Add support for custom EDNS options in GoDNS.

A handful of EDNS options have been standardized, and they each have a type defined in GoDNS.  However there is currently no way a development team can use GoDNS with internally defined options, or with new options that may be proposed in the future.

This change solves the problem by giving users an EDNS0_CUSTOM type to allow clients to send, and servers to receive, custom EDNS options.

client_test.go

@@ -62,6 +62,79 @@ func TestClientEDNS0(t *testing.T) {
 	}
 }
 
+// Validates the transmission and parsing of custom EDNS0 options.
+func TestClientEDNS0Custom(t *testing.T) {
+	handler := func(w ResponseWriter, req *Msg) {
+		m := new(Msg)
+		m.SetReply(req)
+
+		m.Extra = make([]RR, 1, 2)
+		m.Extra[0] = &TXT{Hdr: RR_Header{Name: m.Question[0].Name, Rrtype: TypeTXT, Class: ClassINET, Ttl: 0}, Txt: []string{"Hello custom edns"}}
+
+		// If the custom options are what we expect, then reflect them back.
+		ec1 := req.Extra[0].(*OPT).Option[0].(*EDNS0_CUSTOM).String()
+		ec2 := req.Extra[0].(*OPT).Option[1].(*EDNS0_CUSTOM).String()
+		if ec1 == "1979:0x0707" && ec2 == "1997:0x0601" {
+			m.Extra = append(m.Extra, req.Extra[0])
+		}
+
+		w.WriteMsg(m)
+	}
+
+	HandleFunc("miek.nl.", handler)
+	defer HandleRemove("miek.nl.")
+
+	s, addrstr, err := RunLocalUDPServer("127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("Unable to run test server: %s", err)
+	}
+	defer s.Shutdown()
+
+	m := new(Msg)
+	m.SetQuestion("miek.nl.", TypeTXT)
+
+	ec1 := &EDNS0_CUSTOM{Code: 1979, Data: []byte{7, 7}}
+	ec2 := &EDNS0_CUSTOM{Code: 1997, Data: []byte{6, 1}}
+	o := &OPT{Hdr: RR_Header{Name: ".", Rrtype: TypeOPT}, Option: []EDNS0{ec1, ec2}}
+	m.Extra = append(m.Extra, o)
+
+	c := new(Client)
+	r, _, e := c.Exchange(m, addrstr)
+	if e != nil {
+		t.Logf("failed to exchange: %s", e.Error())
+		t.Fail()
+	}
+
+	if r != nil && r.Rcode != RcodeSuccess {
+		t.Log("failed to get a valid answer")
+		t.Fail()
+		t.Logf("%v\n", r)
+	}
+
+	txt := r.Extra[0].(*TXT).Txt[0]
+	if txt != "Hello custom edns" {
+		t.Log("Unexpected result for miek.nl", txt, "!= Hello custom edns")
+		t.Fail()
+	}
+
+	// Validate the custom options in the reply.
+	exp := "1979:0x0707"
+	got := r.Extra[1].(*OPT).Option[0].(*EDNS0_CUSTOM).String()
+	if got != exp {
+		t.Log("failed to get custom edns0 answer; got %s, expected %s", got, exp)
+		t.Fail()
+		t.Logf("%v\n", r)
+	}
+
+	exp = "1997:0x0601"
+	got = r.Extra[1].(*OPT).Option[1].(*EDNS0_CUSTOM).String()
+	if got != exp {
+		t.Log("failed to get custom edns0 answer; got %s, expected %s", got, exp)
+		t.Fail()
+		t.Logf("%v\n", r)
+	}
+}
+
 func TestSingleSingleInflight(t *testing.T) {
 	HandleFunc("miek.nl.", HelloServer)
 	defer HandleRemove("miek.nl.")

edns.go

@@ -68,6 +68,8 @@ func (rr *OPT) String() string {
 			s += "\n; DS HASH UNDERSTOOD: " + o.String()
 		case *EDNS0_N3U:
 			s += "\n; NSEC3 HASH UNDERSTOOD: " + o.String()
+		case *EDNS0_CUSTOM:
+			s += "\n; CUSTOM OPT: " + o.String()
 		}
 	}
 	return s
@@ -76,8 +78,9 @@ func (rr *OPT) String() string {
 func (rr *OPT) len() int {
 	l := rr.Hdr.len()
 	for i := 0; i < len(rr.Option); i++ {
+		l += 4 // Account for 2-byte option code and 2-byte option length.
 		lo, _ := rr.Option[i].pack()
-		l += 2 + len(lo)
+		l += len(lo)
 	}
 	return l
 }
@@ -475,3 +478,31 @@ func (e *EDNS0_EXPIRE) unpack(b []byte) error {
 	e.Expire = uint32(b[0])<<24 | uint32(b[1])<<16 | uint32(b[2])<<8 | uint32(b[3])
 	return nil
 }
+
+type EDNS0_CUSTOM struct {
+	Code uint16
+	Data []byte
+}
+
+func (e *EDNS0_CUSTOM) Option() uint16 { return e.Code }
+func (e *EDNS0_CUSTOM) String() string {
+	return strconv.FormatInt(int64(e.Code), 10) + ":0x" + hex.EncodeToString(e.Data)
+}
+
+func (e *EDNS0_CUSTOM) pack() ([]byte, error) {
+	b := make([]byte, len(e.Data))
+	copied := copy(b, e.Data)
+	if copied != len(e.Data) {
+		return nil, ErrBuf
+	}
+	return b, nil
+}
+
+func (e *EDNS0_CUSTOM) unpack(b []byte) error {
+	e.Data = make([]byte, len(b))
+	copied := copy(e.Data, b)
+	if copied != len(b) {
+		return ErrBuf
+	}
+	return nil
+}

msg.go

@@ -1048,7 +1048,12 @@ func unpackStructValue(val reflect.Value, msg []byte, off int) (off1 int, err er
 					edns = append(edns, e)
 					off = off1 + int(optlen)
 				default:
-					// do nothing?
+					e := new(EDNS0_CUSTOM)
+					e.Code = code
+					if err := e.unpack(msg[off1 : off1+int(optlen)]); err != nil {
+						return lenmsg, err
+					}
+					edns = append(edns, e)
 					off = off1 + int(optlen)
 				}
 				if off < lenrd {