add tracing for sent and received packets

internal/ackhandler/interfaces.go

@@ -39,6 +39,9 @@ type SentPacketHandler interface {
 
 	GetAlarmTimeout() time.Time
 	OnAlarm() error
+
+	// report some congestion statistics. For tracing only.
+	GetStats() *State
 }
 
 // ReceivedPacketHandler handles ACKs needed to send for incoming packets
@@ -50,3 +53,12 @@ type ReceivedPacketHandler interface {
 	GetAlarmTimeout() time.Time
 	GetAckFrame(protocol.EncryptionLevel) *wire.AckFrame
 }
+
+type State struct {
+	MinRTT      time.Duration
+	SmoothedRTT time.Duration
+	LatestRTT   time.Duration
+
+	BytesInFlight    protocol.ByteCount
+	CongestionWindow protocol.ByteCount
+}

internal/ackhandler/sent_packet_handler.go

@@ -670,3 +670,13 @@ func (h *sentPacketHandler) ResetForRetry() error {
 	h.updateLossDetectionAlarm()
 	return nil
 }
+
+func (h *sentPacketHandler) GetStats() *State {
+	return &State{
+		MinRTT:           h.rttStats.MinRTT(),
+		SmoothedRTT:      h.rttStats.SmoothedOrInitialRTT(),
+		LatestRTT:        h.rttStats.LatestRTT(),
+		BytesInFlight:    h.bytesInFlight,
+		CongestionWindow: h.congestion.GetCongestionWindow(),
+	}
+}

internal/mocks/ackhandler/sent_packet_handler.go

@@ -106,6 +106,20 @@ func (mr *MockSentPacketHandlerMockRecorder) GetLowestPacketNotConfirmedAcked()
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "GetLowestPacketNotConfirmedAcked", reflect.TypeOf((*MockSentPacketHandler)(nil).GetLowestPacketNotConfirmedAcked))
 }
 
+// GetStats mocks base method
+func (m *MockSentPacketHandler) GetStats() *ackhandler.State {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "GetStats")
+	ret0, _ := ret[0].(*ackhandler.State)
+	return ret0
+}
+
+// GetStats indicates an expected call of GetStats
+func (mr *MockSentPacketHandlerMockRecorder) GetStats() *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "GetStats", reflect.TypeOf((*MockSentPacketHandler)(nil).GetStats))
+}
+
 // OnAlarm mocks base method
 func (m *MockSentPacketHandler) OnAlarm() error {
 	m.ctrl.T.Helper()