multisite-no-self-ping.php

<?php
/**
 * Multisite No Self Ping
 *
 * @package     MultisiteNoSelfPing
 * @author      Bernhard Kau
 * @license     GPLv3
 *
 * @wordpress-plugin
 * Plugin Name: Multisite No Self Ping
 * Plugin URI: https://kau-boys.de
 * Description: Disables self pings for all blogs on a multisite.
 * Version: 0.1
 * Author: Bernhard Kau
 * Author URI: https://kau-boys.de
 * License: GPLv3
 * License URI: http://www.gnu.org/licenses/gpl-3.0.txt
 */

/**
 * Prevent pings to multisite links
 *
 * @param array $links The array of links to ping
 */
function multisite_no_self_ping( &$links ) {
	$sites     = get_sites();
	$site_urls = array();

	foreach ( $sites as $site ) {
		$site_urls[] = get_home_url( $site->blog_id );
	}

	foreach ( $links as $key => $link ) {
		foreach ( $site_urls as $site_url ) {
			if ( 0 === strpos( $link, $site_url ) ) {
				unset( $links[ $key ] );
			}
		}
	}
}

add_action( 'pre_ping', 'multisite_no_self_ping' );