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Merge pull request #91 from matrix-org/module-history-vis

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History visibility module
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Kegsay 2015-10-15 11:02:24 +01:00
commit 3a2c8cd4b3
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2
specification/0-events.rst
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@ -26,8 +26,6 @@ prefixed with ``m.``
{{m_room_create_event}}
{{m_room_history_visibility_event}}
{{m_room_join_rules_event}}
{{m_room_member_event}}

62
specification/modules/history_visibility.rst
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@ -1,21 +1,54 @@
Room History Visibility
-----------------------
=======================
.. _module:history-visibility:
Whether a member of a room can see the events that happened in a room from
before they joined the room is controlled by the ``history_visibility`` key
of the ``m.room.history_visibility`` state event. The valid values for
``history_visibility`` are:
This module adds support for controlling the visibility of previous events in a
room.
- ``shared``
- ``invited``
- ``joined``
In all cases, 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 seen any events which they
were allowed to see before they left the room, but no events received after they
left.
By default if no ``history_visibility`` is set it is assumed to be ``shared``.
The three options for the ``m.room.history_visibility`` event are:
The rules governing whether a user is allowed to see an event depend solely on
the state of the room at that event:
- ``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`` - Previous 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`` - Previous 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``.
.. 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.
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.
Server behaviour
----------------
By default if no ``history_visibility`` is set the visibility is assumed to be
``shared``. The rules governing whether a user is allowed to see an event depend
solely on the state of the room *at that event*:
1. If the user was joined, allow.
2. If the user was invited and the ``history_visibility`` was set to
@ -24,3 +57,10 @@ the state of the room at that event:
was set to ``shared``, allow.
4. Otherwise, deny.
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.