Presence Events

PubNub triggers presence events as users come online or go offline from the application.

Subscription with Presence

You must create a subscription with Presence enabled to receive Presence events. For more information, refer to each SDK's Publish and Subscribe documentation.

Clients can receive these events directly or use webhooks to keep a user's online/offline status up to date. Use these events to keep track of active/inactive users and the total occupancy of the channel.

Presence webhooks

PubNub can invoke a REST endpoint on your server when presence events occur. For more information, refer to Events & Actions.

Presence Event Types​

There are five main types of presence events:

EventsDescription
join
Fires when a user subscribes to a channel.
leave
Fires when a user unsubscribes from a channel.
timeout
Fires when the subscriber doesn't make any activity on a channel in a given period of time. By default, this occurs after 300 seconds for most SDKs. This interval can be customized on the client using the presenceTimeout property (the name can differ depending on the SDK).

Also, you can configure the client to send heartbeat intervals (using the heartbeatInterval property) to ensure periodic pings to avoid timeouts by signaling active connections.
state-change
Fires anytime the user's state is changed.
interval
Fires in interval mode to provide an occupancy count and optionally include delta changes.

Add Presence Listeners​

Receiving presence events requires a Presence listener. Presence events will be received for all channels within a subscription to which you added the listener and enabled Presence events.

User ID / UUID

User ID is also referred to as UUID/uuid in some APIs and server responses but holds the value of the userId parameter you set during initialization.

Event DataDescription
action
The Presence event action type: join, leave, timeout, state-change, interval
channel
The channel on which the Presence action happened
occupancy
The total number of subscribers on the channel when the event occurred
uuid
The User ID of the client that published the message
timetoken
The timetoken when the Presence action took place (when PubNub published the event)
data
The state of the client that changed
subscription
The channel group or wildcard subscription pattern that the channel belongs to (if applicable)
subscription.addListener({
  presence: function (p) {
    const action = p.action; // Can be join, leave, timeout, state-change, or interval
    const channelName = p.channel; // Channel to which the message belongs
    const occupancy = p.occupancy; // Number of users subscribed to the channel
    const state = p.state; // User state
    const channelGroup = p.subscription; //  Channel group or wildcard subscription match, if any
    const publishTime = p.timestamp; // Publish timetoken
    const timetoken = p.timetoken; // Current timetoken
    const uuid = p.uuid; // UUIDs of users who are subscribed to the channel
  }
}

Subscribe to Presence Channel​

When you enable the receivePresenceEvents option (name may vary across SDKs), and subscribe to a channel, the SDK automatically subscribes you the relevant presence channels.

Presence channels are sister channels where presence events are published. If you don't wish to subscribe to all presence channels in your list, you can subscribe to individual channels by appending -pnpres to the channel name. For example, the presence channel for ch1 is ch1-pnpres.

Subscribe to presence channel only

If you wish to only subscribe to the presence channel and not the main channel (to avoid increasing its occupancy, for example), subscribe to the main channel's presence -pnpres channel.

Once you've created the subscription with the receivePresenceEvents param enabled, and added presence listeners, call subscribe() to receive presence events. Your client will now start receiving presence events in real time as users join and leave channels.

// create a subscription from a channel entity
const channel = pubnub.channel('channel_1')
const subscription1 = channel.subscription({ receivePresenceEvents: true });

// subscribe and start receiving real-time updates
subscription1.subscribe();

If you want to subscribe to a bunch of channels but only want to listen for presence events on some of them, you can create two subscription sets: one with the receivePresenceEvents option enabled for the channels you want to receive Presence updates, and one without the option for channels you don't want to receive the updates. For more information about subscription sets, refer to Subscription types.

Presence Event Modes​

The channel presence mode indicates when presence events are triggered for that channel. There are two modes: announce and interval. The mode is determined by the occupancy count (total actively subscribed clients on that channel) in relation to the Presence Announce Max setting on the Admin Portal.

This feature prevents high occupancy channels from becoming too noisy with presence events. If you require the announce mode to be in effect past 100 occupants, please contact PubNub Support.

Announce Mode​

If the channel occupancy is less than the Announce Max setting (defaults to 20), the channel is in announce mode. In this mode, join, leave, timeout and state-change events are sent to subscribed clients as and when they're triggered.

User ID / UUID

User ID is also referred to as UUID/uuid in some APIs and server responses but holds the value of the userId parameter you set during initialization.

{
  "action": "join",
  "channel": "chats.room1",
  "subscribedChannel": "chats.room1-pnpres",
  "timetoken": "15119466699655811",
  "occupancy": 2,
  "uuid": "user123",
  "timestamp": 1511946669
}

Interval Mode​

When a channel's occupancy exceeds the Announce Max setting, the channel goes into interval mode. In this mode, the join, leave, timeout events are replaced by an interval event which is sent every few seconds with the total occupancy on the channel. The Interval setting is also configurable for the settings page.

Triggering state-change events

The state-change events are always triggered regardless of which presence mode is active on a channel.

Presence Deltas​

Additionally, you can enable the Presence Deltas setting from the Admin Portal. When this flag is enabled, interval events will also include a list of clients (User IDs) that joined, left or timed-out since the last interval event. The following is a simple representation of a Presence Delta event payload.

{
  "action": "interval",
  "channel": "chats.megachat",
  "occupancy": 27,
  "join": ["user123","user88"],
  "leave": ["user20", "user11", "user14"],
  "timeout": ["user42"],
  "subscribedChannel": "chats.megachat-pnpres",
  "timestamp": 1511947739,
  "timetoken": "15119477396210903",
  "hereNowRefresh": false
}
Here now refresh flag

Both the Presence Deltas on a channel in Interval mode and the Presence Interval Webhooks behave similarly when the payload size exceeds the maximum limit.

If the presence delta data increases the payload beyond the maximum publish size (32KB), the excess data is removed, and a hereNowRefresh flag is included in the payload. This flag indicates that you should use the Here Now API to retrieve the list of currently active User IDs.

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