CopyFrom pattern for DNS and use it for Cookie

dns/definitions.go

@@ -9,6 +9,7 @@ import (
 
 // common errors. Taken from golang.org/x/net/dns/dnsmessage module.
 var (
+	errNoResponse         = errors.New("no DNS response")
 	errNameTooLong        = errors.New("DNS name exceeds maximum length")
 	errNoNullTerm         = errors.New("DNS name missing null terminator")
 	errCalcLen            = errors.New("DNS calculated name label length exceeds remaining buffer length")
@@ -141,6 +142,10 @@ func (flags HeaderFlags) String() string {
 	return string(flags.appendF(buf))
 }
 
+func (flags RCode) Error() string {
+	return flags.String()
+}
+
 func (flags HeaderFlags) appendF(buf []byte) []byte {
 	writeBit := func(b bool, s string) {
 		if b {