Don't use a vector for the key of the auth chain cache

We only ever get and insert one element in the vector

src/database/rooms.rs

@@ -88,7 +88,7 @@ pub struct Rooms {
     pub(super) referencedevents: Arc<dyn Tree>,
 
     pub(super) pdu_cache: Mutex<LruCache<EventId, Arc<PduEvent>>>,
-    pub(super) auth_chain_cache: Mutex<LruCache<Vec<EventId>, HashSet<EventId>>>,
+    pub(super) auth_chain_cache: Mutex<LruCache<EventId, HashSet<EventId>>>,
 }
 
 impl Rooms {
@@ -2657,7 +2657,7 @@ impl Rooms {
     #[tracing::instrument(skip(self))]
     pub fn auth_chain_cache(
         &self,
-    ) -> std::sync::MutexGuard<'_, LruCache<Vec<EventId>, HashSet<EventId>>> {
+    ) -> std::sync::MutexGuard<'_, LruCache<EventId, HashSet<EventId>>> {
         self.auth_chain_cache.lock().unwrap()
     }
 }

src/server_server.rs

@@ -1760,14 +1760,14 @@ fn get_auth_chain(starting_events: Vec<EventId>, db: &Database) -> Result<HashSe
     let mut cache = db.rooms.auth_chain_cache();
 
     for event_id in &starting_events {
-        if let Some(cached) = cache.get_mut(&[event_id.clone()][..]) {
+        if let Some(cached) = cache.get_mut(event_id) {
             full_auth_chain.extend(cached.iter().cloned());
         } else {
             drop(cache);
             let mut auth_chain = HashSet::new();
             get_auth_chain_recursive(&event_id, &mut auth_chain, db)?;
             cache = db.rooms.auth_chain_cache();
-            cache.insert(vec![event_id.clone()], auth_chain.clone());
+            cache.insert(event_id.clone(), auth_chain.clone());
             full_auth_chain.extend(auth_chain);
         };
     }