add a logging.NullConnectionTracer

The NullConnectionTracer can be embedded, to make it easier to access just a
few of the calls.

codecov.yml

@@ -12,6 +12,7 @@ coverage:
     - internal/utils/newconnectionid_linkedlist.go
     - internal/utils/packetinterval_linkedlist.go
     - internal/utils/linkedlist/linkedlist.go
+    - logging/null_connection_tracer.go
     - fuzzing/
     - metrics/
   status:

logging/null_connection_tracer.go

@@ -0,0 +1,45 @@
+package logging
+
+import (
+	"net"
+	"time"
+)
+
+// The NullConnectionTracer is a ConnectionTracer that does nothing.
+// It is useful for embedding. Don't modify this variable!
+var NullConnectionTracer ConnectionTracer = &nullConnectionTracer{}
+
+type nullConnectionTracer struct{}
+
+var _ ConnectionTracer = &nullConnectionTracer{}
+
+func (n nullConnectionTracer) StartedConnection(local, remote net.Addr, srcConnID, destConnID ConnectionID) {
+}
+
+func (n nullConnectionTracer) NegotiatedVersion(chosen VersionNumber, clientVersions, serverVersions []VersionNumber) {
+}
+func (n nullConnectionTracer) ClosedConnection(err error)                                         {}
+func (n nullConnectionTracer) SentTransportParameters(*TransportParameters)                       {}
+func (n nullConnectionTracer) ReceivedTransportParameters(*TransportParameters)                   {}
+func (n nullConnectionTracer) RestoredTransportParameters(*TransportParameters)                   {}
+func (n nullConnectionTracer) SentPacket(*ExtendedHeader, ByteCount, *AckFrame, []Frame)          {}
+func (n nullConnectionTracer) ReceivedVersionNegotiationPacket(*Header, []VersionNumber)          {}
+func (n nullConnectionTracer) ReceivedRetry(*Header)                                              {}
+func (n nullConnectionTracer) ReceivedPacket(hdr *ExtendedHeader, size ByteCount, frames []Frame) {}
+func (n nullConnectionTracer) BufferedPacket(PacketType)                                          {}
+func (n nullConnectionTracer) DroppedPacket(PacketType, ByteCount, PacketDropReason)              {}
+func (n nullConnectionTracer) UpdatedMetrics(rttStats *RTTStats, cwnd, bytesInFlight ByteCount, packetsInFlight int) {
+}
+func (n nullConnectionTracer) AcknowledgedPacket(EncryptionLevel, PacketNumber)            {}
+func (n nullConnectionTracer) LostPacket(EncryptionLevel, PacketNumber, PacketLossReason)  {}
+func (n nullConnectionTracer) UpdatedCongestionState(CongestionState)                      {}
+func (n nullConnectionTracer) UpdatedPTOCount(uint32)                                      {}
+func (n nullConnectionTracer) UpdatedKeyFromTLS(EncryptionLevel, Perspective)              {}
+func (n nullConnectionTracer) UpdatedKey(keyPhase KeyPhase, remote bool)                   {}
+func (n nullConnectionTracer) DroppedEncryptionLevel(EncryptionLevel)                      {}
+func (n nullConnectionTracer) DroppedKey(KeyPhase)                                         {}
+func (n nullConnectionTracer) SetLossTimer(TimerType, EncryptionLevel, time.Time)          {}
+func (n nullConnectionTracer) LossTimerExpired(timerType TimerType, level EncryptionLevel) {}
+func (n nullConnectionTracer) LossTimerCanceled()                                          {}
+func (n nullConnectionTracer) Close()                                                      {}
+func (n nullConnectionTracer) Debug(name, msg string)                                      {}