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User following

Terminology

The following terminology is used throughout this document:

User: A person with an account on a Funkwhale server or ActivityPub-enabled platform.
Follow: The act of subscribing to a user’s activities to render them in a feed as they occur.
Object: A collection of information - formatted as JSON-LD - that represents entities such as content, users, or activities performed in Funkwhale. See the ActivityPub specification for more details.
Activity: A verb that describes an action targeting an Object. This informs the receiving server what it needs to do with the object. For example: Create, Delete, Undo, Follow, Block.
Actor: An ActivityPub object representing an entity capable of performing actions. See the ActivityPub specification for more details.
Requesting user: The user who sends a request. For example: If Bob requests to follow Alice, Bob is the requesting user.
Target user: The user who is the subject of a request. For example: If Bob requests to follow Alice, Alice is the target user.

The issue

Funkwhale is an audio platform with an emphasis on social interaction across a federated network of servers. To this end, Funkwhale users should be able to interact with one another in meaningful ways.

Funkwhale users broadcast the following activity when using the software:

Favoriting content
Listening to content

Users across the federated web should be able to follow Funkwhale accounts to receive this activity in their streams.

Proposed solution

To facilitate this, Funkwhale uses the following mechanisms:

The Funkwhale client API for user to user interactions on the same server
ActivityPub for server-to-server (S2S) interactions between users

Users should be able to discover other users using the Webfinger protocol and render their public details in a manner compliant with the platform they use. Within Funkwhale, user activity should be rendered natively. Other Fediverse software may choose how to render this information.

This specification outlines the workflows for the following actions for local and remote requests:

User discovery
User follows
User unfollows
User blocking

User discovery

Funkwhale implements the Webfinger protocol for account discovery. When the requesting user enters the target user’s federation handle, Funkwhale should attempt to resolve the location of the target user by querying the acct: resource with the URL encoded handle.

Webfinger request

$ curl -X GET \
-H "Content-type: application/json" \
'https://open.audio/.well-known/webfinger?resource=acct:user%40open.audio'

Response

{
  "subject": "acct:user@open.audio",
  "links": [
    {
      "rel": "self",
      "href": "https://open.audio/federation/actors/user",
      "type": "application/activity+json"
    }
  ],
  "aliases": ["https://open.audio/federation/actors/user"]
}

Web app behavior

When a requesting user enters the handle of a target user in the search bar, Funkwhale does the following:

Verifies the handle is well-formed
Forwards the request to the server

The server is responsible for dereferencing the Webfinger query. The server does the following:

Queries the domain for the account using Webfinger
- If the domain doesn’t have a Webfinger endpoint, returns a meaningful error message. This must be displayed to the user.
- If the server is subject to a domain filter, or is filtering the requesting server, returns a meaningful error message. This must be displayed to the user.
- If no user is found on the domain, returns a meaningful error message.
If a matching user is found, the server should return the URL of the resource to the web app. The web app should then redirect the requesting user to a user page that shows the target user’s profile image and preferred username
- If the target user has set their activity to public, the web app should render their Favorites and Recently Listened activity

flowchart TD search([A requesting user enters a fediverse handle\nin the search bar]) --> query(Funkwhale queries the target domain) query --> webfinger{Does the target server\support Webfinger?} subgraph Request verification webfinger -->|no| error([The server returns an error message]) webfinger -->|yes| filter{Is the requesting server subject\nto a domain filter or vice versa?} filter -->|yes| error filter -->|no| userfound{Was the target user found\non the server?} userfound -->|no| error end userfound -->|yes| redirect([The user is redirected to a profile page\nin the web app])

Following users

Following a user is a process by which a requesting user subscribes to the activities of a target user. If the target user accepts the follow request, the requesting user receives any new activities in their home feed.

API behavior

Follow requests should be handled by an endpoint using a POST request. This request must immediately return a status message to the client.

POST /api/v2/users/{id}/follow

When the server receives a follow request, it creates a follow_request object containing the status of the follow request which is used to display request information to the target user in their notifications.

Note

If the target user has configured their profile to be public, all Follows are Accepted immediately.

ActivityPub behavior

If the target user is on a different server to the requesting user, the request is handled using the ActivityPub Follow activity:

A Follow activity is posted to the requesting user’s outbox collection with the target user as the recipient
The target user receives the request in their inbox collection
The target user then needs to Accept or Reject the Follow
- If the target user accepts the follow, the requesting user is added to the target user’s following collection. The target user is added to the requesting user’s followers collection
- If the target user rejects the follow, the requesting user is not added to the target user’s following collection. The target user is not added to the requesting user’s followers collection

sequenceDiagram autonumber Bob ->> Bob's Outbox : Follow request note over Bob's Outbox, Bob's Inbox : Bob's ActivityPub collections Bob's Outbox ->> Alice's Inbox : Follow request note over Alice's Inbox, Alice's Outbox : Alice's ActivityPub collections Alice's Inbox ->> Alice : Display follow request activate Alice alt if Alice accepts Bob's request Alice -->> Alice's Outbox : Accept follow Alice's Outbox --> Bob's Inbox : Accept Bob's Inbox --> Bob : Display following end alt if Alice rejects Bob's request Alice -->> Alice's Inbox : Reject follow end

Note

If the target user has configured their activity to be public, all Follows are Accepted immediately.

Web app behavior

In the Funkwhale web app, the requesting user sees a Follow button on the target user’s profile page. When they select this button, the following happens:

If the target user’s profile can be followed, an action button is displayed.
When the requesting user attempts the follow the target user, the button should change to a Pending status.
If the target user Accepts the follow request, the button should update to show a Following status.

Unfollowing users

Following a user is a process by which a requesting user unsubscribes from the activities of a target user. A requesting user may unfollow a target user unilaterally at any time to stop receiving updates.

API behavior

Follow requests should be handled by an endpoint using a POST request. This request must immediately return a status message to the client.

POST /api/v2/users/{id}/unfollow

ActivityPub behavior

If the target user is on a different server to the requesting user, the request is handled using the ActivityPub Undo activity:

An Undo activity is posted to the requesting user’s outbox collection with a Follow activity as the target
The target user is removed from the requesting user’s following collection
The target user receives the undo request in their inbox collection
The requesting user is removed from the target user’s followers collection

sequenceDiagram autonumber Bob ->> Bob's Outbox : Undo request note over Bob, Bob's Outbox : The target user is removed Bob's Outbox ->> Alice's Inbox : Undo Follow note over Alice's Inbox, Alice : The requesting user is removed

Web app behavior

When a requesting user unfollows a target user, the UI must update to visually indicate that the action has succeeded. All activities relating to the target user must be visually hidden.

Blocking users

When one user blocks another, no information may be shared between them. Blocking is a unilateral action that can be taken by both requesting and target actors to prevent the other from interacting with them.

API behavior

Block requests should be handled by an endpoint using a POST request. This request must immediately return a status message to the client.

POST /api/v2/users/{id}/block

ActivityPub behavior

If the the blocked user is on a different server to the blocking user, the request is handled using the ActivityPub Block activity with the blocked user’s Actor as a target.

A Block activity is posted to the blocking user’s outbox collection with the blocked user’s Actor the target
- If the blocked user was previously in the blocking user’s following collection, they are removed
- If the blocked user was previously in the blocking user’s followers collection, they are removed

Warning

As noted in the ActivityPub spec, the blocked user must not be informed of the Block activity.

Web app behavior

When a blocking user blocks a blocked user, the UI must update to visually indicate that the action has succeeded. All activities relating to the blocked user must be visually hidden.

If a blocking user navigates to the profile of a blocked user who has blocked them, the UI must not reflect that they are blocked. The blocking user must be able to send a follow request which is not sent to the blocked user.

Unblocking users

Blocking users can unilaterally reverse blocks they have imposed on blocked users. This enables them to request to follow the blocked user’s activities again.

API behavior

Unblock requests should be handled by an endpoint using a POST request. This request must immediately return a status message to the client.

POST /api/v2/users/{id}/unblock

ActivityPub behavior

If the blocked user is on a different server to the blocking user, the request is handled using the ActivityPub Undo activity.

Web app behavior

When a blocking user unblocks a blocked user, the UI must update to visually indicate that the action has succeeded. The Follow button must become active and interactive again.

Availability

App frontend
CLI

Responsible parties

The following working groups are responsible for implementing this feature:

The Backend group is responsible for building the API endpoints and ActivityPub S2S logic
The Design group is responsible for drafting designs for the web app interactions
The Frontend group is responsible for implementing the designs from the Design group and adding support for the new API
The Documentation group is responsible for finalizing the specification of the feature and documenting it for users

Open questions

The API actions and endpoint names are placeholders. We need to decide what they should be called
What limitations are there when fetching activities from remote actors?
How should a user’s followers collection, following collection, and pending requests be displayed in the web app?
How are followed activities fetched and displayed to a user?

Minimum viable product

The MVP for this feature is to implement the backend logic to enable Funkwhale users to follow one another. This can be added to the web app using existing profile fetching logic.

Next steps

Once the backend logic is implemented, the frontend implementation should be revisited to improve the UX and discoverability. Additional features such as showing federated favorites on audio objects should also be considered.