Is it possible to send shared Arc<Message> via the websocket connection?

[sukhmel]

Sorry for bothering again

In my application, I have a lot of broadcasted messages, and a lot of cloning done because of that. I've tried to choose Arc<Message> as SplitSink::Item so that I have SplitSink<WebSocket, Arc<Message> as a sending half, but it doesn't compile

Is there a way not to clone messages that would be broadcast to several WebSocket SplitSinks? Maybe I'm just doing it wrong 🤔

what I'm doing is something like this:

struct Handler {

    /// Split socket into sender and receiver
    async fn handle_socket(&self, socket: WebSocket) {
        let (sender, _) = socket.split::<Arc<Message>>();
        /* ... */  
        self.senders.insert(key, sender);
    }
    
    /// Try to send the same messages to lots of senders
    async fn broadcast(&self, messages: Vec<String>) {
        let messages = messages
            .into_iter()
            .map(|Message::Text)
            .map(Arc::new)
            .collect::<Vec<_>>();
        for sender in self.senders.values_mut() {
            let mut stream = tokio_stream::iter(messages.clone()).map(anyhow::Ok);
            sender
                .send_all(&mut stream)
                .await
                .unwrap();
        }
    }
}

This probably depends on what tokio-tungstenite is capable of. If so, I will file an issue there also.

Edit: or maybe I need to find another SplitSink implementation 🤔
compilation errors are as follows:

345 | /         sender
346 | |             .send(
    | |             -^^^^ method cannot be called on `SplitSink<WebSocket, Arc<Message>>` due to unsatisfied trait bounds
    | |_____________|


47  |   pub struct SplitSink<S, Item> {
    |   -----------------------------
    |   |
    |   doesn't satisfy `_: Sink<_>`
    |   doesn't satisfy `_: SinkExt<_>`
    |
    = note: the following trait bounds were not satisfied:
            `SplitSink<axum::extract::ws::WebSocket, Arc<axum::extract::ws::Message>>: futures::Sink<_>`
            which is required by `SplitSink<axum::extract::ws::WebSocket, Arc<axum::extract::ws::Message>>: SinkExt<_>`

[davidpdrsn]

Nope you need to clone the messages.

[sukhmel]

As far as I understand from axum and tungstenite sources, this is because tungstenite accepts owned messages, is that correct? Or is there something else that prevents this kind of shared message to be sent?

[davidpdrsn]

As far as I understand from axum and tungstenite sources, this is because tungstenite accepts owned messages, is that correct?

Yes that is correct.

The data needs to be cloned to be written to the socket anyway so I'm not sure using shared messages would help much. If this is something you really need consider asking the tungstenite folk about it.

[sukhmel]

yeah, I've found an unmerged PR with a discussion of problems that arise from sharing data, will leave a link for posterity