memcache-session.inc in Memcache API and Integration 6

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5 memcache-session.inc
User session handling functions.
An alternative to includes/session.inc.
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memcache-session.inc
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<?php

require_once dirname(__FILE__) . '/dmemcache.inc';

/**
 * @file
 * User session handling functions.
 *
 * An alternative to includes/session.inc.
 */

/**
 * Implement hook_user() using a required module's namespace since memcache is
 * not a module and thus can't implement hooks directly.
 */
function filter_user($op, &$edit, &$account, $category = NULL) {
  if ($op == 'update') {

    // Invalidate cached user object.
    cache_clear_all($account->uid, 'users');
  }
}
function sess_open($save_path, $session_name) {
  return TRUE;
}
function sess_close() {
  return TRUE;
}
function sess_read($key) {
  global $user;

  // Write and Close handlers are called after destructing objects since PHP 5.0.5
  // Thus destructors can use sessions but session handler can't use objects.
  // So we are moving session closure before destructing objects.
  register_shutdown_function('session_write_close');

  // Handle the case of first time visitors and clients that don't store
  // cookies (eg. web crawlers).
  if (!isset($_COOKIE[session_name()])) {
    $user = drupal_anonymous_user();
    return '';
  }

  // Otherwise, if the session is still active, we have a record of the
  // client's session in memcache.
  $session = dmemcache_get($key, 'session');
  $user = sess_user_load($session);

  // Record whether this session contains data so that in sess_write() it can
  // be determined whether to skip a write.
  if ($user->session_data_present_at_load = !empty($session->session)) {

    // Set a global value for the original session value to be compared against
    // during sess_write().
    $GLOBALS['memcache_session_last_read'] = array(
      'sid' => $session->sid,
      'value' => $user->session,
    );
  }
  return $user->session;
}

/**
 * Write a session to session storage.
 *
 * We have the following cases to handle.
 * 1. Anonymous user
 *   1a. Without session data.
 *   1b. With session data.
 *   1c. Session saving has been turned off programatically
 *       (see session_save_session()).
 *   1d. Without session data but had session data at the beginning of the request
 *       (thus a write must be made to clear stored session data).
 * 2. Authenticated user.
 *   2a. Without session data.
 *   2b. With session data.
 *   2c. Session saving has been turned off programatically
 *       (see session_save_session()).
 *
 * @param $key
 *   The session ID.
 * @param $value
 *   Any data to store in the session.
 * @return
 *   TRUE.
 */
function sess_write($key, $value) {
  global $user;

  // If the client doesn't have a session, and one isn't being created ($value),
  // do nothing. If session saving has been turned off, do nothing.
  // Cases 1a, 1c, and 2c are covered here.
  if (!session_save_session() || $user->uid == 0 && empty($_COOKIE[session_name()]) && empty($value)) {
    return TRUE;
  }

  // Prepare the information to be saved.
  $session = new stdClass();
  $session->sid = $key;
  $session->uid = $user->uid;
  $session->cache = isset($user->cache) ? $user->cache : '';
  $session->hostname = ip_address();
  $session->session = $value;
  $session->timestamp = $_SERVER['REQUEST_TIME'];

  // Be sure that we have the latest user object.  If user_save() has been
  // called, we need to refresh the object from the database.
  $user = sess_user_load($session);

  // If this is an authenticated user, or there is something to save in the
  // session, or this is an anonymous user who currently has nothing in the
  // session but did have something in session storage, write it to memcache.
  // If $user->session_data_present_at_load is not set, the current user
  // was created during this request and it's safest to do a write.
  // Cases 1b, 1d, 2a, and 2b are covered here.
  if ($user->uid || !empty($value) || empty($value) && (!isset($user->session_data_present_at_load) || $user->session_data_present_at_load)) {

    // Additionally, check if the session has changed since it was loaded.
    // if not, only write with the same frequency as session_write_interval.
    $last_read = isset($GLOBALS['memcache_session_last_read']) ? $GLOBALS['memcache_session_last_read'] : FALSE;
    $is_changed = empty($last_read) || $last_read['sid'] != $key || $last_read['value'] != $value;
    if ($is_changed || time() - $user->timestamp > variable_get('session_write_interval', 360)) {
      dmemcache_set($key, $session, ini_get('session.gc_maxlifetime'), 'session');
      $session_write = TRUE;
    }
    if ($user->uid && time() - $user->access > variable_get('session_write_interval', 360)) {

      // Update user->access if the session_write_interval threshold has
      // passed.
      db_query('UPDATE {users} SET access = %d WHERE uid = %d', $session->timestamp, $user->uid);

      // Update the user access time so that the dmemcache_set() call
      // caches the updated time.
      $user->access = $session->timestamp;
      $access_update = TRUE;
    }

    // If either the session $user->access has been updated, refresh the cached
    // user object.
    if (!empty($session_write) || !empty($access_update)) {

      // Always update the cached user object if the session has changed.
      $user->timestamp = $session->timestamp;

      // If users.access has been updated, also refresh the cached user object.
      // Data stored in session is stored in session memcache; no need
      // to duplicate it in users memcache.
      unset($user->session);
      unset($user->session_data_present_at_load);

      // Store the session id so we can locate the session with the user id.
      $user->sid = $key;
      dmemcache_set($user->uid, $user, ini_get('session.gc_maxlifetime'), 'users');
    }
  }
  return TRUE;
}
function sess_regenerate() {

  // We code around http://bugs.php.net/bug.php?id=32802 by destroying
  // the session cookie by setting expiration in the past (a negative
  // value).  This issue only arises in PHP versions before 4.4.0,
  // regardless of the Drupal configuration.
  // TODO: remove this when we require at least PHP 4.4.0
  if (isset($_COOKIE[session_name()])) {
    setcookie(session_name(), '', $_SERVER['REQUEST_TIME'] - 42000, '/');
  }

  // Store the current (anonymous) session id.
  $old_session_id = session_id();

  // Generate the new (authenticated) session id.
  session_regenerate_id();
  $key = session_id();

  // Grab the user's information that is cached with the anonymous key.
  $info = dmemcache_get($old_session_id, 'session');

  // Update it.
  $info->sid = $key;

  // Store it with the new key.
  dmemcache_set($key, $info, ini_get('session.gc_maxlifetime'), 'session');

  // Clear the old data from the cache.
  dmemcache_delete($old_session_id, 'session');
}

/**
 * Counts how many users have sessions. Can count either anonymous sessions, authenticated sessions, or both.
 * Would be insane slow with memcached as we would need to retrieve at least the stats of all object.
 * Not implemented.
 */
function sess_count($timestamp = 0, $anonymous = true) {
}

/**
 * Called by PHP session handling with the PHP session ID to end a user's session.
 *
 * @param  string $sid
 *   the session id
 */
function sess_destroy_sid($sid) {
  dmemcache_delete($sid, 'session');

  // If the session ID being destroyed is the one of the current user,
  // clean-up his/her session data and cookie.
  if ($sid == session_id()) {
    global $user;

    // Reset $_SESSION and $user to prevent a new session from being started
    // in drupal_session_commit()
    $_SESSION = array();
    $user = drupal_anonymous_user();

    // Unset the session cookie.
    if (isset($_COOKIE[session_name()])) {
      $params = session_get_cookie_params();
      if (version_compare(PHP_VERSION, '5.2.0') === 1) {
        setcookie(session_name(), '', $_SERVER['REQUEST_TIME'] - 3600, $params['path'], $params['domain'], $params['secure'], $params['httponly']);
      }
      else {
        setcookie(session_name(), '', $_SERVER['REQUEST_TIME'] - 3600, $params['path'], $params['domain'], $params['secure']);
      }
      unset($_COOKIE[session_name()]);
    }
  }
}

/**
 * End a specific user's session.
 */
function sess_destroy_uid($uid) {
  $user = dmemcache_get($uid, 'users');
  if (is_object($user) && isset($user->sid)) {
    dmemcache_delete($user->sid, 'session');
  }
  dmemcache_delete($uid, 'users');
}
function sess_gc($lifetime) {

  // Automatic with memcached.
  // Be sure to adjust 'php_value session.gc_maxlifetime' to a large enough
  // value. For example, if you want user sessions to stay in your database
  // for three weeks before deleting them, you need to set gc_maxlifetime
  // to '1814400'. At that value, only after a user doesn't log in after
  // three weeks (1814400 seconds) will his/her session be removed.
  return TRUE;
}

/**
 * Determine whether to save session data of the current request.
 *
 * This function allows the caller to temporarily disable writing of session data,
 * should the request end while performing potentially dangerous operations, such as
 * manipulating the global $user object.  See http://drupal.org/node/218104 for usage
 *
 * @param $status
 *   Disables writing of session data when FALSE, (re-)enables writing when TRUE.
 * @return
 *   FALSE if writing session data has been disabled. Otherwise, TRUE.
 */
function session_save_session($status = NULL) {
  static $save_session = TRUE;
  if (isset($status)) {
    $save_session = $status;
  }
  return $save_session;
}

/**
 * Create the user object.
 *
 * @param $session
 *   The session object (see sess_write() for the structure).
 * @return $user
 *   The user object.
 */
function sess_user_load($session) {

  // We found the client's session record and they are an authenticated user.
  if ($session && $session->uid != 0) {
    $user = dmemcache_get($session->uid, 'users');

    // If the 'users' memcache bin is unavailable, $user will be NULL.
    // If the cached user was not found in the 'users' memcache bin, $user will
    // be FALSE.
    // In either of these cases, the user must be retrieved from the database.
    if (empty($user->uid) && isset($session->uid) && $session->uid != 0) {
      $user = db_fetch_object(db_query('SELECT u.* FROM {users} u WHERE u.uid = %d', $session->uid));
      if (!$user->status) {
        $user = drupal_anonymous_user($session->session);
      }
      else {
        $user = drupal_unpack($user);

        // Add roles element to $user
        $user->roles = array();
        $user->roles[DRUPAL_AUTHENTICATED_RID] = 'authenticated user';
        $result = db_query("SELECT r.rid, r.name FROM {role} r INNER JOIN {users_roles} ur ON ur.rid = r.rid WHERE ur.uid = %d", $user->uid);
        while ($role = db_fetch_object($result)) {
          $user->roles[$role->rid] = $role->name;
        }
      }

      // Normally we would join the session and user tables. But we already
      // have the session information. So add that in.
      $user->sid = $session->sid;
      $user->cache = $session->cache;
      $user->hostname = $session->hostname;
      $user->timestamp = $session->timestamp;

      // Write back to memcache before setting $user->session since this
      // is available separately.
      dmemcache_set($user->uid, $user, ini_get('session.gc_maxlifetime'), 'users');
      $user->session = empty($session->session) ? '' : $session->session;
    }
    else {
      if ($user->uid && $user->status) {

        // Got a user object from 'users' memcache bin. Mark it in case modules
        // want to know that this user was created from memcache.
        $user->from_cache = TRUE;
        $user->session = empty($session->session) ? '' : $session->session;
      }
      else {

        // We will only get here when the session has a nonzero uid, a user object
        // was successfully retrieved from the 'users' bin, and that user
        // object's uid is 0. Not sure why this would ever happen. Leaving former
        // comment in:
        // This is a rare case that we have a session cached, but no session user object cached.
        // This usually only happens if you kill memcached and restart it.
        $user = drupal_anonymous_user($session->session);
      }
    }
  }
  else {
    $session = isset($session->session) ? $session->session : '';
    $user = drupal_anonymous_user($session);
  }
  return $user;
}
Functions

Name	Description
filter_user	Implement hook_user() using a required module's namespace since memcache is not a module and thus can't implement hooks directly.
session_save_session	Determine whether to save session data of the current request.
sess_close
sess_count	Counts how many users have sessions. Can count either anonymous sessions, authenticated sessions, or both. Would be insane slow with memcached as we would need to retrieve at least the stats of all object. Not implemented.
sess_destroy_sid	Called by PHP session handling with the PHP session ID to end a user's session.
sess_destroy_uid	End a specific user's session.
sess_gc
sess_open
sess_read
sess_regenerate
sess_user_load	Create the user object.
sess_write	Write a session to session storage.
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memcache-session.inc in Memcache API and Integration 6

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