Announce and Undo(Announce) in Mastodon

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NodeBB federates out the Announce activity in two ways.

  1. The “plain object” way, which is an Announce activity wrapping an object (either a uri or the full object itself.)
  2. The “1b12” way, which is an Announce activity wrapping another activity (e.g. Create)

Up until now I haven’t needed to handle the reverse (which in AP-speak is the “undo” of an activity), but since NodeBB sends Announce when moving a topic *in to category, it now makes sense to Undo(Announce) when moving a topic out* of a category.

My first interop test with Mastodon didn’t work, and it turns out that Mastodon checks the id of the embedded Announce for a match. It doesn’t infer it based on actor/object combination.

Once I matched up the IDs, the Undo was processed correctly.

I also noticed that Announces sent from Mastodon have a published property, although this is not relevant in Undo parsing.

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What does undoing an announce do, in Mastodon? Remove a boost?

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OP

Yep, that’s basically it. It’s not really a concept in threadiverse implementations since group actors do the Announcing for synchronization.

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Lemmy uses Announce/Undo/Delete and similar activites. So the outermost activity is always Announce from the community. To me Undo/Announce doesnt make much sense, it was already announced and you cant take that back. Its the delete action which is reverted.

Mastodon compatibility is another thing, you likely need a lot of ugly hacks for that.

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OP edited

You’re right! We don’t federate out Announce(Undo(Object)) precisely because threadiverse implementations already do Announce(Delete).

This is purely for microblogs, but it does merit discussion for that reason alone 🙂

Edit: your reply does remind me that we don’t currently handle Announce(Undo(Like)) though, so thanks!

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