feat(bonfire): don't fan out UserUpdate (server) by default

crates/bonfire/src/events/state.rs

@@ -1,10 +1,12 @@
 use std::{
     collections::{HashMap, HashSet},
     sync::Arc,
+    time::Duration,
 };
 
-use async_std::sync::RwLock;
+use async_std::sync::{Mutex, RwLock};
 use lru::LruCache;
+use lru_time_cache::{LruCache as LruTimeCache, TimedEntry};
 use revolt_database::{Channel, Member, Server, User};
 
 /// Enumeration representing some change in subscriptions
@@ -34,6 +36,7 @@ pub enum SubscriptionStateChange {
 #[derive(Debug)]
 pub struct Cache {
     pub user_id: String,
+    pub is_bot: bool,
 
     pub users: HashMap<String, User>,
     pub channels: HashMap<String, Channel>,
@@ -47,6 +50,7 @@ impl Default for Cache {
     fn default() -> Self {
         Cache {
             user_id: Default::default(),
+            is_bot: false,
 
             users: Default::default(),
             channels: Default::default(),
@@ -65,7 +69,9 @@ pub struct State {
     pub session_id: String,
     pub private_topic: String,
     pub state: SubscriptionStateChange,
+
     pub subscribed: Arc<RwLock<HashSet<String>>>,
+    pub active_servers: Arc<Mutex<LruTimeCache<String, ()>>>,
 }
 
 impl State {
@@ -86,6 +92,10 @@ impl State {
         State {
             cache,
             subscribed: Arc::new(RwLock::new(subscribed)),
+            active_servers: Arc::new(Mutex::new(LruTimeCache::with_expiry_duration_and_capacity(
+                Duration::from_secs(900),
+                5,
+            ))),
             session_id,
             private_topic,
             state: SubscriptionStateChange::Reset,
@@ -94,6 +104,39 @@ impl State {
 
     /// Apply currently queued state
     pub async fn apply_state(&mut self) -> SubscriptionStateChange {
+        // Check if we need to change subscriptions to member event topics
+        if !self.cache.is_bot {
+            enum Server {
+                Subscribe(String),
+                Unsubscribe(String),
+            }
+
+            let active_server_changes: Vec<Server> = {
+                let mut active_servers = self.active_servers.lock().await;
+                active_servers
+                    .notify_iter()
+                    .map(|e| match e {
+                        TimedEntry::Valid(k, _) => Server::Subscribe(format!("{}u", k)),
+                        TimedEntry::Expired(k, _) => Server::Unsubscribe(format!("{}u", k)),
+                    })
+                    .collect()
+                // It is bad practice to open more than one Mutex at once and could
+                // lead to a deadlock, so instead we choose to collect the changes.
+            };
+
+            for entry in active_server_changes {
+                match entry {
+                    Server::Subscribe(k) => {
+                        self.insert_subscription(k).await;
+                    }
+                    Server::Unsubscribe(k) => {
+                        self.remove_subscription(&k).await;
+                    }
+                }
+            }
+        }
+
+        // Flush changes to subscriptions
         let state = std::mem::replace(&mut self.state, SubscriptionStateChange::None);
         let mut subscribed = self.subscribed.write().await;
         if let SubscriptionStateChange::Change { add, remove } = &state {