filter.module

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<?php
// $Id: filter.module,v 1.311 2009/12/14 13:32:53 dries Exp $

/**
 * @file
 * Framework for handling filtering of content.
 */

/**
 * Implements hook_help().
 */
function filter_help($path, $arg) {
  switch ($path) {
    case 'admin/help#filter':
      $output = '';
      $output .= '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('The Filter module allows administrators to configure text formats. A text format defines the HTML tags, codes, and other input allowed in content and comments, and is a key feature in guarding against potentially damaging input from malicious users. For more information, see the online handbook entry for <a href="@filter">Filter module</a>.', array('@filter' => 'http://drupal.org/handbook/modules/filter/')) . '</p>';
      $output .= '<h3>' . t('Uses') . '</h3>';
      $output .= '<dl>';
      $output .= '<dt>' . t('Applying filters to text') . '</dt>';
      $output .= '<dd>' . t('Each text format uses filters to manipulate text, and most formats apply several different filters to text in a specific order. Each filter is designed for a specific purpose, and generally either adds, removes or transforms elements within user-entered text before it is displayed. A filter does not change the actual content, but instead, modifies it temporarily before it is displayed. One filter may remove unapproved HTML tags, while another automatically adds HTML to make URLS display as clickable links.') . '</dd>';
      $output .= '<dt>' . t('Defining text formats') . '</dt>';
      $output .= '<dd>' . t('There are three formats included by default; <em>Filtered HTML</em> (which allows only an administrator-approved subset of HTML tags), <em>Full HTML</em> (which allows the full set of HTML tags), and <em>Plain text</em> (which removes all HTML tags). Additional formats may be created by an administrator on the <a href="@text-formats">Text formats page</a>.', array('@text-formats' => url('admin/config/content/formats'))) . '</dd>';
      $output .= '<dt>' . t('Choosing a text format') . '</dt>';
      $output .= '<dd>' . t('Users with access to more than one text format can use the <em>Text format</em> fieldset to choose between available text formats when creating or editing multi-line content. Administrators can determine the text formats available to each user role, and control the order of formats listed in the <em>Text format</em> fieldset on the <a href="@text-formats">Text formats page</a>.', array('@text-formats' => url('admin/config/content/formats'))) . '</dd>';
      $output .= '</dl>';
      return $output;

    case 'admin/config/content/formats':
      $output = '<p>' . t("Control which HTML tags and other formatting can be used for text input. Don't allow too much formatting for untrusted users. This can be a serious security risk.") . '</p>';
      $output .= '<p>' . t('Text formats are presented in the order you arrange them below. Configure a text format to change its behavior.') . '</p>';
      return $output;

    case 'admin/config/content/formats/%':
      $output = '<p>' . t('A text format contains filters that change the user input, for example stripping out malicious HTML or making URLs clickable. Filters are executed from top to bottom and the order is important, since one filter may prevent another filter from doing its job. For example, when URLs are converted into links before disallowed HTML tags are removed, all links may be removed. When this happens, the order of filters may need to be re-arranged.') . '</p>';
      return $output;
  }
}

/**
 * Implements hook_theme().
 */
function filter_theme() {
  return array(
    'filter_admin_overview' => array(
      'render element' => 'form',
      'file' => 'filter.admin.inc',
    ),
    'filter_admin_format_filter_order' => array(
      'render element' => 'element',
      'file' => 'filter.admin.inc',
    ),
    'filter_tips' => array(
      'variables' => array('tips' => NULL, 'long' => FALSE),
      'file' => 'filter.pages.inc',
    ),
    'filter_tips_more_info' => array(
      'variables' => array(),
    ),
    'filter_guidelines' => array(
      'variables' => array('format' => NULL),
    ),
  );
}

/**
 * Implements hook_menu().
 */
function filter_menu() {
  $items['filter/tips'] = array(
    'title' => 'Compose tips',
    'page callback' => 'filter_tips_long',
    'access callback' => TRUE,
    'type' => MENU_SUGGESTED_ITEM,
    'file' => 'filter.pages.inc',
  );
  $items['admin/config/content/formats'] = array(
    'title' => 'Text formats',
    'description' => 'Configure how content input by users is filtered, including allowed HTML tags. Also allows enabling of module-provided filters.',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('filter_admin_overview'),
    'access arguments' => array('administer filters'),
    'file' => 'filter.admin.inc',
  );
  $items['admin/config/content/formats/list'] = array(
    'title' => 'List',
    'type' => MENU_DEFAULT_LOCAL_TASK,
  );
  $items['admin/config/content/formats/add'] = array(
    'title' => 'Add text format',
    'page callback' => 'filter_admin_format_page',
    'access arguments' => array('administer filters'),
    'type' => MENU_LOCAL_ACTION,
    'weight' => 1,
    'file' => 'filter.admin.inc',
  );
  $items['admin/config/content/formats/%filter_format'] = array(
    'type' => MENU_CALLBACK,
    'title callback' => 'filter_admin_format_title',
    'title arguments' => array(4),
    'page callback' => 'filter_admin_format_page',
    'page arguments' => array(4),
    'access arguments' => array('administer filters'),
    'file' => 'filter.admin.inc',
  );
  $items['admin/config/content/formats/%filter_format/delete'] = array(
    'title' => 'Delete text format',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('filter_admin_delete', 4),
    'access callback' => '_filter_delete_format_access',
    'access arguments' => array(4),
    'type' => MENU_CALLBACK,
    'file' => 'filter.admin.inc',
  );
  return $items;
}

/**
 * Access callback for deleting text formats.
 *
 * @param $format
 *   A text format object.
 * @return
 *   TRUE if the text format can be deleted by the current user, FALSE
 *   otherwise.
 */
function _filter_delete_format_access($format) {
  // The fallback format can never be deleted.
  return user_access('administer filters') && ($format->format != filter_fallback_format());
}

/**
 * Load a text format object from the database.
 *
 * @param $format_id
 *   The format ID.
 *
 * @return
 *   A fully-populated text format object.
 */
function filter_format_load($format_id) {
  $formats = filter_formats();
  return isset($formats[$format_id]) ? $formats[$format_id] : FALSE;
}

/**
 * Save a text format object to the database.
 *
 * @param $format
 *   A format object using the properties:
 *   - 'name': The title of the text format.
 *   - 'format': (optional) The internal ID of the text format. If omitted, a
 *     new text format is created.
 *   - 'roles': (optional) An associative array containing the roles allowed to
 *     access/use the text format.
 *   - 'filters': (optional) An associative, multi-dimensional array of filters
 *     assigned to the text format, using the properties:
 *     - 'weight': The weight of the filter in the text format.
 *     - 'status': A boolean indicating whether the filter is enabled in the
 *       text format.
 *     - 'module': The name of the module implementing the filter.
 *     - 'settings': (optional) An array of configured settings for the filter.
 *       See hook_filter_info() for details.
 */
function filter_format_save(&$format) {
  $format->name = trim($format->name);
  $format->cache = _filter_format_is_cacheable($format);

  // Add a new text format.
  if (empty($format->format)) {
    $return = drupal_write_record('filter_format', $format);
  }
  else {
    $return = drupal_write_record('filter_format', $format, 'format');
  }

  $filter_info = filter_get_filters();
  // Programmatic saves may not contain any filters.
  if (!isset($format->filters)) {
    $format->filters = array();
  }
  foreach ($filter_info as $name => $filter) {
    // Add new filters without weight to the bottom.
    if (!isset($format->filters[$name]['weight'])) {
      $format->filters[$name]['weight'] = 10;
    }
    $format->filters[$name]['status'] = isset($format->filters[$name]['status']) ? $format->filters[$name]['status'] : 0;
    $format->filters[$name]['module'] = $filter['module'];

    // If settings were passed, only ensure default settings.
    if (isset($format->filters[$name]['settings'])) {
      if (isset($filter['default settings'])) {
        $format->filters[$name]['settings'] = array_merge($filter['default settings'], $format->filters[$name]['settings']);
      }
    }
    // Otherwise, use default settings or fall back to an empty array.
    else {
      $format->filters[$name]['settings'] = isset($filter['default settings']) ? $filter['default settings'] : array();
    }

    $fields = array();
    $fields['weight'] = $format->filters[$name]['weight'];
    $fields['status'] = $format->filters[$name]['status'];
    $fields['module'] = $format->filters[$name]['module'];
    $fields['settings'] = serialize($format->filters[$name]['settings']);

    db_merge('filter')
      ->key(array(
        'format' => $format->format,
        'name' => $name,
      ))
      ->fields($fields)
      ->execute();
  }

  if ($return == SAVED_NEW) {
    module_invoke_all('filter_format_insert', $format);
  }
  else {
    module_invoke_all('filter_format_update', $format);
    // Explicitly indicate that the format was updated. We need to do this
    // since if the filters were updated but the format object itself was not,
    // the call to drupal_write_record() above would not return an indication
    // that anything had changed.
    $return = SAVED_UPDATED;

    // Clear the filter cache whenever a text format is updated.
    cache_clear_all($format->format . ':', 'cache_filter', TRUE);
  }

  filter_formats_reset();

  return $return;
}

/**
 * Delete a text format.
 *
 * @param $format
 *   The text format object to be deleted.
 */
function filter_format_delete($format) {
  db_delete('filter_format')
    ->condition('format', $format->format)
    ->execute();
  db_delete('filter')
    ->condition('format', $format->format)
    ->execute();

  // Allow modules to react on text format deletion.
  $fallback = filter_format_load(filter_fallback_format());
  module_invoke_all('filter_format_delete', $format, $fallback);

  filter_formats_reset();
  cache_clear_all($format->format . ':', 'cache_filter', TRUE);
}

/**
 * Display a text format form title.
 */
function filter_admin_format_title($format) {
  return $format->name;
}

/**
 * Implements hook_permission().
 */
function filter_permission() {
  $perms['administer filters'] = array(
    'title' => t('Administer and use any text formats and filters'),
    'description' => theme('placeholder', array('text' => t('Warning: This permission may have security implications depending on how the text format is configured.'))),
  );

  // Generate permissions for each text format. Warn the administrator that any
  // of them are potentially unsafe.
  foreach (filter_formats() as $format) {
    $permission = filter_permission_name($format);
    if (!empty($permission)) {
      // Only link to the text format configuration page if the user who is
      // viewing this will have access to that page.
      $format_name_replacement = user_access('administer filters') ? l($format->name, 'admin/config/content/formats/' . $format->format) : theme('placeholder', array('text' => $format->name));
      $perms[$permission] = array(
        'title' => t("Use the !text_format text format", array('!text_format' => $format_name_replacement,)),
        'description' => theme('placeholder', array('text' => t('Warning: This permission may have security implications depending on how the text format is configured.'))),
      );
    }
  }
  return $perms;
}

/**
 * Returns the machine-readable permission name for a provided text format.
 *
 * @param $format
 *   An object representing a text format.
 * @return
 *   The machine-readable permission name, or FALSE if the provided text format
 *   is malformed or is the fallback format (which is available to all users).
 */
function filter_permission_name($format) {
  if (isset($format->format) && $format->format != filter_fallback_format()) {
    return 'use text format ' . $format->format;
  }
  return FALSE;
}

/**
 * Implements hook_cron().
 *
 * Expire outdated filter cache entries
 */
function filter_cron() {
  cache_clear_all(NULL, 'cache_filter');
}

/**
 * Retrieve a list of text formats, ordered by weight.
 *
 * @param $account
 *   (optional) If provided, only those formats that are allowed for this user
 *   account will be returned. All formats will be returned otherwise.
 * @return
 *   An array of text format objects, keyed by the format ID and ordered by
 *   weight.
 *
 * @see filter_formats_reset()
 */
function filter_formats($account = NULL) {
  $formats = &drupal_static(__FUNCTION__, array());

  // Statically cache all existing formats upfront.
  if (!isset($formats['all'])) {
    $formats['all'] = db_select('filter_format', 'ff')
      ->addTag('translatable')
      ->fields('ff')
      ->orderBy('weight')
      ->execute()
      ->fetchAllAssoc('format');
  }

  // Build a list of user-specific formats.
  if (isset($account) && !isset($formats['user'][$account->uid])) {
    $formats['user'][$account->uid] = array();
    foreach ($formats['all'] as $format) {
      if (filter_access($format, $account)) {
        $formats['user'][$account->uid][$format->format] = $format;
      }
    }
  }

  return isset($account) ? $formats['user'][$account->uid] : $formats['all'];
}

/**
 * Resets the static cache of all text formats.
 *
 * @see filter_formats()
 */
function filter_formats_reset() {
  drupal_static_reset('filter_list_format');
  drupal_static_reset('filter_formats');
}

/**
 * Retrieves a list of roles that are allowed to use a given text format.
 *
 * @param $format
 *   An object representing the text format.
 * @return
 *   An array of role names, keyed by role ID.
 */
function filter_get_roles_by_format($format) {
  // Handle the fallback format upfront (all roles have access to this format).
  if ($format->format == filter_fallback_format()) {
    return user_roles();
  }
  // Do not list any roles if the permission does not exist.
  $permission = filter_permission_name($format);
  return !empty($permission) ? user_roles(FALSE, $permission) : array();
}

/**
 * Retrieves a list of text formats that are allowed for a given role.
 *
 * @param $rid
 *   The user role ID to retrieve text formats for.
 * @return
 *   An array of text format objects that are allowed for the role, keyed by
 *   the text format ID and ordered by weight.
 */
function filter_get_formats_by_role($rid) {
  $formats = array();
  foreach (filter_formats() as $format) {
    $roles = filter_get_roles_by_format($format);
    if (isset($roles[$rid])) {
      $formats[$format->format] = $format;
    }
  }
  return $formats;
}

/**
 * Returns the ID of the default text format for a particular user.
 *
 * The default text format is the first available format that the user is
 * allowed to access, when the formats are ordered by weight. It should
 * generally be used as a default choice when presenting the user with a list
 * of possible text formats (for example, in a node creation form).
 *
 * Conversely, when existing content that does not have an assigned text format
 * needs to be filtered for display, the default text format is the wrong
 * choice, because it is not guaranteed to be consistent from user to user, and
 * some trusted users may have an unsafe text format set by default, which
 * should not be used on text of unknown origin. Instead, the fallback format
 * returned by filter_fallback_format() should be used, since that is intended
 * to be a safe, consistent format that is always available to all users.
 *
 * @param $account
 *   (optional) The user account to check. Defaults to the currently logged-in
 *   user.
 * @return
 *   The ID of the user's default text format.
 *
 * @see filter_fallback_format()
 */
function filter_default_format($account = NULL) {
  global $user;
  if (!isset($account)) {
    $account = $user;
  }
  // Get a list of formats for this user, ordered by weight. The first one
  // available is the user's default format.
  $formats = filter_formats($account);
  $format = reset($formats);
  return $format->format;
}

/**
 * Returns the ID of the fallback text format that all users have access to.
 */
function filter_fallback_format() {
  // This variable is automatically set in the database for all installations
  // of Drupal. In the event that it gets deleted somehow, there is no safe
  // default to return, since we do not want to risk making an existing (and
  // potentially unsafe) text format on the site automatically available to all
  // users. Returning NULL at least guarantees that this cannot happen.
  return variable_get('filter_fallback_format');
}

/**
 * Returns the title of the fallback text format.
 */
function filter_fallback_format_title() {
  $fallback_format = filter_format_load(filter_fallback_format());
  return filter_admin_format_title($fallback_format);
}

/**
 * Return a list of all filters provided by modules.
 */
function filter_get_filters() {
  $filters = &drupal_static(__FUNCTION__, array());

  if (empty($filters)) {
    foreach (module_implements('filter_info') as $module) {
      $info = module_invoke($module, 'filter_info');
      if (isset($info) && is_array($info)) {
        // Assign the name of the module implementing the filters and ensure
        // default values.
        foreach (array_keys($info) as $name) {
          $info[$name]['module'] = $module;
          $info[$name] += array(
            'description' => '',
            'weight' => 0,
          );
        }
        $filters = array_merge($filters, $info);
      }
    }
    // Allow modules to alter filter definitions.
    drupal_alter('filter_info', $filters);

    uasort($filters, '_filter_list_cmp');
  }

  return $filters;
}

/**
 * Helper function for sorting the filter list by filter name.
 */
function _filter_list_cmp($a, $b) {
  return strcmp($a['title'], $b['title']);
}

/**
 * Check if text in a certain text format is allowed to be cached.
 *
 * This function can be used to check whether the result of the filtering
 * process can be cached. A text format may allow caching depending on the
 * filters enabled.
 *
 * @param $format_id
 *   The text format ID to check.
 * @return
 *   TRUE if the given text format allows caching, FALSE otherwise.
 */
function filter_format_allowcache($format_id) {
  $format = filter_format_load($format_id);
  return !empty($format->cache);
}

/**
 * Helper function to determine whether the output of a given text format can be cached.
 *
 * The output of a given text format can be cached when all enabled filters in
 * the text format allow caching.
 *
 * @param $format
 *   The text format object to check.
 * @return
 *   TRUE if all the filters enabled in the given text format allow caching,
 *   FALSE otherwise.
 *
 * @see filter_format_save()
 */
function _filter_format_is_cacheable($format) {
  if (empty($format->filters)) {
    return TRUE;
  }
  $filter_info = filter_get_filters();
  foreach ($format->filters as $name => $filter) {
    // By default, 'cache' is TRUE for all filters unless specified otherwise.
    if (!empty($filter['status']) && isset($filter_info[$name]['cache']) && !$filter_info[$name]['cache']) {
      return FALSE;
    }
  }
  return TRUE;
}

/**
 * Retrieve a list of filters for a given text format.
 *
 * Note that this function returns all associated filters regardless of whether
 * they are enabled or disabled. All functions working with the filter
 * information outside of filter administration should test for $filter->status
 * before performing actions with the filter.
 *
 * @param $format_id
 *   The format ID to retrieve filters for.
 *
 * @return
 *   An array of filter objects associated to the given text format, keyed by
 *   filter name.
 */
function filter_list_format($format_id) {
  $filters = &drupal_static(__FUNCTION__, array());
  $filter_info = filter_get_filters();

  if (!isset($filters['all'])) {
    $result = db_query('SELECT * FROM {filter} ORDER BY weight, module, name');
    foreach ($result as $record) {
      $filters['all'][$record->format][$record->name] = $record;
    }
  }

  if (!isset($filters[$format_id])) {
    $format_filters = array();
    foreach ($filters['all'][$format_id] as $name => $filter) {
      if (isset($filter_info[$name])) {
        $filter->title = $filter_info[$name]['title'];
        // Unpack stored filter settings.
        $filter->settings = (isset($filter->settings) ? unserialize($filter->settings) : array());

        $format_filters[$name] = $filter;
      }
    }
    $filters[$format_id] = $format_filters;
  }

  return isset($filters[$format_id]) ? $filters[$format_id] : array();
}

/**
 * Run all the enabled filters on a piece of text.
 *
 * Note: Because filters can inject JavaScript or execute PHP code, security is
 * vital here. When a user supplies a text format, you should validate it using
 * filter_access() before accepting/using it. This is normally done in the
 * validation stage of the Form API. You should for example never make a preview
 * of content in a disallowed format.
 *
 * @param $text
 *   The text to be filtered.
 * @param $format_id
 *   The format id of the text to be filtered. If no format is assigned, the
 *   fallback format will be used.
 * @param $langcode
 *   Optional: the language code of the text to be filtered, e.g. 'en' for
 *   English. This allows filters to be language aware so language specific
 *   text replacement can be implemented.
 * @param $cache
 *   Boolean whether to cache the filtered output in the {cache_filter} table.
 *   The caller may set this to FALSE when the output is already cached
 *   elsewhere to avoid duplicate cache lookups and storage.
 */
function check_markup($text, $format_id = NULL, $langcode = '', $cache = FALSE) {
  if (empty($format_id)) {
    $format_id = filter_fallback_format();
  }
  $format = filter_format_load($format_id);

  // Check for a cached version of this piece of text.
  $cache = $cache && !empty($format->cache);
  $cache_id = '';
  if ($cache) {
    $cache_id = $format->format . ':' . $langcode . ':' . md5($text);
    if ($cached = cache_get($cache_id, 'cache_filter')) {
      return $cached->data;
    }
  }

  // Convert all Windows and Mac newlines to a single newline, so filters only
  // need to deal with one possibility.
  $text = str_replace(array("\r\n", "\r"), "\n", $text);

  // Get a complete list of filters, ordered properly.
  $filters = filter_list_format($format->format);
  $filter_info = filter_get_filters();

  // Give filters the chance to escape HTML-like data such as code or formulas.
  foreach ($filters as $name => $filter) {
    if ($filter->status && isset($filter_info[$name]['prepare callback']) && function_exists($filter_info[$name]['prepare callback'])) {
      $function = $filter_info[$name]['prepare callback'];
      $text = $function($text, $filter, $format, $langcode, $cache, $cache_id);
    }
  }

  // Perform filtering.
  foreach ($filters as $name => $filter) {
    if ($filter->status && isset($filter_info[$name]['process callback']) && function_exists($filter_info[$name]['process callback'])) {
      $function = $filter_info[$name]['process callback'];
      $text = $function($text, $filter, $format, $langcode, $cache, $cache_id);
    }
  }

  // Store in cache with a minimum expiration time of 1 day.
  if ($cache) {
    cache_set($cache_id, $text, 'cache_filter', REQUEST_TIME + (60 * 60 * 24));
  }

  return $text;
}

/**
 * Generates a selector for choosing a format in a form.
 *
 * @param $selected_format
 *   The ID of the format that is currently selected; uses the default format
 *   for the current user if not provided.
 * @param $weight
 *   The weight of the form element within the form.
 * @param $parents
 *   The parents array of the element. Required when defining multiple text
 *   formats on a single form or having a different parent than 'format'.
 *
 * @return
 *   Form API array for the form element.
 *
 * @ingroup forms
 */
function filter_form($selected_format = NULL, $weight = NULL, $parents = array('format')) {
  global $user;

  // Use the default format for this user if none was selected.
  if (empty($selected_format)) {
    $selected_format = filter_default_format($user);
  }

  // Get a list of formats that the current user has access to.
  $formats = filter_formats($user);

  drupal_add_js('misc/form.js');
  drupal_add_css(drupal_get_path('module', 'filter') . '/filter.css');
  $element_id = drupal_html_id('edit-' . implode('-', $parents));

  $form = array(
    '#type' => 'fieldset',
    '#weight' => $weight,
    '#attributes' => array('class' => array('filter-wrapper')),
  );
  $form['format_guidelines'] = array(
    '#prefix' => '<div id="' . $element_id . '-guidelines" class="filter-guidelines">',
    '#suffix' => '</div>',
    '#weight' => 2,
  );
  foreach ($formats as $format) {
    $options[$format->format] = $format->name;
    $form['format_guidelines'][$format->format] = array(
      '#markup' => theme('filter_guidelines', array('format' => $format)),
    );
  }
  $form['format'] = array(
    '#type' => 'select',
    '#title' => t('Text format'),
    '#options' => $options,
    '#default_value' => $selected_format,
    '#parents' => $parents,
    '#access' => count($formats) > 1,
    '#id' => $element_id,
    '#attributes' => array('class' => array('filter-list')),
  );
  $form['format_help'] = array(
    '#prefix' => '<div id="' . $element_id . '-help" class="filter-help">',
    '#markup' => theme('filter_tips_more_info'),
    '#suffix' => '</div>',
    '#weight' => 1,
  );

  return $form;
}

/**
 * Checks if a user has access to a particular text format.
 *
 * @param $format
 *   An object representing the text format.
 * @param $account
 *   (optional) The user account to check access for; if omitted, the currently
 *   logged-in user is used.
 *
 * @return
 *   Boolean TRUE if the user is allowed to access the given format.
 */
function filter_access($format, $account = NULL) {
  global $user;
  if (!isset($account)) {
    $account = $user;
  }
  // Handle special cases up front. All users have access to the fallback
  // format, and administrators have access to all formats.
  if (user_access('administer filters', $account) || $format->format == filter_fallback_format()) {
    return TRUE;
  }
  // Check the permission if one exists; otherwise, we have a non-existent
  // format so we return FALSE.
  $permission = filter_permission_name($format);
  return !empty($permission) && user_access($permission, $account);
}

/**
 * Helper function for fetching filter tips.
 */
function _filter_tips($format_id, $long = FALSE) {
  global $user;

  $formats = filter_formats($user);
  $filter_info = filter_get_filters();

  $tips = array();

  // If only listing one format, extract it from the $formats array.
  if ($format_id != -1) {
    $formats = array($formats[$format_id]);
  }

  foreach ($formats as $format) {
    $filters = filter_list_format($format->format);
    $tips[$format->name] = array();
    foreach ($filters as $name => $filter) {
      if ($filter->status && isset($filter_info[$name]['tips callback']) && function_exists($filter_info[$name]['tips callback'])) {
        $tip = $filter_info[$name]['tips callback']($filter, $format, $long);
        $tips[$format->name][$name] = array('tip' => $tip, 'id' => $name);
      }
    }
  }

  return $tips;
}

/**
 * Parses an HTML snippet and returns it as a DOM object.
 *
 * This function loads the body part of a partial (X)HTML document
 * and returns a full DOMDocument object that represents this document.
 * You can use filter_dom_serialize() to serialize this DOMDocument
 * back to a XHTML snippet.
 *
 * @param $text
 *   The partial (X)HTML snippet to load. Invalid mark-up
 *   will be corrected on import.
 * @return
 *   A DOMDocument that represents the loaded (X)HTML snippet.
 */
function filter_dom_load($text) {
  // Suppress all libxml warnings during loading of HTML.
  libxml_use_internal_errors(TRUE);
  $document = new DOMDocument();
  $document->loadHTML('<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /></head><body>' . $text . '</body></html>');

  return $document;
}

/**
 * Converts a DOM object back to an HTML snippet.
 *
 * The function serializes the body part of a DOMDocument
 * back to an XHTML snippet.
 *
 * The resulting XHTML snippet will be properly formatted
 * to be compatible with HTML user agents.
 *
 * @param $dom_document
 *   A DOMDocument object to serialize, only the tags below
 *   the first <body> node will be converted.
 * @return
 *   A valid (X)HTML snippet, as a string.
 */
function filter_dom_serialize($dom_document) {
  $body_node = $dom_document->getElementsByTagName('body')->item(0);
  $body_content = '';
  foreach ($body_node->childNodes as $child_node) {
    $body_content .= $dom_document->saveXML($child_node);
  }
  return preg_replace('|<([^>]*)/>|i', '<$1 />', $body_content);
}

/**
 * Format a link to the more extensive filter tips.
 *
 * @ingroup themeable
 */
function theme_filter_tips_more_info() {
  return '<p>' . l(t('More information about text formats'), 'filter/tips') . '</p>';
}

/**
 * Format guidelines for a text format.
 *
 * @param $variables
 *   An associative array containing:
 *   - format: An object representing a text format.
 *
 * @ingroup themeable
 */
function theme_filter_guidelines($variables) {
  $format = $variables['format'];

  $name = isset($format->name) ? '<label>' . $format->name . ':</label>' : '';
  return '<div id="filter-guidelines-' . $format->format . '" class="filter-guidelines-item">' . $name . theme('filter_tips', array('tips' => _filter_tips($format->format, FALSE))) . '</div>';
}

/**
 * @name Standard filters
 * @{
 * Filters implemented by the filter.module.
 */

/**
 * Implements hook_filter_info().
 */
function filter_filter_info() {
  $filters['filter_html'] = array(
    'title' => t('Limit allowed HTML tags'),
    'process callback' => '_filter_html',
    'settings callback' => '_filter_html_settings',
    'default settings' => array(
      'allowed_html' => '<a> <em> <strong> <cite> <blockquote> <code> <ul> <ol> <li> <dl> <dt> <dd>',
      'filter_html_help' => 1,
      'filter_html_nofollow' => 0,
    ),
    'tips callback' => '_filter_html_tips',
    'weight' => -10,
  );
  $filters['filter_autop'] = array(
    'title' => t('Convert line breaks into HTML (i.e. <code>&lt;br&gt;</code> and <code>&lt;p&gt;</code>)'),
    'process callback' => '_filter_autop',
    'tips callback' => '_filter_autop_tips',
  );
  $filters['filter_url'] = array(
    'title' => t('Convert URLs into links'),
    'process callback' => '_filter_url',
    'settings callback' => '_filter_url_settings',
    'default settings' => array(
      'filter_url_length' => 72,
    ),
    'tips callback' => '_filter_url_tips',
  );
  $filters['filter_htmlcorrector'] = array(
    'title' =>  t('Correct faulty and chopped off HTML'),
    'process callback' => '_filter_htmlcorrector',
    'weight' => 10,
  );
  $filters['filter_html_escape'] = array(
    'title' => t('Display any HTML as plain text'),
    'process callback' => '_filter_html_escape',
    'tips callback' => '_filter_html_escape_tips',
    'weight' => -10,
  );
  return $filters;
}

/**
 * Settings callback for the HTML filter.
 */
function _filter_html_settings($form, &$form_state, $filter, $format, $defaults) {
  $settings['allowed_html'] = array(
    '#type' => 'textfield',
    '#title' => t('Allowed HTML tags'),
    '#default_value' => isset($filter->settings['allowed_html']) ? $filter->settings['allowed_html'] : $defaults['allowed_html'],
    '#maxlength' => 1024,
    '#description' => t('A list of HTML tags that can be used. JavaScript event attributes, JavaScript URLs, and CSS are always stripped.'),
  );
  $settings['filter_html_help'] = array(
    '#type' => 'checkbox',
    '#title' => t('Display basic HTML help in long filter tips'),
    '#default_value' => isset($filter->settings['filter_html_help']) ? $filter->settings['filter_html_help'] : $defaults['filter_html_help'],
  );
  $settings['filter_html_nofollow'] = array(
    '#type' => 'checkbox',
    '#title' => t('Add rel="nofollow" to all links'),
    '#default_value' => isset($filter->settings['filter_html_nofollow']) ? $filter->settings['filter_html_nofollow'] : $defaults['filter_html_nofollow'],
  );
  return $settings;
}

/**
 * HTML filter. Provides filtering of input into accepted HTML.
 */
function _filter_html($text, $filter) {
  $allowed_tags = preg_split('/\s+|<|>/', $filter->settings['allowed_html'], -1, PREG_SPLIT_NO_EMPTY);
  $text = filter_xss($text, $allowed_tags);

  if ($filter->settings['filter_html_nofollow']) {
    $html_dom = filter_dom_load($text);
    $links = $html_dom->getElementsByTagName('a');
    foreach($links as $link) {
      $link->setAttribute('rel', 'nofollow');
    }
    $text = filter_dom_serialize($html_dom);
  }

  return trim($text);
}

/**
 * Filter tips callback for HTML filter.
 */
function _filter_html_tips($filter, $format, $long = FALSE) {
  global $base_url;

  if (!($allowed_html = $filter->settings['allowed_html'])) {
    return;
  }
  $output = t('Allowed HTML tags: @tags', array('@tags' => $allowed_html));
  if (!$long) {
    return $output;
  }

  $output = '<p>' . $output . '</p>';
  if (!$filter->settings['filter_html_help']) {
    return $output;
  }

  $output .= '<p>' . t('This site allows HTML content. While learning all of HTML may feel intimidating, learning how to use a very small number of the most basic HTML "tags" is very easy. This table provides examples for each tag that is enabled on this site.') . '</p>';
  $output .= '<p>' . t('For more information see W3C\'s <a href="@html-specifications">HTML Specifications</a> or use your favorite search engine to find other sites that explain HTML.', array('@html-specifications' => 'http://www.w3.org/TR/html/')) . '</p>';
  $tips = array(
    'a' => array(t('Anchors are used to make links to other pages.'), '<a href="' . $base_url . '">' . variable_get('site_name', 'Drupal') . '</a>'),
    'br' => array(t('By default line break tags are automatically added, so use this tag to add additional ones. Use of this tag is different because it is not used with an open/close pair like all the others. Use the extra " /" inside the tag to maintain XHTML 1.0 compatibility'), t('Text with <br />line break')),
    'p' => array(t('By default paragraph tags are automatically added, so use this tag to add additional ones.'), '<p>' . t('Paragraph one.') . '</p> <p>' . t('Paragraph two.') . '</p>'),
    'strong' => array(t('Strong'), '<strong>' . t('Strong') . '</strong>'),
    'em' => array(t('Emphasized'), '<em>' . t('Emphasized') . '</em>'),
    'cite' => array(t('Cited'), '<cite>' . t('Cited') . '</cite>'),
    'code' => array(t('Coded text used to show programming source code'), '<code>' . t('Coded') . '</code>'),
    'b' => array(t('Bolded'), '<b>' . t('Bolded') . '</b>'),
    'u' => array(t('Underlined'), '<u>' . t('Underlined') . '</u>'),
    'i' => array(t('Italicized'), '<i>' . t('Italicized') . '</i>'),
    'sup' => array(t('Superscripted'), t('<sup>Super</sup>scripted')),
    'sub' => array(t('Subscripted'), t('<sub>Sub</sub>scripted')),
    'pre' => array(t('Preformatted'), '<pre>' . t('Preformatted') . '</pre>'),
    'abbr' => array(t('Abbreviation'), t('<abbr title="Abbreviation">Abbrev.</abbr>')),
    'acronym' => array(t('Acronym'), t('<acronym title="Three-Letter Acronym">TLA</acronym>')),
    'blockquote' => array(t('Block quoted'), '<blockquote>' . t('Block quoted') . '</blockquote>'),
    'q' => array(t('Quoted inline'), '<q>' . t('Quoted inline') . '</q>'),
    // Assumes and describes tr, td, th.
    'table' => array(t('Table'), '<table> <tr><th>' . t('Table header') . '</th></tr> <tr><td>' . t('Table cell') . '</td></tr> </table>'),
    'tr' => NULL, 'td' => NULL, 'th' => NULL,
    'del' => array(t('Deleted'), '<del>' . t('Deleted') . '</del>'),
    'ins' => array(t('Inserted'), '<ins>' . t('Inserted') . '</ins>'),
     // Assumes and describes li.
    'ol' => array(t('Ordered list - use the &lt;li&gt; to begin each list item'), '<ol> <li>' . t('First item') . '</li> <li>' . t('Second item') . '</li> </ol>'),
    'ul' => array(t('Unordered list - use the &lt;li&gt; to begin each list item'), '<ul> <li>' . t('First item') . '</li> <li>' . t('Second item') . '</li> </ul>'),
    'li' => NULL,
    // Assumes and describes dt and dd.
    'dl' => array(t('Definition lists are similar to other HTML lists. &lt;dl&gt; begins the definition list, &lt;dt&gt; begins the definition term and &lt;dd&gt; begins the definition description.'), '<dl> <dt>' . t('First term') . '</dt> <dd>' . t('First definition') . '</dd> <dt>' . t('Second term') . '</dt> <dd>' . t('Second definition') . '</dd> </dl>'),
    'dt' => NULL, 'dd' => NULL,
    'h1' => array(t('Heading'), '<h1>' . t('Title') . '</h1>'),
    'h2' => array(t('Heading'), '<h2>' . t('Subtitle') . '</h2>'),
    'h3' => array(t('Heading'), '<h3>' . t('Subtitle three') . '</h3>'),
    'h4' => array(t('Heading'), '<h4>' . t('Subtitle four') . '</h4>'),
    'h5' => array(t('Heading'), '<h5>' . t('Subtitle five') . '</h5>'),
    'h6' => array(t('Heading'), '<h6>' . t('Subtitle six') . '</h6>')
  );
  $header = array(t('Tag Description'), t('You Type'), t('You Get'));
  preg_match_all('/<([a-z0-9]+)[^a-z0-9]/i', $allowed_html, $out);
  foreach ($out[1] as $tag) {
    if (array_key_exists($tag, $tips)) {
      if ($tips[$tag]) {
        $rows[] = array(
          array('data' => $tips[$tag][0], 'class' => array('description')),
          array('data' => '<code>' . check_plain($tips[$tag][1]) . '</code>', 'class' => array('type')),
          array('data' => $tips[$tag][1], 'class' => array('get'))
        );
      }
    }
    else {
      $rows[] = array(
        array('data' => t('No help provided for tag %tag.', array('%tag' => $tag)), 'class' => array('description'), 'colspan' => 3),
      );
    }
  }
  $output .= theme('table', array('header' => $header, 'rows' => $rows));

  $output .= '<p>' . t('Most unusual characters can be directly entered without any problems.') . '</p>';
  $output .= '<p>' . t('If you do encounter problems, try using HTML character entities. A common example looks like &amp;amp; for an ampersand &amp; character. For a full list of entities see HTML\'s <a href="@html-entities">entities</a> page. Some of the available characters include:', array('@html-entities' => 'http://www.w3.org/TR/html4/sgml/entities.html')) . '</p>';

  $entities = array(
    array(t('Ampersand'), '&amp;'),
    array(t('Greater than'), '&gt;'),
    array(t('Less than'), '&lt;'),
    array(t('Quotation mark'), '&quot;'),
  );
  $header = array(t('Character Description'), t('You Type'), t('You Get'));
  unset($rows);
  foreach ($entities as $entity) {
    $rows[] = array(
      array('data' => $entity[0], 'class' => array('description')),
      array('data' => '<code>' . check_plain($entity[1]) . '</code>', 'class' => array('type')),
      array('data' => $entity[1], 'class' => array('get'))
    );
  }
  $output .= theme('table', array('header' => $header, 'rows' => $rows));
  return $output;
}

/**
 * Settings callback for URL filter.
 */
function _filter_url_settings($form, &$form_state, $filter, $format, $defaults) {
  $settings['filter_url_length'] = array(
    '#type' => 'textfield',
    '#title' => t('Maximum link text length'),
    '#default_value' => isset($filter->settings['filter_url_length']) ? $filter->settings['filter_url_length'] : $defaults['filter_url_length'],
    '#size' => 5,
    '#maxlength' => 4,
    '#field_suffix' => t('characters'),
    '#description' => t('URLs longer than this number of characters will be truncated to prevent long strings that break formatting. The link itself will be retained; just the text portion of the link will be truncated.'),
  );
  return $settings;
}

/**
 * URL filter. Automatically converts text web addresses (URLs, e-mail addresses,
 * ftp links, etc.) into hyperlinks.
 */
function _filter_url($text, $filter) {
  // Pass length to regexp callback
  _filter_url_trim(NULL, $filter->settings['filter_url_length']);

  $text = ' ' . $text . ' ';

  // Match absolute URLs.
  $text = preg_replace_callback("`(<p>|<li>|<br\s*/?>|[ \n\r\t\(])((http://|https://|ftp://|mailto:|smb://|afp://|file://|gopher://|news://|ssl://|sslv2://|sslv3://|tls://|tcp://|udp://)([a-zA-Z0-9@:%_+*~#?&=.,/;-]*[a-zA-Z0-9@:%_+*~#&=/;-]))([.,?!]*?)(?=(</p>|</li>|<br\s*/?>|[ \n\r\t\)]))`i", '_filter_url_parse_full_links', $text);

  // Match e-mail addresses.
  $text = preg_replace("`(<p>|<li>|<br\s*/?>|[ \n\r\t\(])([A-Za-z0-9._-]+@[A-Za-z0-9._+-]+\.[A-Za-z]{2,4})([.,?!]*?)(?=(</p>|</li>|<br\s*/?>|[ \n\r\t\)]))`i", '\1<a href="mailto:\2">\2</a>\3', $text);

  // Match www domains/addresses.
  $text = preg_replace_callback("`(<p>|<li>|[ \n\r\t\(])(www\.[a-zA-Z0-9@:%_+*~#?&=.,/;-]*[a-zA-Z0-9@:%_+~#\&=/;-])([.,?!]*?)(?=(</p>|</li>|<br\s*/?>|[ \n\r\t\)]))`i", '_filter_url_parse_partial_links', $text);
  $text = substr($text, 1, -1);

  return $text;
}

/**
 * Make links out of absolute URLs.
 */
function _filter_url_parse_full_links($match) {
  $match[2] = decode_entities($match[2]);
  $caption = check_plain(_filter_url_trim($match[2]));
  $match[2] = check_url($match[2]);
  return $match[1] . '<a href="' . $match[2] . '" title="' . $match[2] . '">' . $caption . '</a>' . $match[5];
}

/**
 * Make links out of domain names starting with "www."
 */
function _filter_url_parse_partial_links($match) {
  $match[2] = decode_entities($match[2]);
  $caption = check_plain(_filter_url_trim($match[2]));
  $match[2] = check_plain($match[2]);
  return $match[1] . '<a href="http://' . $match[2] . '" title="' . $match[2] . '">' . $caption . '</a>' . $match[3];
}

/**
 * Shortens long URLs to http://www.example.com/long/url...
 */
function _filter_url_trim($text, $length = NULL) {
  static $_length;
  if ($length !== NULL) {
    $_length = $length;
  }

  // Use +3 for '...' string length.
  if (strlen($text) > $_length + 3) {
    $text = substr($text, 0, $_length) . '...';
  }

  return $text;
}

/**
 * Filter tips callback for URL filter.
 */
function _filter_url_tips($filter, $format, $long = FALSE) {
  return t('Web page addresses and e-mail addresses turn into links automatically.');
}

/**
 * Scan input and make sure that all HTML tags are properly closed and nested.
 */
function _filter_htmlcorrector($text) {
  return filter_dom_serialize(filter_dom_load($text));
}

/**
 * Convert line breaks into <p> and <br> in an intelligent fashion.
 * Based on: http://photomatt.net/scripts/autop
 */
function _filter_autop($text) {
  // All block level tags
  $block = '(?:table|thead|tfoot|caption|colgroup|tbody|tr|td|th|div|dl|dd|dt|ul|ol|li|pre|select|form|blockquote|address|p|h[1-6]|hr)';

  // Split at <pre>, <script>, <style> and </pre>, </script>, </style> tags.
  // We don't apply any processing to the contents of these tags to avoid messing
  // up code. We look for matched pairs and allow basic nesting. For example:
  // "processed <pre> ignored <script> ignored </script> ignored </pre> processed"
  $chunks = preg_split('@(</?(?:pre|script|style|object)[^>]*>)@i', $text, -1, PREG_SPLIT_DELIM_CAPTURE);
  // Note: PHP ensures the array consists of alternating delimiters and literals
  // and begins and ends with a literal (inserting NULL as required).
  $ignore = FALSE;
  $ignoretag = '';
  $output = '';
  foreach ($chunks as $i => $chunk) {
    if ($i % 2) {
      // Opening or closing tag?
      $open = ($chunk[1] != '/');
      list($tag) = preg_split('/[ >]/', substr($chunk, 2 - $open), 2);
      if (!$ignore) {
        if ($open) {
          $ignore = TRUE;
          $ignoretag = $tag;
        }
      }
      // Only allow a matching tag to close it.
      elseif (!$open && $ignoretag == $tag) {
        $ignore = FALSE;
        $ignoretag = '';
      }
    }
    elseif (!$ignore) {
      $chunk = preg_replace('|\n*$|', '', $chunk) . "\n\n"; // just to make things a little easier, pad the end
      $chunk = preg_replace('|<br />\s*<br />|', "\n\n", $chunk);
      $chunk = preg_replace('!(<' . $block . '[^>]*>)!', "\n$1", $chunk); // Space things out a little
      $chunk = preg_replace('!(</' . $block . '>)!', "$1\n\n", $chunk); // Space things out a little
      $chunk = preg_replace("/\n\n+/", "\n\n", $chunk); // take care of duplicates
      $chunk = preg_replace('/^\n|\n\s*\n$/', '', $chunk);
      $chunk = '<p>' . preg_replace('/\n\s*\n\n?(.)/', "</p>\n<p>$1", $chunk) . "</p>\n"; // make paragraphs, including one at the end
      $chunk = preg_replace("|<p>(<li.+?)</p>|", "$1", $chunk); // problem with nested lists
      $chunk = preg_replace('|<p><blockquote([^>]*)>|i', "<blockquote$1><p>", $chunk);
      $chunk = str_replace('</blockquote></p>', '</p></blockquote>', $chunk);
      $chunk = preg_replace('|<p>\s*</p>\n?|', '', $chunk); // under certain strange conditions it could create a P of entirely whitespace
      $chunk = preg_replace('!<p>\s*(</?' . $block . '[^>]*>)!', "$1", $chunk);
      $chunk = preg_replace('!(</?' . $block . '[^>]*>)\s*</p>!', "$1", $chunk);
      $chunk = preg_replace('|(?<!<br />)\s*\n|', "<br />\n", $chunk); // make line breaks
      $chunk = preg_replace('!(</?' . $block . '[^>]*>)\s*<br />!', "$1", $chunk);
      $chunk = preg_replace('!<br />(\s*</?(?:p|li|div|th|pre|td|ul|ol)>)!', '$1', $chunk);
      $chunk = preg_replace('/&([^#])(?![A-Za-z0-9]{1,8};)/', '&amp;$1', $chunk);
    }
    $output .= $chunk;
  }
  return $output;
}

/**
 * Filter tips callback for auto-paragraph filter.
 */
function _filter_autop_tips($filter, $format, $long = FALSE) {
  if ($long) {
    return t('Lines and paragraphs are automatically recognized. The &lt;br /&gt; line break, &lt;p&gt; paragraph and &lt;/p&gt; close paragraph tags are inserted automatically. If paragraphs are not recognized simply add a couple blank lines.');
  }
  else {
    return t('Lines and paragraphs break automatically.');
  }
}

/**
 * Escapes all HTML tags, so they will be visible instead of being effective.
 */
function _filter_html_escape($text) {
  return trim(check_plain($text));
}

/**
 * Filter tips callback for HTML escaping filter.
 */
function _filter_html_escape_tips($filter, $format, $long = FALSE) {
  return t('No HTML tags allowed.');
}

/**
 * @} End of "Standard filters".
 */