
  25  namespace core\session;
  26  
  27  defined('MOODLE_INTERNAL') || die();
  28  
  29  /**
  30   * Memcached based session handler.
  31   *
  32   * @package    core
  33   * @copyright  2013 Petr Skoda {@link http://skodak.org}
  34   * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  35   */
  36  class memcached extends handler {
  37      /** @var string $savepath save_path string  */
  38      protected $savepath;
  39  
  40      /** @var array $servers list of servers parsed from save_path */
  41      protected $servers;
  42  
  43      /** @var string $prefix session key prefix  */
  44      protected $prefix;
  45  
  46      /** @var int $acquiretimeout how long to wait for session lock */
  47      protected $acquiretimeout = 120;
  48  
  49      /**
  50       * @var int $lockexpire how long to wait before expiring the lock so that other requests
  51       * may continue execution, ignored if PECL memcached is below version 2.2.0.
  52       */
  53      protected $lockexpire = 7200;
  54  
  55      /**
  56       * @var integer $lockretrysleep Used for memcached 3.x (PHP7), the amount of time to
  57       * sleep between attempts to acquire the session lock. Mimics the deprecated config
  58       * memcached.sess_lock_wait.
  59       */
  60      protected $lockretrysleep = 150;
  61  
  62      /**
  63       * Create new instance of handler.
  64       */
  65      public function __construct() {
  66          global $CFG;
  67  
  68          if (empty($CFG->session_memcached_save_path)) {
  69              $this->savepath = '';
  70          } else {
  71              $this->savepath =  $CFG->session_memcached_save_path;
  72          }
  73  
  74          if (empty($this->savepath)) {
  75              $this->servers = array();
  76          } else {
  77              $this->servers = self::connection_string_to_memcache_servers($this->savepath);
  78          }
  79  
  80          if (empty($CFG->session_memcached_prefix)) {
  81              $this->prefix = ini_get('memcached.sess_prefix');
  82          } else {
  83              $this->prefix = $CFG->session_memcached_prefix;
  84          }
  85  
  86          if (!empty($CFG->session_memcached_acquire_lock_timeout)) {
  87              $this->acquiretimeout = (int)$CFG->session_memcached_acquire_lock_timeout;
  88          }
  89  
  90          if (!empty($CFG->session_memcached_lock_expire)) {
  91              $this->lockexpire = (int)$CFG->session_memcached_lock_expire;
  92          }
  93  
  94          if (!empty($CFG->session_memcached_lock_retry_sleep)) {
  95              $this->lockretrysleep = (int)$CFG->session_memcached_lock_retry_sleep;
  96          }
  97      }
  98  
  99      /**
 100       * Start the session.
 101       * @return bool success
 102       */
 103      public function start() {
 104          ini_set('memcached.sess_locking', $this->requires_write_lock() ? '1' : '0');
 105  
 106          // NOTE: memcached before 2.2.0 expires session locks automatically after max_execution_time,
 107          //       this leads to major difference compared to other session drivers that timeout
 108          //       and stop the second request execution instead.
 109  
 110          $default = ini_get('max_execution_time');
 111          set_time_limit($this->acquiretimeout);
 112  
 113          $isnewsession = empty($_COOKIE[session_name()]);
 114          $starttimer = microtime(true);
 115  
 116          $result = parent::start();
 117  
 118          // If session_start returned TRUE, but it took as long
 119          // as the timeout value, and the $_SESSION returned is
 120          // empty when should not have been (isnewsession false)
 121          // then assume it did timeout and is invalid.
 122          // Add 1 second to elapsed time to account for inexact
 123          // timings in php_memcached_session.c.
 124          // @TODO Remove this check when php-memcached is fixed
 125          // to return false after key lock acquisition timeout.
 126          if (!$isnewsession && $result && count($_SESSION) == 0
 127              && (microtime(true) - $starttimer + 1) >= floatval($this->acquiretimeout)) {
 128              $result = false;
 129          }
 130  
 131          set_time_limit($default);
 132          return $result;
 133      }
 134  
 135      /**
 136       * Init session handler.
 137       */
 138      public function init() {
 139          if (!extension_loaded('memcached')) {
 140              throw new exception('sessionhandlerproblem', 'error', '', null, 'memcached extension is not loaded');
 141          }
 142          $version = phpversion('memcached');
 143          if (!$version or version_compare($version, '2.0') < 0) {
 144              throw new exception('sessionhandlerproblem', 'error', '', null, 'memcached extension version must be at least 2.0');
 145          }
 146          if (empty($this->savepath)) {
 147              throw new exception('sessionhandlerproblem', 'error', '', null, '$CFG->session_memcached_save_path must be specified in config.php');
 148          }
 149  
 150          ini_set('session.save_handler', 'memcached');
 151          ini_set('session.save_path', $this->savepath);
 152          ini_set('memcached.sess_prefix', $this->prefix);
 153          ini_set('memcached.sess_lock_expire', $this->lockexpire);
 154  
 155          if (version_compare($version, '3.0.0-dev') >= 0) {
 156              // With memcached 3.x (PHP 7) we configure the max retries to make and the time to sleep between each retry.
 157              // There are two sleep config values, an initial and a max value.
 158              // After each attempt the memcached module adjusts the sleep value to be the lesser of the configured max
 159              // value, or 2X the previous value.
 160              // With default memcached.ini configs (5, 1s, 2s) the result is only 5 attempts to lock over 9 sec.
 161              // To mimic the behavior of the 2.2.x module so we get more attempts and much more frequently, config both
 162              // sleep values to the old default value of 150 msec (making it constant) and calculate number of retries
 163              // using the existing Moodle config $CFG->session_memcached_acquire_lock_timeout.
 164              // Doing this so admins configure session lock attempt timeout in familiar terms, and more straight-forward
 165              // to detect if lock attempt timeout has occurred in start().
 166              // If _min and _max values are not equal, the actual lock acquire timeout will not be the expected
 167              // configured value in $CFG->session_memcached_acquire_lock_timeout; this will cause session data loss when
 168              // failure to acquire the lock is not detected.
 169              ini_set('memcached.sess_lock_wait_min', $this->lockretrysleep);
 170              ini_set('memcached.sess_lock_wait_max', $this->lockretrysleep);
 171              ini_set('memcached.sess_lock_retries', (int)(($this->acquiretimeout * 1000) / $this->lockretrysleep) + 1);
 172          } else {
 173              // With memcached 2.2.x we configure max time to attempt lock, and accept default value (in memcached.ini)
 174              // for sleep time between each attempt (usually 150 msec), then memcached calculates the max number of
 175              // retries to make.
 176              ini_set('memcached.sess_lock_max_wait', $this->acquiretimeout);
 177          }
 178  
 179      }
 180  
 181      /**
 182       * Check the backend contains data for this session id.
 183       *
 184       * Note: this is intended to be called from manager::session_exists() only.
 185       *
 186       * @param string $sid
 187       * @return bool true if session found.
 188       */
 189      public function session_exists($sid) {
 190          if (!$this->servers) {
 191              return false;
 192          }
 193  
 194          // Go through the list of all servers because
 195          // we do not know where the session handler put the
 196          // data.
 197  
 198          foreach ($this->servers as $server) {
 199              list($host, $port) = $server;
 200              $memcached = new \Memcached();
 201              $memcached->addServer($host, $port);
 202              $value = $memcached->get($this->prefix . $sid);
 203              $memcached->quit();
 204              if ($value !== false) {
 205                  return true;
 206              }
 207          }
 208  
 209          return false;
 210      }
 211  
 212      /**
 213       * Kill all active sessions, the core sessions table is
 214       * purged afterwards.
 215       */
 216      public function kill_all_sessions() {
 217          global $DB;
 218          if (!$this->servers) {
 219              return;
 220          }
 221  
 222          // Go through the list of all servers because
 223          // we do not know where the session handler put the
 224          // data.
 225  
 226          $memcacheds = array();
 227          foreach ($this->servers as $server) {
 228              list($host, $port) = $server;
 229              $memcached = new \Memcached();
 230              $memcached->addServer($host, $port);
 231              $memcacheds[] = $memcached;
 232          }
 233  
 234          // Note: this can be significantly improved by fetching keys from memcached,
 235          //       but we need to make sure we are not deleting somebody else's sessions.
 236  
 237          $rs = $DB->get_recordset('sessions', array(), 'id DESC', 'id, sid');
 238          foreach ($rs as $record) {
 239              foreach ($memcacheds as $memcached) {
 240                  $memcached->delete($this->prefix . $record->sid);
 241              }
 242          }
 243          $rs->close();
 244  
 245          foreach ($memcacheds as $memcached) {
 246              $memcached->quit();
 247          }
 248      }
 249  
 250      /**
 251       * Kill one session, the session record is removed afterwards.
 252       * @param string $sid
 253       */
 254      public function kill_session($sid) {
 255          if (!$this->servers) {
 256              return;
 257          }
 258  
 259          // Go through the list of all servers because
 260          // we do not know where the session handler put the
 261          // data.
 262  
 263          foreach ($this->servers as $server) {
 264              list($host, $port) = $server;
 265              $memcached = new \Memcached();
 266              $memcached->addServer($host, $port);
 267              $memcached->delete($this->prefix . $sid);
 268              $memcached->quit();
 269          }
 270      }
 271  
 272      /**
 273       * Convert a connection string to an array of servers.
 274       *
 275       * "abc:123, xyz:789" to
 276       *  [
 277       *      ['abc', '123'],
 278       *      ['xyz', '789'],
 279       *  ]
 280       *
 281       * @param   string  $str save_path value containing memcached connection string
 282       * @return  array[]
 283       */
 284      protected static function connection_string_to_memcache_servers(string $str) : array {
 285          $servers = [];
 286          $parts   = explode(',', $str);
 287          foreach ($parts as $part) {
 288              $part = trim($part);
 289              $pos  = strrpos($part, ':');
 290              if ($pos !== false) {
 291                  $host = substr($part, 0, $pos);
 292                  $port = substr($part, ($pos + 1));
 293              } else {
 294                  $host = $part;
 295                  $port = 11211;
 296              }
 297              $servers[] = [$host, $port];
 298          }
 299          return $servers;
 300      }
 301  }