wire: save ECN counts on the ACK frame (#3829)

internal/wire/ack_frame.go

@@ -90,13 +90,22 @@ func parseAckFrame(r *bytes.Reader, typ uint64, ackDelayExponent uint8, _ protoc
 		return nil, errInvalidAckRanges
 	}
 
-	// parse (and skip) the ECN section
 	if ecn {
-		for i := 0; i < 3; i++ {
+		ect0, err := quicvarint.Read(r)
-			if _, err := quicvarint.Read(r); err != nil {
+		if err != nil {
-				return nil, err
+			return nil, err
-			}
 		}
+		frame.ECT0 = ect0
+		ect1, err := quicvarint.Read(r)
+		if err != nil {
+			return nil, err
+		}
+		frame.ECT1 = ect1
+		ecnce, err := quicvarint.Read(r)
+		if err != nil {
+			return nil, err
+		}
+		frame.ECNCE = ecnce
 	}
 
 	return frame, nil

internal/wire/ack_frame_test.go

@@ -170,6 +170,9 @@ var _ = Describe("ACK Frame (for IETF QUIC)", func() {
 				Expect(frame.LargestAcked()).To(Equal(protocol.PacketNumber(100)))
 				Expect(frame.LowestAcked()).To(Equal(protocol.PacketNumber(90)))
 				Expect(frame.HasMissingRanges()).To(BeFalse())
+				Expect(frame.ECT0).To(BeEquivalentTo(0x42))
+				Expect(frame.ECT1).To(BeEquivalentTo(0x12345))
+				Expect(frame.ECNCE).To(BeEquivalentTo(0x12345678))
 				Expect(b.Len()).To(BeZero())
 			})