Filter collection by member type

[evanp]

"As an ActivityPub API client developer, I want a way to filter a collection by the type of the members, so I can show the members that are relevant to my application."

A good example would be a geosocial client, which is just looking for Arrive, Leave, and Travel activities. Without a filter, the client has to load all the activities, and filter on the client side.

[mariusor]

I somehow missed this collection of issues when it was created, but I have a FEP with a possible suggestion for filtering: FEP-6066

This is already used in the servers built with support for GoActivityPub storage backends.

[naturzukunft]

see also https://codeberg.org/fediverse/fep/src/branch/main/fep/34c1/fep-34c1.md

FEP-34c1: Collection Filtering using TREE Hypermedia Vocabulary
This FEP proposes using the TREE Hypermedia Vocabulary for client-initiated filter requests on ActivityPub Collections (especially Inbox). Clients can send a filter as a JSON-LD object via HTTP POST to retrieve a filtered subset of the collection.

This enables use cases such as:

• Home Timeline: Content lifecycle activities (Create, Update, Delete, Announce) from followed actors, visible to public or followers
• Mentions: Activities addressed to the actor via as:to or as:cc
• Private Messages: Activities not addressed to as:Public (DMs, followers-only, group messages)
• Media Filter: Only activities with images or videos

[mariusor]

Inbox/Outbox collections have only one HTTP POST behaviour that's acceptable, so any proposal that requires additional functionality added there is not compatible (in my opinion) with the spec.

That's why I intentionally kept the filtering capabilities to GET query parameters in FEP-6066.

[naturzukunft]

fep-34c1 extends a collection with a filter endpoint; otherwise, it has no effect on the collection. The filter endpoint itself is HTTP POST. The collection remains unaffected except for the additional property; fep-34c1 is backward compatible.

[mariusor]

Ah, sorry, I missed that. I guess I made the same mistake in the comments thread on socialhub.