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maybe_redirect_404()

Correct 404 redirects when NOBLOGREDIRECT is defined.

Source

File: wp-includes/ms-functions.php 

function maybe_redirect_404() {
	if ( is_main_site() && is_404() && defined( 'NOBLOGREDIRECT' ) ) {
		/**
		 * Filters the redirect URL for 404s on the main site.
		 *
		 * The filter is only evaluated if the NOBLOGREDIRECT constant is defined.
		 *
		 * @since 3.0.0
		 *
		 * @param string $no_blog_redirect The redirect URL defined in NOBLOGREDIRECT.
		 */
		$destination = apply_filters( 'blog_redirect_404', NOBLOGREDIRECT );

		if ( $destination ) {
			if ( '%siteurl%' === $destination ) {
				$destination = network_home_url();
			}

			wp_redirect( $destination );
			exit;
		}
	}
}

Uses

Uses Description
wp-includes/pluggable.php: wp_redirect()

Redirects to another page.
wp-includes/query.php: is_404()

Determines whether the query has resulted in a 404 (returns no results).
wp-includes/functions.php: is_main_site()

Determine whether a site is the main site of the current network.
wp-includes/link-template.php: network_home_url()

Retrieves the home URL for the current network.
wp-includes/plugin.php: apply_filters()

Calls the callback functions that have been added to a filter hook.
wp-includes/ms-functions.php: blog_redirect_404

Filters the redirect URL for 404s on the main site.

Changelog

Version Description
MU (3.0.0) Introduced.

© 2003–2019 WordPress Foundation
Licensed under the GNU GPLv2+ License.
https://developer.wordpress.org/reference/functions/maybe_redirect_404