small patch for EDNS0 cookie support (#350)

* Add EDNS0 Cookie (option 10) support.

* Add EDNS0 Cookie processing.

* Fix nits.

* Add EDNS0 cookie support mention.

README.md

@@ -62,7 +62,7 @@ Send pull request if you want to be listed here.
 * Server side programming (mimicking the net/http package);
 * Client side programming;
 * DNSSEC: signing, validating and key generation for DSA, RSA and ECDSA;
-* EDNS0, NSID;
+* EDNS0, NSID, Cookies;
 * AXFR/IXFR;
 * TSIG, SIG(0);
 * DNS over TLS: optional encrypted connection between client and server;
@@ -141,6 +141,7 @@ Example programs can be found in the `github.com/miekg/exdns` repository.
 * 7553 - URI record
 * xxxx - EDNS0 DNS Update Lease (draft)
 * yyyy - DNS over TLS: Initiation and Performance Considerations (draft)
+* xxxx - Domain Name System (DNS) Cookies (draft-ietf-dnsop-cookies)
 
 ## Loosely based upon
 

edns.go

@@ -17,6 +17,7 @@ const (
 	EDNS0N3U         = 0x7     // NSEC3 Hash Understood
 	EDNS0SUBNET      = 0x8     // client-subnet (RFC6891)
 	EDNS0EXPIRE      = 0x9     // EDNS0 expire
+	EDNS0COOKIE      = 0xa     // EDNS0 Cookie
 	EDNS0SUBNETDRAFT = 0x50fa  // Don't use! Use EDNS0SUBNET
 	EDNS0LOCALSTART  = 0xFDE9  // Beginning of range reserved for local/experimental use (RFC6891)
 	EDNS0LOCALEND    = 0xFFFE  // End of range reserved for local/experimental use (RFC6891)
@@ -56,6 +57,8 @@ func (rr *OPT) String() string {
 			if o.(*EDNS0_SUBNET).DraftOption {
 				s += " (draft)"
 			}
+		case *EDNS0_COOKIE:
+			s += "\n; COOKIE: " + o.String()
 		case *EDNS0_UL:
 			s += "\n; UPDATE LEASE: " + o.String()
 		case *EDNS0_LLQ:
@@ -286,6 +289,32 @@ func (e *EDNS0_SUBNET) String() (s string) {
 	return
 }
 
+// The Cookie EDNS0 option
+//
+//o := new(dns.OPT)
+//o.Hdr.Name = "."
+//o.Hdr.Rrtype = dns.TypeOPT
+//e := new(dns.EDNS0_COOKIE)
+//e.Code = dns.EDNS0COOKIE
+//e.Cookie = "24a5ac.."
+//o.Option = append(o.Option, e)
+type EDNS0_COOKIE struct {
+	Code   uint16 // Always EDNS0COOKIE
+	Cookie string // Hex-encoded cookie data
+}
+
+func (e *EDNS0_COOKIE) pack() ([]byte, error) {
+	h, err := hex.DecodeString(e.Cookie)
+	if err != nil {
+		return nil, err
+	}
+	return h, nil
+}
+
+func (e *EDNS0_COOKIE) Option() uint16        { return EDNS0COOKIE }
+func (e *EDNS0_COOKIE) unpack(b []byte) error { e.Cookie = hex.EncodeToString(b); return nil }
+func (e *EDNS0_COOKIE) String() string        { return e.Cookie }
+
 // The EDNS0_UL (Update Lease) (draft RFC) option is used to tell the server to set
 // an expiration on an update RR. This is helpful for clients that cannot clean
 // up after themselves. This is a draft RFC and more information can be found at

msg.go

@@ -953,6 +953,13 @@ func unpackStructValue(val reflect.Value, msg []byte, off int) (off1 int, err er
 					if code == EDNS0SUBNETDRAFT {
 						e.DraftOption = true
 					}
+				case EDNS0COOKIE:
+					e := new(EDNS0_COOKIE)
+					if err := e.unpack(msg[off1 : off1+int(optlen)]); err != nil {
+						return lenmsg, err
+					}
+					edns = append(edns, e)
+					off = off1 + int(optlen)
 				case EDNS0UL:
 					e := new(EDNS0_UL)
 					if err := e.unpack(msg[off1 : off1+int(optlen)]); err != nil {