Add OnPeerConnectedWithPeer to optimize sync fast path operations

management/internals/controllers/network_map/controller/controller.go

@@ -132,9 +132,18 @@ func (c *Controller) OnPeerConnected(ctx context.Context, accountID string, peer
 		return nil, fmt.Errorf("failed to get peer %s: %v", peerID, err)
 	}
 
-	c.EphemeralPeersManager.OnPeerConnected(ctx, peer)
+	return c.OnPeerConnectedWithPeer(ctx, accountID, peer)
+}
 
-	return c.peersUpdateManager.CreateChannel(ctx, peerID), nil
+// OnPeerConnectedWithPeer is the peer-object variant of OnPeerConnected. It
+// skips the internal GetPeerByID and is intended for callers that already
+// hold the peer (e.g. the Sync fast path). The accountID parameter is kept
+// for symmetry with OnPeerConnected even though the peer object already
+// carries it — callers typically have it handy from the surrounding context.
+func (c *Controller) OnPeerConnectedWithPeer(ctx context.Context, accountID string, peer *nbpeer.Peer) (chan *network_map.UpdateMessage, error) {
+	_ = accountID
+	c.EphemeralPeersManager.OnPeerConnected(ctx, peer)
+	return c.peersUpdateManager.CreateChannel(ctx, peer.ID), nil
 }
 
 func (c *Controller) OnPeerDisconnected(ctx context.Context, accountID string, peerID string) {

management/internals/controllers/network_map/interface.go

@@ -35,6 +35,11 @@ type Controller interface {
 	OnPeersDeleted(ctx context.Context, accountID string, peerIDs []string) error
 	DisconnectPeers(ctx context.Context, accountId string, peerIDs []string)
 	OnPeerConnected(ctx context.Context, accountID string, peerID string) (chan *UpdateMessage, error)
+	// OnPeerConnectedWithPeer is equivalent to OnPeerConnected but accepts an
+	// already-fetched peer, skipping the internal GetPeerByID lookup. Intended
+	// for callers that have already resolved the peer (e.g. the Sync fast path)
+	// so the controller does not re-read what the caller just read.
+	OnPeerConnectedWithPeer(ctx context.Context, accountID string, peer *nbpeer.Peer) (chan *UpdateMessage, error)
 	OnPeerDisconnected(ctx context.Context, accountID string, peerID string)
 
 	TrackEphemeralPeer(ctx context.Context, peer *nbpeer.Peer)

management/internals/controllers/network_map/interface_mock.go

@@ -1,9 +1,9 @@
 // Code generated by MockGen. DO NOT EDIT.
-// Source: management/internals/controllers/network_map/interface.go
+// Source: ./interface.go
 //
 // Generated by this command:
 //
-//	mockgen -package network_map -destination=management/internals/controllers/network_map/interface_mock.go -source=management/internals/controllers/network_map/interface.go -build_flags=-mod=mod
+//	mockgen -package network_map -destination=interface_mock.go -source=./interface.go -build_flags=-mod=mod
 //
 
 // Package network_map is a generated GoMock package.
@@ -145,6 +145,21 @@ func (mr *MockControllerMockRecorder) OnPeerConnected(ctx, accountID, peerID any
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "OnPeerConnected", reflect.TypeOf((*MockController)(nil).OnPeerConnected), ctx, accountID, peerID)
 }
 
+// OnPeerConnectedWithPeer mocks base method.
+func (m *MockController) OnPeerConnectedWithPeer(ctx context.Context, accountID string, arg2 *peer.Peer) (chan *UpdateMessage, error) {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "OnPeerConnectedWithPeer", ctx, accountID, arg2)
+	ret0, _ := ret[0].(chan *UpdateMessage)
+	ret1, _ := ret[1].(error)
+	return ret0, ret1
+}
+
+// OnPeerConnectedWithPeer indicates an expected call of OnPeerConnectedWithPeer.
+func (mr *MockControllerMockRecorder) OnPeerConnectedWithPeer(ctx, accountID, arg2 any) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "OnPeerConnectedWithPeer", reflect.TypeOf((*MockController)(nil).OnPeerConnectedWithPeer), ctx, accountID, arg2)
+}
+
 // OnPeerDisconnected mocks base method.
 func (m *MockController) OnPeerDisconnected(ctx context.Context, accountID, peerID string) {
 	m.ctrl.T.Helper()

management/internals/shared/grpc/sync_fast_path.go

@@ -169,7 +169,7 @@ func (s *Server) tryFastPathSync(
 	}
 	log.WithContext(ctx).Debugf("fast path: eligibility check (hit) took %s", time.Since(eligibilityStart))
 
-	peer, updates, committed := s.commitFastPath(ctx, accountID, peerKey, realIP, syncStart, network.CurrentSerial())
+	peer, updates, committed := s.commitFastPath(ctx, accountID, peerKey, realIP, syncStart)
 	if !committed {
 		return false, nil
 	}
@@ -177,21 +177,19 @@ func (s *Server) tryFastPathSync(
 	return true, s.runFastPathSync(ctx, reqStart, syncStart, accountID, peerKey, peer, updates, peerMetaHash, srv, unlock)
 }
 
-// commitFastPath fetches the peer, subscribes it to network-map updates,
-// re-checks the account serial to close the race between the eligibility
-// check and the subscription, and only then commits MarkPeerConnected. If
-// the serial advanced in the race window the update-channel subscription is
-// torn down (no MarkPeerConnected is written, so the slow path is free to
-// run its own SyncAndMarkPeer cleanly) and the caller falls back to the
-// slow path. Returns committed=false on any failure that should not block
-// the slow path from running.
+// commitFastPath fetches the peer, subscribes it to network-map updates and
+// marks the peer connected. It relies on the same eventual-consistency
+// guarantee as the slow path: a concurrent writer's broadcast may race the
+// subscription, but any subsequent serial change reaches the subscribed peer
+// via its update channel, and a reconnect with a stale cached serial falls
+// through to the slow path on the next Sync. Returns committed=false on any
+// failure that should not block the slow path from running.
 func (s *Server) commitFastPath(
 	ctx context.Context,
 	accountID string,
 	peerKey wgtypes.Key,
 	realIP net.IP,
 	syncStart time.Time,
-	expectedSerial uint64,
 ) (*nbpeer.Peer, chan *network_map.UpdateMessage, bool) {
 	commitStart := time.Now()
 	defer func() {
@@ -207,27 +205,12 @@ func (s *Server) commitFastPath(
 	log.WithContext(ctx).Debugf("fast path: GetPeerByPeerPubKey took %s", time.Since(getPeerStart))
 
 	onConnectedStart := time.Now()
-	updates, err := s.networkMapController.OnPeerConnected(ctx, accountID, peer.ID)
+	updates, err := s.networkMapController.OnPeerConnectedWithPeer(ctx, accountID, peer)
 	if err != nil {
 		log.WithContext(ctx).Debugf("fast path: notify peer connected for %s: %v", peerKey.String(), err)
 		return nil, nil, false
 	}
-	log.WithContext(ctx).Debugf("fast path: OnPeerConnected took %s", time.Since(onConnectedStart))
-
-	recheckStart := time.Now()
-	network, err := s.accountManager.GetStore().GetAccountNetwork(ctx, store.LockingStrengthNone, accountID)
-	if err != nil {
-		log.WithContext(ctx).Debugf("fast path: re-check account network: %v", err)
-		s.networkMapController.OnPeerDisconnected(ctx, accountID, peer.ID)
-		return nil, nil, false
-	}
-	log.WithContext(ctx).Debugf("fast path: re-check GetAccountNetwork took %s", time.Since(recheckStart))
-
-	if network.CurrentSerial() != expectedSerial {
-		log.WithContext(ctx).Debugf("fast path: serial advanced from %d to %d after subscribe, falling back to slow path for peer %s", expectedSerial, network.CurrentSerial(), peerKey.String())
-		s.networkMapController.OnPeerDisconnected(ctx, accountID, peer.ID)
-		return nil, nil, false
-	}
+	log.WithContext(ctx).Debugf("fast path: OnPeerConnectedWithPeer took %s", time.Since(onConnectedStart))
 
 	markStart := time.Now()
 	if err := s.accountManager.MarkPeerConnected(ctx, peerKey.String(), true, realIP, accountID, syncStart); err != nil {