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FEP-171b: Conversation Containers (#448)
Reviewed-on: https://codeberg.org/fediverse/fep/pulls/448 Co-authored-by: silverpill <silverpill@firemail.cc> Co-committed-by: silverpill <silverpill@firemail.cc>
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silverpill
silverpill
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{
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"@context": {
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"collectionOf": "https://fediversity.site/apschema#collectionOf"
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}
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}
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---
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slug: "171b"
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authors: silverpill <@silverpill@mitra.social>
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status: DRAFT
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dateReceived: 2024-11-23
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discussionsTo: https://socialhub.activitypub.rocks/t/fep-171b-conversation-containers/4766
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---
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# FEP-171b: Conversation Containers
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## Summary
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This document specifies a model for managing conversations in [ActivityPub] network as collections. It is based on the implementation of [Conversation Containers][Containers] in [Streams](https://codeberg.org/streams/streams).
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In this model conversations are managed by the actor that created the initial post of a conversation thread. Such conversations take place within a specific audience and may be moderated.
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## Requirements
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC-2119].
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## Containers
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A conversation container is implemented as a collection. Every item in that collection is an `Add` activity where `object` is another activity (such as `Create`, `Update`, `Delete`, `Like`, `Dislike`, `EmojiReact` or `Announce`). The conversation owner distributes `Add` activities to other participants, thus keeping their views of the conversation synchronized.
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### Container collection
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- Collection type MUST be `OrderedCollection`.
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- Collection items MUST be in chronological order.
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- Collection MUST have an `attributedTo` property containing the `id` of the conversation owner.
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- Collection SHOULD have `collectionOf` property with value `Activity`.
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>[!NOTE]
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>The required collection type might be changed to a more descriptive one (such as `Context`) in a future version of this document. That will allow identification of `Add` activities belonging to a conversation container by the value of `Add.target.type`.
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>[!NOTE]
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>In addition to the conversation container collection, implementers MAY provide collection that represents the conversation tree and contains posts.
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### Adding activities to a conversation
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Conversation owner can add any activity to the conversation. However, if a `context` property is present on the activity, its value SHOULD be identical to the ID of a conversation container.
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When activity is added to the conversation, its owner sends an `Add` activity to the conversation audience (usually defined by a top-level post).
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`Add` activities published by the conversation owner MUST have a `target` property containing a partial object:
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- `type`: `OrderedCollection`
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- `id`: the `id` of the conversation container.
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- `attributedTo`: the `id` of the collection owner.
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`Add` activities published by the conversation owner MUST be added to the conversation container collection.
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>[!NOTE]
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>The "conversation outbox" model where the `target` of `Add` activity is a collection of `Add` activities is not compatible with ActivityStreams definition of [Add](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-add) activity, according to which *Add activity indicates that the actor has added the object to the target*.
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### Top-level post
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The top-level post MUST have a `context` property indicating a conversation container.
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>[!NOTE]
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>The usage of a `context` property in conversation containers differs from recommendations provided in [FEP-7888].
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### Interactions
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All activities in a conversation SHOULD only be delivered to the conversation owner.
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Conversation participants SHOULD reject conversation activities that have not been added to the conversation by its owner.
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The audience of a reply MUST be copied from a conversation root.
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Reply with a different audience can be created by starting a new conversation and including a [FEP-e232] link to the post instead of specifying it in `inReplyTo`.
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### Moderation
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To remove a post from a conversation, its owner publishes a `Delete` activity where `object` is the post that must be removed. This activity is then wrapped in `Add` activity and distributed to the conversation audience.
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>[!NOTE]
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>Actor shouldn't be able to delete objects it didn't create. In a future version of this document `Delete` might be replaced with `Remove(target: Thread)`.
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### Backfilling
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Conversation participants can retrieve missing activities by reading the conversation container collection.
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## Authentication
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When an ActivityPub server receives an `Add` activity in its inbox, it MUST perform the authentication procedure according to [FEP-fe34]:
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- If `Add.object` is not embedded, fetch it. If location of the fetched activity has the same origin as `Add.object`, add it to the conversation.
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- If `Add.object` is embedded, check whether `Add.actor` and `Add.object.actor` have the same origin.
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- If origins are equal, add `Add.object` to the conversation.
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- If origins are different and [FEP-8b32] integrity proof is present, verify the proof. If the proof is valid, add `Add.object` to the conversation.
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- If integrity proof is not present, fetch `Add.object` by its `id`. If location of the fetched activity has the same origin as `Add.object.id`, add fetched activity to the conversation.
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>[!WARNING]
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>Sometimes activities have non-dereferenceable identifiers. That may prevent their authentication.
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## Examples
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Example of an `Add` activity for a reply to a followers-only post:
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```json
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{
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"@context": [
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"https://www.w3.org/ns/activitystreams"
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],
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"type": "Add",
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"id": "https://alice.example/activities/add/1",
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"actor": "https://alice.example/actors/1",
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"object": {
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"@context": [
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"https://www.w3.org/ns/activitystreams"
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],
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"type": "Create",
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"id": "https://bob.example/activities/create/1",
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"actor": "https://bob.example/actors/1",
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"context": "https://alice.example/contexts/1",
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"object": {
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"@context": [
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"https://www.w3.org/ns/activitystreams"
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],
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"type": "Note",
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"id": "https://bob.example/posts/1",
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"inReplyTo": "https://alice.example/posts/1",
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"content": "This is a reply",
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"to": [
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"https://alice.example/actors/1",
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"https://alice.example/actors/1/followers"
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]
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},
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"to": [
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"https://alice.example/actors/1",
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"https://alice.example/actors/1/followers"
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]
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},
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"target": {
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"type": "OrderedCollection",
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"id": "https://alice.example/contexts/1",
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"attributedTo": "https://alice.example/actors/1"
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},
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"to": [
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"https://bob.example/actors/1",
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"https://alice.example/actors/1/followers"
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]
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}
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```
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Example of a container of a followers-only conversation:
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```json
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{
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"@context": [
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"https://www.w3.org/ns/activitystreams"
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],
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"type": "OrderedCollection",
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"id": "https://alice.example/contexts/1",
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"attributedTo": "https://alice.example/actors/1",
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"orderedItems": [
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"https://alice.example/activities/add/1"
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]
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}
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```
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## Comparison with other proposals
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- [FEP-400e]: The `object` of `Add` is an object, not an activity, and conversation collection contains added objects. `Reject(Create)` activity is generated for rejected posts. Conversation participants are expected to add a `target` property to posts.
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- [FEP-1b12](https://codeberg.org/fediverse/fep/src/branch/main/fep/1b12/fep-1b12.md): `Announce` activity is used instead of `Add`. Conversation and related activities are synchronized between participants, but conversation backfilling mechanism is not specified.
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- [GoToSocial Interaction Policy](https://docs.gotosocial.org/en/latest/federation/posts/#interaction-policy): conversation is managed separately for each post (in a conversation container the owner has authority over the entire thread). `Accept` or `Reject` activity is generated for every interaction (in a conversation container `Add` activity is generated when activity is approved, and rejected activities are ignored). Conversation is not synchronized between participants, but can be backfilled by recursively fetching `replies` collections.
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## Implementations
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- [Streams](https://codeberg.org/streams/streams)
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## References
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- Christine Lemmer Webber, Jessica Tallon, [ActivityPub], 2018
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- Mike Macgirvin, [Containers], 2024
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- S. Bradner, [Key words for use in RFCs to Indicate Requirement Levels][RFC-2119], 1997
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- Gregory Klyushnikov, [FEP-400e: Publicly-appendable ActivityPub collections][FEP-400e], 2021
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- a, [FEP-7888: Demystifying the context property][FEP-7888], 2023
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- silverpill, [FEP-e232: Object Links][FEP-e232], 2022
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- silverpill, [FEP-fe34: Origin-based security model][FEP-fe34], 2024
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- silverpill, [FEP-8b32: Object Integrity Proofs][FEP-8b32], 2022
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[ActivityPub]: https://www.w3.org/TR/activitypub/
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[Containers]: https://fediversity.site/help/develop/en/Containers
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[RFC-2119]: https://tools.ietf.org/html/rfc2119.html
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[FEP-400e]: https://codeberg.org/fediverse/fep/src/branch/main/fep/400e/fep-400e.md
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[FEP-7888]: https://codeberg.org/fediverse/fep/src/branch/main/fep/7888/fep-7888.md
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[FEP-e232]: https://codeberg.org/fediverse/fep/src/branch/main/fep/e232/fep-e232.md
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[FEP-fe34]: https://codeberg.org/fediverse/fep/src/branch/main/fep/fe34/fep-fe34.md
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[FEP-8b32]: https://codeberg.org/fediverse/fep/src/branch/main/fep/8b32/fep-8b32.md
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## Copyright
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CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
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To the extent possible under law, the authors of this Fediverse Enhancement Proposal have waived all copyright and related or neighboring rights to this work.
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