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Presence

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Manage user presence and their status in a channel.

In Signaling solutions, it is often important to know a user's current online status. For example, in instant messaging, chat applications, and online collaboration tools, users need to see the availability of their contacts. This information is typically displayed as a status message or icon next to a user's name. Presence features in Signaling SDK enable you to monitor join, leave, and status change notifications for users in a channel. Using Presence, you can:

  • Get a list of users currently in a channel and their temporary status data.
  • Get a list of channels a specified user has joined or is subscribed to.
  • Get, set, or remove user statuses.
  • Receive real-time event notifications when users join or leave specified channels.
  • Receive user status change event notifications in real time.

Understand the tech

Presence provides real-time information about the availability, and the current status of users, for effective communication and collaboration. It enables you to retrieve a list of users in a channel, or to query the list of channels for a specific user. The following figure illustrates how you integrate presence features into your app.

Presence workflow

Prerequisites

Ensure that you have integrated the Signaling SDK in your project, and implemented the framework functionality from the SDK quickstart page.

Presence features require Signaling SDK version 2.2.0 or later.

Implement presence features

Using presence, you can implement the following features:

Get channel users

To obtain a list of online users in a channel, call getOnlineUsers. Depending on your parameter settings, this method returns a list of online user IDs in a channel and their temporary status data, or just the number of online users in the channel. You do not need to join a channel to call this method. This method is applicable to both message channels and stream channels. Use the channelType parameter to specify the channel type.

After obtaining the initial online users list, update it in real time through onPresenceEvent event notifications.

Refer to the following sample code to query the list of online users in a channel and their current status:

PresenceOptions options;
options.includeState = true;
options.includeUserId =true;

uint64_t requestId;
rtmClient->getPresence()->getOnlineUsers("channelName", RTM_CHANNEL_TYPE_MESSAGE, options, requestId);

After you call this method, the SDK triggers the onGetOnlineUsersResult callback to return the call result.

class RtmEventHandler : public IRtmEventHandler {
    void onGetOnlineUsersResult(const uint64_t requestId, const UserState *userStateList, const size_t count, const char *nextPage, RTM_ERROR_CODE errorCode) override {
        if (errorCode != RTM_ERROR_OK) {
            printf("getOnlineUsers failed error is %d reason is %s\n", errorCode, getErrorReason(errorCode));
        } else {
            printf("getOnlineUsers success\n");
            for (int i = 0 ;i < count; i++) {
                printf("user: %s\n", userStateList[i].userId);
                for (int j = 0 ; j < userStateList[i].statesCount; j++) {
                    printf("key: %s value: %s\n", userStateList[i].states[j].key, userStateList[i].states[j].value);
                }
            }
        }
    }
};

The getOnlineUsers method retrieves one page of data at a time. Each page contains up to 100 online users. If the channel has more than 100 users, the nextPage field in the returned result contains a bookmark for the next page. After each query, check if nextPage is not empty to determine if there is more data. To retrieve the next page, set the page field in PresenceOptions to the value of nextPage. Repeat this process until nextPage is null. Refer to the following code:

PresenceOptions options;
options.includeState = true;
options.includeUserId =true;
options.page = "your_Next_Page_Bookmark";

uint64_t requestId;
rtmClient->getPresence()->getOnlineUsers("channelName", RTM_CHANNEL_TYPE_MESSAGE, options, requestId);

When there is a large number of users in a channel, you may only care about the total number of online users, and not their identities or temporary status. To get the total channel occupancy, set includeState and includeUserId in PresenceOptions to false.

PresenceOptions options;
options.includeState = false;
options.includeUserId =false;

uint64_t requestId;
rtmClient->getPresence()->getOnlineUsers("channelName", RTM_CHANNEL_TYPE_MESSAGE, options, requestId);

In this case, only the totalOccupancy property in the result is valid while all other fields are empty.

You cannot set includeState to true and includeUserId to false at the same time. To get the temporary status of users, you must also retrieve their user IDs.

Get user channels

The getUserChannels method enables you to query which channels a user is currently in. This includes the message channels a user has subscribed to and the stream channels they have joined. This method is particularly useful for tracking user paths. Refer to the following sample code:

uint64_t requestId;
rtmClient->getPresence()->getUserChannels("tony", requestId);

After you call this method, the SDK triggers the onGetUserChannelsResult callback to return the call result.

class RtmEventHandler : public IRtmEventHandler {
    void onGetUserChannelsResult(const uint64_t requestId, const ChannelInfo *channels, const size_t count, RTM_ERROR_CODE errorCode) override {
        if (errorCode != RTM_ERROR_OK) {
            printf("getUserChannels failed error is %d reason is %s\n", errorCode, getErrorReason(errorCode));
        } else {
            printf("getUserChannels success\n");
            for (int i = 0; i < count; i++) {
                printf("channel: %s channel type: %d\n", channels[i].channelName, channels[i].channelType);
            }
        }
    }
};

The getUserChannels method returns complete query results about the channels and their types that the queried user is in, without pagination.

User status management

Signaling enables you to set and delete user status messages for the local user in each channel. The SDK notifies other online users in the channel of these changes through event notifications. This feature is useful in use-cases where user status sharing is required, such as real-time synchronization of the user's microphone status, mood, personal signature, score, and message input status.

Signaling does not permanently save the status data. When a user unsubscribes from a channel, times out, or exits a channel, the data is deleted. To save user data permanently, use the Store user metadata feature.

When a user's temporary status changes, Signaling triggers an RTM_PRESENCE_EVENT_TYPE_REMOTE_STATE_CHANGED event notification in real-time. Users who set withPresence = true when joining the channel, receive the event notification.

Set status

Using presence, you can set the temporary user status for the local user. When you set the status before subscribing to or joining a channel, the data is cached on the client and does not take effect immediately. The status is updated and corresponding event notifications are triggered when you subscribe to or join a channel. The setState method applies to both message and stream channels; use the channelType parameter to specify the channel type.

std::vector<StateItem> items;
StateItem item;
item.key = "Mode";
item.value = "Happy";
items.emplace_back(item);

uint64_t requestId;
rtm_client->getPresence()->setState("channelName", RTM_CHANNEL_TYPE_MESSAGE, items.data(), items.size(), requestId);

After you call this method, the SDK triggers the onPresenceSetStateResult callback to return the API call result.

class RtmEventHandler : public IRtmEventHandler {
    void onPresenceSetStateResult(const uint64_t requestId, RTM_ERROR_CODE errorCode) override {
        if (errorCode != RTM_ERROR_OK) {
            printf("SetState failed error is %d reason is %s\n", errorCode, getErrorReason(errorCode));
        } else {
            printf("SetState success\n");
        }
    }
};

When using setState to set temporary user status, if the specified key already exists, its value is overwritten by the new value. If the specified key does not exist, a new key/value pair is added.

Get status

To obtain the temporary user status set by a user in a specified channel, use the getState method:

uint64_t requestId;
rtm_client->getPresence()->getState("channelName", RTM_CHANNEL_TYPE_MESSAGE, "tony", requestId);

After you call this method, the SDK triggers the onPresenceGetStateResult callback to return the API call result.

class RtmEventHandler : public IRtmEventHandler {
    void onPresenceGetStateResult(const uint64_t requestId, const UserState &state, RTM_ERROR_CODE errorCode) override {
        if (errorCode != RTM_ERROR_OK) {
            printf("GetState failed error is %d reason is %s\n", errorCode, getErrorReason(errorCode));
        } else {
            printf("GetState user id: %s success\n", state.userId);
            for (int i = 0; i < state.statesCount; i++) {
                printf("key: %s, value: %s\n", state.states[i].key, state.states[i].value);
            }
        }
    }
};

Use the getState method to obtain the temporary status of other online users in the channel. If the queried user is not present in the specified channel, an error message is returned by the SDK.

Delete status

Each user can set up to 32 key/value pairs in a channel. To remove items that are no longer needed, call removeState with a list of keys. The removeState method only deletes temporary user status data for the local user.

std::vector<const char*> keys;
keys.push_back("Mode");
keys.push_back("Mic");

uint64_t requestId;
rtmClient->getPresence()->removeState("channelName", RTM_CHANNEL_TYPE_MESSAGE, keys.data(), keys.size(), requestId);

After you call this method, the SDK triggers the onPresenceRemoveStateResult callback to return the API call result.

class RtmEventHandler : public IRtmEventHandler {
void onPresenceRemoveStateResult(const uint64_t requestId, RTM_ERROR_CODE errorCode) override {
    if (errorCode != RTM_ERROR_OK) {
        printf("RemoveState failed error is %d reason is %s\n", errorCode, getErrorReason(errorCode));
    } else {
        printf("RemoveState success\n");
    }
}
};

Both the setState and removeState methods trigger RTM_PRESENCE_EVENT_TYPE_REMOTE_STATE_CHANGED event notifications. Users who join the channel with withPresence set to true receive event notifications containing full data of the user's temporary status.

Receive presence event notifications

A presence event notification returns the PresenceEvent data structure, which includes the RTM_PRESENCE_EVENT_TYPE. parameter.

To receive presence event notifications, implement an event listener. See event listeners for details. In addition, set the withPresence parameter to true when subscribing to or joining a channel.

Event notification modes

The presence event notification mode determines how subscribed users receive event notifications. There are two notification modes:

  • Announce: Real-time notification mode
  • Interval: Scheduled notification mode

You set the Max number of instant event value in Agora Console to specify the condition for switching between the two modes. The scheduled notification mode helps prevent event noise that results from a large number of online users in the channel. See Presence configuration for details.

Real-time notification mode

If the number of instant notifications in the channel is less than the Max number of instant event value, presence event notifications operate in real-time notification mode. In this mode, RTM_PRESENCE_EVENT_TYPE_REMOTE_JOIN_CHANNEL, RTM_PRESENCE_EVENT_TYPE_REMOTE_LEAVE_CHANNEL, RTM_PRESENCE_EVENT_TYPE_REMOTE_TIMEOUT, and RTM_PRESENCE_EVENT_TYPE_REMOTE_STATE_CHANGED notifications are sent to the client in real-time.

{
      type: RTM_PRESENCE_EVENT_TYPE_REMOTE_JOIN_CHANNEL;
      channelType: RTM_CHANNEL_TYPE_MESSAGE;
      channelName: "test_channel";
      publisher: "publisher_name";
      states: [];
      interval: [];
      snapshot: [];
      timestamp: 1710487149497;
}

Scheduled notification mode

When the number of online users in the channel exceeds the Max number of instant event value, the channel switches to the scheduled notification mode. In this mode, RTM_PRESENCE_EVENT_TYPE_REMOTE_JOIN_CHANNEL, RTM_PRESENCE_EVENT_TYPE_REMOTE_LEAVE_CHANNEL, RTM_PRESENCE_EVENT_TYPE_REMOTE_TIMEOUT, and RTM_PRESENCE_EVENT_TYPE_REMOTE_STATE_CHANGED events are replaced by RTM_PRESENCE_EVENT_TYPE_INTERVAL events and sent to all users in the channel at specific time intervals. Users receive the following notification:

{
      "type": "RTM_PRESENCE_EVENT_TYPE_INTERVAL",
      "channelType": "RTM_CHANNEL_TYPE_MESSAGE",
      "channelName": "Chat_room",
      "publisher": "Tony",
      "interval": {
          "remote_join": ["Tony", "Lily"],
          "remote_leave": ["Jason"],
          "remote_timeout": ["Wendy"],
          "remote_state_change": [
              {
                  "userId": "Harvard",
                  "states": [
                      { "Mic": "False" },
                      { "Position": "Washington" }
                  ]
              },
              {
                  "userId": "Harvard",
                  "states": [
                      { "Mic": "False" },
                      { "Position": "Washington" }
                  ]
              }
          ]
      },
      "snapshot": {
          "userStateList": []
      },
      "timestamp": 1710487149497
}

Reference

This section contains content that completes the information on this page, or points you to documentation that explains other aspects to this product.

API reference

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