You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
92 lines
3.8 KiB
Markdown
92 lines
3.8 KiB
Markdown
---
|
|
type: module
|
|
weight: 120
|
|
---
|
|
|
|
### Room History Visibility
|
|
|
|
This module adds support for controlling the visibility of previous
|
|
events in a room.
|
|
|
|
In all cases except `world_readable`, a user needs to join a room to
|
|
view events in that room. Once they have joined a room, they will gain
|
|
access to a subset of events in the room. How this subset is chosen is
|
|
controlled by the `m.room.history_visibility` event outlined below.
|
|
After a user has left a room, they may see any events which they were
|
|
allowed to see before they left the room, but no events received after
|
|
they left.
|
|
|
|
The four options for the `m.room.history_visibility` event are:
|
|
|
|
- `world_readable` - All events while this is the
|
|
`m.room.history_visibility` value may be shared by any participating
|
|
homeserver with anyone, regardless of whether they have ever joined
|
|
the room.
|
|
- `shared` - Previous events are always accessible to newly joined
|
|
members. All events in the room are accessible, even those sent when
|
|
the member was not a part of the room.
|
|
- `invited` - Events are accessible to newly joined members from the
|
|
point they were invited onwards. Events stop being accessible when
|
|
the member's state changes to something other than `invite` or
|
|
`join`.
|
|
- `joined` - Events are accessible to newly joined members from the
|
|
point they joined the room onwards. Events stop being accessible
|
|
when the member's state changes to something other than `join`.
|
|
|
|
{{% boxes/warning %}}
|
|
These options are applied at the point an event is *sent*. Checks are
|
|
performed with the state of the `m.room.history_visibility` event when
|
|
the event in question is added to the DAG. This means clients cannot
|
|
retrospectively choose to show or hide history to new users if the
|
|
setting at that time was more restrictive.
|
|
{{% /boxes/warning %}}
|
|
|
|
#### Events
|
|
|
|
{{m\_room\_history\_visibility\_event}}
|
|
|
|
#### Client behaviour
|
|
|
|
Clients that implement this module MUST present to the user the possible
|
|
options for setting history visibility when creating a room.
|
|
|
|
Clients may want to display a notice that their events may be read by
|
|
non-joined people if the value is set to `world_readable`.
|
|
|
|
#### Server behaviour
|
|
|
|
By default if no `history_visibility` is set, or if the value is not
|
|
understood, the visibility is assumed to be `shared`. The rules
|
|
governing whether a user is allowed to see an event depend on the state
|
|
of the room *at that event*.
|
|
|
|
1. If the `history_visibility` was set to `world_readable`, allow.
|
|
2. If the user's `membership` was `join`, allow.
|
|
3. If `history_visibility` was set to `shared`, and the user joined the
|
|
room at any point after the event was sent, allow.
|
|
4. If the user's `membership` was `invite`, and the
|
|
`history_visibility` was set to `invited`, allow.
|
|
5. Otherwise, deny.
|
|
|
|
For `m.room.history_visibility` events themselves, the user should be
|
|
allowed to see the event if the `history_visibility` before *or* after
|
|
the event would allow them to see it. (For example, a user should be
|
|
able to see `m.room.history_visibility` events which change the
|
|
`history_visibility` from `world_readable` to `joined` *or* from
|
|
`joined` to `world_readable`, even if that user was not a member of the
|
|
room.)
|
|
|
|
Likewise, for the user's own `m.room.member` events, the user should be
|
|
allowed to see the event if their `membership` before *or* after the
|
|
event would allow them to see it. (For example, a user can always see
|
|
`m.room.member` events which set their membership to `join`, or which
|
|
change their membership from `join` to any other value, even if
|
|
`history_visibility` is `joined`.)
|
|
|
|
#### Security considerations
|
|
|
|
The default value for `history_visibility` is `shared` for
|
|
backwards-compatibility reasons. Clients need to be aware that by not
|
|
setting this event they are exposing all of their room history to anyone
|
|
in the room.
|