implement version-dependent parsing of the Public Header

internal/utils/byteorder.go

@@ -3,6 +3,8 @@ package utils
 import (
 	"bytes"
 	"io"
+
+	"github.com/lucas-clemente/quic-go/protocol"
 )
 
 // A ByteOrder specifies how to convert byte sequences into 16-, 32-, or 64-bit unsigned integers.
@@ -23,3 +25,12 @@ type ByteOrder interface {
 	ReadUfloat16(io.ByteReader) (uint64, error)
 	WriteUfloat16(*bytes.Buffer, uint64)
 }
+
+// GetByteOrder gets the ByteOrder (little endian or big endian) used to represent values on the wire
+// from QUIC 39, values are encoded in big endian, before that in little endian
+func GetByteOrder(v protocol.VersionNumber) ByteOrder {
+	if v < protocol.Version39 {
+		return LittleEndian
+	}
+	return BigEndian
+}

internal/utils/byteorder_test.go

@@ -0,0 +1,18 @@
+package utils
+
+import (
+	"github.com/lucas-clemente/quic-go/protocol"
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Byte Order", func() {
+	It("says little Little Endian before QUIC 39", func() {
+		Expect(GetByteOrder(protocol.Version36)).To(Equal(LittleEndian))
+		Expect(GetByteOrder(protocol.Version37)).To(Equal(LittleEndian))
+	})
+
+	It("says little Little Endian for QUIC 39", func() {
+		Expect(GetByteOrder(protocol.Version39)).To(Equal(BigEndian))
+	})
+})