Ticket #44306: slow-post-embeds.php

<?php
/**
 * Plugin Name: Slow Post Embeds
 * Description: This tests an (uncommon) scenario where a post embed iframe finishes loading before the host page is able to load wp-embed.js and fire the DOMContentLoaded event. In this scenario (filed as <a href="https://core.trac.wordpress.org/ticket/44306">#44306</a>), the embed will fail to get the height set since the host page missed the height message from the post embed window.
 * Author: Weston Ruter
 */

namespace Slow_Post_Embeds;

const QUERY_VAR = 'slow_redirect_url';

add_filter(
        'script_loader_src',
        static function ( $url, $handle ) {
                if ( 'wp-embed' === $handle ) {
                        $url = add_query_arg(
                                [
                                        QUERY_VAR    => rawurlencode( $url ),
                                        'cache_bust' => wp_rand(),
                                ],
                                home_url( '/' )
                        );
                }
                return $url;
        },
        10,
        2
);

add_action(
        'template_redirect',
        static function () {
                if ( ! isset( $_GET[ QUERY_VAR ] ) ) {
                        return;
                }

                $url = wp_validate_redirect( wp_unslash( $_GET[ QUERY_VAR ] ) );
                if ( ! $url ) {
                        return;
                }

                sleep( 3 );
                wp_redirect( $url, 302 );
                exit;
        }
);