Logging Failed Redirects

WordPress has a built-in function called wp_safe_redirect().  This allows you to create redirects in code, but only to whitelisted domains (via the allowed_redirect_hosts filter).

The downside to this is that you have to remember to whitelist the domains.  It’s easy to forget if you’re doing a lot of redirects, for instance with the WPCOM Legacy Redirector plugin.

When this happens, all un-whitelisted redirects will be redirected by default to /wp-admin/ instead, and can cause a headache trying to figure out what’s going wrong.

I had an idea to solve this problem.  A simple logging plugin that logs failed redirects and adds a dashboard widget to show the domains and number of times the redirect has failed:

The code behind this:

<?php
class Emrikol_WSRD_Dashboard {
	public static function instance() {
		static $instance = false;
		if ( ! $instance ) {
			$instance = new Emrikol_WSRD_Dashboard();
		}
		return $instance;
	}

	public function __construct() {
		add_action( 'init', array( $this, 'init' ) );
		add_filter( 'allowed_redirect_hosts', array( $this, 'check_redirect' ), PHP_INT_MAX, 2 );
	}

	public function init() {
		if ( $this->is_admin() && isset( $_GET['wsrd_delete'] ) && check_admin_referer( 'wsrd_delete' ) && isset( $_GET['ID'] ) ) {
			$post_id = (int) $_GET['ID'];

			if ( 'wsrd' !== get_post_type( $post_id ) ) {
				// This isn't the right post type, abort!
				add_action( 'admin_notices', array( $this, 'message_log_not_deleted' ) );
				return;
			}

			$delete = wp_delete_post( $post_id, true );
			wp_cache_delete( 'wsrd_report' );

			if ( $delete ) {
				add_action( 'admin_notices', array( $this, 'message_log_deleted' ) );
			} else {
				add_action( 'admin_notices', array( $this, 'message_log_not_deleted' ) );
			}
		}

		$args = array(
			'supports' => array( 'title' ),
			'public'   => false,
		);
		register_post_type( 'wsrd', $args );

		add_action( 'wp_dashboard_setup', array( $this, 'add_dashboard_widgets' ) );
	}

	public function add_dashboard_widgets() {
		if ( $this->is_admin() ) {
			wp_add_dashboard_widget( 'emrikol_wsrd_dashboard', 'Failed Safe Redirects', array( $this, 'show_admin_dashboard' ) );
		}
	}

	public function check_redirect( $allowed_hosts, $redirect_host ) {
		if ( ! in_array( $redirect_host, $allowed_hosts, true ) ) {
			// No redirect, please record.
			$found_host = new WP_Query( array(
				'fields'                 => 'ids',
				'name'                   => md5( $redirect_host ),
				'post_type'              => 'wsrd',
				'post_status'            => 'any',
				'no_found_rows'          => true,
				'posts_per_page'         => 1,
				'update_post_term_cache' => false,
				'update_post_meta_cache' => false,
			) );

			if ( empty( $found_host->posts ) ) {
				// No past redirect log found, create one.
				$args   = array(
					'post_name'  => md5( $redirect_host ),
					'post_title' => $redirect_host,
					'post_type'  => 'wsrd',
					'meta_input' => array(
						'count' => 1,
					),
				);
				$insert = wp_insert_post( $args );
			} else {
				// Found!  Update count.
				$count = absint( get_post_meta( $found_host->posts[0], 'count', true ) );
				$count++;
				update_post_meta( $found_host->posts[0], 'count', $count );
			}
		}
		// We don't want to modify, always return allowed hosts unharmed.
		return $allowed_hosts;
	}

	public function show_admin_dashboard() {
		global $wpdb;

		$report = wp_cache_get( 'wsrd_report' );
		if ( false === $report ) {
			$report = $wpdb->get_results( "SELECT ID, post_title AS host, meta_value AS count FROM $wpdb->posts LEFT JOIN $wpdb->postmeta ON ( $wpdb->posts.ID = $wpdb->postmeta.post_id ) WHERE post_type='wsrd'  ORDER BY ABS( count ) DESC LIMIT 20;" );
			wp_cache_set( 'wsrd_report', $report, 'default', MINUTE_IN_SECONDS * 5 );
		}

		?>
		<style>
			table#wsrd {
				border-collapse: collapse;
				width: 100%;
			}
			table#wsrd th {
				background: #f5f5f5;
			}

			table#wsrd th, table#wsrd td {
				border: 1px solid #f5f5f5;
				padding: 8px;
			}

			table#wsrd tr:nth-child(even) {
				background: #fafafa;
			}
		</style>
		<div class="activity-block">
			<?php if ( empty( $report ) ) : ?>
			<p><strong>None Found!</strong></p>
			<?php else : ?>
			<table id="wsrd">
				<thead>
					<tr>
						<th>Domain</th>
						<th>Count</th>
						<th>Control</th>
					</tr>
				</thead>
				<tbody>
					<?php foreach ( $report as $line ) : ?>
						<tr>
							<td><?php echo esc_html( $line->host ); ?></td>
							<td><?php echo esc_html( $line->count ); ?></td>
							<td><a href="<?php echo esc_url( wp_nonce_url( add_query_arg( array( 'wsrd_delete' => true, 'ID' => rawurlencode( $line->ID ) ), admin_url() ), 'wsrd_delete' ) ); ?>">Delete</a></td>
						</tr>
					<?php endforeach; ?>
				</tbody>
			</table>
			<?php endif; ?>
		</div>
		<?php
	}

	public function message_log_deleted() {
		echo '<div id="message" class="notice notice-success is-dismissible"><p>Redirect log deleted!</p></div>';
	}

	public function message_log_not_deleted() {
		echo '<div id="message" class="notice notice-error is-dismissible"><p>Redirect log delete failed!</p></div>';
	}


	private function is_admin() {
		if ( current_user_can( 'manage_options' ) ) {
			return true;
		}
		return false;
	}
}
Emrikol_WSRD_Dashboard::instance();

Query Caching (and a little extra)

By default, WordPress does not cache WP_Query queries.  Doing so can greatly improve performance.  The way I do this is via the Advanced Post Cache plugin:

By running this plugin (hopefully as an mu-plugin) with a persistent object cache, WP_Query calls, along with get_post() calls (only if suppress_filters is false) will be cached.

Bonus!

Now that we’re caching queries, here’s how I do a little extra caching to squeeze out a tiny bit more performance:

<?php
// By default Jetpack does not cache responses from Instagram oembeds.
add_filter( 'instagram_cache_oembed_api_response_body', '__return_true' );

// Cache WP Dashboard Recent Posts Query
add_filter( 'dashboard_recent_posts_query_args', 'cache_dashboard_recent_posts_query_args', 10, 1 );
function cache_dashboard_recent_posts_query_args( $query_args ) {
	$query_args['cache_results'] = true;
	$query_args['suppress_filters'] = false;
	return $query_args;
}

// Cache WP Dashboard Recent Drafts Query
add_filter( 'dashboard_recent_drafts_query_args', 'cache_dashboard_recent_drafts_query_args', 10, 1 );
function cache_dashboard_recent_drafts_query_args( $query_args ) {
	$query_args['suppress_filters'] = false;
	return $query_args;
}

// Cache comment counts, https://github.com/Automattic/vip-code-performance/blob/master/core-fix-comment-counts-caching.php
add_filter( 'wp_count_comments', 'wpcom_vip_cache_full_comment_counts', 10, 2 );
function wpcom_vip_cache_full_comment_counts( $counts = false , $post_id = 0 ){
	//We are only caching the global comment counts for now since those are often in the millions while the per page one is usually more reasonable.
	if ( 0 !== $post_id ) {
		return $counts;
	}

	$cache_key = "vip-comments-{$post_id}";
	$stats_object = wp_cache_get( $cache_key );

	//retrieve comments in the same way wp_count_comments() does
	if ( false === $stats_object ) {
		$stats = get_comment_count( $post_id );
		$stats['moderated'] = $stats['awaiting_moderation'];
		unset( $stats['awaiting_moderation'] );
		$stats_object = (object) $stats;

		wp_cache_set( $cache_key, $stats_object, 'default', 30 * MINUTE_IN_SECONDS );
	}

	return $stats_object;
}

// Cache monthly media array.
add_filter( 'media_library_months_with_files', 'wpcom_vip_media_library_months_with_files' );
function wpcom_vip_media_library_months_with_files() {
	$months = wp_cache_get( 'media_library_months_with_files', 'extra-caching' );

	if ( false === $months ) {
		global $wpdb;
		$months = $wpdb->get_results( $wpdb->prepare( "
			SELECT DISTINCT YEAR( post_date ) AS year, MONTH( post_date ) AS month
			FROM $wpdb->posts
			WHERE post_type = %s
			ORDER BY post_date DESC
			", 'attachment' )
		);
		wp_cache_set( 'media_library_months_with_files', $months, 'extra-caching' );
	}

	return $months;
}

add_action( 'add_attachment', 'media_library_months_with_files_bust_cache' );
function media_library_months_with_files_bust_cache( $post_id ) {
	if ( defined( 'WP_IMPORTING' ) && WP_IMPORTING ) {
		return;
	}

	// What month/year is the most recent attachment?
	global $wpdb;
	$months = $wpdb->get_results( $wpdb->prepare( "
			SELECT DISTINCT YEAR( post_date ) AS year, MONTH( post_date ) AS month
			FROM $wpdb->posts
			WHERE post_type = %s
			ORDER BY post_date DESC
			LIMIT 1
		", 'attachment' )
	);

	// Simplify by assigning the object to $months
	$months = array_shift( array_values( $months ) );

	// Compare the dates of the new, and most recent, attachment
	if (
		! $months->year == get_the_time( 'Y', $post_id ) &&
		! $months->month == get_the_time( 'm', $post_id )
	) {
		// the new attachment is not in the same month/year as the
		// most recent attachment, so we need to refresh the transient
		wp_cache_delete( 'media_library_months_with_files', 'extra-caching' );
	}
}

Gutenberg, Code, and Highlighting

One of the great things about Gutenberg is the ability to compartmentalize different types of content within blocks.  One of the blocks that I’ve been using a lot of recently is the code block.  This block by default will render something like this:

#include <stdio.h>
int main()
{
   // printf() displays the string inside quotation
   printf("Hello, World!");
   return 0;
}

While this is acceptable, it’s not very pretty.  I used to use the SyntaxHighlighter Evolved.  Unfortunately this doesn’t work perfectly with Gutenberg at the moment, and I was hoping for something in a block.  Luckily I found this…

Marcus Kazmierczak has made a plugin to extend the core code block to allow syntax highlighting:

#include <stdio.h>
int main()
{
   // printf() displays the string inside quotation
   printf("Hello, World!");
   return 0;
}

I really like this and I think it compliments Gutenberg nicely 🙂

Securing WordPress Plugins with more Plugins

I’ve written before about disabling plugin deactivation in WordPress, but I’ve finally used that knowledge in practice–on this site.

The Problem

Let’s say you’re going along your day, developing things, and fixing things, and making the world a better place when all of a sudden you get a call from a client that their website is broken!!  After a bit of panicking and digging around, it turns out that they’ve been “optimizing” things by disabling random, but critical, plugins on the site.

The Solution

One way that you might fix this is to not install the plugins via the WordPress UI and require() them either in the theme directory, or as an mu-plugin.  The downside with this is that you lose the ability to easily and auto-update the plugins (if you’re okay with that).  You also the ability to easily see what plugins are active and installed in the admin UI.

The way I’ve got around this is to create this helper function inside an mu-plugin that allows the plugins to be installed and managed in the UI, but not disabled:

<?php
/**
 * Secures a plugin from accidental disabling in the UI.
 *
 * If a plugin is necessary for a site to function, it should not be disabled.
 * This functionc can also optionally "force" activate a plugin without having to
 * activate it in the plugin UI.  Forcing activation will cause it to skip all
 * core plugin activation hooks.
 *
 * @param string  $plugin              Plugin file to secure.
 * @param boolean $force_activation    Optional. Whether to force load the plugin. Default false.
 */
function emrikol_secure_plugin( $plugin, $force_activation = false ) {
	$proper_plugin_name = false;

	// Match if properly named: wp-plugin (wp-plugin/wp-plugin.php).
	if ( file_exists( WP_PLUGIN_DIR . '/' . $plugin . '/' . $plugin . '.php' ) && is_file( WP_PLUGIN_DIR . '/' . $plugin . '/' . $plugin . '.php' ) ) {
		$proper_plugin_name = $plugin . '/' . $plugin . '.php';
	} else {
		// Match if improperly named: wp-plugin/cool-plugin.php.
		if ( file_exists( WP_PLUGIN_DIR . '/' . $plugin ) && is_file( WP_PLUGIN_DIR . '/' . $plugin ) ) {
			$proper_plugin_name = $plugin;
		}
	}

	if ( false !== $proper_plugin_name ) {
		if ( true === $force_activation ) {
			// Always list the plugin as active.
			add_filter( 'option_active_plugins', function( $active_plugins ) use ( $proper_plugin_name ) {
				// Crappy hack to prevent infinite loops.  Surely there's a better way.
				global $emrikol_is_updating_active_plugins;

				if ( true === $emrikol_is_updating_active_plugins ) {
					unset( $emrikol_is_updating_active_plugins );
					return array_unique( $active_plugins );
				}

				if ( ! in_array( $proper_plugin_name, $active_plugins, true ) ) {
					$active_plugins[]                   = $proper_plugin_name;
					$emrikol_is_updating_active_plugins = true;

					update_option( 'active_plugins', array_unique( $active_plugins ) );
				}
				return array_unique( $active_plugins );
			}, 1000, 1 );
		}

		// Ensure the plugin doesn't get disabled somehow.
		// TODO: Diff arrays.  Only run if the plugin is being removed.
		add_filter( 'pre_update_option_active_plugins', function ( $active_plugins ) use ( $proper_plugin_name ) {
			if ( ! in_array( $proper_plugin_name, $active_plugins, true ) ) {
				$active_plugins[] = $proper_plugin_name;
			}
			return array_unique( $active_plugins );
		}, 1000, 1 );

		// Remove the disable button.
		$plugin_basename = plugin_basename( $proper_plugin_name );
		add_filter( "plugin_action_links_$plugin_basename", function( $links ) use ( $proper_plugin_name, $force_activation ) {
			if ( isset( $links['deactivate'] ) ) {
				$links['deactivate'] = sprintf(
					'<span class="emrikol-secure-plugin wp-ui-text-primary">%s</span>',
					$force_activation ? 'Plugin Activated via Theme Code' : 'Plugin Secured via Theme Code'
				);
			}
			return $links;
		}, 1000, 1 );
	}
}

It’s not perfect, but it’s working for me right now.  Like, right now on this site as you’re reading this. I’ve added it as an mu-plugin like so:

<?php
require_once( plugin_dir_path( __FILE__ ) . 'emrikol-defaults/secure-plugins.php' );

emrikol_secure_plugin( 'akismet' );
emrikol_secure_plugin( 'amp' );
emrikol_secure_plugin( 'jetpack' );
emrikol_secure_plugin( 'wp-super-cache/wp-cache.php' );

As you can see, this completely removes the “Deactivate” link in the UI:

The emrikol_secure_plugin() function takes two arguments:

  1. The plugin to secure.  This can either be the plugin slug (ex. jetpack) or the full plugin path if the plugin doesn’t follow standard naming conventions (wp-super-cache/wp-cache.php)
  2. A boolean, defaults to false.  If it is true the plugin will be forced to activate without user intervention.  This can be used to activate a plugin on a new install without having to manually enable it in the UI or via WP-CLI

CSS & JS Concatenation in WordPress

At WordPress.com VIP one of the features we have on our platform is automated concatenation of Javascript and CSS files when registered through the core WordPress wp_enqueue__*() functions.

We do this using the nginx-http-concat plugin:

This plugin was written to work with nginx, but the server running derrick.blog is Apache.  I’ve worked around this and have nginx-http-concat running fully in WordPress, with added caching.

The bulk of the plugin is this file, which does all of the work of caching and calling the nignx-http-concat plugin:

<?php
// phpcs:disable WordPress.VIP.SuperGlobalInputUsage.AccessDetected, WordPress.Security.ValidatedSanitizedInput, WordPress.VIP.FileSystemWritesDisallow, WordPress.VIP.RestrictedFunctions.file_get_contents_file_get_contents, WordPress.WP.AlternativeFunctions.file_get_contents_file_get_contents, WordPress.WP.AlternativeFunctions.file_system_read_file_get_contents, WordPress.WP.AlternativeFunctions.file_system_read_file_put_contents, WordPress.WP.AlternativeFunctions.json_encode_json_encode
if ( isset( $_SERVER['REQUEST_URI'] ) && '/_static/' === substr( $_SERVER['REQUEST_URI'], 0, 9 ) ) {
	$cache_file      = WP_HTTP_CONCAT_CACHE . '/' . md5( $_SERVER['REQUEST_URI'] );
	$cache_file_meta = WP_HTTP_CONCAT_CACHE . '/meta-' . md5( $_SERVER['REQUEST_URI'] );

	if ( file_exists( $cache_file ) ) {
		if ( time() - filemtime( $cache_file ) > 2 * 3600 ) {
			// file older than 2 hours, delete cache.
			unlink( $cache_file );
			unlink( $cache_file_meta );
		} else {
			// file younger than 2 hours, return cache.
			if ( file_exists( $cache_file_meta ) ) {
				$meta = json_decode( file_get_contents( $cache_file_meta ) );
				if ( null !== $meta && isset( $meta->headers ) ) {
					foreach ( $meta->headers as $header ) {
						header( $header );
					}
				}
			}
			echo file_get_contents( $cache_file ); // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- We need to trust this unfortunately.
			die();
		}
	}
	ob_start();
	require_once 'nginx-http-concat/ngx-http-concat.php';

	$output = ob_get_clean();
	$meta   = array(
		'headers' => headers_list(),
	);

	file_put_contents( $cache_file, $output );
	file_put_contents( $cache_file_meta, json_encode( $meta ) );
	echo $output; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- We need to trust this unfortunately.
	die();
}

This little bit of code in wp-config.php is what calls the above file, before WordPress even initializes, to make this as speedy as possible:

define( 'WP_HTTP_CONCAT_CACHE', dirname(__FILE__) . '/wp-content/cache/http-concat-cache' );
require_once dirname(__FILE__) . '/wp-content/mu-plugins/emrikol-defaults/config-nginx-http-concat.php';

Finally, in an mu-plugin these lines enable the nginx-http-concat plugin:

if ( ! is_admin() ) {
	require_once( plugin_dir_path( __FILE__ ) . 'emrikol-defaults/nginx-http-concat/cssconcat.php' );
	require_once( plugin_dir_path( __FILE__ ) . 'emrikol-defaults/nginx-http-concat/jsconcat.php' );
}

You’ll notice the is_admin() check, because at this time, the nginx-http-concat plugin doesn’t play nice with Gutenberg.  It’s probably going to get fixed soon, but in the meantime, I’ll just leave it disabled for wp-admin

All of this could definitely be packed into a legit plugin, and even leave room for other features, such as:

  • An admin UI for enabling/disabling under certain condition
  • A “clear cache” button
  • A cron event to regularly delete expired cache items

As it is now though, I’m just leaving it be to see how well it works.  Wish me luck 🙂