[WIP] Voila as an ExtensionApp

[Zsailer]

I went ahead and started refactoring Voila to use the ExtensionApp in jupyter_server. It greatly simplifies the main application.

Using this API, Voila can be initialized, configured and launched from the command line, and you can generate configuration files using the --generate-config flag.

It can also be loaded as a Jupyter server extension, allowing you to serve Voila side-by-side with other client applications running on one server.

One thing to note is that all static files are now served behind the url namespace static/voila/ (this is automatically set up by ExtensionApp).

This should be working. Let me know if you have issues with testing it out.

@SylvainCorlay @maartenbreddels

[Zsailer]

To test this out,

1. Clone and install jupyter_server master (the latest release won't work).
2. Checkout this PR's branch
3. Install using pip install . (this updates the voila CLI and server extension entry points).

Start Voila by either 1) running directly:

jupyter voila

or loading as a server extension

jupyter server --ServerApp.default_url='/voila'`

[Zsailer]

Also, I've opened jupyter-server/jupyter_server#59 to simplify how extensions configuration gets passed to extension handlers. This should help simplify some of the changes here.

Once that PR is merged in jupyter_server, I'll update this PR.

[timkpaine]

checking this now

[Zsailer]

Thanks, @timkpaine.

I think this will require a pretty significant refactor of Voila's tests. I'm happy to work on this if you can confirm that the ExtensionApp seems like a good solution for Voila.

[timkpaine]

@Zsailer I really would like to use my jupyterlab LoginHandler for Voila, rather than having to do any custom weirdness, so I think this makes sense to do. Im not a maintainer of voila though so its up for @SylvainCorlay to decide.

[Zsailer]

I really would like to use my jupyterlab LoginHandler for Voila

Definitely—though, you may have to wait for JupyterLab to adopt jupyter_server as it's core server (unless you're already using Lab without the classic notebook server).

[timkpaine]

I don't need full compatibility, just the bare minimum

[maartenbreddels]

Excellent work! I like seeing all the red. Should this now work with the latest jupyter-server release?

[Zsailer]

@maartenbreddels Great! Glad you like it!

I just got back from holiday, so I'm catching up on emails+Github threads. I'm hoping to rebase this PR later this week. It should work with the latest jupyter_server, but I'll verify and ping you again soon.

[Zsailer]

Ok, once jupyter-server/jupyter_server#70 is merged, this should be working (with standalone mode).

[maartenbreddels]

Impressive work!
The test do not run on the CI because of the flake8 issues, it may be useful to run the following test locally:

py.test tests/app/execute_test.py

I also noticed that if I run jupyter-voila notebooks/basics.ipynb, it will open the wrong url (http://localhost:8891/notebooks/basics.ipynb?token=...)

[Zsailer]

The tests need some refactoring after these significant changes. I started working on that last week but didn't quite finish. I'll try to update the tests over the next day or two.

[Zsailer]

I also noticed that if I run jupyter-voila notebooks/basics.ipynb,

Good catch! Looking into this issue now.

[vidartf]

I believe this would also be relevant? jupyter-server/jupyter_server#80

[timkpaine]

@Zsailer anything I can do to help?

[Zsailer]

Closing in favor of #492. Thanks, @maartenbreddels!