Document the streaming endpoint

docs/development/API/differences_in_mastoapi_responses.md

@@ -357,6 +357,122 @@ The message payload consist of:
   - `follower_count`: follower count
   - `following_count`: following count
 
+### Authenticating via `sec-websocket-protocol` header
+
+Pleroma allows to authenticate via the `sec-websocket-protocol` header, for example, if your access token is `your-access-token`, you can authenticate using the following:
+
+```
+sec-websocket-protocol: your-access-token
+```
+
+### Authenticating after connection via `pleroma:authenticate` event
+
+Pleroma allows to authenticate after connection is established, via the `pleroma:authenticate` event. For example, if your access token is `your-access-token`, you can send the following after the connection is established:
+
+```
+{"type": "pleroma:authenticate", "token": "your-access-token"}
+```
+
+### Response to client-sent events
+
+Pleroma will respond to client-sent events that it recognizes. Supported event types are:
+
+- `subscribe`
+- `unsubscribe`
+- `pleroma:authenticate`
+
+The reply will be in the following format:
+
+```
+{
+  "event": "pleroma:respond",
+  "payload": "{\"type\": \"<type of the client-sent event>\", \"result\": \"<result of the action>\", \"error\": \"<error code>\"}"
+}
+```
+
+Result of the action can be either `success`, `ignored` or `error`. If it is `error`, the `error` property will contain the error code. Otherwise, the `error` property will not be present. Below are some examples:
+
+```
+{
+  "event": "pleroma:respond",
+  "payload": "{\"type\": \"pleroma:authenticate\", \"result\": \"success\"}"
+}
+
+{
+  "event": "pleroma:respond",
+  "payload": "{\"type\": \"subscribe\", \"result\": \"ignored\"}"
+}
+
+{
+  "event": "pleroma:respond",
+  "payload": "{\"type\": \"unsubscribe\", \"result\": \"error\", \"error\": \"bad_topic\"}"
+}
+```
+
+If the sent event is not of a type that Pleroma supports, it will not reply.
+
+### The `stream` attribute of a server-sent event
+
+Technically, this is in Mastodon, but its documentation does nothing to specify its format.
+
+This attribute appears on every event type except `pleroma:respond` and `delete`. It helps clients determine where they should display the new statuses.
+
+The value of the attribute is an array containing one or two elements. The first element is the type of the stream. The second is the identifier related to that specific stream, if applicable.
+
+For the following stream types, there is a second element in the array:
+
+- `list`: The second element is the id of the list.
+- `hashtag`: The second element is the name of the hashtag.
+- `public:remote:media` and `public:remote`: The second element is the domain of the corresponding instance.
+
+For all other stream types, there is no second element.
+
+Some examples of valid `stream` values:
+
+- `list:1`: List of id 1.
+- `hashtag:mew`: The hashtag #mew.
+- `user:notifications`: Notifications for the current user.
+- `user`: Home timeline.
+- `public:remote:mew.moe`: Public posts from the instance mew.moe .
+
+### The unified streaming endpoint
+
+If you do not specify a stream to connect to when requesting `/api/v1/streaming`, you will enter a connection that subscribes to no streams. After the connection is established, you can authenticate and then subscribe to different streams.
+
+### List of supported streams
+
+Below is a list of supported streams by Pleroma. To make a single-stream WebSocket connection, append the string specified in "Query style" to the streaming endpoint url.
+To subscribe to a stream after the connection is established, merge the JSON object specified in "Subscribe style" with `{"type": "subscribe"}`. To unsubscribe, merge it with `{"type": "unsubscribe"}`.
+
+For example, to receive updates on the list 1, you can connect to `/api/v1/streaming/?stream=list&list=1`, or send
+
+```
+{"type": "subscribe", "stream": "list", "list": 1}
+```
+
+upon establishing the websocket connection.
+
+To unsubscribe to list 1, send
+
+```
+{"type": "unsubscribe", "stream": "list", "list": 1}
+```
+
+Note that if you specify a stream that requires a logged-in user in the query string (for example, `user` or `list`), you have to specify the access token when you are trying to establish the connection, i.e. in the query string or via the `sec-websocket-protocol` header.
+
+- `list`
+  - Query style: `?stream=list&list=<id>`
+  - Subscribe style: `{"stream": "list", "list": <id>}`
+- `public`, `public:local`, `public:media`, `public:local:media`, `user`, `user:pleroma_chat`, `user:notifications`, `direct`
+  - Query style: `?stream=<stream name>`
+  - Subscribe style: `{"stream": "<stream name>"}`
+- `hashtag`
+  - Query style: `?stream=hashtag&tag=<name>`
+  - Subscribe style: `{"stream": "hashtag", "tag": "<name>"}`
+- `public:remote`, `public:remote:media`
+  - Query style: `?stream=<stream name>&instance=<instance domain>`
+  - Subscribe style: `{"stream": "<stream name>", "instance": "<instance domain>"}`
+
 ## User muting and thread muting
 
 Both user muting and thread muting can be done for only a certain time by adding an `expires_in` parameter to the API calls and giving the expiration time in seconds.