Fix opening files from the CLI

[jtpio]

Investigate ways to fix #6914

[github-actions]

👈 Launch a Binder on branch jtpio/notebook/redirect-regex

[jtpio]

So the idea if that we should be able to open files from the CLI by using the existing /tree/<file> redirection logic.

[jtpio]

cc @parmentelat if you want to try with the built artifacts: https://github.com/jupyter/notebook/actions/runs/5356963835?pr=6946

[jtpio]

For reference file_url_prefix is documented here in Jupyter Server: https://jupyter-server.readthedocs.io/en/latest/developers/extensions.html#anatomy-of-an-extensionapp

file_url_prefix: the prefix URL added when opening a document directly from the command line. For example, classic Notebook uses /notebooks to open a document at http://localhost:8888/notebooks/path/to/notebook.ipynb.

[jtpio]

So the idea of using /tree is that there is already a redirect handler to open either with /edit or /notebooks:

notebook/notebook/app.py

Lines 127 to 160 in 7f1a2f4

	async def get(self, path=None):
	"""
	Display appropriate page for given path.
	- A directory listing is shown if path is a directory
	- Redirected to notebook page if path is a notebook
	- Render the raw file if path is any other file
	"""
	path = path.strip("/")
	cm = self.contents_manager
	if await ensure_async(cm.dir_exists(path=path)):
	if await ensure_async(cm.is_hidden(path)) and not cm.allow_hidden:
	self.log.info("Refusing to serve hidden directory, via 404 Error")
	raise web.HTTPError(404)
	# Set treePath for routing to the directory
	page_config = self.get_page_config()
	page_config["treePath"] = path
	tpl = self.render_template("tree.html", page_config=page_config)
	return self.write(tpl)
	elif await ensure_async(cm.file_exists(path)):
	# it's not a directory, we have redirecting to do
	model = await ensure_async(cm.get(path, content=False))
	if model["type"] == "notebook":
	url = ujoin(self.base_url, "notebooks", url_escape(path))
	else:
	# Return raw content if file is not a notebook
	url = ujoin(self.base_url, "files", url_escape(path))
	self.log.debug("Redirecting %s to %s", self.request.path, url)
	self.redirect(url)
	else:
	raise web.HTTPError(404)