matrix-spec-proposals/content/client-server-api/modules/room_previews.md

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Room Previews

It is sometimes desirable to offer a preview of a room, where a user can "lurk" and read messages posted to the room, without joining the room. This can be particularly effective when combined with Guest Access.

Previews are implemented via the world_readable Room History Visibility. setting, along with a special version of the GET /events endpoint.

Client behaviour

A client wishing to view a room without joining it should call GET /rooms/:room_id/initialSync, followed by GET /events. Clients will need to do this in parallel for each room they wish to view.

Clients can of course also call other endpoints such as GET /rooms/:room_id/messages and GET /search to access events outside the /events stream.

{{peeking_events_cs_http_api}}

Server behaviour

For clients which have not joined a room, servers are required to only return events where the room state at the event had the m.room.history_visibility state event present with history_visibility value world_readable.

Security considerations

Clients may wish to display to their users that rooms which are world_readable may be showing messages to non-joined users. There is no way using this module to find out whether any non-joined guest users do see events in the room, or to list or count any lurking users.