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Developer Documentation
- Bug fixes for general core bugs in 3.11.x will end 14 Nov 2022 (12 months plus 6 months extension).
- Bug fixes for security issues in 3.11.x will end 13 Nov 2023 (18 months plus 12 months extension).
- PHP version: minimum PHP 7.3.0 Note: minimum PHP version has increased since Moodle 3.10. PHP 7.4.x is supported too.
/lib/classes/session/ -> manager.php (source)
Differences Between: [Versions 310 and 311] [Versions 311 and 400] [Versions 311 and 401] [Versions 311 and 402] [Versions 311 and 403] [Versions 39 and 311]
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 * Session manager class. 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 use html_writer; 30 31 /** 32 * Session manager, this is the public Moodle API for sessions. 33 * 34 * Following PHP functions MUST NOT be used directly: 35 * - session_start() - not necessary, lib/setup.php starts session automatically, 36 * use define('NO_MOODLE_COOKIE', true) if session not necessary. 37 * - session_write_close() - use \core\session\manager::write_close() instead. 38 * - session_destroy() - use require_logout() instead. 39 * 40 * @package core 41 * @copyright 2013 Petr Skoda {@link http://skodak.org} 42 * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later 43 */ 44 class manager { 45 /** @var int A hard cutoff of maximum stored history */ 46 const MAXIMUM_STORED_SESSION_HISTORY = 50; 47 48 /** @var int The recent session locks array is reset if there is a time gap more than this value in seconds */ 49 const SESSION_RESET_GAP_THRESHOLD = 1; 50 51 /** @var handler $handler active session handler instance */ 52 protected static $handler; 53 54 /** @var bool $sessionactive Is the session active? */ 55 protected static $sessionactive = null; 56 57 /** @var string $logintokenkey Key used to get and store request protection for login form. */ 58 protected static $logintokenkey = 'core_auth_login'; 59 60 /** @var array Stores the the SESSION before a request is performed, used to check incorrect read-only modes */ 61 private static $priorsession = []; 62 63 /** 64 * @var bool Used to trigger the SESSION mutation warning without actually preventing SESSION mutation. 65 * This variable is used to "copy" what the $requireslock parameter does in start_session(). 66 * Once requireslock is set in start_session it's later accessible via $handler->requires_write_lock, 67 * When using $CFG->enable_read_only_sessions_debug mode, this variable serves the same purpose without 68 * actually setting the handler as requiring a write lock. 69 */ 70 private static $requireslockdebug; 71 72 /** 73 * If the current session is not writeable, abort it, and re-open it 74 * requesting (and blocking) until a write lock is acquired. 75 * If current session was already opened with an intentional write lock, 76 * this call will not do anything. 77 * NOTE: Even when using a session handler that does not support non-locking sessions, 78 * if the original session was not opened with the explicit intention of being locked, 79 * this will still restart your session so that code behaviour matches as closely 80 * as practical across environments. 81 * 82 * @param bool $readonlysession Used by debugging logic to determine if whatever 83 * triggered the restart (e.g., a webservice) declared 84 * itself as read only. 85 */ 86 public static function restart_with_write_lock(bool $readonlysession) { 87 global $CFG; 88 89 self::$requireslockdebug = !$readonlysession; 90 91 if (self::$sessionactive && !self::$handler->requires_write_lock()) { 92 @self::$handler->abort(); 93 self::$sessionactive = false; 94 self::start_session(true); 95 } 96 } 97 98 /** 99 * Start user session. 100 * 101 * Note: This is intended to be called only from lib/setup.php! 102 */ 103 public static function start() { 104 global $CFG, $DB, $PERF; 105 106 if (isset(self::$sessionactive)) { 107 debugging('Session was already started!', DEBUG_DEVELOPER); 108 return; 109 } 110 111 // Grab the time before session lock starts. 112 $PERF->sessionlock['start'] = microtime(true); 113 self::load_handler(); 114 115 // Init the session handler only if everything initialised properly in lib/setup.php file 116 // and the session is actually required. 117 if (empty($DB) or empty($CFG->version) or !defined('NO_MOODLE_COOKIES') or NO_MOODLE_COOKIES or CLI_SCRIPT) { 118 self::$sessionactive = false; 119 self::init_empty_session(); 120 return; 121 } 122 123 if (defined('READ_ONLY_SESSION') && !empty($CFG->enable_read_only_sessions)) { 124 $requireslock = !READ_ONLY_SESSION; 125 } else { 126 $requireslock = true; // For backwards compatibility, we default to assuming that a lock is needed. 127 } 128 129 // By default make the two variables the same. This means that when they are 130 // checked below in start_session and write_close there is no possibility for 131 // the debug version to "accidentally" execute the debug mode. 132 self::$requireslockdebug = $requireslock; 133 if (defined('READ_ONLY_SESSION') && !empty($CFG->enable_read_only_sessions_debug)) { 134 // Only change the debug variable if READ_ONLY_SESSION is declared, 135 // as would happen with the real requireslock variable. 136 self::$requireslockdebug = !READ_ONLY_SESSION; 137 } 138 139 self::start_session($requireslock); 140 } 141 142 /** 143 * Handles starting a session. 144 * 145 * @param bool $requireslock If this is false then no write lock will be acquired, 146 * and the session will be read-only. 147 */ 148 private static function start_session(bool $requireslock) { 149 global $PERF, $CFG; 150 151 try { 152 self::$handler->init(); 153 self::$handler->set_requires_write_lock($requireslock); 154 self::prepare_cookies(); 155 $isnewsession = empty($_COOKIE[session_name()]); 156 157 if (!self::$handler->start()) { 158 // Could not successfully start/recover session. 159 throw new \core\session\exception(get_string('servererror')); 160 } 161 162 // Grab the time when session lock starts. 163 $PERF->sessionlock['gained'] = microtime(true); 164 $PERF->sessionlock['wait'] = $PERF->sessionlock['gained'] - $PERF->sessionlock['start']; 165 self::initialise_user_session($isnewsession); 166 self::$sessionactive = true; // Set here, so the session can be cleared if the security check fails. 167 self::check_security(); 168 169 if (!$requireslock || !self::$requireslockdebug) { 170 self::$priorsession = (array) $_SESSION['SESSION']; 171 } 172 173 if (!empty($CFG->enable_read_only_sessions) && isset($_SESSION['SESSION']->cachestore_session)) { 174 $caches = join(', ', array_keys($_SESSION['SESSION']->cachestore_session)); 175 $caches = str_replace('default_session-', '', $caches); 176 throw new \moodle_exception("The session caches can not be in the session store when " 177 . "enable_read_only_sessions is enabled. Please map all session mode caches to be outside of the " 178 . "default session store before enabling this features. Found these definitions in the session: $caches"); 179 } 180 181 // Link global $USER and $SESSION, 182 // this is tricky because PHP does not allow references to references 183 // and global keyword uses internally once reference to the $GLOBALS array. 184 // The solution is to use the $GLOBALS['USER'] and $GLOBALS['$SESSION'] 185 // as the main storage of data and put references to $_SESSION. 186 $GLOBALS['USER'] = $_SESSION['USER']; 187 $_SESSION['USER'] =& $GLOBALS['USER']; 188 $GLOBALS['SESSION'] = $_SESSION['SESSION']; 189 $_SESSION['SESSION'] =& $GLOBALS['SESSION']; 190 191 } catch (\Exception $ex) { 192 self::init_empty_session(); 193 self::$sessionactive = false; 194 throw $ex; 195 } 196 } 197 198 /** 199 * Returns current page performance info. 200 * 201 * @return array perf info 202 */ 203 public static function get_performance_info() { 204 global $CFG, $PERF; 205 206 if (!session_id()) { 207 return array(); 208 } 209 210 self::load_handler(); 211 $size = display_size(strlen(session_encode())); 212 $handler = get_class(self::$handler); 213 214 $info = array(); 215 $info['size'] = $size; 216 $info['html'] = html_writer::div("Session ($handler): $size", "sessionsize"); 217 $info['txt'] = "Session ($handler): $size "; 218 219 if (!empty($CFG->debugsessionlock)) { 220 $sessionlock = self::get_session_lock_info(); 221 if (!empty($sessionlock['held'])) { 222 // The page displays the footer and the session has been closed. 223 $sessionlocktext = "Session lock held: ".number_format($sessionlock['held'], 3)." secs"; 224 } else { 225 // The session hasn't yet been closed and so we assume now with microtime. 226 $sessionlockheld = microtime(true) - $PERF->sessionlock['gained']; 227 $sessionlocktext = "Session lock open: ".number_format($sessionlockheld, 3)." secs"; 228 } 229 $info['txt'] .= $sessionlocktext; 230 $info['html'] .= html_writer::div($sessionlocktext, "sessionlockstart"); 231 $sessionlockwaittext = "Session lock wait: ".number_format($sessionlock['wait'], 3)." secs"; 232 $info['txt'] .= $sessionlockwaittext; 233 $info['html'] .= html_writer::div($sessionlockwaittext, "sessionlockwait"); 234 } 235 236 return $info; 237 } 238 239 /** 240 * Get fully qualified name of session handler class. 241 * 242 * @return string The name of the handler class 243 */ 244 public static function get_handler_class() { 245 global $CFG, $DB; 246 247 if (PHPUNIT_TEST) { 248 return '\core\session\file'; 249 } else if (!empty($CFG->session_handler_class)) { 250 return $CFG->session_handler_class; 251 } else if (!empty($CFG->dbsessions) and $DB->session_lock_supported()) { 252 return '\core\session\database'; 253 } 254 255 return '\core\session\file'; 256 } 257 258 /** 259 * Create handler instance. 260 */ 261 protected static function load_handler() { 262 if (self::$handler) { 263 return; 264 } 265 266 // Find out which handler to use. 267 $class = self::get_handler_class(); 268 self::$handler = new $class(); 269 } 270 271 /** 272 * Empty current session, fill it with not-logged-in user info. 273 * 274 * This is intended for installation scripts, unit tests and other 275 * special areas. Do NOT use for logout and session termination 276 * in normal requests! 277 */ 278 public static function init_empty_session() { 279 global $CFG; 280 281 if (isset($GLOBALS['SESSION']->notifications)) { 282 // Backup notifications. These should be preserved across session changes until the user fetches and clears them. 283 $notifications = $GLOBALS['SESSION']->notifications; 284 } 285 $GLOBALS['SESSION'] = new \stdClass(); 286 287 $GLOBALS['USER'] = new \stdClass(); 288 $GLOBALS['USER']->id = 0; 289 290 if (!empty($notifications)) { 291 // Restore notifications. 292 $GLOBALS['SESSION']->notifications = $notifications; 293 } 294 if (isset($CFG->mnet_localhost_id)) { 295 $GLOBALS['USER']->mnethostid = $CFG->mnet_localhost_id; 296 } else { 297 // Not installed yet, the future host id will be most probably 1. 298 $GLOBALS['USER']->mnethostid = 1; 299 } 300 301 // Link global $USER and $SESSION. 302 $_SESSION = array(); 303 $_SESSION['USER'] =& $GLOBALS['USER']; 304 $_SESSION['SESSION'] =& $GLOBALS['SESSION']; 305 } 306 307 /** 308 * Make sure all cookie and session related stuff is configured properly before session start. 309 */ 310 protected static function prepare_cookies() { 311 global $CFG; 312 313 $cookiesecure = is_moodle_cookie_secure(); 314 315 if (!isset($CFG->cookiehttponly)) { 316 $CFG->cookiehttponly = 0; 317 } 318 319 // Set sessioncookie variable if it isn't already. 320 if (!isset($CFG->sessioncookie)) { 321 $CFG->sessioncookie = ''; 322 } 323 $sessionname = 'MoodleSession'.$CFG->sessioncookie; 324 325 // Make sure cookie domain makes sense for this wwwroot. 326 if (!isset($CFG->sessioncookiedomain)) { 327 $CFG->sessioncookiedomain = ''; 328 } else if ($CFG->sessioncookiedomain !== '') { 329 $host = parse_url($CFG->wwwroot, PHP_URL_HOST); 330 if ($CFG->sessioncookiedomain !== $host) { 331 if (substr($CFG->sessioncookiedomain, 0, 1) === '.') { 332 if (!preg_match('|^.*'.preg_quote($CFG->sessioncookiedomain, '|').'$|', $host)) { 333 // Invalid domain - it must be end part of host. 334 $CFG->sessioncookiedomain = ''; 335 } 336 } else { 337 if (!preg_match('|^.*\.'.preg_quote($CFG->sessioncookiedomain, '|').'$|', $host)) { 338 // Invalid domain - it must be end part of host. 339 $CFG->sessioncookiedomain = ''; 340 } 341 } 342 } 343 } 344 345 // Make sure the cookiepath is valid for this wwwroot or autodetect if not specified. 346 if (!isset($CFG->sessioncookiepath)) { 347 $CFG->sessioncookiepath = ''; 348 } 349 if ($CFG->sessioncookiepath !== '/') { 350 $path = parse_url($CFG->wwwroot, PHP_URL_PATH).'/'; 351 if ($CFG->sessioncookiepath === '') { 352 $CFG->sessioncookiepath = $path; 353 } else { 354 if (strpos($path, $CFG->sessioncookiepath) !== 0 or substr($CFG->sessioncookiepath, -1) !== '/') { 355 $CFG->sessioncookiepath = $path; 356 } 357 } 358 } 359 360 // Discard session ID from POST, GET and globals to tighten security, 361 // this is session fixation prevention. 362 unset($GLOBALS[$sessionname]); 363 unset($_GET[$sessionname]); 364 unset($_POST[$sessionname]); 365 unset($_REQUEST[$sessionname]); 366 367 // Compatibility hack for non-browser access to our web interface. 368 if (!empty($_COOKIE[$sessionname]) && $_COOKIE[$sessionname] == "deleted") { 369 unset($_COOKIE[$sessionname]); 370 } 371 372 // Set configuration. 373 session_name($sessionname); 374 375 $sessionoptions = [ 376 'lifetime' => 0, 377 'path' => $CFG->sessioncookiepath, 378 'domain' => $CFG->sessioncookiedomain, 379 'secure' => $cookiesecure, 380 'httponly' => $CFG->cookiehttponly, 381 ]; 382 383 if (self::should_use_samesite_none()) { 384 // If $samesite is empty, we don't want there to be any SameSite attribute. 385 $sessionoptions['samesite'] = 'None'; 386 } 387 388 session_set_cookie_params($sessionoptions); 389 390 ini_set('session.use_trans_sid', '0'); 391 ini_set('session.use_only_cookies', '1'); 392 ini_set('session.use_strict_mode', '0'); // We have custom protection in session init. 393 ini_set('session.serialize_handler', 'php'); // We can move to 'php_serialize' after we require PHP 5.5.4 form Moodle. 394 395 // Moodle does normal session timeouts, this is for leftovers only. 396 ini_set('session.gc_probability', 1); 397 ini_set('session.gc_divisor', 1000); 398 ini_set('session.gc_maxlifetime', 60*60*24*4); 399 } 400 401 /** 402 * Initialise $_SESSION, handles google access 403 * and sets up not-logged-in user properly. 404 * 405 * WARNING: $USER and $SESSION are set up later, do not use them yet! 406 * 407 * @param bool $newsid is this a new session in first http request? 408 */ 409 protected static function initialise_user_session($newsid) { 410 global $CFG, $DB; 411 412 $sid = session_id(); 413 if (!$sid) { 414 // No session, very weird. 415 error_log('Missing session ID, session not started!'); 416 self::init_empty_session(); 417 return; 418 } 419 420 if (!$record = $DB->get_record('sessions', array('sid'=>$sid), 'id, sid, state, userid, lastip, timecreated, timemodified')) { 421 if (!$newsid) { 422 if (!empty($_SESSION['USER']->id)) { 423 // This should not happen, just log it, we MUST not produce any output here! 424 error_log("Cannot find session record $sid for user ".$_SESSION['USER']->id.", creating new session."); 425 } 426 // Prevent session fixation attacks. 427 session_regenerate_id(true); 428 } 429 $_SESSION = array(); 430 } 431 unset($sid); 432 433 if (isset($_SESSION['USER']->id)) { 434 if (!empty($_SESSION['USER']->realuser)) { 435 $userid = $_SESSION['USER']->realuser; 436 } else { 437 $userid = $_SESSION['USER']->id; 438 } 439 440 // Verify timeout first. 441 $maxlifetime = $CFG->sessiontimeout; 442 $timeout = false; 443 if (isguestuser($userid) or empty($userid)) { 444 // Ignore guest and not-logged in timeouts, there is very little risk here. 445 $timeout = false; 446 447 } else if ($record->timemodified < time() - $maxlifetime) { 448 $timeout = true; 449 $authsequence = get_enabled_auth_plugins(); // Auths, in sequence. 450 foreach ($authsequence as $authname) { 451 $authplugin = get_auth_plugin($authname); 452 if ($authplugin->ignore_timeout_hook($_SESSION['USER'], $record->sid, $record->timecreated, $record->timemodified)) { 453 $timeout = false; 454 break; 455 } 456 } 457 } 458 459 if ($timeout) { 460 if (defined('NO_SESSION_UPDATE') && NO_SESSION_UPDATE) { 461 return; 462 } 463 session_regenerate_id(true); 464 $_SESSION = array(); 465 $DB->delete_records('sessions', array('id'=>$record->id)); 466 467 } else { 468 // Update session tracking record. 469 470 $update = new \stdClass(); 471 $updated = false; 472 473 if ($record->userid != $userid) { 474 $update->userid = $record->userid = $userid; 475 $updated = true; 476 } 477 478 $ip = getremoteaddr(); 479 if ($record->lastip != $ip) { 480 $update->lastip = $record->lastip = $ip; 481 $updated = true; 482 } 483 484 $updatefreq = empty($CFG->session_update_timemodified_frequency) ? 20 : $CFG->session_update_timemodified_frequency; 485 486 if ($record->timemodified == $record->timecreated) { 487 // Always do first update of existing record. 488 $update->timemodified = $record->timemodified = time(); 489 $updated = true; 490 491 } else if ($record->timemodified < time() - $updatefreq) { 492 // Update the session modified flag only once every 20 seconds. 493 $update->timemodified = $record->timemodified = time(); 494 $updated = true; 495 } 496 497 if ($updated && (!defined('NO_SESSION_UPDATE') || !NO_SESSION_UPDATE)) { 498 $update->id = $record->id; 499 $DB->update_record('sessions', $update); 500 } 501 502 return; 503 } 504 } else { 505 if ($record) { 506 // This happens when people switch session handlers... 507 session_regenerate_id(true); 508 $_SESSION = array(); 509 $DB->delete_records('sessions', array('id'=>$record->id)); 510 } 511 } 512 unset($record); 513 514 $timedout = false; 515 if (!isset($_SESSION['SESSION'])) { 516 $_SESSION['SESSION'] = new \stdClass(); 517 if (!$newsid) { 518 $timedout = true; 519 } 520 } 521 522 $user = null; 523 524 if (!empty($CFG->opentowebcrawlers)) { 525 if (\core_useragent::is_web_crawler()) { 526 $user = guest_user(); 527 } 528 $referer = get_local_referer(false); 529 if (!empty($CFG->guestloginbutton) and !$user and !empty($referer)) { 530 // Automatically log in users coming from search engine results. 531 if (strpos($referer, 'google') !== false ) { 532 $user = guest_user(); 533 } else if (strpos($referer, 'altavista') !== false ) { 534 $user = guest_user(); 535 } 536 } 537 } 538 539 // Setup $USER and insert the session tracking record. 540 if ($user) { 541 self::set_user($user); 542 self::add_session_record($user->id); 543 } else { 544 self::init_empty_session(); 545 self::add_session_record(0); 546 } 547 548 if ($timedout) { 549 $_SESSION['SESSION']->has_timed_out = true; 550 } 551 } 552 553 /** 554 * Insert new empty session record. 555 * @param int $userid 556 * @return \stdClass the new record 557 */ 558 protected static function add_session_record($userid) { 559 global $DB; 560 $record = new \stdClass(); 561 $record->state = 0; 562 $record->sid = session_id(); 563 $record->sessdata = null; 564 $record->userid = $userid; 565 $record->timecreated = $record->timemodified = time(); 566 $record->firstip = $record->lastip = getremoteaddr(); 567 568 $record->id = $DB->insert_record('sessions', $record); 569 570 return $record; 571 } 572 573 /** 574 * Do various session security checks. 575 * 576 * WARNING: $USER and $SESSION are set up later, do not use them yet! 577 * @throws \core\session\exception 578 */ 579 protected static function check_security() { 580 global $CFG; 581 582 if (!empty($_SESSION['USER']->id) and !empty($CFG->tracksessionip)) { 583 // Make sure current IP matches the one for this session. 584 $remoteaddr = getremoteaddr(); 585 586 if (empty($_SESSION['USER']->sessionip)) { 587 $_SESSION['USER']->sessionip = $remoteaddr; 588 } 589 590 if ($_SESSION['USER']->sessionip != $remoteaddr) { 591 // This is a security feature - terminate the session in case of any doubt. 592 self::terminate_current(); 593 throw new exception('sessionipnomatch2', 'error'); 594 } 595 } 596 } 597 598 /** 599 * Login user, to be called from complete_user_login() only. 600 * @param \stdClass $user 601 */ 602 public static function login_user(\stdClass $user) { 603 global $DB; 604 605 // Regenerate session id and delete old session, 606 // this helps prevent session fixation attacks from the same domain. 607 608 $sid = session_id(); 609 session_regenerate_id(true); 610 $DB->delete_records('sessions', array('sid'=>$sid)); 611 self::add_session_record($user->id); 612 613 // Let enrol plugins deal with new enrolments if necessary. 614 enrol_check_plugins($user); 615 616 // Setup $USER object. 617 self::set_user($user); 618 } 619 620 /** 621 * Returns a valid setting for the SameSite cookie attribute. 622 * 623 * @return string The desired setting for the SameSite attribute on the cookie. Empty string indicates the SameSite attribute 624 * should not be set at all. 625 */ 626 private static function should_use_samesite_none(): bool { 627 // We only want None or no attribute at this point. When we have cookie handling compatible with Lax, 628 // we can look at checking a setting. 629 630 // Browser support for none is not consistent yet. There are known issues with Safari, and IE11. 631 // Things are stablising, however as they're not stable yet we will deal specifically with the version of chrome 632 // that introduces a default of lax, setting it to none for the current version of chrome (2 releases before the change). 633 // We also check you are using secure cookies and HTTPS because if you are not running over HTTPS 634 // then setting SameSite=None will cause your session cookie to be rejected. 635 if (\core_useragent::is_chrome() && \core_useragent::check_chrome_version('78') && is_moodle_cookie_secure()) { 636 return true; 637 } 638 return false; 639 } 640 641 /** 642 * Terminate current user session. 643 * @return void 644 */ 645 public static function terminate_current() { 646 global $DB; 647 648 if (!self::$sessionactive) { 649 self::init_empty_session(); 650 self::$sessionactive = false; 651 return; 652 } 653 654 try { 655 $DB->delete_records('external_tokens', array('sid'=>session_id(), 'tokentype'=>EXTERNAL_TOKEN_EMBEDDED)); 656 } catch (\Exception $ignored) { 657 // Probably install/upgrade - ignore this problem. 658 } 659 660 // Initialize variable to pass-by-reference to headers_sent(&$file, &$line). 661 $file = null; 662 $line = null; 663 if (headers_sent($file, $line)) { 664 error_log('Cannot terminate session properly - headers were already sent in file: '.$file.' on line '.$line); 665 } 666 667 // Write new empty session and make sure the old one is deleted. 668 $sid = session_id(); 669 session_regenerate_id(true); 670 $DB->delete_records('sessions', array('sid'=>$sid)); 671 self::init_empty_session(); 672 self::add_session_record($_SESSION['USER']->id); // Do not use $USER here because it may not be set up yet. 673 self::write_close(); 674 } 675 676 /** 677 * No more changes in session expected. 678 * Unblocks the sessions, other scripts may start executing in parallel. 679 */ 680 public static function write_close() { 681 global $PERF, $ME, $CFG; 682 683 if (self::$sessionactive) { 684 // Grab the time when session lock is released. 685 $PERF->sessionlock['released'] = microtime(true); 686 if (!empty($PERF->sessionlock['gained'])) { 687 $PERF->sessionlock['held'] = $PERF->sessionlock['released'] - $PERF->sessionlock['gained']; 688 } 689 $PERF->sessionlock['url'] = me(); 690 self::update_recent_session_locks($PERF->sessionlock); 691 self::sessionlock_debugging(); 692 693 $requireslock = self::$handler->requires_write_lock(); 694 if (!$requireslock || !self::$requireslockdebug) { 695 // Compare the array of the earlier session data with the array now, if 696 // there is a difference then a lock is required. 697 $arraydiff = self::array_session_diff( 698 self::$priorsession, 699 (array) $_SESSION['SESSION'] 700 ); 701 702 if ($arraydiff) { 703 $error = "Script $ME defined READ_ONLY_SESSION but the following SESSION attributes were changed:"; 704 foreach ($arraydiff as $key => $value) { 705 $error .= ' $SESSION->' . $key; 706 } 707 // This will emit an error if debugging is on, even if $CFG->enable_read_only_sessions 708 // is not true as we need to surface this class of errors. 709 error_log($error); // phpcs:ignore 710 } 711 } 712 } 713 714 // More control over whether session data 715 // is persisted or not. 716 if (self::$sessionactive && session_id()) { 717 // Write session and release lock only if 718 // indication session start was clean. 719 self::$handler->write_close(); 720 } else { 721 // Otherwise, if possible lock exists want 722 // to clear it, but do not write session. 723 // If the $handler has not been set then 724 // there is no session to abort. 725 if (isset(self::$handler)) { 726 @self::$handler->abort(); 727 } 728 } 729 730 self::$sessionactive = false; 731 } 732 733 /** 734 * Does the PHP session with given id exist? 735 * 736 * The session must exist both in session table and actual 737 * session backend and the session must not be timed out. 738 * 739 * Timeout evaluation is simplified, the auth hooks are not executed. 740 * 741 * @param string $sid 742 * @return bool 743 */ 744 public static function session_exists($sid) { 745 global $DB, $CFG; 746 747 if (empty($CFG->version)) { 748 // Not installed yet, do not try to access database. 749 return false; 750 } 751 752 // Note: add sessions->state checking here if it gets implemented. 753 if (!$record = $DB->get_record('sessions', array('sid' => $sid), 'id, userid, timemodified')) { 754 return false; 755 } 756 757 if (empty($record->userid) or isguestuser($record->userid)) { 758 // Ignore guest and not-logged-in timeouts, there is very little risk here. 759 } else if ($record->timemodified < time() - $CFG->sessiontimeout) { 760 return false; 761 } 762 763 // There is no need the existence of handler storage in public API. 764 self::load_handler(); 765 return self::$handler->session_exists($sid); 766 } 767 768 /** 769 * Return the number of seconds remaining in the current session. 770 * @param string $sid 771 */ 772 public static function time_remaining($sid) { 773 global $DB, $CFG; 774 775 if (empty($CFG->version)) { 776 // Not installed yet, do not try to access database. 777 return ['userid' => 0, 'timeremaining' => $CFG->sessiontimeout]; 778 } 779 780 // Note: add sessions->state checking here if it gets implemented. 781 if (!$record = $DB->get_record('sessions', array('sid' => $sid), 'id, userid, timemodified')) { 782 return ['userid' => 0, 'timeremaining' => $CFG->sessiontimeout]; 783 } 784 785 if (empty($record->userid) or isguestuser($record->userid)) { 786 // Ignore guest and not-logged-in timeouts, there is very little risk here. 787 return ['userid' => 0, 'timeremaining' => $CFG->sessiontimeout]; 788 } else { 789 return ['userid' => $record->userid, 'timeremaining' => $CFG->sessiontimeout - (time() - $record->timemodified)]; 790 } 791 } 792 793 /** 794 * Fake last access for given session, this prevents session timeout. 795 * @param string $sid 796 */ 797 public static function touch_session($sid) { 798 global $DB; 799 800 // Timeouts depend on core sessions table only, no need to update anything in external stores. 801 802 $sql = "UPDATE {sessions} SET timemodified = :now WHERE sid = :sid"; 803 $DB->execute($sql, array('now'=>time(), 'sid'=>$sid)); 804 } 805 806 /** 807 * Terminate all sessions unconditionally. 808 */ 809 public static function kill_all_sessions() { 810 global $DB; 811 812 self::terminate_current(); 813 814 self::load_handler(); 815 self::$handler->kill_all_sessions(); 816 817 try { 818 $DB->delete_records('sessions'); 819 } catch (\dml_exception $ignored) { 820 // Do not show any warnings - might be during upgrade/installation. 821 } 822 } 823 824 /** 825 * Terminate give session unconditionally. 826 * @param string $sid 827 */ 828 public static function kill_session($sid) { 829 global $DB; 830 831 self::load_handler(); 832 833 if ($sid === session_id()) { 834 self::write_close(); 835 } 836 837 self::$handler->kill_session($sid); 838 839 $DB->delete_records('sessions', array('sid'=>$sid)); 840 } 841 842 /** 843 * Terminate all sessions of given user unconditionally. 844 * @param int $userid 845 * @param string $keepsid keep this sid if present 846 */ 847 public static function kill_user_sessions($userid, $keepsid = null) { 848 global $DB; 849 850 $sessions = $DB->get_records('sessions', array('userid'=>$userid), 'id DESC', 'id, sid'); 851 foreach ($sessions as $session) { 852 if ($keepsid and $keepsid === $session->sid) { 853 continue; 854 } 855 self::kill_session($session->sid); 856 } 857 } 858 859 /** 860 * Terminate other sessions of current user depending 861 * on $CFG->limitconcurrentlogins restriction. 862 * 863 * This is expected to be called right after complete_user_login(). 864 * 865 * NOTE: 866 * * Do not use from SSO auth plugins, this would not work. 867 * * Do not use from web services because they do not have sessions. 868 * 869 * @param int $userid 870 * @param string $sid session id to be always keep, usually the current one 871 * @return void 872 */ 873 public static function apply_concurrent_login_limit($userid, $sid = null) { 874 global $CFG, $DB; 875 876 // NOTE: the $sid parameter is here mainly to allow testing, 877 // in most cases it should be current session id. 878 879 if (isguestuser($userid) or empty($userid)) { 880 // This applies to real users only! 881 return; 882 } 883 884 if (empty($CFG->limitconcurrentlogins) or $CFG->limitconcurrentlogins < 0) { 885 return; 886 } 887 888 $count = $DB->count_records('sessions', array('userid' => $userid)); 889 890 if ($count <= $CFG->limitconcurrentlogins) { 891 return; 892 } 893 894 $i = 0; 895 $select = "userid = :userid"; 896 $params = array('userid' => $userid); 897 if ($sid) { 898 if ($DB->record_exists('sessions', array('sid' => $sid, 'userid' => $userid))) { 899 $select .= " AND sid <> :sid"; 900 $params['sid'] = $sid; 901 $i = 1; 902 } 903 } 904 905 $sessions = $DB->get_records_select('sessions', $select, $params, 'timecreated DESC', 'id, sid'); 906 foreach ($sessions as $session) { 907 $i++; 908 if ($i <= $CFG->limitconcurrentlogins) { 909 continue; 910 } 911 self::kill_session($session->sid); 912 } 913 } 914 915 /** 916 * Set current user. 917 * 918 * @param \stdClass $user record 919 */ 920 public static function set_user(\stdClass $user) { 921 global $ADMIN; 922 $GLOBALS['USER'] = $user; 923 unset($GLOBALS['USER']->description); // Conserve memory. 924 unset($GLOBALS['USER']->password); // Improve security. 925 if (isset($GLOBALS['USER']->lang)) { 926 // Make sure it is a valid lang pack name. 927 $GLOBALS['USER']->lang = clean_param($GLOBALS['USER']->lang, PARAM_LANG); 928 } 929 930 // Relink session with global $USER just in case it got unlinked somehow. 931 $_SESSION['USER'] =& $GLOBALS['USER']; 932 933 // Nullify the $ADMIN tree global. If we're changing users, then this is now stale and must be generated again if needed. 934 $ADMIN = null; 935 936 // Init session key. 937 sesskey(); 938 } 939 940 /** 941 * Periodic timed-out session cleanup. 942 */ 943 public static function gc() { 944 global $CFG, $DB; 945 946 // This may take a long time... 947 \core_php_time_limit::raise(); 948 949 $maxlifetime = $CFG->sessiontimeout; 950 951 try { 952 // Kill all sessions of deleted and suspended users without any hesitation. 953 $rs = $DB->get_recordset_select('sessions', "userid IN (SELECT id FROM {user} WHERE deleted <> 0 OR suspended <> 0)", array(), 'id DESC', 'id, sid'); 954 foreach ($rs as $session) { 955 self::kill_session($session->sid); 956 } 957 $rs->close(); 958 959 // Kill sessions of users with disabled plugins. 960 $authsequence = get_enabled_auth_plugins(); 961 $authsequence = array_flip($authsequence); 962 unset($authsequence['nologin']); // No login means user cannot login. 963 $authsequence = array_flip($authsequence); 964 965 list($notplugins, $params) = $DB->get_in_or_equal($authsequence, SQL_PARAMS_QM, '', false); 966 $rs = $DB->get_recordset_select('sessions', "userid IN (SELECT id FROM {user} WHERE auth $notplugins)", $params, 'id DESC', 'id, sid'); 967 foreach ($rs as $session) { 968 self::kill_session($session->sid); 969 } 970 $rs->close(); 971 972 // Now get a list of time-out candidates - real users only. 973 $sql = "SELECT u.*, s.sid, s.timecreated AS s_timecreated, s.timemodified AS s_timemodified 974 FROM {user} u 975 JOIN {sessions} s ON s.userid = u.id 976 WHERE s.timemodified < :purgebefore AND u.id <> :guestid"; 977 $params = array('purgebefore' => (time() - $maxlifetime), 'guestid'=>$CFG->siteguest); 978 979 $authplugins = array(); 980 foreach ($authsequence as $authname) { 981 $authplugins[$authname] = get_auth_plugin($authname); 982 } 983 $rs = $DB->get_recordset_sql($sql, $params); 984 foreach ($rs as $user) { 985 foreach ($authplugins as $authplugin) { 986 /** @var \auth_plugin_base $authplugin*/ 987 if ($authplugin->ignore_timeout_hook($user, $user->sid, $user->s_timecreated, $user->s_timemodified)) { 988 continue 2; 989 } 990 } 991 self::kill_session($user->sid); 992 } 993 $rs->close(); 994 995 // Delete expired sessions for guest user account, give them larger timeout, there is no security risk here. 996 $params = array('purgebefore' => (time() - ($maxlifetime * 5)), 'guestid'=>$CFG->siteguest); 997 $rs = $DB->get_recordset_select('sessions', 'userid = :guestid AND timemodified < :purgebefore', $params, 'id DESC', 'id, sid'); 998 foreach ($rs as $session) { 999 self::kill_session($session->sid); 1000 } 1001 $rs->close(); 1002 1003 // Delete expired sessions for userid = 0 (not logged in), better kill them asap to release memory. 1004 $params = array('purgebefore' => (time() - $maxlifetime)); 1005 $rs = $DB->get_recordset_select('sessions', 'userid = 0 AND timemodified < :purgebefore', $params, 'id DESC', 'id, sid'); 1006 foreach ($rs as $session) { 1007 self::kill_session($session->sid); 1008 } 1009 $rs->close(); 1010 1011 // Cleanup letfovers from the first browser access because it may set multiple cookies and then use only one. 1012 $params = array('purgebefore' => (time() - 60*3)); 1013 $rs = $DB->get_recordset_select('sessions', 'userid = 0 AND timemodified = timecreated AND timemodified < :purgebefore', $params, 'id ASC', 'id, sid'); 1014 foreach ($rs as $session) { 1015 self::kill_session($session->sid); 1016 } 1017 $rs->close(); 1018 1019 } catch (\Exception $ex) { 1020 debugging('Error gc-ing sessions: '.$ex->getMessage(), DEBUG_NORMAL, $ex->getTrace()); 1021 } 1022 } 1023 1024 /** 1025 * Is current $USER logged-in-as somebody else? 1026 * @return bool 1027 */ 1028 public static function is_loggedinas() { 1029 return !empty($GLOBALS['USER']->realuser); 1030 } 1031 1032 /** 1033 * Returns the $USER object ignoring current login-as session 1034 * @return \stdClass user object 1035 */ 1036 public static function get_realuser() { 1037 if (self::is_loggedinas()) { 1038 return $_SESSION['REALUSER']; 1039 } else { 1040 return $GLOBALS['USER']; 1041 } 1042 } 1043 1044 /** 1045 * Login as another user - no security checks here. 1046 * @param int $userid 1047 * @param \context $context 1048 * @param bool $generateevent Set to false to prevent the loginas event to be generated 1049 * @return void 1050 */ 1051 public static function loginas($userid, \context $context, $generateevent = true) { 1052 global $USER; 1053 1054 if (self::is_loggedinas()) { 1055 return; 1056 } 1057 1058 // Switch to fresh new $_SESSION. 1059 $_SESSION = array(); 1060 $_SESSION['REALSESSION'] = clone($GLOBALS['SESSION']); 1061 $GLOBALS['SESSION'] = new \stdClass(); 1062 $_SESSION['SESSION'] =& $GLOBALS['SESSION']; 1063 1064 // Create the new $USER object with all details and reload needed capabilities. 1065 $_SESSION['REALUSER'] = clone($GLOBALS['USER']); 1066 $user = get_complete_user_data('id', $userid); 1067 $user->realuser = $_SESSION['REALUSER']->id; 1068 $user->loginascontext = $context; 1069 1070 // Let enrol plugins deal with new enrolments if necessary. 1071 enrol_check_plugins($user); 1072 1073 if ($generateevent) { 1074 // Create event before $USER is updated. 1075 $event = \core\event\user_loggedinas::create( 1076 array( 1077 'objectid' => $USER->id, 1078 'context' => $context, 1079 'relateduserid' => $userid, 1080 'other' => array( 1081 'originalusername' => fullname($USER, true), 1082 'loggedinasusername' => fullname($user, true) 1083 ) 1084 ) 1085 ); 1086 } 1087 1088 // Set up global $USER. 1089 \core\session\manager::set_user($user); 1090 1091 if ($generateevent) { 1092 $event->trigger(); 1093 } 1094 1095 // Queue migrating the messaging data, if we need to. 1096 if (!get_user_preferences('core_message_migrate_data', false, $userid)) { 1097 // Check if there are any legacy messages to migrate. 1098 if (\core_message\helper::legacy_messages_exist($userid)) { 1099 \core_message\task\migrate_message_data::queue_task($userid); 1100 } else { 1101 set_user_preference('core_message_migrate_data', true, $userid); 1102 } 1103 } 1104 } 1105 1106 /** 1107 * Add a JS session keepalive to the page. 1108 * 1109 * A JS session keepalive script will be called to update the session modification time every $frequency seconds. 1110 * 1111 * Upon failure, the specified error message will be shown to the user. 1112 * 1113 * @param string $identifier The string identifier for the message to show on failure. 1114 * @param string $component The string component for the message to show on failure. 1115 * @param int $frequency The update frequency in seconds. 1116 * @param int $timeout The timeout of each request in seconds. 1117 * @throws coding_exception IF the frequency is longer than the session lifetime. 1118 */ 1119 public static function keepalive($identifier = 'sessionerroruser', $component = 'error', $frequency = null, $timeout = 0) { 1120 global $CFG, $PAGE; 1121 1122 if ($frequency) { 1123 if ($frequency > $CFG->sessiontimeout) { 1124 // Sanity check the frequency. 1125 throw new \coding_exception('Keepalive frequency is longer than the session lifespan.'); 1126 } 1127 } else { 1128 // A frequency of sessiontimeout / 10 matches the timeouts in core/network amd module. 1129 $frequency = $CFG->sessiontimeout / 10; 1130 } 1131 1132 $PAGE->requires->js_call_amd('core/network', 'keepalive', array( 1133 $frequency, 1134 $timeout, 1135 get_string($identifier, $component) 1136 )); 1137 } 1138 1139 /** 1140 * Generate a new login token and store it in the session. 1141 * 1142 * @return array The current login state. 1143 */ 1144 private static function create_login_token() { 1145 global $SESSION; 1146 1147 $state = [ 1148 'token' => random_string(32), 1149 'created' => time() // Server time - not user time. 1150 ]; 1151 1152 if (!isset($SESSION->logintoken)) { 1153 $SESSION->logintoken = []; 1154 } 1155 1156 // Overwrite any previous values. 1157 $SESSION->logintoken[self::$logintokenkey] = $state; 1158 1159 return $state; 1160 } 1161 1162 /** 1163 * Get the current login token or generate a new one. 1164 * 1165 * All login forms generated from Moodle must include a login token 1166 * named "logintoken" with the value being the result of this function. 1167 * Logins will be rejected if they do not include this token as well as 1168 * the username and password fields. 1169 * 1170 * @return string The current login token. 1171 */ 1172 public static function get_login_token() { 1173 global $CFG, $SESSION; 1174 1175 $state = false; 1176 1177 if (!isset($SESSION->logintoken)) { 1178 $SESSION->logintoken = []; 1179 } 1180 1181 if (array_key_exists(self::$logintokenkey, $SESSION->logintoken)) { 1182 $state = $SESSION->logintoken[self::$logintokenkey]; 1183 } 1184 if (empty($state)) { 1185 $state = self::create_login_token(); 1186 } 1187 1188 // Check token lifespan. 1189 if ($state['created'] < (time() - $CFG->sessiontimeout)) { 1190 $state = self::create_login_token(); 1191 } 1192 1193 // Return the current session login token. 1194 if (array_key_exists('token', $state)) { 1195 return $state['token']; 1196 } else { 1197 return false; 1198 } 1199 } 1200 1201 /** 1202 * Check the submitted value against the stored login token. 1203 * 1204 * @param mixed $token The value submitted in the login form that we are validating. 1205 * If false is passed for the token, this function will always return true. 1206 * @return boolean If the submitted token is valid. 1207 */ 1208 public static function validate_login_token($token = false) { 1209 global $CFG; 1210 1211 if (!empty($CFG->alternateloginurl) || !empty($CFG->disablelogintoken)) { 1212 // An external login page cannot generate the login token we need to protect CSRF on 1213 // login requests. 1214 // Other custom login workflows may skip this check by setting disablelogintoken in config. 1215 return true; 1216 } 1217 if ($token === false) { 1218 // authenticate_user_login is a core function was extended to validate tokens. 1219 // For existing uses other than the login form it does not 1220 // validate that a token was generated. 1221 // Some uses that do not validate the token are login/token.php, 1222 // or an auth plugin like auth/ldap/auth.php. 1223 return true; 1224 } 1225 1226 $currenttoken = self::get_login_token(); 1227 1228 // We need to clean the login token so the old one is not valid again. 1229 self::create_login_token(); 1230 1231 if ($currenttoken !== $token) { 1232 // Fail the login. 1233 return false; 1234 } 1235 return true; 1236 } 1237 1238 /** 1239 * Get the recent session locks array. 1240 * 1241 * @return array Recent session locks array. 1242 */ 1243 public static function get_recent_session_locks() { 1244 global $SESSION; 1245 1246 if (!isset($SESSION->recentsessionlocks)) { 1247 // This will hold the pages that blocks other page. 1248 $SESSION->recentsessionlocks = array(); 1249 } 1250 1251 return $SESSION->recentsessionlocks; 1252 } 1253 1254 /** 1255 * Updates the recent session locks. 1256 * 1257 * This function will store session lock info of all the pages visited. 1258 * 1259 * @param array $sessionlock Session lock array. 1260 */ 1261 public static function update_recent_session_locks($sessionlock) { 1262 global $CFG, $SESSION; 1263 1264 if (empty($CFG->debugsessionlock)) { 1265 return; 1266 } 1267 1268 $readonlysession = defined('READ_ONLY_SESSION') && READ_ONLY_SESSION; 1269 $readonlydebugging = !empty($CFG->enable_read_only_sessions) || !empty($CFG->enable_read_only_sessions_debug); 1270 if ($readonlysession && $readonlydebugging) { 1271 return; 1272 } 1273 1274 $SESSION->recentsessionlocks = self::get_recent_session_locks(); 1275 array_push($SESSION->recentsessionlocks, $sessionlock); 1276 1277 self::cleanup_recent_session_locks(); 1278 } 1279 1280 /** 1281 * Reset recent session locks array if there is a time gap more than SESSION_RESET_GAP_THRESHOLD. 1282 */ 1283 public static function cleanup_recent_session_locks() { 1284 global $SESSION; 1285 1286 $locks = self::get_recent_session_locks(); 1287 1288 if (count($locks) > self::MAXIMUM_STORED_SESSION_HISTORY) { 1289 // Keep the last MAXIMUM_STORED_SESSION_HISTORY locks and ignore the rest. 1290 $locks = array_slice($locks, -1 * self::MAXIMUM_STORED_SESSION_HISTORY); 1291 } 1292 1293 if (count($locks) > 2) { 1294 for ($i = count($locks) - 1; $i > 0; $i--) { 1295 // Calculate the gap between session locks. 1296 $gap = $locks[$i]['released'] - $locks[$i - 1]['start']; 1297 if ($gap >= self::SESSION_RESET_GAP_THRESHOLD) { 1298 // Remove previous locks if the gap is 1 second or more. 1299 $SESSION->recentsessionlocks = array_slice($locks, $i); 1300 break; 1301 } 1302 } 1303 } 1304 } 1305 1306 /** 1307 * Get the page that blocks other pages at a specific timestamp. 1308 * 1309 * Look for a page whose lock was gained before that timestamp, and released after that timestamp. 1310 * 1311 * @param float $time Time before session lock starts. 1312 * @return array|null 1313 */ 1314 public static function get_locked_page_at($time) { 1315 $recentsessionlocks = self::get_recent_session_locks(); 1316 foreach ($recentsessionlocks as $recentsessionlock) { 1317 if ($time >= $recentsessionlock['gained'] && 1318 $time <= $recentsessionlock['released']) { 1319 return $recentsessionlock; 1320 } 1321 } 1322 } 1323 1324 /** 1325 * Display the page which blocks other pages. 1326 * 1327 * @return string 1328 */ 1329 public static function display_blocking_page() { 1330 global $PERF; 1331 1332 $page = self::get_locked_page_at($PERF->sessionlock['start']); 1333 $output = "Script ".me()." was blocked for "; 1334 $output .= number_format($PERF->sessionlock['wait'], 3); 1335 if ($page != null) { 1336 $output .= " second(s) by script: "; 1337 $output .= $page['url']; 1338 } else { 1339 $output .= " second(s) by an unknown script."; 1340 } 1341 1342 return $output; 1343 } 1344 1345 /** 1346 * Get session lock info of the current page. 1347 * 1348 * @return array 1349 */ 1350 public static function get_session_lock_info() { 1351 global $PERF; 1352 1353 if (!isset($PERF->sessionlock)) { 1354 return null; 1355 } 1356 return $PERF->sessionlock; 1357 } 1358 1359 /** 1360 * Display debugging info about slow and blocked script. 1361 */ 1362 public static function sessionlock_debugging() { 1363 global $CFG, $PERF; 1364 1365 if (!empty($CFG->debugsessionlock)) { 1366 if (isset($PERF->sessionlock['held']) && $PERF->sessionlock['held'] > $CFG->debugsessionlock) { 1367 debugging("Script ".me()." locked the session for ".number_format($PERF->sessionlock['held'], 3) 1368 ." seconds, it should close the session using \core\session\manager::write_close().", DEBUG_NORMAL); 1369 } 1370 1371 if (isset($PERF->sessionlock['wait']) && $PERF->sessionlock['wait'] > $CFG->debugsessionlock) { 1372 $output = self::display_blocking_page(); 1373 debugging($output, DEBUG_DEVELOPER); 1374 } 1375 } 1376 } 1377 1378 /** 1379 * Compares two arrays outputs the difference. 1380 * 1381 * Note this does not use array_diff_assoc due to 1382 * the use of stdClasses in Moodle sessions. 1383 * 1384 * @param array $array1 1385 * @param array $array2 1386 * @return array 1387 */ 1388 private static function array_session_diff(array $array1, array $array2) : array { 1389 $difference = []; 1390 foreach ($array1 as $key => $value) { 1391 if (!isset($array2[$key])) { 1392 $difference[$key] = $value; 1393 } else if ($array2[$key] !== $value) { 1394 $difference[$key] = $value; 1395 } 1396 } 1397 1398 return $difference; 1399 } 1400 }
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