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<?php
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// $Id$
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/**
 * @file
 * Functions that need to be loaded on every Drupal request.
 */
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/**
 * The current system version.
 */
define('VERSION', '7.0-dev');

/**
 * Core API compatibility.
 */
define('DRUPAL_CORE_COMPATIBILITY', '7.x');

/**
 * Minimum supported version of PHP.
 */
define('DRUPAL_MINIMUM_PHP',    '5.2.0');

/**
 * Minimum recommended value of PHP memory_limit.
 */
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define('DRUPAL_MINIMUM_PHP_MEMORY_LIMIT',    '32M');
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/**
 * Minimum supported version of MySQL, if it is used.
 */
define('DRUPAL_MINIMUM_MYSQL',  '5.0');

/**
 * Minimum supported version of PostgreSQL, if it is used.
 */
define('DRUPAL_MINIMUM_PGSQL',  '8.3');

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/**
 * Indicates that the item should never be removed unless explicitly told to
 * using cache_clear_all() with a cache ID.
 */
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define('CACHE_PERMANENT', 0);
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/**
 * Indicates that the item should be removed at the next general cache wipe.
 */
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define('CACHE_TEMPORARY', -1);
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/**
 * Indicates that page caching is disabled.
 */
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define('CACHE_DISABLED', 0);
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/**
 * Indicates that page caching is enabled, using "normal" mode.
 */
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define('CACHE_NORMAL', 1);
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/**
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 * Log message severity -- Emergency: system is unusable.
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 *
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 * @see watchdog()
 * @see watchdog_severity_levels()
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 */
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define('WATCHDOG_EMERG', 0);

/**
 * Log message severity -- Alert: action must be taken immediately.
 *
 * @see watchdog()
 * @see watchdog_severity_levels()
 */
define('WATCHDOG_ALERT', 1);

/**
 * Log message severity -- Critical: critical conditions.
 *
 * @see watchdog()
 * @see watchdog_severity_levels()
 */
define('WATCHDOG_CRITICAL', 2);

/**
 * Log message severity -- Error: error conditions.
 *
 * @see watchdog()
 * @see watchdog_severity_levels()
 */
define('WATCHDOG_ERROR', 3);

/**
 * Log message severity -- Warning: warning conditions.
 *
 * @see watchdog()
 * @see watchdog_severity_levels()
 */
define('WATCHDOG_WARNING', 4);

/**
 * Log message severity -- Notice: normal but significant condition.
 *
 * @see watchdog()
 * @see watchdog_severity_levels()
 */
define('WATCHDOG_NOTICE', 5);

/**
 * Log message severity -- Informational: informational messages.
 *
 * @see watchdog()
 * @see watchdog_severity_levels()
 */
define('WATCHDOG_INFO', 6);

/**
 * Log message severity -- Debug: debug-level messages.
 *
 * @see watchdog()
 * @see watchdog_severity_levels()
 */
define('WATCHDOG_DEBUG', 7);
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/**
 * First bootstrap phase: initialize configuration.
 */
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define('DRUPAL_BOOTSTRAP_CONFIGURATION', 0);
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/**
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 * Second bootstrap phase: try to serve a cached page.
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 */
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define('DRUPAL_BOOTSTRAP_PAGE_CACHE', 1);
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/**
 * Third bootstrap phase: initialize database layer.
 */
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define('DRUPAL_BOOTSTRAP_DATABASE', 2);
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/**
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 * Fourth bootstrap phase: initialize the variable system.
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 */
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define('DRUPAL_BOOTSTRAP_VARIABLES', 3);
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/**
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 * Fifth bootstrap phase: initialize session handling.
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 */
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define('DRUPAL_BOOTSTRAP_SESSION', 4);
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/**
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 * Sixth bootstrap phase: set up the page header.
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 */
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define('DRUPAL_BOOTSTRAP_PAGE_HEADER', 5);
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/**
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 * Seventh bootstrap phase: find out language of the page.
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 */
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define('DRUPAL_BOOTSTRAP_LANGUAGE', 6);
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/**
 * Final bootstrap phase: Drupal is fully loaded; validate and fix
 * input data.
 */
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define('DRUPAL_BOOTSTRAP_FULL', 7);
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/**
 * Role ID for anonymous users; should match what's in the "role" table.
 */
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define('DRUPAL_ANONYMOUS_RID', 1);
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/**
 * Role ID for authenticated users; should match what's in the "role" table.
 */
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define('DRUPAL_AUTHENTICATED_RID', 2);

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/**
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 * The number of bytes in a kilobyte. For more information, visit
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 * http://en.wikipedia.org/wiki/Kilobyte.
 */
define('DRUPAL_KILOBYTE', 1024);

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/**
 * The language code used when no language is explicitly assigned.
 *
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 * Defined by ISO639-2 for "Undetermined".
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 */
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define('LANGUAGE_NONE', 'und');
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/**
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 * The type of language used to define the content language.
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 */
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define('LANGUAGE_TYPE_CONTENT', 'language');
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/**
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 * The type of language used to select the user interface.
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 */
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define('LANGUAGE_TYPE_INTERFACE', 'language_interface');
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/**
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 * The type of language used for URLs.
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 */
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define('LANGUAGE_TYPE_URL', 'language_url');
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/**
 * Language written left to right. Possible value of $language->direction.
 */
define('LANGUAGE_LTR', 0);

/**
 * Language written right to left. Possible value of $language->direction.
 */
define('LANGUAGE_RTL', 1);

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/**
 * For convenience, define a short form of the request time global.
 */
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define('REQUEST_TIME', $_SERVER['REQUEST_TIME']);
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/**
 * @name Title text filtering flags
 * @{
 * Flags for use in drupal_set_title().
 */

/**
 * Flag for drupal_set_title(); text is not sanitized, so run check_plain().
 */
define('CHECK_PLAIN', 0);

/**
 * Flag for drupal_set_title(); text has already been sanitized.
 */
define('PASS_THROUGH', -1);

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/**
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 * Signals that the registry lookup cache should be reset.
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 */
define('REGISTRY_RESET_LOOKUP_CACHE', 1);

/**
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 * Signals that the registry lookup cache should be written to storage.
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 */
define('REGISTRY_WRITE_LOOKUP_CACHE', 2);

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/**
 * @} End of "Title text filtering flags".
 */


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/**
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 * Start the timer with the specified name. If you start and stop the same
 * timer multiple times, the measured intervals will be accumulated.
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 *
 * @param name
 *   The name of the timer.
 */
function timer_start($name) {
  global $timers;

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  $timers[$name]['start'] = microtime(TRUE);
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  $timers[$name]['count'] = isset($timers[$name]['count']) ? ++$timers[$name]['count'] : 1;
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}

/**
 * Read the current timer value without stopping the timer.
 *
 * @param name
 *   The name of the timer.
 * @return
 *   The current timer value in ms.
 */
function timer_read($name) {
  global $timers;

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  if (isset($timers[$name]['start'])) {
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    $stop = microtime(TRUE);
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    $diff = round(($stop - $timers[$name]['start']) * 1000, 2);
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    if (isset($timers[$name]['time'])) {
      $diff += $timers[$name]['time'];
    }
    return $diff;
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  }
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  return $timers[$name]['time'];
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}

/**
 * Stop the timer with the specified name.
 *
 * @param name
 *   The name of the timer.
 * @return
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 *   A timer array. The array contains the number of times the timer has been
 *   started and stopped (count) and the accumulated timer value in ms (time).
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 */
function timer_stop($name) {
  global $timers;

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  if (isset($timers[$name]['time'])) {
    $timers[$name]['time'] += timer_read($name);
  }
  else {
    $timers[$name]['time'] = timer_read($name);
  }
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  unset($timers[$name]['start']);

  return $timers[$name];
}
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/**
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 * Find the appropriate configuration directory.
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 *
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 * Try finding a matching configuration directory by stripping the website's
 * hostname from left to right and pathname from right to left. The first
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 * configuration file found will be used; the remaining will ignored. If no
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 * configuration file is found, return a default value '$confdir/default'.
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 *
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 * Example for a fictitious site installed at
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 * http://www.drupal.org:8080/mysite/test/ the 'settings.php' is searched in
 * the following directories:
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 *
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 *  1. $confdir/8080.www.drupal.org.mysite.test
 *  2. $confdir/www.drupal.org.mysite.test
 *  3. $confdir/drupal.org.mysite.test
 *  4. $confdir/org.mysite.test
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 *
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 *  5. $confdir/8080.www.drupal.org.mysite
 *  6. $confdir/www.drupal.org.mysite
 *  7. $confdir/drupal.org.mysite
 *  8. $confdir/org.mysite
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 *
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 *  9. $confdir/8080.www.drupal.org
 * 10. $confdir/www.drupal.org
 * 11. $confdir/drupal.org
 * 12. $confdir/org
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 *
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 * 13. $confdir/default
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 *
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 * If a file named sites.php is present in the $confdir, it will be loaded
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 * prior to scanning for directories. It should define an associative array
 * named $sites, which maps domains to directories. It should be in the form
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 * of:
 *
 * $sites = array(
 *   'The url to alias' => 'A directory within the sites directory'
 * );
 *
 * For example:
 *
 * $sites = array(
 *   'devexample.com' => 'example.com',
 *   'localhost/example' => 'example.com',
 * );
 *
 * The above array will cause Drupal to look for a directory named
 * "example.com" in the sites directory whenever a request comes from
 * "example.com", "devexample.com", or "localhost/example". That is useful
 * on development servers, where the domain name may not be the same as the
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 * domain of the live server. Since Drupal stores file paths into the database
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 * (files, system table, etc.) this will ensure the paths are correct while
 * accessed on development servers.
 *
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 * @param $require_settings
 *   Only configuration directories with an existing settings.php file
 *   will be recognized. Defaults to TRUE. During initial installation,
 *   this is set to FALSE so that Drupal can detect a matching directory,
 *   then create a new settings.php file in it.
 * @param reset
 *   Force a full search for matching directories even if one had been
 *   found previously.
 * @return
 *   The path of the matching directory.
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 */
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function conf_path($require_settings = TRUE, $reset = FALSE) {
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  $conf = &drupal_static(__FUNCTION__, '');
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  if ($conf && !$reset) {
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    return $conf;
  }
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  $confdir = 'sites';
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  $sites = array();
  if (file_exists(DRUPAL_ROOT . '/' . $confdir . '/sites.php')) {
    // This will overwrite $sites with the desired mappings.
    include(DRUPAL_ROOT . '/' . $confdir . '/sites.php');
  }

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  $uri = explode('/', $_SERVER['SCRIPT_NAME'] ? $_SERVER['SCRIPT_NAME'] : $_SERVER['SCRIPT_FILENAME']);
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  $server = explode('.', implode('.', array_reverse(explode(':', rtrim($_SERVER['HTTP_HOST'], '.')))));
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  for ($i = count($uri) - 1; $i > 0; $i--) {
    for ($j = count($server); $j > 0; $j--) {
      $dir = implode('.', array_slice($server, -$j)) . implode('.', array_slice($uri, 0, $i));
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      if (isset($sites[$dir]) && file_exists(DRUPAL_ROOT . '/' . $confdir . '/' . $sites[$dir])) {
        $dir = $sites[$dir];
      }
      if (file_exists(DRUPAL_ROOT . '/' . $confdir . '/' . $dir . '/settings.php') || (!$require_settings && file_exists(DRUPAL_ROOT . '/' . $confdir . '/' . $dir))) {
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        $conf = "$confdir/$dir";
        return $conf;
      }
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    }
  }
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  $conf = "$confdir/default";
  return $conf;
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}

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/**
 * Set appropriate server variables needed for command line scripts to work.
 *
 * This function can be called by command line scripts before bootstrapping
 * Drupal, to ensure that the page loads with the desired server parameters.
 * This is because many parts of Drupal assume that they are running in a web
 * browser and therefore use information from the global PHP $_SERVER variable
 * that does not get set when Drupal is run from the command line.
 *
 * In many cases, the default way in which this function populates the $_SERVER
 * variable is sufficient, and it can therefore be called without passing in
 * any input. However, command line scripts running on a multisite installation
 * (or on any installation that has settings.php stored somewhere other than
 * the sites/default folder) need to pass in the URL of the site to allow
 * Drupal to detect the correct location of the settings.php file. Passing in
 * the 'url' parameter is also required for functions like request_uri() to
 * return the expected values.
 *
 * Most other parameters do not need to be passed in, but may be necessary in
 * some cases; for example, if Drupal's ip_address() function needs to return
 * anything but the standard localhost value ('127.0.0.1'), the command line
 * script should pass in the desired value via the 'REMOTE_ADDR' key.
 *
 * @param $variables
 *   (optional) An associative array of variables within $_SERVER that should
 *   be replaced. If the special element 'url' is provided in this array, it
 *   will be used to populate some of the server defaults; it should be set to
 *   the URL of the current page request, excluding any $_GET request but
 *   including the script name (e.g., http://www.example.com/mysite/index.php).
 *
 * @see conf_path()
 * @see request_uri()
 * @see ip_address()
 */
function drupal_override_server_variables($variables = array()) {
  // Set defaults based on the provided URL.
  if (isset($variables['url'])) {
    $url = parse_url($variables['url']);
    unset($variables['url']);
  }
  else {
    $url = array();
  }
  $url += array(
    'path' => '',
    'host' => 'localhost',
  );
  $defaults = array(
    'HTTP_HOST' => $url['host'],
    'SCRIPT_NAME' => $url['path'],
    'REMOTE_ADDR' => '127.0.0.1',
    'REQUEST_METHOD' => 'GET',
    'SERVER_NAME' => NULL,
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    'SERVER_SOFTWARE' => NULL,
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    'HTTP_USER_AGENT' => NULL,
  );
  // Replace elements of the $_SERVER array, as appropriate.
  $_SERVER = $variables + $_SERVER + $defaults;
}

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/**
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 * Initialize PHP environment.
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 */
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function drupal_environment_initialize() {
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  if (!isset($_SERVER['HTTP_REFERER'])) {
    $_SERVER['HTTP_REFERER'] = '';
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  }
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  if (!isset($_SERVER['SERVER_PROTOCOL']) || ($_SERVER['SERVER_PROTOCOL'] != 'HTTP/1.0' && $_SERVER['SERVER_PROTOCOL'] != 'HTTP/1.1')) {
    $_SERVER['SERVER_PROTOCOL'] = 'HTTP/1.0';
  }
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  if (isset($_SERVER['HTTP_HOST'])) {
    // As HTTP_HOST is user input, ensure it only contains characters allowed
    // in hostnames. See RFC 952 (and RFC 2181).
    // $_SERVER['HTTP_HOST'] is lowercased here per specifications.
    $_SERVER['HTTP_HOST'] = strtolower($_SERVER['HTTP_HOST']);
    if (!drupal_valid_http_host($_SERVER['HTTP_HOST'])) {
      // HTTP_HOST is invalid, e.g. if containing slashes it may be an attack.
      header($_SERVER['SERVER_PROTOCOL'] . ' 400 Bad Request');
      exit;
    }
  }
  else {
    // Some pre-HTTP/1.1 clients will not send a Host header. Ensure the key is
    // defined for E_ALL compliance.
    $_SERVER['HTTP_HOST'] = '';
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  }

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  // Enforce E_ALL, but allow users to set levels not part of E_ALL.
  error_reporting(E_ALL | error_reporting());
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  // Override PHP settings required for Drupal to work properly.
  // sites/default/default.settings.php contains more runtime settings.
  // The .htaccess file contains settings that cannot be changed at runtime.
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  // Prevent PHP from generating HTML error messages.
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  ini_set('html_errors', 0);
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  // Don't escape quotes when reading files from the database, disk, etc.
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  ini_set('magic_quotes_runtime', '0');
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  // Use session cookies, not transparent sessions that puts the session id in
  // the query string.
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  ini_set('session.use_cookies', '1');
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  ini_set('session.use_only_cookies', '1');
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  ini_set('session.use_trans_sid', '0');
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  // Don't send HTTP headers using PHP's session handler.
  ini_set('session.cache_limiter', 'none');
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  // Use httponly session cookies.
  ini_set('session.cookie_httponly', '1');
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}

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/**
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 * Validate that a hostname (for example $_SERVER['HTTP_HOST']) is safe.
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 *
 * @return
 *  TRUE if only containing valid characters, or FALSE otherwise.
 */
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function drupal_valid_http_host($host) {
  return preg_match('/^\[?(?:[a-zA-Z0-9-:\]_]+\.?)+$/', $host);
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}

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/**
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 * Loads the configuration and sets the base URL, cookie domain, and
 * session name correctly.
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 */
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function drupal_settings_initialize() {
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  global $base_url, $base_path, $base_root;

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  // Export the following settings.php variables to the global namespace
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  global $databases, $db_prefix, $cookie_domain, $conf, $installed_profile, $update_free_access, $db_url, $is_https, $base_secure_url, $base_insecure_url;
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  $conf = array();

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  if (file_exists(DRUPAL_ROOT . '/' . conf_path() . '/settings.php')) {
    include_once DRUPAL_ROOT . '/' . conf_path() . '/settings.php';
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  }
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  if (isset($base_url)) {
    // Parse fixed base URL from settings.php.
    $parts = parse_url($base_url);
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    $http_protocol = $parts['scheme'];
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    if (!isset($parts['path'])) {
      $parts['path'] = '';
    }
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    $base_path = $parts['path'] . '/';
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    // Build $base_root (everything until first slash after "scheme://").
    $base_root = substr($base_url, 0, strlen($base_url) - strlen($parts['path']));
  }
  else {
    // Create base URL
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    $http_protocol = (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == 'on') ? 'https' : 'http';
    $base_root = $http_protocol . '://' . $_SERVER['HTTP_HOST'];
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    $base_url = $base_root;
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    // $_SERVER['SCRIPT_NAME'] can, in contrast to $_SERVER['PHP_SELF'], not
    // be modified by a visitor.
    if ($dir = trim(dirname($_SERVER['SCRIPT_NAME']), '\,/')) {
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      $base_path = "/$dir";
      $base_url .= $base_path;
      $base_path .= '/';
    }
    else {
      $base_path = '/';
    }
  }
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  $is_https = $http_protocol == 'https';
  $base_secure_url = str_replace('http://', 'https://', $base_url);
  $base_insecure_url = str_replace('https://', 'http://', $base_url);
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  if ($cookie_domain) {
    // If the user specifies the cookie domain, also use it for session name.
    $session_name = $cookie_domain;
  }
  else {
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    // Otherwise use $base_url as session name, without the protocol
    // to use the same session identifiers across http and https.
    list( , $session_name) = explode('://', $base_url, 2);
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    // We escape the hostname because it can be modified by a visitor.
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    if (!empty($_SERVER['HTTP_HOST'])) {
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      $cookie_domain = check_plain($_SERVER['HTTP_HOST']);
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    }
  }
  // Strip leading periods, www., and port numbers from cookie domain.
  $cookie_domain = ltrim($cookie_domain, '.');
  if (strpos($cookie_domain, 'www.') === 0) {
    $cookie_domain = substr($cookie_domain, 4);
  }
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  $cookie_domain = explode(':', $cookie_domain);
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  $cookie_domain = '.' . $cookie_domain[0];
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  // Per RFC 2109, cookie domains must contain at least one dot other than the
  // first. For hosts such as 'localhost' or IP Addresses we don't set a cookie domain.
  if (count(explode('.', $cookie_domain)) > 2 && !is_numeric(str_replace('.', '', $cookie_domain))) {
    ini_set('session.cookie_domain', $cookie_domain);
  }
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  // To prevent session cookies from being hijacked, a user can configure the
  // SSL version of their website to only transfer session cookies via SSL by
  // using PHP's session.cookie_secure setting. The browser will then use two
  // separate session cookies for the HTTPS and HTTP versions of the site. So we
  // must use different session identifiers for HTTPS and HTTP to prevent a
  // cookie collision.
  if ($is_https) {
    ini_set('session.cookie_secure', TRUE);
  }
  $prefix = ini_get('session.cookie_secure') ? 'SSESS' : 'SESS';
  session_name($prefix . md5($session_name));
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}

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/**
 * Returns and optionally sets the filename for a system item (module,
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 * theme, etc.). The filename, whether provided, cached, or retrieved
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 * from the database, is only returned if the file exists.
 *
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 * This function plays a key role in allowing Drupal's resources (modules
 * and themes) to be located in different places depending on a site's
 * configuration. For example, a module 'foo' may legally be be located
 * in any of these three places:
 *
 * modules/foo/foo.module
 * sites/all/modules/foo/foo.module
 * sites/example.com/modules/foo/foo.module
 *
 * Calling drupal_get_filename('module', 'foo') will give you one of
 * the above, depending on where the module is located.
 *
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 * @param $type
 *   The type of the item (i.e. theme, theme_engine, module).
 * @param $name
 *   The name of the item for which the filename is requested.
 * @param $filename
 *   The filename of the item if it is to be set explicitly rather
 *   than by consulting the database.
 *
 * @return
 *   The filename of the requested item.
 */
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function drupal_get_filename($type, $name, $filename = NULL) {
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  // The location of files will not change during the request, so do not use
  // drupal_static().
  static $files = array();
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  if (!isset($files[$type])) {
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    $files[$type] = array();
  }

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  if (!empty($filename) && file_exists($filename)) {
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    $files[$type][$name] = $filename;
  }
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  elseif (isset($files[$type][$name])) {
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    // nothing
  }
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  // Verify that we have an active database connection, before querying
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  // the database. This is required because this function is called both
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  // before we have a database connection (i.e. during installation) and
  // when a database connection fails.
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  else {
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    try {
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      if (function_exists('db_query')) {
        $file = db_query("SELECT filename FROM {system} WHERE name = :name AND type = :type", array(':name' => $name, ':type' => $type))->fetchField();
        if (file_exists($file)) {
          $files[$type][$name] = $file;
        }
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      }
    }
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    catch (Exception $e) {
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      // The database table may not exist because Drupal is not yet installed,
      // or the database might be down. We have a fallback for this case so we
      // hide the error completely.
    }
    // Fallback to searching the filesystem if the database could not find the
    // file or the file returned by the database is not found.
    if (!isset($files[$type][$name])) {
      // We have a consistent directory naming: modules, themes...
      $dir = $type . 's';
      if ($type == 'theme_engine') {
        $dir = 'themes/engines';
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        $extension = 'engine';
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      }
      elseif ($type == 'theme') {
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        $extension = 'info';
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      }
      else {
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        $extension = $type;
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      }

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      if (!function_exists('drupal_system_listing')) {
        require_once DRUPAL_ROOT . '/includes/common.inc';
      }
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      // Scan the appropriate directories for all files with the requested
      // extension, not just the file we are currently looking for. This
      // prevents unnecessary scans from being repeated when this function is
      // called more than once in the same page request.
      $matches = drupal_system_listing("/\.$extension$/", $dir, 'name', 0);
      foreach ($matches as $matched_name => $file) {
        $files[$type][$matched_name] = $file->uri;
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      }
    }
  }

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  if (isset($files[$type][$name])) {
    return $files[$type][$name];
  }
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}

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/**
 * Load the persistent variable table.
 *
 * The variable table is composed of values that have been saved in the table
 * with variable_set() as well as those explicitly specified in the configuration
 * file.
 */
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function variable_initialize($conf = array()) {
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  // NOTE: caching the variables improves performance by 20% when serving cached pages.
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  if ($cached = cache_get('variables', 'cache_bootstrap')) {
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    $variables = $cached->data;
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  }
  else {
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    $variables = array_map('unserialize', db_query('SELECT name, value FROM {variable}')->fetchAllKeyed());
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    cache_set('variables', $variables, 'cache_bootstrap');
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  }

  foreach ($conf as $name => $value) {
    $variables[$name] = $value;
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  }

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  return $variables;
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}

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/**
 * Return a persistent variable.
 *
 * @param $name
 *   The name of the variable to return.
 * @param $default
 *   The default value to use if this variable has never been set.
 * @return
 *   The value of the variable.
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 *
 * @see variable_del(), variable_set()
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 */
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function variable_get($name, $default = NULL) {
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  global $conf;

  return isset($conf[$name]) ? $conf[$name] : $default;
}

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/**
 * Set a persistent variable.
 *
 * @param $name
 *   The name of the variable to set.
 * @param $value
 *   The value to set. This can be any PHP data type; these functions take care
 *   of serialization as necessary.
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 *
 * @see variable_del(), variable_get()
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 */
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function variable_set($name, $value) {
  global $conf;

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  db_merge('variable')->key(array('name' => $name))->fields(array('value' => serialize($value)))->execute();
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  cache_clear_all('variables', 'cache_bootstrap');
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  $conf[$name] = $value;
}

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/**
 * Unset a persistent variable.
 *
 * @param $name
 *   The name of the variable to undefine.
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 *
 * @see variable_get(), variable_set()
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 */
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function variable_del($name) {
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  global $conf;

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  db_delete('variable')
    ->condition('name', $name)
    ->execute();
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  cache_clear_all('variables', 'cache_bootstrap');
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  unset($conf[$name]);
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}

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/**
 * Retrieve the current page from the cache.
 *
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 * Note: we do not serve cached pages to authenticated users, or to anonymous
 * users when $_SESSION is non-empty. $_SESSION may contain status messages
 * from a form submission, the contents of a shopping cart, or other user-
 * specific content that should not be cached and displayed to other users.
 *
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 * @param $check_only
 *   (optional) Set to TRUE to only return whether a previous call found a
 *   cache entry.
 *
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 * @return
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 *   The cache object, if the page was found in the cache, NULL otherwise.
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 */
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function drupal_page_get_cache($check_only = FALSE) {
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  global $base_root;
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  static $cache_hit = FALSE;

  if ($check_only) {
    return $cache_hit;
  }
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  if (drupal_page_is_cacheable()) {
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    $cache = cache_get($base_root . request_uri(), 'cache_page');
    if ($cache !== FALSE) {
      $cache_hit = TRUE;
    }
    return $cache;
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  }
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}

/**
 * Determine the cacheability of the current page.
 *
 * @param $allow_caching
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 *   Set to FALSE if you want to prevent this page to get cached.
 *
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 * @return
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 *   TRUE if the current page can be cached, FALSE otherwise.
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 */
function drupal_page_is_cacheable($allow_caching = NULL) {
  $allow_caching_static = &drupal_static(__FUNCTION__, TRUE);
  if (isset($allow_caching)) {
    $allow_caching_static = $allow_caching;
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  }
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  return $allow_caching_static && ($_SERVER['REQUEST_METHOD'] == 'GET' || $_SERVER['REQUEST_METHOD'] == 'HEAD')
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    && !drupal_is_cli();
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}

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/**
 * Call all init or exit hooks without including all modules.
 *
 * @param $hook
 *   The name of the bootstrap hook we wish to invoke.
 */
function bootstrap_invoke_all($hook) {
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  // _drupal_bootstrap_page_cache() already loaded the bootstrap modules, so we
  // don't need to tell module_list() to reset its bootstrap list.
  foreach (module_list(FALSE, TRUE) as $module) {
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    drupal_load('module', $module);
    module_invoke($module, $hook);
  }
}

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/**
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 * Includes a file with the provided type and name. This prevents
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 * including a theme, engine, module, etc., more than once.
 *
 * @param $type
 *   The type of item to load (i.e. theme, theme_engine, module).
 * @param $name
 *   The name of the item to load.
 *
 * @return
 *   TRUE if the item is loaded or has already been loaded.
 */
function drupal_load($type, $name) {
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  // Once a file is included this can't be reversed during a request so do not
  // use drupal_static() here.
  static $files = array();
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  if (isset($files[$type][$name])) {
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    return TRUE;
  }

  $filename = drupal_get_filename($type, $name);

  if ($filename) {
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    include_once DRUPAL_ROOT . '/' . $filename;
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    $files[$type][$name] = TRUE;

    return TRUE;
  }

  return FALSE;
}

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/**
 * Set an HTTP response header for the current page.
 *
 * Note: When sending a Content-Type header, always include a 'charset' type,
 * too. This is necessary to avoid security bugs (e.g. UTF-7 XSS).
 *
 * @param $name
 *   The HTTP header name, or a status code followed by a reason phrase, e.g.
 *   "404 Not Found".
 * @param $value
 *   The HTTP header value; if omitted, the specified header is unset.
 * @param $append
 *   Whether to append the value to an existing header or to replace it.
 */
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function drupal_add_http_header($name = NULL, $value = NULL, $append = FALSE) {
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  // The headers as name/value pairs.
  $headers = &drupal_static(__FUNCTION__, array());

  if (!isset($name)) {
    return $headers;
  }

  // Save status codes using the special key ":status".
  if (preg_match('/^\d{3} /', $name)) {
    $value = $name;
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    $name = $name_lower = ':status';
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  }
  else {
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    $name_lower = strtolower($name);
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  }
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  _drupal_set_preferred_header_name($name);
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  if (!isset($value)) {
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    $headers[$name_lower] = FALSE;
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  }
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  elseif (isset($headers[$name_lower]) && $append) {
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    // Multiple headers with identical names may be combined using comma (RFC
    // 2616, section 4.2).
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    $headers[$name_lower] .= ',' . $value;
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  }
  else {
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    $headers[$name_lower] = $value;
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  }
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  drupal_send_headers(array($name => $headers[$name_lower]), TRUE);
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}

/**
 * Get the HTTP response headers for the current page.
 *
 * @param $name
 *   An HTTP header name. If omitted, all headers are returned as name/value
 *   pairs. If an array value is FALSE, the header has been unset.
 * @return
 *   A string containing the header value, or FALSE if the header has been set,
 *   or NULL if the header has not been set.
 */
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function drupal_get_http_header($name = NULL) {
  $headers = drupal_add_http_header();
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  if (isset($name)) {
    $name = strtolower($name);
    return isset($headers[$name]) ? $headers[$name] : NULL;
  }
  else {
    return $headers;
  }
}

/**
 * Header names are case-insensitive, but for maximum compatibility they should
 * follow "common form" (see RFC 2617, section 4.2).
 */
function _drupal_set_preferred_header_name($name = NULL) {
  static $header_names = array();

  if (!isset($name)) {
    return $header_names;
  }
  $header_names[strtolower($name)] = $name;
}

/**
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 * Send the HTTP response headers previously set using drupal_add_http_header().
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 * Add default headers, unless they have been replaced or unset using
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 * drupal_add_http_header().
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 *
 * @param $default_headers
 *   An array of headers as name/value pairs.
 * @param $single
 *   If TRUE and headers have already be sent, send only the specified header.
 */
function drupal_send_headers($default_headers = array(), $only_default = FALSE) {
  $headers_sent = &drupal_static(__FUNCTION__, FALSE);
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  $headers = drupal_get_http_header();
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  if ($only_default && $headers_sent) {
    $headers = array();
  }
  $headers_sent = TRUE;

  $header_names = _drupal_set_preferred_header_name();
  foreach ($default_headers as $name => $value) {
    $name_lower = strtolower($name);
    if (!isset($headers[$name_lower])) {
      $headers[$name_lower] = $value;
      $header_names[$name_lower] = $name;
    }
  }
  foreach ($headers as $name_lower => $value) {
    if ($name_lower == ':status') {
      header($_SERVER['SERVER_PROTOCOL'] . ' ' . $value);
    }
    // Skip headers that have been unset.
    elseif ($value) {
      header($header_names[$name_lower] . ': ' . $value);
    }
  }
}

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/**
 * Set HTTP headers in preparation for a page response.
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 *
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 * Authenticated users are always given a 'no-cache' header, and will fetch a
 * fresh page on every request. This prevents authenticated users from seeing
 * locally cached pages.
 *
 * Also give each page a unique ETag. This will force clients to include both
 * an If-Modified-Since header and an If-None-Match header when doing
 * conditional requests for the page (required by RFC 2616, section 13.3.4),
 * making the validation more robust. This is a workaround for a bug in Mozilla
 * Firefox that is triggered when Drupal's caching is enabled and the user
 * accesses Drupal via an HTTP proxy (see
 * https://bugzilla.mozilla.org/show_bug.cgi?id=269303): When an authenticated
 * user requests a page, and then logs out and requests the same page again,
 * Firefox may send a conditional request based on the page that was cached
 * locally when the user was logged in. If this page did not have an ETag
 * header, the request only contains an If-Modified-Since header. The date will
 * be recent, because with authenticated users the Last-Modified header always
 * refers to the time of the request. If the user accesses Drupal via a proxy
 * server, and the proxy already has a cached copy of the anonymous page with an
 * older Last-Modified date, the proxy may respond with 304 Not Modified, making
 * the client think that the anonymous and authenticated pageviews are
 * identical.
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 *
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 * @see drupal_page_set_cache()
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 */
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function drupal_page_header() {
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  $headers_sent = &drupal_static(__FUNCTION__, FALSE);
  if ($headers_sent) {
    return TRUE;
  }
  $headers_sent = TRUE;

  $default_headers = array(
    'Expires' => 'Sun, 19 Nov 1978 05:00:00 GMT',
    'Last-Modified' => gmdate(DATE_RFC1123, REQUEST_TIME),
    'Cache-Control' => 'no-cache, must-revalidate, post-check=0, pre-check=0',
    'ETag' => '"' . REQUEST_TIME . '"',
  );
  drupal_send_headers($default_headers);
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}
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/**
 * Set HTTP headers in preparation for a cached page response.
 *
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 * The headers allow as much as possible in proxies and browsers without any
 * particular knowledge about the pages. Modules can override these headers
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 * using drupal_add_http_header().
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 *
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 * If the request is conditional (using If-Modified-Since and If-None-Match),
 * and the conditions match those currently in the cache, a 304 Not Modified
 * response is sent.
 */
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function drupal_serve_page_from_cache(stdClass $cache) {
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  // Negotiate whether to use compression.
  $page_compression = variable_get('page_compression', TRUE) && extension_loaded('zlib');
  $return_compressed = $page_compression && isset($_SERVER['HTTP_ACCEPT_ENCODING']) && strpos($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip') !== FALSE;

  // Get headers set in hook_boot(). Keys are lower-case.
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  $hook_boot_headers = drupal_get_http_header();
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  // Headers generated in this function, that may be replaced or unset using
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  // drupal_add_http_headers(). Keys are mixed-case.
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  $default_headers = array();

  foreach ($cache->headers as $name => $value) {
    // In the case of a 304 response, certain headers must be sent, and the
    // remaining may not (see RFC 2616, section 10.3.5). Do not override
    // headers set in hook_boot().
    $name_lower = strtolower($name);
    if (in_array($name_lower, array('content-location', 'expires', 'cache-control', 'vary')) && !isset($hook_boot_headers[$name_lower])) {
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      drupal_add_http_header($name, $value);
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      unset($cache->headers[$name]);
    }
  }

  // If a cache is served from a HTTP proxy without hitting the web server,
  // the boot and exit hooks cannot be fired, so only allow caching in
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  // proxies if boot hooks are disabled. If the client send a session cookie,
  // do not bother caching the page in a public proxy, because the cached copy
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  // will only be served to that particular user due to Vary: Cookie, unless
  // the Vary header has been replaced or unset in hook_boot() (see below).
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  $max_age = !variable_get('page_cache_invoke_hooks', TRUE) && (!isset($_COOKIE[session_name()]) || isset($hook_boot_headers['vary'])) ? variable_get('cache_lifetime', 0) : 0;
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  $default_headers['Cache-Control'] = 'public, max-age=' . $max_age;

  // Entity tag should change if the output changes.
  $etag = '"' . $cache->created . '-' . intval($return_compressed) . '"';
  header('Etag: ' . $etag);
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  // See if the client has provided the required HTTP headers.
  $if_modified_since = isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) ? strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) : FALSE;
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  $if_none_match = isset($_SERVER['HTTP_IF_NONE_MATCH']) ? stripslashes($_SERVER['HTTP_IF_NONE_MATCH']) : FALSE;

  if ($if_modified_since && $if_none_match
      && $if_none_match == $etag // etag must match
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      && $if_modified_since == $cache->created) {  // if-modified-since must match
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    header($_SERVER['SERVER_PROTOCOL'] . ' 304 Not Modified');
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    drupal_send_headers($default_headers);
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    return;
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  }
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  // Send the remaining headers.
  foreach ($cache->headers as $name => $value) {
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    drupal_add_http_header($name, $value);
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  }
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  $default_headers['Last-Modified'] = gmdate(DATE_RFC1123, $cache->created);
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  // HTTP/1.0 proxies does not support the Vary header, so prevent any caching
  // by sending an Expires date in the past. HTTP/1.1 clients ignores the
  // Expires header if a Cache-Control: max-age= directive is specified (see RFC
  // 2616, section 14.9.3).
  $default_headers['Expires'] = 'Sun, 19 Nov 1978 05:00:00 GMT';

  drupal_send_headers($default_headers);

  // Allow HTTP proxies to cache pages for anonymous users without a session
  // cookie. The Vary header is used to indicates the set of request-header
  // fields that fully determines whether a cache is permitted to use the
  // response to reply to a subsequent request for a given URL without
  // revalidation. If a Vary header has been set in hook_boot(), it is assumed
  // that the module knows how to cache the page.
  if (!isset($hook_boot_headers['vary']) && !variable_get('omit_vary_cookie')) {
    header('Vary: Cookie');
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  }