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function rest_api_loaded() {
	if ( empty( $GLOBALS['wp']->query_vars['rest_route'] ) ) {
		return;
	}

	// Return an error message if query_var is not a string.
	if ( ! is_string( $GLOBALS['wp']->query_vars['rest_route'] ) ) {
		$rest_type_error = new WP_Error(
			'rest_path_invalid_type',
			__( 'The rest route parameter must be a string.' ),
			array( 'status' => 400 )
		);
		wp_die( $rest_type_error );
	}

	/**
	 * Whether this is a REST Request.
	 *
	 * @since 4.4.0
	 * @var bool
	 */
	define( 'REST_REQUEST', true );

	// Initialize the server.
	$server = rest_get_server();

	// Fire off the request.
	$route = untrailingslashit( $GLOBALS['wp']->query_vars['rest_route'] );
	if ( empty( $route ) ) {
		$route = '/';
	}
	$server->serve_request( $route );

	// We're done.
	die();
}