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<?php

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use Drupal\Component\Utility\Crypt;
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use Drupal\Core\Cache\Cache;
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use Symfony\Component\DependencyInjection\Container;
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use Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException;
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use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
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use Symfony\Component\Yaml\Parser;
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use Drupal\Component\PhpStorage\PhpStorageFactory;
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use Drupal\Component\Utility\NestedArray;
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use Drupal\Core\Cache\CacheBackendInterface;
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use Drupal\Core\Datetime\DrupalDateTime;
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use Drupal\Core\Database\Database;
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use Drupal\Core\SystemListingInfo;
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use Drupal\Core\Template\Attribute;
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/**
 * @file
 * Common functions that many Drupal modules will need to reference.
 *
 * The functions that are critical and need to be available even when serving
 * a cached page are instead located in bootstrap.inc.
 */

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/**
 * @defgroup php_wrappers PHP wrapper functions
 * @{
 * Functions that are wrappers or custom implementations of PHP functions.
 *
 * Certain PHP functions should not be used in Drupal. Instead, Drupal's
 * replacement functions should be used.
 *
 * For example, for improved or more secure UTF8-handling, or RFC-compliant
 * handling of URLs in Drupal.
 *
 * For ease of use and memorizing, all these wrapper functions use the same name
 * as the original PHP function, but prefixed with "drupal_". Beware, however,
 * that not all wrapper functions support the same arguments as the original
 * functions.
 *
 * You should always use these wrapper functions in your code.
 *
 * Wrong:
 * @code
 *   $my_substring = substr($original_string, 0, 5);
 * @endcode
 *
 * Correct:
 * @code
 *   $my_substring = drupal_substr($original_string, 0, 5);
 * @endcode
 *
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 * @}
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 */

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/**
 * Return status for saving which involved creating a new item.
 */
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const SAVED_NEW = 1;
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/**
 * Return status for saving which involved an update to an existing item.
 */
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const SAVED_UPDATED = 2;
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/**
 * Return status for saving which deleted an existing item.
 */
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const SAVED_DELETED = 3;
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/**
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 * The default aggregation group for system CSS files added to the page.
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 */
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const CSS_AGGREGATE_SYSTEM = -100;
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/**
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 * The default aggregation group for CSS files added to the page.
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 */
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const CSS_AGGREGATE_DEFAULT = 0;
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/**
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 * The default aggregation group for theme CSS files added to the page.
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 */
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const CSS_AGGREGATE_THEME = 100;

/**
 * The default weight for CSS rules that style HTML elements ("base" styles).
 */
const CSS_BASE = -200;

/**
 * The default weight for CSS rules that layout a page.
 */
const CSS_LAYOUT = -100;

/**
 * The default weight for CSS rules that style design components (and their associated states and skins.)
 */
const CSS_COMPONENT = 0;

/**
 * The default weight for CSS rules that style states and are not included with components.
 */
const CSS_STATE = 100;

/**
 * The default weight for CSS rules that style skins and are not included with components.
 */
const CSS_SKIN = 200;
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/**
 * The default group for JavaScript settings added to the page.
 */
const JS_SETTING = -200;

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/**
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 * The default group for JavaScript and jQuery libraries added to the page.
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 */
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const JS_LIBRARY = -100;
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/**
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 * The default group for module JavaScript code added to the page.
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 */
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const JS_DEFAULT = 0;
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/**
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 * The default group for theme JavaScript code added to the page.
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 */
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const JS_THEME = 100;
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/**
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 * @defgroup block_caching Block Caching
 * @{
 * Constants that define each block's caching state.
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 *
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 * Modules specify how their blocks can be cached in their hook_block_info()
 * implementations. Caching can be turned off (DRUPAL_NO_CACHE), managed by the
 * module declaring the block (DRUPAL_CACHE_CUSTOM), or managed by the core
 * Block module. If the Block module is managing the cache, you can specify that
 * the block is the same for every page and user (DRUPAL_CACHE_GLOBAL), or that
 * it can change depending on the page (DRUPAL_CACHE_PER_PAGE) or by user
 * (DRUPAL_CACHE_PER_ROLE or DRUPAL_CACHE_PER_USER). Page and user settings can
 * be combined with a bitwise-binary or operator; for example,
 * DRUPAL_CACHE_PER_ROLE | DRUPAL_CACHE_PER_PAGE means that the block can change
 * depending on the user role or page it is on.
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 *
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 * The block cache is cleared when the 'content' cache tag is invalidated,
 * following the same pattern as the page cache (node, comment, user, taxonomy
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 * added or updated...).
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 *
 * Note that user 1 is excluded from block caching.
 */

/**
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 * The block should not get cached.
 *
 * This setting should be used:
 * - For simple blocks (notably those that do not perform any db query), where
 *   querying the db cache would be more expensive than directly generating the
 *   content.
 * - For blocks that change too frequently.
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 */
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const DRUPAL_NO_CACHE = -1;
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/**
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 * The block is handling its own caching in its hook_block_view().
 *
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 * This setting is useful when time based expiration is needed or a site uses a
 * node access which invalidates standard block cache.
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 */
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const DRUPAL_CACHE_CUSTOM = -2;
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/**
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 * The block or element can change depending on the user's roles.
 *
 * This is the default setting for blocks, used when the block does not specify
 * anything.
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 */
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const DRUPAL_CACHE_PER_ROLE = 0x0001;
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/**
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 * The block or element can change depending on the user.
 *
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 * This setting can be resource-consuming for sites with large number of users,
 * and thus should only be used when DRUPAL_CACHE_PER_ROLE is not sufficient.
 */
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const DRUPAL_CACHE_PER_USER = 0x0002;
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/**
 * The block or element can change depending on the page being viewed.
 */
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const DRUPAL_CACHE_PER_PAGE = 0x0004;
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/**
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 * The block or element is the same for every user and page that it is visible.
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 */
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const DRUPAL_CACHE_GLOBAL = 0x0008;
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/**
 * @} End of "defgroup block_caching".
 */

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/**
 * The delimiter used to split plural strings.
 *
 * This is the ETX (End of text) character and is used as a minimal means to
 * separate singular and plural variants in source and translation text. It
 * was found to be the most compatible delimiter for the supported databases.
 */
const LOCALE_PLURAL_DELIMITER = "\03";

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/**
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 * Adds content to a specified region.
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 *
 * @param $region
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 *   Page region the content is added to.
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 * @param $data
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 *   Content to be added.
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 */
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function drupal_add_region_content($region = NULL, $data = NULL) {
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  static $content = array();

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  if (isset($region) && isset($data)) {
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    $content[$region][] = $data;
  }
  return $content;
}

/**
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 * Gets assigned content for a given region.
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 *
 * @param $region
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 *   A specified region to fetch content for. If NULL, all regions will be
 *   returned.
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 * @param $delimiter
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 *   Content to be inserted between imploded array elements.
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 */
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function drupal_get_region_content($region = NULL, $delimiter = ' ') {
  $content = drupal_add_region_content();
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  if (isset($region)) {
    if (isset($content[$region]) && is_array($content[$region])) {
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      return implode($delimiter, $content[$region]);
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    }
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  }
  else {
    foreach (array_keys($content) as $region) {
      if (is_array($content[$region])) {
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        $content[$region] = implode($delimiter, $content[$region]);
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      }
    }
    return $content;
  }
}

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/**
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 * Gets the name of the currently active installation profile.
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 *
 * When this function is called during Drupal's initial installation process,
 * the name of the profile that's about to be installed is stored in the global
 * installation state. At all other times, the standard Drupal systems variable
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 * table contains the name of the current profile, and we can call
 * variable_get() to determine what one is active.
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 *
 * @return $profile
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 *   The name of the installation profile.
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 */
function drupal_get_profile() {
  global $install_state;

  if (isset($install_state['parameters']['profile'])) {
    $profile = $install_state['parameters']['profile'];
  }
  else {
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    $profile = variable_get('install_profile', 'standard');
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  }

  return $profile;
}


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/**
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 * Sets the breadcrumb trail for the current page.
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 *
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 * @param $breadcrumb
 *   Array of links, starting with "home" and proceeding up to but not including
 *   the current page.
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 */
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function drupal_set_breadcrumb($breadcrumb = NULL) {
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  $stored_breadcrumb = &drupal_static(__FUNCTION__);
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  if (isset($breadcrumb)) {
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    $stored_breadcrumb = $breadcrumb;
  }
  return $stored_breadcrumb;
}

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/**
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 * Gets the breadcrumb trail for the current page.
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 */
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function drupal_get_breadcrumb() {
  $breadcrumb = drupal_set_breadcrumb();

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  if (!isset($breadcrumb)) {
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    $breadcrumb = menu_get_active_breadcrumb();
  }

  return $breadcrumb;
}

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/**
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 * Adds output to the HEAD tag of the HTML page.
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 *
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 * This function can be called as long as the headers aren't sent. Pass no
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 * arguments (or NULL for both) to retrieve the currently stored elements.
 *
 * @param $data
 *   A renderable array. If the '#type' key is not set then 'html_tag' will be
 *   added as the default '#type'.
 * @param $key
 *   A unique string key to allow implementations of hook_html_head_alter() to
 *   identify the element in $data. Required if $data is not NULL.
 *
 * @return
 *   An array of all stored HEAD elements.
 *
 * @see theme_html_tag()
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 */
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function drupal_add_html_head($data = NULL, $key = NULL) {
  $stored_head = &drupal_static(__FUNCTION__);
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  if (!isset($stored_head)) {
    // Make sure the defaults, including Content-Type, come first.
    $stored_head = _drupal_default_html_head();
  }

  if (isset($data) && isset($key)) {
    if (!isset($data['#type'])) {
      $data['#type'] = 'html_tag';
    }
    $stored_head[$key] = $data;
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  }
  return $stored_head;
}

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/**
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 * Returns elements that are always displayed in the HEAD tag of the HTML page.
 */
function _drupal_default_html_head() {
  // Add default elements. Make sure the Content-Type comes first because the
  // IE browser may be vulnerable to XSS via encoding attacks from any content
  // that comes before this META tag, such as a TITLE tag.
  $elements['system_meta_content_type'] = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array(
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      'charset' => 'utf-8',
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    ),
    // Security: This always has to be output first.
    '#weight' => -1000,
  );
  // Show Drupal and the major version number in the META GENERATOR tag.
  // Get the major version.
  list($version, ) = explode('.', VERSION);
  $elements['system_meta_generator'] = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array(
      'name' => 'Generator',
      'content' => 'Drupal ' . $version . ' (http://drupal.org)',
    ),
  );
  // Also send the generator in the HTTP header.
  $elements['system_meta_generator']['#attached']['drupal_add_http_header'][] = array('X-Generator', $elements['system_meta_generator']['#attributes']['content']);
  return $elements;
}

/**
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 * Retrieves output to be displayed in the HEAD tag of the HTML page.
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 */
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function drupal_get_html_head() {
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  $elements = drupal_add_html_head();
  drupal_alter('html_head', $elements);
  return drupal_render($elements);
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}

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/**
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 * Adds a feed URL for the current page.
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 *
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 * This function can be called as long the HTML header hasn't been sent.
 *
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 * @param $url
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 *   An internal system path or a fully qualified external URL of the feed.
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 * @param $title
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 *   The title of the feed.
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 */
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function drupal_add_feed($url = NULL, $title = '') {
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  $stored_feed_links = &drupal_static(__FUNCTION__, array());
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  if (isset($url)) {
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    $stored_feed_links[$url] = theme('feed_icon', array('url' => $url, 'title' => $title));
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    drupal_add_html_head_link(array(
      'rel' => 'alternate',
      'type' => 'application/rss+xml',
      'title' => $title,
      // Force the URL to be absolute, for consistency with other <link> tags
      // output by Drupal.
      'href' => url($url, array('absolute' => TRUE)),
    ));
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  }
  return $stored_feed_links;
}

/**
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 * Gets the feed URLs for the current page.
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 *
 * @param $delimiter
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 *   A delimiter to split feeds by.
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 */
function drupal_get_feeds($delimiter = "\n") {
  $feeds = drupal_add_feed();
  return implode($feeds, $delimiter);
}

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/**
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 * @defgroup http_handling HTTP handling
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 * @{
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 * Functions to properly handle HTTP responses.
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 */

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/**
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 * Processes a URL query parameter array to remove unwanted elements.
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 *
 * @param $query
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 *   (optional) An array to be processed. Defaults to $_GET.
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 * @param $exclude
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 *   (optional) A list of $query array keys to remove. Use "parent[child]" to
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 *   exclude nested items.
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 * @param $parent
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 *   Internal use only. Used to build the $query array key for nested items.
 *
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 * @return
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 *   An array containing query parameters, which can be used for url().
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 */
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function drupal_get_query_parameters(array $query = NULL, array $exclude = array(), $parent = '') {
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  // Set defaults, if none given.
  if (!isset($query)) {
    $query = $_GET;
  }
  // If $exclude is empty, there is nothing to filter.
  if (empty($exclude)) {
    return $query;
  }
  elseif (!$parent) {
    $exclude = array_flip($exclude);
  }
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  $params = array();
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  foreach ($query as $key => $value) {
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    $string_key = ($parent ? $parent . '[' . $key . ']' : $key);
    if (isset($exclude[$string_key])) {
      continue;
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    }

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    if (is_array($value)) {
      $params[$key] = drupal_get_query_parameters($value, $exclude, $string_key);
    }
    else {
      $params[$key] = $value;
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    }
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  }

  return $params;
}

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/**
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 * Splits a URL-encoded query string into an array.
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 *
 * @param $query
 *   The query string to split.
 *
 * @return
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 *   An array of URL decoded couples $param_name => $value.
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 */
function drupal_get_query_array($query) {
  $result = array();
  if (!empty($query)) {
    foreach (explode('&', $query) as $param) {
      $param = explode('=', $param);
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      $result[$param[0]] = isset($param[1]) ? rawurldecode($param[1]) : '';
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    }
  }
  return $result;
}

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/**
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 * Parses an array into a valid, rawurlencoded query string.
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 *
 * This differs from http_build_query() as we need to rawurlencode() (instead of
 * urlencode()) all query parameters.
 *
 * @param $query
 *   The query parameter array to be processed, e.g. $_GET.
 * @param $parent
 *   Internal use only. Used to build the $query array key for nested items.
 *
 * @return
 *   A rawurlencoded string which can be used as or appended to the URL query
 *   string.
 *
 * @see drupal_get_query_parameters()
 * @ingroup php_wrappers
 */
function drupal_http_build_query(array $query, $parent = '') {
  $params = array();

  foreach ($query as $key => $value) {
    $key = ($parent ? $parent . '[' . rawurlencode($key) . ']' : rawurlencode($key));
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    // Recurse into children.
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    if (is_array($value)) {
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      $params[] = drupal_http_build_query($value, $key);
    }
    // If a query parameter value is NULL, only append its key.
    elseif (!isset($value)) {
      $params[] = $key;
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    }
    else {
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      // For better readability of paths in query strings, we decode slashes.
      $params[] = $key . '=' . str_replace('%2F', '/', rawurlencode($value));
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    }
  }

  return implode('&', $params);
}

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/**
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 * Prepares a 'destination' URL query parameter for use with drupal_goto().
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 *
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 * Used to direct the user back to the referring page after completing a form.
 * By default the current URL is returned. If a destination exists in the
 * previous request, that destination is returned. As such, a destination can
 * persist across multiple pages.
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 *
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 * @return
 *   An associative array containing the key:
 *   - destination: The path provided via the destination query string or, if
 *     not available, the current path.
 *
 * @see current_path()
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 * @see drupal_goto()
 */
function drupal_get_destination() {
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  $destination = &drupal_static(__FUNCTION__);

  if (isset($destination)) {
    return $destination;
  }

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  if (isset($_GET['destination'])) {
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    $destination = array('destination' => $_GET['destination']);
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  }
  else {
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    $path = current_path();
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    $query = drupal_http_build_query(drupal_get_query_parameters());
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    if ($query != '') {
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      $path .= '?' . $query;
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    }
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    $destination = array('destination' => $path);
  }
  return $destination;
}

/**
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 * Parses a system URL string into an associative array suitable for url().
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 *
 * This function should only be used for URLs that have been generated by the
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 * system, such as via url(). It should not be used for URLs that come from
 * external sources, or URLs that link to external resources.
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 *
 * The returned array contains a 'path' that may be passed separately to url().
 * For example:
 * @code
 *   $options = drupal_parse_url($_GET['destination']);
 *   $my_url = url($options['path'], $options);
 *   $my_link = l('Example link', $options['path'], $options);
 * @endcode
 *
 * This is required, because url() does not support relative URLs containing a
 * query string or fragment in its $path argument. Instead, any query string
 * needs to be parsed into an associative query parameter array in
 * $options['query'] and the fragment into $options['fragment'].
 *
 * @param $url
 *   The URL string to parse, f.e. $_GET['destination'].
 *
 * @return
 *   An associative array containing the keys:
 *   - 'path': The path of the URL. If the given $url is external, this includes
 *     the scheme and host.
 *   - 'query': An array of query parameters of $url, if existent.
 *   - 'fragment': The fragment of $url, if existent.
 *
 * @see url()
 * @see drupal_goto()
 * @ingroup php_wrappers
 */
function drupal_parse_url($url) {
  $options = array(
    'path' => NULL,
    'query' => array(),
    'fragment' => '',
  );

  // External URLs: not using parse_url() here, so we do not have to rebuild
  // the scheme, host, and path without having any use for it.
  if (strpos($url, '://') !== FALSE) {
    // Split off everything before the query string into 'path'.
    $parts = explode('?', $url);
    $options['path'] = $parts[0];
    // If there is a query string, transform it into keyed query parameters.
    if (isset($parts[1])) {
      $query_parts = explode('#', $parts[1]);
      parse_str($query_parts[0], $options['query']);
      // Take over the fragment, if there is any.
      if (isset($query_parts[1])) {
        $options['fragment'] = $query_parts[1];
      }
    }
  }
  // Internal URLs.
  else {
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    // parse_url() does not support relative URLs, so make it absolute. E.g. the
    // relative URL "foo/bar:1" isn't properly parsed.
    $parts = parse_url('http://example.com/' . $url);
    // Strip the leading slash that was just added.
    $options['path'] = substr($parts['path'], 1);
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    if (isset($parts['query'])) {
      parse_str($parts['query'], $options['query']);
    }
    if (isset($parts['fragment'])) {
      $options['fragment'] = $parts['fragment'];
    }
  }

  return $options;
}

/**
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 * Encodes a Drupal path for use in a URL.
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 *
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 * For aesthetic reasons slashes are not escaped.
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 *
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 * Note that url() takes care of calling this function, so a path passed to that
 * function should not be encoded in advance.
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 *
 * @param $path
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 *   The Drupal path to encode.
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 */
function drupal_encode_path($path) {
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  return str_replace('%2F', '/', rawurlencode($path));
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}

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/**
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 * Sends the user to a different Drupal page.
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 *
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 * This issues an on-site HTTP redirect. The function makes sure the redirected
 * URL is formatted correctly.
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 *
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 * If a destination was specified in the current request's URI (i.e.,
 * $_GET['destination']) then it will override the $path and $options values
 * passed to this function. This provides the flexibility to build a link to
 * user/login and override the default redirection so that the user is
 * redirected to a specific path after logging in:
 * @code
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 *   $query = array('destination' => "node/$node->nid");
 *   $link = l(t('Log in'), 'user/login', array('query' => $query));
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 * @endcode
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 *
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 * Drupal will ensure that messages set by drupal_set_message() and other
 * session data are written to the database before the user is redirected.
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 *
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 * This function ends the request; use it instead of a return in your menu
 * callback.
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 *
 * @param $path
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 *   (optional) A Drupal path or a full URL, which will be passed to url() to
 *   compute the redirect for the URL.
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 * @param $options
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 *   (optional) An associative array of additional URL options to pass to url().
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 * @param $http_response_code
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 *   (optional) The HTTP status code to use for the redirection, defaults to
 *   302. The valid values for 3xx redirection status codes are defined in
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 *   @link http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3 RFC 2616 @endlink
 *   and the
 *   @link http://tools.ietf.org/html/draft-reschke-http-status-308-07 draft for the new HTTP status codes: @endlink
 *   - 301: Moved Permanently (the recommended value for most redirects).
 *   - 302: Found (default in Drupal and PHP, sometimes used for spamming search
 *     engines).
 *   - 303: See Other.
 *   - 304: Not Modified.
 *   - 305: Use Proxy.
 *   - 307: Temporary Redirect.
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 *
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 * @see drupal_get_destination()
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 * @see url()
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 */
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function drupal_goto($path = '', array $options = array(), $http_response_code = 302) {
  // A destination in $_GET always overrides the function arguments.
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  // We do not allow absolute URLs to be passed via $_GET, as this can be an
  // attack vector, with the following exception:
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  // - Absolute URLs that point to this site (i.e. same base URL and
  //   base path) are allowed.
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  if (isset($_GET['destination']) && (!url_is_external($_GET['destination']) || _external_url_is_local($_GET['destination']))) {
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    $destination = drupal_parse_url($_GET['destination']);
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    $path = $destination['path'];
    $options['query'] = $destination['query'];
    $options['fragment'] = $destination['fragment'];
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  }

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  drupal_alter('drupal_goto', $path, $options, $http_response_code);

  // The 'Location' HTTP header must be absolute.
  $options['absolute'] = TRUE;
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  $url = url($path, $options);
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  header('Location: ' . $url, TRUE, $http_response_code);
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  // The "Location" header sends a redirect status code to the HTTP daemon. In
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  // some cases this can be wrong, so we make sure none of the code below the
  // drupal_goto() call gets executed upon redirection.
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  drupal_exit($url);
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}

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/**
 * Determines if an external URL points to this Drupal installation.
 *
 * @param $url
 *   A string containing an external URL, such as "http://example.com/foo".
 *
 * @return
 *   TRUE if the URL has the same domain and base path.
 */
function _external_url_is_local($url) {
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  $url_parts = parse_url($url);
  $base_host = parse_url($GLOBALS['base_url'], PHP_URL_HOST);
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  if (!isset($url_parts['path'])) {
    return ($url_parts['host'] == $base_host);
  }
  else {
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    // When comparing base paths, we need a trailing slash to make sure a
    // partial URL match isn't occuring. Since base_path() always returns with
    // a trailing slash, we don't need to add the trailing slash here.
    return ($url_parts['host'] == $base_host && stripos($url_parts['path'], base_path()) === 0);
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  }
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}

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/**
 * Helper function for determining hosts excluded from needing a proxy.
 *
 * @return
 *   TRUE if a proxy should be used for this host.
 */
function _drupal_http_use_proxy($host) {
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  $proxy_exceptions = settings()->get('proxy_exceptions', array('localhost', '127.0.0.1'));
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  return !in_array(strtolower($host), $proxy_exceptions, TRUE);
}

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/**
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 * @} End of "defgroup http_handling".
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 */
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/**
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 * @defgroup validation Input validation
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 * @{
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 * Functions to validate user input.
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 */

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/**
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 * Verifies the syntax of the given e-mail address.
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 *
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 * This uses the
 * @link http://php.net/manual/filter.filters.validate.php PHP e-mail validation filter. @endlink
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 *
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 * @param $mail
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 *   A string containing an e-mail address.
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 *
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 * @return
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 *   TRUE if the address is in a valid format.
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 */
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function valid_email_address($mail) {
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  return (bool)filter_var($mail, FILTER_VALIDATE_EMAIL);
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}

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/**
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 * Verifies the syntax of the given URL.
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 *
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 * This function should only be used on actual URLs. It should not be used for
 * Drupal menu paths, which can contain arbitrary characters.
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 * Valid values per RFC 3986.
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 * @param $url
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 *   The URL to verify.
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 * @param $absolute
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 *   Whether the URL is absolute (beginning with a scheme such as "http:").
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 *
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 * @return
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 *   TRUE if the URL is in a valid format.
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 */
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function valid_url($url, $absolute = FALSE) {
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  if ($absolute) {
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    return (bool)preg_match("
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      /^                                                      # Start at the beginning of the text
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      (?:ftp|https?|feed):\/\/                                # Look for ftp, http, https or feed schemes
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      (?:                                                     # Userinfo (optional) which is typically
        (?:(?:[\w\.\-\+!$&'\(\)*\+,;=]|%[0-9a-f]{2})+:)*      # a username or a username and password
        (?:[\w\.\-\+%!$&'\(\)*\+,;=]|%[0-9a-f]{2})+@          # combination
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      )?
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      (?:
        (?:[a-z0-9\-\.]|%[0-9a-f]{2})+                        # A domain name or a IPv4 address
        |(?:\[(?:[0-9a-f]{0,4}:)*(?:[0-9a-f]{0,4})\])         # or a well formed IPv6 address
      )
      (?::[0-9]+)?                                            # Server port number (optional)
      (?:[\/|\?]
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        (?:[\w#!:\.\?\+=&@$'~*,;\/\(\)\[\]\-]|%[0-9a-f]{2})   # The path and query (optional)
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      *)?
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    $/xi", $url);
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  }
  else {
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    return (bool)preg_match("/^(?:[\w#!:\.\?\+=&@$'~*,;\/\(\)\[\]\-]|%[0-9a-f]{2})+$/i", $url);
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  }
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}

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/**
 * Verifies that a number is a multiple of a given step.
 *
 * The implementation assumes it is dealing with IEEE 754 double precision
 * floating point numbers that are used by PHP on most systems.
 *
 * This is based on the number/range verification methods of webkit.
 *
 * @param $value
 *   The value that needs to be checked.
 * @param $step
 *   The step scale factor. Must be positive.
 * @param $offset
 *   (optional) An offset, to which the difference must be a multiple of the
 *   given step.
 *
 * @return bool
 *   TRUE if no step mismatch has occured, or FALSE otherwise.
 *
 * @see http://opensource.apple.com/source/WebCore/WebCore-1298/html/NumberInputType.cpp
 */
function valid_number_step($value, $step, $offset = 0.0) {
  $double_value = (double) abs($value - $offset);

  // The fractional part of a double has 53 bits. The greatest number that could
  // be represented with that is 2^53. If the given value is even bigger than
  // $step * 2^53, then dividing by $step will result in a very small remainder.
  // Since that remainder can't even be represented with a single precision
  // float the following computation of the remainder makes no sense and we can
  // safely ignore it instead.
  if ($double_value / pow(2.0, 53) > $step) {
    return TRUE;
  }

  // Now compute that remainder of a division by $step.
  $remainder = (double) abs($double_value - $step * round($double_value / $step));

  // $remainder is a double precision floating point number. Remainders that
  // can't be represented with single precision floats are acceptable. The
  // fractional part of a float has 24 bits. That means remainders smaller than
  // $step * 2^-24 are acceptable.
  $computed_acceptable_error = (double)($step / pow(2.0, 24));

  return $computed_acceptable_error >= $remainder || $remainder >= ($step - $computed_acceptable_error);
}

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

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/**
 * @defgroup sanitization Sanitization functions
 * @{
 * Functions to sanitize values.
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 *
 * See http://drupal.org/writing-secure-code for information
 * on writing secure code.
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 */

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/**
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 * Strips dangerous protocols (e.g. 'javascript:') from a URI.
 *
 * This function must be called for all URIs within user-entered input prior
 * to being output to an HTML attribute value. It is often called as part of
 * check_url() or filter_xss(), but those functions return an HTML-encoded
 * string, so this function can be called independently when the output needs to
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 * be a plain-text string for passing to t(), l(),
 * Drupal\Core\Template\Attribute, or another function that will call
 * check_plain() separately.
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 *
 * @param $uri
 *   A plain-text URI that might contain dangerous protocols.
 *
 * @return
 *   A plain-text URI stripped of dangerous protocols. As with all plain-text
 *   strings, this return value must not be output to an HTML page without
 *   check_plain() being called on it. However, it can be passed to functions
 *   expecting plain-text strings.
 *
 * @see check_url()
 */
function drupal_strip_dangerous_protocols($uri) {
  static $allowed_protocols;

  if (!isset($allowed_protocols)) {
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    // filter_xss_admin() is called by the installer and update.php, in which
    // case the configuration may not exist (yet). Provide a minimal default set
    // of allowed protocols for these cases.
    $allowed_protocols = array_flip(config('system.filter')->get('protocols') ?: array('http', 'https'));
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  }

  // Iteratively remove any invalid protocol found.
  do {
    $before = $uri;
    $colonpos = strpos($uri, ':');
    if ($colonpos > 0) {
      // We found a colon, possibly a protocol. Verify.
      $protocol = substr($uri, 0, $colonpos);
      // If a colon is preceded by a slash, question mark or hash, it cannot
      // possibly be part of the URL scheme. This must be a relative URL, which
      // inherits the (safe) protocol of the base document.
      if (preg_match('![/?#]!', $protocol)) {
        break;
      }
      // Check if this is a disallowed protocol. Per RFC2616, section 3.2.3
      // (URI Comparison) scheme comparison must be case-insensitive.
      if (!isset($allowed_protocols[strtolower($protocol)])) {
        $uri = substr($uri, $colonpos + 1);
      }
    }
  } while ($before != $uri);

  return $uri;
}

/**
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 * Strips dangerous protocols from a URI and encodes it for output to HTML.
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 *
 * @param $uri
 *   A plain-text URI that might contain dangerous protocols.
 *
 * @return
 *   A URI stripped of dangerous protocols and encoded for output to an HTML
 *   attribute value. Because it is already encoded, it should not be set as a
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 *   value within a $attributes array passed to Drupal\Core\Template\Attribute,
 *   because Drupal\Core\Template\Attribute expects those values to be
 *   plain-text strings. To pass a filtered URI to
 *   Drupal\Core\Template\Attribute, call drupal_strip_dangerous_protocols()
 *   instead.
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 *
 * @see drupal_strip_dangerous_protocols()
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 */
function check_url($uri) {
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  return check_plain(drupal_strip_dangerous_protocols($uri));
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}

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/**
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 * Applies a very permissive XSS/HTML filter for admin-only use.
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 *
 * Use only for fields where it is impractical to use the
 * whole filter system, but where some (mainly inline) mark-up
 * is desired (so check_plain() is not acceptable).
 *
 * Allows all tags that can be used inside an HTML body, save
 * for scripts and styles.
 */
function filter_xss_admin($string) {
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  return filter_xss($string, array('a', 'abbr', 'acronym', 'address', 'article', 'aside', 'b', 'bdi', 'bdo', 'big', 'blockquote', 'br', 'caption', 'cite', 'code', 'col', 'colgroup', 'command', 'dd', 'del', 'details', 'dfn', 'div', 'dl', 'dt', 'em', 'figcaption', 'figure', 'footer', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'header', 'hgroup', 'hr', 'i', 'img', 'ins', 'kbd', 'li', 'mark', 'menu', 'meter', 'nav', 'ol', 'output', 'p', 'pre', 'progress', 'q', 'rp', 'rt', 'ruby', 's', 'samp', 'section', 'small', 'span', 'strong', 'sub', 'summary', 'sup', 'table', 'tbody', 'td', 'tfoot', 'th', 'thead', 'time', 'tr', 'tt', 'u', 'ul', 'var', 'wbr'));
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}

/**
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 * Filters HTML to prevent cross-site-scripting (XSS) vulnerabilities.