Source

File: wp-includes/ms-load.php

function get_site_by_path( $domain, $path, $segments = null ) {
	$path_segments = array_filter( explode( '/', trim( $path, '/' ) ) );

	/**
	 * Filters the number of path segments to consider when searching for a site.
	 *
	 * @since 3.9.0
	 *
	 * @param int|null $segments The number of path segments to consider. WordPress by default looks at
	 *                           one path segment following the network path. The function default of
	 *                           null only makes sense when you know the requested path should match a site.
	 * @param string   $domain   The requested domain.
	 * @param string   $path     The requested path, in full.
	 */
	$segments = apply_filters( 'site_by_path_segments_count', $segments, $domain, $path );

	if ( null !== $segments && count( $path_segments ) > $segments ) {
		$path_segments = array_slice( $path_segments, 0, $segments );
	}

	$paths = array();

	while ( count( $path_segments ) ) {
		$paths[] = '/' . implode( '/', $path_segments ) . '/';
		array_pop( $path_segments );
	}

	$paths[] = '/';

	/**
	 * Determine a site by its domain and path.
	 *
	 * This allows one to short-circuit the default logic, perhaps by
	 * replacing it with a routine that is more optimal for your setup.
	 *
	 * Return null to avoid the short-circuit. Return false if no site
	 * can be found at the requested domain and path. Otherwise, return
	 * a site object.
	 *
	 * @since 3.9.0
	 *
	 * @param null|false|WP_Site $site     Site value to return by path. Default null
	 *                                     to continue retrieving the site.
	 * @param string             $domain   The requested domain.
	 * @param string             $path     The requested path, in full.
	 * @param int|null           $segments The suggested number of paths to consult.
	 *                                     Default null, meaning the entire path was to be consulted.
	 * @param string[]           $paths    The paths to search for, based on $path and $segments.
	 */
	$pre = apply_filters( 'pre_get_site_by_path', null, $domain, $path, $segments, $paths );
	if ( null !== $pre ) {
		if ( false !== $pre && ! $pre instanceof WP_Site ) {
			$pre = new WP_Site( $pre );
		}
		return $pre;
	}

	/*
	 * @todo
	 * Caching, etc. Consider alternative optimization routes,
	 * perhaps as an opt-in for plugins, rather than using the pre_* filter.
	 * For example: The segments filter can expand or ignore paths.
	 * If persistent caching is enabled, we could query the DB for a path <> '/'
	 * then cache whether we can just always ignore paths.
	 */

	// Either www or non-www is supported, not both. If a www domain is requested,
	// query for both to provide the proper redirect.
	$domains = array( $domain );
	if ( 'www.' === substr( $domain, 0, 4 ) ) {
		$domains[] = substr( $domain, 4 );
	}

	$args = array(
		'number'                 => 1,
		'update_site_meta_cache' => false,
	);

	if ( count( $domains ) > 1 ) {
		$args['domain__in']               = $domains;
		$args['orderby']['domain_length'] = 'DESC';
	} else {
		$args['domain'] = array_shift( $domains );
	}

	if ( count( $paths ) > 1 ) {
		$args['path__in']               = $paths;
		$args['orderby']['path_length'] = 'DESC';
	} else {
		$args['path'] = array_shift( $paths );
	}

	$result = get_sites( $args );
	$site   = array_shift( $result );

	if ( $site ) {
		return $site;
	}

	return false;
}