Report FBU metrics as untracked for service-mode proxied sessions instead of as zero

client/internal/engine_vnc.go

@@ -153,6 +153,7 @@ func (e *Engine) startVNCServer(authConfig *sshauth.Config) error {
 				MaxFBURects:   t.MaxFBURects,
 				MaxWriteBytes: t.MaxWriteBytes,
 				WriteNanos:    t.WriteNanos,
+				FBUsTracked:   t.FBUsTracked,
 			})
 		}
 	}

client/internal/metrics/influxdb.go

@@ -115,20 +115,26 @@ func (m *influxDBMetrics) RecordVNCSessionTick(_ context.Context, agentInfo Agen
 	m.mu.Lock()
 	defer m.mu.Unlock()
 
+	fields := map[string]float64{
+		"period_seconds":     tick.Period.Seconds(),
+		"bytes_out":          float64(tick.BytesOut),
+		"writes":             float64(tick.Writes),
+		"max_write_bytes":    float64(tick.MaxWriteBytes),
+		"write_time_seconds": float64(tick.WriteNanos) / 1e9,
+	}
+	// Left out rather than written as zero when they were not observed, so a
+	// service-mode session does not read as one that sent no updates.
+	if tick.FBUsTracked {
+		fields["fbus"] = float64(tick.FBUs)
+		fields["max_fbu_bytes"] = float64(tick.MaxFBUBytes)
+		fields["max_fbu_rects"] = float64(tick.MaxFBURects)
+	}
+
 	m.samples = append(m.samples, influxSample{
 		measurement: "netbird_vnc_traffic",
 		tags:        tags,
-		fields: map[string]float64{
-			"period_seconds":     tick.Period.Seconds(),
-			"bytes_out":          float64(tick.BytesOut),
-			"writes":             float64(tick.Writes),
-			"fbus":               float64(tick.FBUs),
-			"max_fbu_bytes":      float64(tick.MaxFBUBytes),
-			"max_fbu_rects":      float64(tick.MaxFBURects),
-			"max_write_bytes":    float64(tick.MaxWriteBytes),
-			"write_time_seconds": float64(tick.WriteNanos) / 1e9,
-		},
-		timestamp: time.Now(),
+		fields:      fields,
+		timestamp:   time.Now(),
 	})
 	m.trimLocked()
 }

client/internal/metrics/metrics.go

@@ -100,6 +100,9 @@ type VNCSessionTick struct {
 	MaxFBURects   uint64
 	MaxWriteBytes uint64
 	WriteNanos    uint64
+	// FBUsTracked is false when the FBU fields could not be observed (a
+	// service-mode proxy). They are then unknown rather than zero.
+	FBUsTracked bool
 }
 
 // ConnectionStageTimestamps holds timestamps for each connection stage

client/vnc/server/metrics_conn.go

@@ -23,6 +23,11 @@ type SessionTick struct {
 	MaxFBURects   uint64
 	MaxWriteBytes uint64
 	WriteNanos    uint64
+	// FBUsTracked is false when the connection carried framebuffer updates it
+	// could not see the boundaries of, which is the case for a service-mode
+	// proxy relaying bytes to a per-session agent. FBUs, MaxFBUBytes and
+	// MaxFBURects then mean "unknown", not "none".
+	FBUsTracked bool
 }
 
 // sessionTickInterval is how often metricsConn emits a SessionTick. One
@@ -40,6 +45,9 @@ type metricsConn struct {
 	net.Conn
 
 	recorder func(SessionTick)
+	// framed is true when the session writing through this connection marks
+	// its FramebufferUpdate boundaries with beginFBU/endFBU.
+	framed bool
 
 	bytesOut   atomic.Uint64
 	writes     atomic.Uint64
@@ -72,9 +80,22 @@ type metricsConn struct {
 }
 
 func newMetricsConn(c net.Conn, recorder func(SessionTick)) net.Conn {
+	return newMetricsConnFramed(c, recorder, true)
+}
+
+// newProxyMetricsConn wraps a connection whose bytes are relayed to a session
+// running elsewhere, the service-mode agent. Nothing on this side sees where
+// one FramebufferUpdate ends and the next begins, so its ticks carry byte and
+// write counts only and report the FBU fields as untracked.
+func newProxyMetricsConn(c net.Conn, recorder func(SessionTick)) net.Conn {
+	return newMetricsConnFramed(c, recorder, false)
+}
+
+func newMetricsConnFramed(c net.Conn, recorder func(SessionTick), framed bool) net.Conn {
 	m := &metricsConn{
 		Conn:      c,
 		recorder:  recorder,
+		framed:    framed,
 		tickStart: time.Now(),
 		done:      make(chan struct{}),
 	}
@@ -137,6 +158,7 @@ func (m *metricsConn) flushTick(final bool) {
 		MaxFBURects:   maxRects,
 		MaxWriteBytes: maxPkt,
 		WriteNanos:    dns,
+		FBUsTracked:   m.framed,
 	})
 }
 

client/vnc/server/server_darwin.go

@@ -57,7 +57,7 @@ func (s *Server) serviceAcceptLoop(ln net.Listener) {
 			continue
 		}
 		enableTCPKeepAlive(conn, s.log)
-		metered := newMetricsConn(conn, s.sessionRecorder)
+		metered := newProxyMetricsConn(conn, s.sessionRecorder)
 		s.retrackConn(conn, metered)
 		if !s.beginHandler() {
 			s.releaseConnSlot()

client/vnc/server/server_windows.go

@@ -416,7 +416,7 @@ func (s *Server) serviceAcceptLoop(ln net.Listener) {
 			continue
 		}
 		enableTCPKeepAlive(conn, s.log)
-		metered := newMetricsConn(conn, s.sessionRecorder)
+		metered := newProxyMetricsConn(conn, s.sessionRecorder)
 		s.retrackConn(conn, metered)
 		if !s.beginHandler() {
 			s.releaseConnSlot()