[client] Drain buffered tick when coalesce window expires

client/server/status_stream.go

@@ -1,20 +1,27 @@
 package server
 
 import (
+	"context"
+	"time"
+
 	log "github.com/sirupsen/logrus"
 
 	"github.com/netbirdio/netbird/client/proto"
 )
 
+const statusCoalesceWindow = 200 * time.Millisecond
+
 // SubscribeStatus pushes a fresh StatusResponse on every connection state
 // change. The first message is the current snapshot, so a re-subscribing
 // client doesn't need to also call Status. Subsequent messages fire when
 // the peer recorder reports any of: connected/disconnected/connecting,
 // management or signal flip, address change, or peers list change.
 //
-// The change channel coalesces bursts to a single tick. If the consumer
-// is slow the daemon drops extras (not blocks), and the next snapshot
-// the consumer pulls already reflects everything.
+// Bursts are coalesced deterministically: the first tick after a quiet
+// period is sent immediately, then a short window swallows the rest of the
+// burst and a single trailing snapshot covers whatever arrived meanwhile.
+// Every send is a full snapshot of the recorder's current state, so
+// swallowed ticks lose no information.
 func (s *Server) SubscribeStatus(req *proto.StatusRequest, stream proto.DaemonService_SubscribeStatusServer) error {
 	subID, ch := s.statusRecorder.SubscribeToStateChanges()
 	defer func() {
@@ -37,12 +44,50 @@ func (s *Server) SubscribeStatus(req *proto.StatusRequest, stream proto.DaemonSe
 			if err := s.sendStatusSnapshot(req, stream); err != nil {
 				return err
 			}
+			pending, open := collectStatusBurst(stream.Context(), ch)
+			if pending {
+				if err := s.sendStatusSnapshot(req, stream); err != nil {
+					return err
+				}
+			}
+			if !open {
+				return nil
+			}
 		case <-stream.Context().Done():
 			return nil
 		}
 	}
 }
 
+// collectStatusBurst waits out the coalesce window, absorbing further ticks.
+// pending reports whether any tick arrived; open is false when the channel
+// closed or the stream context ended.
+func collectStatusBurst(ctx context.Context, ch <-chan struct{}) (pending, open bool) {
+	timer := time.NewTimer(statusCoalesceWindow)
+	defer timer.Stop()
+	for {
+		select {
+		case _, ok := <-ch:
+			if !ok {
+				return pending, false
+			}
+			pending = true
+		case <-timer.C:
+			select {
+			case _, ok := <-ch:
+				if !ok {
+					return pending, false
+				}
+				pending = true
+			default:
+			}
+			return pending, true
+		case <-ctx.Done():
+			return false, false
+		}
+	}
+}
+
 func (s *Server) sendStatusSnapshot(req *proto.StatusRequest, stream proto.DaemonService_SubscribeStatusServer) error {
 	resp, err := s.buildStatusResponse(stream.Context(), req)
 	if err != nil {