`KeyError` in `handle_disconnect` after updating to NiceGUI 2.11.0

[trivedihoney]

Description

Description

NiceGUI Version - 2.11.0

In older versions of NiceGUI,
I was getting KeyError error in del Client.instances[self.id], similar to the one mentioned in #4253.
I was expecting PR #4285 to resolve this issue and I haven't observed that error after the update, but I am observing a new error as shown below.

2025-02-04 06:02:46,768 ERROR disconnect async handler error
Traceback (most recent call last):
  File "C:\HT\OTS\.venv\Lib\site-packages\engineio\async_server.py", line 494, in run_async_handler
    return await self.handlers[event](*args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\HT\OTS\.venv\Lib\site-packages\socketio\async_server.py", line 692, in _handle_eio_disconnect
    await self._handle_disconnect(eio_sid, n)
  File "C:\HT\OTS\.venv\Lib\site-packages\socketio\async_server.py", line 585, in _handle_disconnect
    await self._trigger_event('disconnect', namespace, sid)
  File "C:\HT\OTS\.venv\Lib\site-packages\socketio\async_server.py", line 641, in _trigger_event
    ret = handler(*args)
          ^^^^^^^^^^^^^^
  File "C:\HT\OTS\.venv\Lib\site-packages\nicegui\nicegui.py", line 187, in _on_disconnect
    client.handle_disconnect(sid)
  File "C:\HT\OTS\.venv\Lib\site-packages\nicegui\client.py", line 260, in handle_disconnect
    document_id = self._socket_to_document_id.pop(socket_id)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
KeyError: 'xxxE8YdygxY7cDsKAxxx'

[rodja]

Thanks for bringing this up. We think that may happen when a socketio disconnect happens before the handshake is performed. I could not yet reproduce it locally but we see this kind of errors on https://nicegui.io, too.
A simple fix would be to early exit the Client.handle_disconnect if the socket_id can not be found in the _socket_to_document_id dictionary.

[rodja]

@chriswi93 do you also see this error? Does anyone has an idea on how it might be reproduced?

[chriswi93]

Thanks for bringing this up. We think that may happen when a socketio disconnect happens before the handshake is performed. I could not yet reproduce it locally but we see this kind of errors on https://nicegui.io, too. A simple fix would be to early exit the Client.handle_disconnect if the socket_id can not be found in the _socket_to_document_id dictionary.

I think there are two possible scenarios:
Either it is actually possible that for a new socket id a disconnect event can happen before the actual handshake is performed or there are multiple disconnects for the same socket id.

And yes, I agree that in both scenarios it might be enough to just exit the Client.handle_disconnect if the socket_id does not exist in _socket_to_document_id.

I still try to reproduce it. Would be better to know the actual reason before we change anything.