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