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/**
 * 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' =&gt; get_blog_count(),
		'users' =&gt; 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-&gt;userblog_id );
			$primary = get_site( $first_blog-&gt;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-&gt;userblog_id, $user_id, 'subscriber' );

		if ( ! is_wp_error( $result ) ) {
			update_user_meta( $user_id, 'primary_blog', $first_blog-&gt;userblog_id );
			$primary = $first_blog;
		}
	}

	if ( ( ! is_object( $primary ) ) || ( 1 == $primary-&gt;archived || 1 == $primary-&gt;spam || 1 == $primary-&gt;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 ) &amp;&amp; count( $blogs ) &gt; 0 ) {
			foreach ( (array) $blogs as $blog_id =&gt; $blog ) {
				if ( get_current_network_id() != $blog-&gt;site_id ) {
					continue;
				}
				$details = get_site( $blog_id );
				if ( is_object( $details ) &amp;&amp; 0 == $details-&gt;archived &amp;&amp; 0 == $details-&gt;spam &amp;&amp; 0 == $details-&gt;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-&gt;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-&gt;domain );
	}

	$user-&gt;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-&gt;userblog_id == $blog_id ) {
				continue;
			}
			$new_id     = $blog-&gt;userblog_id;
			$new_domain = $blog-&gt;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-&gt;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-&gt;get_col( $wpdb-&gt;prepare( &quot;SELECT ID FROM $wpdb-&gt;posts WHERE post_author = %d&quot;, $user_id ) );
		$link_ids = $wpdb-&gt;get_col( $wpdb-&gt;prepare( &quot;SELECT link_id FROM $wpdb-&gt;links WHERE link_owner = %d&quot;, $user_id ) );

		if ( ! empty( $post_ids ) ) {
			$wpdb-&gt;query( $wpdb-&gt;prepare( &quot;UPDATE $wpdb-&gt;posts SET post_author = %d WHERE post_author = %d&quot;, $reassign, $user_id ) );
			array_walk( $post_ids, 'clean_post_cache' );
		}

		if ( ! empty( $link_ids ) ) {
			$wpdb-&gt;query( $wpdb-&gt;prepare( &quot;UPDATE $wpdb-&gt;links SET link_owner = %d WHERE link_owner = %d&quot;, $reassign, $user_id ) );
			array_walk( $link_ids, 'clean_bookmark_cache' );
		}
	}

	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'                 =&gt; $domain,
		'path'                   =&gt; $path,
		'fields'                 =&gt; 'ids',
		'number'                 =&gt; 1,
		'update_site_meta_cache' =&gt; 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 &amp;&amp; ! is_array( $banned_names ) ) {
		$banned_names = explode( &quot;\n&quot;, $banned_names );
	}

	$is_email_address_unsafe = false;

	if ( $banned_names &amp;&amp; is_array( $banned_names ) &amp;&amp; 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;
			}

			$dotted_domain = &quot;.$banned_domain&quot;;
			if ( substr( $normalized_email, -strlen( $dotted_domain ) ) === $dotted_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 &quot;unsafe&quot;. 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-&gt;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-&gt;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-&gt;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-&gt;add( 'user_name', __( 'Sorry, that username is not allowed.' ) );
	}

	if ( ! is_email( $user_email ) ) {
		$errors-&gt;add( 'user_email', __( 'Please enter a valid email address.' ) );
	} elseif ( is_email_address_unsafe( $user_email ) ) {
		$errors-&gt;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 ) &lt; 4 ) {
		$errors-&gt;add( 'user_name', __( 'Username must be at least 4 characters.' ) );
	}

	if ( strlen( $user_name ) &gt; 60 ) {
		$errors-&gt;add( 'user_name', __( 'Username may not be longer than 60 characters.' ) );
	}

	// All numeric?
	if ( preg_match( '/^[0-9]*$/', $user_name ) ) {
		$errors-&gt;add( 'user_name', __( 'Sorry, usernames must have letters too!' ) );
	}

	$limited_email_domains = get_site_option( 'limited_email_domains' );
	if ( is_array( $limited_email_domains ) &amp;&amp; ! 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-&gt;add( 'user_email', __( 'Sorry, that email address is not allowed!' ) );
		}
	}

	// Check if the username has been used already.
	if ( username_exists( $user_name ) ) {
		$errors-&gt;add( 'user_name', __( 'Sorry, that username already exists!' ) );
	}

	// Check if the email address has been used already.
	if ( email_exists( $user_email ) ) {
		$errors-&gt;add(
			'user_email',
			sprintf(
				/* translators: %s: Link to the login page. */
				__( '&lt;strong&gt;Error:&lt;/strong&gt; This email address is already registered. &lt;a href=&quot;%s&quot;&gt;Log in&lt;/a&gt; with this address or choose another one.' ),
				wp_login_url()
			)
		);
	}

	// Has someone already signed up for this username?
	$signup = $wpdb-&gt;get_row( $wpdb-&gt;prepare( &quot;SELECT * FROM $wpdb-&gt;signups WHERE user_login = %s&quot;, $user_name ) );
	if ( $signup instanceof stdClass ) {
		$registered_at = mysql2date( 'U', $signup-&gt;registered );
		$now           = time();
		$diff          = $now - $registered_at;
		// If registered more than two days ago, cancel registration and let this signup go through.
		if ( $diff &gt; 2 * DAY_IN_SECONDS ) {
			$wpdb-&gt;delete( $wpdb-&gt;signups, array( 'user_login' =&gt; $user_name ) );
		} else {
			$errors-&gt;add( 'user_name', __( 'That username is currently reserved but may be available in a couple of days.' ) );
		}
	}

	$signup = $wpdb-&gt;get_row( $wpdb-&gt;prepare( &quot;SELECT * FROM $wpdb-&gt;signups WHERE user_email = %s&quot;, $user_email ) );
	if ( $signup instanceof stdClass ) {
		$diff = time() - mysql2date( 'U', $signup-&gt;registered );
		// If registered more than two days ago, cancel registration and let this signup go through.
		if ( $diff &gt; 2 * DAY_IN_SECONDS ) {
			$wpdb-&gt;delete( $wpdb-&gt;signups, array( 'user_email' =&gt; $user_email ) );
		} else {
			$errors-&gt;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'     =&gt; $user_name,
		'orig_username' =&gt; $orig_username,
		'user_email'    =&gt; $user_email,
		'errors'        =&gt; $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 blog name provided by the user. Must be unique.
 * @param string         $blog_title The blog 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, blog name, blog 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-&gt;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-&gt;add( 'blogname', __( 'Please enter a site name.' ) );
	}

	if ( preg_match( '/[^a-z0-9]+/', $blogname ) ) {
		$errors-&gt;add( 'blogname', __( 'Site names can only contain lowercase letters (a-z) and numbers.' ) );
	}

	if ( in_array( $blogname, $illegal_names, true ) ) {
		$errors-&gt;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 ) &lt; $minimum_site_name_length ) {
		/* translators: %s: Minimum site name length. */
		$errors-&gt;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() &amp;&amp; $wpdb-&gt;get_var( $wpdb-&gt;prepare( 'SELECT post_name FROM ' . $wpdb-&gt;get_blog_prefix( $current_network-&gt;site_id ) . &quot;posts WHERE post_type = 'page' AND post_name = %s&quot;, $blogname ) ) ) {
		$errors-&gt;add( 'blogname', __( 'Sorry, you may not use that site name.' ) );
	}

	// All numeric?
	if ( preg_match( '/^[0-9]*$/', $blogname ) ) {
		$errors-&gt;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-&gt;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-&gt;id ) ) {
		$errors-&gt;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 ) &amp;&amp; ( $user-&gt;user_login != $blogname ) ) ) {
			$errors-&gt;add( 'blogname', __( 'Sorry, that site is reserved!' ) );
		}
	}

	// Has someone already signed up for this domain?
	// TODO: Check email too?
	$signup = $wpdb-&gt;get_row( $wpdb-&gt;prepare( &quot;SELECT * FROM $wpdb-&gt;signups WHERE domain = %s AND path = %s&quot;, $mydomain, $path ) );
	if ( $signup instanceof stdClass ) {
		$diff = time() - mysql2date( 'U', $signup-&gt;registered );
		// If registered more than two days ago, cancel registration and let this signup go through.
		if ( $diff &gt; 2 * DAY_IN_SECONDS ) {
			$wpdb-&gt;delete(
				$wpdb-&gt;signups,
				array(
					'domain' =&gt; $mydomain,
					'path'   =&gt; $path,
				)
			);
		} else {
			$errors-&gt;add( 'blogname', __( 'That site is currently reserved but may be available in a couple days.' ) );
		}
	}

	$result = array(
		'domain'     =&gt; $mydomain,
		'path'       =&gt; $path,
		'blogname'   =&gt; $blogname,
		'blog_title' =&gt; $blog_title,
		'user'       =&gt; $user,
		'errors'     =&gt; $errors,
	);

	/**
	 * Filters site details and error messages following registration.
	 *
	 * @since MU (3.0.0)
	 *
	 * @param array $result {
	 *     Array of domain, path, blog name, blog 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.
	 * }
	 */
	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-&gt;insert(
		$wpdb-&gt;signups,
		array(
			'domain'         =&gt; $domain,
			'path'           =&gt; $path,
			'title'          =&gt; $title,
			'user_login'     =&gt; $user,
			'user_email'     =&gt; $user_email,
			'registered'     =&gt; current_time( 'mysql', true ),
			'activation_key' =&gt; $key,
			'meta'           =&gt; 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-&gt;insert(
		$wpdb-&gt;signups,
		array(
			'domain'         =&gt; '',
			'path'           =&gt; '',
			'title'          =&gt; '',
			'user_login'     =&gt; $user,
			'user_email'     =&gt; $user_email,
			'registered'     =&gt; current_time( 'mysql', true ),
			'activation_key' =&gt; $key,
			'meta'           =&gt; 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 ) {
		$activate_url = network_site_url( &quot;wp-activate.php?key=$key&quot; );
	} else {
		$activate_url = &quot;http://{$domain}{$path}wp-activate.php?key=$key&quot;; // @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';
	$message_headers = &quot;From: \&quot;{$from_name}\&quot; &lt;{$admin_email}&gt;\n&quot; . 'Content-Type: text/plain; charset=&quot;' . get_option( 'blog_charset' ) . &quot;\&quot;\n&quot;;

	$user            = get_user_by( 'login', $user_login );
	$switched_locale = $user &amp;&amp; switch_to_user_locale( $user-&gt;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. */
			__( &quot;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&quot; ),
			$domain,
			$path,
			$title,
			$user_login,
			$user_email,
			$key,
			$meta
		),
		$activate_url,
		esc_url( &quot;http://{$domain}{$path}&quot; ),
		$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 &amp;&amp; switch_to_user_locale( $user-&gt;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';
	$message_headers = &quot;From: \&quot;{$from_name}\&quot; &lt;{$admin_email}&gt;\n&quot; . 'Content-Type: text/plain; charset=&quot;' . get_option( 'blog_charset' ) . &quot;\&quot;\n&quot;;
	$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. */
			__( &quot;To activate your user, please click the following link:\n\n%s\n\nAfter you activate, you will receive *another email* with your login.&quot; ),
			$user_login,
			$user_email,
			$key,
			$meta
		),
		site_url( &quot;wp-activate.php?key=$key&quot; )
	);

	$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-&gt;get_row( $wpdb-&gt;prepare( &quot;SELECT * FROM $wpdb-&gt;signups WHERE activation_key = %s&quot;, $key ) );

	if ( empty( $signup ) ) {
		return new WP_Error( 'invalid_key', __( 'Invalid activation key.' ) );
	}

	if ( $signup-&gt;active ) {
		if ( empty( $signup-&gt;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-&gt;meta );
	$password = wp_generate_password( 12, false );

	$user_id = username_exists( $signup-&gt;user_login );

	if ( ! $user_id ) {
		$user_id = wpmu_create_user( $signup-&gt;user_login, $password, $signup-&gt;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-&gt;domain ) ) {
		$wpdb-&gt;update(
			$wpdb-&gt;signups,
			array(
				'active'    =&gt; 1,
				'activated' =&gt; $now,
			),
			array( 'activation_key' =&gt; $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'  =&gt; $user_id,
			'password' =&gt; $password,
			'meta'     =&gt; $meta,
		);
	}

	$blog_id = wpmu_create_blog( $signup-&gt;domain, $signup-&gt;path, $signup-&gt;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-&gt;get_error_code() ) {
			$blog_id-&gt;add_data( $signup );
			$wpdb-&gt;update(
				$wpdb-&gt;signups,
				array(
					'active'    =&gt; 1,
					'activated' =&gt; $now,
				),
				array( 'activation_key' =&gt; $key )
			);
		}
		return $blog_id;
	}

	$wpdb-&gt;update(
		$wpdb-&gt;signups,
		array(
			'active'    =&gt; 1,
			'activated' =&gt; $now,
		),
		array( 'activation_key' =&gt; $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-&gt;title, $meta );

	return array(
		'blog_id'  =&gt; $blog_id,
		'user_id'  =&gt; $user_id,
		'password' =&gt; $password,
		'title'    =&gt; $signup-&gt;title,
		'meta'     =&gt; $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-&gt;delete( $wpdb-&gt;signups, array( 'user_login' =&gt; $user-&gt;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=&gt;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' =&gt; 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'     =&gt; $domain,
			'path'       =&gt; $path,
			'network_id' =&gt; $network_id,
		),
		array_intersect_key( $options, array_flip( $allowed_data_fields ) )
	);

	// Data to pass to wp_initialize_site().
	$site_initialization_data = array(
		'title'   =&gt; $title,
		'user_id' =&gt; $user_id,
		'options' =&gt; 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( 'last_changed', microtime(), 'sites' );

	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-&gt;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-&gt;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-&gt;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'             =&gt; $network_id,
		'domain'                 =&gt; $domain,
		'path'                   =&gt; $path,
		'fields'                 =&gt; 'ids',
		'number'                 =&gt; 1,
		'update_site_meta_cache' =&gt; 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 &quot;N/A&quot; 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 &quot;N/A&quot; 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-&gt;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-&gt;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 &quot;N/A&quot; 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';
	$message_headers = &quot;From: \&quot;{$from_name}\&quot; &lt;{$admin_email}&gt;\n&quot; . 'Content-Type: text/plain; charset=&quot;' . get_option( 'blog_charset' ) . &quot;\&quot;\n&quot;;
	$message         = $welcome_email;

	if ( empty( $current_network-&gt;site_name ) ) {
		$current_network-&gt;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-&gt;site_name, wp_unslash( $title ) ) );

	wp_mail( $user-&gt;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-&gt;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()-&gt;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-&gt;user_login,
		get_site_url( $site-&gt;id ),
		get_blog_option( $site-&gt;id, 'blogname' )
	);

	$header = sprintf(
		'From: &quot;%1$s&quot; &lt;%2$s&gt;',
		_x( 'Site Admin', 'email &quot;From&quot; field' ),
		$email
	);

	$new_site_email = array(
		'to'      =&gt; $email,
		'subject' =&gt; $subject,
		'message' =&gt; $message,
		'headers' =&gt; $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-&gt;site_name, $welcome_email );
	$welcome_email = str_replace( 'USERNAME', $user-&gt;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';
	$message_headers = &quot;From: \&quot;{$from_name}\&quot; &lt;{$admin_email}&gt;\n&quot; . 'Content-Type: text/plain; charset=&quot;' . get_option( 'blog_charset' ) . &quot;\&quot;\n&quot;;
	$message         = $welcome_email;

	if ( empty( $current_network-&gt;site_name ) ) {
		$current_network-&gt;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-&gt;site_name, $user-&gt;user_login ) );

	wp_mail( $user-&gt;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-&gt;get_blog_prefix( $blog-&gt;userblog_id );
		$recent_post = $wpdb-&gt;get_row( $wpdb-&gt;prepare( &quot;SELECT ID, post_date_gmt FROM {$prefix}posts WHERE post_author = %d AND post_type = 'post' AND post_status = 'publish' ORDER BY post_date_gmt DESC LIMIT 1&quot;, $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 &gt; $most_recent_post['post_gmt_ts'] ) ) {
				$most_recent_post = array(
					'blog_id'       =&gt; $blog-&gt;userblog_id,
					'post_id'       =&gt; $recent_post['ID'],
					'post_date_gmt' =&gt; $recent_post['post_date_gmt'],
					'post_gmt_ts'   =&gt; $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 =&gt; $mime ) {
			if ( '' !== $ext &amp;&amp; false !== strpos( $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) $wpdb-&gt;get_var( &quot;SELECT COUNT(ID) FROM {$wpdb-&gt;posts} WHERE post_status = 'publish' and post_type = 'post'&quot; ) );
}

/**
 * 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-&gt;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-&gt;insert(
			$wpdb-&gt;registration_log,
			array(
				'email'           =&gt; $user-&gt;user_email,
				'IP'              =&gt; preg_replace( '/[^0-9., ]/', '', wp_unslash( $_SERVER['REMOTE_ADDR'] ) ),
				'blog_id'         =&gt; $blog_id,
				'date_registered' =&gt; 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()-&gt;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'] ) &gt; ( 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.' ) . '&lt;br /&gt;', 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() {
	$id = mt_rand();
	echo &quot;&lt;input type='hidden' name='signup_form_id' value='{$id}' /&gt;&quot;;
	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']-&gt;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() &amp;&amp; is_404() &amp;&amp; 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 ( false === strpos( $_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 &lt;a href=&quot;%s&quot;&gt;homepage&lt;/a&gt;.' ),
				home_url()
			)
		);
	}

	wp_die(
		sprintf(
			/* translators: 1: Home URL, 2: Admin URL. */
			__( 'You have been added to this site. Please visit the &lt;a href=&quot;%1$s&quot;&gt;homepage&lt;/a&gt; or &lt;a href=&quot;%2$s&quot;&gt;log in&lt;/a&gt; using your username and password.' ),
			home_url(),
			admin_url()
		),
		__( 'WordPress &amp;rsaquo; Success' ),
		array( 'response' =&gt; 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()-&gt;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-&gt;Hostname = get_network()-&gt;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 &amp;&amp; isset( $user-&gt;spam ) &amp;&amp; 1 == $user-&gt;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 blog URL with proper scheme.
	}

	if ( force_ssl_content() &amp;&amp; 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' ) &amp;&amp; ! 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'             =&gt; $network_id,
			'spam'                   =&gt; 0,
			'deleted'                =&gt; 0,
			'archived'               =&gt; 0,
			'count'                  =&gt; true,
			'update_site_meta_cache' =&gt; 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 &lt; 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 ) &lt;= 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 &gt; 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'     =&gt; $hash,
		'newemail' =&gt; $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-&gt;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'      =&gt; $old_email,
		/* translators: Network admin email change notification email subject. %s: Network title. */
		'subject' =&gt; __( '[%s] Network Admin Email Changed' ),
		'message' =&gt; $email_change_text,
		'headers' =&gt; '',
	);
	// 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']
	);
}
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