*
			 * 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->_page_key_extension['useragent'] ) {
			$vary = 'Accept-Encoding,User-Agent,Cookie';
			$headers['Content-Encoding'] = $compression;
			//compressed
		} elseif ( $compression ) {
			$vary = 'Accept-Encoding';
			$headers['Content-Encoding'] = $compression;
			//uncompressed && UAG
		} elseif ( $this->_page_key_extension['useragent'] ) {
			$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 = htmlspecialchars( stripslashes( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) ); // phpcs:ignore

			// 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 = htmlspecialchars( stripslashes( $_SERVER['HTTP_IF_NONE_MATCH'] ) ); // phpcs:ignore
			$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 );
			$m = null;
			if ( preg_match( '~\s*content-type\s*:([^;]+)~', $header, $m ) ) {
				$content_type = trim( $m[1] );
			}
		}

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

	/**
	 * Fills $_request_url_fragments['path'], $_request_url_fragments['querystring']
	 * with cache-related normalized values
	 */
	private function _preprocess_request_uri() {
		$p = explode( '?', $this->_request_uri, 2 );

		$this->_request_url_fragments['path'] = $p[0];
		$this->_request_url_fragments['querystring'] =
			( empty( $p[1] ) ? '' : '?' . $p[1] );

		$this->_request_url_fragments = $this->_normalize_url_fragments(
			$this->_request_url_fragments );
	}



	private function _normalize_url_fragments( $fragments ) {
		$fragments = w3tc_apply_filters( 'pagecache_normalize_url_fragments',
			$fragments );
		$fragments['querystring'] = $this->_normalize_querystring(
			$fragments['querystring'] );

		return $fragments;
	}



	private function _normalize_querystring( $querystring ) {
		$ignore_qs = $this->_config->get_array( 'pgcache.accept.qs' );
		$ignore_qs = w3tc_apply_filters( 'pagecache_extract_accept_qs', $ignore_qs );
		Util_Rule::array_trim( $ignore_qs );

		if ( empty( $ignore_qs ) || empty( $querystring ) ) {
			return $querystring;
		}

		$querystring_naked = substr( $querystring, 1 );

		foreach ( $ignore_qs as $qs ) {
			$m = null;
			if ( strpos( $qs, '=' ) === false ) {
				$regexp = Util_Environment::preg_quote( str_replace( '+', ' ', $qs ) );
				if ( @preg_match( "~^(.*?&|)$regexp(=[^&]*)?(&.*|)$~i", $querystring_naked, $m ) ) {
					$querystring_naked = $m[1] . $m[3];
				}
			} else {
				$regexp = Util_Environment::preg_quote( str_replace( '+', ' ', $qs ) );

				if ( @preg_match( "~^(.*?&|)$regexp(&.*|)$~i", $querystring_naked, $m ) ) {
					$querystring_naked = $m[1] . $m[2];
				}
			}
		}

		$querystring_naked = preg_replace( '~[&]+~', '&', $querystring_naked );
		$querystring_naked = trim( $querystring_naked, '&' );

		return empty( $querystring_naked ) ? '' : '?' . $querystring_naked;
	}

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

	private function _maybe_save_cached_result( $buffer, $response_headers, $has_dynamic ) {
		$mobile_group = $this->_page_key_extension['useragent'];
		$referrer_group = $this->_page_key_extension['referrer'];
		$encryption = $this->_page_key_extension['encryption'];
		$compression_header = $this->_page_key_extension['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 );

		$headers = $this->_get_cached_headers( $response_headers['plain'] );
		if ( !empty( $headers['Status-Code'] ) ) {
			$is_404 = ( $headers['Status-Code'] == 404 );
		} elseif ( function_exists( 'is_404' ) ) {
			$is_404 = is_404();
		} else {
			$is_404 = false;
		}

		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'] ) ) {
				$cache = $this->_get_cache( $this->_page_key_extension['group'] );

				foreach ( $compressions_to_store as $_compression ) {
					$_page_key = $this->_get_page_key(
						array_merge( $this->_page_key_extension,
							array( 'compression' => $_compression ) ) );
					$cache->hard_delete( $_page_key );
				}

				return $buffer;
			}
		}

		$content_type = '';
		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( $this->_page_key_extension['group'] );

		/**
		 * Store different versions of cache
		 */
		$buffers = array();
		$something_was_set = false;

		foreach ( $compressions_to_store as $_compression ) {
			$this->_set_extract_page_key(
				array_merge( $this->_page_key_extension,
					array(
						'compression' => $_compression,
						'content_type' => $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 ( !empty( $_compression ) ) {
				$_data['c'] = $_compression;
			}
			if ( $has_dynamic )
				$_data['has_dynamic'] = true;

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

			if ( !empty( $_data ) ) {
				$cache->set( $this->_page_key, $_data, $this->_lifetime, $this->_page_group );
				$something_was_set = true;
			}
		}

		if ( $something_was_set ) {
			$this->process_status = 'miss_fill';
		} else {
			$this->process_status = 'miss_third_party';
		}

		// 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 ) {
		global $w3tc_start_microtime;
		$time_ms = 0;
		if ( !empty( $w3tc_start_microtime ) ) {
			$time_ms = (int)( ( microtime( true ) - $w3tc_start_microtime ) * 1000 );
			$storage->counter_add( 'pagecache_requests_time_10ms', (int)( $time_ms / 10 ) );
		}

		if ( !empty( $this->process_status ) ) {
			// see registered keys in PgCache_Plugin.w3tc_usage_statistics_metrics
			$storage->counter_add( 'php_requests_pagecache_' . $this->process_status, 1 );

			if ( $this->_debug ) {
				self::log( 'finished in ' . $time_ms .
					' size ' . $this->output_size .
					' with process status ' .
					$this->process_status .
					' reason ' . $this->cache_reject_reason);
			}
		}
	}

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

		$filename = Util_Debug::log_filename( 'pagecache' );

		return @file_put_contents( $filename, $data, FILE_APPEND );
	}
}