Source

File: wp-includes/class-wp-network.php

public static function get_by_path( $domain = '', $path = '', $segments = null ) {
		$domains = array( $domain );
		$pieces  = explode( '.', $domain );

		/*
		 * It's possible one domain to search is 'com', but it might as well
		 * be 'localhost' or some other locally mapped domain.
		 */
		while ( array_shift( $pieces ) ) {
			if ( ! empty( $pieces ) ) {
				$domains[] = implode( '.', $pieces );
			}
		}

		/*
		 * If we've gotten to this function during normal execution, there is
		 * more than one network installed. At this point, who knows how many
		 * we have. Attempt to optimize for the situation where networks are
		 * only domains, thus meaning paths never need to be considered.
		 *
		 * This is a very basic optimization; anything further could have
		 * drawbacks depending on the setup, so this is best done per-installation.
		 */
		$using_paths = true;
		if ( wp_using_ext_object_cache() ) {
			$using_paths = wp_cache_get( 'networks_have_paths', 'site-options' );
			if ( false === $using_paths ) {
				$using_paths = get_networks(
					array(
						'number'       => 1,
						'count'        => true,
						'path__not_in' => '/',
					)
				);
				wp_cache_add( 'networks_have_paths', $using_paths, 'site-options' );
			}
		}

		$paths = array();
		if ( $using_paths ) {
			$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. The function default of null only makes sense when you
			 *                           know the requested path should match a network.
			 * @param string   $domain   The requested domain.
			 * @param string   $path     The requested path, in full.
			 */
			$segments = apply_filters( 'network_by_path_segments_count', $segments, $domain, $path );

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

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

			$paths[] = '/';
		}

		/**
		 * Determine a network 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 network
		 * can be found at the requested domain and path. Otherwise, return
		 * an object from wp_get_network().
		 *
		 * @since 3.9.0
		 *
		 * @param null|bool|WP_Network $network  Network value to return by path. Default null
		 *                                       to continue retrieving the network.
		 * @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[]             $paths    Array of paths to search for, based on `$path` and `$segments`.
		 */
		$pre = apply_filters( 'pre_get_network_by_path', null, $domain, $path, $segments, $paths );
		if ( null !== $pre ) {
			return $pre;
		}

		if ( ! $using_paths ) {
			$networks = get_networks(
				array(
					'number'     => 1,
					'orderby'    => array(
						'domain_length' => 'DESC',
					),
					'domain__in' => $domains,
				)
			);

			if ( ! empty( $networks ) ) {
				return array_shift( $networks );
			}

			return false;
		}

		$networks = get_networks(
			array(
				'orderby'    => array(
					'domain_length' => 'DESC',
					'path_length'   => 'DESC',
				),
				'domain__in' => $domains,
				'path__in'   => $paths,
			)
		);

		/*
		 * Domains are sorted by length of domain, then by length of path.
		 * The domain must match for the path to be considered. Otherwise,
		 * a network with the path of / will suffice.
		 */
		$found = false;
		foreach ( $networks as $network ) {
			if ( ( $network->domain === $domain ) || ( "www.{$network->domain}" === $domain ) ) {
				if ( in_array( $network->path, $paths, true ) ) {
					$found = true;
					break;
				}
			}
			if ( '/' === $network->path ) {
				$found = true;
				break;
			}
		}

		if ( true === $found ) {
			return $network;
		}

		return false;
	}