function bbp_do_ajax( $action = '' ) {

	// Bail if not a bbPress specific AJAX request
	if ( ! bbp_is_ajax() ) {
		return;
	}

	// Set WordPress core AJAX constant for back-compat
	if ( ! defined( 'DOING_AJAX' ) ) {
		define( 'DOING_AJAX', true );
	}

	// Setup AJAX headers
	bbp_ajax_headers();

	// Compat for targeted action hooks (without $action param)
	$action = empty( $action )
		? sanitize_key( $_REQUEST['action'] ) // isset checked by bbp_is_ajax()
		: $action;

	// Setup action key
	$key = "bbp_ajax_{$action}";

	// Bail if no action is registered
	if ( empty( $action ) || ! has_action( $key ) ) {
		wp_die( '0', 400 );
	}

	// Everything is 200 OK.
	bbp_set_200();

	// Execute custom bbPress AJAX action
	do_action( $key );

	// All done
	wp_die( '0' );
}