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### Presence
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Each user has the concept of presence information. This encodes:
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- Whether the user is currently online
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- How recently the user was last active (as seen by the server)
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- Whether a given client considers the user to be currently idle
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- Arbitrary information about the user's current status (e.g. "in a
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meeting").
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This information is collated from both per-device (`online`, `idle`,
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`last_active`) and per-user (status) data, aggregated by the user's
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homeserver and transmitted as an `m.presence` event. Presence events are
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sent to interested parties where users share a room membership.
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User's presence state is represented by the `presence` key, which is an
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enum of one of the following:
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- `online` : The default state when the user is connected to an event
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stream.
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- `unavailable` : The user is not reachable at this time e.g. they are
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idle.
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- `offline` : The user is not connected to an event stream or is
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explicitly suppressing their profile information from being sent.
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#### Events
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{{% event-group group_name="m.presence" %}}
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#### Client behaviour
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Clients can manually set/get their presence using the HTTP APIs listed
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below.
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{{% http-api spec="client-server" api="presence" %}}
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##### Last active ago
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The server maintains a timestamp of the last time it saw a pro-active
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event from the user. A pro-active event may be sending a message to a
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room or changing presence state to `online`. This timestamp is presented
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via a key called `last_active_ago` which gives the relative number of
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milliseconds since the pro-active event.
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To reduce the number of presence updates sent to clients the server may
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include a `currently_active` boolean field when the presence state is
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`online`. When true, the server will not send further updates to the
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last active time until an update is sent to the client with either a)
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`currently_active` set to false or b) a presence state other than
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`online`. During this period clients must consider the user to be
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currently active, irrespective of the last active time.
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The last active time must be up to date whenever the server gives a
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presence event to the client. The `currently_active` mechanism should
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purely be used by servers to stop sending continuous presence updates,
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as opposed to disabling last active tracking entirely. Thus clients can
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fetch up to date last active times by explicitly requesting the presence
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for a given user.
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##### Idle timeout
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The server will automatically set a user's presence to `unavailable` if
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their last active time was over a threshold value (e.g. 5 minutes).
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Clients can manually set a user's presence to `unavailable`. Any
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activity that bumps the last active time on any of the user's clients
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will cause the server to automatically set their presence to `online`.
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#### Security considerations
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Presence information is shared with all users who share a room with the
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target user. In large public rooms this could be undesirable.
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