Exception filters

Gateways do not support custom exception filters yet. #[use_filters(...)] below #[websocket_gateway] produces a compile error (#[use_filters] is not supported on WebSocket gateways), and global filters (app.use_global_filters, Provider::app_filter) only apply to HTTP routes.

What does exist is the built-in filter: any error from a guard, interceptor, pipe, or handler is turned into an exception frame with a fixed shape.

Error	data of the exception frame
WsException::new("msg")	{ "status": "error", "message": "msg" }
WsException::object(obj)	obj, as is
Another HttpException	{ "status": "error", "message", ...rest of its body }
Unknown error or panic	{ "status": "error", "message": "Internal server error" } (and it is logged)

If the client's frame carried an id, the exception frame repeats it (see acknowledgements).

Alternatives

To control the format of errors:

• Build the error with its final shape using WsException::object(json!({ ... })). Tertulia does this to include codes like ROOM_FULL or NOT_IN_ROOM that the client can interpret.
• Translate errors in an interceptor. An interceptor declared on the gateway sees the Err returned by next.handle().await and can replace it with a WsException:

#[injectable]
pub struct WsErrorsInterceptor;

#[async_trait]
impl CorvisInterceptor for WsErrorsInterceptor {
    async fn intercept(&self, _ctx: &ExecutionContext, next: CallHandler) -> HandlerResult {
        next.handle().await.map_err(|e| {
            if e.get_status() == 404 {
                WsException::object(json!({ "status": "error", "code": "NOT_FOUND", "message": e.message() }))
            } else {
                e
            }
        })
    }
}

Interceptors run after guards, so errors thrown by a guard do not go through them.