friends connection status system

src-common/src/lib.rs

@@ -31,6 +31,7 @@ pub enum ClientMessage {
         signature: String,
     },
     SyncFriendProfiles,
+    SyncFriendStatuses,
     Signed {
         payload: String,
         signature: String,
@@ -106,6 +107,13 @@ pub enum ServerMessage {
     FriendProfiles {
         profiles: Vec<Profile>,
     },
+    FriendStatusChanged {
+        friend_id: String,
+        online: bool,
+    },
+    FriendStatuses {
+        friend_ids: Vec<String>,
+    },
     FriendLiveData {
         friend_id: String,
         payload: String,

src-server/src/network/interactions.rs

@@ -10,7 +10,7 @@ use wyd_common::{
     MAX_INTERACTION_PAYLOAD_BYTES, ServerMessage, interaction_bytes,
 };
 
-use super::{Clients, verify};
+use super::{Clients, are_mutual_friends, verify};
 
 pub(super) async fn relay(
     clients: &Clients,
@@ -28,10 +28,7 @@ pub(super) async fn relay(
             .filter(|client| client.connection_id == connection_id)?;
         let recipient = clients
             .get(recipient_id)
-            .filter(|recipient| {
+            .filter(|recipient| are_mutual_friends(public_key, source, recipient_id, recipient))
-                source.friends.iter().any(|friend| friend == recipient_id)
-                    && recipient.friends.iter().any(|friend| friend == public_key)
-            })
             .map(|recipient| recipient.sender.clone());
         (source.key, recipient)
     };

src-server/src/network/mod.rs

@@ -14,11 +14,11 @@ use futures_util::{SinkExt, StreamExt};
 use tokio::sync::{Mutex, mpsc};
 use uuid::Uuid;
 use wyd_common::{
-    ClientMessage, Profile, ServerMessage, friends_bytes, message_bytes, profile_bytes,
+    ClientMessage, Profile, ServerMessage, message_bytes, profile_bytes, register_bytes,
-    register_bytes,
 };
 
 mod interactions;
+mod presence;
 
 type Clients = Arc<Mutex<HashMap<String, Client>>>;
 
@@ -31,6 +31,11 @@ struct Client {
     sender: mpsc::Sender<Message>,
 }
 
+fn are_mutual_friends(source_id: &str, source: &Client, friend_id: &str, friend: &Client) -> bool {
+    source.friends.iter().any(|id| id == friend_id)
+        && friend.friends.iter().any(|id| id == source_id)
+}
+
 pub fn routes() -> Router {
     Router::new()
         .route("/v1/ws", get(upgrade))
@@ -79,7 +84,10 @@ async fn connected(mut socket: WebSocket, clients: Clients) {
     let connection_id = Uuid::new_v4();
     let public_key = profile.id.clone();
     let (sender, mut outgoing) = mpsc::channel(32);
-    clients.lock().await.insert(
+    let previous_friends = clients
+        .lock()
+        .await
+        .insert(
             public_key.clone(),
             Client {
                 connection_id,
@@ -88,11 +96,13 @@ async fn connected(mut socket: WebSocket, clients: Clients) {
                 friends,
                 sender,
             },
-    );
+        )
+        .map(|client| client.friends);
     if send(&mut socket, &ServerMessage::Registered).await.is_err() {
-        remove(&clients, &public_key, connection_id).await;
+        presence::disconnected(&clients, &public_key, connection_id).await;
         return;
     }
+    presence::connected(&clients, &public_key, previous_friends).await;
 
     let (mut writer, mut reader) = socket.split();
     let mut ping = tokio::time::interval(Duration::from_secs(20));
@@ -143,7 +153,17 @@ async fn connected(mut socket: WebSocket, clients: Clients) {
                         }
                     }
                     Ok(ClientMessage::FriendsUpdated { friends, signature }) => {
-                        if !update_friends(&clients, &public_key, connection_id, friends, &signature).await {
+                        let Some(friend_ids) = presence::update_friends(
+                            &clients,
+                            &public_key,
+                            connection_id,
+                            friends,
+                            &signature,
+                        ).await else {
+                            break;
+                        };
+                        let message = ServerMessage::FriendStatuses { friend_ids };
+                        if writer.send(Message::Text(serde_json::to_string(&message).unwrap().into())).await.is_err() {
                             break;
                         }
                     }
@@ -156,6 +176,15 @@ async fn connected(mut socket: WebSocket, clients: Clients) {
                             break;
                         }
                     }
+                    Ok(ClientMessage::SyncFriendStatuses) => {
+                        let Some(friend_ids) = presence::snapshot(&clients, &public_key, connection_id).await else {
+                            break;
+                        };
+                        let message = ServerMessage::FriendStatuses { friend_ids };
+                        if writer.send(Message::Text(serde_json::to_string(&message).unwrap().into())).await.is_err() {
+                            break;
+                        }
+                    }
                     _ => break,
                 }
                 Some(Ok(Message::Ping(data))) => {
@@ -167,7 +196,7 @@ async fn connected(mut socket: WebSocket, clients: Clients) {
         }
     }
 
-    remove(&clients, &public_key, connection_id).await;
+    presence::disconnected(&clients, &public_key, connection_id).await;
 }
 
 async fn update_profile(
@@ -209,27 +238,6 @@ async fn update_profile(
     true
 }
 
-async fn update_friends(
-    clients: &Clients,
-    public_key: &str,
-    connection_id: Uuid,
-    friends: Vec<String>,
-    signature: &str,
-) -> bool {
-    let mut clients = clients.lock().await;
-    let Some(client) = clients
-        .get_mut(public_key)
-        .filter(|client| client.connection_id == connection_id)
-    else {
-        return false;
-    };
-    if !verify(&client.key, &friends_bytes(&friends), signature) {
-        return false;
-    }
-    client.friends = friends;
-    true
-}
-
 async fn friend_profiles(
     clients: &Clients,
     public_key: &str,
@@ -270,8 +278,7 @@ async fn relay_live_data(
         .iter()
         .filter(|(recipient_id, recipient)| {
             recipient_id.as_str() != public_key
-                && source.friends.iter().any(|friend| friend == *recipient_id)
+                && are_mutual_friends(public_key, source, recipient_id, recipient)
-                && recipient.friends.iter().any(|friend| friend == public_key)
         })
         .map(|(_, recipient)| recipient.sender.clone())
         .collect();
@@ -291,16 +298,6 @@ async fn relay_live_data(
     true
 }
 
-async fn remove(clients: &Clients, public_key: &str, connection_id: Uuid) {
-    let mut clients = clients.lock().await;
-    if clients
-        .get(public_key)
-        .is_some_and(|client| client.connection_id == connection_id)
-    {
-        clients.remove(public_key);
-    }
-}
-
 async fn send(socket: &mut WebSocket, message: &ServerMessage) -> Result<(), axum::Error> {
     socket
         .send(Message::Text(
@@ -328,6 +325,7 @@ fn verify(key: &VerifyingKey, bytes: &[u8], signature: &str) -> bool {
 #[cfg(test)]
 mod tests {
     use ed25519_dalek::{Signer, SigningKey};
+    use wyd_common::friends_bytes;
 
     use super::*;
 
@@ -492,7 +490,7 @@ mod tests {
             URL_SAFE_NO_PAD.encode(signing_key.sign(&friends_bytes(&friends)).to_bytes());
 
         assert!(
-            update_friends(
+            presence::update_friends(
                 &clients,
                 &public_key,
                 connection_id,
@@ -500,6 +498,7 @@ mod tests {
                 &signature,
             )
             .await
+            .is_some()
         );
         assert_eq!(
             clients.lock().await.get(&public_key).unwrap().friends,
@@ -565,6 +564,108 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    async fn presence_sync_and_disconnect_broadcast_require_mutual_friendship() {
+        let signing_key = SigningKey::from_bytes(&[7; 32]);
+        let connection_id = Uuid::new_v4();
+        let (source_sender, _source_receiver) = mpsc::channel(4);
+        let (mutual_sender, mut mutual_receiver) = mpsc::channel(4);
+        let (one_way_sender, mut one_way_receiver) = mpsc::channel(4);
+        let clients = Clients::default();
+        let mut registry = clients.lock().await;
+        registry.insert(
+            "source".to_owned(),
+            Client {
+                connection_id,
+                key: signing_key.verifying_key(),
+                profile: Profile {
+                    id: "source".to_owned(),
+                    display_name: "Source".to_owned(),
+                },
+                friends: vec!["mutual".to_owned()],
+                sender: source_sender,
+            },
+        );
+        registry.insert(
+            "mutual".to_owned(),
+            Client {
+                connection_id: Uuid::new_v4(),
+                key: signing_key.verifying_key(),
+                profile: Profile {
+                    id: "mutual".to_owned(),
+                    display_name: "Mutual".to_owned(),
+                },
+                friends: vec!["source".to_owned()],
+                sender: mutual_sender,
+            },
+        );
+        registry.insert(
+            "one-way".to_owned(),
+            Client {
+                connection_id: Uuid::new_v4(),
+                key: signing_key.verifying_key(),
+                profile: Profile {
+                    id: "one-way".to_owned(),
+                    display_name: "One way".to_owned(),
+                },
+                friends: vec!["source".to_owned()],
+                sender: one_way_sender,
+            },
+        );
+        drop(registry);
+
+        assert_eq!(
+            presence::snapshot(&clients, "source", connection_id)
+                .await
+                .expect("current session"),
+            ["mutual"]
+        );
+        assert!(
+            presence::snapshot(&clients, "source", Uuid::new_v4())
+                .await
+                .is_none()
+        );
+
+        presence::broadcast_status(&clients, "source", true).await;
+        assert_friend_status(mutual_receiver.recv().await, "source", true);
+        assert!(one_way_receiver.try_recv().is_err());
+
+        let no_friends = Vec::new();
+        let signature =
+            URL_SAFE_NO_PAD.encode(signing_key.sign(&friends_bytes(&no_friends)).to_bytes());
+        assert_eq!(
+            presence::update_friends(&clients, "source", connection_id, no_friends, &signature,)
+                .await,
+            Some(Vec::new())
+        );
+        assert_friend_status(mutual_receiver.recv().await, "source", false);
+
+        let mutual_friends = vec!["mutual".to_owned()];
+        let signature =
+            URL_SAFE_NO_PAD.encode(signing_key.sign(&friends_bytes(&mutual_friends)).to_bytes());
+        assert_eq!(
+            presence::update_friends(
+                &clients,
+                "source",
+                connection_id,
+                mutual_friends,
+                &signature,
+            )
+            .await,
+            Some(vec!["mutual".to_owned()])
+        );
+        assert_friend_status(mutual_receiver.recv().await, "source", true);
+
+        presence::disconnected(&clients, "source", Uuid::new_v4()).await;
+        assert!(clients.lock().await.contains_key("source"));
+        assert!(mutual_receiver.try_recv().is_err());
+
+        presence::disconnected(&clients, "source", connection_id).await;
+        assert_friend_status(mutual_receiver.recv().await, "source", false);
+        assert!(one_way_receiver.try_recv().is_err());
+        assert!(!clients.lock().await.contains_key("source"));
+    }
+
     #[tokio::test]
     async fn live_data_relay_requires_valid_session_signature_and_mutual_friendship() {
         let signing_key = SigningKey::from_bytes(&[7; 32]);
@@ -669,4 +770,17 @@ mod tests {
         );
         assert!(mutual_receiver.try_recv().is_err());
     }
+
+    fn assert_friend_status(message: Option<Message>, expected_id: &str, expected_online: bool) {
+        let Message::Text(message) = message.expect("friend receives status") else {
+            panic!("expected text status");
+        };
+        let ServerMessage::FriendStatusChanged { friend_id, online } =
+            serde_json::from_str(&message).expect("decode friend status")
+        else {
+            panic!("expected friend status");
+        };
+        assert_eq!(friend_id, expected_id);
+        assert_eq!(online, expected_online);
+    }
 }

src-server/src/network/presence.rs

@@ -0,0 +1,179 @@
+use axum::extract::ws::Message;
+use tokio::sync::mpsc;
+use uuid::Uuid;
+use wyd_common::{ServerMessage, friends_bytes};
+
+use super::{Clients, are_mutual_friends, verify};
+
+pub(super) async fn connected(
+    clients: &Clients,
+    public_key: &str,
+    previous_friends: Option<Vec<String>>,
+) {
+    if let Some(previous_friends) = previous_friends {
+        broadcast_friendship_changes(clients, public_key, &previous_friends).await;
+    } else {
+        broadcast_status(clients, public_key, true).await;
+    }
+}
+
+pub(super) async fn update_friends(
+    clients: &Clients,
+    public_key: &str,
+    connection_id: Uuid,
+    friends: Vec<String>,
+    signature: &str,
+) -> Option<Vec<String>> {
+    let mut clients = clients.lock().await;
+    let previous_friends = {
+        let client = clients
+            .get_mut(public_key)
+            .filter(|client| client.connection_id == connection_id)?;
+        if !verify(&client.key, &friends_bytes(&friends), signature) {
+            return None;
+        }
+        std::mem::replace(&mut client.friends, friends.clone())
+    };
+
+    let mut notifications = Vec::new();
+    let mut online_friend_ids = Vec::new();
+    for (friend_id, friend) in clients.iter().filter(|(id, _)| id.as_str() != public_key) {
+        let was_visible = mutual_friends(public_key, &previous_friends, friend_id, &friend.friends);
+        let is_visible = mutual_friends(public_key, &friends, friend_id, &friend.friends);
+        if is_visible {
+            online_friend_ids.push(friend_id.clone());
+        }
+        if was_visible != is_visible {
+            notifications.push((friend.sender.clone(), public_key.to_owned(), is_visible));
+        }
+    }
+    drop(clients);
+
+    send_notifications(notifications).await;
+    online_friend_ids.sort_unstable();
+    Some(online_friend_ids)
+}
+
+pub(super) async fn snapshot(
+    clients: &Clients,
+    public_key: &str,
+    connection_id: Uuid,
+) -> Option<Vec<String>> {
+    let clients = clients.lock().await;
+    let source = clients
+        .get(public_key)
+        .filter(|client| client.connection_id == connection_id)?;
+    let mut friend_ids = clients
+        .iter()
+        .filter(|(friend_id, friend)| {
+            friend_id.as_str() != public_key && visible_to(public_key, source, friend_id, friend)
+        })
+        .map(|(friend_id, _)| friend_id.clone())
+        .collect::<Vec<_>>();
+    friend_ids.sort_unstable();
+    Some(friend_ids)
+}
+
+pub(super) async fn broadcast_status(clients: &Clients, public_key: &str, online: bool) {
+    let recipients = {
+        let clients = clients.lock().await;
+        let Some(source) = clients.get(public_key) else {
+            return;
+        };
+        clients
+            .iter()
+            .filter(|(friend_id, friend)| {
+                friend_id.as_str() != public_key
+                    && visible_to(public_key, source, friend_id, friend)
+            })
+            .map(|(_, friend)| friend.sender.clone())
+            .collect::<Vec<_>>()
+    };
+    let message = status_message(public_key.to_owned(), online);
+    for recipient in recipients {
+        let _ = recipient.send(message.clone()).await;
+    }
+}
+
+pub(super) async fn disconnected(clients: &Clients, public_key: &str, connection_id: Uuid) {
+    let recipients = {
+        let mut clients = clients.lock().await;
+        if !clients
+            .get(public_key)
+            .is_some_and(|client| client.connection_id == connection_id)
+        {
+            return;
+        }
+        let source = clients
+            .remove(public_key)
+            .expect("checked registered client");
+        clients
+            .iter()
+            .filter(|(friend_id, friend)| visible_to(public_key, &source, friend_id, friend))
+            .map(|(_, friend)| friend.sender.clone())
+            .collect::<Vec<_>>()
+    };
+    let message = status_message(public_key.to_owned(), false);
+    for recipient in recipients {
+        let _ = recipient.send(message.clone()).await;
+    }
+}
+
+async fn broadcast_friendship_changes(
+    clients: &Clients,
+    public_key: &str,
+    previous_friends: &[String],
+) {
+    let notifications = {
+        let clients = clients.lock().await;
+        let Some(source) = clients.get(public_key) else {
+            return;
+        };
+        clients
+            .iter()
+            .filter(|(friend_id, _)| friend_id.as_str() != public_key)
+            .filter_map(|(friend_id, friend)| {
+                let was_visible =
+                    mutual_friends(public_key, previous_friends, friend_id, &friend.friends);
+                let is_visible = visible_to(public_key, source, friend_id, friend);
+                (was_visible != is_visible)
+                    .then(|| (friend.sender.clone(), public_key.to_owned(), is_visible))
+            })
+            .collect::<Vec<_>>()
+    };
+    send_notifications(notifications).await;
+}
+
+async fn send_notifications(notifications: Vec<(mpsc::Sender<Message>, String, bool)>) {
+    for (recipient, friend_id, online) in notifications {
+        let _ = recipient.send(status_message(friend_id, online)).await;
+    }
+}
+
+fn visible_to(
+    source_id: &str,
+    source: &super::Client,
+    viewer_id: &str,
+    viewer: &super::Client,
+) -> bool {
+    // Apply the source profile's per-friend online-visibility preference here.
+    are_mutual_friends(source_id, source, viewer_id, viewer)
+}
+
+fn mutual_friends(
+    source_id: &str,
+    source_friends: &[String],
+    viewer_id: &str,
+    viewer_friends: &[String],
+) -> bool {
+    source_friends.iter().any(|friend| friend == viewer_id)
+        && viewer_friends.iter().any(|friend| friend == source_id)
+}
+
+fn status_message(friend_id: String, online: bool) -> Message {
+    Message::Text(
+        serde_json::to_string(&ServerMessage::FriendStatusChanged { friend_id, online })
+            .expect("friend status serializes")
+            .into(),
+    )
+}

src-tauri/src/cursor/mod.rs

@@ -46,6 +46,16 @@ impl CursorState {
         positions_by_user.insert(user_id, positions);
         Ok(positions_by_user.clone())
     }
+
+    fn remove(
+        &self,
+        user_ids: &[String],
+    ) -> Result<Option<HashMap<String, CursorPositions>>, String> {
+        let mut positions_by_user = self.0.write().map_err(|error| error.to_string())?;
+        let previous_len = positions_by_user.len();
+        positions_by_user.retain(|user_id, _| !user_ids.contains(user_id));
+        Ok((positions_by_user.len() != previous_len).then(|| positions_by_user.clone()))
+    }
 }
 
 // Was private, but for some reason LSP
@@ -125,6 +135,23 @@ pub(crate) fn emit_position(handle: &AppHandle, user_id: String, positions: Curs
     }
 }
 
+pub(crate) fn remove_positions(handle: &AppHandle, user_ids: &[String]) {
+    if user_ids.is_empty() {
+        return;
+    }
+    let positions = match handle.state::<CursorState>().remove(user_ids) {
+        Ok(Some(positions)) => positions,
+        Ok(None) => return,
+        Err(error) => {
+            eprintln!("Failed to remove offline cursor positions: {error}");
+            return;
+        }
+    };
+    if let Err(error) = (CursorPositionChanged { positions }).emit(handle) {
+        eprintln!("Failed to emit cursor position removal: {error}");
+    }
+}
+
 /// Convert absolute to normalized coordinates (0.12, 0.78), or normalized to absolute (1234, 567)
 pub fn transform_cursor_pos(
     pos: &CursorPosition,
@@ -181,6 +208,13 @@ mod tests {
         let snapshot = state.update("local".to_owned(), positions(3.0)).unwrap();
         assert_eq!(snapshot.len(), 2);
         assert_eq!(snapshot["local"].raw.x, 3.0);
+
+        let snapshot = state
+            .remove(&["friend".to_owned()])
+            .unwrap()
+            .expect("friend cursor removed");
+        assert_eq!(snapshot.keys().collect::<Vec<_>>(), ["local"]);
+        assert!(state.remove(&["missing".to_owned()]).unwrap().is_none());
     }
 
     #[test]

src-tauri/src/lib.rs

@@ -71,6 +71,7 @@ fn specta_builder() -> tauri_specta::Builder<tauri::Wry> {
             profile::update_profile,
             keypair::get_public_key,
             network::list_statuses,
+            network::list_friend_statuses,
             images::pick_and_send_image,
             images::send_image_bytes,
             interactions::send_interaction,
@@ -81,6 +82,7 @@ fn specta_builder() -> tauri_specta::Builder<tauri::Wry> {
             remotes::RemotesChanged,
             profile::ProfileChanged,
             network::NetworkStatusChanged,
+            network::FriendStatusesChanged,
             cursor::CursorPositionChanged,
             ufa::ForegroundAppChanged,
             ufa::FriendForegroundAppChanged,

src-tauri/src/network/mod.rs

@@ -23,6 +23,10 @@ use crate::keypair::AppKeypair;
 use crate::live_data::LiveData;
 use crate::remotes::{self, Remote, RemotesChanged};
 
+mod presence;
+
+use presence::{Change as FriendPresenceChange, FriendPresence};
+
 type Statuses = Arc<Mutex<HashMap<String, (u64, ConnectionStatus)>>>;
 
 #[derive(Debug, Clone, Serialize, Deserialize, Type)]
@@ -48,6 +52,12 @@ pub struct NetworkStatusChanged {
     pub statuses: Vec<ConnectionStatus>,
 }
 
+#[derive(Debug, Clone, Serialize, Deserialize, Type, Event)]
+#[serde(rename_all = "camelCase")]
+pub struct FriendStatusesChanged {
+    pub friend_ids: Vec<String>,
+}
+
 struct Connection {
     remote: Remote,
     sender: mpsc::Sender<String>,
@@ -66,6 +76,7 @@ struct InteractionRequest {
 pub struct Network {
     connections: Mutex<HashMap<String, Connection>>,
     statuses: Statuses,
+    friend_presence: Arc<FriendPresence>,
     profile: watch::Sender<crate::user::User>,
     friends: watch::Sender<Vec<String>>,
     keypair: AppKeypair,
@@ -173,6 +184,7 @@ impl Network {
             if let Some(connection) = connections.remove(&id) {
                 connection.task.abort();
                 remove_status(&self.statuses, &id, connection.generation);
+                apply_friend_presence_change(handle, self.friend_presence.remove(&id));
             }
         }
 
@@ -193,6 +205,7 @@ impl Network {
             let task = tauri::async_runtime::spawn(run(
                 handle.clone(),
                 self.statuses.clone(),
+                self.friend_presence.clone(),
                 remote.clone(),
                 generation,
                 self.profile.subscribe(),
@@ -228,6 +241,7 @@ pub async fn init(handle: &AppHandle) -> Result<(), Box<dyn std::error::Error>>
     let network = Network {
         connections: Mutex::new(HashMap::new()),
         statuses: Statuses::default(),
+        friend_presence: Arc::default(),
         profile,
         friends,
         keypair,
@@ -252,9 +266,10 @@ pub async fn init(handle: &AppHandle) -> Result<(), Box<dyn std::error::Error>>
             if *current == ids {
                 return false;
             }
-            *current = ids;
+            *current = ids.clone();
             true
         });
+        apply_friend_presence_change(&listener_handle, network.friend_presence.retain(&ids));
     });
     Ok(())
 }
@@ -262,6 +277,7 @@ pub async fn init(handle: &AppHandle) -> Result<(), Box<dyn std::error::Error>>
 async fn run(
     handle: AppHandle,
     statuses: Statuses,
+    friend_presence: Arc<FriendPresence>,
     remote: Remote,
     generation: u64,
     mut profiles: watch::Receiver<crate::user::User>,
@@ -281,6 +297,7 @@ async fn run(
         if let Err(error) = connect(
             &handle,
             &statuses,
+            &friend_presence,
             &remote,
             generation,
             &mut profiles,
@@ -293,6 +310,7 @@ async fn run(
         {
             eprintln!("remote {} disconnected: {error}", remote.id);
         }
+        apply_friend_presence_change(&handle, friend_presence.remove(&remote.id));
         changed(
             &handle,
             &statuses,
@@ -307,6 +325,7 @@ async fn run(
 async fn connect(
     handle: &AppHandle,
     statuses: &Statuses,
+    friend_presence: &FriendPresence,
     remote: &Remote,
     generation: u64,
     profiles: &mut watch::Receiver<crate::user::User>,
@@ -354,6 +373,7 @@ async fn connect(
             .send(InteractionDeliveryStatus::Unavailable);
     }
     send(&mut writer, &ClientMessage::SyncFriendProfiles).await?;
+    send(&mut writer, &ClientMessage::SyncFriendStatuses).await?;
     changed(
         handle,
         statuses,
@@ -421,6 +441,21 @@ async fn connect(
                             eprintln!("failed to synchronize friend profiles: {error}");
                         }
                     }
+                    ServerMessage::FriendStatusChanged { friend_id, online } => {
+                        update_friend_presence(
+                            handle,
+                            friend_presence,
+                            &remote.id,
+                            friend_id,
+                            online,
+                        );
+                    }
+                    ServerMessage::FriendStatuses { friend_ids } => {
+                        apply_friend_presence_change(
+                            handle,
+                            friend_presence.replace(&remote.id, friend_ids),
+                        );
+                    }
                     ServerMessage::FriendLiveData { friend_id, payload } => {
                         match serde_json::from_str(&payload) {
                             Ok(LiveData::Cursor { positions }) => {
@@ -471,6 +506,42 @@ pub fn list_statuses(
     Ok(statuses)
 }
 
+#[tauri::command]
+#[specta::specta]
+pub fn list_friend_statuses(network: State<'_, Network>) -> Result<Vec<String>, String> {
+    network.friend_presence.snapshot()
+}
+
+fn update_friend_presence(
+    handle: &AppHandle,
+    presence: &FriendPresence,
+    remote_id: &str,
+    friend_id: String,
+    online: bool,
+) {
+    apply_friend_presence_change(handle, presence.update(remote_id, friend_id, online));
+}
+
+fn apply_friend_presence_change(
+    handle: &AppHandle,
+    result: Result<Option<FriendPresenceChange>, String>,
+) {
+    match result {
+        Ok(Some(change)) => {
+            crate::cursor::remove_positions(handle, &change.went_offline);
+            if let Err(error) = (FriendStatusesChanged {
+                friend_ids: change.online,
+            })
+            .emit(handle)
+            {
+                eprintln!("failed to emit friend statuses: {error}");
+            }
+        }
+        Ok(None) => {}
+        Err(error) => eprintln!("failed to update friend presence: {error}"),
+    }
+}
+
 fn changed(
     handle: &AppHandle,
     statuses: &Statuses,

src-tauri/src/network/presence.rs

@@ -0,0 +1,165 @@
+use std::collections::{HashMap, HashSet};
+use std::sync::Mutex;
+
+#[derive(Debug, PartialEq, Eq)]
+pub(super) struct Change {
+    pub(super) online: Vec<String>,
+    pub(super) went_offline: Vec<String>,
+}
+
+#[derive(Default)]
+pub(super) struct FriendPresence(Mutex<HashMap<String, HashSet<String>>>);
+
+impl FriendPresence {
+    pub(super) fn replace(
+        &self,
+        remote_id: &str,
+        friend_ids: Vec<String>,
+    ) -> Result<Option<Change>, String> {
+        let mut by_remote = self.0.lock().map_err(|error| error.to_string())?;
+        let before = aggregate(&by_remote);
+        let friend_ids = friend_ids.into_iter().collect::<HashSet<_>>();
+        if friend_ids.is_empty() {
+            by_remote.remove(remote_id);
+        } else {
+            by_remote.insert(remote_id.to_owned(), friend_ids);
+        }
+        Ok(diff(before, &by_remote))
+    }
+
+    pub(super) fn update(
+        &self,
+        remote_id: &str,
+        friend_id: String,
+        online: bool,
+    ) -> Result<Option<Change>, String> {
+        let mut by_remote = self.0.lock().map_err(|error| error.to_string())?;
+        let before = aggregate(&by_remote);
+        if online {
+            by_remote
+                .entry(remote_id.to_owned())
+                .or_default()
+                .insert(friend_id);
+        } else if let Some(friend_ids) = by_remote.get_mut(remote_id) {
+            friend_ids.remove(&friend_id);
+            if friend_ids.is_empty() {
+                by_remote.remove(remote_id);
+            }
+        }
+        Ok(diff(before, &by_remote))
+    }
+
+    pub(super) fn remove(&self, remote_id: &str) -> Result<Option<Change>, String> {
+        let mut by_remote = self.0.lock().map_err(|error| error.to_string())?;
+        let before = aggregate(&by_remote);
+        by_remote.remove(remote_id);
+        Ok(diff(before, &by_remote))
+    }
+
+    pub(super) fn retain(&self, known_friend_ids: &[String]) -> Result<Option<Change>, String> {
+        let known_friend_ids = known_friend_ids.iter().collect::<HashSet<_>>();
+        let mut by_remote = self.0.lock().map_err(|error| error.to_string())?;
+        let before = aggregate(&by_remote);
+        by_remote.retain(|_, friend_ids| {
+            friend_ids.retain(|friend_id| known_friend_ids.contains(friend_id));
+            !friend_ids.is_empty()
+        });
+        Ok(diff(before, &by_remote))
+    }
+
+    pub(super) fn snapshot(&self) -> Result<Vec<String>, String> {
+        let by_remote = self.0.lock().map_err(|error| error.to_string())?;
+        let mut friend_ids = aggregate(&by_remote).into_iter().collect::<Vec<_>>();
+        friend_ids.sort_unstable();
+        Ok(friend_ids)
+    }
+}
+
+fn aggregate(by_remote: &HashMap<String, HashSet<String>>) -> HashSet<String> {
+    by_remote
+        .values()
+        .flat_map(|friend_ids| friend_ids.iter().cloned())
+        .collect()
+}
+
+fn diff(before: HashSet<String>, by_remote: &HashMap<String, HashSet<String>>) -> Option<Change> {
+    let after = aggregate(by_remote);
+    if before == after {
+        return None;
+    }
+    let mut went_offline = before.difference(&after).cloned().collect::<Vec<_>>();
+    let mut online = after.into_iter().collect::<Vec<_>>();
+    went_offline.sort_unstable();
+    online.sort_unstable();
+    Some(Change {
+        online,
+        went_offline,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{Change, FriendPresence};
+
+    #[test]
+    fn friend_stays_online_while_any_remote_reports_presence() {
+        let presence = FriendPresence::default();
+        assert_eq!(
+            presence
+                .replace("remote-a", vec!["friend".to_owned()])
+                .unwrap(),
+            Some(Change {
+                online: vec!["friend".to_owned()],
+                went_offline: Vec::new(),
+            })
+        );
+        assert!(
+            presence
+                .replace("remote-b", vec!["friend".to_owned()])
+                .unwrap()
+                .is_none()
+        );
+        assert!(presence.remove("remote-a").unwrap().is_none());
+        assert_eq!(
+            presence.remove("remote-b").unwrap(),
+            Some(Change {
+                online: Vec::new(),
+                went_offline: vec!["friend".to_owned()],
+            })
+        );
+    }
+
+    #[test]
+    fn incremental_updates_and_friend_removal_share_the_same_snapshot() {
+        let presence = FriendPresence::default();
+        presence
+            .replace("remote", vec!["kept".to_owned(), "removed".to_owned()])
+            .unwrap();
+
+        assert_eq!(
+            presence
+                .update("remote", "added".to_owned(), true)
+                .unwrap()
+                .expect("friend came online")
+                .online,
+            ["added", "kept", "removed"]
+        );
+        assert_eq!(
+            presence
+                .update("remote", "added".to_owned(), false)
+                .unwrap()
+                .expect("friend went offline")
+                .went_offline,
+            ["added"]
+        );
+        assert_eq!(
+            presence
+                .retain(&["kept".to_owned()])
+                .unwrap()
+                .expect("unknown friend was removed")
+                .went_offline,
+            ["removed"]
+        );
+        assert_eq!(presence.snapshot().unwrap(), ["kept"]);
+    }
+}

src/lib/bindings.ts

@@ -44,6 +44,9 @@ async getPublicKey() : Promise<string> {
 async listStatuses() : Promise<ConnectionStatus[]> {
     return await TAURI_INVOKE("list_statuses");
 },
+async listFriendStatuses() : Promise<string[]> {
+    return await TAURI_INVOKE("list_friend_statuses");
+},
 async pickAndSendImage(recipientId: string) : Promise<boolean> {
     return await TAURI_INVOKE("pick_and_send_image", { recipientId });
 },
@@ -66,6 +69,7 @@ cursorPositionChanged: CursorPositionChanged,
 foregroundAppChanged: ForegroundAppChanged,
 friendForegroundAppChanged: FriendForegroundAppChanged,
 friendInteractionReceived: FriendInteractionReceived,
+friendStatusesChanged: FriendStatusesChanged,
 friendsChanged: FriendsChanged,
 networkStatusChanged: NetworkStatusChanged,
 profileChanged: ProfileChanged,
@@ -75,6 +79,7 @@ cursorPositionChanged: "cursor-position-changed",
 foregroundAppChanged: "foreground-app-changed",
 friendForegroundAppChanged: "friend-foreground-app-changed",
 friendInteractionReceived: "friend-interaction-received",
+friendStatusesChanged: "friend-statuses-changed",
 friendsChanged: "friends-changed",
 networkStatusChanged: "network-status-changed",
 profileChanged: "profile-changed",
@@ -107,6 +112,7 @@ mapped: CursorPosition }
 export type ForegroundAppChanged = { meta: AppMeta }
 export type FriendForegroundAppChanged = { friendId: string; meta: AppMeta }
 export type FriendInteractionReceived = { interactionId: string; friendId: string; content: InteractionContent }
+export type FriendStatusesChanged = { friendIds: string[] }
 export type FriendsChanged = { friends: User[] }
 export type InteractionContent = { type: "text"; text: string } | { type: "wave" } | { type: "image"; mediaType: string; data: string }
 export type NetworkStatusChanged = { statuses: ConnectionStatus[] }

src/lib/components/friend-statuses.svelte

@@ -0,0 +1,29 @@
+<script lang="ts">
+  import {
+    friendStatusesListenerError,
+    onlineFriendIds,
+  } from "$lib/listeners/friend-statuses";
+  import { friends, friendsListenerError } from "$lib/listeners/friends";
+</script>
+
+<section>
+  <h1>Friend statuses</h1>
+
+  {#if $friendsListenerError || $friendStatusesListenerError}
+    <p aria-live="polite">
+      {$friendsListenerError || $friendStatusesListenerError}
+    </p>
+  {:else if $friends.length === 0}
+    <p>No friends configured.</p>
+  {:else}
+    <ul aria-live="polite">
+      {#each $friends as friend (friend.id)}
+        {@const online = $onlineFriendIds.has(friend.id)}
+        <li>
+          <strong>{friend.displayName}</strong>: {online ? "Online" : "Offline"}
+          <small>({friend.id})</small>
+        </li>
+      {/each}
+    </ul>
+  {/if}
+</section>

src/lib/listeners/friend-statuses.ts

@@ -0,0 +1,31 @@
+import { writable } from "svelte/store";
+import { commands, events } from "$lib/bindings";
+import { removeFriendForegroundApps } from "./live-metadata";
+
+export const onlineFriendIds = writable<Set<string>>(new Set());
+export const friendStatusesListenerError = writable("");
+
+export async function initFriendStatusesListener() {
+  let current = new Set<string>();
+
+  const apply = (friendIds: string[]) => {
+    const next = new Set(friendIds);
+    const wentOffline = [...current].filter((friendId) => !next.has(friendId));
+    current = next;
+    onlineFriendIds.set(next);
+
+    removeFriendForegroundApps(wentOffline);
+  };
+
+  const unlisten = await events.friendStatusesChanged.listen((event) => {
+    apply(event.payload.friendIds);
+  });
+
+  try {
+    apply(await commands.listFriendStatuses());
+  } catch (error) {
+    friendStatusesListenerError.set(String(error));
+  }
+
+  return unlisten;
+}

src/lib/listeners/index.ts

@@ -1,4 +1,5 @@
 import { initConnectionStatusesListener } from "./connection-status";
+import { initFriendStatusesListener } from "./friend-statuses";
 import { initFriendsListener } from "./friends";
 import { initInteractionListener } from "./interactions";
 import { initLiveMetadataListeners } from "./live-metadata";
@@ -16,6 +17,7 @@ export function initAppListeners(): Unlisten {
     initRemotesListener(),
     initProfileListener(),
     initConnectionStatusesListener(),
+    initFriendStatusesListener(),
     initLiveMetadataListeners(),
     initInteractionListener(),
   ])

src/lib/listeners/live-metadata.ts

@@ -19,6 +19,17 @@ export const liveMetadata = writable<LiveMetadata>({
 });
 export const liveMetadataListenerError = writable("");
 
+export function removeFriendForegroundApps(friendIds: string[]) {
+  if (friendIds.length === 0) return;
+  const removed = new Set(friendIds);
+  liveMetadata.update((metadata) => ({
+    ...metadata,
+    foregroundApps: new Map(
+      [...metadata.foregroundApps].filter(([userId]) => !removed.has(userId)),
+    ),
+  }));
+}
+
 export async function initLiveMetadataListeners() {
   let localId = "";
   let pendingLocalForegroundApp: AppMeta | null = null;

src/routes/+page.svelte

@@ -1,5 +1,6 @@
 <script>
   import FriendsList from "$lib/components/friends-list.svelte";
+  import FriendStatuses from "$lib/components/friend-statuses.svelte";
   import ConnectionStatus from "$lib/components/connection-status.svelte";
   import Profile from "$lib/components/profile.svelte";
   import RemotesList from "$lib/components/remotes-list.svelte";
@@ -13,6 +14,9 @@
   <div>
     <FriendsList />
   </div>
+  <div>
+    <FriendStatuses />
+  </div>
   <div>
     <RemotesList />
   </div>

src/routes/scene/+page.svelte

@@ -2,6 +2,7 @@
   import { onMount } from "svelte";
   import Popover from "$lib/components/popover.svelte";
   import { friends } from "$lib/listeners/friends";
+  import { onlineFriendIds } from "$lib/listeners/friend-statuses";
   import { incomingInteraction } from "$lib/listeners/interactions";
   import { liveMetadata } from "$lib/listeners/live-metadata";
   import { profile } from "$lib/listeners/profile";
@@ -28,6 +29,18 @@
     return () => window.clearTimeout(timer);
   });
 
+  $effect(() => {
+    if (
+      selectedUserId &&
+      selectedUserId !== $liveMetadata.localId &&
+      !$onlineFriendIds.has(selectedUserId)
+    ) {
+      selectedUserId = null;
+      selectedUserX = null;
+      lockedPopoverUserId = null;
+    }
+  });
+
   function displayName(userId: string) {
     return $profile?.id === userId
       ? $profile.displayName
@@ -65,7 +78,7 @@
       {@const popoverId = `scene-user-${index}`}
       {@const interaction =
         $incomingInteraction?.friendId === userId ? $incomingInteraction : null}
-      {#if cursor}
+      {#if cursor && (userId === $liveMetadata.localId || $onlineFriendIds.has(userId))}
         {@const renderedX =
           selectedUserId === userId ? selectedUserX : cursor.mapped.x}
         <div