Add JSON+LD markup for Google sitelinks search box

google-sitelinks-search-box-json-ld

<?php
    add_action( 'wp_footer', 'rp_add_google_search_markup' );
    function rp_add_google_search_markup() {
        if ( is_front_page() ) {
        ?>
            <script type="application/ld+json">
            {
                "@context": "http://schema.org",
                "@type": "WebSite",
                "url": "<?php echo esc_url( home_url( '/' ) ); ?>",
                "potentialAction": {
                    "@type": "SearchAction",
                    "target": "<?php echo esc_url( home_url( '/' ) ); ?>?s={s}",
                    "query-input": "name=s"
                }
            }
            </script>
<?php
        }
    }
?>