Chats are a way to represent an IM-style conversation between two actors. They are not the same as direct messages and they are not `Status`es, even though they have a lot in common.
## Why Chats?
There are no 'visibility levels' in ActivityPub, their definition is purely a Mastodon convention. Direct Messaging between users on the fediverse has mostly been modeled by using ActivityPub addressing following Mastodon conventions on normal `Note` objects. In this case, a 'direct message' would be a message that has no followers addressed and also does not address the special public actor, but just the recipients in the `to` field. It would still be a `Note` and is presented with other `Note`s as a `Status` in the API.
This is an awkward setup for a few reasons:
- As DMs generally still follow the usual `Status` conventions, it is easy to accidentally pull somebody into a DM thread by mentioning them. (e.g. "I hate @badguy so much")
- It is possible to go from a publicly addressed `Status` to a DM reply, back to public, then to a 'followers only' reply, and so on. This can be become very confusing, as it is unclear which user can see which part of the conversation.
- The standard `Status` format of implicit addressing also leads to rather ugly results if you try to display the messages as a chat, because all the recipients are always mentioned by name in the message.
- As direct messages are posted with the same api call (and usually same frontend component) as public messages, accidentally making a public message private or vice versa can happen easily. Client bugs can also lead to this, accidentally making private messages public.
As a measure to improve this situation, the `Conversation` concept and related Pleroma extensions were introduced. While it made it possible to work around a few of the issues, many of the problems remained and it didn't see much adoption because it was too complicated to use correctly.
## Chats explained
For this reasons, Chats are a new and different entity, both in the API as well as in ActivityPub. A quick overview:
- Chats are meant to represent an instant message conversation between two actors. For now these are only 1-on-1 conversations, but the other actor can be a group in the future.
- Chat messages have the ActivityPub type `ChatMessage`. They are not `Note`s. Servers that don't understand them will just drop them.
- The only addressing allowed in `ChatMessage`s is one single ActivityPub actor in the `to` field.
- There's always only one Chat between two actors. If you start chatting with someone and later start a 'new' Chat, the old Chat will be continued.
-`ChatMessage`s are posted with a different api, making it very hard to accidentally send a message to the wrong person.
-`ChatMessage`s don't show up in the existing timelines.
- Chats can never go from private to public. They are always private between the two actors.
## Caveats
- Chats are NOT E2E encrypted (yet). Security is still the same as email.
In general, the way to send a `ChatMessage` is to first create a `Chat`, then post a message to that `Chat`. `Group`s will later be supported by making them a sub-type of `Account`.
This is the overview of using the API. The API is also documented via OpenAPI, so you can view it and play with it by pointing SwaggerUI or a similar OpenAPI tool to `https://yourinstance.tld/api/openapi`.
- idempotency_key: The copy of the `idempotency-key` HTTP request header that can be used for optimistic message sending. Included only during the first few minutes after the message creation.
There's a new `pleroma:chat_mention` notification, which has this form. It is not given out in the notifications endpoint by default, you need to explicitly request it with `include_types[]=pleroma:chat_mention`:
There is an additional `user:pleroma_chat` stream. Incoming chat messages will make the current chat be sent to this `user` stream. The `event` of an incoming chat message is `pleroma:chat_update`. The payload is the updated chat with the incoming chat message in the `last_message` field.
