logging / qlog: add support for DPLPMTUD (#4517)

* logging / qlog: add support for DPLPMTUD

* improve the MTU discovery integration test

qlog/connection_tracer.go

@@ -76,6 +76,9 @@ func NewConnectionTracer(w io.WriteCloser, p logging.Perspective, odcid protocol
 		LostPacket: func(encLevel protocol.EncryptionLevel, pn protocol.PacketNumber, lossReason logging.PacketLossReason) {
 			t.LostPacket(encLevel, pn, lossReason)
 		},
+		UpdatedMTU: func(mtu logging.ByteCount, done bool) {
+			t.UpdatedMTU(mtu, done)
+		},
 		UpdatedCongestionState: func(state logging.CongestionState) {
 			t.UpdatedCongestionState(state)
 		},
@@ -367,6 +370,10 @@ func (t *connectionTracer) LostPacket(encLevel protocol.EncryptionLevel, pn prot
 	})
 }
 
+func (t *connectionTracer) UpdatedMTU(mtu protocol.ByteCount, done bool) {
+	t.recordEvent(time.Now(), &eventMTUUpdated{mtu: mtu, done: done})
+}
+
 func (t *connectionTracer) UpdatedCongestionState(state logging.CongestionState) {
 	t.recordEvent(time.Now(), &eventCongestionStateUpdated{state: congestionState(state)})
 }

qlog/connection_tracer_test.go

@@ -94,7 +94,7 @@ var _ = Describe("Tracing", func() {
 		Expect(m).To(HaveKey("title"))
 		Expect(m).To(HaveKey("trace"))
 		trace := m["trace"].(map[string]interface{})
-		Expect(trace).To(HaveKey(("common_fields")))
+		Expect(trace).To(HaveKey("common_fields"))
 		commonFields := trace["common_fields"].(map[string]interface{})
 		Expect(commonFields).To(HaveKeyWithValue("ODCID", "deadbeef"))
 		Expect(commonFields).To(HaveKeyWithValue("group_id", "deadbeef"))
@@ -723,6 +723,17 @@ var _ = Describe("Tracing", func() {
 			Expect(ev).To(HaveKeyWithValue("trigger", "reordering_threshold"))
 		})
 
+		It("records MTU discovery updates", func() {
+			tracer.UpdatedMTU(1337, true)
+			tracer.Close()
+			entry := exportAndParseSingle(buf)
+			Expect(entry.Time).To(BeTemporally("~", time.Now(), scaleDuration(10*time.Millisecond)))
+			Expect(entry.Name).To(Equal("recovery:mtu_updated"))
+			ev := entry.Event
+			Expect(ev).To(HaveKeyWithValue("mtu", float64(1337)))
+			Expect(ev).To(HaveKeyWithValue("done", true))
+		})
+
 		It("records congestion state updates", func() {
 			tracer.UpdatedCongestionState(logging.CongestionStateCongestionAvoidance)
 			tracer.Close()

qlog/event.go

@@ -294,6 +294,20 @@ type metrics struct {
 	PacketsInFlight  int
 }
 
+type eventMTUUpdated struct {
+	mtu  protocol.ByteCount
+	done bool
+}
+
+func (e eventMTUUpdated) Category() category { return categoryRecovery }
+func (e eventMTUUpdated) Name() string       { return "mtu_updated" }
+func (e eventMTUUpdated) IsNil() bool        { return false }
+
+func (e eventMTUUpdated) MarshalJSONObject(enc *gojay.Encoder) {
+	enc.Uint64Key("mtu", uint64(e.mtu))
+	enc.BoolKey("done", e.done)
+}
+
 type eventMetricsUpdated struct {
 	Last    *metrics
 	Current *metrics