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()
+}