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43 lines
1.6 KiB
Markdown
43 lines
1.6 KiB
Markdown
4 years ago
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---
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type: module
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weight: 170
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---
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### Room Previews
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It is sometimes desirable to offer a preview of a room, where a user can
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"lurk" and read messages posted to the room, without joining the room.
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This can be particularly effective when combined with [Guest Access]().
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Previews are implemented via the `world_readable` [Room History
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Visibility](). setting, along with a special version of the [GET
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/events](#get-matrix-client-%CLIENT_MAJOR_VERSION%-events) endpoint.
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#### Client behaviour
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A client wishing to view a room without joining it should call [GET
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/rooms/:room\_id/initialSync](#get-matrix-client-%CLIENT_MAJOR_VERSION%-rooms-roomid-initialsync),
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followed by [GET /events](#peeking_events_api). Clients will need to do
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this in parallel for each room they wish to view.
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Clients can of course also call other endpoints such as [GET
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/rooms/:room\_id/messages](#get-matrix-client-%CLIENT_MAJOR_VERSION%-rooms-roomid-messages)
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and [GET /search](#get-matrix-client-%CLIENT_MAJOR_VERSION%-search) to
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access events outside the `/events` stream.
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{{peeking\_events\_cs\_http\_api}}
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#### Server behaviour
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For clients which have not joined a room, servers are required to only
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return events where the room state at the event had the
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`m.room.history_visibility` state event present with
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`history_visibility` value `world_readable`.
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#### Security considerations
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Clients may wish to display to their users that rooms which are
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`world_readable` *may* be showing messages to non-joined users. There is
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no way using this module to find out whether any non-joined guest users
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*do* see events in the room, or to list or count any lurking users.
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