sanitize_option( string $option, string $value )

function sanitize_option( $option, $value ) {
	global $wpdb;

	$original_value = $value;
	$error = '';

	switch ( $option ) {
		case 'admin_email' :
		case 'new_admin_email' :
			$value = $wpdb->strip_invalid_text_for_column( $wpdb->options, 'option_value', $value );
			if ( is_wp_error( $value ) ) {
				$error = $value->get_error_message();
			} else {
				$value = sanitize_email( $value );
				if ( ! is_email( $value ) ) {
					$error = __( 'The email address entered did not appear to be a valid email address. Please enter a valid email address.' );
				}
			}
			break;

		case 'thumbnail_size_w':
		case 'thumbnail_size_h':
		case 'medium_size_w':
		case 'medium_size_h':
		case 'medium_large_size_w':
		case 'medium_large_size_h':
		case 'large_size_w':
		case 'large_size_h':
		case 'mailserver_port':
		case 'comment_max_links':
		case 'page_on_front':
		case 'page_for_posts':
		case 'rss_excerpt_length':
		case 'default_category':
		case 'default_email_category':
		case 'default_link_category':
		case 'close_comments_days_old':
		case 'comments_per_page':
		case 'thread_comments_depth':
		case 'users_can_register':
		case 'login_custom_image_state':
		case 'login_custom_image_id':
		case 'start_of_week':
		case 'site_icon':
			$value = absint( $value );
			break;

		case 'posts_per_page':
		case 'posts_per_rss':
			$value = (int) $value;
			if ( empty($value) )
				$value = 1;
			if ( $value < -1 )
				$value = abs($value);
			break;

		case 'default_ping_status':
		case 'default_comment_status':
			// Options that if not there have 0 value but need to be something like "closed"
			if ( $value == '0' || $value == '')
				$value = 'closed';
			break;

		case 'blogdescription':
		case 'blogname':
			$value = $wpdb->strip_invalid_text_for_column( $wpdb->options, 'option_value', $value );
			if ( $value !== $original_value ) {
				$value = $wpdb->strip_invalid_text_for_column( $wpdb->options, 'option_value', wp_encode_emoji( $original_value ) );
			}

			if ( is_wp_error( $value ) ) {
				$error = $value->get_error_message();
			} else {
				$value = esc_html( $value );
			}
			break;

		case 'blog_charset':
			$value = preg_replace('/[^a-zA-Z0-9_-]/', '', $value); // strips slashes
			break;

		case 'blog_public':
			// This is the value if the settings checkbox is not checked on POST. Don't rely on this.
			if ( null === $value )
				$value = 1;
			else
				$value = intval( $value );
			break;

		case 'date_format':
		case 'time_format':
		case 'mailserver_url':
		case 'mailserver_login':
		case 'mailserver_pass':
		case 'upload_path':
			$value = $wpdb->strip_invalid_text_for_column( $wpdb->options, 'option_value', $value );
			if ( is_wp_error( $value ) ) {
				$error = $value->get_error_message();
			} else {
				$value = strip_tags( $value );
				$value = wp_kses_data( $value );
			}
			break;

		case 'ping_sites':
			$value = explode( "\n", $value );
			$value = array_filter( array_map( 'trim', $value ) );
			$value = array_filter( array_map( 'esc_url_raw', $value ) );
			$value = implode( "\n", $value );
			break;

		case 'gmt_offset':
			$value = preg_replace('/[^0-9:.-]/', '', $value); // strips slashes
			break;

		case 'siteurl':
			$value = $wpdb->strip_invalid_text_for_column( $wpdb->options, 'option_value', $value );
			if ( is_wp_error( $value ) ) {
				$error = $value->get_error_message();
			} else {
				if ( preg_match( '#http(s?)://(.+)#i', $value ) ) {
					$value = esc_url_raw( $value );
				} else {
					$error = __( 'The ClassicPress address you entered did not appear to be a valid URL. Please enter a valid URL.' );
				}
			}
			break;

		case 'home':
			$value = $wpdb->strip_invalid_text_for_column( $wpdb->options, 'option_value', $value );
			if ( is_wp_error( $value ) ) {
				$error = $value->get_error_message();
			} else {
				if ( preg_match( '#http(s?)://(.+)#i', $value ) ) {
					$value = esc_url_raw( $value );
				} else {
					$error = __( 'The Site address you entered did not appear to be a valid URL. Please enter a valid URL.' );
				}
			}
			break;

		case 'WPLANG':
			$allowed = get_available_languages();
			if ( ! is_multisite() && defined( 'WPLANG' ) && '' !== WPLANG && 'en_US' !== WPLANG ) {
				$allowed[] = WPLANG;
			}
			if ( ! in_array( $value, $allowed ) && ! empty( $value ) ) {
				$value = get_option( $option );
			}
			break;

		case 'illegal_names':
			$value = $wpdb->strip_invalid_text_for_column( $wpdb->options, 'option_value', $value );
			if ( is_wp_error( $value ) ) {
				$error = $value->get_error_message();
			} else {
				if ( ! is_array( $value ) )
					$value = explode( ' ', $value );

				$value = array_values( array_filter( array_map( 'trim', $value ) ) );

				if ( ! $value )
					$value = '';
			}
			break;

		case 'limited_email_domains':
		case 'banned_email_domains':
			$value = $wpdb->strip_invalid_text_for_column( $wpdb->options, 'option_value', $value );
			if ( is_wp_error( $value ) ) {
				$error = $value->get_error_message();
			} else {
				if ( ! is_array( $value ) )
					$value = explode( "\n", $value );

				$domains = array_values( array_filter( array_map( 'trim', $value ) ) );
				$value = array();

				foreach ( $domains as $domain ) {
					if ( ! preg_match( '/(--|\.\.)/', $domain ) && preg_match( '|^([a-zA-Z0-9-\.])+$|', $domain ) ) {
						$value[] = $domain;
					}
				}
				if ( ! $value )
					$value = '';
			}
			break;

		case 'timezone_string':
			$allowed_zones = timezone_identifiers_list();
			if ( ! in_array( $value, $allowed_zones ) && ! empty( $value ) ) {
				$error = __( 'The timezone you have entered is not valid. Please select a valid timezone.' );
			}
			break;

		case 'permalink_structure':
		case 'category_base':
		case 'tag_base':
			$value = $wpdb->strip_invalid_text_for_column( $wpdb->options, 'option_value', $value );
			if ( is_wp_error( $value ) ) {
				$error = $value->get_error_message();
			} else {
				$value = esc_url_raw( $value );
				$value = str_replace( 'http://', '', $value );
			}

			if ( 'permalink_structure' === $option && '' !== $value && ! preg_match( '/%[^\/%]+%/', $value ) ) {
				$error = sprintf(
					/* translators: %s: Codex URL */
					__( 'A structure tag is required when using custom permalinks. <a href="%s">Learn more</a>' ),
					__( 'https://codex.wordpress.org/Using_Permalinks#Choosing_your_permalink_structure' )
				);
			}
			break;

		case 'default_role' :
			if ( ! get_role( $value ) && get_role( 'subscriber' ) )
				$value = 'subscriber';
			break;

		case 'moderation_keys':
		case 'blacklist_keys':
			$value = $wpdb->strip_invalid_text_for_column( $wpdb->options, 'option_value', $value );
			if ( is_wp_error( $value ) ) {
				$error = $value->get_error_message();
			} else {
				$value = explode( "\n", $value );
				$value = array_filter( array_map( 'trim', $value ) );
				$value = array_unique( $value );
				$value = implode( "\n", $value );
			}
			break;
	}

	if ( ! empty( $error ) ) {
		$value = get_option( $option );
		if ( function_exists( 'add_settings_error' ) ) {
			add_settings_error( $option, "invalid_{$option}", $error );
		}
	}

	/**
	 * Filters an option value following sanitization.
	 *
	 * @since WP-2.3.0
	 * @since WP-4.3.0 Added the `$original_value` parameter.
	 *
	 * @param string $value          The sanitized option value.
	 * @param string $option         The option name.
	 * @param string $original_value The original value passed to the function.
	 */
	return apply_filters( "sanitize_option_{$option}", $value, $option, $original_value );
}