common.inc

<?php

/**
 * @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.
 */

use Drupal\Component\Serialization\Json;
use Drupal\Component\Serialization\Yaml;
use Drupal\Component\Serialization\Exception\InvalidDataTypeException;
use Drupal\Component\Utility\Bytes;
use Drupal\Component\Utility\Crypt;
use Drupal\Component\Utility\Html;
use Drupal\Component\Utility\Number;
use Drupal\Component\Utility\SafeMarkup;
use Drupal\Component\Utility\SortArray;
use Drupal\Component\Utility\String;
use Drupal\Component\Utility\Tags;
use Drupal\Component\Utility\UrlHelper;
use Drupal\Core\Cache\Cache;
use Drupal\Core\Language\LanguageInterface;
use Drupal\Core\Site\Settings;
use Drupal\Core\Url;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpFoundation\Request;
use Drupal\Core\PhpStorage\PhpStorageFactory;
use Drupal\Component\Utility\NestedArray;
use Drupal\Core\Datetime\DrupalDateTime;
use Drupal\Core\Routing\GeneratorNotInitializedException;
use Drupal\Core\Template\Attribute;
use Drupal\Core\Render\Element;
use Drupal\Core\Session\AnonymousUserSession;

/**
 * @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
 *   $my_substring = Unicode::substr($original_string, 0, 5);
 * @endcode
 *
 * @}
 */

/**
 * Return status for saving which involved creating a new item.
 */
const SAVED_NEW = 1;

/**
 * Return status for saving which involved an update to an existing item.
 */
const SAVED_UPDATED = 2;

/**
 * Return status for saving which deleted an existing item.
 */
const SAVED_DELETED = 3;

/**
 * The default aggregation group for CSS files added to the page.
 */
const CSS_AGGREGATE_DEFAULT = 0;

/**
 * The default aggregation group for theme CSS files added to the page.
 */
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 themes.)
 */
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 themes and are not included with components.
 */
const CSS_THEME = 200;

/**
 * The default group for JavaScript settings added to the page.
 */
const JS_SETTING = -200;

/**
 * The default group for JavaScript and jQuery libraries added to the page.
 */
const JS_LIBRARY = -100;

/**
 * The default group for module JavaScript code added to the page.
 */
const JS_DEFAULT = 0;

/**
 * The default group for theme JavaScript code added to the page.
 */
const JS_THEME = 100;

/**
 * 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";

/**
 * Adds output to the HEAD tag of the HTML page.
 *
 * This function can be called as long as the headers aren't sent. Pass no
 * 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 $data is not NULL.
 *
 * @return
 *   An array of all stored HEAD elements.
 *
 * @see \Drupal\Core\Render\Element\HtmlTag::preRenderHtmlTag()
 *
 * @deprecated in Drupal 8.0.x, will be removed before Drupal 8.0.0
 *   Use #attached on render arrays.
 */
function _drupal_add_html_head($data = NULL, $key = NULL) {
  $stored_head = &drupal_static(__FUNCTION__, array());

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

/**
 * Retrieves output to be displayed in the HEAD tag of the HTML page.
 *
 * @param bool $render
 *   If TRUE render the HEAD elements, otherwise return just the elements.
 *
 * @return string|array
 *   Return the rendered HTML head or the elements itself.
 *
 * @deprecated in Drupal 8.0.x, will be removed before Drupal 8.0.0
 *   Use #attached on render arrays.
 */
function drupal_get_html_head($render = TRUE) {
  $elements = _drupal_add_html_head();
  \Drupal::moduleHandler()->alter('html_head', $elements);
  if ($render) {
    return drupal_render($elements);
  }
  else {
    return $elements;
  }
}

/**
 * Prepares a 'destination' URL query parameter for use with url().
 *
 * 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.
 *
 * @return
 *   An associative array containing the key:
 *   - destination: The path provided via the destination query string or, if
 *     not available, the current path.
 *
 * @ingroup form_api
 */
function drupal_get_destination() {
  $destination = &drupal_static(__FUNCTION__);

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

  $query = \Drupal::request()->query;
  if ($query->has('destination')) {
    $destination = array('destination' => $query->get('destination'));
  }
  else {
    $path = \Drupal::routeMatch()->getRouteName() ? Url::fromRouteMatch(\Drupal::routeMatch())->getInternalPath() : '';
    $query = UrlHelper::buildQuery(UrlHelper::filterQueryParameters($query->all()));
    if ($query != '') {
      $path .= '?' . $query;
    }
    $destination = array('destination' => $path);
  }
  return $destination;
}

/**
 * @defgroup validation Input validation
 * @{
 * Functions to validate user input.
 */

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

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

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

/**
 * Strips dangerous protocols from a URI and encodes it for output to HTML.
 *
 * @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
 *   value within a $attributes array passed to Drupal\Core\Template\Attribute,
 *   because Drupal\Core\Template\Attribute expects those values to be
 *   plain-text strings. To pass a filtered URI to
 *   Drupal\Core\Template\Attribute, call
 *   \Drupal\Component\Utility\UrlHelper::stripDangerousProtocols() instead.
 *
 * @see \Drupal\Component\Utility\UrlHelper::stripDangerousProtocols()
 * @see \Drupal\Component\Utility\String::checkPlain()
 */
function check_url($uri) {
  return String::checkPlain(UrlHelper::stripDangerousProtocols($uri));
}

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

/**
 * @defgroup format Formatting
 * @{
 * Functions to format numbers, strings, dates, etc.
 */

/**
 * Formats XML elements.
 *
 * Note: It is the caller's responsibility to sanitize any input parameters.
 * This function does not perform sanitization.
 *
 * @param $array
 *   An array where each item represents an element and is either a:
 *   - (key => value) pair (<key>value</key>)
 *   - Associative array with fields:
 *     - 'key': The element name. Element names are not sanitized, so do not
 *       pass user input.
 *     - 'value': element contents
 *     - 'attributes': associative array of element attributes
 *
 * In both cases, 'value' can be a simple string, or it can be another array
 * with the same format as $array itself for nesting.
 */
function format_xml_elements($array) {
  $output = '';
  foreach ($array as $key => $value) {
    if (is_numeric($key)) {
      if ($value['key']) {
        $output .= ' <' . $value['key'];
        if (isset($value['attributes']) && is_array($value['attributes'])) {
          $output .= new Attribute($value['attributes']);
        }

        if (isset($value['value']) && $value['value'] != '') {
          $output .= '>' . (is_array($value['value']) ? format_xml_elements($value['value']) : String::checkPlain($value['value'])) . '</' . $value['key'] . ">\n";
        }
        else {
          $output .= " />\n";
        }
      }
    }
    else {
      $output .= ' <' . $key . '>' . (is_array($value) ? format_xml_elements($value) : String::checkPlain($value)) . "</$key>\n";
    }
  }
  // @todo This is marking the output string as safe HTML, but we have only
  //   sanitized the attributes and tag values, not the tag names, and we
  //   cannot guarantee the assembled markup is safe. Consider a fix in:
  //   https://www.drupal.org/node/2296885
  return SafeMarkup::set($output);
}

/**
 * Generates a string representation for the given byte count.
 *
 * @param $size
 *   A size in bytes.
 * @param $langcode
 *   Optional language code to translate to a language other than what is used
 *   to display the page.
 *
 * @return
 *   A translated string representation of the size.
 */
function format_size($size, $langcode = NULL) {
  if ($size < Bytes::KILOBYTE) {
    return \Drupal::translation()->formatPlural($size, '1 byte', '@count bytes', array(), array('langcode' => $langcode));
  }
  else {
    $size = $size / Bytes::KILOBYTE; // Convert bytes to kilobytes.
    $units = array(
      t('@size KB', array(), array('langcode' => $langcode)),
      t('@size MB', array(), array('langcode' => $langcode)),
      t('@size GB', array(), array('langcode' => $langcode)),
      t('@size TB', array(), array('langcode' => $langcode)),
      t('@size PB', array(), array('langcode' => $langcode)),
      t('@size EB', array(), array('langcode' => $langcode)),
      t('@size ZB', array(), array('langcode' => $langcode)),
      t('@size YB', array(), array('langcode' => $langcode)),
    );
    foreach ($units as $unit) {
      if (round($size, 2) >= Bytes::KILOBYTE) {
        $size = $size / Bytes::KILOBYTE;
      }
      else {
        break;
      }
    }
    return str_replace('@size', round($size, 2), $unit);
  }
}

/**
 * Formats a date, using a date type or a custom date format string.
 *
 * @param $timestamp
 *   A UNIX timestamp to format.
 * @param $type
 *   (optional) The format to use, one of:
 *   - One of the built-in formats: 'short', 'medium',
 *     'long', 'html_datetime', 'html_date', 'html_time',
 *     'html_yearless_date', 'html_week', 'html_month', 'html_year'.
 *   - The name of a date type defined by a date format config entity.
 *   - The machine name of an administrator-defined date format.
 *   - 'custom', to use $format.
 *   Defaults to 'medium'.
 * @param $format
 *   (optional) If $type is 'custom', a PHP date format string suitable for
 *   input to date(). Use a backslash to escape ordinary text, so it does not
 *   get interpreted as date format characters.
 * @param $timezone
 *   (optional) Time zone identifier, as described at
 *   http://php.net/manual/timezones.php Defaults to the time zone used to
 *   display the page.
 * @param $langcode
 *   (optional) Language code to translate to. Defaults to the language used to
 *   display the page.
 *
 * @return
 *   A translated date string in the requested format.
 *
 * @see \Drupal\Core\Datetime\DateFormatter::format()
 */
function format_date($timestamp, $type = 'medium', $format = '', $timezone = NULL, $langcode = NULL) {
  return \Drupal::service('date.formatter')->format($timestamp, $type, $format, $timezone, $langcode);
}

/**
 * Returns an ISO8601 formatted date based on the given date.
 *
 * @param $date
 *   A UNIX timestamp.
 *
 * @return string
 *   An ISO8601 formatted date.
 */
function date_iso8601($date) {
  // The DATE_ISO8601 constant cannot be used here because it does not match
  // date('c') and produces invalid RDF markup.
  return date('c', $date);
}

/**
 * Translates a formatted date string.
 *
 * Callback for preg_replace_callback() within format_date().
 */
function _format_date_callback(array $matches = NULL, $new_langcode = NULL) {
  // We cache translations to avoid redundant and rather costly calls to t().
  static $cache, $langcode;

  if (!isset($matches)) {
    $langcode = $new_langcode;
    return;
  }

  $code = $matches[1];
  $string = $matches[2];

  if (!isset($cache[$langcode][$code][$string])) {
    $options = array(
      'langcode' => $langcode,
    );

    if ($code == 'F') {
      $options['context'] = 'Long month name';
    }

    if ($code == '') {
      $cache[$langcode][$code][$string] = $string;
    }
    else {
      $cache[$langcode][$code][$string] = t($string, array(), $options);
    }
  }
  return $cache[$langcode][$code][$string];
}

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

/**
 * Generates an internal or external URL.
 *
 * When creating links in modules, consider whether l() could be a better
 * alternative than url().
 *
 * @see \Drupal\Core\Url::fromUri()
 * @see \Drupal\Core\Url::fromRoute()
 * @see \Drupal\Core\Url::toString()
 *
 * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.0.
 *   Use \Drupal\Core\Url::fromRoute() for internal paths served by Drupal
 *   controllers or \Drupal\Core\Url::fromUri() for external paths or
 *   non-controller or sub-domain URIs such as core/install.php. Note that
 *   \Drupal\Core\Url::fromUri() expects a valid URI including the scheme. URIs
 *   from the same sub-domain that are not handled by Drupal controllers should
 *   be prepended with base://. For example:
 * @code
 * $installer_url = \Drupal\Core\Url::fromUri('base://core/install.php')->toString();
 * $external_url = \Drupal\Core\Url::fromUri('http://example.com', ['query' => ['foo' => 'bar']])->toString();
 * $internal_url = \Drupal\Core\Url::fromRoute('system.admin')->toString();
 * @endcode
 */
function _url($path = NULL, array $options = array()) {
  return \Drupal::urlGenerator()->generateFromPath($path, $options);
}

/**
 * Formats an attribute string for an HTTP header.
 *
 * @param $attributes
 *   An associative array of attributes such as 'rel'.
 *
 * @return
 *   A ; separated string ready for insertion in a HTTP header. No escaping is
 *   performed for HTML entities, so this string is not safe to be printed.
 */
function drupal_http_header_attributes(array $attributes = array()) {
  foreach ($attributes as $attribute => &$data) {
    if (is_array($data)) {
      $data = implode(' ', $data);
    }
    $data = $attribute . '="' . $data . '"';
  }
  return $attributes ? ' ' . implode('; ', $attributes) : '';
}

/**
 * Formats an internal or external URL link as an HTML anchor tag.
 *
 * This function correctly handles aliased paths and adds an 'active' class
 * attribute to links that point to the current page (for theming), so all
 * internal links output by modules should be generated by this function if
 * possible.
 *
 * However, for links enclosed in translatable text you should use t() and
 * embed the HTML anchor tag directly in the translated string. For example:
 * @code
 * t('Visit the <a href="@url">settings</a> page', array('@url' => \Drupal::url('system.admin')));
 * @endcode
 * This keeps the context of the link title ('settings' in the example) for
 * translators.
 *
 * This function does not support generating links from internal routes. For
 * that use \Drupal\Core\Utility\LinkGenerator::generate(), which is exposed via
 * the 'link_generator' service. It requires an internal route name and does not
 * support external URLs. Using Drupal 7 style system paths should be avoided if
 * possible but l() should still be used when rendering links to external URLs.
 *
 * @param string|array $text
 *   The link text for the anchor tag as a translated string or render array.
 * @param string $path
 *   The internal path or external URL being linked to, such as "node/34" or
 *   "http://example.com/foo". After the url() function is called to construct
 *   the URL from $path and $options, the resulting URL is passed through
 *   \Drupal\Component\Utility\String::checkPlain() before it is inserted into
 *   the HTML anchor tag, to ensure well-formed HTML. See url() for more
 *   information and notes.
 * @param array $options
 *   An associative array of additional options. Defaults to an empty array. It
 *   may contain the following elements.
 *   - 'attributes': An associative array of HTML attributes to apply to the
 *     anchor tag. If element 'class' is included, it must be an array; 'title'
 *     must be a string; other elements are more flexible, as they just need
 *     to work as an argument for the constructor of the class
 *     Drupal\Core\Template\Attribute($options['attributes']).
 *   - 'html' (default FALSE): Whether $text is HTML or just plain-text. For
 *     example, to make an image tag into a link, this must be set to TRUE, or
 *     you will see the escaped HTML image tag. $text is not sanitized if
 *     'html' is TRUE. The calling function must ensure that $text is already
 *     safe.
 *   - 'language': An optional language object. If the path being linked to is
 *     internal to the site, $options['language'] is used to determine whether
 *     the link is "active", or pointing to the current page (the language as
 *     well as the path must match). This element is also used by url().
 *   - 'set_active_class': Whether l() should compare the $path, language and
 *     query options to the current URL to determine whether the link is
 *     "active". Defaults to FALSE. If TRUE, an "active" class will be applied
 *     to the link. It is important to use this sparingly since it is usually
 *     unnecessary and requires extra processing.
 *     For anonymous users, the "active" class will be calculated on the server,
 *     because most sites serve each anonymous user the same cached page anyway.
 *     For authenticated users, the "active" class will be calculated on the
 *     client (through JavaScript), only data- attributes are added to links to
 *     prevent breaking the render cache. The JavaScript is added in
 *     system_page_attachments().
 *   - Additional $options elements used by the url() function.
 *
 * @return string
 *   An HTML string containing a link to the given path.
 *
 * @see _url()
 * @see system_page_attachments()
 * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.0.
 *   Use \Drupal::l($text, $url) where $url is an instance of
 *   \Drupal\Core\Url. To build a \Drupal\Core\Url object for internal paths
 *   served by Drupal controllers use \Drupal\Core\Url::fromRoute(). For
 *   external paths or non-controller or sub-domain URIs such as
 *   core/install.php use \Drupal\Core\Url::fromUri(). Note that
 *   \Drupal\Core\Url::fromUri() expects a valid URI including the scheme. URIs
 *   from the same sub-domain that are not handled by Drupal controllers should
 *   be prepended with base://. For example:
 * @code
 * $installer_url = \Drupal\Core\Url::fromUri('base://core/install.php')->toString();
 * $installer_link = \Drupal::l($text, $installer_url);
 * $external_url = \Drupal\Core\Url::fromUri('http://example.com', ['query' => ['foo' => 'bar']])->toString();
 * $external_link = \Drupal::l($text, $external_url);
 * $internal_url = \Drupal\Core\Url::fromRoute('system.admin')->toString();
 * $internal_link = \Drupal::l($text, $internal_url);
 * @endcode
 */
function _l($text, $path, array $options = array()) {
  // Start building a structured representation of our link to be altered later.
  $variables = array(
    'text' => is_array($text) ? drupal_render($text) : $text,
    'path' => $path,
    'options' => $options,
  );

  // Merge in default options.
  $variables['options'] += array(
    'attributes' => array(),
    'query' => array(),
    'html' => FALSE,
    'language' => NULL,
    'set_active_class' => FALSE,
  );

  // Add a hreflang attribute if we know the language of this link's url and
  // hreflang has not already been set.
  if (!empty($variables['options']['language']) && !isset($variables['options']['attributes']['hreflang'])) {
    $variables['options']['attributes']['hreflang'] = $variables['options']['language']->getId();
  }

  // Set the "active" class if the 'set_active_class' option is not empty.
  if (!empty($variables['options']['set_active_class'])) {
    // Add a "data-drupal-link-query" attribute to let the drupal.active-link
    // library know the query in a standardized manner.
    if (!empty($variables['options']['query'])) {
      $query = $variables['options']['query'];
      ksort($query);
      $variables['options']['attributes']['data-drupal-link-query'] = Json::encode($query);
    }

    // Add a "data-drupal-link-system-path" attribute to let the
    // drupal.active-link library know the path in a standardized manner.
    if (!isset($variables['options']['attributes']['data-drupal-link-system-path'])) {
      $variables['options']['attributes']['data-drupal-link-system-path'] = \Drupal::service('path.alias_manager')->getPathByAlias($path);
    }
  }

  // Remove all HTML and PHP tags from a tooltip, calling expensive strip_tags()
  // only when a quick strpos() gives suspicion tags are present.
  if (isset($variables['options']['attributes']['title']) && strpos($variables['options']['attributes']['title'], '<') !== FALSE) {
    $variables['options']['attributes']['title'] = strip_tags($variables['options']['attributes']['title']);
  }

  // Allow other modules to modify the structure of the link.
  \Drupal::moduleHandler()->alter('link', $variables);

  // Move attributes out of options. url() doesn't need them.
  $attributes = new Attribute($variables['options']['attributes']);
  unset($variables['options']['attributes']);

  // The result of url() is a plain-text URL. Because we are using it here
  // in an HTML argument context, we need to encode it properly.
  $url = String::checkPlain(_url($variables['path'], $variables['options']));

  // Sanitize the link text if necessary.
  $text = $variables['options']['html'] ? $variables['text'] : String::checkPlain($variables['text']);
  return SafeMarkup::set('<a href="' . $url . '"' . $attributes . '>' . $text . '</a>');
}

/**
 * Attempts to set the PHP maximum execution time.
 *
 * This function is a wrapper around the PHP function set_time_limit().
 * When called, set_time_limit() restarts the timeout counter from zero.
 * In other words, if the timeout is the default 30 seconds, and 25 seconds
 * into script execution a call such as set_time_limit(20) is made, the
 * script will run for a total of 45 seconds before timing out.
 *
 * If the current time limit is not unlimited it is possible to decrease the
 * total time limit if the sum of the new time limit and the current time spent
 * running the script is inferior to the original time limit. It is inherent to
 * the way set_time_limit() works, it should rather be called with an
 * appropriate value every time you need to allocate a certain amount of time
 * to execute a task than only once at the beginning of the script.
 *
 * Before calling set_time_limit(), we check if this function is available
 * because it could be disabled by the server administrator. We also hide all
 * the errors that could occur when calling set_time_limit(), because it is
 * not possible to reliably ensure that PHP or a security extension will
 * not issue a warning/error if they prevent the use of this function.
 *
 * @param $time_limit
 *   An integer specifying the new time limit, in seconds. A value of 0
 *   indicates unlimited execution time.
 *
 * @ingroup php_wrappers
 */
function drupal_set_time_limit($time_limit) {
  if (function_exists('set_time_limit')) {
    $current = ini_get('max_execution_time');
    // Do not set time limit if it is currently unlimited.
    if ($current != 0) {
      @set_time_limit($time_limit);
    }
  }
}

/**
 * Returns the base URL path (i.e., directory) of the Drupal installation.
 *
 * base_path() adds a "/" to the beginning and end of the returned path if the
 * path is not empty. At the very least, this will return "/".
 *
 * Examples:
 * - http://example.com returns "/" because the path is empty.
 * - http://example.com/drupal/folder returns "/drupal/folder/".
 */
function base_path() {
  return $GLOBALS['base_path'];
}

/**
 * Adds a LINK tag with a distinct 'rel' attribute to the page's HEAD.
 *
 * This function can be called as long the HTML header hasn't been sent, which
 * on normal pages is up through the preprocess step of _theme('html'). Adding
 * a link will overwrite a prior link with the exact same 'rel' and 'href'
 * attributes.
 *
 * @param $attributes
 *   Associative array of element attributes including 'href' and 'rel'.
 * @param $header
 *   Optional flag to determine if a HTTP 'Link:' header should be sent.
 *
 * @deprecated in Drupal 8.0.x, will be removed before Drupal 8.0.0
 *   Use #attached on render arrays.
 */
function _drupal_add_html_head_link($attributes, $header = FALSE) {
  $element = array(
    '#tag' => 'link',
    '#attributes' => $attributes,
  );
  $href = $attributes['href'];

  if ($header) {
    // Also add a HTTP header "Link:".
    $href = '<' . String::checkPlain($attributes['href']) . '>;';
    unset($attributes['href']);
    $element['#attached']['http_header'][] = array('Link',  $href . drupal_http_header_attributes($attributes), TRUE);
  }

  _drupal_add_html_head($element, 'html_head_link:' . $attributes['rel'] . ':' . $href);
}

/**
 * Adds a cascading stylesheet to the stylesheet queue.
 *
 * Calling drupal_static_reset('_drupal_add_css') will clear all cascading
 * stylesheets added so far.
 *
 * If CSS aggregation/compression is enabled, all cascading style sheets added
 * with $options['preprocess'] set to TRUE will be merged into one aggregate
 * file and compressed by removing all extraneous white space.
 * Externally hosted stylesheets are never aggregated or compressed.
 *
 * The reason for aggregating the files is outlined quite thoroughly here:
 * http://www.die.net/musings/page_load_time/ "Load fewer external objects. Due
 * to request overhead, one bigger file just loads faster than two smaller ones
 * half its size."
 *
 * $options['preprocess'] should be only set to TRUE when a file is required for
 * all typical visitors and most pages of a site. It is critical that all
 * preprocessed files are added unconditionally on every page, even if the
 * files do not happen to be needed on a page.
 *
 * Non-preprocessed files should only be added to the page when they are
 * actually needed.
 *
 * @param $data
 *   (optional) The stylesheet data to be added, depending on what is passed
 *   through to the $options['type'] parameter:
 *   - 'file': The path to the CSS file relative to the base_path(), or a
 *     stream wrapper URI. For example: "modules/devel/devel.css" or
 *     "public://generated_css/stylesheet_1.css". Note that Modules should
 *     always prefix the names of their CSS files with the module name; for
 *     example, system-menus.css rather than simply menus.css. Themes can
 *     override module-supplied CSS files based on their filenames, and this
 *     prefixing helps prevent confusing name collisions for theme developers.
 *     See drupal_get_css() where the overrides are performed.
 *   - 'external': The absolute path to an external CSS file that is not hosted
 *     on the local server. These files will not be aggregated if CSS
 *     aggregation is enabled.
 * @param $options
 *   (optional) A string defining the 'type' of CSS that is being added in the
 *   $data parameter ('file' or 'external'), or an array which can have any or
 *   all of the following keys:
 *   - 'type': The type of stylesheet being added. Available options are 'file'
 *     or 'external'. Defaults to 'file'.
 *   - 'basename': Force a basename for the file being added. Modules are
 *     expected to use stylesheets with unique filenames, but integration of
 *     external libraries may make this impossible. The basename of
 *     'core/modules/node/node.css' is 'node.css'. If the external library
 *     "node.js" ships with a 'node.css', then a different, unique basename
 *     would be 'node.js.css'.
 *   - 'group': A number identifying the aggregation group in which to add the
 *     stylesheet. Available constants are:
 *     - CSS_AGGREGATE_DEFAULT: (default) Any module-layer CSS.
 *     - CSS_AGGREGATE_THEME: Any theme-layer CSS.
 *     The aggregate group number affects load order and the CSS cascade.
 *     Stylesheets in an aggregate with a lower group number will be output to
 *     the page before stylesheets in an aggregate with a higher group number,
 *     so CSS within higher aggregate groups can take precedence over CSS
 *     within lower aggregate groups.
 *   - 'every_page': For optimal front-end performance when aggregation is
 *     enabled, this should be set to TRUE if the stylesheet is present on every
 *     page of the website for users for whom it is present at all. This
 *     defaults to FALSE. It is set to TRUE for stylesheets added via module and
 *     theme .info.yml files. Modules that add stylesheets within
 *     hook_page_attachments() implementations, or from other code that ensures
 *     that the stylesheet is added to all website pages, should also set this flag
 *     to TRUE. All stylesheets within the same group that have the 'every_page'
 *     flag set to TRUE and do not have 'preprocess' set to FALSE are aggregated
 *     together into a single aggregate file, and that aggregate file can be
 *     reused across a user's entire site visit, leading to faster navigation
 *     between pages.
 *     However, stylesheets that are only needed on pages less frequently
 *     visited, can be added by code that only runs for those particular pages,
 *     and that code should not set the 'every_page' flag. This minimizes the
 *     size of the aggregate file that the user needs to download when first
 *     visiting the website. Stylesheets without the 'every_page' flag are
 *     aggregated into a separate aggregate file. This other aggregate file is
 *     likely to change from page to page, and each new aggregate file needs to
 *     be downloaded when first encountered, so it should be kept relatively
 *     small by ensuring that most commonly needed stylesheets are added to
 *     every page.
 *   - 'weight': The weight of the stylesheet specifies the order in which the
 *     CSS will appear relative to other stylesheets with the same aggregate
 *     group and 'every_page' flag. The exact ordering of stylesheets is as
 *     follows:
 *     - First by aggregate group.
 *     - Then by the 'every_page' flag, with TRUE coming before FALSE.
 *     - Then by weight.
 *     - Then by the order in which the CSS was added. For example, all else
 *       being the same, a stylesheet added by a call to _drupal_add_css() that
 *       happened later in the page request gets added to the page after one for
 *       which _drupal_add_css() happened earlier in the page request.
 *     Available constants are:
 *     - CSS_BASE: Styles for HTML elements ("base" styles).
 *     - CSS_LAYOUT: Styles that layout a page.
 *     - CSS_COMPONENT: Styles for design components (and their associated
 *       states and themes.)
 *     - CSS_STATE: Styles for states that are not included with components.
 *     - CSS_THEME: Styles for themes that are not included with components.
 *     The weight numbers follow the SMACSS convention of CSS categorization.
 *     See http://drupal.org/node/1887922
 *   - 'media': The media type for the stylesheet, e.g., all, print, screen.
 *     Defaults to 'all'. It is extremely important to leave this set to 'all'
 *     or it will negatively impact front-end performance. Instead add a @media
 *     block to the included CSS file.
 *   - 'preprocess': If TRUE and CSS aggregation/compression is enabled, the
 *     styles will be aggregated and compressed. Defaults to TRUE.
 *   - 'browsers': An array containing information specifying which browsers
 *     should load the CSS item. See
 *     \Drupal\Core\Render\Element\HtmlTag::preRenderConditionalComments() for
 *     details.
 *
 * @return
 *   An array of queued cascading stylesheets.
 *
 * @deprecated as of Drupal 8.0. Use the #attached key in render arrays instead.
 *
 * @see drupal_get_css()
 */
function _drupal_add_css($data = NULL, $options = NULL) {
  $css = &drupal_static(__FUNCTION__, array());

  // Construct the options, taking the defaults into consideration.
  if (isset($options)) {
    if (!is_array($options)) {
      $options = array('type' => $options);
    }
  }
  else {
    $options = array();
  }