forgejo/docs/unsure-where-to-put/adr-how-to-trigger-activities.md
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# How to Trigger Activities
## Status
Proposal
## Context
While implementing the trigger of federated stars we have to handle the distribution of corresponding Like-Activities to the federated repositories.
This must be done consistently and without circularity, such that a repository starring by a user leads to exactly one added star in every federated repository.
## Decision
## Choices
### 1. Star Activity Triggers Sending of Star Activity to Federated Repositories
In this case the star federation process would look like:
1. Repo on an instance receives a star (regardless of whether via UI or federation)
2. Instance federates star to all repos that are set as federated repositories.
#### Problem - Circularity And Inconsistency
Circular federation would lead to a infinite circular distribution of Like-Activities:
1. Given a repo on the 3 instances A, B, C.
Repo on instance A has set repo on instance B as federation repo.
Repo on instance B has set repo on instance C as federation repo.
Repo on instance C has set repo on instance A as federation repo.
2. User stars repo on instance A via UI.
3. Instance A sends Like-Activity to repo on instance B.
4. Instance B creates local FederatedUser, stars the repo and sends Like-Activity to repo on instance C.
5. Instance C creates local FederatedUser, stars the repo and sends Like-Activity to repo on instance A.
6. Instance A creates local FederatedUser, since the Actor of the Like-Activity is the local FederatedUser created on instance C.
Thus, the repo on instance A gets another star by this user and sends Like-Activity to the repo on instance C.
7. The circular distribution of Like-Activities continues, since the actor is always the local FederatedUser of the sending instance.
### 2. Only Repository-Starring By Authenticated User Triggers Sending of Star Activity to Federated Repositories
In this case the star federation process would look like:
1. Case: Repo on an instance receives a star by an authenticated user via UI/API:
1. Repository gets starred by the authenticated User.
2. Instance federates star to all repos that are set as federated repositories.
2. Case: Repo on an instance receives a star via a Like-Activity:
1. Instance creates FederatedUser and stars the repository.
2. No further star federation to federated repos is triggered.
## See also