Sendable Crash even on 2.13.0 / Swift 5.7 about websocket-kit HOT 6 CLOSED

@PatrickPijnappel what does your web socket code look like? We're probably missing a hop somewhere

from websocket-kit.

@0xTim Basically this:

self.queue.async {
    // (…)
    webSocket.onBinary { [weak self] _, data in // Called from arbitrary queue
        guard let self = self else { return }
        // (…)
    }
}

from websocket-kit.

What is self in this instance and queue? Im assuming the web socket is being created outside of the queue closure?

from websocket-kit.

self is a custom (final) class and queue is a serial DispatchQueue. The web socket is being created elsewhere on another queue using effectively

WebSocket.connect(to: url, on: app.eventLoopGroup.next()) { webSocket in
    queue.async { self.webSocket = webSocket }
}

from websocket-kit.

@PatrickPijnappel ah ok, I misread this initially.

Setting the WS callbacks must be done on the Websocket's EventLoop. We assumed this was the case before but had no way to enforce this at a compiler level before Sendable. Doing it off the event loop might have worked but could easily caused crashes before and for us to be Sendable compliant we have to enforce it.

One workaround might be to wrap your calls in

websocket.eventLoop.execute {
  websocket.onBinary {
    // ...
  }
}

That should enforce that the mutations are done on the correct event loop, but mixing concurrency, event loops and dispatch queues like this is always going to cause issues

from websocket-kit.

@0xTim Ah i see, thank you!

from websocket-kit.