Normalize os_path

[martinRenou]

This fixes an issue causing access to local files in Voila considered forbidden:

Accessing a file ./jupyter.svg in Voila (jupyter.svg being under the root_dir) results in a:

  File "/home/martin/micromamba/envs/voila/lib/python3.10/site-packages/mistune.py", line 661, in _process_link
    return self.renderer.image(link, title, text)
  File "/home/martin/github/voila/voila/exporter.py", line 34, in image
    content = contents_manager.get(src, format='base64')
  File "/home/martin/micromamba/envs/voila/lib/python3.10/site-packages/jupyter_server/services/contents/filemanager.py", line 386, in get
    raise web.HTTPError(404, four_o_four)
tornado.web.HTTPError: HTTP 404: Not Found (file or directory does not exist: './jupyter.svg')

This was because the root_dir was set to /home/martin/github/voila/tests/notebooks and the path /home/martin/github/voila/tests/notebooks/./jupyter.svg was considered "hidden" by jupyter_server, while it's not. Normalizing the path fixes it.

[davidbrochart]

This also transforms the path to an absolute path, which we may not want.

[davidbrochart]

My bad, it doesn't.

[martinRenou]

Oh cool! Thanks for checking

[martinRenou]

I don't have the rights for adding labels. Maybe a maintenance or bug label would fit?

[martinRenou]

It would be amazing if this could be backported to a 1.17.2 🙏🏽

[blink1073]

Thanks!

[blink1073]

@meeseeksdev please backport to 1.x

[martinRenou]

Thank you!

[krassowski]

Bumping urgency of a patch release soon: the issue also affects jupyterlab-git (Error Loading Notebook Diff: file or directory does not exist: './notebook.ipynb'). I verified that this PR fixes it there too. Thank you all for the quick fix and backport!

[blink1073]

In progress now