Yoast SEO sitemap performance mitigations

yoast-sitemap-mitigations.php

<?php
// Yoast sitemap performance improvements.

/**
 * Objects are cached for 24 hours and changes will be applied upon next sitemap update.
 */
add_filter( 'wpseo_enable_xml_sitemap_transient_caching', '__return_true' );

add_action( 'parse_request', 'filter_yoast_sitemap_cache_maxage' );
add_action( 'parse_request', 'block_query_string_sitemap_requests' );

/**
 * Hooks the parse_request action to insert cache control max-age headers for sitemaps.
 *
 * @param \WP $wp The WP object, passed by reference
 */
function filter_yoast_sitemap_cache_maxage( WP $wp ): void {
	if ( str_starts_with( $wp->matched_query, 'sitemap' ) ) {
		header( 'Cache-Control: max-age=' . ( 12 * HOUR_IN_SECONDS ) );
	}
}

/**
 * Block /sitemap requests if there's a query string. Prevent
 * expensive queries resulting from an origin hit from a bad actor
 * with a cache-busting string.
 *
 * @param \WP $wp The WP object, passed by reference
 */
function block_query_string_sitemap_requests( WP $wp ): void {
	if (
		str_starts_with( $wp->matched_query, 'sitemap' )
		&& ( ! empty( $_SERVER['QUERY_STRING'] ) )
	) {
		header( 'HTTP/1.1 403 Forbidden' );
		exit;
	}
}