TimeoutError is not handled properly

[mmmommm]

Description

TimeoutError is not handled properly and display Invalid response 504.

Normally, I would like error messages to be displayed on the UI of Jupyter when an error occurs, but it seems that the status code 504 is not being handled properly, and an error message saying 'invalid response 504' is displayed. When I changed it to RuntimeError, the error message started to be displayed correctly.

I haven't checked other places, so I don't know, but it might be happening elsewhere as well.

Reproduce

If the launch of the kernel server's k8s pod fails, handle_launch_timeout should be called from container.py to reproduce the issue.

Expected behavior

The appropriate error message is displayed.

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