change supported version to slice, since the order matters for the SHLO

protocol/version.go

@@ -1,8 +1,23 @@
 package protocol
 
+import (
+	"bytes"
+
+	"github.com/lucas-clemente/quic-go/utils"
+)
+
 // VersionNumber is a version number as int
 type VersionNumber int
 
+// SupportedVersions lists the versions that the server supports
+var SupportedVersions = []VersionNumber{
+	30,
+	32,
+}
+
+// SupportedVersionsAsTags is needed for the SHLO crypto message
+var SupportedVersionsAsTags []byte
+
 // VersionNumberToTag maps version numbers ('32') to tags ('Q032')
 func VersionNumberToTag(vn VersionNumber) uint32 {
 	v := uint32(vn)
@@ -13,3 +28,21 @@ func VersionNumberToTag(vn VersionNumber) uint32 {
 func VersionTagToNumber(v uint32) VersionNumber {
 	return VersionNumber(((v>>8)&0xff-'0')*100 + ((v>>16)&0xff-'0')*10 + ((v>>24)&0xff - '0'))
 }
+
+// IsSupportedVersion returns true if the server supports this version
+func IsSupportedVersion(v VersionNumber) bool {
+	for _, t := range SupportedVersions {
+		if t == v {
+			return true
+		}
+	}
+	return false
+}
+
+func init() {
+	var b bytes.Buffer
+	for _, v := range SupportedVersions {
+		utils.WriteUint32(&b, VersionNumberToTag(v))
+	}
+	SupportedVersionsAsTags = b.Bytes()
+}

protocol/version_test.go

@@ -17,4 +17,8 @@ var _ = Describe("Version", func() {
 		Expect(protocol.VersionNumberToTag(protocol.VersionNumber(123))).To(Equal(uint32('Q' + '1'<<8 + '2'<<16 + '3'<<24)))
 		Expect(protocol.VersionNumberToTag(protocol.VersionNumber(30))).To(Equal(uint32('Q' + '0'<<8 + '3'<<16 + '0'<<24)))
 	})
+
+	It("has proper tag list", func() {
+		Expect(protocol.SupportedVersionsAsTags).To(Equal([]byte("Q030Q032")))
+	})
 })