feed ECN feedback into the congestion controller

internal/ackhandler/ecn.go

@@ -21,6 +21,13 @@ const (
 // must fit into an uint8, otherwise numSentTesting and numLostTesting must have a larger type
 const numECNTestingPackets = 10
 
+type ecnHandler interface {
+	SentPacket(protocol.PacketNumber, protocol.ECN)
+	Mode() protocol.ECN
+	HandleNewlyAcked(packets []*packet, ect0, ect1, ecnce int64) (congested bool)
+	LostPacket(protocol.PacketNumber)
+}
+
 // The ecnTracker performs ECN validation of a path.
 // Once failed, it doesn't do any re-validation of the path.
 // It is designed only work for 1-RTT packets, it doesn't handle multiple packet number spaces.
@@ -42,6 +49,8 @@ type ecnTracker struct {
 	logger utils.Logger
 }
 
+var _ ecnHandler = &ecnTracker{}
+
 func newECNTracker(logger utils.Logger, tracer logging.ConnectionTracer) *ecnTracker {
 	return &ecnTracker{
 		firstTestingPacket: protocol.InvalidPacketNumber,