Kernels don't get the query string if --Voila.base_url is specified and preheating is turned on

[vkaidalov-rft]

Description

Hi!
When I was updating Voila from 0.3.1 to 0.3.5 on my machine, I saw that the preheated kernels produced some warning messages even before leaving the kernels pool. After taking a look at the recent changes, I found out that specifying the VOILA_WS_BASE_URL env. variable was now required to use the --Voila.base_url parameter.

Reproduce

1. Create a get_qs_example.ipynb file with the following code:

from voila.utils import get_query_string
print(get_query_string())

2. Run the Voila server as follows:

voila get_qs_example.ipynb --preheat_kernel=True --pool_size=5 --no-browser --Voila.base_url='/example-base-url/'

3. See the following warnings in the Voila logs:

[Voila] Using /var/folders/44/nmhwstjd0cvg9yzpq0463l600000gn/T to store connection files
[Voila] Storing connection files in /var/folders/44/nmhwstjd0cvg9yzpq0463l600000gn/T/voila_54cdmtsg.
[Voila] Serving static files from /Users/vadym_kaidalov/opt/miniconda3/envs/playground/lib/python3.10/site-packages/voila/static.
[Voila] Voilà is running at:
http://localhost:8866/example-base-url/
[Voila] WARNING | Notebook get_qs_example.ipynb is not trusted
[Voila] WARNING | Notebook get_qs_example.ipynb is not trusted
[Voila] WARNING | Notebook get_qs_example.ipynb is not trusted
[Voila] WARNING | Notebook get_qs_example.ipynb is not trusted
[Voila] WARNING | Notebook get_qs_example.ipynb is not trusted
[Voila] Kernel started: 5a1dc72b-acac-4fe1-961b-b0d023c5c588
[Voila] Kernel started: fe5a586b-c425-4397-a5a7-240e21865d74
[Voila] Kernel started: 7801ca4b-214c-49b5-bf40-774ae1c0c457
[Voila] Kernel started: 04a9568f-b42c-46e0-a242-7addefb6a067
[Voila] Kernel started: e22cdcc1-547e-4e52-9ca7-b8de8d199d45
[Voila] Kernel pool of get_qs_example.ipynb is filled with 5 kernel(s)
WARNING:tornado.access:404 GET /voila/query/04a9568f-b42c-46e0-a242-7addefb6a067 (127.0.0.1) 1.77ms
WARNING:tornado.access:404 GET /voila/query/fe5a586b-c425-4397-a5a7-240e21865d74 (127.0.0.1) 0.41ms
WARNING:tornado.access:404 GET /voila/query/7801ca4b-214c-49b5-bf40-774ae1c0c457 (127.0.0.1) 0.39ms
WARNING:tornado.access:404 GET /voila/query/e22cdcc1-547e-4e52-9ca7-b8de8d199d45 (127.0.0.1) 2.39ms
WARNING:tornado.access:404 GET /voila/query/5a1dc72b-acac-4fe1-961b-b0d023c5c588 (127.0.0.1) 1.62ms

According to the source code, the VoilaHandler ignores the WebSocket connection error and goes on with an empty query string value.
4. Go to http://localhost:8866/example-base-url/?foo1=bar1&foo2=bar2 in the browser and see None instead of the expected foo1=bar1&foo2=bar2 value.

Expected behavior

I managed to modify my bash script to make app work correctly by providing the VOILA_WS_BASE_URL env. var. as follows:

voila get_qs_example.ipynb --preheat_kernel=True --pool_size=5 --no-browser --Voila.base_url='/example-base-url/' --VoilaKernelManager.kernel_pools_config="{'get_qs_example.ipynb': {'pool_size': 5, 'kernel_env_variables': {'VOILA_WS_BASE_URL': '/example-base-url/'}}}"

However, it's still a breaking change as I had to modify my bash script and I would expect Voila to use the value of --Voila.base_url parameter if the VOILA_WS_BASE_URL variable hasn't been specified.