<?php
namespace W3TC;

// To support legacy updates with old add-ins
if ( class_exists( 'PgCache_ContentGrabber' ) )
	return;

/**
 * W3 PgCache
 */

/**
 * class PgCache
 */
class PgCache_ContentGrabber {
	/**
	 * Advanced cache config
	 */
	var $_config = null;

	/**
	 * Caching flag
	 *
	 * @var boolean
	 */
	var $_caching = false;

	/**
	 * Time start
	 *
	 * @var double
	 */
	var $_time_start = 0;

	/**
	 * Lifetime
	 *
	 * @var integer
	 */
	var $_lifetime = 0;

	/**
	 * Enhanced mode flag
	 *
	 * @var boolean
	 */
	var $_enhanced_mode = false;

	/**
	 * Debug flag
	 *
	 * @var boolean
	 */
	var $_debug = false;

	/**
	 * Request host
	 *
	 * @var string
	 */
	var $_request_host = '';

	/**
	 * Request URI
	 *
	 * @var string
	 */
	var $_request_uri = '';

	/**
	 * Page key
	 *
	 * @var string
	 */
	var $_page_key = '';

	/**
	 * Shutdown buffer
	 *
	 * @var string
	 */
	var $_shutdown_buffer = '';

	/**
	 * Mobile object
	 *
	 * @var W3_Mobile
	 */
	var $_mobile = null;

	/**
	 * Referrer object
	 *
	 * @var W3_Referrer
	 */
	var $_referrer = null;

	/**
	 * Cache reject reason
	 *
	 * @var string
	 */
	var $cache_reject_reason = '';

	/**
	 *
	 *
	 * @var If sitemap was matched
	 */
	var $_sitemap_matched;

	/**
	 *
	 *
	 * @var bool If cached page should be displayed after init
	 */
	var $_late_init = false;

	var $_cached_data = null;

	var $_old_exists = false;

	/**
	 * PHP5 Constructor
	 */
	function __construct() {
		$this->_config = Dispatcher::config();
		$this->_debug = $this->_config->get_boolean( 'pgcache.debug' );

		$request_host = Util_Environment::host();
		$this->_request_host = $request_host;

		$this->_request_uri = $_SERVER['REQUEST_URI'];
		$this->_lifetime = $this->_config->get_integer( 'pgcache.lifetime' );
		$this->_late_init = $this->_config->get_boolean( 'pgcache.late_init' );
		$this->_late_caching = $this->_config->get_boolean( 'pgcache.late_caching' );
		$this->_enhanced_mode = ( $this->_config->get_string( 'pgcache.engine' ) == 'file_generic' );

		if ( $this->_config->get_boolean( 'mobile.enabled' ) ) {
			$this->_mobile = Dispatcher::component( 'Mobile_UserAgent' );
		}

		if ( $this->_config->get_boolean( 'referrer.enabled' ) ) {
			$this->_referrer = Dispatcher::component( 'Mobile_Referrer' );
		}
	}

	/**
	 * Do cache logic
	 */
	function process() {
		/**
		 * Skip caching for some pages
		 */
		switch ( true ) {
		case defined( 'DONOTCACHEPAGE' ):
			if ( $this->_debug ) {
				self::log( 'skip processing because of DONOTCACHEPAGE constant' );
			}
			return;
		case defined( 'DOING_AJAX' ):
		case defined( 'DOING_CRON' ):
		case defined( 'APP_REQUEST' ):
		case defined( 'XMLRPC_REQUEST' ):
		case defined( 'WP_ADMIN' ):
		case ( defined( 'SHORTINIT' ) && SHORTINIT ):
			if ( $this->_debug ) {
				self::log( 'skip processing because of generic constant' );
			}
			return;
		}

		/**
		 * Do page cache logic
		 */
		if ( $this->_debug ) {
			$this->_time_start = Util_Debug::microtime();
		}

		$this->_caching = $this->_can_cache();
		global $w3_late_init;

		if ( $this->_debug ) {
			self::log( 'start, can_cache: ' .
				( $this->_caching ? 'true' : 'false' ) );
		}

		if ( $this->_caching && !$this->_late_caching ) {
			$this->_cached_data = $this->_extract_cached_page( false );
			if ( $this->_cached_data ) {
				if ( $this->_late_init ) {
					$w3_late_init = true;
					return;
				} else {
					$this->process_cached_page_and_exit( $this->_cached_data );
					// if is passes here - exit is not possible now and
					// will happen on init
					return;
				}
			} else
				$this->_late_init = false;
		} else {
			$this->_late_init = false;
		}
		$w3_late_init = $this->_late_init;
		/**
		 * Start output buffering
		 */
		Util_Bus::add_ob_callback( 'pagecache', array( $this, 'ob_callback' ) );
	}

	/**
	 * Extracts page from cache
	 *
	 * @return boolean
	 */
	function _extract_cached_page( $with_filter ) {
		$cache = $this->_get_cache();

		$mobile_group = $this->_get_mobile_group();
		$referrer_group = $this->_get_referrer_group();
		$encryption = $this->_get_encryption();
		$compression = $this->_get_compression();

		$group = '';
		$sitemap_regex = $this->_config->get_string( 'pgcache.purge.sitemap_regex' );
		if ( $sitemap_regex && preg_match( '/' . $sitemap_regex . '/', basename( $this->_request_uri ) ) ) {
			$group = 'sitemaps';
			$this->_sitemap_matched = true;
		} else {
			$this->_sitemap_matched = false;
		}

		/**
		 * Check if page is cached
		 */
		if ( !$this->_set_extract_page_key( $mobile_group, $referrer_group,
				$encryption, $compression, '', $with_filter ) ) {
			$data = null;
		} else {
			$data = $cache->get_with_old( $this->_page_key, $group );
			list( $data, $this->_old_exists ) = $data;
		}

		/**
		 * Try to get uncompressed version of cache
		 */
		if ( $compression && !$data ) {
			if ( !$this->_set_extract_page_key( $mobile_group,
					$referrer_group, $encryption, false, '', $with_filter ) ) {
				$data = null;
			} else {
				$data = $cache->get_with_old( $this->_page_key, $group );
				list( $data, $this->_old_exists ) = $data;
				$compression = false;
			}
		}

		if ( !$data ) {
			if ( $this->_debug ) {
				self::log( 'no cache entry for ' . $this->_page_key );
			}

			return null;
		}

		$data['compression'] = $compression;

		return $data;
	}



	private function _set_extract_page_key( $mobile_group, $referrer_group,
		$encryption, $compression, $content_type = '', $with_filter ) {
		$this->_page_key = $this->_get_page_key( $mobile_group, $referrer_group,
			$encryption, $compression, $content_type );

		if ( $with_filter ) {
			// return empty value if caching should not happen
			$this->_page_key = apply_filters( 'w3tc_page_extract_key',
				$this->_page_key );
		}

		if ( !empty( $this->_page_key ) )
			return true;

		$this->caching = false;
		$this->cache_reject_reason =
			'w3tc_page_extract_key filter result forced not to cache';

		return false;
	}



	/**
	 * Process extracted cached pages
	 *
	 * @param unknown $data
	 */
	private function process_cached_page_and_exit( $data ) {
		/**
		 * Do Bad Behavior check
		 */
		$this->_bad_behavior();

		$is_404 = $data['404'];
		$headers = $data['headers'];
		$content = $data['content'];
		$has_dynamic = isset( $data['has_dynamic'] ) && $data['has_dynamic'];
		$etag = md5( $content );

		if ( $has_dynamic ) {
			// its last modification date is now, and any compression
			// browser wants cant be used, since its compressed now
			$time = time();
			$compression = $this->_get_compression();
		} else {
			$time = $data['time'];
			$compression = $data['compression'];
		}

		/**
		 * Send headers
		 */
		$this->_send_headers( $is_404, $time, $etag, $compression, $headers );
		if ( isset( $_SERVER['REQUEST_METHOD'] ) && $_SERVER['REQUEST_METHOD'] == 'HEAD' )
			return;

		// parse dynamic content and compress if it's dynamic page with mfuncs
		if ( $has_dynamic ) {
			$content = $this->_parse_dynamic( $content );
			$content = $this->_compress( $content, $compression );
		}

		echo $content;
		Dispatcher::usage_statistics_apply_before_init_and_exit( array( $this,
				'w3tc_usage_statistics_of_request' ) );
	}

	/**
	 * Output buffering callback
	 *
	 * @param string  $buffer
	 * @return string
	 */
	function ob_callback( $buffer ) {
		if ( !$this->_is_cacheable_content_type() ) {
			if ( $this->_debug )
				self::log( 'storing cached page - not a cached content' );

			return $buffer;
		}

		$compression = false;
		$has_dynamic = $this->_has_dynamic( $buffer );
		$original_can_cache = $this->_can_cache2( $buffer );
		$can_cache = apply_filters( 'w3tc_can_cache', $original_can_cache, $this, $buffer );
		if ( $can_cache != $original_can_cache )
			$this->cache_reject_reason = 'Third-party plugin has modified caching activity';
		if ( $this->_debug ) {
			self::log( 'storing cached page: ' .
				( $can_cache ? 'true' : 'false' ) .
				' original ' . ( $this->_caching ? ' true' : 'false' ) .
				' reason ' . $this->cache_reject_reason );
		}

		if ( $can_cache ) {
			$buffer = $this->_maybe_save_cached_result( $buffer, $has_dynamic );
		} else {
			if ( $has_dynamic ) {
				// send common headers since output will be compressed
				$compression_header = $this->_get_compression();
				if ( defined( 'W3TC_PAGECACHE_OUTPUT_COMPRESSION_OFF' ) )
					$compression_header = false;
				$headers = $this->_get_common_headers( $compression_header );
				$this->_headers( $headers );
			}

			// remove cached entries if its not cached anymore
			if ( $this->cache_reject_reason ) {
				if ( $this->_old_exists ) {
					$cache = $this->_get_cache();

					$mobile_group = $this->_get_mobile_group();
					$referrer_group = $this->_get_referrer_group();
					$encryption = $this->_get_encryption();
					$compressions_to_store = $this->_get_compressions();
					$content_type = '';

					foreach ( $compressions_to_store as $_compression ) {
						$_page_key = $this->_get_page_key( $mobile_group,
							$referrer_group, $encryption, $_compression,
							$content_type );
						$cache->hard_delete( $_page_key );
					}
				}
			}
		}

		/**
		 * We can't capture output in ob_callback
		 * so we use shutdown function
		 */
		if ( $has_dynamic ) {
			$this->_shutdown_buffer = $buffer;

			$buffer = '';

			register_shutdown_function( array(
					$this,
					'shutdown'
				) );
		}

		return $buffer;
	}

	/**
	 * Shutdown callback
	 *
	 * @return void
	 */
	public function shutdown() {
		$compression = $this->_get_compression();

		// Parse dynamic content
		$buffer = $this->_parse_dynamic( $this->_shutdown_buffer );

		// Compress page according to headers already set
		echo $this->_compress( $buffer, $compression );
	}

	/**
	 * Checks if can we do cache logic
	 *
	 * @return boolean
	 */
	private function _can_cache() {
		/**
		 * Don't cache in console mode
		 */
		if ( PHP_SAPI === 'cli' ) {
			$this->cache_reject_reason = 'Console mode';

			return false;
		}

		/**
		 * Skip if session defined
		 */
		if ( defined( 'SID' ) && SID != '' ) {
			$this->cache_reject_reason = 'Session started';

			return false;
		}

		if ( !$this->_config->get_boolean('pgcache.cache.ssl') && Util_Environment::is_https() ) {
            $this->cache_reject_reason = 'SSL caching disabled';

        	return false;
        }

		/**
		 * Skip if posting
		 */
		if ( isset( $_SERVER['REQUEST_METHOD'] ) && in_array( strtoupper( $_SERVER['REQUEST_METHOD'] ), array( 'DELETE', 'PUT', 'OPTIONS', 'TRACE', 'CONNECT', 'POST' ) ) ) {
			$this->cache_reject_reason = sprintf( 'Requested method is %s', $_SERVER['REQUEST_METHOD'] );

			return false;
		}

		/**
		 * Skip if HEAD request
		 */
		if ( isset( $_SERVER['REQUEST_METHOD'] ) && strtoupper( $_SERVER['REQUEST_METHOD'] ) == 'HEAD' &&
			( $this->_enhanced_mode || $this->_config->get_boolean( 'pgcache.reject.request_head' ) ) ) {
			$this->cache_reject_reason = 'Requested method is HEAD';

			return false;
		}

		/**
		 * Skip if there is query in the request uri
		 */
		if ( !$this->_check_query_string() &&
			( !$this->_config->get_boolean( 'pgcache.cache.query' ) ||
				$this->_config->get_string( 'pgcache.engine' ) == 'file_generic' ) &&
			strstr( $this->_request_uri, '?' ) !== false ) {
			$this->cache_reject_reason = 'Requested URI contains query';

			return false;
		}

		/**
		 * Check request URI
		 */
		if ( !in_array( $_SERVER['PHP_SELF'], $this->_config->get_array( 'pgcache.accept.files' ) ) && !$this->_check_request_uri() ) {
			$this->cache_reject_reason = 'Requested URI is rejected';

			return false;
		}

		/**
		 * Check User Agent
		 */
		if ( !$this->_check_ua() ) {
			$this->cache_reject_reason = 'User agent is rejected';

			return false;
		}

		/**
		 * Check WordPress cookies
		 */
		if ( !$this->_check_cookies() ) {
			$this->cache_reject_reason = 'Cookie is rejected';

			return false;
		}

		/**
		 * Skip if user is logged in or user role is logged in
		 */
		if ( $this->_config->get_boolean( 'pgcache.reject.logged' ) ) {
			if ( !$this->_check_logged_in() ) {
				$this->cache_reject_reason = 'User is logged in';
				return false;
			}
		} else {
			if ( !$this->_check_logged_in_role_allowed() ) {
				$this->cache_reject_reason = 'Rejected user role is logged in';
				return false;
			}
		}

		return true;
	}

	/**
	 * Checks if can we do cache logic
	 *
	 * @param string  $buffer
	 * @return boolean
	 */
	private function _can_cache2( $buffer ) {
		/**
		 * Skip if caching is disabled
		 */
		if ( !$this->_caching ) {
			return false;
		}

		/**
		 * Check for database error
		 */
		if ( Util_Content::is_database_error( $buffer ) ) {
			$this->cache_reject_reason = 'Database error occurred';

			return false;
		}

		/**
		 * Check for DONOTCACHEPAGE constant
		 */
		if ( defined( 'DONOTCACHEPAGE' ) && DONOTCACHEPAGE ) {
			$this->cache_reject_reason = 'DONOTCACHEPAGE constant is defined';

			return false;
		}

		/**
		 * Don't cache 404 pages
		 */
		if ( !$this->_config->get_boolean( 'pgcache.cache.404' ) && function_exists( 'is_404' ) && is_404() ) {
			$this->cache_reject_reason = 'Page is 404';

			return false;
		}

		/**
		 * Don't cache homepage
		 */
		if ( !$this->_config->get_boolean( 'pgcache.cache.home' ) && function_exists( 'is_home' ) && is_home() ) {
			$this->cache_reject_reason = is_front_page() && is_home() ? 'Page is front page' : 'Page is posts page';

			return false;
		}

		/**
		 * Don't cache front page
		 */
		if ( $this->_config->get_boolean( 'pgcache.reject.front_page' ) && function_exists( 'is_front_page' ) && is_front_page() && !is_home() ) {
			$this->cache_reject_reason = 'Page is front page';

			return false;
		}

		/**
		 * Don't cache feed
		 */
		if ( !$this->_config->get_boolean( 'pgcache.cache.feed' ) && function_exists( 'is_feed' ) && is_feed() ) {
			$this->cache_reject_reason = 'Page is feed';

			return false;
		}

		/**
		 * Check if page contains dynamic tags
		 */
		if ( $this->_enhanced_mode && $this->_has_dynamic( $buffer ) ) {
			$this->cache_reject_reason = 'Page contains dynamic tags (mfunc or mclude) can not be cached in enhanced mode';

			return false;
		}

		return true;
	}

	public function get_cache_stats_size( $timeout_time ) {
		$cache = $this->_get_cache();
		if ( method_exists( $cache, 'get_stats_size' ) )
			return $cache->get_stats_size( $timeout_time );

		return null;
	}

	public function get_usage_statistics_cache_config() {
		$engine = $this->_config->get_string( 'pgcache.engine' );

		switch ( $engine ) {
		case 'memcached':
			$engineConfig = array(
				'servers' => $this->_config->get_array( 'pgcache.memcached.servers' ),
				'persistent' => $this->_config->get_boolean( 'pgcache.memcached.persistent' ),
				'aws_autodiscovery' => $this->_config->get_boolean( 'pgcache.memcached.aws_autodiscovery' ),
				'username' => $this->_config->get_string( 'pgcache.memcached.username' ),
				'password' => $this->_config->get_string( 'pgcache.memcached.password' )
			);
			break;

		case 'redis':
			$engineConfig = array(
				'servers' => $this->_config->get_array( 'pgcache.redis.servers' ),
				'persistent' => $this->_config->get_boolean( 'pgcache.redis.persistent' ),
				'dbid' => $this->_config->get_integer( 'pgcache.redis.dbid' ),
				'password' => $this->_config->get_string( 'pgcache.redis.password' )
			);
			break;

		case 'file_generic':
			$engine = 'file';
			break;

		default:
			$engineConfig = array();
		}

		$engineConfig['engine'] = $engine;
		return $engineConfig;
	}

	/**
	 * Returns cache object
	 *
	 * @return W3_Cache_Base
	 */
	function _get_cache() {
		static $cache = null;

		if ( is_null( $cache ) ) {
			$engine = $this->_config->get_string( 'pgcache.engine' );

			switch ( $engine ) {
			case 'memcached':
				$engineConfig = array(
					'servers' => $this->_config->get_array( 'pgcache.memcached.servers' ),
					'persistent' => $this->_config->get_boolean( 'pgcache.memcached.persistent' ),
					'aws_autodiscovery' => $this->_config->get_boolean( 'pgcache.memcached.aws_autodiscovery' ),
					'username' => $this->_config->get_string( 'pgcache.memcached.username' ),
					'password' => $this->_config->get_string( 'pgcache.memcached.password' )
				);
				break;

			case 'redis':
				$engineConfig = array(
					'servers' => $this->_config->get_array( 'pgcache.redis.servers' ),
					'persistent' => $this->_config->get_boolean( 'pgcache.redis.persistent' ),
					'dbid' => $this->_config->get_integer( 'pgcache.redis.dbid' ),
					'password' => $this->_config->get_string( 'pgcache.redis.password' )
				);
				break;

			case 'file':
				$engineConfig = array(
					'section' => 'page',
					'flush_parent' => ( Util_Environment::blog_id() == 0 ),
					'locking' => $this->_config->get_boolean( 'pgcache.file.locking' ),
					'flush_timelimit' => $this->_config->get_integer( 'timelimit.cache_flush' )
				);
				break;

			case 'file_generic':
				if ( Util_Environment::blog_id() == 0 )
					$flush_dir = W3TC_CACHE_PAGE_ENHANCED_DIR;
				else
					$flush_dir = W3TC_CACHE_PAGE_ENHANCED_DIR . '/' . Util_Environment::host();

				$engineConfig = array(
					'exclude' => array(
						'.htaccess'
					),
					'expire' => $this->_lifetime,
					'cache_dir' => W3TC_CACHE_PAGE_ENHANCED_DIR,
					'locking' => $this->_config->get_boolean( 'pgcache.file.locking' ),
					'flush_timelimit' => $this->_config->get_integer( 'timelimit.cache_flush' ),
					'flush_dir' => $flush_dir,
				);
				break;

			default:
				$engineConfig = array();
			}

			$engineConfig['use_expired_data'] = true;
			$engineConfig['module'] = 'pgcache';
			$engineConfig['host'] = '';   // host is always put to a key
			$engineConfig['instance_id'] = Util_Environment::instance_id();

			$cache = Cache::instance( $engine, $engineConfig );
		}

		return $cache;
	}

	/**
	 * Checks request URI
	 *
	 * @return boolean
	 */
	function _check_request_uri() {
		$auto_reject_uri = array(
			'wp-login',
			'wp-register'
		);

		foreach ( $auto_reject_uri as $uri ) {
			if ( strstr( $this->_request_uri, $uri ) !== false ) {
				return false;
			}
		}

		$reject_uri = $this->_config->get_array( 'pgcache.reject.uri' );
		$reject_uri = array_map( array( '\W3TC\Util_Environment', 'parse_path' ), $reject_uri );

		foreach ( $reject_uri as $expr ) {
			$expr = trim( $expr );
			if ( $expr != '' && preg_match( '~' . $expr . '~i', $this->_request_uri ) ) {
				return false;
			}
		}

		return true;
	}

	/**
	 * Checks User Agent
	 *
	 * @return boolean
	 */
	function _check_ua() {
		$uas = $this->_config->get_array( 'pgcache.reject.ua' );

		$uas = array_merge( $uas, array( W3TC_POWERED_BY ) );

		foreach ( $uas as $ua ) {
			if ( !empty( $ua ) ) {
				if ( isset( $_SERVER['HTTP_USER_AGENT'] ) &&
					stristr( $_SERVER['HTTP_USER_AGENT'], $ua ) !== false )
					return false;
			}
		}

		return true;
	}

	/**
	 * Checks WordPress cookies
	 *
	 * @return boolean
	 */
	function _check_cookies() {
		foreach ( array_keys( $_COOKIE ) as $cookie_name ) {
			if ( $cookie_name == 'wordpress_test_cookie' ) {
				continue;
			}
			if ( preg_match( '/^(wp-postpass|comment_author)/', $cookie_name ) ) {
				return false;
			}
		}

		foreach ( $this->_config->get_array( 'pgcache.reject.cookie' ) as $reject_cookie ) {
			if ( !empty( $reject_cookie ) ) {
				foreach ( array_keys( $_COOKIE ) as $cookie_name ) {
					if ( strstr( $cookie_name, $reject_cookie ) !== false ) {
						return false;
					}
				}
			}
		}

		return true;
	}

	/**
	 * Check if user is logged in
	 *
	 * @return boolean
	 */
	function _check_logged_in() {
		foreach ( array_keys( $_COOKIE ) as $cookie_name ) {
			if ( strpos( $cookie_name, 'wordpress_logged_in' ) === 0 )
				return false;
		}

		return true;
	}

	/**
	 * Check if logged in user role is allwed to be cached
	 *
	 * @return boolean
	 */
	function _check_logged_in_role_allowed() {
		if ( !$this->_config->get_boolean( 'pgcache.reject.logged_roles' ) )
			return true;
		$roles = $this->_config->get_array( 'pgcache.reject.roles' );

		if ( empty( $roles ) )
			return true;

		foreach ( array_keys( $_COOKIE ) as $cookie_name ) {
			if ( strpos( $cookie_name, 'w3tc_logged_' ) === 0 ) {
				foreach ( $roles as $role ) {
					if ( strstr( $cookie_name, md5( NONCE_KEY . $role ) ) )
						return false;
				}
			}
		}

		return true;
	}

	/**
	 * Checks if rules file present and creates it if not
	 */
	function _check_rules_present() {
		if ( Util_Environment::is_nginx() )
			return;   // nginx store it in a single file

		$filename = Util_Rule::get_pgcache_rules_cache_path();
		if ( file_exists( $filename ) )
			return;

		// we call it as little times as possible
		// its expensive, but have to restore lost .htaccess file
		$e = Dispatcher::component( 'PgCache_Environment' );
		try {
			$e->fix_on_wpadmin_request( $this->_config, true );
		} catch ( \Exception $ex ) {
		}
	}

	/**
	 * Compress data
	 *
	 * @param string  $data
	 * @param string  $compression
	 * @return string
	 */
	function _compress( $data, $compression ) {
		switch ( $compression ) {
		case 'gzip':
			$data = gzencode( $data );
			break;

		case 'deflate':
			$data = gzdeflate( $data );
			break;
		}

		return $data;
	}

	/**
	 * Returns current mobile group
	 *
	 * @return string
	 */
	function _get_mobile_group() {
		if ( $this->_mobile ) {
			return $this->_mobile->get_group();
		}

		return '';
	}

	/**
	 * Returns current referrer group
	 *
	 * @return string
	 */
	function _get_referrer_group() {
		if ( $this->_referrer ) {
			return $this->_referrer->get_group();
		}

		return '';
	}

	/**
	 * Returns current encryption
	 *
	 * @return string
	 */
	function _get_encryption() {
		if ( Util_Environment::is_https() ) {
			return 'ssl';
		}

		return '';
	}

	/**
	 * Returns current compression
	 *
	 * @return boolean
	 */
	function _get_compression() {
		if ( $this->_debug )   // cannt generate/use compressed files during debug mode
			return false;

		if ( !Util_Environment::is_zlib_enabled() && !$this->_is_buggy_ie() ) {
			$compressions = $this->_get_compressions();

			foreach ( $compressions as $compression ) {
				if ( is_string( $compression ) &&
					isset( $_SERVER['HTTP_ACCEPT_ENCODING'] ) &&
					stristr( $_SERVER['HTTP_ACCEPT_ENCODING'], $compression ) !== false ) {
					return $compression;
				}
			}
		}

		return false;
	}

	/**
	 * Returns array of compressions
	 *
	 * @return array
	 */
	function _get_compressions() {
		$compressions = array(
			false
		);

		if ( $this->_config->get_boolean( 'browsercache.enabled' ) &&
			$this->_config->get_boolean( 'browsercache.html.compression' ) &&
			function_exists( 'gzencode' ) ) {
			$compressions[] = 'gzip';
		}

		return $compressions;
	}

	/**
	 * Returns array of response headers
	 *
	 * @return array
	 */
	function _get_response_headers() {
		$headers_kv = array();
		$headers_plain = array();

		if ( function_exists( 'headers_list' ) ) {
			$headers_list = headers_list();
			if ( $headers_list ) {
				foreach ( $headers_list as $header ) {
					$pos = strpos( $header, ':' );
					if ( $pos ) {
						$header_name = substr( $header, 0, $pos );
						$header_value = substr( $header, $pos + 1 );
					} else {
						$header_name = $header;
						$header_value = '';
					}
					$headers_kv[$header_name] = $header_value;
					$headers_plain[] = array(
						'name' => $header_name,
						'value' => $header_value
					);
				}
			}
		}

		return array(
			'kv' => $headers_kv,
			'plain' => $headers_plain
		);
	}

	/**
	 * Checks for buggy IE6 that doesn't support compression
	 *
	 * @return boolean
	 */
	function _is_buggy_ie() {
		if ( isset( $_SERVER['HTTP_USER_AGENT'] ) ) {
			$ua = $_SERVER['HTTP_USER_AGENT'];

			if ( strpos( $ua, 'Mozilla/4.0 (compatible; MSIE ' ) === 0 && strpos( $ua, 'Opera' ) === false ) {
				$version = (float) substr( $ua, 30 );

				return $version < 6 || ( $version == 6 && strpos( $ua, 'SV1' ) === false );
			}
		}

		return false;
	}

	/**
	 * Returns array of data headers
	 *
	 * @return array
	 */
	function _get_cached_headers( $response_headers ) {
		$data_headers = array();
		$cache_headers = array_merge(
			array( 'Location' ),
			$this->_config->get_array( 'pgcache.cache.headers' )
		);

		if ( function_exists( 'http_response_code' ) ) {   // php5.3 compatibility
			$data_headers['Status-Code'] = http_response_code();
		}

		$repeating_headers = array(
			'link',
			'cookie',
			'set-cookie'
		);
		$repeating_headers = apply_filters( 'w3tc_repeating_headers',
			$repeating_headers );

		foreach ( $response_headers as $i ) {
			$header_name = $i['name'];
			$header_value = $i['value'];

			foreach ( $cache_headers as $cache_header_name ) {
				if ( strcasecmp( $header_name, $cache_header_name ) == 0 ) {
					$header_name_lo = strtolower( $header_name );
					if ( in_array($header_name_lo, $repeating_headers) ) {
						// headers may repeat
						$data_headers[] = array(
							'n' => $header_name,
							'v' => $header_value
						);
					} else {
						$data_headers[$header_name] = $header_value;
					}
				}
			}
		}

		return $data_headers;
	}

	/**
	 * Returns page key
	 *
	 * @param string  $mobile_group
	 * @param string  $referrer_group
	 * @param string  $encryption
	 * @param string  $compression
	 * @param string  $content_type
	 * @param string  $request_uri
	 * @return string
	 */
	function _get_page_key( $mobile_group = '', $referrer_group = '',
		$encryption = '', $compression = '', $content_type = '', $request_url = '' ) {

		if ( $request_url ) {
			$parts = parse_url( $request_url );
			$key = $parts['host'] .
				( isset( $parts['path'] ) ? $parts['path'] : '' ) .
				( isset( $parts['query'] ) ? '?' . $parts['query'] : '' );
		} else
			$key = $this->_request_host . $this->_request_uri;

		// replace fragment
		$key = preg_replace( '~#.*$~', '', $key );
		$key = strtolower( $key );   // host/uri in different cases means the same page in wp

		if ( $this->_enhanced_mode ) {
			// URL decode
			$key = urldecode( $key );

			// replace double slashes
			$key = preg_replace( '~[/\\\]+~', '/', $key );

			// replace query string
			$key = preg_replace( '~\?.*$~', '', $key );

			// replace index.php
			$key = str_replace( '/index.php', '/', $key );

			// trim slash
			$key = ltrim( $key, '/' );

			if ( $key && substr( $key, -1 ) != '/' ) {
				$key .= '/';
			}

			$key .= '_index';
		} else {
			if ( $this->_check_query_string() )
				// replace query string
				$key = preg_replace( '~\?.*$~', '', $key );

			$key = md5( $key );
		}

		/**
		 * Append mobile group
		 */
		if ( $mobile_group ) {
			$key .= '_' . $mobile_group;
		}

		/**
		 * Append referrer group
		 */
		if ( $referrer_group ) {
			$key .= '_' . $referrer_group;
		}

		/**
		 * Append encryption
		 */
		if ( $encryption ) {
			$key .= '_' . $encryption;
		}

		if ( Util_Environment::is_preview_mode() ) {
			$key .= '_preview';
		}

		if ( $this->_enhanced_mode ) {
			/**
			 * Append HTML extension.
			 * For nginx - we create .xml cache entries and redirect to them
			 */
			if ( Util_Environment::is_nginx() && substr( $content_type, 0, 8 ) == 'text/xml' &&
				$this->_config->get_boolean( 'pgcache.cache.nginx_handle_xml' ) )
				$key .= '.xml';
			else
				$key .= '.html';
		}

		/**
		 * Append compression
		 */
		if ( $compression ) {
			$key .= '_' . $compression;
		}

		return $key;
	}

	/**
	 * Returns debug info
	 *
	 * @param boolean $cache
	 * @param string  $reason
	 * @param boolean $status
	 * @param double  $time
	 * @return string
	 */
	public function w3tc_footer_comment( $strings ) {
		$strings[] = sprintf(
			__( 'Page Caching using %s%s', 'w3-total-cache' ),
			Cache::engine_name( $this->_config->get_string( 'pgcache.engine' ) ),
			( $this->cache_reject_reason != ''
				? sprintf( ' (%s)', $this->cache_reject_reason )
				: '' ) );


		if ( $this->_debug ) {
			$time_total = Util_Debug::microtime() - $this->_time_start;
			$engine = $this->_config->get_string( 'pgcache.engine' );
			$strings[] = "Page cache debug info:";
			$strings[] = sprintf( "%s%s", str_pad( 'Engine: ', 20 ), Cache::engine_name( $engine ) );
			$strings[] = sprintf( "%s%s", str_pad( 'Cache key: ', 20 ), $this->_page_key );

			if ( $this->cache_reject_reason != '' ) {
				$strings[] = sprintf( "%s%s", str_pad( 'Reject reason: ', 20 ),
					$this->cache_reject_reason );
			}

			$strings[] = sprintf( "%s%.3fs", str_pad( 'Creation Time: ', 20 ), time() );

			$headers = $this->_get_response_headers();

			if ( count( $headers['plain'] ) ) {
				$strings[] = "Header info:";

				foreach ( $headers['plain'] as $i ) {
					$strings[] = sprintf( "%s%s",
						str_pad( $i['name'] . ': ', 20 ),
						Util_Content::escape_comment( $i['value'] ) );
				}
			}
		}

		return $strings;
	}

	/**
	 * Sends headers
	 *
	 * @param array   $headers
	 * @return boolean
	 */
	function _headers( $headers ) {
		if ( headers_sent() )
			return false;

		$repeating = array();
		// headers are sent as name->value and array(n=>, v=>)
		// to support repeating headers
		foreach ( $headers as $name0 => $value0 ) {
			if ( isset( $value0['n'] ) ) {
				$name = $value0['n'];
				$value = $value0['v'];
			} else {
				$name = $name0;
				$value = $value0;
			}

			if ( $name == 'Status' ) {
				@header( $headers['Status'] );
			} elseif ( $name == 'Status-Code' ) {
				if ( function_exists( 'http_response_code' ) )   // php5.3 compatibility)
					@http_response_code( $headers['Status-Code'] );
			} else {
				@header( $name . ': ' . $value, !isset( $repeating[$name] ) );
				$repeating[$name] = true;
			}
		}

		return true;
	}

	/**
	 * Sends headers
	 *
	 * @param boolean $is_404
	 * @param string  $etag
	 * @param integer $time
	 * @param string  $compression
	 * @param array   $custom_headers
	 * @return boolean
	 */
	function _send_headers( $is_404, $time, $etag, $compression, $custom_headers = array() ) {
		$exit = false;
		$headers = ( is_array( $custom_headers ) ? $custom_headers : array() );
		$curr_time = time();

		$bc_lifetime = $this->_config->get_integer(
			'browsercache.html.lifetime' );

		$expires = ( is_null( $time ) ? $curr_time : $time ) + $bc_lifetime;
		$max_age = ( $expires > $curr_time ? $expires - $curr_time : 0 );

		if ( $is_404 ) {
			/**
			 * Add 404 header
			 */
			$headers['Status'] = 'HTTP/1.1 404 Not Found';
		} elseif ( ( !is_null( $time ) && $this->_check_modified_since( $time ) ) || $this->_check_match( $etag ) ) {
			/**
			 * Add 304 header
			 */
			$headers['Status'] = 'HTTP/1.1 304 Not Modified';

			/**
			 * Don't send content if it isn't modified
			 */
			$exit = true;
		}

		if ( $this->_config->get_boolean( 'browsercache.enabled' ) ) {

			if ( $this->_config->get_boolean( 'browsercache.html.last_modified' ) ) {
				$headers['Last-Modified'] = Util_Content::http_date( $time );
			}

			if ( $this->_config->get_boolean( 'browsercache.html.expires' ) ) {
				$headers['Expires'] = Util_Content::http_date( $expires );
			}

			if ( $this->_config->get_boolean( 'browsercache.html.cache.control' ) ) {
				switch ( $this->_config->get_string( 'browsercache.html.cache.policy' ) ) {
				case 'cache':
					$headers['Pragma'] = 'public';
					$headers['Cache-Control'] = 'public';
					break;

				case 'cache_public_maxage':
					$headers['Pragma'] = 'public';
					$headers['Cache-Control'] = sprintf( 'max-age=%d, public', $max_age );
					break;

				case 'cache_validation':
					$headers['Pragma'] = 'public';
					$headers['Cache-Control'] = 'public, must-revalidate, proxy-revalidate';
					break;

				case 'cache_noproxy':
					$headers['Pragma'] = 'public';
					$headers['Cache-Control'] = 'private, must-revalidate';
					break;

				case 'cache_maxage':
					$headers['Pragma'] = 'public';
					$headers['Cache-Control'] = sprintf( 'max-age=%d, public, must-revalidate, proxy-revalidate', $max_age );
					break;

				case 'no_cache':
					$headers['Pragma'] = 'no-cache';
					$headers['Cache-Control'] = 'max-age=0, private, no-store, no-cache, must-revalidate';
					break;
				}
			}

			if ( $this->_config->get_boolean( 'browsercache.html.etag' ) ) {
				$headers['ETag'] = '"' . $etag . '"';
			}
		}


		$headers = array_merge( $headers,
			$this->_get_common_headers( $compression ) );

		/**
		 * Send headers to client
		 */
		$result = $this->_headers( $headers );

		if ( $exit )
			exit();

		return $result;
	}

	/**
	 * Returns headers to send regardless is page caching is active
	 */
	function _get_common_headers( $compression ) {
		$headers = array();

		if ( $this->_config->get_boolean( 'browsercache.enabled' ) ) {
			if ( $this->_config->get_boolean( 'browsercache.html.w3tc' ) ) {
				$headers['X-Powered-By'] = Util_Environment::w3tc_header();
			}
		}

		$vary = '';
		//compressed && UAG
		if ( $compression && $this->_get_mobile_group() ) {
			$vary = 'Accept-Encoding,User-Agent,Cookie';
			$headers['Content-Encoding'] = $compression;
			//compressed
		} elseif ( $compression ) {
			$vary = 'Accept-Encoding';
			$headers['Content-Encoding'] = $compression;
			//uncompressed && UAG
		} elseif ( $this->_get_mobile_group() ) {
			$vary = 'User-Agent,Cookie';
		}

		//Add Cookie to vary if user logged in and not previously set
		if ( !$this->_check_logged_in() && strpos( $vary, 'Cookie' ) === false ) {
			if ( $vary )
				$vary .= ',Cookie';
			else
				$vary = 'Cookie';
		}

		/**
		 * Add vary header
		 */
		if ( $vary )
			$headers['Vary'] = $vary;

		/**
		 * Disable caching for preview mode
		 */
		if ( Util_Environment::is_preview_mode() ) {
			$headers['Pragma'] = 'private';
			$headers['Cache-Control'] = 'private';
		}

		return $headers;
	}

	/**
	 * Check if content was modified by time
	 *
	 * @param integer $time
	 * @return boolean
	 */
	function _check_modified_since( $time ) {
		if ( !empty( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) ) {
			$if_modified_since = $_SERVER['HTTP_IF_MODIFIED_SINCE'];

			// IE has tacked on extra data to this header, strip it
			if ( ( $semicolon = strrpos( $if_modified_since, ';' ) ) !== false ) {
				$if_modified_since = substr( $if_modified_since, 0, $semicolon );
			}

			return $time == strtotime( $if_modified_since );
		}

		return false;
	}

	/**
	 * Check if content was modified by etag
	 *
	 * @param string  $etag
	 * @return boolean
	 */
	function _check_match( $etag ) {
		if ( !empty( $_SERVER['HTTP_IF_NONE_MATCH'] ) ) {
			$if_none_match = ( get_magic_quotes_gpc() ? stripslashes( $_SERVER['HTTP_IF_NONE_MATCH'] ) : $_SERVER['HTTP_IF_NONE_MATCH'] );
			$client_etags = explode( ',', $if_none_match );

			foreach ( $client_etags as $client_etag ) {
				$client_etag = trim( $client_etag );

				if ( $etag == $client_etag ) {
					return true;
				}
			}
		}

		return false;
	}

	/**
	 * Bad Behavior support
	 *
	 * @return void
	 */
	function _bad_behavior() {
		$bb_file = $this->_config->get_string( 'pgcache.bad_behavior_path' );
		if ( $bb_file != '' )
			require_once $bb_file;
	}

	/**
	 * Parses dynamic tags
	 */
	function _parse_dynamic( $buffer ) {
		if ( !defined( 'W3TC_DYNAMIC_SECURITY' ) )
			return $buffer;

		$buffer = preg_replace_callback( '~<!--\s*mfunc\s*' . W3TC_DYNAMIC_SECURITY . '(.*)-->(.*)<!--\s*/mfunc\s*' . W3TC_DYNAMIC_SECURITY . '\s*-->~Uis', array(
				$this,
				'_parse_dynamic_mfunc'
			), $buffer );

		$buffer = preg_replace_callback( '~<!--\s*mclude\s*' . W3TC_DYNAMIC_SECURITY . '(.*)-->(.*)<!--\s*/mclude\s*' . W3TC_DYNAMIC_SECURITY . '\s*-->~Uis', array(
				$this,
				'_parse_dynamic_mclude'
			), $buffer );

		return $buffer;
	}

	/**
	 * Parse dynamic mfunc callback
	 *
	 * @param array   $matches
	 * @return string
	 */
	function _parse_dynamic_mfunc( $matches ) {
		$code1 = trim( $matches[1] );
		$code2 = trim( $matches[2] );
		$code = ( $code1 ? $code1 : $code2 );

		if ( $code ) {
			$code = trim( $code, ';' ) . ';';

			try {
				ob_start();
				$result = eval( $code );
				$output = ob_get_contents();
				ob_end_clean();
			} catch ( \Exception $ex ) {
				$result = false;
			}

			if ( $result === false ) {
				$output = sprintf( 'Unable to execute code: %s', htmlspecialchars( $code ) );
			}
		} else {
			$output = htmlspecialchars( 'Invalid mfunc tag syntax. The correct format is: <!-- W3TC_DYNAMIC_SECURITY mfunc PHP code --><!-- /mfunc W3TC_DYNAMIC_SECURITY --> or <!-- W3TC_DYNAMIC_SECURITY mfunc -->PHP code<!-- /mfunc W3TC_DYNAMIC_SECURITY -->.' );
		}

		return $output;
	}

	/**
	 * Parse dynamic mclude callback
	 *
	 * @param array   $matches
	 * @return string
	 */
	function _parse_dynamic_mclude( $matches ) {
		$file1 = trim( $matches[1] );
		$file2 = trim( $matches[2] );

		$file = ( $file1 ? $file1 : $file2 );

		if ( $file ) {
			$file = ABSPATH . $file;

			if ( file_exists( $file ) && is_readable( $file ) ) {
				ob_start();
				include $file;
				$output = ob_get_contents();
				ob_end_clean();
			} else {
				$output = sprintf( 'Unable to open file: %s', htmlspecialchars( $file ) );
			}
		} else {
			$output = htmlspecialchars( 'Incorrect mclude tag syntax. The correct format is: <!-- mclude W3TC_DYNAMIC_SECURITY path/to/file.php --><!-- /mclude W3TC_DYNAMIC_SECURITY --> or <!-- mclude W3TC_DYNAMIC_SECURITY -->path/to/file.php<!-- /mclude W3TC_DYNAMIC_SECURITY -->.' );
		}

		return $output;
	}

	/**
	 * Checks if buffer has dynamic tags
	 *
	 * @param string  $buffer
	 * @return boolean
	 */
	function _has_dynamic( $buffer ) {
		if ( !defined( 'W3TC_DYNAMIC_SECURITY' ) )
			return false;

		return preg_match( '~<!--\s*m(func|clude)\s*' . W3TC_DYNAMIC_SECURITY . '(.*)-->(.*)<!--\s*/m(func|clude)\s*' . W3TC_DYNAMIC_SECURITY . '\s*-->~Uis', $buffer );
	}

	/**
	 * Check whether requested page has content type that can be cached
	 *
	 * @return bool
	 */
	private function _is_cacheable_content_type() {
		$content_type = '';
		$headers = headers_list();
		foreach ( $headers as $header ) {
			$header = strtolower( $header );
			if ( stripos( $header, 'content-type' ) !== false ) {
				$temp = explode( ';', $header );
				$temp = array_shift( $temp );
				$temp = explode( ':', $temp );
				$content_type = trim( $temp[1] );
			}
		}

		$cache_headers = apply_filters( 'w3tc_is_cacheable_content_type',
			array(
				'' /* redirects, they have only Location header set */,
				'application/json', 'text/html', 'text/xml',
				'application/xhtml+xml'
			)
		);
		return in_array( $content_type, $cache_headers );
	}

	private function _check_query_string() {
		$accept_qs = $this->_config->get_array( 'pgcache.accept.qs' );
		foreach ( $_GET as $key => $value ) {
			if ( !in_array( strtolower( $key ), $accept_qs ) )
				return false;
		}
		return true;
	}

	/**
	 *
	 */
	public function delayed_cache_print() {
		if ( $this->_late_caching && $this->_caching ) {
			$this->_cached_data = $this->_extract_cached_page( true );
			if ( $this->_cached_data ) {
				global $w3_late_caching_succeeded;
				$w3_late_caching_succeeded  = true;

				$this->process_cached_page_and_exit( $this->_cached_data );
				// if is passes here - exit is not possible now and
				// will happen on init
				return;
			}
		}

		if ( $this->_late_init && $this->_caching ) {
			$this->process_cached_page_and_exit( $this->_cached_data );
			// if is passes here - exit is not possible now and
			// will happen on init
			return;
		}
	}

	/**
	 *
	 *
	 * @param unknown $buffer
	 * @param unknown $has_dynamic
	 * @return array
	 */
	private function _maybe_save_cached_result( $buffer, $has_dynamic ) {
		if ( empty( $buffer ) ) {
			$this->cache_reject_reason = 'Empty response';
			return $buffer;
		}

		$mobile_group = $this->_get_mobile_group();
		$referrer_group = $this->_get_referrer_group();
		$encryption = $this->_get_encryption();
		$compression_header = $this->_get_compression();
		$compressions_to_store = $this->_get_compressions();

		/**
		 * Don't compress here for debug mode or dynamic tags
		 * because we need to modify buffer before send it to client
		 */
		if ( $this->_debug || $has_dynamic ) {
			$compressions_to_store = array( false );
		}

		// right now dont return compressed buffer if we are dynamic,
		// that will happen on shutdown after processing dynamic stuff
		$compression_of_returned_content =
			( $has_dynamic ? false : $compression_header );

		$content_type = '';
		$is_404 = ( function_exists( 'is_404' ) ? is_404() : false );
		$response_headers = $this->_get_response_headers();
		$headers = $this->_get_cached_headers( $response_headers['plain'] );

		if ( !empty( $response_headers['kv']['Content-Encoding'] ) ) {
			$this->cache_reject_reason = 'Response is compressed';
			return $buffer;
		}

		if ( $this->_enhanced_mode ) {
			// redirect issued, if we have some old cache entries
			// they will be turned into fresh files and catch further requests
			if ( isset( $response_headers['kv']['Location'] ) ) {
				foreach ( $compressions_to_store as $_compression ) {
					$_page_key = $this->_get_page_key( $mobile_group,
						$referrer_group, $encryption, $_compression,
						$content_type );
					$cache = $this->_get_cache();
					$cache->hard_delete( $_page_key );
				}

				return $buffer;
			}
		}

		if ( $this->_enhanced_mode && !$this->_late_init ) {
			register_shutdown_function( array(
					$this,
					'_check_rules_present'
				) );

			if ( isset( $response_headers['kv']['Content-Type'] ) )
				$content_type = $response_headers['kv']['Content-Type'];
		}

		$time = time();
		$cache = $this->_get_cache();

		/**
		 * Store different versions of cache
		 */
		$buffers = array();
		$group = '';
		if ( !isset( $this->_sitemap_matched ) ) {
			$sitemap_regex =
				$this->_config->get_string( 'pgcache.purge.sitemap_regex' );
			if ( $sitemap_regex && preg_match( '/' . $sitemap_regex . '/', basename( $this->_request_uri ) ) ) {
				$group = 'sitemaps';
				$this->_sitemap_matched = true;
			}
		} elseif ( $this->_sitemap_matched )
			$group = 'sitemaps';

		foreach ( $compressions_to_store as $_compression ) {
			$this->_set_extract_page_key( $mobile_group,
				$referrer_group, $encryption, $_compression,
				$content_type, true );
			if ( empty( $this->_page_key ) )
				continue;

			// Compress content
			$buffers[$_compression] = $this->_compress( $buffer, $_compression );

			// Store cache data
			$_data = array(
				'404' => $is_404,
				'headers' => $headers,
				'time' => $time,
				'content' => $buffers[$_compression]
			);
			if ( $has_dynamic )
				$_data['has_dynamic'] = true;

			$_data = apply_filters( 'w3tc_pagecache_set', $_data, $this->_page_key );

			if ( !empty( $_data ) )
				$cache->set( $this->_page_key, $_data, $this->_lifetime, $group );
		}

		// Change buffer if using compression
		if ( defined( 'W3TC_PAGECACHE_OUTPUT_COMPRESSION_OFF' ) ) {
			$compression_header = false;
		} elseif ( $compression_of_returned_content &&
			isset( $buffers[$compression_of_returned_content] ) ) {
			$buffer = $buffers[$compression_of_returned_content];
		}

		// Calculate content etag
		$etag = md5( $buffer );

		// Send headers
		$this->_send_headers( $is_404, $time, $etag, $compression_header,
			$headers );
		return $buffer;
	}

	public function w3tc_usage_statistics_of_request( $storage ) {
		$storage->counter_add( 'pagecache_requests_total', 1 );
		if ( $this->_cached_data )
			$storage->counter_add( 'pagecache_requests_hits', 1 );

		global $w3tc_start_microtime;
		if ( !empty( $w3tc_start_microtime ) ) {
			$ms10 = (int)( ( microtime( true ) - $w3tc_start_microtime ) * 100 );
			$storage->counter_add( 'pagecache_requests_time_10ms', $ms10 );
		}
	}



	/**
	 * Log
	 */
	static private function log( $msg ) {
		$data = sprintf( "[%s] [%s] [%s] %s\n", date( 'r' ),
			$_SERVER['REQUEST_URI'],
			( !empty( $_SERVER['HTTP_REFERER'] ) ? $_SERVER['HTTP_REFERER'] : '-' ),
			$msg );
		$data = strtr( $data, '<>', '..' );

		$filename = Util_Debug::log_filename( 'pagecache' );
		return @file_put_contents( $filename, $data, FILE_APPEND );
	}
}
