Adding upstream version 6.4.3+dfsg1.upstream/6.4.3+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2901 insertions, 0 deletions

diff --git a/wp-includes/ms-functions.php b/wp-includes/ms-functions.php
new file mode 100644
index 0000000..09ee2a5
--- /dev/null
+++ b/wp-includes/ms-functions.php
@@ -0,0 +1,2901 @@
+<?php
+/**
+ * Multisite WordPress API
+ *
+ * @package WordPress
+ * @subpackage Multisite
+ * @since 3.0.0
+ */
+
+/**
+ * Gets the network's site and user counts.
+ *
+ * @since MU (3.0.0)
+ *
+ * @return int[] {
+ *     Site and user count for the network.
+ *
+ *     @type int $blogs Number of sites on the network.
+ *     @type int $users Number of users on the network.
+ * }
+ */
+function get_sitestats() {
+	$stats = array(
+		'blogs' => get_blog_count(),
+		'users' => get_user_count(),
+	);
+
+	return $stats;
+}
+
+/**
+ * Gets one of a user's active blogs.
+ *
+ * Returns the user's primary blog, if they have one and
+ * it is active. If it's inactive, function returns another
+ * active blog of the user. If none are found, the user
+ * is added as a Subscriber to the Dashboard Blog and that blog
+ * is returned.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param int $user_id The unique ID of the user
+ * @return WP_Site|void The blog object
+ */
+function get_active_blog_for_user( $user_id ) {
+	$blogs = get_blogs_of_user( $user_id );
+	if ( empty( $blogs ) ) {
+		return;
+	}
+
+	if ( ! is_multisite() ) {
+		return $blogs[ get_current_blog_id() ];
+	}
+
+	$primary_blog = get_user_meta( $user_id, 'primary_blog', true );
+	$first_blog   = current( $blogs );
+	if ( false !== $primary_blog ) {
+		if ( ! isset( $blogs[ $primary_blog ] ) ) {
+			update_user_meta( $user_id, 'primary_blog', $first_blog->userblog_id );
+			$primary = get_site( $first_blog->userblog_id );
+		} else {
+			$primary = get_site( $primary_blog );
+		}
+	} else {
+		// TODO: Review this call to add_user_to_blog too - to get here the user must have a role on this blog?
+		$result = add_user_to_blog( $first_blog->userblog_id, $user_id, 'subscriber' );
+
+		if ( ! is_wp_error( $result ) ) {
+			update_user_meta( $user_id, 'primary_blog', $first_blog->userblog_id );
+			$primary = $first_blog;
+		}
+	}
+
+	if ( ( ! is_object( $primary ) ) || ( 1 == $primary->archived || 1 == $primary->spam || 1 == $primary->deleted ) ) {
+		$blogs = get_blogs_of_user( $user_id, true ); // If a user's primary blog is shut down, check their other blogs.
+		$ret   = false;
+		if ( is_array( $blogs ) && count( $blogs ) > 0 ) {
+			foreach ( (array) $blogs as $blog_id => $blog ) {
+				if ( get_current_network_id() != $blog->site_id ) {
+					continue;
+				}
+				$details = get_site( $blog_id );
+				if ( is_object( $details ) && 0 == $details->archived && 0 == $details->spam && 0 == $details->deleted ) {
+					$ret = $details;
+					if ( get_user_meta( $user_id, 'primary_blog', true ) != $blog_id ) {
+						update_user_meta( $user_id, 'primary_blog', $blog_id );
+					}
+					if ( ! get_user_meta( $user_id, 'source_domain', true ) ) {
+						update_user_meta( $user_id, 'source_domain', $details->domain );
+					}
+					break;
+				}
+			}
+		} else {
+			return;
+		}
+		return $ret;
+	} else {
+		return $primary;
+	}
+}
+
+/**
+ * Gets the number of active sites on the installation.
+ *
+ * The count is cached and updated twice daily. This is not a live count.
+ *
+ * @since MU (3.0.0)
+ * @since 3.7.0 The `$network_id` parameter has been deprecated.
+ * @since 4.8.0 The `$network_id` parameter is now being used.
+ *
+ * @param int|null $network_id ID of the network. Default is the current network.
+ * @return int Number of active sites on the network.
+ */
+function get_blog_count( $network_id = null ) {
+	return get_network_option( $network_id, 'blog_count' );
+}
+
+/**
+ * Gets a blog post from any site on the network.
+ *
+ * This function is similar to get_post(), except that it can retrieve a post
+ * from any site on the network, not just the current site.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param int $blog_id ID of the blog.
+ * @param int $post_id ID of the post being looked for.
+ * @return WP_Post|null WP_Post object on success, null on failure
+ */
+function get_blog_post( $blog_id, $post_id ) {
+	switch_to_blog( $blog_id );
+	$post = get_post( $post_id );
+	restore_current_blog();
+
+	return $post;
+}
+
+/**
+ * Adds a user to a blog, along with specifying the user's role.
+ *
+ * Use the {@see 'add_user_to_blog'} action to fire an event when users are added to a blog.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param int    $blog_id ID of the blog the user is being added to.
+ * @param int    $user_id ID of the user being added.
+ * @param string $role    User role.
+ * @return true|WP_Error True on success or a WP_Error object if the user doesn't exist
+ *                       or could not be added.
+ */
+function add_user_to_blog( $blog_id, $user_id, $role ) {
+	switch_to_blog( $blog_id );
+
+	$user = get_userdata( $user_id );
+
+	if ( ! $user ) {
+		restore_current_blog();
+		return new WP_Error( 'user_does_not_exist', __( 'The requested user does not exist.' ) );
+	}
+
+	/**
+	 * Filters whether a user should be added to a site.
+	 *
+	 * @since 4.9.0
+	 *
+	 * @param true|WP_Error $retval  True if the user should be added to the site, error
+	 *                               object otherwise.
+	 * @param int           $user_id User ID.
+	 * @param string        $role    User role.
+	 * @param int           $blog_id Site ID.
+	 */
+	$can_add_user = apply_filters( 'can_add_user_to_blog', true, $user_id, $role, $blog_id );
+
+	if ( true !== $can_add_user ) {
+		restore_current_blog();
+
+		if ( is_wp_error( $can_add_user ) ) {
+			return $can_add_user;
+		}
+
+		return new WP_Error( 'user_cannot_be_added', __( 'User cannot be added to this site.' ) );
+	}
+
+	if ( ! get_user_meta( $user_id, 'primary_blog', true ) ) {
+		update_user_meta( $user_id, 'primary_blog', $blog_id );
+		$site = get_site( $blog_id );
+		update_user_meta( $user_id, 'source_domain', $site->domain );
+	}
+
+	$user->set_role( $role );
+
+	/**
+	 * Fires immediately after a user is added to a site.
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param int    $user_id User ID.
+	 * @param string $role    User role.
+	 * @param int    $blog_id Blog ID.
+	 */
+	do_action( 'add_user_to_blog', $user_id, $role, $blog_id );
+
+	clean_user_cache( $user_id );
+	wp_cache_delete( $blog_id . '_user_count', 'blog-details' );
+
+	restore_current_blog();
+
+	return true;
+}
+
+/**
+ * Removes a user from a blog.
+ *
+ * Use the {@see 'remove_user_from_blog'} action to fire an event when
+ * users are removed from a blog.
+ *
+ * Accepts an optional `$reassign` parameter, if you want to
+ * reassign the user's blog posts to another user upon removal.
+ *
+ * @since MU (3.0.0)
+ *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ *
+ * @param int $user_id  ID of the user being removed.
+ * @param int $blog_id  Optional. ID of the blog the user is being removed from. Default 0.
+ * @param int $reassign Optional. ID of the user to whom to reassign posts. Default 0.
+ * @return true|WP_Error True on success or a WP_Error object if the user doesn't exist.
+ */
+function remove_user_from_blog( $user_id, $blog_id = 0, $reassign = 0 ) {
+	global $wpdb;
+
+	switch_to_blog( $blog_id );
+	$user_id = (int) $user_id;
+
+	/**
+	 * Fires before a user is removed from a site.
+	 *
+	 * @since MU (3.0.0)
+	 * @since 5.4.0 Added the `$reassign` parameter.
+	 *
+	 * @param int $user_id  ID of the user being removed.
+	 * @param int $blog_id  ID of the blog the user is being removed from.
+	 * @param int $reassign ID of the user to whom to reassign posts.
+	 */
+	do_action( 'remove_user_from_blog', $user_id, $blog_id, $reassign );
+
+	/*
+	 * If being removed from the primary blog, set a new primary
+	 * if the user is assigned to multiple blogs.
+	 */
+	$primary_blog = get_user_meta( $user_id, 'primary_blog', true );
+	if ( $primary_blog == $blog_id ) {
+		$new_id     = '';
+		$new_domain = '';
+		$blogs      = get_blogs_of_user( $user_id );
+		foreach ( (array) $blogs as $blog ) {
+			if ( $blog->userblog_id == $blog_id ) {
+				continue;
+			}
+			$new_id     = $blog->userblog_id;
+			$new_domain = $blog->domain;
+			break;
+		}
+
+		update_user_meta( $user_id, 'primary_blog', $new_id );
+		update_user_meta( $user_id, 'source_domain', $new_domain );
+	}
+
+	$user = get_userdata( $user_id );
+	if ( ! $user ) {
+		restore_current_blog();
+		return new WP_Error( 'user_does_not_exist', __( 'That user does not exist.' ) );
+	}
+
+	$user->remove_all_caps();
+
+	$blogs = get_blogs_of_user( $user_id );
+	if ( count( $blogs ) === 0 ) {
+		update_user_meta( $user_id, 'primary_blog', '' );
+		update_user_meta( $user_id, 'source_domain', '' );
+	}
+
+	if ( $reassign ) {
+		$reassign = (int) $reassign;
+		$post_ids = $wpdb->get_col( $wpdb->prepare( "SELECT ID FROM $wpdb->posts WHERE post_author = %d", $user_id ) );
+		$link_ids = $wpdb->get_col( $wpdb->prepare( "SELECT link_id FROM $wpdb->links WHERE link_owner = %d", $user_id ) );
+
+		if ( ! empty( $post_ids ) ) {
+			$wpdb->query( $wpdb->prepare( "UPDATE $wpdb->posts SET post_author = %d WHERE post_author = %d", $reassign, $user_id ) );
+			array_walk( $post_ids, 'clean_post_cache' );
+		}
+
+		if ( ! empty( $link_ids ) ) {
+			$wpdb->query( $wpdb->prepare( "UPDATE $wpdb->links SET link_owner = %d WHERE link_owner = %d", $reassign, $user_id ) );
+			array_walk( $link_ids, 'clean_bookmark_cache' );
+		}
+	}
+
+	clean_user_cache( $user_id );
+	restore_current_blog();
+
+	return true;
+}
+
+/**
+ * Gets the permalink for a post on another blog.
+ *
+ * @since MU (3.0.0) 1.0
+ *
+ * @param int $blog_id ID of the source blog.
+ * @param int $post_id ID of the desired post.
+ * @return string The post's permalink.
+ */
+function get_blog_permalink( $blog_id, $post_id ) {
+	switch_to_blog( $blog_id );
+	$link = get_permalink( $post_id );
+	restore_current_blog();
+
+	return $link;
+}
+
+/**
+ * Gets a blog's numeric ID from its URL.
+ *
+ * On a subdirectory installation like example.com/blog1/,
+ * $domain will be the root 'example.com' and $path the
+ * subdirectory '/blog1/'. With subdomains like blog1.example.com,
+ * $domain is 'blog1.example.com' and $path is '/'.
+ *
+ * @since MU (3.0.0)
+ *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ *
+ * @param string $domain Website domain.
+ * @param string $path   Optional. Not required for subdomain installations. Default '/'.
+ * @return int 0 if no blog found, otherwise the ID of the matching blog.
+ */
+function get_blog_id_from_url( $domain, $path = '/' ) {
+	$domain = strtolower( $domain );
+	$path   = strtolower( $path );
+	$id     = wp_cache_get( md5( $domain . $path ), 'blog-id-cache' );
+
+	if ( -1 == $id ) { // Blog does not exist.
+		return 0;
+	} elseif ( $id ) {
+		return (int) $id;
+	}
+
+	$args   = array(
+		'domain'                 => $domain,
+		'path'                   => $path,
+		'fields'                 => 'ids',
+		'number'                 => 1,
+		'update_site_meta_cache' => false,
+	);
+	$result = get_sites( $args );
+	$id     = array_shift( $result );
+
+	if ( ! $id ) {
+		wp_cache_set( md5( $domain . $path ), -1, 'blog-id-cache' );
+		return 0;
+	}
+
+	wp_cache_set( md5( $domain . $path ), $id, 'blog-id-cache' );
+
+	return $id;
+}
+
+//
+// Admin functions.
+//
+
+/**
+ * Checks an email address against a list of banned domains.
+ *
+ * This function checks against the Banned Email Domains list
+ * at wp-admin/network/settings.php. The check is only run on
+ * self-registrations; user creation at wp-admin/network/users.php
+ * bypasses this check.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param string $user_email The email provided by the user at registration.
+ * @return bool True when the email address is banned, false otherwise.
+ */
+function is_email_address_unsafe( $user_email ) {
+	$banned_names = get_site_option( 'banned_email_domains' );
+	if ( $banned_names && ! is_array( $banned_names ) ) {
+		$banned_names = explode( "\n", $banned_names );
+	}
+
+	$is_email_address_unsafe = false;
+
+	if ( $banned_names && is_array( $banned_names ) && false !== strpos( $user_email, '@', 1 ) ) {
+		$banned_names     = array_map( 'strtolower', $banned_names );
+		$normalized_email = strtolower( $user_email );
+
+		list( $email_local_part, $email_domain ) = explode( '@', $normalized_email );
+
+		foreach ( $banned_names as $banned_domain ) {
+			if ( ! $banned_domain ) {
+				continue;
+			}
+
+			if ( $email_domain === $banned_domain ) {
+				$is_email_address_unsafe = true;
+				break;
+			}
+
+			if ( str_ends_with( $normalized_email, ".$banned_domain" ) ) {
+				$is_email_address_unsafe = true;
+				break;
+			}
+		}
+	}
+
+	/**
+	 * Filters whether an email address is unsafe.
+	 *
+	 * @since 3.5.0
+	 *
+	 * @param bool   $is_email_address_unsafe Whether the email address is "unsafe". Default false.
+	 * @param string $user_email              User email address.
+	 */
+	return apply_filters( 'is_email_address_unsafe', $is_email_address_unsafe, $user_email );
+}
+
+/**
+ * Sanitizes and validates data required for a user sign-up.
+ *
+ * Verifies the validity and uniqueness of user names and user email addresses,
+ * and checks email addresses against allowed and disallowed domains provided by
+ * administrators.
+ *
+ * The {@see 'wpmu_validate_user_signup'} hook provides an easy way to modify the sign-up
+ * process. The value $result, which is passed to the hook, contains both the user-provided
+ * info and the error messages created by the function. {@see 'wpmu_validate_user_signup'}
+ * allows you to process the data in any way you'd like, and unset the relevant errors if
+ * necessary.
+ *
+ * @since MU (3.0.0)
+ *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ *
+ * @param string $user_name  The login name provided by the user.
+ * @param string $user_email The email provided by the user.
+ * @return array {
+ *     The array of user name, email, and the error messages.
+ *
+ *     @type string   $user_name     Sanitized and unique username.
+ *     @type string   $orig_username Original username.
+ *     @type string   $user_email    User email address.
+ *     @type WP_Error $errors        WP_Error object containing any errors found.
+ * }
+ */
+function wpmu_validate_user_signup( $user_name, $user_email ) {
+	global $wpdb;
+
+	$errors = new WP_Error();
+
+	$orig_username = $user_name;
+	$user_name     = preg_replace( '/\s+/', '', sanitize_user( $user_name, true ) );
+
+	if ( $user_name != $orig_username || preg_match( '/[^a-z0-9]/', $user_name ) ) {
+		$errors->add( 'user_name', __( 'Usernames can only contain lowercase letters (a-z) and numbers.' ) );
+		$user_name = $orig_username;
+	}
+
+	$user_email = sanitize_email( $user_email );
+
+	if ( empty( $user_name ) ) {
+		$errors->add( 'user_name', __( 'Please enter a username.' ) );
+	}
+
+	$illegal_names = get_site_option( 'illegal_names' );
+	if ( ! is_array( $illegal_names ) ) {
+		$illegal_names = array( 'www', 'web', 'root', 'admin', 'main', 'invite', 'administrator' );
+		add_site_option( 'illegal_names', $illegal_names );
+	}
+	if ( in_array( $user_name, $illegal_names, true ) ) {
+		$errors->add( 'user_name', __( 'Sorry, that username is not allowed.' ) );
+	}
+
+	/** This filter is documented in wp-includes/user.php */
+	$illegal_logins = (array) apply_filters( 'illegal_user_logins', array() );
+
+	if ( in_array( strtolower( $user_name ), array_map( 'strtolower', $illegal_logins ), true ) ) {
+		$errors->add( 'user_name', __( 'Sorry, that username is not allowed.' ) );
+	}
+
+	if ( ! is_email( $user_email ) ) {
+		$errors->add( 'user_email', __( 'Please enter a valid email address.' ) );
+	} elseif ( is_email_address_unsafe( $user_email ) ) {
+		$errors->add( 'user_email', __( 'You cannot use that email address to signup. There are problems with them blocking some emails from WordPress. Please use another email provider.' ) );
+	}
+
+	if ( strlen( $user_name ) < 4 ) {
+		$errors->add( 'user_name', __( 'Username must be at least 4 characters.' ) );
+	}
+
+	if ( strlen( $user_name ) > 60 ) {
+		$errors->add( 'user_name', __( 'Username may not be longer than 60 characters.' ) );
+	}
+
+	// All numeric?
+	if ( preg_match( '/^[0-9]*$/', $user_name ) ) {
+		$errors->add( 'user_name', __( 'Sorry, usernames must have letters too!' ) );
+	}
+
+	$limited_email_domains = get_site_option( 'limited_email_domains' );
+	if ( is_array( $limited_email_domains ) && ! empty( $limited_email_domains ) ) {
+		$limited_email_domains = array_map( 'strtolower', $limited_email_domains );
+		$emaildomain           = strtolower( substr( $user_email, 1 + strpos( $user_email, '@' ) ) );
+		if ( ! in_array( $emaildomain, $limited_email_domains, true ) ) {
+			$errors->add( 'user_email', __( 'Sorry, that email address is not allowed!' ) );
+		}
+	}
+
+	// Check if the username has been used already.
+	if ( username_exists( $user_name ) ) {
+		$errors->add( 'user_name', __( 'Sorry, that username already exists!' ) );
+	}
+
+	// Check if the email address has been used already.
+	if ( email_exists( $user_email ) ) {
+		$errors->add(
+			'user_email',
+			sprintf(
+				/* translators: %s: Link to the login page. */
+				__( '<strong>Error:</strong> This email address is already registered. <a href="%s">Log in</a> with this address or choose another one.' ),
+				wp_login_url()
+			)
+		);
+	}
+
+	// Has someone already signed up for this username?
+	$signup = $wpdb->get_row( $wpdb->prepare( "SELECT * FROM $wpdb->signups WHERE user_login = %s", $user_name ) );
+	if ( $signup instanceof stdClass ) {
+		$registered_at = mysql2date( 'U', $signup->registered );
+		$now           = time();
+		$diff          = $now - $registered_at;
+		// If registered more than two days ago, cancel registration and let this signup go through.
+		if ( $diff > 2 * DAY_IN_SECONDS ) {
+			$wpdb->delete( $wpdb->signups, array( 'user_login' => $user_name ) );
+		} else {
+			$errors->add( 'user_name', __( 'That username is currently reserved but may be available in a couple of days.' ) );
+		}
+	}
+
+	$signup = $wpdb->get_row( $wpdb->prepare( "SELECT * FROM $wpdb->signups WHERE user_email = %s", $user_email ) );
+	if ( $signup instanceof stdClass ) {
+		$diff = time() - mysql2date( 'U', $signup->registered );
+		// If registered more than two days ago, cancel registration and let this signup go through.
+		if ( $diff > 2 * DAY_IN_SECONDS ) {
+			$wpdb->delete( $wpdb->signups, array( 'user_email' => $user_email ) );
+		} else {
+			$errors->add( 'user_email', __( 'That email address has already been used. Please check your inbox for an activation email. It will become available in a couple of days if you do nothing.' ) );
+		}
+	}
+
+	$result = array(
+		'user_name'     => $user_name,
+		'orig_username' => $orig_username,
+		'user_email'    => $user_email,
+		'errors'        => $errors,
+	);
+
+	/**
+	 * Filters the validated user registration details.
+	 *
+	 * This does not allow you to override the username or email of the user during
+	 * registration. The values are solely used for validation and error handling.
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param array $result {
+	 *     The array of user name, email, and the error messages.
+	 *
+	 *     @type string   $user_name     Sanitized and unique username.
+	 *     @type string   $orig_username Original username.
+	 *     @type string   $user_email    User email address.
+	 *     @type WP_Error $errors        WP_Error object containing any errors found.
+	 * }
+	 */
+	return apply_filters( 'wpmu_validate_user_signup', $result );
+}
+
+/**
+ * Processes new site registrations.
+ *
+ * Checks the data provided by the user during blog signup. Verifies
+ * the validity and uniqueness of blog paths and domains.
+ *
+ * This function prevents the current user from registering a new site
+ * with a blogname equivalent to another user's login name. Passing the
+ * $user parameter to the function, where $user is the other user, is
+ * effectively an override of this limitation.
+ *
+ * Filter {@see 'wpmu_validate_blog_signup'} if you want to modify
+ * the way that WordPress validates new site signups.
+ *
+ * @since MU (3.0.0)
+ *
+ * @global wpdb   $wpdb   WordPress database abstraction object.
+ * @global string $domain
+ *
+ * @param string         $blogname   The site name provided by the user. Must be unique.
+ * @param string         $blog_title The site title provided by the user.
+ * @param WP_User|string $user       Optional. The user object to check against the new site name.
+ *                                   Default empty string.
+ * @return array {
+ *     Array of domain, path, site name, site title, user and error messages.
+ *
+ *     @type string         $domain     Domain for the site.
+ *     @type string         $path       Path for the site. Used in subdirectory installations.
+ *     @type string         $blogname   The unique site name (slug).
+ *     @type string         $blog_title Blog title.
+ *     @type string|WP_User $user       By default, an empty string. A user object if provided.
+ *     @type WP_Error       $errors     WP_Error containing any errors found.
+ * }
+ */
+function wpmu_validate_blog_signup( $blogname, $blog_title, $user = '' ) {
+	global $wpdb, $domain;
+
+	$current_network = get_network();
+	$base            = $current_network->path;
+
+	$blog_title = strip_tags( $blog_title );
+
+	$errors        = new WP_Error();
+	$illegal_names = get_site_option( 'illegal_names' );
+	if ( false == $illegal_names ) {
+		$illegal_names = array( 'www', 'web', 'root', 'admin', 'main', 'invite', 'administrator' );
+		add_site_option( 'illegal_names', $illegal_names );
+	}
+
+	/*
+	 * On sub dir installations, some names are so illegal, only a filter can
+	 * spring them from jail.
+	 */
+	if ( ! is_subdomain_install() ) {
+		$illegal_names = array_merge( $illegal_names, get_subdirectory_reserved_names() );
+	}
+
+	if ( empty( $blogname ) ) {
+		$errors->add( 'blogname', __( 'Please enter a site name.' ) );
+	}
+
+	if ( preg_match( '/[^a-z0-9]+/', $blogname ) ) {
+		$errors->add( 'blogname', __( 'Site names can only contain lowercase letters (a-z) and numbers.' ) );
+	}
+
+	if ( in_array( $blogname, $illegal_names, true ) ) {
+		$errors->add( 'blogname', __( 'That name is not allowed.' ) );
+	}
+
+	/**
+	 * Filters the minimum site name length required when validating a site signup.
+	 *
+	 * @since 4.8.0
+	 *
+	 * @param int $length The minimum site name length. Default 4.
+	 */
+	$minimum_site_name_length = apply_filters( 'minimum_site_name_length', 4 );
+
+	if ( strlen( $blogname ) < $minimum_site_name_length ) {
+		/* translators: %s: Minimum site name length. */
+		$errors->add( 'blogname', sprintf( _n( 'Site name must be at least %s character.', 'Site name must be at least %s characters.', $minimum_site_name_length ), number_format_i18n( $minimum_site_name_length ) ) );
+	}
+
+	// Do not allow users to create a site that conflicts with a page on the main blog.
+	if ( ! is_subdomain_install() && $wpdb->get_var( $wpdb->prepare( 'SELECT post_name FROM ' . $wpdb->get_blog_prefix( $current_network->site_id ) . "posts WHERE post_type = 'page' AND post_name = %s", $blogname ) ) ) {
+		$errors->add( 'blogname', __( 'Sorry, you may not use that site name.' ) );
+	}
+
+	// All numeric?
+	if ( preg_match( '/^[0-9]*$/', $blogname ) ) {
+		$errors->add( 'blogname', __( 'Sorry, site names must have letters too!' ) );
+	}
+
+	/**
+	 * Filters the new site name during registration.
+	 *
+	 * The name is the site's subdomain or the site's subdirectory
+	 * path depending on the network settings.
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param string $blogname Site name.
+	 */
+	$blogname = apply_filters( 'newblogname', $blogname );
+
+	$blog_title = wp_unslash( $blog_title );
+
+	if ( empty( $blog_title ) ) {
+		$errors->add( 'blog_title', __( 'Please enter a site title.' ) );
+	}
+
+	// Check if the domain/path has been used already.
+	if ( is_subdomain_install() ) {
+		$mydomain = $blogname . '.' . preg_replace( '|^www\.|', '', $domain );
+		$path     = $base;
+	} else {
+		$mydomain = $domain;
+		$path     = $base . $blogname . '/';
+	}
+	if ( domain_exists( $mydomain, $path, $current_network->id ) ) {
+		$errors->add( 'blogname', __( 'Sorry, that site already exists!' ) );
+	}
+
+	/*
+	 * Do not allow users to create a site that matches an existing user's login name,
+	 * unless it's the user's own username.
+	 */
+	if ( username_exists( $blogname ) ) {
+		if ( ! is_object( $user ) || ( is_object( $user ) && ( $user->user_login != $blogname ) ) ) {
+			$errors->add( 'blogname', __( 'Sorry, that site is reserved!' ) );
+		}
+	}
+
+	/*
+	 * Has someone already signed up for this domain?
+	 * TODO: Check email too?
+	 */
+	$signup = $wpdb->get_row( $wpdb->prepare( "SELECT * FROM $wpdb->signups WHERE domain = %s AND path = %s", $mydomain, $path ) );
+	if ( $signup instanceof stdClass ) {
+		$diff = time() - mysql2date( 'U', $signup->registered );
+		// If registered more than two days ago, cancel registration and let this signup go through.
+		if ( $diff > 2 * DAY_IN_SECONDS ) {
+			$wpdb->delete(
+				$wpdb->signups,
+				array(
+					'domain' => $mydomain,
+					'path'   => $path,
+				)
+			);
+		} else {
+			$errors->add( 'blogname', __( 'That site is currently reserved but may be available in a couple days.' ) );
+		}
+	}
+
+	$result = array(
+		'domain'     => $mydomain,
+		'path'       => $path,
+		'blogname'   => $blogname,
+		'blog_title' => $blog_title,
+		'user'       => $user,
+		'errors'     => $errors,
+	);
+
+	/**
+	 * Filters site details and error messages following registration.
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param array $result {
+	 *     Array of domain, path, site name, site title, user and error messages.
+	 *
+	 *     @type string         $domain     Domain for the site.
+	 *     @type string         $path       Path for the site. Used in subdirectory installations.
+	 *     @type string         $blogname   The unique site name (slug).
+	 *     @type string         $blog_title Site title.
+	 *     @type string|WP_User $user       By default, an empty string. A user object if provided.
+	 *     @type WP_Error       $errors     WP_Error containing any errors found.
+	 * }
+	 */
+	return apply_filters( 'wpmu_validate_blog_signup', $result );
+}
+
+/**
+ * Records site signup information for future activation.
+ *
+ * @since MU (3.0.0)
+ *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ *
+ * @param string $domain     The requested domain.
+ * @param string $path       The requested path.
+ * @param string $title      The requested site title.
+ * @param string $user       The user's requested login name.
+ * @param string $user_email The user's email address.
+ * @param array  $meta       Optional. Signup meta data. By default, contains the requested privacy setting and lang_id.
+ */
+function wpmu_signup_blog( $domain, $path, $title, $user, $user_email, $meta = array() ) {
+	global $wpdb;
+
+	$key = substr( md5( time() . wp_rand() . $domain ), 0, 16 );
+
+	/**
+	 * Filters the metadata for a site signup.
+	 *
+	 * The metadata will be serialized prior to storing it in the database.
+	 *
+	 * @since 4.8.0
+	 *
+	 * @param array  $meta       Signup meta data. Default empty array.
+	 * @param string $domain     The requested domain.
+	 * @param string $path       The requested path.
+	 * @param string $title      The requested site title.
+	 * @param string $user       The user's requested login name.
+	 * @param string $user_email The user's email address.
+	 * @param string $key        The user's activation key.
+	 */
+	$meta = apply_filters( 'signup_site_meta', $meta, $domain, $path, $title, $user, $user_email, $key );
+
+	$wpdb->insert(
+		$wpdb->signups,
+		array(
+			'domain'         => $domain,
+			'path'           => $path,
+			'title'          => $title,
+			'user_login'     => $user,
+			'user_email'     => $user_email,
+			'registered'     => current_time( 'mysql', true ),
+			'activation_key' => $key,
+			'meta'           => serialize( $meta ),
+		)
+	);
+
+	/**
+	 * Fires after site signup information has been written to the database.
+	 *
+	 * @since 4.4.0
+	 *
+	 * @param string $domain     The requested domain.
+	 * @param string $path       The requested path.
+	 * @param string $title      The requested site title.
+	 * @param string $user       The user's requested login name.
+	 * @param string $user_email The user's email address.
+	 * @param string $key        The user's activation key.
+	 * @param array  $meta       Signup meta data. By default, contains the requested privacy setting and lang_id.
+	 */
+	do_action( 'after_signup_site', $domain, $path, $title, $user, $user_email, $key, $meta );
+}
+
+/**
+ * Records user signup information for future activation.
+ *
+ * This function is used when user registration is open but
+ * new site registration is not.
+ *
+ * @since MU (3.0.0)
+ *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ *
+ * @param string $user       The user's requested login name.
+ * @param string $user_email The user's email address.
+ * @param array  $meta       Optional. Signup meta data. Default empty array.
+ */
+function wpmu_signup_user( $user, $user_email, $meta = array() ) {
+	global $wpdb;
+
+	// Format data.
+	$user       = preg_replace( '/\s+/', '', sanitize_user( $user, true ) );
+	$user_email = sanitize_email( $user_email );
+	$key        = substr( md5( time() . wp_rand() . $user_email ), 0, 16 );
+
+	/**
+	 * Filters the metadata for a user signup.
+	 *
+	 * The metadata will be serialized prior to storing it in the database.
+	 *
+	 * @since 4.8.0
+	 *
+	 * @param array  $meta       Signup meta data. Default empty array.
+	 * @param string $user       The user's requested login name.
+	 * @param string $user_email The user's email address.
+	 * @param string $key        The user's activation key.
+	 */
+	$meta = apply_filters( 'signup_user_meta', $meta, $user, $user_email, $key );
+
+	$wpdb->insert(
+		$wpdb->signups,
+		array(
+			'domain'         => '',
+			'path'           => '',
+			'title'          => '',
+			'user_login'     => $user,
+			'user_email'     => $user_email,
+			'registered'     => current_time( 'mysql', true ),
+			'activation_key' => $key,
+			'meta'           => serialize( $meta ),
+		)
+	);
+
+	/**
+	 * Fires after a user's signup information has been written to the database.
+	 *
+	 * @since 4.4.0
+	 *
+	 * @param string $user       The user's requested login name.
+	 * @param string $user_email The user's email address.
+	 * @param string $key        The user's activation key.
+	 * @param array  $meta       Signup meta data. Default empty array.
+	 */
+	do_action( 'after_signup_user', $user, $user_email, $key, $meta );
+}
+
+/**
+ * Sends a confirmation request email to a user when they sign up for a new site. The new site will not become active
+ * until the confirmation link is clicked.
+ *
+ * This is the notification function used when site registration
+ * is enabled.
+ *
+ * Filter {@see 'wpmu_signup_blog_notification'} to bypass this function or
+ * replace it with your own notification behavior.
+ *
+ * Filter {@see 'wpmu_signup_blog_notification_email'} and
+ * {@see 'wpmu_signup_blog_notification_subject'} to change the content
+ * and subject line of the email sent to newly registered users.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param string $domain     The new blog domain.
+ * @param string $path       The new blog path.
+ * @param string $title      The site title.
+ * @param string $user_login The user's login name.
+ * @param string $user_email The user's email address.
+ * @param string $key        The activation key created in wpmu_signup_blog().
+ * @param array  $meta       Optional. Signup meta data. By default, contains the requested privacy setting and lang_id.
+ * @return bool
+ */
+function wpmu_signup_blog_notification( $domain, $path, $title, $user_login, $user_email, $key, $meta = array() ) {
+	/**
+	 * Filters whether to bypass the new site email notification.
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param string|false $domain     Site domain, or false to prevent the email from sending.
+	 * @param string       $path       Site path.
+	 * @param string       $title      Site title.
+	 * @param string       $user_login User login name.
+	 * @param string       $user_email User email address.
+	 * @param string       $key        Activation key created in wpmu_signup_blog().
+	 * @param array        $meta       Signup meta data. By default, contains the requested privacy setting and lang_id.
+	 */
+	if ( ! apply_filters( 'wpmu_signup_blog_notification', $domain, $path, $title, $user_login, $user_email, $key, $meta ) ) {
+		return false;
+	}
+
+	// Send email with activation link.
+	if ( ! is_subdomain_install() || get_current_network_id() != 1 ) {
+		$activate_url = network_site_url( "wp-activate.php?key=$key" );
+	} else {
+		$activate_url = "http://{$domain}{$path}wp-activate.php?key=$key"; // @todo Use *_url() API.
+	}
+
+	$activate_url = esc_url( $activate_url );
+
+	$admin_email = get_site_option( 'admin_email' );
+
+	if ( '' === $admin_email ) {
+		$admin_email = 'support@' . wp_parse_url( network_home_url(), PHP_URL_HOST );
+	}
+
+	$from_name       = ( '' !== get_site_option( 'site_name' ) ) ? esc_html( get_site_option( 'site_name' ) ) : 'WordPress';
+	$message_headers = "From: \"{$from_name}\" <{$admin_email}>\n" . 'Content-Type: text/plain; charset="' . get_option( 'blog_charset' ) . "\"\n";
+
+	$user            = get_user_by( 'login', $user_login );
+	$switched_locale = $user && switch_to_user_locale( $user->ID );
+
+	$message = sprintf(
+		/**
+		 * Filters the message content of the new blog notification email.
+		 *
+		 * Content should be formatted for transmission via wp_mail().
+		 *
+		 * @since MU (3.0.0)
+		 *
+		 * @param string $content    Content of the notification email.
+		 * @param string $domain     Site domain.
+		 * @param string $path       Site path.
+		 * @param string $title      Site title.
+		 * @param string $user_login User login name.
+		 * @param string $user_email User email address.
+		 * @param string $key        Activation key created in wpmu_signup_blog().
+		 * @param array  $meta       Signup meta data. By default, contains the requested privacy setting and lang_id.
+		 */
+		apply_filters(
+			'wpmu_signup_blog_notification_email',
+			/* translators: New site notification email. 1: Activation URL, 2: New site URL. */
+			__( "To activate your site, please click the following link:\n\n%1\$s\n\nAfter you activate, you will receive *another email* with your login.\n\nAfter you activate, you can visit your site here:\n\n%2\$s" ),
+			$domain,
+			$path,
+			$title,
+			$user_login,
+			$user_email,
+			$key,
+			$meta
+		),
+		$activate_url,
+		esc_url( "http://{$domain}{$path}" ),
+		$key
+	);
+
+	$subject = sprintf(
+		/**
+		 * Filters the subject of the new blog notification email.
+		 *
+		 * @since MU (3.0.0)
+		 *
+		 * @param string $subject    Subject of the notification email.
+		 * @param string $domain     Site domain.
+		 * @param string $path       Site path.
+		 * @param string $title      Site title.
+		 * @param string $user_login User login name.
+		 * @param string $user_email User email address.
+		 * @param string $key        Activation key created in wpmu_signup_blog().
+		 * @param array  $meta       Signup meta data. By default, contains the requested privacy setting and lang_id.
+		 */
+		apply_filters(
+			'wpmu_signup_blog_notification_subject',
+			/* translators: New site notification email subject. 1: Network title, 2: New site URL. */
+			_x( '[%1$s] Activate %2$s', 'New site notification email subject' ),
+			$domain,
+			$path,
+			$title,
+			$user_login,
+			$user_email,
+			$key,
+			$meta
+		),
+		$from_name,
+		esc_url( 'http://' . $domain . $path )
+	);
+
+	wp_mail( $user_email, wp_specialchars_decode( $subject ), $message, $message_headers );
+
+	if ( $switched_locale ) {
+		restore_previous_locale();
+	}
+
+	return true;
+}
+
+/**
+ * Sends a confirmation request email to a user when they sign up for a new user account (without signing up for a site
+ * at the same time). The user account will not become active until the confirmation link is clicked.
+ *
+ * This is the notification function used when no new site has
+ * been requested.
+ *
+ * Filter {@see 'wpmu_signup_user_notification'} to bypass this function or
+ * replace it with your own notification behavior.
+ *
+ * Filter {@see 'wpmu_signup_user_notification_email'} and
+ * {@see 'wpmu_signup_user_notification_subject'} to change the content
+ * and subject line of the email sent to newly registered users.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param string $user_login The user's login name.
+ * @param string $user_email The user's email address.
+ * @param string $key        The activation key created in wpmu_signup_user()
+ * @param array  $meta       Optional. Signup meta data. Default empty array.
+ * @return bool
+ */
+function wpmu_signup_user_notification( $user_login, $user_email, $key, $meta = array() ) {
+	/**
+	 * Filters whether to bypass the email notification for new user sign-up.
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param string $user_login User login name.
+	 * @param string $user_email User email address.
+	 * @param string $key        Activation key created in wpmu_signup_user().
+	 * @param array  $meta       Signup meta data. Default empty array.
+	 */
+	if ( ! apply_filters( 'wpmu_signup_user_notification', $user_login, $user_email, $key, $meta ) ) {
+		return false;
+	}
+
+	$user            = get_user_by( 'login', $user_login );
+	$switched_locale = $user && switch_to_user_locale( $user->ID );
+
+	// Send email with activation link.
+	$admin_email = get_site_option( 'admin_email' );
+
+	if ( '' === $admin_email ) {
+		$admin_email = 'support@' . wp_parse_url( network_home_url(), PHP_URL_HOST );
+	}
+
+	$from_name       = ( '' !== get_site_option( 'site_name' ) ) ? esc_html( get_site_option( 'site_name' ) ) : 'WordPress';
+	$message_headers = "From: \"{$from_name}\" <{$admin_email}>\n" . 'Content-Type: text/plain; charset="' . get_option( 'blog_charset' ) . "\"\n";
+	$message         = sprintf(
+		/**
+		 * Filters the content of the notification email for new user sign-up.
+		 *
+		 * Content should be formatted for transmission via wp_mail().
+		 *
+		 * @since MU (3.0.0)
+		 *
+		 * @param string $content    Content of the notification email.
+		 * @param string $user_login User login name.
+		 * @param string $user_email User email address.
+		 * @param string $key        Activation key created in wpmu_signup_user().
+		 * @param array  $meta       Signup meta data. Default empty array.
+		 */
+		apply_filters(
+			'wpmu_signup_user_notification_email',
+			/* translators: New user notification email. %s: Activation URL. */
+			__( "To activate your user, please click the following link:\n\n%s\n\nAfter you activate, you will receive *another email* with your login." ),
+			$user_login,
+			$user_email,
+			$key,
+			$meta
+		),
+		site_url( "wp-activate.php?key=$key" )
+	);
+
+	$subject = sprintf(
+		/**
+		 * Filters the subject of the notification email of new user signup.
+		 *
+		 * @since MU (3.0.0)
+		 *
+		 * @param string $subject    Subject of the notification email.
+		 * @param string $user_login User login name.
+		 * @param string $user_email User email address.
+		 * @param string $key        Activation key created in wpmu_signup_user().
+		 * @param array  $meta       Signup meta data. Default empty array.
+		 */
+		apply_filters(
+			'wpmu_signup_user_notification_subject',
+			/* translators: New user notification email subject. 1: Network title, 2: New user login. */
+			_x( '[%1$s] Activate %2$s', 'New user notification email subject' ),
+			$user_login,
+			$user_email,
+			$key,
+			$meta
+		),
+		$from_name,
+		$user_login
+	);
+
+	wp_mail( $user_email, wp_specialchars_decode( $subject ), $message, $message_headers );
+
+	if ( $switched_locale ) {
+		restore_previous_locale();
+	}
+
+	return true;
+}
+
+/**
+ * Activates a signup.
+ *
+ * Hook to {@see 'wpmu_activate_user'} or {@see 'wpmu_activate_blog'} for events
+ * that should happen only when users or sites are self-created (since
+ * those actions are not called when users and sites are created
+ * by a Super Admin).
+ *
+ * @since MU (3.0.0)
+ *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ *
+ * @param string $key The activation key provided to the user.
+ * @return array|WP_Error An array containing information about the activated user and/or blog.
+ */
+function wpmu_activate_signup( $key ) {
+	global $wpdb;
+
+	$signup = $wpdb->get_row( $wpdb->prepare( "SELECT * FROM $wpdb->signups WHERE activation_key = %s", $key ) );
+
+	if ( empty( $signup ) ) {
+		return new WP_Error( 'invalid_key', __( 'Invalid activation key.' ) );
+	}
+
+	if ( $signup->active ) {
+		if ( empty( $signup->domain ) ) {
+			return new WP_Error( 'already_active', __( 'The user is already active.' ), $signup );
+		} else {
+			return new WP_Error( 'already_active', __( 'The site is already active.' ), $signup );
+		}
+	}
+
+	$meta     = maybe_unserialize( $signup->meta );
+	$password = wp_generate_password( 12, false );
+
+	$user_id = username_exists( $signup->user_login );
+
+	if ( ! $user_id ) {
+		$user_id = wpmu_create_user( $signup->user_login, $password, $signup->user_email );
+	} else {
+		$user_already_exists = true;
+	}
+
+	if ( ! $user_id ) {
+		return new WP_Error( 'create_user', __( 'Could not create user' ), $signup );
+	}
+
+	$now = current_time( 'mysql', true );
+
+	if ( empty( $signup->domain ) ) {
+		$wpdb->update(
+			$wpdb->signups,
+			array(
+				'active'    => 1,
+				'activated' => $now,
+			),
+			array( 'activation_key' => $key )
+		);
+
+		if ( isset( $user_already_exists ) ) {
+			return new WP_Error( 'user_already_exists', __( 'That username is already activated.' ), $signup );
+		}
+
+		/**
+		 * Fires immediately after a new user is activated.
+		 *
+		 * @since MU (3.0.0)
+		 *
+		 * @param int    $user_id  User ID.
+		 * @param string $password User password.
+		 * @param array  $meta     Signup meta data.
+		 */
+		do_action( 'wpmu_activate_user', $user_id, $password, $meta );
+
+		return array(
+			'user_id'  => $user_id,
+			'password' => $password,
+			'meta'     => $meta,
+		);
+	}
+
+	$blog_id = wpmu_create_blog( $signup->domain, $signup->path, $signup->title, $user_id, $meta, get_current_network_id() );
+
+	// TODO: What to do if we create a user but cannot create a blog?
+	if ( is_wp_error( $blog_id ) ) {
+		/*
+		 * If blog is taken, that means a previous attempt to activate this blog
+		 * failed in between creating the blog and setting the activation flag.
+		 * Let's just set the active flag and instruct the user to reset their password.
+		 */
+		if ( 'blog_taken' === $blog_id->get_error_code() ) {
+			$blog_id->add_data( $signup );
+			$wpdb->update(
+				$wpdb->signups,
+				array(
+					'active'    => 1,
+					'activated' => $now,
+				),
+				array( 'activation_key' => $key )
+			);
+		}
+		return $blog_id;
+	}
+
+	$wpdb->update(
+		$wpdb->signups,
+		array(
+			'active'    => 1,
+			'activated' => $now,
+		),
+		array( 'activation_key' => $key )
+	);
+
+	/**
+	 * Fires immediately after a site is activated.
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param int    $blog_id       Blog ID.
+	 * @param int    $user_id       User ID.
+	 * @param string $password      User password.
+	 * @param string $signup_title  Site title.
+	 * @param array  $meta          Signup meta data. By default, contains the requested privacy setting and lang_id.
+	 */
+	do_action( 'wpmu_activate_blog', $blog_id, $user_id, $password, $signup->title, $meta );
+
+	return array(
+		'blog_id'  => $blog_id,
+		'user_id'  => $user_id,
+		'password' => $password,
+		'title'    => $signup->title,
+		'meta'     => $meta,
+	);
+}
+
+/**
+ * Deletes an associated signup entry when a user is deleted from the database.
+ *
+ * @since 5.5.0
+ *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ *
+ * @param int      $id       ID of the user to delete.
+ * @param int|null $reassign ID of the user to reassign posts and links to.
+ * @param WP_User  $user     User object.
+ */
+function wp_delete_signup_on_user_delete( $id, $reassign, $user ) {
+	global $wpdb;
+
+	$wpdb->delete( $wpdb->signups, array( 'user_login' => $user->user_login ) );
+}
+
+/**
+ * Creates a user.
+ *
+ * This function runs when a user self-registers as well as when
+ * a Super Admin creates a new user. Hook to {@see 'wpmu_new_user'} for events
+ * that should affect all new users, but only on Multisite (otherwise
+ * use {@see 'user_register'}).
+ *
+ * @since MU (3.0.0)
+ *
+ * @param string $user_name The new user's login name.
+ * @param string $password  The new user's password.
+ * @param string $email     The new user's email address.
+ * @return int|false Returns false on failure, or int $user_id on success.
+ */
+function wpmu_create_user( $user_name, $password, $email ) {
+	$user_name = preg_replace( '/\s+/', '', sanitize_user( $user_name, true ) );
+
+	$user_id = wp_create_user( $user_name, $password, $email );
+	if ( is_wp_error( $user_id ) ) {
+		return false;
+	}
+
+	// Newly created users have no roles or caps until they are added to a blog.
+	delete_user_option( $user_id, 'capabilities' );
+	delete_user_option( $user_id, 'user_level' );
+
+	/**
+	 * Fires immediately after a new user is created.
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param int $user_id User ID.
+	 */
+	do_action( 'wpmu_new_user', $user_id );
+
+	return $user_id;
+}
+
+/**
+ * Creates a site.
+ *
+ * This function runs when a user self-registers a new site as well
+ * as when a Super Admin creates a new site. Hook to {@see 'wpmu_new_blog'}
+ * for events that should affect all new sites.
+ *
+ * On subdirectory installations, $domain is the same as the main site's
+ * domain, and the path is the subdirectory name (eg 'example.com'
+ * and '/blog1/'). On subdomain installations, $domain is the new subdomain +
+ * root domain (eg 'blog1.example.com'), and $path is '/'.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param string $domain     The new site's domain.
+ * @param string $path       The new site's path.
+ * @param string $title      The new site's title.
+ * @param int    $user_id    The user ID of the new site's admin.
+ * @param array  $options    Optional. Array of key=>value pairs used to set initial site options.
+ *                           If valid status keys are included ('public', 'archived', 'mature',
+ *                           'spam', 'deleted', or 'lang_id') the given site status(es) will be
+ *                           updated. Otherwise, keys and values will be used to set options for
+ *                           the new site. Default empty array.
+ * @param int    $network_id Optional. Network ID. Only relevant on multi-network installations.
+ *                           Default 1.
+ * @return int|WP_Error Returns WP_Error object on failure, the new site ID on success.
+ */
+function wpmu_create_blog( $domain, $path, $title, $user_id, $options = array(), $network_id = 1 ) {
+	$defaults = array(
+		'public' => 0,
+	);
+	$options  = wp_parse_args( $options, $defaults );
+
+	$title   = strip_tags( $title );
+	$user_id = (int) $user_id;
+
+	// Check if the domain has been used already. We should return an error message.
+	if ( domain_exists( $domain, $path, $network_id ) ) {
+		return new WP_Error( 'blog_taken', __( 'Sorry, that site already exists!' ) );
+	}
+
+	if ( ! wp_installing() ) {
+		wp_installing( true );
+	}
+
+	$allowed_data_fields = array( 'public', 'archived', 'mature', 'spam', 'deleted', 'lang_id' );
+
+	$site_data = array_merge(
+		array(
+			'domain'     => $domain,
+			'path'       => $path,
+			'network_id' => $network_id,
+		),
+		array_intersect_key( $options, array_flip( $allowed_data_fields ) )
+	);
+
+	// Data to pass to wp_initialize_site().
+	$site_initialization_data = array(
+		'title'   => $title,
+		'user_id' => $user_id,
+		'options' => array_diff_key( $options, array_flip( $allowed_data_fields ) ),
+	);
+
+	$blog_id = wp_insert_site( array_merge( $site_data, $site_initialization_data ) );
+
+	if ( is_wp_error( $blog_id ) ) {
+		return $blog_id;
+	}
+
+	wp_cache_set_sites_last_changed();
+
+	return $blog_id;
+}
+
+/**
+ * Notifies the network admin that a new site has been activated.
+ *
+ * Filter {@see 'newblog_notify_siteadmin'} to change the content of
+ * the notification email.
+ *
+ * @since MU (3.0.0)
+ * @since 5.1.0 $blog_id now supports input from the {@see 'wp_initialize_site'} action.
+ *
+ * @param WP_Site|int $blog_id    The new site's object or ID.
+ * @param string      $deprecated Not used.
+ * @return bool
+ */
+function newblog_notify_siteadmin( $blog_id, $deprecated = '' ) {
+	if ( is_object( $blog_id ) ) {
+		$blog_id = $blog_id->blog_id;
+	}
+
+	if ( 'yes' !== get_site_option( 'registrationnotification' ) ) {
+		return false;
+	}
+
+	$email = get_site_option( 'admin_email' );
+
+	if ( is_email( $email ) == false ) {
+		return false;
+	}
+
+	$options_site_url = esc_url( network_admin_url( 'settings.php' ) );
+
+	switch_to_blog( $blog_id );
+	$blogname = get_option( 'blogname' );
+	$siteurl  = site_url();
+	restore_current_blog();
+
+	$msg = sprintf(
+		/* translators: New site notification email. 1: Site URL, 2: User IP address, 3: URL to Network Settings screen. */
+		__(
+			'New Site: %1$s
+URL: %2$s
+Remote IP address: %3$s
+
+Disable these notifications: %4$s'
+		),
+		$blogname,
+		$siteurl,
+		wp_unslash( $_SERVER['REMOTE_ADDR'] ),
+		$options_site_url
+	);
+	/**
+	 * Filters the message body of the new site activation email sent
+	 * to the network administrator.
+	 *
+	 * @since MU (3.0.0)
+	 * @since 5.4.0 The `$blog_id` parameter was added.
+	 *
+	 * @param string     $msg     Email body.
+	 * @param int|string $blog_id The new site's ID as an integer or numeric string.
+	 */
+	$msg = apply_filters( 'newblog_notify_siteadmin', $msg, $blog_id );
+
+	/* translators: New site notification email subject. %s: New site URL. */
+	wp_mail( $email, sprintf( __( 'New Site Registration: %s' ), $siteurl ), $msg );
+
+	return true;
+}
+
+/**
+ * Notifies the network admin that a new user has been activated.
+ *
+ * Filter {@see 'newuser_notify_siteadmin'} to change the content of
+ * the notification email.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param int $user_id The new user's ID.
+ * @return bool
+ */
+function newuser_notify_siteadmin( $user_id ) {
+	if ( 'yes' !== get_site_option( 'registrationnotification' ) ) {
+		return false;
+	}
+
+	$email = get_site_option( 'admin_email' );
+
+	if ( is_email( $email ) == false ) {
+		return false;
+	}
+
+	$user = get_userdata( $user_id );
+
+	$options_site_url = esc_url( network_admin_url( 'settings.php' ) );
+
+	$msg = sprintf(
+		/* translators: New user notification email. 1: User login, 2: User IP address, 3: URL to Network Settings screen. */
+		__(
+			'New User: %1$s
+Remote IP address: %2$s
+
+Disable these notifications: %3$s'
+		),
+		$user->user_login,
+		wp_unslash( $_SERVER['REMOTE_ADDR'] ),
+		$options_site_url
+	);
+
+	/**
+	 * Filters the message body of the new user activation email sent
+	 * to the network administrator.
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param string  $msg  Email body.
+	 * @param WP_User $user WP_User instance of the new user.
+	 */
+	$msg = apply_filters( 'newuser_notify_siteadmin', $msg, $user );
+
+	/* translators: New user notification email subject. %s: User login. */
+	wp_mail( $email, sprintf( __( 'New User Registration: %s' ), $user->user_login ), $msg );
+
+	return true;
+}
+
+/**
+ * Checks whether a site name is already taken.
+ *
+ * The name is the site's subdomain or the site's subdirectory
+ * path depending on the network settings.
+ *
+ * Used during the new site registration process to ensure
+ * that each site name is unique.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param string $domain     The domain to be checked.
+ * @param string $path       The path to be checked.
+ * @param int    $network_id Optional. Network ID. Only relevant on multi-network installations.
+ *                           Default 1.
+ * @return int|null The site ID if the site name exists, null otherwise.
+ */
+function domain_exists( $domain, $path, $network_id = 1 ) {
+	$path   = trailingslashit( $path );
+	$args   = array(
+		'network_id'             => $network_id,
+		'domain'                 => $domain,
+		'path'                   => $path,
+		'fields'                 => 'ids',
+		'number'                 => 1,
+		'update_site_meta_cache' => false,
+	);
+	$result = get_sites( $args );
+	$result = array_shift( $result );
+
+	/**
+	 * Filters whether a site name is taken.
+	 *
+	 * The name is the site's subdomain or the site's subdirectory
+	 * path depending on the network settings.
+	 *
+	 * @since 3.5.0
+	 *
+	 * @param int|null $result     The site ID if the site name exists, null otherwise.
+	 * @param string   $domain     Domain to be checked.
+	 * @param string   $path       Path to be checked.
+	 * @param int      $network_id Network ID. Only relevant on multi-network installations.
+	 */
+	return apply_filters( 'domain_exists', $result, $domain, $path, $network_id );
+}
+
+/**
+ * Notifies the site administrator that their site activation was successful.
+ *
+ * Filter {@see 'wpmu_welcome_notification'} to disable or bypass.
+ *
+ * Filter {@see 'update_welcome_email'} and {@see 'update_welcome_subject'} to
+ * modify the content and subject line of the notification email.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param int    $blog_id  Site ID.
+ * @param int    $user_id  User ID.
+ * @param string $password User password, or "N/A" if the user account is not new.
+ * @param string $title    Site title.
+ * @param array  $meta     Optional. Signup meta data. By default, contains the requested privacy setting and lang_id.
+ * @return bool Whether the email notification was sent.
+ */
+function wpmu_welcome_notification( $blog_id, $user_id, $password, $title, $meta = array() ) {
+	$current_network = get_network();
+
+	/**
+	 * Filters whether to bypass the welcome email sent to the site administrator after site activation.
+	 *
+	 * Returning false disables the welcome email.
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param int|false $blog_id  Site ID, or false to prevent the email from sending.
+	 * @param int       $user_id  User ID of the site administrator.
+	 * @param string    $password User password, or "N/A" if the user account is not new.
+	 * @param string    $title    Site title.
+	 * @param array     $meta     Signup meta data. By default, contains the requested privacy setting and lang_id.
+	 */
+	if ( ! apply_filters( 'wpmu_welcome_notification', $blog_id, $user_id, $password, $title, $meta ) ) {
+		return false;
+	}
+
+	$user = get_userdata( $user_id );
+
+	$switched_locale = switch_to_user_locale( $user_id );
+
+	$welcome_email = get_site_option( 'welcome_email' );
+	if ( false == $welcome_email ) {
+		/* translators: Do not translate USERNAME, SITE_NAME, BLOG_URL, PASSWORD: those are placeholders. */
+		$welcome_email = __(
+			'Howdy USERNAME,
+
+Your new SITE_NAME site has been successfully set up at:
+BLOG_URL
+
+You can log in to the administrator account with the following information:
+
+Username: USERNAME
+Password: PASSWORD
+Log in here: BLOG_URLwp-login.php
+
+We hope you enjoy your new site. Thanks!
+
+--The Team @ SITE_NAME'
+		);
+	}
+
+	$url = get_blogaddress_by_id( $blog_id );
+
+	$welcome_email = str_replace( 'SITE_NAME', $current_network->site_name, $welcome_email );
+	$welcome_email = str_replace( 'BLOG_TITLE', $title, $welcome_email );
+	$welcome_email = str_replace( 'BLOG_URL', $url, $welcome_email );
+	$welcome_email = str_replace( 'USERNAME', $user->user_login, $welcome_email );
+	$welcome_email = str_replace( 'PASSWORD', $password, $welcome_email );
+
+	/**
+	 * Filters the content of the welcome email sent to the site administrator after site activation.
+	 *
+	 * Content should be formatted for transmission via wp_mail().
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param string $welcome_email Message body of the email.
+	 * @param int    $blog_id       Site ID.
+	 * @param int    $user_id       User ID of the site administrator.
+	 * @param string $password      User password, or "N/A" if the user account is not new.
+	 * @param string $title         Site title.
+	 * @param array  $meta          Signup meta data. By default, contains the requested privacy setting and lang_id.
+	 */
+	$welcome_email = apply_filters( 'update_welcome_email', $welcome_email, $blog_id, $user_id, $password, $title, $meta );
+
+	$admin_email = get_site_option( 'admin_email' );
+
+	if ( '' === $admin_email ) {
+		$admin_email = 'support@' . wp_parse_url( network_home_url(), PHP_URL_HOST );
+	}
+
+	$from_name       = ( '' !== get_site_option( 'site_name' ) ) ? esc_html( get_site_option( 'site_name' ) ) : 'WordPress';
+	$message_headers = "From: \"{$from_name}\" <{$admin_email}>\n" . 'Content-Type: text/plain; charset="' . get_option( 'blog_charset' ) . "\"\n";
+	$message         = $welcome_email;
+
+	if ( empty( $current_network->site_name ) ) {
+		$current_network->site_name = 'WordPress';
+	}
+
+	/* translators: New site notification email subject. 1: Network title, 2: New site title. */
+	$subject = __( 'New %1$s Site: %2$s' );
+
+	/**
+	 * Filters the subject of the welcome email sent to the site administrator after site activation.
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param string $subject Subject of the email.
+	 */
+	$subject = apply_filters( 'update_welcome_subject', sprintf( $subject, $current_network->site_name, wp_unslash( $title ) ) );
+
+	wp_mail( $user->user_email, wp_specialchars_decode( $subject ), $message, $message_headers );
+
+	if ( $switched_locale ) {
+		restore_previous_locale();
+	}
+
+	return true;
+}
+
+/**
+ * Notifies the Multisite network administrator that a new site was created.
+ *
+ * Filter {@see 'send_new_site_email'} to disable or bypass.
+ *
+ * Filter {@see 'new_site_email'} to filter the contents.
+ *
+ * @since 5.6.0
+ *
+ * @param int $site_id Site ID of the new site.
+ * @param int $user_id User ID of the administrator of the new site.
+ * @return bool Whether the email notification was sent.
+ */
+function wpmu_new_site_admin_notification( $site_id, $user_id ) {
+	$site  = get_site( $site_id );
+	$user  = get_userdata( $user_id );
+	$email = get_site_option( 'admin_email' );
+
+	if ( ! $site || ! $user || ! $email ) {
+		return false;
+	}
+
+	/**
+	 * Filters whether to send an email to the Multisite network administrator when a new site is created.
+	 *
+	 * Return false to disable sending the email.
+	 *
+	 * @since 5.6.0
+	 *
+	 * @param bool    $send Whether to send the email.
+	 * @param WP_Site $site Site object of the new site.
+	 * @param WP_User $user User object of the administrator of the new site.
+	 */
+	if ( ! apply_filters( 'send_new_site_email', true, $site, $user ) ) {
+		return false;
+	}
+
+	$switched_locale = false;
+	$network_admin   = get_user_by( 'email', $email );
+
+	if ( $network_admin ) {
+		// If the network admin email address corresponds to a user, switch to their locale.
+		$switched_locale = switch_to_user_locale( $network_admin->ID );
+	} else {
+		// Otherwise switch to the locale of the current site.
+		$switched_locale = switch_to_locale( get_locale() );
+	}
+
+	$subject = sprintf(
+		/* translators: New site notification email subject. %s: Network title. */
+		__( '[%s] New Site Created' ),
+		get_network()->site_name
+	);
+
+	$message = sprintf(
+		/* translators: New site notification email. 1: User login, 2: Site URL, 3: Site title. */
+		__(
+			'New site created by %1$s
+
+Address: %2$s
+Name: %3$s'
+		),
+		$user->user_login,
+		get_site_url( $site->id ),
+		get_blog_option( $site->id, 'blogname' )
+	);
+
+	$header = sprintf(
+		'From: "%1$s" <%2$s>',
+		_x( 'Site Admin', 'email "From" field' ),
+		$email
+	);
+
+	$new_site_email = array(
+		'to'      => $email,
+		'subject' => $subject,
+		'message' => $message,
+		'headers' => $header,
+	);
+
+	/**
+	 * Filters the content of the email sent to the Multisite network administrator when a new site is created.
+	 *
+	 * Content should be formatted for transmission via wp_mail().
+	 *
+	 * @since 5.6.0
+	 *
+	 * @param array $new_site_email {
+	 *     Used to build wp_mail().
+	 *
+	 *     @type string $to      The email address of the recipient.
+	 *     @type string $subject The subject of the email.
+	 *     @type string $message The content of the email.
+	 *     @type string $headers Headers.
+	 * }
+	 * @param WP_Site $site         Site object of the new site.
+	 * @param WP_User $user         User object of the administrator of the new site.
+	 */
+	$new_site_email = apply_filters( 'new_site_email', $new_site_email, $site, $user );
+
+	wp_mail(
+		$new_site_email['to'],
+		wp_specialchars_decode( $new_site_email['subject'] ),
+		$new_site_email['message'],
+		$new_site_email['headers']
+	);
+
+	if ( $switched_locale ) {
+		restore_previous_locale();
+	}
+
+	return true;
+}
+
+/**
+ * Notifies a user that their account activation has been successful.
+ *
+ * Filter {@see 'wpmu_welcome_user_notification'} to disable or bypass.
+ *
+ * Filter {@see 'update_welcome_user_email'} and {@see 'update_welcome_user_subject'} to
+ * modify the content and subject line of the notification email.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param int    $user_id  User ID.
+ * @param string $password User password.
+ * @param array  $meta     Optional. Signup meta data. Default empty array.
+ * @return bool
+ */
+function wpmu_welcome_user_notification( $user_id, $password, $meta = array() ) {
+	$current_network = get_network();
+
+	/**
+	 * Filters whether to bypass the welcome email after user activation.
+	 *
+	 * Returning false disables the welcome email.
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param int    $user_id  User ID.
+	 * @param string $password User password.
+	 * @param array  $meta     Signup meta data. Default empty array.
+	 */
+	if ( ! apply_filters( 'wpmu_welcome_user_notification', $user_id, $password, $meta ) ) {
+		return false;
+	}
+
+	$welcome_email = get_site_option( 'welcome_user_email' );
+
+	$user = get_userdata( $user_id );
+
+	$switched_locale = switch_to_user_locale( $user_id );
+
+	/**
+	 * Filters the content of the welcome email after user activation.
+	 *
+	 * Content should be formatted for transmission via wp_mail().
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param string $welcome_email The message body of the account activation success email.
+	 * @param int    $user_id       User ID.
+	 * @param string $password      User password.
+	 * @param array  $meta          Signup meta data. Default empty array.
+	 */
+	$welcome_email = apply_filters( 'update_welcome_user_email', $welcome_email, $user_id, $password, $meta );
+	$welcome_email = str_replace( 'SITE_NAME', $current_network->site_name, $welcome_email );
+	$welcome_email = str_replace( 'USERNAME', $user->user_login, $welcome_email );
+	$welcome_email = str_replace( 'PASSWORD', $password, $welcome_email );
+	$welcome_email = str_replace( 'LOGINLINK', wp_login_url(), $welcome_email );
+
+	$admin_email = get_site_option( 'admin_email' );
+
+	if ( '' === $admin_email ) {
+		$admin_email = 'support@' . wp_parse_url( network_home_url(), PHP_URL_HOST );
+	}
+
+	$from_name       = ( '' !== get_site_option( 'site_name' ) ) ? esc_html( get_site_option( 'site_name' ) ) : 'WordPress';
+	$message_headers = "From: \"{$from_name}\" <{$admin_email}>\n" . 'Content-Type: text/plain; charset="' . get_option( 'blog_charset' ) . "\"\n";
+	$message         = $welcome_email;
+
+	if ( empty( $current_network->site_name ) ) {
+		$current_network->site_name = 'WordPress';
+	}
+
+	/* translators: New user notification email subject. 1: Network title, 2: New user login. */
+	$subject = __( 'New %1$s User: %2$s' );
+
+	/**
+	 * Filters the subject of the welcome email after user activation.
+	 *
+	 * @since MU (3.0.0)
+	 *
+	 * @param string $subject Subject of the email.
+	 */
+	$subject = apply_filters( 'update_welcome_user_subject', sprintf( $subject, $current_network->site_name, $user->user_login ) );
+
+	wp_mail( $user->user_email, wp_specialchars_decode( $subject ), $message, $message_headers );
+
+	if ( $switched_locale ) {
+		restore_previous_locale();
+	}
+
+	return true;
+}
+
+/**
+ * Gets the current network.
+ *
+ * Returns an object containing the 'id', 'domain', 'path', and 'site_name'
+ * properties of the network being viewed.
+ *
+ * @see wpmu_current_site()
+ *
+ * @since MU (3.0.0)
+ *
+ * @global WP_Network $current_site The current network.
+ *
+ * @return WP_Network The current network.
+ */
+function get_current_site() {
+	global $current_site;
+	return $current_site;
+}
+
+/**
+ * Gets a user's most recent post.
+ *
+ * Walks through each of a user's blogs to find the post with
+ * the most recent post_date_gmt.
+ *
+ * @since MU (3.0.0)
+ *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ *
+ * @param int $user_id User ID.
+ * @return array Contains the blog_id, post_id, post_date_gmt, and post_gmt_ts.
+ */
+function get_most_recent_post_of_user( $user_id ) {
+	global $wpdb;
+
+	$user_blogs       = get_blogs_of_user( (int) $user_id );
+	$most_recent_post = array();
+
+	/*
+	 * Walk through each blog and get the most recent post
+	 * published by $user_id.
+	 */
+	foreach ( (array) $user_blogs as $blog ) {
+		$prefix      = $wpdb->get_blog_prefix( $blog->userblog_id );
+		$recent_post = $wpdb->get_row( $wpdb->prepare( "SELECT ID, post_date_gmt FROM {$prefix}posts WHERE post_author = %d AND post_type = 'post' AND post_status = 'publish' ORDER BY post_date_gmt DESC LIMIT 1", $user_id ), ARRAY_A );
+
+		// Make sure we found a post.
+		if ( isset( $recent_post['ID'] ) ) {
+			$post_gmt_ts = strtotime( $recent_post['post_date_gmt'] );
+
+			/*
+			 * If this is the first post checked
+			 * or if this post is newer than the current recent post,
+			 * make it the new most recent post.
+			 */
+			if ( ! isset( $most_recent_post['post_gmt_ts'] ) || ( $post_gmt_ts > $most_recent_post['post_gmt_ts'] ) ) {
+				$most_recent_post = array(
+					'blog_id'       => $blog->userblog_id,
+					'post_id'       => $recent_post['ID'],
+					'post_date_gmt' => $recent_post['post_date_gmt'],
+					'post_gmt_ts'   => $post_gmt_ts,
+				);
+			}
+		}
+	}
+
+	return $most_recent_post;
+}
+
+//
+// Misc functions.
+//
+
+/**
+ * Checks an array of MIME types against a list of allowed types.
+ *
+ * WordPress ships with a set of allowed upload filetypes,
+ * which is defined in wp-includes/functions.php in
+ * get_allowed_mime_types(). This function is used to filter
+ * that list against the filetypes allowed provided by Multisite
+ * Super Admins at wp-admin/network/settings.php.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param array $mimes
+ * @return array
+ */
+function check_upload_mimes( $mimes ) {
+	$site_exts  = explode( ' ', get_site_option( 'upload_filetypes', 'jpg jpeg png gif' ) );
+	$site_mimes = array();
+	foreach ( $site_exts as $ext ) {
+		foreach ( $mimes as $ext_pattern => $mime ) {
+			if ( '' !== $ext && str_contains( $ext_pattern, $ext ) ) {
+				$site_mimes[ $ext_pattern ] = $mime;
+			}
+		}
+	}
+	return $site_mimes;
+}
+
+/**
+ * Updates a blog's post count.
+ *
+ * WordPress MS stores a blog's post count as an option so as
+ * to avoid extraneous COUNTs when a blog's details are fetched
+ * with get_site(). This function is called when posts are published
+ * or unpublished to make sure the count stays current.
+ *
+ * @since MU (3.0.0)
+ *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ *
+ * @param string $deprecated Not used.
+ */
+function update_posts_count( $deprecated = '' ) {
+	global $wpdb;
+	update_option( 'post_count', (int) $wpdb->get_var( "SELECT COUNT(ID) FROM {$wpdb->posts} WHERE post_status = 'publish' and post_type = 'post'" ) );
+}
+
+/**
+ * Logs the user email, IP, and registration date of a new site.
+ *
+ * @since MU (3.0.0)
+ * @since 5.1.0 Parameters now support input from the {@see 'wp_initialize_site'} action.
+ *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ *
+ * @param WP_Site|int $blog_id The new site's object or ID.
+ * @param int|array   $user_id User ID, or array of arguments including 'user_id'.
+ */
+function wpmu_log_new_registrations( $blog_id, $user_id ) {
+	global $wpdb;
+
+	if ( is_object( $blog_id ) ) {
+		$blog_id = $blog_id->blog_id;
+	}
+
+	if ( is_array( $user_id ) ) {
+		$user_id = ! empty( $user_id['user_id'] ) ? $user_id['user_id'] : 0;
+	}
+
+	$user = get_userdata( (int) $user_id );
+	if ( $user ) {
+		$wpdb->insert(
+			$wpdb->registration_log,
+			array(
+				'email'           => $user->user_email,
+				'IP'              => preg_replace( '/[^0-9., ]/', '', wp_unslash( $_SERVER['REMOTE_ADDR'] ) ),
+				'blog_id'         => $blog_id,
+				'date_registered' => current_time( 'mysql' ),
+			)
+		);
+	}
+}
+
+/**
+ * Ensures that the current site's domain is listed in the allowed redirect host list.
+ *
+ * @see wp_validate_redirect()
+ * @since MU (3.0.0)
+ *
+ * @param array|string $deprecated Not used.
+ * @return string[] {
+ *     An array containing the current site's domain.
+ *
+ *     @type string $0 The current site's domain.
+ * }
+ */
+function redirect_this_site( $deprecated = '' ) {
+	return array( get_network()->domain );
+}
+
+/**
+ * Checks whether an upload is too big.
+ *
+ * @since MU (3.0.0)
+ *
+ * @blessed
+ *
+ * @param array $upload An array of information about the newly-uploaded file.
+ * @return string|array If the upload is under the size limit, $upload is returned. Otherwise returns an error message.
+ */
+function upload_is_file_too_big( $upload ) {
+	if ( ! is_array( $upload ) || defined( 'WP_IMPORTING' ) || get_site_option( 'upload_space_check_disabled' ) ) {
+		return $upload;
+	}
+
+	if ( strlen( $upload['bits'] ) > ( KB_IN_BYTES * get_site_option( 'fileupload_maxk', 1500 ) ) ) {
+		/* translators: %s: Maximum allowed file size in kilobytes. */
+		return sprintf( __( 'This file is too big. Files must be less than %s KB in size.' ) . '<br />', get_site_option( 'fileupload_maxk', 1500 ) );
+	}
+
+	return $upload;
+}
+
+/**
+ * Adds a nonce field to the signup page.
+ *
+ * @since MU (3.0.0)
+ */
+function signup_nonce_fields() {
+	$id = mt_rand();
+	echo "<input type='hidden' name='signup_form_id' value='{$id}' />";
+	wp_nonce_field( 'signup_form_' . $id, '_signup_form', false );
+}
+
+/**
+ * Processes the signup nonce created in signup_nonce_fields().
+ *
+ * @since MU (3.0.0)
+ *
+ * @param array $result
+ * @return array
+ */
+function signup_nonce_check( $result ) {
+	if ( ! strpos( $_SERVER['PHP_SELF'], 'wp-signup.php' ) ) {
+		return $result;
+	}
+
+	if ( ! wp_verify_nonce( $_POST['_signup_form'], 'signup_form_' . $_POST['signup_form_id'] ) ) {
+		$result['errors']->add( 'invalid_nonce', __( 'Unable to submit this form, please try again.' ) );
+	}
+
+	return $result;
+}
+
+/**
+ * Corrects 404 redirects when NOBLOGREDIRECT is defined.
+ *
+ * @since MU (3.0.0)
+ */
+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;
+		}
+	}
+}
+
+/**
+ * Adds a new user to a blog by visiting /newbloguser/{key}/.
+ *
+ * This will only work when the user's details are saved as an option
+ * keyed as 'new_user_{key}', where '{key}' is a hash generated for the user to be
+ * added, as when a user is invited through the regular WP Add User interface.
+ *
+ * @since MU (3.0.0)
+ */
+function maybe_add_existing_user_to_blog() {
+	if ( ! str_contains( $_SERVER['REQUEST_URI'], '/newbloguser/' ) ) {
+		return;
+	}
+
+	$parts = explode( '/', $_SERVER['REQUEST_URI'] );
+	$key   = array_pop( $parts );
+
+	if ( '' === $key ) {
+		$key = array_pop( $parts );
+	}
+
+	$details = get_option( 'new_user_' . $key );
+	if ( ! empty( $details ) ) {
+		delete_option( 'new_user_' . $key );
+	}
+
+	if ( empty( $details ) || is_wp_error( add_existing_user_to_blog( $details ) ) ) {
+		wp_die(
+			sprintf(
+				/* translators: %s: Home URL. */
+				__( 'An error occurred adding you to this site. Go to the <a href="%s">homepage</a>.' ),
+				home_url()
+			)
+		);
+	}
+
+	wp_die(
+		sprintf(
+			/* translators: 1: Home URL, 2: Admin URL. */
+			__( 'You have been added to this site. Please visit the <a href="%1$s">homepage</a> or <a href="%2$s">log in</a> using your username and password.' ),
+			home_url(),
+			admin_url()
+		),
+		__( 'WordPress &rsaquo; Success' ),
+		array( 'response' => 200 )
+	);
+}
+
+/**
+ * Adds a user to a blog based on details from maybe_add_existing_user_to_blog().
+ *
+ * @since MU (3.0.0)
+ *
+ * @param array|false $details {
+ *     User details. Must at least contain values for the keys listed below.
+ *
+ *     @type int    $user_id The ID of the user being added to the current blog.
+ *     @type string $role    The role to be assigned to the user.
+ * }
+ * @return true|WP_Error|void True on success or a WP_Error object if the user doesn't exist
+ *                            or could not be added. Void if $details array was not provided.
+ */
+function add_existing_user_to_blog( $details = false ) {
+	if ( is_array( $details ) ) {
+		$blog_id = get_current_blog_id();
+		$result  = add_user_to_blog( $blog_id, $details['user_id'], $details['role'] );
+
+		/**
+		 * Fires immediately after an existing user is added to a site.
+		 *
+		 * @since MU (3.0.0)
+		 *
+		 * @param int           $user_id User ID.
+		 * @param true|WP_Error $result  True on success or a WP_Error object if the user doesn't exist
+		 *                               or could not be added.
+		 */
+		do_action( 'added_existing_user', $details['user_id'], $result );
+
+		return $result;
+	}
+}
+
+/**
+ * Adds a newly created user to the appropriate blog
+ *
+ * To add a user in general, use add_user_to_blog(). This function
+ * is specifically hooked into the {@see 'wpmu_activate_user'} action.
+ *
+ * @since MU (3.0.0)
+ *
+ * @see add_user_to_blog()
+ *
+ * @param int    $user_id  User ID.
+ * @param string $password User password. Ignored.
+ * @param array  $meta     Signup meta data.
+ */
+function add_new_user_to_blog( $user_id, $password, $meta ) {
+	if ( ! empty( $meta['add_to_blog'] ) ) {
+		$blog_id = $meta['add_to_blog'];
+		$role    = $meta['new_role'];
+		remove_user_from_blog( $user_id, get_network()->site_id ); // Remove user from main blog.
+
+		$result = add_user_to_blog( $blog_id, $user_id, $role );
+
+		if ( ! is_wp_error( $result ) ) {
+			update_user_meta( $user_id, 'primary_blog', $blog_id );
+		}
+	}
+}
+
+/**
+ * Corrects From host on outgoing mail to match the site domain.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param PHPMailer $phpmailer The PHPMailer instance (passed by reference).
+ */
+function fix_phpmailer_messageid( $phpmailer ) {
+	$phpmailer->Hostname = get_network()->domain;
+}
+
+/**
+ * Determines whether a user is marked as a spammer, based on user login.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param string|WP_User $user Optional. Defaults to current user. WP_User object,
+ *                             or user login name as a string.
+ * @return bool
+ */
+function is_user_spammy( $user = null ) {
+	if ( ! ( $user instanceof WP_User ) ) {
+		if ( $user ) {
+			$user = get_user_by( 'login', $user );
+		} else {
+			$user = wp_get_current_user();
+		}
+	}
+
+	return $user && isset( $user->spam ) && 1 == $user->spam;
+}
+
+/**
+ * Updates this blog's 'public' setting in the global blogs table.
+ *
+ * Public blogs have a setting of 1, private blogs are 0.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param int $old_value The old public value.
+ * @param int $value     The new public value.
+ */
+function update_blog_public( $old_value, $value ) {
+	update_blog_status( get_current_blog_id(), 'public', (int) $value );
+}
+
+/**
+ * Determines whether users can self-register, based on Network settings.
+ *
+ * @since MU (3.0.0)
+ *
+ * @return bool
+ */
+function users_can_register_signup_filter() {
+	$registration = get_site_option( 'registration' );
+	return ( 'all' === $registration || 'user' === $registration );
+}
+
+/**
+ * Ensures that the welcome message is not empty. Currently unused.
+ *
+ * @since MU (3.0.0)
+ *
+ * @param string $text
+ * @return string
+ */
+function welcome_user_msg_filter( $text ) {
+	if ( ! $text ) {
+		remove_filter( 'site_option_welcome_user_email', 'welcome_user_msg_filter' );
+
+		/* translators: Do not translate USERNAME, PASSWORD, LOGINLINK, SITE_NAME: those are placeholders. */
+		$text = __(
+			'Howdy USERNAME,
+
+Your new account is set up.
+
+You can log in with the following information:
+Username: USERNAME
+Password: PASSWORD
+LOGINLINK
+
+Thanks!
+
+--The Team @ SITE_NAME'
+		);
+		update_site_option( 'welcome_user_email', $text );
+	}
+	return $text;
+}
+
+/**
+ * Determines whether to force SSL on content.
+ *
+ * @since 2.8.5
+ *
+ * @param bool $force
+ * @return bool True if forced, false if not forced.
+ */
+function force_ssl_content( $force = '' ) {
+	static $forced_content = false;
+
+	if ( ! $force ) {
+		$old_forced     = $forced_content;
+		$forced_content = $force;
+		return $old_forced;
+	}
+
+	return $forced_content;
+}
+
+/**
+ * Formats a URL to use https.
+ *
+ * Useful as a filter.
+ *
+ * @since 2.8.5
+ *
+ * @param string $url URL.
+ * @return string URL with https as the scheme.
+ */
+function filter_SSL( $url ) {  // phpcs:ignore WordPress.NamingConventions.ValidFunctionName.FunctionNameInvalid
+	if ( ! is_string( $url ) ) {
+		return get_bloginfo( 'url' ); // Return home site URL with proper scheme.
+	}
+
+	if ( force_ssl_content() && is_ssl() ) {
+		$url = set_url_scheme( $url, 'https' );
+	}
+
+	return $url;
+}
+
+/**
+ * Schedules update of the network-wide counts for the current network.
+ *
+ * @since 3.1.0
+ */
+function wp_schedule_update_network_counts() {
+	if ( ! is_main_site() ) {
+		return;
+	}
+
+	if ( ! wp_next_scheduled( 'update_network_counts' ) && ! wp_installing() ) {
+		wp_schedule_event( time(), 'twicedaily', 'update_network_counts' );
+	}
+}
+
+/**
+ * Updates the network-wide counts for the current network.
+ *
+ * @since 3.1.0
+ * @since 4.8.0 The `$network_id` parameter has been added.
+ *
+ * @param int|null $network_id ID of the network. Default is the current network.
+ */
+function wp_update_network_counts( $network_id = null ) {
+	wp_update_network_user_counts( $network_id );
+	wp_update_network_site_counts( $network_id );
+}
+
+/**
+ * Updates the count of sites for the current network.
+ *
+ * If enabled through the {@see 'enable_live_network_counts'} filter, update the sites count
+ * on a network when a site is created or its status is updated.
+ *
+ * @since 3.7.0
+ * @since 4.8.0 The `$network_id` parameter has been added.
+ *
+ * @param int|null $network_id ID of the network. Default is the current network.
+ */
+function wp_maybe_update_network_site_counts( $network_id = null ) {
+	$is_small_network = ! wp_is_large_network( 'sites', $network_id );
+
+	/**
+	 * Filters whether to update network site or user counts when a new site is created.
+	 *
+	 * @since 3.7.0
+	 *
+	 * @see wp_is_large_network()
+	 *
+	 * @param bool   $small_network Whether the network is considered small.
+	 * @param string $context       Context. Either 'users' or 'sites'.
+	 */
+	if ( ! apply_filters( 'enable_live_network_counts', $is_small_network, 'sites' ) ) {
+		return;
+	}
+
+	wp_update_network_site_counts( $network_id );
+}
+
+/**
+ * Updates the network-wide users count.
+ *
+ * If enabled through the {@see 'enable_live_network_counts'} filter, update the users count
+ * on a network when a user is created or its status is updated.
+ *
+ * @since 3.7.0
+ * @since 4.8.0 The `$network_id` parameter has been added.
+ *
+ * @param int|null $network_id ID of the network. Default is the current network.
+ */
+function wp_maybe_update_network_user_counts( $network_id = null ) {
+	$is_small_network = ! wp_is_large_network( 'users', $network_id );
+
+	/** This filter is documented in wp-includes/ms-functions.php */
+	if ( ! apply_filters( 'enable_live_network_counts', $is_small_network, 'users' ) ) {
+		return;
+	}
+
+	wp_update_network_user_counts( $network_id );
+}
+
+/**
+ * Updates the network-wide site count.
+ *
+ * @since 3.7.0
+ * @since 4.8.0 The `$network_id` parameter has been added.
+ *
+ * @param int|null $network_id ID of the network. Default is the current network.
+ */
+function wp_update_network_site_counts( $network_id = null ) {
+	$network_id = (int) $network_id;
+	if ( ! $network_id ) {
+		$network_id = get_current_network_id();
+	}
+
+	$count = get_sites(
+		array(
+			'network_id'             => $network_id,
+			'spam'                   => 0,
+			'deleted'                => 0,
+			'archived'               => 0,
+			'count'                  => true,
+			'update_site_meta_cache' => false,
+		)
+	);
+
+	update_network_option( $network_id, 'blog_count', $count );
+}
+
+/**
+ * Updates the network-wide user count.
+ *
+ * @since 3.7.0
+ * @since 4.8.0 The `$network_id` parameter has been added.
+ * @since 6.0.0 This function is now a wrapper for wp_update_user_counts().
+ *
+ * @param int|null $network_id ID of the network. Default is the current network.
+ */
+function wp_update_network_user_counts( $network_id = null ) {
+	wp_update_user_counts( $network_id );
+}
+
+/**
+ * Returns the space used by the current site.
+ *
+ * @since 3.5.0
+ *
+ * @return int Used space in megabytes.
+ */
+function get_space_used() {
+	/**
+	 * Filters the amount of storage space used by the current site, in megabytes.
+	 *
+	 * @since 3.5.0
+	 *
+	 * @param int|false $space_used The amount of used space, in megabytes. Default false.
+	 */
+	$space_used = apply_filters( 'pre_get_space_used', false );
+
+	if ( false === $space_used ) {
+		$upload_dir = wp_upload_dir();
+		$space_used = get_dirsize( $upload_dir['basedir'] ) / MB_IN_BYTES;
+	}
+
+	return $space_used;
+}
+
+/**
+ * Returns the upload quota for the current blog.
+ *
+ * @since MU (3.0.0)
+ *
+ * @return int Quota in megabytes.
+ */
+function get_space_allowed() {
+	$space_allowed = get_option( 'blog_upload_space' );
+
+	if ( ! is_numeric( $space_allowed ) ) {
+		$space_allowed = get_site_option( 'blog_upload_space' );
+	}
+
+	if ( ! is_numeric( $space_allowed ) ) {
+		$space_allowed = 100;
+	}
+
+	/**
+	 * Filters the upload quota for the current site.
+	 *
+	 * @since 3.7.0
+	 *
+	 * @param int $space_allowed Upload quota in megabytes for the current blog.
+	 */
+	return apply_filters( 'get_space_allowed', $space_allowed );
+}
+
+/**
+ * Determines if there is any upload space left in the current blog's quota.
+ *
+ * @since 3.0.0
+ *
+ * @return int of upload space available in bytes.
+ */
+function get_upload_space_available() {
+	$allowed = get_space_allowed();
+	if ( $allowed < 0 ) {
+		$allowed = 0;
+	}
+	$space_allowed = $allowed * MB_IN_BYTES;
+	if ( get_site_option( 'upload_space_check_disabled' ) ) {
+		return $space_allowed;
+	}
+
+	$space_used = get_space_used() * MB_IN_BYTES;
+
+	if ( ( $space_allowed - $space_used ) <= 0 ) {
+		return 0;
+	}
+
+	return $space_allowed - $space_used;
+}
+
+/**
+ * Determines if there is any upload space left in the current blog's quota.
+ *
+ * @since 3.0.0
+ * @return bool True if space is available, false otherwise.
+ */
+function is_upload_space_available() {
+	if ( get_site_option( 'upload_space_check_disabled' ) ) {
+		return true;
+	}
+
+	return (bool) get_upload_space_available();
+}
+
+/**
+ * Filters the maximum upload file size allowed, in bytes.
+ *
+ * @since 3.0.0
+ *
+ * @param int $size Upload size limit in bytes.
+ * @return int Upload size limit in bytes.
+ */
+function upload_size_limit_filter( $size ) {
+	$fileupload_maxk         = (int) get_site_option( 'fileupload_maxk', 1500 );
+	$max_fileupload_in_bytes = KB_IN_BYTES * $fileupload_maxk;
+
+	if ( get_site_option( 'upload_space_check_disabled' ) ) {
+		return min( $size, $max_fileupload_in_bytes );
+	}
+
+	return min( $size, $max_fileupload_in_bytes, get_upload_space_available() );
+}
+
+/**
+ * Determines whether or not we have a large network.
+ *
+ * The default criteria for a large network is either more than 10,000 users or more than 10,000 sites.
+ * Plugins can alter this criteria using the {@see 'wp_is_large_network'} filter.
+ *
+ * @since 3.3.0
+ * @since 4.8.0 The `$network_id` parameter has been added.
+ *
+ * @param string   $using      'sites' or 'users'. Default is 'sites'.
+ * @param int|null $network_id ID of the network. Default is the current network.
+ * @return bool True if the network meets the criteria for large. False otherwise.
+ */
+function wp_is_large_network( $using = 'sites', $network_id = null ) {
+	$network_id = (int) $network_id;
+	if ( ! $network_id ) {
+		$network_id = get_current_network_id();
+	}
+
+	if ( 'users' === $using ) {
+		$count = get_user_count( $network_id );
+
+		$is_large_network = wp_is_large_user_count( $network_id );
+
+		/**
+		 * Filters whether the network is considered large.
+		 *
+		 * @since 3.3.0
+		 * @since 4.8.0 The `$network_id` parameter has been added.
+		 *
+		 * @param bool   $is_large_network Whether the network has more than 10000 users or sites.
+		 * @param string $component        The component to count. Accepts 'users', or 'sites'.
+		 * @param int    $count            The count of items for the component.
+		 * @param int    $network_id       The ID of the network being checked.
+		 */
+		return apply_filters( 'wp_is_large_network', $is_large_network, 'users', $count, $network_id );
+	}
+
+	$count = get_blog_count( $network_id );
+
+	/** This filter is documented in wp-includes/ms-functions.php */
+	return apply_filters( 'wp_is_large_network', $count > 10000, 'sites', $count, $network_id );
+}
+
+/**
+ * Retrieves a list of reserved site on a sub-directory Multisite installation.
+ *
+ * @since 4.4.0
+ *
+ * @return string[] Array of reserved names.
+ */
+function get_subdirectory_reserved_names() {
+	$names = array(
+		'page',
+		'comments',
+		'blog',
+		'files',
+		'feed',
+		'wp-admin',
+		'wp-content',
+		'wp-includes',
+		'wp-json',
+		'embed',
+	);
+
+	/**
+	 * Filters reserved site names on a sub-directory Multisite installation.
+	 *
+	 * @since 3.0.0
+	 * @since 4.4.0 'wp-admin', 'wp-content', 'wp-includes', 'wp-json', and 'embed' were added
+	 *              to the reserved names list.
+	 *
+	 * @param string[] $subdirectory_reserved_names Array of reserved names.
+	 */
+	return apply_filters( 'subdirectory_reserved_names', $names );
+}
+
+/**
+ * Sends a confirmation request email when a change of network admin email address is attempted.
+ *
+ * The new network admin address will not become active until confirmed.
+ *
+ * @since 4.9.0
+ *
+ * @param string $old_value The old network admin email address.
+ * @param string $value     The proposed new network admin email address.
+ */
+function update_network_option_new_admin_email( $old_value, $value ) {
+	if ( get_site_option( 'admin_email' ) === $value || ! is_email( $value ) ) {
+		return;
+	}
+
+	$hash            = md5( $value . time() . mt_rand() );
+	$new_admin_email = array(
+		'hash'     => $hash,
+		'newemail' => $value,
+	);
+	update_site_option( 'network_admin_hash', $new_admin_email );
+
+	$switched_locale = switch_to_user_locale( get_current_user_id() );
+
+	/* translators: Do not translate USERNAME, ADMIN_URL, EMAIL, SITENAME, SITEURL: those are placeholders. */
+	$email_text = __(
+		'Howdy ###USERNAME###,
+
+You recently requested to have the network admin email address on
+your network changed.
+
+If this is correct, please click on the following link to change it:
+###ADMIN_URL###
+
+You can safely ignore and delete this email if you do not want to
+take this action.
+
+This email has been sent to ###EMAIL###
+
+Regards,
+All at ###SITENAME###
+###SITEURL###'
+	);
+
+	/**
+	 * Filters the text of the email sent when a change of network admin email address is attempted.
+	 *
+	 * The following strings have a special meaning and will get replaced dynamically:
+	 * ###USERNAME###  The current user's username.
+	 * ###ADMIN_URL### The link to click on to confirm the email change.
+	 * ###EMAIL###     The proposed new network admin email address.
+	 * ###SITENAME###  The name of the network.
+	 * ###SITEURL###   The URL to the network.
+	 *
+	 * @since 4.9.0
+	 *
+	 * @param string $email_text      Text in the email.
+	 * @param array  $new_admin_email {
+	 *     Data relating to the new network admin email address.
+	 *
+	 *     @type string $hash     The secure hash used in the confirmation link URL.
+	 *     @type string $newemail The proposed new network admin email address.
+	 * }
+	 */
+	$content = apply_filters( 'new_network_admin_email_content', $email_text, $new_admin_email );
+
+	$current_user = wp_get_current_user();
+	$content      = str_replace( '###USERNAME###', $current_user->user_login, $content );
+	$content      = str_replace( '###ADMIN_URL###', esc_url( network_admin_url( 'settings.php?network_admin_hash=' . $hash ) ), $content );
+	$content      = str_replace( '###EMAIL###', $value, $content );
+	$content      = str_replace( '###SITENAME###', wp_specialchars_decode( get_site_option( 'site_name' ), ENT_QUOTES ), $content );
+	$content      = str_replace( '###SITEURL###', network_home_url(), $content );
+
+	wp_mail(
+		$value,
+		sprintf(
+			/* translators: Email change notification email subject. %s: Network title. */
+			__( '[%s] Network Admin Email Change Request' ),
+			wp_specialchars_decode( get_site_option( 'site_name' ), ENT_QUOTES )
+		),
+		$content
+	);
+
+	if ( $switched_locale ) {
+		restore_previous_locale();
+	}
+}
+
+/**
+ * Sends an email to the old network admin email address when the network admin email address changes.
+ *
+ * @since 4.9.0
+ *
+ * @param string $option_name The relevant database option name.
+ * @param string $new_email   The new network admin email address.
+ * @param string $old_email   The old network admin email address.
+ * @param int    $network_id  ID of the network.
+ */
+function wp_network_admin_email_change_notification( $option_name, $new_email, $old_email, $network_id ) {
+	$send = true;
+
+	// Don't send the notification to the default 'admin_email' value.
+	if ( 'you@example.com' === $old_email ) {
+		$send = false;
+	}
+
+	/**
+	 * Filters whether to send the network admin email change notification email.
+	 *
+	 * @since 4.9.0
+	 *
+	 * @param bool   $send       Whether to send the email notification.
+	 * @param string $old_email  The old network admin email address.
+	 * @param string $new_email  The new network admin email address.
+	 * @param int    $network_id ID of the network.
+	 */
+	$send = apply_filters( 'send_network_admin_email_change_email', $send, $old_email, $new_email, $network_id );
+
+	if ( ! $send ) {
+		return;
+	}
+
+	/* translators: Do not translate OLD_EMAIL, NEW_EMAIL, SITENAME, SITEURL: those are placeholders. */
+	$email_change_text = __(
+		'Hi,
+
+This notice confirms that the network admin email address was changed on ###SITENAME###.
+
+The new network admin email address is ###NEW_EMAIL###.
+
+This email has been sent to ###OLD_EMAIL###
+
+Regards,
+All at ###SITENAME###
+###SITEURL###'
+	);
+
+	$email_change_email = array(
+		'to'      => $old_email,
+		/* translators: Network admin email change notification email subject. %s: Network title. */
+		'subject' => __( '[%s] Network Admin Email Changed' ),
+		'message' => $email_change_text,
+		'headers' => '',
+	);
+	// Get network name.
+	$network_name = wp_specialchars_decode( get_site_option( 'site_name' ), ENT_QUOTES );
+
+	/**
+	 * Filters the contents of the email notification sent when the network admin email address is changed.
+	 *
+	 * @since 4.9.0
+	 *
+	 * @param array $email_change_email {
+	 *     Used to build wp_mail().
+	 *
+	 *     @type string $to      The intended recipient.
+	 *     @type string $subject The subject of the email.
+	 *     @type string $message The content of the email.
+	 *         The following strings have a special meaning and will get replaced dynamically:
+	 *         - ###OLD_EMAIL### The old network admin email address.
+	 *         - ###NEW_EMAIL### The new network admin email address.
+	 *         - ###SITENAME###  The name of the network.
+	 *         - ###SITEURL###   The URL to the site.
+	 *     @type string $headers Headers.
+	 * }
+	 * @param string $old_email  The old network admin email address.
+	 * @param string $new_email  The new network admin email address.
+	 * @param int    $network_id ID of the network.
+	 */
+	$email_change_email = apply_filters( 'network_admin_email_change_email', $email_change_email, $old_email, $new_email, $network_id );
+
+	$email_change_email['message'] = str_replace( '###OLD_EMAIL###', $old_email, $email_change_email['message'] );
+	$email_change_email['message'] = str_replace( '###NEW_EMAIL###', $new_email, $email_change_email['message'] );
+	$email_change_email['message'] = str_replace( '###SITENAME###', $network_name, $email_change_email['message'] );
+	$email_change_email['message'] = str_replace( '###SITEURL###', home_url(), $email_change_email['message'] );
+
+	wp_mail(
+		$email_change_email['to'],
+		sprintf(
+			$email_change_email['subject'],
+			$network_name
+		),
+		$email_change_email['message'],
+		$email_change_email['headers']
+	);
+}