support JF2

[snarfed]

to oversimplify, it hoists mf2 properties out of the properties field and makes most of them singly-valued. should be straightforward.

spec: https://www.w3.org/TR/jf2/#jf2feed , https://jf2.spec.indieweb.org/

more links:

• http://microformats.org/wiki/jf2
• https://indieweb.org/jf2
• https://github.com/dissolve/jf2
• https://stream.thatmustbe.us/

JF2 Feed: http://dissolve.github.io/jf2/#jf2feed , MIME type application/jf2feed+json

cc @dissolve!

[snarfed]

dupe of #50...but closing that and tracking here instead since there are newer links here.

[snarfed]

Looks like mf2util's interpret_*() functions convert to JF2? https://github.com/kylewm/mf2util#quick-start

cc @capjamesg

[capjamesg]

Good to know! jf2 support would be useful for Microsub servers who need to send jf2 objects to clients. jf2 is thus an efficient way to make sure all data from various different feed types is stored in a standard way in a Microsub back-end.

As far as I can see, mf2util converts mf2 objects to jf2. That's a handy function to have! Although Microsub servers may optionally wish to support RSS, Atom, and JSON Feed, which looks to be out of scope for mf2util.

[capjamesg]

I have implemented RSS / Atom / JSON Feed to jf2 conversion for my Microsub server: https://github.com/capjamesg/microsub/tree/main/feeds

If this logic would be helpful to granary, I can look at the library and see if I can make a pull request.

[snarfed]

Woo, thank you for the offer!

Sadly, granary uses AS1 as its common backplane data format, so to do this properly, we'd need either AS1 <=> jf2 or maybe mf2 <=> jf2.