Edge Browser: Client not disconnecting with "transport close" on reload or tab close

[ajtadeo]

Hi all. I'm having an issue when using Flask SocketIO on an Edge browser which is not disconnecting clients correctly on reloads or tab closes. When I reload my Flask web page on an Edge browser the client does not have a "transport close" disconnect event, and instead a new client is opened. This causes the old client to time out and disconnect with "ping timeout" instead of being cleaned up correctly. I also don't get a "transport close" when I close the tab, which is causing the client to disconnect with a "ping timeout".

Edge logs:

Client connected 1VUtyGxvpgBlmeI0AAAB
# reload occurs
Client connected qR6STtFyUWf3GWzKAAAD
Client disconnected 1VUtyGxvpgBlmeI0AAAB ping timeout
# close tab
Client disconnected qR6STtFyUWf3GWzKAAAD ping timeout

When I try the same application on a Firefox browser, the client correctly disconnects with "transport close" and then reconnects on reload, and disconnects with "transport close" on tab close.

Firefox logs:

Client connected lJZuJS6klR3JTmtfAAAB
# reload occurs
Client disconnected lJZuJS6klR3JTmtfAAAB transport close
Client connected gQUIRZ7z47rWSGNAAAAD
# close tab
Client disconnected gQUIRZ7z47rWSGNAAAAD transport close

Is this an issue with the Edge browser itself or is it a problem with my Flask app? I know there are some issues caused by differences in browsers in the Javascript SocketIO library, but not sure if it's the same case for this library and specifically this problem. Thanks.

Flask SocketIO version: 5.4.1
Javascript SocketIO version: 4.8.0
Edge Browser version: 135.0.3179.85
Firefox Browser version: 137.0.2

[miguelgrinberg]

I'm not sure what can cause this, but my first guess is that the WebSocket connection isn't properly closed by Edge, which in turn causes the server to miss this event and instead time out some time later due to the client not responding to pings anymore.

I'll find a Windows machine to run some tests.

[ajtadeo]

Thank you! Really appreciate your help.

[miguelgrinberg]

Sorry for the delay. I'm testing Edge on Windows 11 here and I'm not seeing the behavior you described. When I close the Edge tab I see "transport close" in the server.

Some details about how I'm testing:

• Edge version 132.0.2957.140 (Official build) (64-bit)
• Server running on Ubuntu with Python 3.13 and latest versions of Flask-SocketIO, python-socketio and python-engineio.
• The server is running app.py from the example directory in this repository, which prints the disconnect reason to the console. From your logs you may also be using this application.

My logs:

Client disconnected mT5pTDf6c7l3Uml9AAAD transport close

How and where are you running your server?