Open jupyter lab url via custom command with placeholder

[antoine-gallix]

Description

I'm trying to use Chrome in app mode to open jupyter lab at startup. Chrome app mode is a stripped down interface made to open applications. I can do it manually with the following command

chromium --app="http://localhost:8888/?token=052b2ab48e31bba526723bb28ccb6445475fb02fdf887356"

I have to get the URL by hand in the shell terminal that runs Jupyter Lab.

I've found the c.NotebookApp.browser option that allows to use a custom command to open the lab. I also found the undocumented possibility to insert the jupyter file string in the command c.NotebookApp.browser = 'chromium --app=%s'. But it seems that the string used in the placeholder is the file version of the lab, the one cited in the jupyter lab terminal window: file:///home/antoine/.local/share/jupyter/runtime/nbserver-20759-open.html. The chrome window opened by jupyter lab at startup complains with the following error:

Access to the file was denied
The file at file:///home/antoine/.local/share/jupyter/runtime/nbserver-27050-open.html is not
 readable. It may have been removed, moved, or file permissions may be preventing access.
ERR_ACCESS_DENIED

To manage to do what I wanted I would need one of the following:

• an option to write the url+token string somewhere in a file so I can use it programatically to open the lab by myself.
• an option to feed the url to the browser string with placeholder, instead of the file version of the lab
• in any case, the placeholder option for browser command is undocumented, I found it by coincidence on a forum. That would be nice to have it.