likely fix for huge net traffic on interface reset (#1267)

agent/deltatracker/deltatracker.go

@@ -37,6 +37,16 @@ func (t *DeltaTracker[K, V]) Set(id K, value V) {
 	t.current[id] = value
 }
 
+// Snapshot returns a copy of the current map.
+// func (t *DeltaTracker[K, V]) Snapshot() map[K]V {
+// 	t.RLock()
+// 	defer t.RUnlock()
+
+// 	copyMap := make(map[K]V, len(t.current))
+// 	maps.Copy(copyMap, t.current)
+// 	return copyMap
+// }
+
 // Deltas returns a map of all calculated deltas for the current interval.
 func (t *DeltaTracker[K, V]) Deltas() map[K]V {
 	t.RLock()
@@ -53,6 +63,15 @@ func (t *DeltaTracker[K, V]) Deltas() map[K]V {
 	return deltas
 }
 
+// Previous returns the previously recorded value for the given key, if it exists.
+func (t *DeltaTracker[K, V]) Previous(id K) (V, bool) {
+	t.RLock()
+	defer t.RUnlock()
+
+	value, ok := t.previous[id]
+	return value, ok
+}
+
 // Delta returns the delta for a single key.
 // Returns 0 if the key doesn't exist or has no previous value.
 func (t *DeltaTracker[K, V]) Delta(id K) V {

agent/network.go

@@ -172,8 +172,24 @@ func (a *Agent) sumAndTrackPerNicDeltas(cacheTimeMs uint16, msElapsed uint64, ne
 		tracker.Set(upKey, v.BytesSent)
 		tracker.Set(downKey, v.BytesRecv)
 		if msElapsed > 0 {
-			upDelta = tracker.Delta(upKey) * 1000 / msElapsed
+			if prevVal, ok := tracker.Previous(upKey); ok {
-			downDelta = tracker.Delta(downKey) * 1000 / msElapsed
+				var deltaBytes uint64
+				if v.BytesSent >= prevVal {
+					deltaBytes = v.BytesSent - prevVal
+				} else {
+					deltaBytes = v.BytesSent
+				}
+				upDelta = deltaBytes * 1000 / msElapsed
+			}
+			if prevVal, ok := tracker.Previous(downKey); ok {
+				var deltaBytes uint64
+				if v.BytesRecv >= prevVal {
+					deltaBytes = v.BytesRecv - prevVal
+				} else {
+					deltaBytes = v.BytesRecv
+				}
+				downDelta = deltaBytes * 1000 / msElapsed
+			}
 		}
 		systemStats.NetworkInterfaces[v.Name] = [4]uint64{upDelta, downDelta, v.BytesSent, v.BytesRecv}
 	}
@@ -212,6 +228,10 @@ func (a *Agent) applyNetworkTotals(
 		a.initializeNetIoStats()
 		delete(a.netIoStats, cacheTimeMs)
 		delete(a.netInterfaceDeltaTrackers, cacheTimeMs)
+		systemStats.NetworkSent = 0
+		systemStats.NetworkRecv = 0
+		systemStats.Bandwidth[0], systemStats.Bandwidth[1] = 0, 0
+		return
 	}
 
 	systemStats.NetworkSent = networkSentPs

agent/network_test.go

@@ -338,6 +338,43 @@ func TestSumAndTrackPerNicDeltas(t *testing.T) {
 	assert.Equal(t, uint64(7000), ni[1])
 }
 
+func TestSumAndTrackPerNicDeltasHandlesCounterReset(t *testing.T) {
+	a := &Agent{
+		netInterfaces:             map[string]struct{}{"eth0": {}},
+		netInterfaceDeltaTrackers: make(map[uint16]*deltatracker.DeltaTracker[string, uint64]),
+	}
+
+	cache := uint16(77)
+
+	// First interval establishes baseline values
+	initial := []psutilNet.IOCountersStat{{Name: "eth0", BytesSent: 4_000, BytesRecv: 6_000}}
+	statsInitial := &system.Stats{}
+	a.ensureNetworkInterfacesMap(statsInitial)
+	_, _ = a.sumAndTrackPerNicDeltas(cache, 0, initial, statsInitial)
+
+	// Second interval increments counters normally so previous snapshot gets populated
+	increment := []psutilNet.IOCountersStat{{Name: "eth0", BytesSent: 9_000, BytesRecv: 11_000}}
+	statsIncrement := &system.Stats{}
+	a.ensureNetworkInterfacesMap(statsIncrement)
+	_, _ = a.sumAndTrackPerNicDeltas(cache, 1_000, increment, statsIncrement)
+
+	niIncrement, ok := statsIncrement.NetworkInterfaces["eth0"]
+	require.True(t, ok)
+	assert.Equal(t, uint64(5_000), niIncrement[0])
+	assert.Equal(t, uint64(5_000), niIncrement[1])
+
+	// Third interval simulates counter reset (values drop below previous totals)
+	reset := []psutilNet.IOCountersStat{{Name: "eth0", BytesSent: 1_200, BytesRecv: 1_500}}
+	statsReset := &system.Stats{}
+	a.ensureNetworkInterfacesMap(statsReset)
+	_, _ = a.sumAndTrackPerNicDeltas(cache, 1_000, reset, statsReset)
+
+	niReset, ok := statsReset.NetworkInterfaces["eth0"]
+	require.True(t, ok)
+	assert.Equal(t, uint64(1_200), niReset[0], "upload delta should match new counter value after reset")
+	assert.Equal(t, uint64(1_500), niReset[1], "download delta should match new counter value after reset")
+}
+
 func TestApplyNetworkTotals(t *testing.T) {
 	tests := []struct {
 		name                  string
@@ -441,10 +478,13 @@ func TestApplyNetworkTotals(t *testing.T) {
 			)
 
 			if tt.expectReset {
-				// Should have reset network tracking state - delta trackers should be cleared
+				// Should have reset network tracking state - maps cleared and stats zeroed
-				// Note: initializeNetIoStats resets the maps, then applyNetworkTotals sets nis back
+				assert.NotContains(t, a.netIoStats, cacheTimeMs, "cache entry should be cleared after reset")
-				assert.Contains(t, a.netIoStats, cacheTimeMs, "cache entry should exist after reset")
 				assert.NotContains(t, a.netInterfaceDeltaTrackers, cacheTimeMs, "tracker should be cleared on reset")
+				assert.Zero(t, systemStats.NetworkSent)
+				assert.Zero(t, systemStats.NetworkRecv)
+				assert.Zero(t, systemStats.Bandwidth[0])
+				assert.Zero(t, systemStats.Bandwidth[1])
 			} else {
 				// Should have applied stats
 				assert.Equal(t, tt.expectedNetworkSent, systemStats.NetworkSent)