Switch to ActivityPub for subscriptions

[acka47]

As there is a problem with our use of WebSub (see #11 (comment)) we will switch to ActivityPub as written in #11 (comment):

Switch to using ActivityPub's subscription mechanism with ActivityStream's Follow activity (as:Follow). See https://www.w3.org/TR/social-web-protocols/#subscribing-with-follow for a short description. Notifications regarding new resources about a subject could then be sent using the as:Add activity (see also https://www.w3.org/TR/activitypub/#add-activity-inbox).

[acka47]

Is created a wiki page for discussing the details on how to implement this: https://github.com/hbz/skohub-pubsub/wiki/ActivityPub-based-SkoHub

[acka47]

I overhauled the wiki page at https://github.com/hbz/skohub-pubsub/wiki/ActivityPub-based-SkoHub as I misunderstood a lot of things when writign the first version. Looking at Mastodon (by adding .json to a toot or other page) helped me a lot.

[acka47]

At our pre-WikidataCon meeting in Berlin, @literarymachine and me noticed that the server to server (S2S) communication is not well documented for ActivityPub, which was confirmed by @mayel in his response to my enquiry on Mastodon.

Today, I again searched for some resources that could help us.

The postman documentation for pubgate, a "Lightweight ActivityPub federator" seems very helpful to me if I am not mistaken.

Furthermore, there is How to implement a basic ActivityPub server (we already looked at this in Berlin) and also the mastodon issue for adding Activitypub support is an interesting read.

(On a side note: It became clear to me while searching for documentation that mostly only the S2S part of Activitypub is implemented while the client-to-server (C2S) part is rather neglected. See this Mastodon post with diagram: https://mstdn.io/@alexl/101489101844227113)

[acka47]

Re. implementations to take a look at, these two make a good impression:

• Epicyon, "a modern ActivityPub compliant server implementing both S2S and C2S protocols and sutable for installation on single board computers" written in Python: .https://code.freedombone.net/bashrc/epicyon
• kroeg, a generic ActivityPub server written in Rust: https://git.puckipedia.com/kroeg/server

[acka47]

This post and the links to further posts also look promising: ActivityPub as it has been understood

[acka47]

On mastodon, I was pointed to the recently established "SocialHub", a discourse instance for AcrtivityPub-related matters: https://socialhub.activitypub.rocks/

We should definitely post some problems/questions we have there.

[acka47]

This is ready to be deployed on production.