Can you show your client code?

@nhooyr go version 1.22.2

conn.addEventListener('open', ev => {
    console.info('websocket connected')
    setTimeout(() => {
      conn.send('ping')
    }, 3000)
  })

Unrelated to the library. Something's wrong with your client code calling close after the connection has been closed. See mqttjs/MQTT.js#1361

I would reopen this as after last update I have received same error with native WebSocket in Chrome, while safari is ok with that.

Ok possible we need to add a guard in c.writeClose to not write a close frame twice. I think that we're writing a close frame, we get a close frame back and then the code doesn't keep track that it already wrote a close frame and so writes a close frame in response to the handshake close frame.

Yes, I saw that it's waiting for closing but CloseNow did not check if it was closed already. I believe that's what's happening.

Is #476 the chosen approach here, and if so anything we can do to get it merged? My application is experiencing this same issue.

I also noticed another project had decided to fork the library in order to pick up this solution: flowey-org@b1784e6.