Some solutions to some common problems found in the plugin Swift Performance.

001-filterbyhttpcode.php

<?php

/*
 * We verify the HTTP code that WordPress will send and then we decide if the current page
 * should be allowed to be cached.
 */
add_filter('swift_performance_is_cacheable', 'dtorrer_swift_iscacheable', 20, 1);
function dtorrer_swift_iscacheable( $cacheable = FALSE ){
	if( FALSE === $cacheable ){ return $cacheable; }
	
	/*
	 * We obtain the status code that will be sent to the user.
	 */
	$current = http_response_code();
	
	/*
	 * If the current HTTP code is one of the list bellow, it should not
	 * be cached. For that, we should return FALSE.
	 */
	$codes = [
		301, 302, 307, 308,
		400, 401, 403, 405, 408, 418, 421,
		500, 502, 503, 504, 508
	];
	
	if( in_array($current, $codes) ){
		return FALSE;
	}
	
	return $cacheable;
}

?>

002-filterbyhttpcode.php

<?php

/*
 * We verify the HTTP code that WordPress will send and then we decide if the current page
 * should be allowed to be cached.
 */
add_filter('swift_performance_is_cacheable', 'dtorrer_swift_iscacheable', 20, 1);
function dtorrer_swift_iscacheable( $cacheable = FALSE ){
	if( FALSE === $cacheable ){ return $cacheable; }
	
	/*
	 * If the HTTP code is not exactly 200, we should not cache it.
	 */
	if( 200 !== http_response_code() ){
		return FALSE;
	}
	
	return $cacheable;
}

?>

003-filterbyurl.php

<?php

/*
 * We look at the requested document and then we decide if it should be allowed
 * to be cached by Swift Performance.
 */
add_filter('swift_performance_is_cacheable', 'dtorrer_swift_iscacheable', 20, 1);
function dtorrer_swift_iscacheable( $cacheable = FALSE ){
	if( FALSE === $cacheable ){ return $cacheable; }

	/*
	 * If any of the next points is accessed, we should return FALSE to prevent
	 * it from being cached.
	 */
	if( isset($_SERVER['REQUEST_URI']) ){
		$list = array(
			'/robots.txt',
			'/xmlrpc.php',
			'/post-sitemap.xml',
			'/sitemap_index.xml',
			'/wp-json/',
			'/page/',
			'/category/',
			'/tag/',
			'/wp-admin/',
			'/project_tag-sitemap.xml',
			'/page-sitemap.xml',
			'/project-sitemap.xml',
			'/project_category-sitemap.xml',
		);
		
		$regex = "(" . implode('|', $list) . ")";
		if( 1 === preg_match($regex, $_SERVER["REQUEST_URI"]) ){
			return FALSE;
		}
	}
	
	return $cacheable;
}

?>

004-cronjobsize.php

<?php

/*
 * We ensure that the cron job is properly hooked uppon activation. Or when run and it is not
 * scheduled already.
 */
register_activation_hook(plugin_basename( __FILE__ ), 'dtorrer_activate_cronswift');
add_action('plugins_loaded', 'dtorrer_activate_cronswift');
function dtorrer_activate_cronswift(){
	if( !wp_next_scheduled('dtorrer_validate_swiftcache') ){
		wp_schedule_event(time(), 'hourly', 'dtorrer_validate_swiftcache');
	}
}

/*
 * We make sure to turn off the cron job when plugin is deactivated.
 */
register_deactivation_hook(plugin_basename( __FILE__ ), 'dtorrer_turnoff_cronswift');
function dtorrer_turnoff_cronswift(){
	wp_clear_scheduled_hook('dtorrer_validate_swiftcache');
}

/*
 * We perform the verification of the cache size of Swift Performance. If it is bigger than expected,
 * then we delete it.
 */
add_action('dtorrer_validate_swiftcache', 'dtorrer_doSwiftCacheVerification');
function dtorrer_doSwiftCacheVerification(){
	/* If the required classes does not exist, we exit */
	if( !class_exists('Swift_Performance_Cache') || !class_exists('Swift_Performance_Lite') ){
		return FALSE;
	}
	
	/* Each page should be around 0.8 MB of size, can be adjusted */
	$pagesize = 0.8;
	
	/* We calculate the needed values */
	$max = (count(Swift_Performance_Lite::get_prebuild_urls(TRUE)) * $pagesize) * (1024 * 1024);
	$directory = trailingslashit(Swift_Performance_Lite::get_option('cache-path')) . SWIFT_PERFORMANCE_CACHE_BASE_DIR;
	$size = Swift_Performance_Lite::cache_dir_size($directory);
	
	/* If the size of the cache is bigger than expected, we purge it */
	if( $size >= $max ){
		global $wpdb;
		$wpdb->query('DROP TABLE IF EXISTS ' . SWIFT_PERFORMANCE_TABLE_PREFIX . 'warmup');
		delete_option(SWIFT_PERFORMANCE_TABLE_PREFIX . 'db_version');
		delete_transient('swift_performance_initial_prebuild_links');
		Swift_Performance_Lite::db_install();
		Swift_Performance_Cache::clear_all_cache();
		Swift_Performance_Lite::get_prebuild_urls();
	}
}


?>

005-cronjobdaily.php

<?php

/*
 * We ensure that the cron job is properly hooked uppon activation. Or when run and it is not
 * scheduled already.
 */
register_activation_hook(plugin_basename( __FILE__ ), 'dtorrer_activate_cronswift');
add_action('plugins_loaded', 'dtorrer_activate_cronswift');
function dtorrer_activate_cronswift(){
	if( !wp_next_scheduled('dtorrer_validate_swiftcache') ){
		wp_schedule_event(time(), 'daily', 'dtorrer_validate_swiftcache');
	}
}

/*
 * We make sure to turn off the cron job when plugin is deactivated.
 */
register_deactivation_hook(plugin_basename( __FILE__ ), 'dtorrer_turnoff_cronswift');
function dtorrer_turnoff_cronswift(){
	wp_clear_scheduled_hook('dtorrer_validate_swiftcache');
}

/*
 * We perform the verification of the cache size of Swift Performance. If it is bigger than expected,
 * then we delete it.
 */
add_action('dtorrer_validate_swiftcache', 'dtorrer_doSwiftCacheVerification');
function dtorrer_doSwiftCacheVerification(){
	/* If the required classes does not exist, we exit */
	if( !class_exists('Swift_Performance_Cache') || !class_exists('Swift_Performance_Lite') ){
		return FALSE;
	}
	
	/* We purge the cache */
	global $wpdb;
	$wpdb->query('DROP TABLE IF EXISTS ' . SWIFT_PERFORMANCE_TABLE_PREFIX . 'warmup');
	delete_option(SWIFT_PERFORMANCE_TABLE_PREFIX . 'db_version');
	delete_transient('swift_performance_initial_prebuild_links');
	Swift_Performance_Lite::db_install();
	Swift_Performance_Cache::clear_all_cache();
	Swift_Performance_Lite::get_prebuild_urls();
}


?>

006-enabledhosts.php

<?php

/*
 * We get a list of "Enabled Hosts" from the cache directory that Swift Performance uses. The directories at the root
 * folder are named after hosts of what Swift has created cache for.
 */
add_filter('swift_performance_enabled_hosts', 'dtorrer_swift_cachedirectories', 20, 1);
function dtorrer_swift_cachedirectories( $list = array() ){
	/*
	 * If we are on a multisite install, we should not mess with this.
	 */
	if( is_multisite() ){ return $list; }
	$dirs = array();
	
	/*
	 * We check if Swift Performance is running and then we get the list of directories from the cache.
	 */
	if( class_exists('Swift_Performance_Lite') ){
		$base = trailingslashit(Swift_Performance_Lite::get_option('cache-path')) . SWIFT_PERFORMANCE_CACHE_BASE_DIR;
		$dirs = glob($base . '*/');
		
		/*
		 * Each directory at the root of the cache of Swift Performance is named after a host, so we can return it
		 * as a list of enabled hosts.
		 */
		if( is_array($dirs) ){
			foreach( $dirs as $key => $current ){
				$dirs[$key] = untrailingslashit(str_replace($base, '', $current));
			}
		}
	}
	
	return array_unique(array_merge($list, $dirs), SORT_STRING);
}

?>