Support download folder as archive in JupyterLite

[psychemedia]

JupyerLite provides an in-browser version of JupyterLab supported by an in-browser WASM based Python environment. Notebooks can be uploaded to JupyterLite and saved to browser storage, along with edited notebooks and data files etc. Being able to easily export notebooks as a zip archive from the in-browser environment would be really useful.

Currently, using the jupyter-archive extension to download a folder as an archive file in Chrome pops up a browser status message to the effect of download.html File wasn't available on site and no archive file is downloaded.

[fcollonval]

Some comments for interested contributors:

• this is not easy to achieve. Despite what it looks like for the end user, the architecture of jupyterlite does not execute any server. Therefore extensions like this one that are doing actions in the server are not easy to integrate in jupyterlite.
• from the previous comment there are two ways to address this:
  • the better: create a jupyterlite extension that run a mocked jupyter server in a web worker using a pyodide interpreter (independent of any kernel web worker)
  • the hack: implement the server logic in new jupyterlite plugin - but I'd prefer to avoid this to not increase the maintenance burden.

Whatever the path, I want to emphasize that it won't be easy as it will require knowledge of storage management in the jupyterlite.