WebSocket race condition causing Miniflare not to send messages

[TimTinkers]

I have code for a WebSocket client that looks like this:

let connection = new WebSocket(EVENT_LISTENER_URL, [ 'protocol' ]);
connection.addEventListener('open', async (event) => {
  await sleep(180); // <- Miniflare does not actually send the message without this line
  connection.send(JSON.stringify({ type: 'REQUEST_ID' })); // this doesn't actually get sent
}

From logging data coming into the Durable Object, I was able to figure out that Miniflare didn't send some of my messages in response to a WebSocket open event without a forced delay of at least 180ms.

[mrbbot]

Hey! 👋 This is interesting. Miniflare queues messages if you haven't called accept yet, so should dispatch all messages it receives. Any chance you're calling accept() after addEventListener("message", (e) => { ... }) in your worker?

[TimTinkers]

Any chance you're calling accept() after addEventListener...

Nope.

      // Create a new WebSocket connection to the caller.
      const [ client, server ] = Object.values(new WebSocketPair());
      server.accept();
      // ...
      server.addEventListener('message', async (event) => { 
        // ...
      });

Definitely calling accept first.

[mrbbot]

Hey! 👋 miniflare@2.0.0-rc.1 has just been released, including a fix for this. You can find the changelog here. Thanks for reporting this, and please let me know if you have any other issues.