Traceback in log despite graceful exit

[madduck]

Prerequisites

• Tried the most recent nightly build
• Checked if your issue is already reported.
• Answered all the questions in this template (Or provide a working crystal ball).

What happened?

If a user just closes the tab without disconnecting (which all users will do), the logs get a traceback:

2023-10-13 12:18:19 WARNING [handle_message] webserver.py : Connection gracefully closed. 1001
2023-10-13 12:18:19 WARNING [handle_message] webserver.py : Traceback (most recent call last):
  File "/srv/managesieve/build/web/script/webserver.py", line 65, in handle_message
    handler.handle_request(context, request)
  File "/srv/managesieve/build/web/script/handler/websocket.py", line 48, in handle_request
    MessagePump().run(websocket, sievesocket)
  File "/srv/managesieve/build/web/script/messagepump.py", line 26, in run
    data = server.recv()
           ^^^^^^^^^^^^^
  File "/srv/managesieve/build/web/script/websocket.py", line 134, in recv
    raise Exception("Connection gracefully closed. "+str(code)+" "+text.decode())
Exception: Connection gracefully closed. 1001

What did you expect to happen?

If it's a graceful closure, then there should be no log entry, definitely not
a traceback.

Which Version

Include information about your system, server and most important if it is about the app or webextension.

• Web app @8a1af600e42bff2440e959a268afcab3385418a1
• NGinX on Debian stable; Firefox 117 on Debian unstable
• Dovecot Pigeonhole on Debian stable