refactor(connlib): batch resource change updates (#5575)

Currently, upon reconnecting, `snownet` returns a list of connection IDs
that have been closed. This was done to avoid emitting many identical
`ResourcesChanged` events. In all other events, `snownet` always only
references a single connection. To align this whilst not duplicating
`ResourcesChanged` events, we use a dedicated `bool` to check, whether
any of the events emitted by `snownet` require updating the clients
about our active resources.

rust/connlib/snownet/src/node.rs

@@ -157,17 +157,20 @@ where
 
         self.pending_events.clear();
 
-        let connections = self.connections.iter_ids().collect::<Vec<_>>();
-        let num_connections = connections.len();
+        let closed_connections = self
+            .connections
+            .iter_ids()
+            .map(Event::ConnectionClosed)
+            .collect::<Vec<_>>();
+        let num_connections = closed_connections.len();
 
-        self.pending_events
-            .push_back(Event::ConnectionsCleared(connections));
+        self.pending_events.extend(closed_connections);
 
         self.host_candidates.clear();
         self.connections.clear();
         self.buffered_transmits.clear();
 
-        tracing::debug!("Cleared {num_connections} connections");
+        tracing::debug!(%num_connections, "Closed all connections as part of reconnecting");
     }
 
     pub fn public_key(&self) -> PublicKey {
@@ -1270,8 +1273,8 @@ pub enum Event<TId> {
     /// All state associated with the connection has been cleared.
     ConnectionFailed(TId),
 
-    /// The referenced connections had their state cleared.
-    ConnectionsCleared(Vec<TId>),
+    /// We closed a connection (e.g. due to inactivity, roaming, etc).
+    ConnectionClosed(TId),
 }
 
 #[derive(Clone, PartialEq)]

rust/connlib/snownet/tests/lib.rs

@@ -634,7 +634,7 @@ impl<R> TestNode<R> {
                     .in_scope(|| other.node.remove_remote_candidate(connection, candidate)),
                 Event::ConnectionEstablished(_)
                 | Event::ConnectionFailed(_)
-                | Event::ConnectionsCleared(_) => {}
+                | Event::ConnectionClosed(_) => {}
             };
         }
     }

rust/connlib/tunnel/src/client.rs

@@ -812,23 +812,13 @@ impl ClientState {
         self.node.handle_timeout(now);
         self.mangled_dns_queries.retain(|_, exp| now < *exp);
 
+        let mut resources_changed = false; // Track this separately to batch together `ResourcesChanged` events.
+
         while let Some(event) = self.node.poll_event() {
             match event {
-                snownet::Event::ConnectionFailed(id) => {
+                snownet::Event::ConnectionFailed(id) | snownet::Event::ConnectionClosed(id) => {
                     self.cleanup_connected_gateway(&id);
-                    self.buffered_events
-                        .push_back(ClientEvent::ResourcesChanged {
-                            resources: self.resources(),
-                        });
-                }
-                snownet::Event::ConnectionsCleared(ids) => {
-                    for id in ids {
-                        self.cleanup_connected_gateway(&id);
-                    }
-                    self.buffered_events
-                        .push_back(ClientEvent::ResourcesChanged {
-                            resources: self.resources(),
-                        });
+                    resources_changed = true;
                 }
                 snownet::Event::NewIceCandidate {
                     connection,
@@ -850,13 +840,17 @@ impl ClientState {
                     }),
                 snownet::Event::ConnectionEstablished(id) => {
                     self.update_site_status_by_gateway(&id, Status::Online);
-                    self.buffered_events
-                        .push_back(ClientEvent::ResourcesChanged {
-                            resources: self.resources(),
-                        });
+                    resources_changed = true;
                 }
             }
         }
+
+        if resources_changed {
+            self.buffered_events
+                .push_back(ClientEvent::ResourcesChanged {
+                    resources: self.resources(),
+                });
+        }
     }
 
     fn update_site_status_by_gateway(&mut self, gateway_id: &GatewayId, status: Status) {

rust/connlib/tunnel/src/gateway.rs

@@ -378,8 +378,7 @@ impl GatewayState {
                             candidate,
                         });
                 }
-                snownet::Event::ConnectionEstablished(_)
-                | snownet::Event::ConnectionsCleared(_) => {}
+                snownet::Event::ConnectionEstablished(_) | snownet::Event::ConnectionClosed(_) => {}
             }
         }
     }

rust/snownet-tests/src/main.rs

@@ -400,7 +400,7 @@ impl<T> Eventloop<T> {
             }
             Some(
                 snownet::Event::InvalidateIceCandidate { .. }
-                | snownet::Event::ConnectionsCleared { .. },
+                | snownet::Event::ConnectionClosed { .. },
             )
             | None => {}
         }