f ( $has_dynamic ) {
			// its last modification date is now, and any compression browser wants cant be used, since its compressed now.
			$time        = time();
			$compression = $this->_page_key_extension['compression'];
		} else {
			$time        = isset( $w3tc_data['time'] ) ? $w3tc_data['time'] : time();
			$compression = $w3tc_data['compression'];
		}

		// Send headers.
		$this->_send_headers( $is_404, $time, $etag, $compression, $headers );
		if ( isset( $_SERVER['REQUEST_METHOD'] ) && 'HEAD' === $_SERVER['REQUEST_METHOD'] ) {
			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; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped

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

	/**
	 * Output buffering callback for caching.
	 *
	 * @param string $buffer The current output buffer.
	 *
	 * @return string Processed buffer to be output.
	 */
	public function ob_callback( $buffer ) {
		$this->output_size = strlen( $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 );

		// Sign dynamic-fragment tags so read-time dispatch can verify integrity (layer 2 of the dispatcher).
		if ( $has_dynamic ) {
			$buffer = $this->_sign_dynamic_tags( $buffer );
		}

		$response_headers = $this->_get_response_headers();

		// TODO: call modifies object state, rename method at least.
		$original_can_cache = $this->_can_write_cache( $buffer, $response_headers );
		$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
			);
		}

		$buffer = str_replace(
			'{w3tc_pagecache_reject_reason}',
			( '' !== $this->cache_reject_reason ? sprintf( ' (%s)', $this->cache_reject_reason ) : '' ),
			$buffer
		);

		if ( $can_cache ) {
			$buffer = $this->_maybe_save_cached_result( $buffer, $response_headers, $has_dynamic );
		} else {
			if ( $has_dynamic ) {
				// send common headers since output will be compressed.
				$compression_header = $this->_page_key_extension['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( $this->_page_key_extension['group'] );

					$compressions_to_store = $this->_get_compressions();

					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 );
					}
				}
			}
		}

		// 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;
	}

	/**
	 * Handles the shutdown process for compressing and outputting the page buffer.
	 *
	 * @return void
	 */
	public function shutdown() {
		$compression = $this->_page_key_extension['compression'];

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

		// Compress page according to headers already set.
		$compressed_buffer = $this->_compress( $buffer, $compression );

		echo $compressed_buffer; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped
	}

	/**
	 * Determines if the cache can be read for the current request.
	 *
	 * @return bool True if cache can be read, false otherwise.
	 */
	private function _can_read_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' ) && ! empty( 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';
			$this->process_status      = 'miss_configuration';
			return false;
		}

		// Skip if posting.
		$request_method = isset( $_SERVER['REQUEST_METHOD'] ) ? htmlspecialchars( stripslashes( $_SERVER['REQUEST_METHOD'] ) ) : '';

		if ( in_array( strtoupper( $request_method ), array( 'DELETE', 'PUT', 'OPTIONS', 'TRACE', 'CONNECT', 'POST' ), true ) ) {
			$this->cache_reject_reason = sprintf( 'Requested method is %s', $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.
		$this->_preprocess_request_uri();

		if ( ! empty( $this->_request_url_fragments['querystring'] ) ) {
			$should_reject_qs = (
				! $this->_config->get_boolean( 'pgcache.cache.query' ) ||
				'file_generic' === $this->_config->get_string( 'pgcache.engine' )
			);

			if (
				$should_reject_qs &&
				'cache' === $this->_config->get_string( 'pgcache.rest' ) &&
				Util_Environment::is_rest_request( $this->_request_uri )
			) {
				$should_reject_qs = false;
			}

			if ( $should_reject_qs ) {
				$this->cache_reject_reason = 'Requested URI contains query';
				$this->process_status      = 'miss_query_string';
				return false;
			}
		}

		// Check request URI.
		if ( ! $this->_passed_accept_files() && ! $this->_passed_reject_uri() ) {
			$this->cache_reject_reason = 'Requested URI is rejected';
			$this->process_status      = 'miss_configuration';
			return false;
		}

		// Check User Agent.
		if ( ! $this->_check_ua() ) {
			$this->cache_reject_reason = 'User agent is rejected';
			if ( ! empty( Util_Request::get_string( 'w3tc_rewrite_test' ) ) ) {
				// special common case - w3tc_rewrite_test check request.
				$this->process_status = 'miss_wp_admin';
			} else {
				$this->process_status = 'miss_configuration';
			}

			return false;
		}

		// Check WordPress cookies.
		if ( ! $this->_check_cookies() ) {
			$this->cache_reject_reason = 'Cookie is rejected';
			$this->process_status      = 'miss_configuration';
			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';
				$this->process_status      = 'miss_logged_in';
				return false;
			}
		} elseif ( ! $this->_check_logged_in_role_allowed() ) {
			$this->cache_reject_reason = 'Rejected user role is logged in';
			$this->process_status      = 'miss_logged_in';
			return false;
		}

		return true;
	}

	/**
	 * Determines if the cache can be written for the given buffer and response headers.
	 *
	 * @param string $buffer The content buffer to potentially cache.
	 * @param array  $response_headers {
	 *     Response headers from the current request.
	 *
	 *     @type array $kv Key-value pairs of response headers.
	 * }
	 *
	 * @return bool True if cache can be written, false otherwise.
	 */
	private function _can_write_cache( $buffer, $response_headers ) {
		// Skip if caching is disabled.
		if ( ! $this->_caching ) {
			return false;
		}

		// Check for DONOTCACHEPAGE constant.
		if ( defined( 'DONOTCACHEPAGE' ) && DONOTCACHEPAGE ) {
			$this->cache_reject_reason = 'DONOTCACHEPAGE constant is defined';
			$this->process_status      = 'miss_third_party';
			return false;
		}

		if ( 'cache' !== $this->_config->get_string( 'pgcache.rest' ) ) {
			if ( defined( 'REST_REQUEST' ) && REST_REQUEST ) {
				$this->cache_reject_reason = 'REST request';
				$this->process_status      = 'miss_api_call';
				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';
			$this->process_status      = 'miss_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';
			$this->process_status      = 'miss_configuration';
			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';
			$this->process_status      = 'miss_configuration';
			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';
			$this->process_status      = 'miss_configuration';
			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';
			$this->process_status      = 'miss_mfunc';
			return false;
		}

		if ( ! $this->_passed_accept_files() ) {
			if ( is_single() ) {
				// Don't cache pages associated with categories.
				if ( $this->_passed_reject_categories() ) {
					$this->cache_reject_reason = 'Page associated with a rejected category';
					$this->process_status      = 'miss_configuration';
					return false;
				}

				// Don't cache pages that use tags.
				if ( $this->_passed_reject_tags() ) {
					$this->cache_reject_reason = 'Page using a rejected tag';
					$this->process_status      = 'miss_configuration';
					return false;
				}
			}

			// Don't cache pages by these authors.
			if ( $this->_passed_reject_authors() ) {
				$this->cache_reject_reason = 'Page written by a rejected author';
				$this->process_status      = 'miss_configuration';
				return false;
			}

			// Don't cache pages using custom fields.
			if ( $this->_passed_reject_custom_fields() ) {
				$this->cache_reject_reason = 'Page using a rejected custom field';
				$this->process_status      = 'miss_configuration';
				return false;
			}
		}

		if ( ! empty( $response_headers['kv']['content-encoding'] ) ) {
			$this->cache_reject_reason = 'Response is compressed';
			$this->process_status      = 'miss_compressed';
			return false;
		}

		if ( empty( $buffer ) && empty( $response_headers['kv']['location'] ) ) {
			$this->cache_reject_reason = 'Empty response';
			$this->process_status      = 'miss_empty_response';
			return false;
		}

		if ( isset( $response_headers['kv']['location'] ) ) {
			/**
			 * Dont cache query-string normalization redirects (e.g. from wp core) when cache key is normalized,
			 * since that cause redirect loop.
			 */

			if (
				$this->_get_page_key( $this->_page_key_extension ) === $this->_get_page_key(
					$this->_page_key_extension,
					$response_headers['kv']['location']
				)
			) {
				$this->cache_reject_reason = 'Normalization redirect';
				$this->process_status      = 'miss_normalization_redirect';
				return false;
			}
		}

		if ( isset( $_SERVER['REQUEST_METHOD'] ) && 'HEAD' === $_SERVER['REQUEST_METHOD'] ) {
			$this->cache_reject_reason = 'HEAD request';
			$this->process_status      = 'miss_request_method';
			return;
		}

		return true;
	}

	/**
	 * Retrieves the size of cache statistics.
	 *
	 * @param int $timeout_time Timeout in seconds for the operation.
	 *
	 * @return int|null The size of the cache statistics, or null if unavailable.
	 */
	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;
	}

	/**
	 * Retrieves usage statistics and configuration for the cache engine.
	 *
	 * @return array Configuration data for the cache engine.
	 */
	public function get_usage_statistics_cache_config() {
		$w3tc_engine = $this->_config->get_string( 'pgcache.engine' );

		switch ( $w3tc_engine ) {
			case 'memcached':
			case 'nginx_memcached':
				$engine_config = 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' ),
					'binary_protocol'   => $this->_config->get_boolean( 'pgcache.memcached.binary_protocol' ),
				);
				break;

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

			case 'file_generic':
				$w3tc_engine = 'file';
				break;

			default:
				$engine_config = array();
		}

		$engine_config['engine'] = $w3tc_engine;

		return $engine_config;
	}

	/**
	 * Retrieves the cache instance for a specific group.
	 *
	 * @param string $w3tc_group Cache group name. Defaults to '*'.
	 *
	 * @return mixed Cache instance.
	 */
	public function _get_cache( $w3tc_group = '*' ) {
		static $caches = array();

		if ( empty( $w3tc_group ) ) {
			$w3tc_group = '*';
		}

		if ( empty( $caches[ $w3tc_group ] ) ) {
			$w3tc_engine      = $this->_config->get_string( 'pgcache.engine' );
			$use_expired_data = true;

			switch ( $w3tc_engine ) {
				case 'memcached':
				case 'nginx_memcached':
					$engine_config = 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' ),
						'binary_protocol'   => $this->_config->get_boolean( 'pgcache.memcached.binary_protocol' ),
						'host'              => Util_Environment::host(),
					);
					break;

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

				case 'file':
					$engine_config = 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':
					/**
					 * Elementor deletes dependent assets when its cache flushes. Serving *_old HTML here keeps
					 * pointing visitors to missing CSS/JS, so disable stale reads when Elementor is detected.
					 */
					$use_expired_data = ! Util_Environment::is_elementor();

					if ( '*' !== $w3tc_group ) {
						$w3tc_engine = 'file';

						$engine_config = array(
							'section'         => 'page',
							'cache_dir'       => W3TC_CACHE_PAGE_ENHANCED_DIR . DIRECTORY_SEPARATOR . Util_Environment::host_port(),
							'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;
					}

					if ( 0 === Util_Environment::blog_id() ) {
						$flush_dir = W3TC_CACHE_PAGE_ENHANCED_DIR;
					} else {
						$flush_dir = W3TC_CACHE_PAGE_ENHANCED_DIR . DIRECTORY_SEPARATOR . Util_Environment::host();
					}

					$engine_config = array(
						'exclude'         => array( // phpcs:ignore WordPressVIPMinimum
							'.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:
					$engine_config = array();
			}

			$engine_config['use_expired_data'] = $use_expired_data;
			$engine_config['module']           = 'pgcache';
			$engine_config['host']             = '';
			$engine_config['instance_id']      = Util_Environment::instance_id();

			$caches[ $w3tc_group ] = Cache::instance( $w3tc_engine, $engine_config );
		}

		return $caches[ $w3tc_group ];
	}

	/**
	 * Determines if the current request passes the reject URI conditions.
	 *
	 * @return bool True if the request passes the reject URI conditions, false otherwise.
	 */
	public function _passed_reject_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;
	}

	/**
	 * Determines if the current request passes the accept files conditions.
	 *
	 * @return bool True if the request passes the accept files conditions, false otherwise.
	 */
	public function _passed_accept_files() {
		$accept_uri = $this->_config->get_array( 'pgcache.accept.files' );
		$accept_uri = array_map( array( '\W3TC\Util_Environment', 'parse_path' ), $accept_uri );

		foreach ( $accept_uri as &$val ) {
			$val = trim( str_replace( '~', '\~', $val ) );
		}

		$accept_uri = array_filter(
			$accept_uri,
			function ( $val ) {
				return '' !== $val;
			}
		);

		if ( ! empty( $accept_uri ) && @preg_match( '~' . implode( '|', $accept_uri ) . '~i', $this->_request_uri ) ) {
			return true;
		}

		return false;
	}

	/**
	 * Determines if the current request is rejected based on categories.
	 *
	 * @return bool True if the request is rejected due to categories, false otherwise.
	 */
	public function _passed_reject_categories() {
		$reject_categories = $this->_config->get_array( 'pgcache.reject.categories' );
		if ( ! empty( $reject_categories ) ) {
			$cats = get_the_category();
			if ( $cats ) {
				foreach ( $cats as $cat ) {
					if ( in_array( $cat->slug, $reject_categories, true ) ) {
						return true;
					}
				}
			}
		}

		return false;
	}

	/**
	 * Determines if the current request is rejected based on tags.
	 *
	 * @return bool True if the request is rejected due to tags, false otherwise.
	 */
	public function _passed_reject_tags() {
		$reject_tags = $this->_config->get_array( 'pgcache.reject.tags' );
		if ( ! empty( $reject_tags ) ) {
			$tags = get_the_tags();
			if ( $tags ) {
				foreach ( $tags as $tag ) {
					if ( in_array( $tag->slug, $reject_tags, true ) ) {
						return true;
					}
				}
			}
		}

		return false;
	}

	/**
	 * Determines if the current request is rejected based on authors.
	 *
	 * @return bool True if the request is rejected due to authors, false otherwise.
	 */
	public function _passed_reject_authors() {
		$reject_authors = $this->_config->get_array( 'pgcache.reject.authors' );
		if ( ! empty( $reject_authors ) ) {
			$author = get_the_author_meta( 'user_login' );
			if ( $author ) {
				if ( in_array( $author, $reject_authors, true ) ) {
					return true;
				}
			}
		}

		return false;
	}

	/**
	 * Determines if the current request is rejected based on custom fields.
	 *
	 * @return bool True if the request is rejected due to custom fields, false otherwise.
	 */
	public function _passed_reject_custom_fields() {
		$reject_custom = $this->_config->get_array( 'pgcache.reject.custom' );
		if ( empty( $reject_custom ) ) {
			return false;
		}

		foreach ( $reject_custom as &$val ) {
			$val = preg_quote( trim( $val ), '~' );
		}

		$reject_custom = implode( '|', array_filter( $reject_custom ) );
		if ( ! empty( $reject_custom ) ) {
			$customs = get_post_custom();
			if ( $customs ) {
				foreach ( $customs as $w3tc_key => $w3tc_value ) {
					if ( @preg_match( '~' . $reject_custom . '~i', $w3tc_key . ( isset( $w3tc_value[0] ) ? "={$w3tc_value[0]}" : '' ) ) ) {
						return true;
					}
				}
			}
		}

		return false;
	}

	/**
	 * Validates the User-Agent against rejection rules.
	 *
	 * @return bool True if the User-Agent passes validation, false otherwise.
	 */
	public 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( htmlspecialchars( stripslashes( $_SERVER['HTTP_USER_AGENT'] ) ), $ua ) !== false
				) {
					return false;
				}
			}
		}

		return true;
	}

	/**
	 * Checks if the current request passes the cookie rejection rules.
	 *
	 * @return bool True if the request passes cookie validation, false otherwise.
	 */
	public function _check_cookies() {
		foreach ( array_keys( $_COOKIE ) as $cookie_name ) {
			if ( 'wordpress_test_cookie' === $cookie_name ) {
				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;
	}

	/**
	 * Checks if the user is logged in and rejects the request if true.
	 *
	 * @return bool True if the user is not logged in, false otherwise.
	 */
	public function _check_logged_in() {
		foreach ( array_keys( $_COOKIE ) as $cookie_name ) {
			if ( strpos( $cookie_name, 'wordpress_logged_in' ) === 0 ) {
				return false;
			}
		}

		return true;
	}


	/**
	 * Validates if a logged-in user's role is allowed.
	 *
	 * @return bool True if the logged-in user's role is allowed, false otherwise.
	 */
	public 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 ) {
					/**
					 * Accept BOTH the new HMAC-SHA256 cookie name and the
					 * legacy MD5(NONCE_KEY . $role) form for one release
					 * window so an upgrade doesn't immediately serve the
					 * logged-out-cache to users whose browsers still hold
					 * the old-named cookie. The legacy lookup is dropped
					 * in the release AFTER this one.
					 */
					if ( strstr( $cookie_name, Util_Cookie::role_cookie_name( $role ) ) ) {
						return false;
					}
					if ( strstr( $cookie_name, Util_Cookie::role_cookie_name_legacy( $role ) ) ) {
						return false;
					}
				}
			}
		}

		return true;
	}

	/**
	 * Ensures that the required cache rules are present.
	 *
	 * @return void
	 */
	public 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 ) { // phpcs:ignore Generic.CodeAnalysis.EmptyStatement.DetectedCatch
			// Exception.
		}
	}

	/**
	 * Compresses the given data using the specified compression method.
	 *
	 * @param string $w3tc_data        The data to be compressed.
	 * @param string $compression The compression method ('gzip', 'deflate', 'br').
	 *
	 * @return string The compressed data.
	 */
	public function _compress( $w3tc_data, $compression ) {
		switch ( $compression ) {
			case 'gzip':
				$w3tc_data = gzencode( $w3tc_data );
				break;

			case 'deflate':
				$w3tc_data = gzdeflate( $w3tc_data );
				break;

			case 'br':
				$w3tc_data = brotli_compress( $w3tc_data );
				break;
		}

		return $w3tc_data;
	}

	/**
	 * Retrieves the key extension used for cache identification.
	 *
	 * @return array An associative array representing the key extension.
	 */
	private function _get_key_extension() {
		$w3tc_extension = array(
			'useragent'           => '',
			'referrer'            => '',
			'cookie'              => '',
			'encryption'          => '',
			'compression'         => $this->_get_compression(),
			'content_type'        => '',
			'cache'               => true,
			'cache_reject_reason' => '',
			'group'               => '',
		);

		if ( $this->_mobile ) {
			$w3tc_extension['useragent'] = $this->_mobile->get_group();
		}

		if ( $this->_referrer ) {
			$w3tc_extension['referrer'] = $this->_referrer->get_group();
		}

		if ( Util_Environment::is_https() ) {
			$w3tc_extension['encryption'] = 'ssl';
		}

		$this->_fill_key_extension_cookie( $w3tc_extension );

		// fill group.
		$w3tc_extension['group'] = $this->get_cache_group_by_uri( $this->_request_uri );
		$w3tc_extension          = w3tc_apply_filters(
			'pagecache_key_extension',
			$w3tc_extension,
			$this->_request_url_fragments['host'],
			$this->_request_uri
		);

		return $w3tc_extension;
	}

	/**
	 * Fills the key extension array with cookie-related information based on configured cookie groups.
	 *
	 * @param array $w3tc_extension {
	 *     Reference to the key extension array.
	 *
	 *     @type string|null $cookie              The name of the matched cookie group, if any.
	 *     @type bool|null   $cache               Whether caching is allowed. Set to false if a matching group disallows caching.
	 *     @type string|null $cache_reject_reason Reason for cache rejection if caching is disabled.
	 * }
	 *
	 * @return void
	 */
	private function _fill_key_extension_cookie( &$w3tc_extension ) {
		if ( ! $this->_config->get_boolean( 'pgcache.cookiegroups.enabled' ) ) {
			return;
		}

		$groups = $this->_config->get_array( 'pgcache.cookiegroups.groups' );
		foreach ( $groups as $group_name => $g ) {
			if ( isset( $g['enabled'] ) && $g['enabled'] ) {
				$cookies = array();
				foreach ( $g['cookies'] as $cookie ) {
					$cookie = trim( $cookie );
					if ( ! empty( $cookie ) ) {
						$cookie = str_replace( '+', ' ', $cookie );
						if ( strpos( $cookie, '=' ) === false ) {
							$cookie .= '=.*';
						}

						$cookies[] = $cookie;
					}
				}

				if ( count( $cookies ) > 0 ) {
					$cookies_regexp = '~^(' . implode( '|', $cookies ) . ')$~i';

					foreach ( $_COOKIE as $w3tc_key => $w3tc_value ) {
						if ( @preg_match( $cookies_regexp, $w3tc_key . '=' . $w3tc_value ) ) {
							$w3tc_extension['cookie'] = $group_name;
							if ( ! $g['cache'] ) {
								$w3tc_extension['cache']               = false;
								$w3tc_extension['cache_reject_reason'] = 'cookiegroup ' . $group_name;
							}

							return;
						}
					}
				}
			}
		}
	}

	/**
	 * Determines the cache group based on the provided URI.
	 *
	 * @param string $uri The URI to analyze.
	 *
	 * @return string The cache group name.
	 */
	protected function get_cache_group_by_uri( $uri ) {
		/**
		 * "!$this->_enhanced_mode" in condition above prevents usage of separate group under disk-enhanced
		 * so that rewrite rules still work. Flushing is handled by workaround in this case.
		 */
		if ( ! $this->_enhanced_mode ) {
			$sitemap_regex = $this->_config->get_string( 'pgcache.purge.sitemap_regex' );
			if ( $sitemap_regex && preg_match( '~' . $sitemap_regex . '~', basename( $uri ) ) ) {
				return 'sitemaps';
			}
		}

		if (
			'cache' === $this->_config->get_string( 'pgcache.rest' ) &&
			Util_Environment::is_rest_request( $uri ) &&
			Util_Environment::is_w3tc_pro( $this->_config )
		) {
			return 'rest';
		}

		return '';
	}

	/**
	 * Retrieves the compression type supported by the server.
	 *
	 * @return string The supported compression type ('gzip', 'br', or empty string).
	 */
	public function _get_compression() {
		if ( $this->_debug ) { // Can't generate/use compressed files during debug mode.
			return '';
		}

		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( htmlspecialchars( stripslashes( $_SERVER['HTTP_ACCEPT_ENCODING'] ) ), $compression ) !== false
				) {
					return $compression;
				}
			}
		}

		return '';
	}

	/**
	 * Retrieves the list of supported compression methods.
	 *
	 * @return array An array of supported compression methods.
	 */
	public function _get_compressions() {
		$compressions = array(
			false,
		);

		if ( defined( 'W3TC_PAGECACHE_STORE_COMPRESSION_OFF' ) ) {
			return $compressions;
		}

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

		if (
			$this->_config->get_boolean( 'browsercache.enabled' ) &&
			$this->_config->get_boolean( 'browsercache.html.brotli' ) &&
			function_exists( 'brotli_compress' )
		) {
			$compressions[] = 'br';
		}

		return $compressions;
	}

	/**
	 * Retrieves the response headers sent by the server.
	 *
	 * @return array An associative array containing 'kv' and 'plain' header representations.
	 */
	public 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  = trim( substr( $header, 0, $pos ) );
						$header_value = trim( substr( $header, $pos + 1 ) );
					} else {
						$header_name  = $header;
						$header_value = '';
					}

					$headers_kv[ strtolower( $header_name ) ] = $header_value;
					$headers_plain[]                          = array(
						'name'  => $header_name,
						'value' => $header_value,
					);
				}
			}
		}

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

	/**
	 * Checks if the user is using a buggy version of Internet Explorer.
	 *
	 * @return bool True if a buggy version of Internet Explorer is detected, false otherwise.
	 */
	public function _is_buggy_ie() {
		if ( isset( $_SERVER['HTTP_USER_AGENT'] ) ) {
			$ua = htmlspecialchars( stripslashes( $_SERVER['HTTP_USER_AGENT'] ) ); // phpcs:ignore

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

				return $version < 6 || ( 6.0 === $version && false === strpos( $ua, 'SV1' ) );
			}
		}

		return false;
	}

	/**
	 * Filters and retrieves cached headers from the response.
	 *
	 * @param array $response_headers {
	 *     An array of response headers.
	 *
	 *     @type string[] $w3tc_name  The header name.
	 *     @type string   $w3tc_value The header value.
	 * }
	 *
	 * @return array {
	 *     An array of cached headers.
	 *
	 *     @type int      $Status-Code  The HTTP status code (if available).
	 *     @type string[] $n            The repeated header name.
	 *     @type string   $v            The repeated header value.
	 *     @type string   $header_name  Cached header name.
	 *     @type string   $header_value Cached header value.
	 * }
	 */
	public function _get_cached_headers( $response_headers ) {
		$data_headers  = array();
		$cache_headers = array_merge(
			array( 'Location', 'X-WP-Total', 'X-WP-TotalPages' ),
			$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 $w3tc_i ) {
			$header_name  = $w3tc_i['name'];
			$header_value = $w3tc_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, true ) ) {
						// headers may repeat.
						$data_headers[] = array(
							'n' => $header_name,
							'v' => $header_value,
						);
					} else {
						$data_headers[ $header_name ] = $header_value;
					}
				}
			}
		}

		return $data_headers;
	}

	/**
	 * Constructs a unique cache key for the page.
	 *
	 * @param array  $page_key_extension {
	 *     An array of page key extensions.
	 *
	 *     @type string $useragent    User agent key extension.
	 *     @type string $referrer     Referrer key extension.
	 *     @type string $cookie       Cookie key extension.
	 *     @type string $encryption   Encryption key extension.
	 *     @type string $w3tc_group        Optional. Cache group key extension.
	 *     @type string $content_type Optional. Content type for XML handling.
	 *     @type string $compression  Optional. Compression type key extension.
	 * }
	 * @param string $request_url Optional. The request URL.
	 *
	 * @return string The constructed cache key.
	 */
	public function _get_page_key( $page_key_extension, $request_url = '' ) {
		// key url part.
		if ( empty( $request_url ) ) {
			$request_url_fragments = $this->_request_url_fragments;
		} else {
			$request_url_fragments = array();

			$parts = wp_parse_url( $request_url );

			if ( isset( $parts['host'] ) ) {
				$request_url_fragments['host'] = $parts['host'] . ( isset( $parts['port'] ) ? ':' . $parts['port'] : '' );
			} else {
				$request_url_fragments['host'] = $this->_request_url_fragments['host'];
			}

			$request_url_fragments['path']        = ( isset( $parts['path'] ) ? $parts['path'] : '' );
			$request_url_fragments['querystring'] = ( isset( $parts['query'] ) ? '?' . $parts['query'] : '' );
			$request_url_fragments                = $this->_normalize_url_fragments( $request_url_fragments );
		}

		$key_urlpart = $request_url_fragments['host'] . ( $request_url_fragments['path'] ?? '' ) .
			( $request_url_fragments['querystring'] ?? '' );

		$key_urlpart = $this->_get_page_key_urlpart( $key_urlpart, $page_key_extension );

		// key extension.
		$key_extension = '';
		$extensions    = array( 'useragent', 'referrer', 'cookie', 'encryption' );
		foreach ( $extensions as $e ) {
			if ( ! empty( $page_key_extension[ $e ] ) ) {
				$key_extension .= '_' . $page_key_extension[ $e ];
			}
		}

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

		// key postfix.
		$key_postfix = '';
		if ( $this->_enhanced_mode && empty( $page_key_extension['group'] ) ) {
			$key_postfix = '.html';
			if ( $this->_config->get_boolean( 'pgcache.cache.nginx_handle_xml' ) ) {
				$content_type = isset( $page_key_extension['content_type'] ) ? $page_key_extension['content_type'] : '';

				if (
					@preg_match( '~(text/xml|text/xsl|application/xhtml\+xml|application/rdf\+xml|application/rss\+xml|application/atom\+xml|application/xml)~i', $content_type ) ||
					preg_match( W3TC_FEED_REGEXP, $request_url_fragments['path'] ) ||
					false !== strpos( $request_url_fragments['path'], '.xsl' )
				) {
					$key_postfix = '.xml';
				}
			}
		}

		// key compression.
		$key_compression = '';
		if ( $page_key_extension['compression'] ) {
			$key_compression = '_' . $page_key_extension['compression'];
		}

		$w3tc_key = w3tc_apply_filters(
			'pagecache_page_key',
			array(
				'key'                => array(
					$key_urlpart,
					$key_extension,
					$key_postfix,
					$key_compression,
				),
				'page_key_extension' => $page_key_extension,
				'url_fragments'      => $this->_request_url_fragments,
			)
		);

		return implode( '', $w3tc_key['key'] );
	}

	/**
	 * Normalizes and modifies the URL part of the page key.
	 *
	 * @param string $w3tc_key  The URL part of the cache key.
	 * @param array  $page_key_extension {
	 *     An array of page key extensions.
	 *
	 *     @type string $w3tc_group Optional. Group identifier for the page key.
	 * }
	 *
	 * @return string The normalized URL part of the cache key.
	 */
	private function _get_page_key_urlpart( $w3tc_key, $page_key_extension ) {
		// remove fragments.
		$w3tc_key = preg_replace( '~#.*$~', '', $w3tc_key );

		// host/uri in different cases means the same page in wp.
		$w3tc_key = strtolower( $w3tc_key );

		if ( empty( $page_key_extension['group'] ) ) {
			if ( $this->_enhanced_mode || $this->_nginx_memcached ) {
				$extra = '';

				// URL decode.
				$w3tc_key = urldecode( $w3tc_key );

				// replace double slashes.
				$w3tc_key = preg_replace( '~[/\\\]+~', '/', $w3tc_key );

				// replace index.php.
				$w3tc_key = str_replace( '/index.php', '/', $w3tc_key );

				// remove querystring.
				$w3tc_key = preg_replace( '~\?.*$~', '', $w3tc_key );

				// make sure one slash is at the end.
				if ( '/' === substr( $w3tc_key, strlen( $w3tc_key ) - 1, 1 ) ) {
					$extra = '_slash';
				}

				$w3tc_key = trim( $w3tc_key, '/' ) . '/';

				if ( $this->_nginx_memcached ) {
					return $w3tc_key;
				}

				return $w3tc_key . '_index' . $extra;
			}
		}

		return md5( $w3tc_key );
	}

	/**
	 * Appends debugging information to the footer comment.
	 *
	 * @param array $strings An array of strings to append debugging information to.
	 *
	 * @return array The modified array of footer comment strings.
	 */
	public function w3tc_footer_comment( $strings ) {
		$strings[] = sprintf(
			// translators: 1: Engine name, 2: Reject reason placeholder, 3: Page key extension.
			__( 'Page Caching using %1$s%2$s%3$s', 'w3-total-cache' ),
			Cache::engine_name( $this->_config->get_string( 'pgcache.engine' ) ),
			'{w3tc_pagecache_reject_reason}',
			isset( $this->_page_key_extension['cookie'] ) ? ' ' . $this->_page_key_extension['cookie'] : ''
		);

		if ( $this->_debug ) {
			$time_total  = Util_Debug::microtime() - $this->_time_start;
			$w3tc_engine = $this->_config->get_string( 'pgcache.engine' );
			$strings[]   = '';
			$strings[]   = 'Page cache debug info:';
			$strings[]   = sprintf( '%s%s', str_pad( 'Engine: ', 20 ), Cache::engine_name( $w3tc_engine ) );
			$strings[]   = sprintf( '%s%s', str_pad( 'Cache key: ', 20 ), $this->_page_key );

			$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 $w3tc_i ) {
					$strings[] = sprintf(
						'%s%s',
						str_pad( $w3tc_i['name'] . ': ', 20 ),
						Util_Content::escape_comment( $w3tc_i['value'] )
					);
				}
			}

			$strings[] = '';
		}

		return $strings;
	}

	/**
	 * Sends the provided headers.
	 *
	 * @param array $headers {
	 *     An associative array of headers to send.
	 *
	 *     @type string       $w3tc_name  The header name.
	 *     @type string|array $w3tc_value The header value or an array with 'n' for the name and 'v' for the value.
	 * }
	 *
	 * @return bool True on success, false if headers were already sent.
	 */
	public 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 ( is_array( $value0 ) && isset( $value0['n'] ) ) {
				$w3tc_name  = $value0['n'];
				$w3tc_value = $value0['v'];
			} else {
				$w3tc_name  = $name0;
				$w3tc_value = $value0;
			}

			if ( 'Status' === $w3tc_name ) {
				@header( $headers['Status'] );
			} elseif ( 'Status-Code' === $w3tc_name ) {
				if ( function_exists( 'http_response_code' ) ) { // php5.3 compatibility.
					@http_response_code( $headers['Status-Code'] );
				}
			} elseif ( ! empty( $w3tc_name ) && ! empty( $w3tc_value ) ) {
				@header( $w3tc_name . ': ' . $w3tc_value, ! isset( $repeating[ $w3tc_name ] ) );
				$repeating[ $w3tc_name ] = true;
			}
		}

		return true;
	}

	/**
	 * Sends caching-related headers.
	 *
	 * @param bool   $is_404         Whether the current request is a 404 error.
	 * @param int    $time           The cache creation time.
	 * @param string $etag           The ETag value.
	 * @param string $compression    The compression method used.
	 * @param array  $custom_headers Optional. Custom headers to include.
	 *
	 * @return void|bool True on success, false if headers were already sent, void if not modified.
	 */
	public 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'] = 'private, no-cache';
						break;

					case 'no_store':
						$headers['Pragma']        = 'no-store';
						$headers['Cache-Control'] = 'no-store';
						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.
		$w3tc_result = $this->_headers( $headers );

		if ( $exit ) {
			exit();
		}

		return $w3tc_result;
	}

	/**
	 * Retrieves common headers for caching purposes.
	 *
	 * @param string|null $compression The compression type to use, if any.
	 *
	 * @return array An associative array of headers to include.
	 */
	public 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;
	}

	/**
	 * Checks if the request's "If-Modified-Since" header matches the given time.
	 *
	 * @param int $time The timestamp to compare against.
	 *
	 * @return bool True if the header matches the given time, false otherwise.
	 */
	public function _check_modified_since( $time ) {
		if ( ! empty( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) ) {
			$if_modified_since = htmlspecialchars( stripslashes( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) );

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

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

		return false;
	}

	/**
	 * Checks if the request's "If-None-Match" header matches the given ETag.
	 *
	 * @param string $etag The ETag to compare against.
	 *
	 * @return bool True if the ETag matches, false otherwise.
	 */
	public 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;
	}

	/**
	 * Executes bad behavior protection if configured.
	 *
	 * @return void
	 */
	public function _bad_behavior() {
		$bb_file = $this->_config->get_string( 'pgcache.bad_behavior_path' );

		if ( '' === $bb_file ) {
			return;
		}

		/**
		 * Allowlist gate for the admin-configured Bad Behavior plugin path
		 *. The legacy code called
		 * `require_once $this->_config->get_string('pgcache.bad_behavior_path')`
		 * with zero validation -- any admin-settable string flowed straight
		 * into require_once. Mass-assignment writes to this key (handled
		 * separately by sec-fix-mass-assignment) gave a subscriber-reachable
		 * RCE primitive.
		 *
		 * The validator below enforces:
		 *   - realpath() canonicalization succeeds (file must exist)
		 *   - the resolved path lives under WP_PLUGIN_DIR, which is the
		 *     correct boundary because operators have multiple legitimate
		 *     install layouts (`bad-behavior`, `bad-behavior-mu`, etc.).
		 *     `/tmp/evil.php`, `/etc/passwd`, and anything else outside
		 *     `WP_PLUGIN_DIR` are rejected. The W3TC plugin directory is
		 *     itself under `WP_PLUGIN_DIR` and is therefore NOT excluded
		 *     by this prefix check; the realpath + `is_file()` checks
		 *     plus the fact that this method is only called from the
		 *     page-cache start path make a self-include via this key a
		 *     non-issue (no W3TC file is a sensible "Bad Behavior" hook).
		 *
		 * Failures are logged via Util_Debug::log('pgcache', ...). User-
		 * influenced path strings pass through the local
		 * `$sanitize_for_log` closure below — it escapes CR/LF to the
		 * literal sequences `\r` / `\n` and replaces any remaining
		 * control byte (`0x00`-`0x1F` / `0x7F`) with `?`, so a crafted
		 * config value cannot forge additional log lines (log-injection).
		 * Kept inline rather than promoted to a Util_Debug helper because
		 * this is the only log site in the file-inclusion fix that
		 * concatenates an admin-controlled string; promoting it would
		 * change the Util_Debug API surface for no other consumer.
		 *
		 * @since 2.10.0
		 */
		$sanitize_for_log = static function ( $w3tc_value ) {
			$w3tc_value = (string) $w3tc_value;
			$w3tc_value = \str_replace( array( "\r", "\n" ), array( '\\r', '\\n' ), $w3tc_value );

			return \preg_replace( '/[\x00-\x1F\x7F]/', '?', $w3tc_value );
		};

		$real = \realpath( $bb_file );

		if ( false === $real || ! \is_file( $real ) ) {
			if ( \class_exists( '\W3TC\Util_Debug' ) ) {
				Util_Debug::log( 'pgcache', 'bad_behavior_path rejected: realpath() failed for ' . $sanitize_for_log( $bb_file ) );
			}
			return;
		}

		$plugin_root = \defined( 'WP_PLUGIN_DIR' ) ? \realpath( WP_PLUGIN_DIR ) : false;

		if ( false === $plugin_root ) {
			if ( \class_exists( '\W3TC\Util_Debug' ) ) {
				Util_Debug::log( 'pgcache', 'bad_behavior_path rejected: WP_PLUGIN_DIR not resolvable' );
			}
			return;
		}

		if ( 0 !== \strpos( $real, $plugin_root . DIRECTORY_SEPARATOR ) ) {
			if ( \class_exists( '\W3TC\Util_Debug' ) ) {
				Util_Debug::log( 'pgcache', 'bad_behavior_path rejected: not under WP_PLUGIN_DIR (' . $sanitize_for_log( $real ) . ')' );
			}
			return;
		}

		require_once $real;
	}

	/**
	 * Parses dynamic content within the provided buffer.
	 *
	 * Security model for the registered-callback dispatcher:
	 *  - Layer 1: dispatch goes through a registered-callback registry
	 *    (the `w3tc_dynamic_callbacks` filter) — raw PHP / file paths are
	 *    refused; only `call:<slug>` payloads dispatch.
	 *  - Layer 2: each tag must carry an HMAC computed at cache-write time
	 *    using the HMAC key returned by `_dynamic_hmac_key()` (see that
	 *    helper's docblock for why it bypasses `wp_salt()`). Read-time
	 *    recomputes and rejects on mismatch. The HMAC is appended to
	 *    the cached tag by `_sign_dynamic_tags()` during the output-
	 *    buffering pass.
	 *  - Layer 3: if `W3TC_DYNAMIC_SECURITY` is undefined / empty / `1`,
	 *    no dispatch happens at all — the buffer is returned untouched.
	 *
	 * @since 2.10.0
	 *
	 * @param string $buffer The content buffer to parse.
	 *
	 * @return string The buffer with parsed dynamic content.
	 */
	public function _parse_dynamic( $buffer ) {
		// The W3TC_DYNAMIC_SECURITY constant should be a unique string and not an int or boolean.
		if ( ! defined( 'W3TC_DYNAMIC_SECURITY' ) || empty( W3TC_DYNAMIC_SECURITY ) || 1 === (int) W3TC_DYNAMIC_SECURITY ) {
			return $buffer;
		}

		$security = preg_quote( W3TC_DYNAMIC_SECURITY, '~' );

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

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

		return $buffer;
	}

	/**
	 * Returns the registry of dynamic callback slugs → callables.
	 *
	 * **Callback contract.** Every registered callable is invoked with
	 * two arguments: `( array $args, string $kind )`. `$args` is the
	 * JSON-decoded payload from the tag (always an array); `$kind` is
	 * the literal string `'mfunc'` or `'mclude'`. The second argument
	 * lets a callback serve both kinds with different rendering, or
	 * assert on `$kind` defensively. Callbacks may declare only
	 * `$args` if they don't need it — PHP discards the extra
	 * positional — but a typed/strict-mode signature MUST accept both.
	 *
	 * Themes and plugins register dispatchable callbacks via:
	 *
	 *     add_filter( 'w3tc_dynamic_callbacks', function( $cbs ) {
	 *         $cbs['my_slug'] = function( $args, $kind ) {
	 *             return '<span>' . esc_html( $args['user'] ?? '' ) . '</span>';
	 *         };
	 *         return $cbs;
	 *     } );
	 *
	 * Then emit a tag like:
	 *
	 *     <!-- mfunc TOKEN call:my_slug {"user":"alice"} --><!-- /mfunc TOKEN -->
	 *
	 * The HMAC envelope (`hmac:<hex>`) is added automatically at
	 * cache-write time; emitters MUST NOT compute it themselves.
	 *
	 * **Cache-miss fallback content.** Use the *inline-header* form (with the
	 * `call:slug` descriptor inside the opening comment) if you want HTML
	 * placed between the comments to survive a cache miss. The *body-form*
	 * (descriptor between the comments) is supported for back-compat but its
	 * body is overwritten by `_sign_dynamic_tags()` at write time — anything
	 * you placed there as fallback markup will be wiped before the cached
	 * file lands on disk.
	 *
	 * @since 2.10.0
	 *
	 * @return array<string,callable> Slug → callable(array $args, string $kind): string
	 */
	private function _get_dynamic_callbacks() {
		if ( ! \function_exists( 'apply_filters' ) ) {
			return array();
		}

		$callbacks = \apply_filters( 'w3tc_dynamic_callbacks', array() );

		return \is_array( $callbacks ) ? $callbacks : array();
	}

	/**
	 * Returns the HMAC secret used to sign dynamic-fragment payloads.
	 *
	 * Derived directly from `AUTH_KEY` + `AUTH_SALT` rather than
	 * `wp_salt('auth')` because the verifier runs from
	 * `advanced-cache.php`, which `wp-settings.php` loads *before*
	 * `wp-includes/pluggable.php` — so `wp_salt()` is undefined on
	 * the regular cache-HIT path for every non-`file_generic` cache
	 * engine (Disk: Basic, memcached, redis, APC, XCache). The
	 * signer runs from `ob_callback()` *after* pluggable is loaded,
	 * so calling `wp_salt('auth')` on the write side would derive
	 * the same constants but the verifier could not match it.
	 *
	 * Using the underlying constants directly gives the same site-
	 * bound rotation behaviour as `wp_salt('auth')` (`wp_salt` is
	 * itself a hash over `AUTH_KEY . AUTH_SALT` for the `auth`
	 * scheme) while remaining stable across the
	 * `advanced-cache.php` → `pluggable.php` boundary and across
	 * CLI test invocations where WordPress is not loaded at all.
	 *
	 * When neither constant is defined (a development site whose
	 * `wp-config.php` was generated without salts), the helper
	 * falls back to `W3TC_DYNAMIC_SECURITY` so the HMAC remains
	 * deterministic for that install rather than degenerating to
	 * an empty key.
	 *
	 * @since 2.10.0
	 *
	 * @return string
	 */
	private function _dynamic_hmac_key() {
		$w3tc_key = defined( 'AUTH_KEY' ) ? (string) AUTH_KEY : '';
		$salt     = defined( 'AUTH_SALT' ) ? (string) AUTH_SALT : '';

		if ( '' === $w3tc_key && '' === $salt ) {
			return defined( 'W3TC_DYNAMIC_SECURITY' ) ? (string) W3TC_DYNAMIC_SECURITY : '';
		}

		return 'w3tc-dynamic|' . $w3tc_key . '|' . $salt;
	}

	/**
	 * Computes the HMAC for a (kind, slug, args-json) tuple.
	 *
	 * @since 2.10.0
	 *
	 * @param string $kind      Tag kind, 'mfunc' or 'mclude'.
	 * @param string $slug      Callback slug.
	 * @param string $args_json The JSON args string in its **canonical
	 *                          form** — i.e. with leading/trailing
	 *                          whitespace trimmed. Both the signing path
	 *                          (`_sign_dynamic_tags`) and the verifying
	 *                          path (`_parse_dynamic_header` →
	 *                          `_dispatch_dynamic`) apply the same
	 *                          `trim()` before calling this helper, so
	 *                          the HMAC is deterministic across write
	 *                          and read for the same tag. Callers MUST
	 *                          NOT pass an untrimmed value; doing so
	 *                          would produce an HMAC that the verifier
	 *                          rejects.
	 *
	 * @return string Lowercase hex sha256 HMAC.
	 */
	public function _dynamic_hmac( $kind, $slug, $args_json ) {
		return \hash_hmac( 'sha256', $kind . '|' . $slug . '|' . $args_json, $this->_dynamic_hmac_key() );
	}

	/**
	 * Parses a mfunc / mclude tag header into (slug, args_json, hmac).
	 *
	 * Accepts the safe form:
	 *
	 *     call:<slug> <json-args> hmac:<hex>
	 *
	 * Whitespace between segments is flexible; `<json-args>` is the
	 * substring between the slug token and `hmac:`.  Returns `null` if
	 * the tag is not in the safe form (no `call:` prefix or no `hmac:`).
	 *
	 * @since 2.10.0
	 *
	 * @param string $header The raw payload header from the tag.
	 *
	 * @return array{slug:string,args_json:string,hmac:string}|null
	 */
	private function _parse_dynamic_header( $header ) {
		$header = trim( $header );

		if ( ! preg_match( '~^call:([A-Za-z0-9_\-\.:]+)\s*(.*?)\s*hmac:([0-9a-f]{64})$~is', $header, $m ) ) {
			return null;
		}

		return array(
			'slug'      => $m[1],
			'args_json' => trim( $m[2] ),
			'hmac'      => strtolower( $m[3] ),
		);
	}

	/**
	 * Decodes a tag's JSON args, returning an empty array for empty / invalid input.
	 *
	 * @since 2.10.0
	 *
	 * @param string $args_json JSON string.
	 *
	 * @return array
	 */
	private function _decode_dynamic_args( $args_json ) {
		if ( '' === $args_json ) {
			return array();
		}

		$decoded = \json_decode( $args_json, true );

		return \is_array( $decoded ) ? $decoded : array();
	}

	/**
	 * Logs a deprecation notice when raw-PHP mfunc / file-path mclude tags
	 * are seen at dispatch time.  These tags are no longer executed — emitters
	 * must migrate to the `call:<slug>` registered-callback form.
	 *
	 * @since 2.10.0
	 *
	 * @param string $kind   'mfunc' or 'mclude'.
	 * @param string $reason Human-readable reason.
	 *
	 * @return void
	 */
	private function _log_dynamic_deprecation( $kind, $reason ) {
		/**
		 * Rate-limit identical (kind|reason) notices to once per 5 minutes
		 * per site. On a high-traffic site, the first cache miss after this
		 * patch ships re-renders every still-cached legacy tag through this
		 * path; without a guard, `_doing_it_wrong()` floods admin notices
		 * (when WP_DEBUG is on) and `error_log()` floods the system log on
		 * every page load until the cache rolls over. The dedupe key uses
		 * md5() rather than the raw string because $reason can contain HMACs
		 * and arbitrary slugs, and transient keys are length-bounded.
		 */
		$dedupe_key = 'w3tc_dyn_dep_' . md5( (string) $kind . '|' . (string) $reason );
		if ( \function_exists( 'get_site_transient' ) && \function_exists( 'set_site_transient' ) ) {
			if ( false !== \get_site_transient( $dedupe_key ) ) {
				return;
			}
			\set_site_transient( $dedupe_key, 1, 300 );
		}

		if ( \function_exists( '_doing_it_wrong' ) ) {
			\_doing_it_wrong(
				\esc_html( $kind ),
				\esc_html(
					sprintf(
						/* translators: 1: tag kind (mfunc/mclude), 2: reason. */
						'W3TC dynamic %1$s tag refused: %2$s. Raw PHP / file-path payloads are no longer dispatched; migrate to the registered-callback form (<!-- %1$s TOKEN call:slug {...} -->) via the `w3tc_dynamic_callbacks` filter.',
						$kind,
						$reason
					)
				),
				'2.10.0'
			);
		} elseif ( \function_exists( 'error_log' ) ) {
			\error_log( // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
				sprintf( '[W3TC] dynamic %s tag refused: %s', $kind, $reason )
			);
		}
	}

	/**
	 * Dispatches a verified, registered callback by slug.
	 *
	 * @since 2.10.0
	 *
	 * @param string $kind 'mfunc' or 'mclude'.
	 * @param string $slug Callback slug.
	 * @param array  $args Decoded JSON args.
	 *
	 * @return string The callback's HTML output, or an error sentinel.
	 */
	private function _dispatch_dynamic_callback( $kind, $slug, $args ) {
		$callbacks = $this->_get_dynamic_callbacks();

		if ( empty( $callbacks ) ) {
			return \htmlspecialchars(
				sprintf( 'W3TC dynamic %s registry is empty; no callbacks registered.', $kind ),
				ENT_QUOTES,
				'UTF-8'
			);
		}

		if ( ! isset( $callbacks[ $slug ] ) || ! \is_callable( $callbacks[ $slug ] ) ) {
			return \htmlspecialchars(
				sprintf( 'W3TC dynamic %s slug "%s" is not registered.', $kind, $slug ),
				ENT_QUOTES,
				'UTF-8'
			);
		}

		try {
			$w3tc_output = \call_user_func( $callbacks[ $slug ], $args, $kind );
		} catch ( \Throwable $ex ) {
			return \htmlspecialchars(
				sprintf( 'W3TC dynamic %s slug "%s" raised an exception.', $kind, $slug ),
				ENT_QUOTES,
				'UTF-8'
			);
		}

		if ( ! \is_string( $w3tc_output ) ) {
			/**
			 * A callback that returns null/false/an array silently coerces to
			 * an empty (or garbled) string and hides the bug from site owners
			 * — the fragment just disappears. Surface it through the same
			 * log channel as the deprecation path so the breakage is visible
			 * (and rate-limited identically) before we coerce.
			 */
			$this->_log_dynamic_deprecation(
				$kind,
				sprintf( 'callback "%s" returned non-string %s', $slug, \gettype( $w3tc_output ) )
			);

			/**
			 * `(string)` on an array or a non-Stringable object raises a PHP
			 * warning and produces the literal `"Array"` / "Object of class …
			 * could not be converted" sentinel. Both are useless in cached
			 * HTML and noisy in the error log. Coerce scalars (which have
			 * useful string forms — `null` → `''`, `false` → `''`, numbers
			 * → the digits) but emit an empty string for the rest.
			 */
			if ( \is_scalar( $w3tc_output ) || ( \is_object( $w3tc_output ) && \method_exists( $w3tc_output, '__toString' ) ) ) {
				return (string) $w3tc_output;
			}

			return '';
		}

		return $w3tc_output;
	}

	/**
	 * Common dispatcher for mfunc / mclude tags.
	 *
	 * Enforces the three security layers:
	 *  1. Refuses unless `W3TC_DYNAMIC_SECURITY` is defined (already gated
	 *     upstream by `_parse_dynamic()`).
	 *  2. Refuses unless the payload is in the `call:<slug>` form with a
	 *     valid HMAC envelope.
	 *  3. Refuses unless the slug is in the registered-callback registry.
	 *
	 * @since 2.10.0
	 *
	 * @param string $kind    'mfunc' or 'mclude'.
	 * @param array  $matches preg_replace_callback matches: [0]=full, [1]=header, [2]=body.
	 *
	 * @return string
	 */
	private function _dispatch_dynamic( $kind, $matches ) {
		$header = isset( $matches[1] ) ? trim( $matches[1] ) : '';
		$body   = isset( $matches[2] ) ? trim( $matches[2] ) : '';

		/**
		 * Prefer the header for the call descriptor; fall back to the body for
		 * the alternate "<!-- mfunc TOKEN -->call:slug ... hmac:hex<!-- /mfunc TOKEN -->" form.
		 */
		$candidate = '' !== $header ? $header : $body;
		$parsed    = $this->_parse_dynamic_header( $candidate );

		if ( null === $parsed ) {
			$this->_log_dynamic_deprecation( $kind, 'raw payload (no call:slug + hmac envelope)' );

			return \htmlspecialchars(
				sprintf( 'W3TC dynamic %s tag refused: missing call:slug + hmac envelope.', $kind ),
				ENT_QUOTES,
				'UTF-8'
			);
		}

		$expected = $this->_dynamic_hmac( $kind, $parsed['slug'], $parsed['args_json'] );

		if ( ! \hash_equals( $expected, $parsed['hmac'] ) ) {
			$this->_log_dynamic_deprecation( $kind, 'HMAC mismatch' );

			return \htmlspecialchars(
				sprintf( 'W3TC dynamic %s tag refused: HMAC mismatch.', $kind ),
				ENT_QUOTES,
				'UTF-8'
			);
		}

		return $this->_dispatch_dynamic_callback( $kind, $parsed['slug'], $this->_decode_dynamic_args( $parsed['args_json'] ) );
	}

	/**
	 * Dispatches a dynamic mfunc tag.
	 *
	 * Previously this method `eval()`'d arbitrary PHP from the tag payload.
	 * That primitive has been removed; only registered callbacks dispatched
	 * via `call:<slug>` + HMAC are honored.
	 *
	 * @since 2.10.0
	 *
	 * @param array $matches The matches from the regular expression.
	 *
	 * @return string The callback's output, or an error message.
	 */
	public function _parse_dynamic_mfunc( $matches ) {
		return $this->_dispatch_dynamic( 'mfunc', $matches );
	}

	/**
	 * Dispatches a dynamic mclude tag.
	 *
	 * Previously this method `include`'d a relative file path supplied
	 * inside the tag.  That primitive has been removed; only registered
	 * callbacks dispatched via `call:<slug>` + HMAC are honored.  Plugins
	 * that need to render an include's output should wrap it in a slug.
	 *
	 * @since 2.10.0
	 *
	 * @param array $matches The matches from the regular expression.
	 *
	 * @return string The callback's output, or an error message.
	 */
	public function _parse_dynamic_mclude( $matches ) {
		return $this->_dispatch_dynamic( 'mclude', $matches );
	}

	/**
	 * Signs every dynamic mfunc / mclude tag in $buffer by appending an
	 * `hmac:<hex>` envelope to the `call:<slug>` descriptor.  Called once
	 * before the buffer is written to the page cache so that later
	 * read-time dispatch can verify integrity.
	 *
	 * Both inline-header form (`<!-- mfunc TOKEN call:slug ... -->...<!-- /mfunc TOKEN -->`)
	 * and between-tags / body form (`<!-- mfunc TOKEN -->call:slug ...<!-- /mfunc TOKEN -->`)
	 * are signed in place, because dispatch accepts both shapes.
	 *
	 * Tags whose payload is not in the safe `call:<slug>` form are left
	 * unsigned — at dispatch time they will fall through to the
	 * deprecation path and refuse to execute.  This is intentional: it
	 * makes back-compat behavior visible (an error in place of the tag)
	 * rather than silently dropping the tag at write time.
	 *
	 * @since 2.10.0
	 *
	 * @param string $buffer Buffer containing rendered HTML.
	 *
	 * @return string Buffer with HMAC envelopes added.
	 */
	public function _sign_dynamic_tags( $buffer ) {
		if ( ! defined( 'W3TC_DYNAMIC_SECURITY' ) || empty( W3TC_DYNAMIC_SECURITY ) || 1 === (int) W3TC_DYNAMIC_SECURITY ) {
			return $buffer;
		}

		$security = preg_quote( W3TC_DYNAMIC_SECURITY, '~' );

		$sign_one = function ( $kind ) {
			return function ( $matches ) use ( $kind ) {
				$header   = isset( $matches[1] ) ? trim( $matches[1] ) : '';
				$body_raw = isset( $matches[2] ) ? $matches[2] : '';
				$body     = trim( $body_raw );

				// If the header already has a complete `call:slug ... hmac:hex` envelope, leave it alone.
				if ( null !== $this->_parse_dynamic_header( $header ) ) {
					return $matches[0];
				}

				// Likewise, leave a fully-signed body-form alone.
				if ( '' === $header && null !== $this->_parse_dynamic_header( $body ) ) {
					return $matches[0];
				}

				/**
				 * Determine where the `call:<slug>` descriptor lives: in the header
				 * (inline form) or in the body (between-tags form).  Both forms are
				 * honored at dispatch time, so both must be signed at write time.
				 */
				if ( preg_match( '~^call:([A-Za-z0-9_\-\.:]+)\s*(.*)$~is', $header, $m ) ) {
					$source = 'header';
				} elseif ( '' === $header && preg_match( '~^call:([A-Za-z0-9_\-\.:]+)\s*(.*)$~is', $body, $m ) ) {
					$source = 'body';
				} else {
					// Raw-PHP / file-path payload — leave unsigned; dispatch will refuse.
					return $matches[0];
				}

				$slug      = $m[1];
				$args_json = trim( $m[2] );
				$hmac      = $this->_dynamic_hmac( $kind, $slug, $args_json );

				$w3tc_descriptor = 'call:' . $slug;
				if ( '' !== $args_json ) {
					$w3tc_descriptor .= ' ' . $args_json;
				}
				$w3tc_descriptor .= ' hmac:' . $hmac;

				if ( 'header' === $source ) {
					return '<!-- ' . $kind . ' ' . W3TC_DYNAMIC_SECURITY . ' ' . $w3tc_descriptor . ' -->' . $body_raw . '<!-- /' . $kind . ' ' . W3TC_DYNAMIC_SECURITY . ' -->';
				}

				return '<!-- ' . $kind . ' ' . W3TC_DYNAMIC_SECURITY . ' -->' . $w3tc_descriptor . '<!-- /' . $kind . ' ' . W3TC_DYNAMIC_SECURITY . ' -->';
			};
		};

		/**
		 * `\s*` (NOT `\s+`) between the security token and the closing
		 * `-->` so we match the same set of tags as `_parse_dynamic` /
		 * `_has_dynamic` (both use `(.*)-->`, accepting zero whitespace).
		 * A tag like `<!-- mfunc TOKEN-->call:slug...<!-- /mfunc TOKEN -->`
		 * would otherwise be detected as dynamic at parse time but never
		 * signed at write time — dispatch would then refuse it for a
		 * missing HMAC envelope.
		 */
		$buffer = preg_replace_callback(
			'~<!--\s*mfunc\s+' . $security . '\s*(.*?)\s*-->(.*?)<!--\s*/mfunc\s+' . $security . '\s*-->~is',
			$sign_one( 'mfunc' ),
			$buffer
		);

		$buffer = preg_replace_callback(
			'~<!--\s*mclude\s+' . $security . '\s*(.*?)\s*-->(.*?)<!--\s*/mclude\s+' . $security . '\s*-->~is',
			$sign_one( 'mclude' ),
			$buffer
		);

		return $buffer;
	}

	/**
	 * Checks if the buffer contains dynamic tags.
	 *
	 * @param string $buffer The content buffer to check.
	 *
	 * @return bool True if dynamic tags are present, false otherwise.
	 */
	public function _has_dynamic( $buffer ) {
		if ( ! defined( 'W3TC_DYNAMIC_SECURITY' ) || empty( W3TC_DYNAMIC_SECURITY ) || 1 === (int) W3TC_DYNAMIC_SECURITY ) {
			return false;
		}

		$security = preg_quote( W3TC_DYNAMIC_SECURITY, '~' );

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

	/**
	 * Determines if the content type is cacheable.
	 *
	 * @return bool True if the content type is cacheable, false otherwise.
	 */
	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, true );
	}

	/**
	 * Preprocesses the request URI into its components.
	 *
	 * @return void
	 */
	private function _preprocess_request_uri() {
		$w3tc_p = explode( '?', $this->_request_uri, 2 );

		$this->_request_url_fragments['path']        = $w3tc_p[0];
		$this->_request_url_fragments['querystring'] = ( empty( $w3tc_p[1] ) ? '' : '?' . $w3tc_p[1] );

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

	/**
	 * Normalizes URL fragments.
	 *
	 * @param array $fragments {
	 *     The URL fragments to normalize.
	 *
	 *     @type string $querystring The query string to normalize.
	 * }
	 *
	 * @return array The normalized 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;
	}

	/**
	 * Normalizes the query string in a URL.
	 *
	 * @param string $querystring The query string to normalize.
	 *
	 * @return string The normalized query string.
	 */
	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;
	}

	/**
	 * Handles delayed cache printing when applicable.
	 *
	 * @return void
	 */
	public function delayed_cache_print() {
		if ( $this->_late_caching && $this->_caching ) {
			$this->_cached_data = $this->_extract_cached_page( true );
			if ( $this->_cached_data ) {
				global $w3tc_w3_late_caching_succeeded;
				$w3tc_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;
		}
	}

	/**
	 * Conditionally saves the cached result with optional compression.
	 *
	 * @param string $buffer            The content buffer to cache.
	 * @param array  $response_headers  The response headers to include in the cache.
	 * @param bool   $has_dynamic       Whether the content includes dynamic tags.
	 *
	 * @return string The buffer, possibly modified for compression.
	 */
	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 = ( '404' === $headers['Status-Code'] );
		} 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;

		do_action(
			'w3tc_pagecache_before_set',
			array(
				'request_url_fragments' => $this->_request_url_fragments,
				'page_key_extension'    => $this->_page_key_extension,
			)
		);

		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;
	}

	/**
	 * Collects usage statistics for the current request.
	 *
	 * @param object $storage The storage object for saving statistics.
	 *
	 * @return void
	 */
	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
				);
			}
		}
	}

	/**
	 * Logs a message to the page cache log.
	 *
	 * @param string $msg The message to log.
	 *
	 * @return bool|int The number of bytes written, or false on failure.
	 */
	protected static function log( $msg ) {
		$w3tc_data = sprintf(
			'[%1$s] [%2$s] [%3$s] %4$s ' . "\n",
			gmdate( 'r' ),
			isset( $_SERVER['REQUEST_URI'] ) ? filter_var( stripslashes( $_SERVER['REQUEST_URI'] ), FILTER_SANITIZE_URL ) : '',
			! empty( $_SERVER['HTTP_REFERER'] ) ? htmlspecialchars( $_SERVER['HTTP_REFERER'] ) : '-',
			$msg
		);
		$w3tc_data = strtr( $w3tc_data, '<>', '..' );
		/**
		 * Assignment used to land in `$date` (typo for `$w3tc_data`),
		 * so the redacted form was never written and the log file kept
		 * the raw `_wpnonce=` value. Keep the variable name on `$w3tc_data`
		 * so the file_put_contents below writes the redacted form.
		 */
		$w3tc_data = Util_Debug::redact_wpnonce( $w3tc_data );

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

		return @file_put_contents( $filename, $w3tc_data, FILE_APPEND );
	}
}