read the ECN bits

internal/protocol/protocol.go

@@ -37,10 +37,10 @@ func (t PacketType) String() string {
 type ECN uint8
 
 const (
-	ECNNon ECN = iota
-	ECT0
-	ECT1
-	ECNCE
+	ECNNon ECN = iota // 00
+	ECT1              // 01
+	ECT0              // 10
+	ECNCE             // 11
 )
 
 // A ByteCount in QUIC

internal/protocol/protocol_test.go

@@ -15,4 +15,11 @@ var _ = Describe("Protocol", func() {
 			Expect(PacketType(10).String()).To(Equal("unknown packet type: 10"))
 		})
 	})
+
+	It("converts ECN bits from the IP header wire to the correct types", func() {
+		Expect(ECN(0)).To(Equal(ECNNon))
+		Expect(ECN(0b00000010)).To(Equal(ECT0))
+		Expect(ECN(0b00000001)).To(Equal(ECT1))
+		Expect(ECN(0b00000011)).To(Equal(ECNCE))
+	})
 })