modules/update/update.module

<?php
// $Id: update.module,v 1.52 2009/10/24 11:41:05 dries Exp $

/**
 * @file
 * The "Update status" module checks for available updates of Drupal core and
 * any installed contributed modules and themes. It warns site administrators
 * if newer releases are available via the system status report
 * (admin/reports/status), the module and theme pages, and optionally via email.
 */

/**
 * URL to check for updates, if a given project doesn't define its own.
 */
define('UPDATE_DEFAULT_URL', 'http://updates.drupal.org/release-history');

// These are internally used constants for this code, do not modify.

/**
 * Project is missing security update(s).
 */
define('UPDATE_NOT_SECURE', 1);

/**
 * Current release has been unpublished and is no longer available.
 */
define('UPDATE_REVOKED', 2);

/**
 * Current release is no longer supported by the project maintainer.
 */
define('UPDATE_NOT_SUPPORTED', 3);

/**
 * Project has a new release available, but it is not a security release.
 */
define('UPDATE_NOT_CURRENT', 4);

/**
 * Project is up to date.
 */
define('UPDATE_CURRENT', 5);

/**
 * Project's status cannot be checked.
 */
define('UPDATE_NOT_CHECKED', -1);

/**
 * No available update data was found for project.
 */
define('UPDATE_UNKNOWN', -2);

/**
 * There was a failure fetching available update data for this project.
 */
define('UPDATE_NOT_FETCHED', -3);

/**
 * We need to (re)fetch available update data for this project.
 */
define('UPDATE_FETCH_PENDING', -4);

/**
 * Maximum number of attempts to fetch available update data from a given host.
 */
define('UPDATE_MAX_FETCH_ATTEMPTS', 2);

/**
 * Maximum number of seconds to try fetching available update data at a time.
 */
define('UPDATE_MAX_FETCH_TIME', 5);

/**
 * Implement hook_help().
 */
function update_help($path, $arg) {
  switch ($path) {
    case 'admin/reports/updates':
      return '<p>' . t('Here you can find information about available updates for your installed modules and themes. Note that each module or theme is part of a "project", which may or may not have the same name, and might include multiple modules or themes within it.') . '</p>';

    case 'admin/appearance':
    case 'admin/config/modules':
      include_once DRUPAL_ROOT . '/includes/install.inc';
      $status = update_requirements('runtime');
      foreach (array('core', 'contrib') as $report_type) {
        $type = 'update_' . $report_type;
        if (isset($status[$type]['severity'])) {
          if ($status[$type]['severity'] == REQUIREMENT_ERROR) {
            drupal_set_message($status[$type]['description'], 'error');
          }
          elseif ($status[$type]['severity'] == REQUIREMENT_WARNING) {
            drupal_set_message($status[$type]['description'], 'warning');
          }
        }
      }

    case 'admin/appearance/update':
    case 'admin/appearance/install':
    case 'admin/config/modules/update':
    case 'admin/config/modules/install':
    case 'admin/reports/updates/update':
    case 'admin/reports/updates/install':
    case 'admin/reports/updates/settings':
    case 'admin/reports/status':
    case 'admin/update/confirm':
      // These pages don't need additional nagging.
      break;

    case 'admin/help#update':
      $output = '<p>' . t("The Update status module periodically checks for new versions of your site's software (including contributed modules and themes), and alerts you to available updates.") . '</p>';
      $output .= '<p>' . t('The <a href="@update-report">report of available updates</a> will alert you when new releases are available for download. You may configure options for update checking frequency and notifications at the <a href="@update-settings">Update status module settings page</a>.', array('@update-report' => url('admin/reports/updates'), '@update-settings' => url('admin/reports/updates/settings'))) . '</p>';
      $output .= '<p>' . t('Please note that in order to provide this information, anonymous usage statistics are sent to drupal.org. If desired, you may disable the Update status module from the <a href="@modules">module administration page</a>.', array('@modules' => url('admin/config/modules'))) . '</p>';
      $output .= '<p>' . t('For more information, see the online handbook entry for <a href="@update">Update status module</a>.', array('@update' => 'http://drupal.org/handbook/modules/update')) . '</p>';
      return $output;

    default:
      // Otherwise, if we're on *any* admin page and there's a security
      // update missing, print an error message about it.
      if (arg(0) == 'admin' && strpos($path, '#') === FALSE
          && user_access('administer site configuration')) {
        include_once DRUPAL_ROOT . '/includes/install.inc';
        $status = update_requirements('runtime');
        foreach (array('core', 'contrib') as $report_type) {
          $type = 'update_' . $report_type;
          if (isset($status[$type])
              && isset($status[$type]['reason'])
              && $status[$type]['reason'] === UPDATE_NOT_SECURE) {
            drupal_set_message($status[$type]['description'], 'error');
          }
        }
      }

  }
}

/**
 * Implement hook_menu().
 */
function update_menu() {
  $items = array();

  $items['admin/reports/updates'] = array(
    'title' => 'Available updates',
    'description' => 'Get a status report about available updates for your installed modules and themes.',
    'page callback' => 'update_status',
    'access arguments' => array('administer site configuration'),
    'weight' => 10,
    'file' => 'update.report.inc',
  );
  $items['admin/reports/updates/list'] = array(
    'title' => 'List',
    'access arguments' => array('administer site configuration'),
    'type' => MENU_DEFAULT_LOCAL_TASK,
  );
  $items['admin/reports/updates/settings'] = array(
    'title' => 'Settings',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('update_settings'),
    'access arguments' => array('administer site configuration'),
    'file' => 'update.settings.inc',
    'type' => MENU_LOCAL_TASK,
    'weight' => 50,
  );
  $items['admin/reports/updates/check'] = array(
    'title' => 'Manual update check',
    'page callback' => 'update_manual_status',
    'access arguments' => array('administer site configuration'),
    'type' => MENU_CALLBACK,
    'file' => 'update.fetch.inc',
  );

  // We want action links for updating projects at a few different locations:
  // both the module and theme administration pages, and on the available
  // updates report itself. The menu items will be mostly identical, except the
  // paths and titles, so we just define them in a loop. We pass in a string
  // indicating what context we're entering the action from, so that can
  // customize the appearance as needed.
  $paths = array(
    'report' => 'admin/reports/updates',
    'module' => 'admin/config/modules',
    'theme' => 'admin/appearance',
  );
  foreach ($paths as $context => $path) {
    $items[$path . '/install'] = array(
      'page callback' => 'drupal_get_form',
      'page arguments' => array('update_manager_install_form', $context),
      'access callback' => 'update_manager_access',
      'access arguments' => array(),
      'weight' => 25,
      'type' => MENU_LOCAL_ACTION,
      'file' => 'update.manager.inc',
    );
    $items[$path . '/update'] = array(
      'page callback' => 'drupal_get_form',
      'page arguments' => array('update_manager_update_form', $context),
      'access callback' => 'update_manager_access',
      'access arguments' => array(),
      'weight' => 20,
      'type' => MENU_LOCAL_ACTION,
      'file' => 'update.manager.inc',
    );
  }
  // Customize the titles of the action links depending on where they appear.
  $items['admin/reports/updates/install']['title'] = 'Install new module or theme';
  $items['admin/reports/updates/update']['title'] = 'Update existing modules and themes';
  $items['admin/config/modules/install']['title'] = 'Install new module';
  $items['admin/config/modules/update']['title'] = 'Update existing modules';
  $items['admin/appearance/install']['title'] = 'Install new theme';
  $items['admin/appearance/update']['title'] = 'Update existing themes';

  // Menu callback used for the confirmation page after all the releases
  // have been downloaded, asking you to backup before installing updates.
  $items['admin/update/confirm'] = array(
    'title' => 'Confirm update',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('update_manager_confirm_update_form'),
    'access callback' => 'update_manager_access',
    'access arguments' => array(),
    'type' => MENU_CALLBACK,
    'file' => 'update.manager.inc',
  );

  return $items;
}

/**
 * Determine if the current user can access the updater menu items.
 *
 * This is used as a menu system access callback. It both enforces the
 * 'administer software updates' permission and the global killswitch for the
 * authorize.php script.
 *
 * @see update_menu()
 */
function update_manager_access() {
  return variable_get('allow_authorize_operations', TRUE) && user_access('administer software updates');
}

/**
 * Implement hook_theme().
 */
function update_theme() {
  return array(
    'update_manager_update_form' => array(
      'render element' => 'form',
      'file' => 'update.manager.inc',
    ),
    'update_last_check' => array(
      'variables' => array('last' => NULL),
    ),
    'update_report' => array(
      'variables' => array('data' => NULL),
    ),
    'update_version' => array(
      'variables' => array('version' => NULL, 'tag' => NULL, 'class' => array()),
    ),
    'update_status_label' => array(
      'variables' => array('status' => NULL),
    ),
  );
}

/**
 * Implement hook_requirements().
 *
 * @return
 *   An array describing the status of the site regarding available updates.
 *   If there is no update data, only one record will be returned, indicating
 *   that the status of core can't be determined. If data is available, there
 *   will be two records: one for core, and another for all of contrib
 *   (assuming there are any contributed modules or themes enabled on the
 *   site). In addition to the fields expected by hook_requirements ('value',
 *   'severity', and optionally 'description'), this array will contain a
 *   'reason' attribute, which is an integer constant to indicate why the
 *   given status is being returned (UPDATE_NOT_SECURE, UPDATE_NOT_CURRENT, or
 *   UPDATE_UNKNOWN). This is used for generating the appropriate e-mail
 *   notification messages during update_cron(), and might be useful for other
 *   modules that invoke update_requirements() to find out if the site is up
 *   to date or not.
 *
 * @see _update_message_text()
 * @see _update_cron_notify()
 */
function update_requirements($phase) {
  if ($phase == 'runtime') {
    if ($available = update_get_available(FALSE)) {
      module_load_include('inc', 'update', 'update.compare');
      $data = update_calculate_project_data($available);
      // First, populate the requirements for core:
      $requirements['update_core'] = _update_requirement_check($data['drupal'], 'core');
      // We don't want to check drupal a second time.
      unset($data['drupal']);
      if (!empty($data)) {
        // Now, sort our $data array based on each project's status. The
        // status constants are numbered in the right order of precedence, so
        // we just need to make sure the projects are sorted in ascending
        // order of status, and we can look at the first project we find.
        uasort($data, '_update_project_status_sort');
        $first_project = reset($data);
        $requirements['update_contrib'] = _update_requirement_check($first_project, 'contrib');
      }
    }
    else {
      $requirements['update_core']['title'] = t('Drupal core update status');
      $requirements['update_core']['value'] = t('No update data available');
      $requirements['update_core']['severity'] = REQUIREMENT_WARNING;
      $requirements['update_core']['reason'] = UPDATE_UNKNOWN;
      $requirements['update_core']['description'] = _update_no_data();
    }
    return $requirements;
  }
}

/**
 * Private helper method to fill in the requirements array.
 *
 * This is shared for both core and contrib to generate the right elements in
 * the array for hook_requirements().
 *
 * @param $project
 *  Array of information about the project we're testing as returned by
 *  update_calculate_project_data().
 * @param $type
 *  What kind of project is this ('core' or 'contrib').
 *
 * @return
 *  An array to be included in the nested $requirements array.
 *
 * @see hook_requirements()
 * @see update_requirements()
 * @see update_calculate_project_data()
 */
function _update_requirement_check($project, $type) {
  $requirement = array();
  if ($type == 'core') {
    $requirement['title'] = t('Drupal core update status');
  }
  else {
    $requirement['title'] = t('Module and theme update status');
  }
  $status = $project['status'];
  if ($status != UPDATE_CURRENT) {
    $requirement['reason'] = $status;
    $requirement['description'] = _update_message_text($type, $status, TRUE);
    $requirement['severity'] = REQUIREMENT_ERROR;
  }
  switch ($status) {
    case UPDATE_NOT_SECURE:
      $requirement_label = t('Not secure!');
      break;
    case UPDATE_REVOKED:
      $requirement_label = t('Revoked!');
      break;
    case UPDATE_NOT_SUPPORTED:
      $requirement_label = t('Unsupported release');
      break;
    case UPDATE_NOT_CURRENT:
      $requirement_label = t('Out of date');
      $requirement['severity'] = REQUIREMENT_WARNING;
      break;
    case UPDATE_UNKNOWN:
    case UPDATE_NOT_CHECKED:
    case UPDATE_NOT_FETCHED:
      $requirement_label = isset($project['reason']) ? $project['reason'] : t('Can not determine status');
      $requirement['severity'] = REQUIREMENT_WARNING;
      break;
    default:
      $requirement_label = t('Up to date');
  }
  if ($status != UPDATE_CURRENT && $type == 'core' && isset($project['recommended'])) {
    $requirement_label .= ' ' . t('(version @version available)', array('@version' => $project['recommended']));
  }
  $requirement['value'] = l($requirement_label, update_manager_access() ? 'admin/reports/updates/update' : 'admin/reports/updates');
  return $requirement;
}

/**
 * Implement hook_cron().
 */
function update_cron() {
  $frequency = variable_get('update_check_frequency', 1);
  $interval = 60 * 60 * 24 * $frequency;
  if ((REQUEST_TIME - variable_get('update_last_check', 0)) > $interval) {
    // If the configured update interval has elapsed, we want to invalidate
    // the cached data for all projects, attempt to re-fetch, and trigger any
    // configured notifications about the new status.
    update_refresh();
    _update_cron_notify();
  }
  else {
    // Otherwise, see if any individual projects are now stale or still
    // missing data, and if so, try to fetch the data.
    update_get_available(TRUE);
  }
}

/**
 * Implement hook_form_FORM_ID_alter().
 *
 * Adds a submit handler to the system modules and themes forms, so that if a
 * site admin saves either form, we invalidate the cache of available updates.
 *
 * @see _update_cache_clear()
 */
function update_form_system_themes_form_alter(&$form, $form_state) {
  $form['#submit'][] = 'update_cache_clear_submit';
}

/**
 * Implement hook_form_FORM_ID_alter().
 *
 * Adds a submit handler to the system modules and themes forms, so that if a
 * site admin saves either form, we invalidate the cache of available updates.
 *
 * @see _update_cache_clear()
 */
function update_form_system_modules_alter(&$form, $form_state) {
  $form['#submit'][] = 'update_cache_clear_submit';
}

/**
 * Helper function for use as a form submit callback.
 */
function update_cache_clear_submit($form, &$form_state) {
  // Clear all update module caches.
  _update_cache_clear();
}

/**
 * Prints a warning message when there is no data about available updates.
 */
function _update_no_data() {
  $destination = drupal_get_destination();
  return t('No information is available about potential new releases for currently installed modules and themes. To check for updates, you may need to <a href="@run_cron">run cron</a> or you can <a href="@check_manually">check manually</a>. Please note that checking for available updates can take a long time, so please be patient.', array(
    '@run_cron' => url('admin/reports/status/run-cron', array('query' => $destination)),
    '@check_manually' => url('admin/reports/updates/check', array('query' => $destination)),
  ));
}

/**
 * Internal helper to try to get the update information from the cache
 * if possible, and to refresh the cache when necessary.
 *
 * In addition to checking the cache lifetime, this function also ensures that
 * there are no .info files for enabled modules or themes that have a newer
 * modification timestamp than the last time we checked for available update
 * data. If any .info file was modified, it almost certainly means a new
 * version of something was installed. Without fresh available update data,
 * the logic in update_calculate_project_data() will be wrong and produce
 * confusing, bogus results.
 *
 * @param $refresh
 *   Boolean to indicate if this method should refresh the cache automatically
 *   if there's no data.
 *
 * @see update_refresh()
 * @see update_get_projects()
 */
function update_get_available($refresh = FALSE) {
  module_load_include('inc', 'update', 'update.compare');
  $needs_refresh = FALSE;

  // Grab whatever data we currently have cached in the DB.
  $available = _update_get_cached_available_releases();
  $num_avail = count($available);

  $projects = update_get_projects();
  foreach ($projects as $key => $project) {
    // If there's no data at all, we clearly need to fetch some.
    if (empty($available[$key])) {
      update_create_fetch_task($project);
      $needs_refresh = TRUE;
      continue;
    }

    // See if the .info file is newer than the last time we checked for data,
    // and if so, mark this project's data as needing to be re-fetched. Any
    // time an admin upgrades their local installation, the .info file will
    // be changed, so this is the only way we can be sure we're not showing
    // bogus information right after they upgrade.
    if ($project['info']['_info_file_ctime'] > $available[$key]['last_fetch']) {
      $available[$key]['fetch_status'] = UPDATE_FETCH_PENDING;
    }

    // If we have project data but no release data, we need to fetch. This
    // can be triggered when we fail to contact a release history server.
    if (empty($available[$key]['releases'])) {
      $available[$key]['fetch_status'] = UPDATE_FETCH_PENDING;
    }

    // If we think this project needs to fetch, actually create the task now
    // and remember that we think we're missing some data.
    if (!empty($available[$key]['fetch_status']) && $available[$key]['fetch_status'] == UPDATE_FETCH_PENDING) {
      update_create_fetch_task($project);
      $needs_refresh = TRUE;
    }
  }

  if ($needs_refresh && $refresh) {
    // Attempt to drain the queue of fetch tasks.
    update_fetch_data();
    // After processing the queue, we've (hopefully) got better data, so pull
    // the latest from the cache again and use that directly.
    $available = _update_get_cached_available_releases();
  }

  return $available;
}

/**
 * Wrapper to load the include file and then create a new fetch task.
 *
 * @see _update_create_fetch_task()
 */
function update_create_fetch_task($project) {
  module_load_include('inc', 'update', 'update.fetch');
  return _update_create_fetch_task($project);
}

/**
 * Wrapper to load the include file and then refresh the release data.
 *
 * @see _update_refresh();
 */
function update_refresh() {
  module_load_include('inc', 'update', 'update.fetch');
  return _update_refresh();
}

/**
 * Wrapper to load the include file and then attempt to fetch update data.
 */
function update_fetch_data() {
  module_load_include('inc', 'update', 'update.fetch');
  return _update_fetch_data();
}

/**
 * Return all currently cached data about available releases for all projects.
 *
 * @return
 *   Array of data about available releases, keyed by project shortname.
 */
function _update_get_cached_available_releases() {
  $data = array();
  $cache_items = _update_get_cache_multiple('available_releases');
  foreach ($cache_items as $cid => $cache) {
    $cache->data['last_fetch'] = $cache->created;
    if ($cache->expire < REQUEST_TIME) {
      $cache->data['fetch_status'] = UPDATE_FETCH_PENDING;
    }
    // The project shortname is embedded in the cache ID, even if there's no
    // data for this project in the DB at all, so use that for the indexes in
    // the array.
    $parts = explode('::', $cid, 2);
    $data[$parts[1]] = $cache->data;
  }
  return $data;
}

/**
 * Implement hook_mail().
 *
 * Constructs the email notification message when the site is out of date.
 *
 * @param $key
 *   Unique key to indicate what message to build, always 'status_notify'.
 * @param $message
 *   Reference to the message array being built.
 * @param $params
 *   Array of parameters to indicate what kind of text to include in the
 *   message body. This is a keyed array of message type ('core' or 'contrib')
 *   as the keys, and the status reason constant (UPDATE_NOT_SECURE, etc) for
 *   the values.
 *
 * @see drupal_mail()
 * @see _update_cron_notify()
 * @see _update_message_text()
 */
function update_mail($key, &$message, $params) {
  $language = $message['language'];
  $langcode = $language->language;
  $message['subject'] .= t('New release(s) available for !site_name', array('!site_name' => variable_get('site_name', 'Drupal')), array('langcode' => $langcode));
  foreach ($params as $msg_type => $msg_reason) {
    $message['body'][] = _update_message_text($msg_type, $msg_reason, FALSE, $language);
  }
  $message['body'][] = t('See the available updates page for more information:', array(), array('langcode' => $langcode)) . "\n" . url('admin/reports/updates', array('absolute' => TRUE, 'language' => $language));
  if (update_manager_access()) {
    $message['body'][] = t('You can automatically install your missing updates using the Update manager:', array(), array('langcode' => $langcode)) . "\n" . url('admin/reports/updates/update', array('absolute' => TRUE, 'language' => $language));
  }
  $settings_url = url('admin/reports/updates/settings', array('absolute' => TRUE));
  if (variable_get('update_notification_threshold', 'all') == 'all') {
    $message['body'][] = t('Your site is currently configured to send these emails when any updates are available. To get notified only for security updates, please visit !url.', array('!url' => $settings_url));
  }
  else {
    $message['body'][] = t('Your site is currently configured to send these emails only when security updates are available. To get notified for any available updates, please visit !url.', array('!url' => $settings_url));
  }
}

/**
 * Helper function to return the appropriate message text when the site is out
 * of date or missing a security update.
 *
 * These error messages are shared by both update_requirements() for the
 * site-wide status report at admin/reports/status and in the body of the
 * notification emails generated by update_cron().
 *
 * @param $msg_type
 *   String to indicate what kind of message to generate. Can be either
 *   'core' or 'contrib'.
 * @param $msg_reason
 *   Integer constant specifying why message is generated.
 * @param $report_link
 *   Boolean that controls if a link to the updates report should be added.
 * @param $language
 *   An optional language object to use.
 * @return
 *   The properly translated error message for the given key.
 */
function _update_message_text($msg_type, $msg_reason, $report_link = FALSE, $language = NULL) {
  $langcode = isset($language) ? $language->language : NULL;
  $text = '';
  switch ($msg_reason) {
    case UPDATE_NOT_SECURE:
      if ($msg_type == 'core') {
        $text = t('There is a security update available for your version of Drupal. To ensure the security of your server, you should update immediately!', array(), array('langcode' => $langcode));
      }
      else {
        $text = t('There are security updates available for one or more of your modules or themes. To ensure the security of your server, you should update immediately!', array(), array('langcode' => $langcode));
      }
      break;

    case UPDATE_REVOKED:
      if ($msg_type == 'core') {
        $text = t('Your version of Drupal has been revoked and is no longer available for download. Upgrading is strongly recommended!', array(), array('langcode' => $langcode));
      }
      else {
        $text = t('The installed version of at least one of your modules or themes has been revoked and is no longer available for download. Upgrading or disabling is strongly recommended!', array(), array('langcode' => $langcode));
      }
      break;

    case UPDATE_NOT_SUPPORTED:
      if ($msg_type == 'core') {
        $text = t('Your version of Drupal is no longer supported. Upgrading is strongly recommended!', array(), array('langcode' => $langcode));
      }
      else {
        $text = t('The installed version of at least one of your modules or themes is no longer supported. Upgrading or disabling is strongly recommended! Please see the project homepage for more details.', array(), array('langcode' => $langcode));
      }
      break;

    case UPDATE_NOT_CURRENT:
      if ($msg_type == 'core') {
        $text = t('There are updates available for your version of Drupal. To ensure the proper functioning of your site, you should update as soon as possible.', array(), array('langcode' => $langcode));
      }
      else {
        $text = t('There are updates available for one or more of your modules or themes. To ensure the proper functioning of your site, you should update as soon as possible.', array(), array('langcode' => $langcode));
      }
      break;

    case UPDATE_UNKNOWN:
    case UPDATE_NOT_CHECKED:
    case UPDATE_NOT_FETCHED:
    case UPDATE_FETCH_PENDING:
      if ($msg_type == 'core') {
        $text = t('There was a problem determining the status of available updates for your version of Drupal.', array(), array('langcode' => $langcode));
      }
      else {
        $text = t('There was a problem determining the status of available updates for one or more of your modules or themes.', array(), array('langcode' => $langcode));
      }
      break;
  }

  if ($report_link) {
    if (update_manager_access()) {
      $text .= ' ' . t('See the <a href="@available_updates">available updates</a> page for more information and to install your missing updates.', array('@available_updates' => url('admin/reports/updates/update', array('language' => $language))), array('langcode' => $langcode));
    }
    else {
      $text .= ' ' . t('See the <a href="@available_updates">available updates</a> page for more information.', array('@available_updates' => url('admin/reports/updates', array('language' => $language))), array('langcode' => $langcode));
    }
  }

  return $text;
}

/**
 * Private sort function to order projects based on their status.
 *
 * @see update_requirements()
 * @see uasort()
 */
function _update_project_status_sort($a, $b) {
  // The status constants are numerically in the right order, so we can
  // usually subtract the two to compare in the order we want. However,
  // negative status values should be treated as if they are huge, since we
  // always want them at the bottom of the list.
  $a_status = $a['status'] > 0 ? $a['status'] : (-10 * $a['status']);
  $b_status = $b['status'] > 0 ? $b['status'] : (-10 * $b['status']);
  return $a_status - $b_status;
}

/**
 * Render the HTML to display the last time we checked for update data.
 *
 * In addition to properly formating the given timestamp, this function also
 * provides a "Check manually" link that refreshes the available update and
 * redirects back to the same page.
 *
 * @param $variables
 *   'last': The timestamp when the site last checked for available updates.
 *
 * @see theme_update_report()
 * @see theme_update_available_updates_form()
 *
 * @ingroup themeable
 */
function theme_update_last_check($variables) {
  $last = $variables['last'];
  $output = '<div class="update checked">';
  $output .= $last ? t('Last checked: @time ago', array('@time' => format_interval(REQUEST_TIME - $last))) : t('Last checked: never');
  $output .= ' <span class="check-manually">(' . l(t('Check manually'), 'admin/reports/updates/check', array('query' => drupal_get_destination())) . ')</span>';
  $output .= "</div>\n";
  return $output;
}

/**
 * @defgroup update_status_cache Private update status cache system
 * @{
 *
 * We specifically do NOT use the core cache API for saving the fetched data
 * about available updates. It is vitally important that this cache is only
 * cleared when we're populating it after successfully fetching new available
 * update data. Usage of the core cache API results in all sorts of potential
 * problems that would result in attempting to fetch available update data all
 * the time, including if a site has a "minimum cache lifetime" (which is both
 * a minimum and a maximum) defined, or if a site uses memcache or another
 * plug-able cache system that assumes volatile caches.
 *
 * Update module still uses the {cache_update} table, but instead of using
 * cache_set(), cache_get(), and cache_clear_all(), there are private helper
 * functions that implement these same basic tasks but ensure that the cache
 * is not prematurely cleared, and that the data is always stored in the
 * database, even if memcache or another cache backend is in use.
 */

/**
 * Store data in the private update status cache table.
 *
 * Note: this function completely ignores the {cache_update}.headers field
 * since that is meaningless for the kinds of data we're caching.
 *
 * @param $cid
 *   The cache ID to save the data with.
 * @param $data
 *   The data to store.
 * @param $expire
 *   One of the following values:
 *   - CACHE_PERMANENT: Indicates that the item should never be removed except
 *     by explicitly using _update_cache_clear().
 *   - A Unix timestamp: Indicates that the item should be kept at least until
 *     the given time, after which it will be invalidated.
 */
function _update_cache_set($cid, $data, $expire) {
  $fields = array(
    'created' => REQUEST_TIME,
    'expire' => $expire,
    'headers' => NULL,
  );
  if (!is_string($data)) {
    $fields['data'] = serialize($data);
    $fields['serialized'] = 1;
  }
  else {
    $fields['data'] = $data;
    $fields['serialized'] = 0;
  }
  db_merge('cache_update')
    ->key(array('cid' => $cid))
    ->fields($fields)
    ->execute();
}

/**
 * Retrieve data from the private update status cache table.
 *
 * @param $cid
 *   The cache ID to retrieve.
 * @return
 *   The data for the given cache ID, or NULL if the ID was not found.
 */
function _update_cache_get($cid) {
  $cache = db_query("SELECT data, created, expire, serialized FROM {cache_update} WHERE cid = :cid", array(':cid' => $cid))->fetchObject();
  if (isset($cache->data)) {
    if ($cache->serialized) {
      $cache->data = unserialize($cache->data);
    }
  }
  return $cache;
}

/**
 * Return an array of cache items with a given cache ID prefix.
 *
 * @return
 *   Associative array of cache items, keyed by cache ID.
 */
function _update_get_cache_multiple($cid_prefix) {
  $data = array();
  $result = db_select('cache_update')
    ->fields('cache_update', array('cid', 'data', 'created', 'expire', 'serialized'))
    ->condition('cache_update.cid', $cid_prefix . '::%', 'LIKE')
    ->execute();
  foreach ($result as $cache) {
    if ($cache) {
      if ($cache->serialized) {
        $cache->data = unserialize($cache->data);
      }
      $data[$cache->cid] = $cache;
    }
  }
  return $data;
}

/**
 * Invalidates cached data relating to update status.
 *
 * @param $cid
 *   Optional cache ID of the record to clear from the private update module
 *   cache. If empty, all records will be cleared from the table.
 * @param $wildcard
 *   If $wildcard is TRUE, cache IDs starting with $cid are deleted in
 *   addition to the exact cache ID specified by $cid.
 */
function _update_cache_clear($cid = NULL, $wildcard = FALSE) {
  if (empty($cid)) {
    db_truncate('cache_update')->execute();
  }
  else {
    $query = db_delete('cache_update');
    if ($wildcard) {
      $query->condition('cid', $cid . '%', 'LIKE');
    }
    else {
      $query->condition('cid', $cid);
    }
    $query->execute();
  }
}

/**
 * Implement hook_flush_caches().
 *
 * Called from update.php (among others) to flush the caches.
 * Since we're running update.php, we are likely to install a new version of
 * something, in which case, we want to check for available update data again.
 * However, because we have our own caching system, we need to directly clear
 * the database table ourselves at this point and return nothing, for example,
 * on sites that use memcache where cache_clear_all() won't know how to purge
 * this data.
 *
 * However, we only want to do this from update.php, since otherwise, we'd
 * lose all the available update data on every cron run. So, we specifically
 * check if the site is in MAINTENANCE_MODE == 'update' (which indicates
 * update.php is running, not update module... alas for overloaded names).
 */
function update_flush_caches() {
  if (defined('MAINTENANCE_MODE') && MAINTENANCE_MODE == 'update') {
    _update_cache_clear();
  }
  return array();
}

/**
 * @} End of "defgroup update_status_cache".
 */