Open all files with /files path except for .html and .svg`

[gnestor]

Closes #2404

[gnestor]

@takluyver Can you review?

[takluyver]

.htm should be treated this way as well, it's a common extension for html files. I wonder if we should be doing it on mime type instead of extension - I think anything that our server offers with mimetype text/html can have the same effect, and that can vary by system. In some cases, installed apps can affect what extensions are recognised for a mimetype.

@minrk @rgbkrk do you know of any file types other than html and svg that we should be displaying in the iframe?

[minrk]

It's probably best to avoid a 'not_safe' blacklist, because it's easy to miss things (like the many synonyms for html) instead having a 'safe' list for things that can be trusted to be displayed raw. It seems like it makes more sense to specify a list of things that don't work in the iframe (are there examples other than PDF?)

[gnestor]

I updated so that is_viewable is used in place of is_not_safe (just includes htm and html). Every other file extensions that isn't editable will be opened using the /files path and handled by the browser. I also updated the is_editable list to be more comprehensive (using the list from https://github.com/sindresorhus/text-extensions/blob/master/text-extensions.json).

[takluyver]

Isn't that the same blacklisting approach just with the name 'viewable' in place of 'not_safe'?

I see xht, xhtml, mht and mhtml in the editable list - in certain circumstances, any of these could be rendered as HTML in a browser, so viewing them should open them in the iframe. This rather validates Min's point about the problems with a blacklist.

[gnestor]

I have updated this PR. The way it works now:

• By default, all files (not directories) are opened using /files prefix and display the "View" button
• If a file is html (according to the list of html extensions and text/html mime type), it's opened using the /view prefix
• If a file is editable (according to the list of editable extensions and text/* and application/* mime types), it's opened using the /edit prefix and displays the "Edit" button
• If a file is a notebook, it's opened using the /notebooks prefix
  • Notebooks can be edited in the text editor using the "Edit" button