[Bug]: Lemmy doesnt forward activities received in community inbox to followers

[Nutomic]

Requirements

• [X] Is this a bug report? For questions or discussions use https://lemmy.ml/c/lemmy_support
• [X] Did you check to see if this issue already exists?
• [X] Is this only a single bug? Do not put multiple bugs in one issue.
• [X] Is this a backend issue? Use the lemmy-ui repo for UI / frontend issues.

Summary

Looking at the recipients of the activities, we see that Lemmy always sends them to the shared inbox of an instance. But Mastodon sent the Like to !activitypub’s personal inbox. It looks like Lemmy processes those activities, meaning that it adds it to its internal vote count, but doesn’t consider them for distribution. Unlike the problem with replies that we saw above, this seems like a bug that can be fixed.

From https://seb.jambor.dev/posts/understanding-activitypub-part-2-lemmy/#voting

The problem is that Lemmy uses shared inbox almost exclusively, so individual user/community inboxes arent well tested.

Steps to Reproduce

1. Like a Lemmy post from Mastodon
2. See like on Lemmy
3. Like isnt being forwarded to other Lemmy instances which follow the community

Technical Details

Version

0.18.4

Edit: This would be fixed by https://github.com/LemmyNet/lemmy/issues/4147