Received start of new message but previous message is unfinished

Question

My web based WebSocket client connects to my Java server this way:

this.ws = new WebSocket(this.url);
  this.ws.onmessage = m => {
    let data;
    try {
      data = JSON.parse(m.data);
    } catch (e) {
      // Log error
      return;
    }
    doALotOfStuff(data);
  };

But then sometimes I get this error in Chrome:

WebSocket connection to 'myServerUrl' failed: Received start of new message but previous message is unfinished.

I found the related source code in Chromium and some discussion about it but this is all about continuation frames and OpCode, a much lower API than the one I have access to from what I understood.

So does this mean I received a message while I was processing the previous one? Meaning I have to call setTimeout(...,0) to handle all my messages asynchronously? But then everybody should do it so why does the browser not handle this?

I have a similar error in Firefox:

The connection to myServerUrl was interrupted while the page was loading.

Which is more confusing I guess because I am not reloading a page, it happens in the middle of a websocket session.

So I guess it might not be Chromium fault but then how do I handle it?

Or am I doing something wrong when sending the messages? I use javax-websocket-api-1.0 and I simply do:

try (Writer writer = session.getBasicRemote().getSendWriter()) {
  JacksonSerializer.serialize(object, writer);
} catch (final SerializerException | IOException e) {
  throw ...;
}

I close the writer everytime I write an object in it so this looks fine to me.

Answer 1

This was indeed due to a bug in the server code. The code I quoted is correct but was not thread-safe so I wrote concurrently into the same session. I fixed it by synchronizing it on the session.