Add fallback local DNS server for iOS

dns/rcode.go

@@ -1,33 +1,17 @@
 package dns
 
-import F "github.com/sagernet/sing/common/format"
-
-const (
-	RCodeSuccess        RCodeError = 0 // NoError
-	RCodeFormatError    RCodeError = 1 // FormErr
-	RCodeServerFailure  RCodeError = 2 // ServFail
-	RCodeNameError      RCodeError = 3 // NXDomain
-	RCodeNotImplemented RCodeError = 4 // NotImp
-	RCodeRefused        RCodeError = 5 // Refused
+import (
+	mDNS "github.com/miekg/dns"
 )
 
-type RCodeError uint16
+const (
+	RcodeFormatError RcodeError = mDNS.RcodeFormatError
+	RcodeNameError   RcodeError = mDNS.RcodeNameError
+	RcodeRefused     RcodeError = mDNS.RcodeRefused
+)
 
-func (e RCodeError) Error() string {
-	switch e {
-	case RCodeSuccess:
-		return "success"
-	case RCodeFormatError:
-		return "format error"
-	case RCodeServerFailure:
-		return "server failure"
-	case RCodeNameError:
-		return "name error"
-	case RCodeNotImplemented:
-		return "not implemented"
-	case RCodeRefused:
-		return "refused"
-	default:
-		return F.ToString("unknown error: ", uint16(e))
-	}
+type RcodeError int
+
+func (e RcodeError) Error() string {
+	return mDNS.RcodeToString[int(e)]
 }