feat: add ip-version param

constant/dns.go

@@ -68,3 +68,46 @@ func (e DNSMode) String() string {
 		return "unknown"
 	}
 }
+
+type DNSPrefer int
+
+const (
+	DualStack DNSPrefer = iota
+	IPv4Only
+	IPv6Only
+	IPv4Prefer
+	IPv6Prefer
+)
+
+var dnsPreferMap = map[string]DNSPrefer{
+	DualStack.String():  DualStack,
+	IPv4Only.String():   IPv4Only,
+	IPv6Only.String():   IPv6Only,
+	IPv4Prefer.String(): IPv4Prefer,
+	IPv6Prefer.String(): IPv6Prefer,
+}
+
+func (d DNSPrefer) String() string {
+	switch d {
+	case DualStack:
+		return "dual"
+	case IPv4Only:
+		return "ipv4"
+	case IPv6Only:
+		return "ipv6"
+	case IPv4Prefer:
+		return "ipv4-prefer"
+	case IPv6Prefer:
+		return "ipv6-prefer"
+	default:
+		return "dual"
+	}
+}
+
+func NewDNSPrefer(prefer string) DNSPrefer {
+	if p, ok := dnsPreferMap[prefer]; ok {
+		return p
+	} else {
+		return DualStack
+	}
+}