share server: implement proxying notebooks hosted on github, similar to what nbviewer provides

[williamstein]

Consider this URL:

https://nbviewer.org/github/sagemanifolds/IntroToManifolds/blob/main/01Manifold_Def.ipynb

that is one of the links from https://sagemanifolds.obspm.fr/intro_to_manifolds.html

It's a notebook that you can see view nbviewer. It's hosted on github here:

https://github.com/sagemanifolds/IntroToManifolds

The point of this ticket is to make it so

https://cocalc.com/github/sagemanifolds/IntroToManifolds/blob/main/01Manifold_Def.ipynb

does the same exact thing... with the added benefit that with a click you can be quickly interactively using the notebook with the Sage kernel right in your web browser, which is something nbviewer/github don't provide (especially not for Sage).

Also, CoCalc can render far more document types than nbviewer, e.g., markdown, latex, etc., so this could be more generally useful.

[williamstein]

One way in which this provides significant value over just cloning the code from

https://github.com/sagemanifolds/IntroToManifolds.git

and hosting it in the normal way on CoCalc, is that if that upstream git repo is updated, then the newer versions are available. For example, I just used git clone to put a copy here:

https://cocalc.com/wstein/support/IntroToManifolds

and this is great, but it's a single point in time and isn't automatically kept in sync with github...

[williamstein]

with the added benefit that with a click you can be quickly interactively using the notebook with the Sage kernel right in your web browser, which is something nbviewer/github don't provide (especially not for Sage).

I want to clarify that there is a "Run this in binder" button on nbviewer specifically for these Sage manifolds notebooks. However, that's not the quality of experience I'm aiming for (or that we already have on cocalc). I just tried that link for one of these notebooks, and you get sent to another page, watch a terminal do something, see a big spinner, get asked for money in a big red box, see that something should be starting, and (I'm timing it with a stopwatch) over 10 minutes later, it still doesn't work. Maybe it's challenging getting sage to work with mybinder robustly, since sage is so big.

[williamstein]

Update: mybinder did successfully load that notebook, but it took exactly 16 minutes according to my stopwatch.
However, loading a second notebook from the repo was then much faster (less than 20 seconds*), but then I quickly got

and it was really broken. I refresh the browser, and got stuck with "Kernel starting, please wait..." for a while, then failed. So maybe mybinder loads but doesn't actually work long for these. In any case, it's clearly not the best possible imaginable experience we want for Sage users. I'm definitely not saying cocalc is either, but I want to try, hence tickets like this one.

I like how in mybinder they somehow add buttons to the Jupyter notebook that provide links back to the Github version of the notebook and the binder version:

[williamstein]

This is now live!

To use it, just make a url like

• https://cocalc.com/github/sagemanifolds/IntroToManifolds
• https://cocalc.com/url/archive.org/download/musing_math/Volume_Solutions_To_Snub_Dodecahedron.ipynb
• https://cocalc.com/gist/darribas/4121857

The URL schema is exactly the same as what https://nbviewer.org uses, i.e., github/<github url>, url/<anything on the internet> and gist/[github user]/[gist id].

The main differences relative to nbviewer are:

• You can put a URL to any file CoCalc can render or edit, and you'll see it. E.g., here's a markdown file: https://cocalc.com/github/sagemathinc/cocalc/blob/master/README.md which nbviewer doesn't render (it only renders ipynb).
  • Here's a whiteboard: https://cocalc.com/github/williamstein/scratch/blob/main/2022-06-27-ws.board
  • And a Sage worksheet: https://cocalc.com/github/williamstein/scratch/blob/main/2022-06-30-061806.sagews
• When you click Edit (analogue of mybinder for some nbviewer content), the content is copied to a project in cocalc and you can use it. E.g., Sage notebooks actually work, since Sage is installed. The mybinder flakiness is avoided. Also all content is editable, not just content that has been setup to work with mybinder.
• That said, editing whole git repos isn't implemented in cocalc yet.
• In CoCalc any time anybody views one of these url proxy's in the share server, a new entry is created in the list of shared documents starting at https://cocalc.com/share/public_paths/page/1
  • Anybody can star one of these to easily come back to it later, and also signify that it is interesting.