Add ISDN record (#1515)

We had the type code, this add the rest. Other RRs from 1183 are also
fully impl. don't know why this one wasn't.

Signed-off-by: Miek Gieben <miek@miek.nl>

README.md

@@ -126,6 +126,7 @@ Example programs can be found in the `github.com/miekg/exdns` repository.
 *all of them*
 
 * 103{4,5} - DNS standard
+* 1183 - ISDN, X25 and other deprecated records
 * 1348 - NSAP record (removed the record)
 * 1982 - Serial Arithmetic
 * 1876 - LOC record

parse_test.go

@@ -1450,6 +1450,23 @@ func TestParseHINFO(t *testing.T) {
 	}
 }
 
+func TestParseISDN(t *testing.T) {
+	dt := map[string]string{
+		"example.net. ISDN A B":         "example.net.	3600	IN	ISDN	\"A\" \"B\"",
+		"example.net. ISDN \"A\" \"B\"": "example.net.	3600	IN	ISDN	\"A\" \"B\"",
+	}
+	for i, o := range dt {
+		rr, err := NewRR(i)
+		if err != nil {
+			t.Error("failed to parse RR: ", err)
+			continue
+		}
+		if rr.String() != o {
+			t.Errorf("`%s' should be equal to\n`%s', but is     `%s'", i, o, rr.String())
+		}
+	}
+}
+
 func TestParseCAA(t *testing.T) {
 	lt := map[string]string{
 		"example.net.	CAA	0 issue \"symantec.com\"":            "example.net.\t3600\tIN\tCAA\t0 issue \"symantec.com\"",

scan_rr.go

@@ -220,6 +220,29 @@ func (rr *HINFO) parse(c *zlexer, o string) *ParseError {
 
 	rr.Cpu = chunks[0]
 	rr.Os = strings.Join(chunks[1:], " ")
+	return nil
+}
+
+// according to RFC 1183 the parsing is identical to HINFO, so just use that code.
+func (rr *ISDN) parse(c *zlexer, o string) *ParseError {
+	chunks, e := endingToTxtSlice(c, "bad ISDN Fields")
+	if e != nil {
+		return e
+	}
+
+	if ln := len(chunks); ln == 0 {
+		return nil
+	} else if ln == 1 {
+		// Can we split it?
+		if out := strings.Fields(chunks[0]); len(out) > 1 {
+			chunks = out
+		} else {
+			chunks = append(chunks, "")
+		}
+	}
+
+	rr.Address = chunks[0]
+	rr.SubAddress = strings.Join(chunks[1:], " ")
 
 	return nil
 }

types.go

@@ -402,6 +402,17 @@ func (rr *X25) String() string {
 	return rr.Hdr.String() + rr.PSDNAddress
 }
 
+// ISDN RR. See RFC 1183, Section 3.2.
+type ISDN struct {
+	Hdr        RR_Header
+	Address    string
+	SubAddress string
+}
+
+func (rr *ISDN) String() string {
+	return rr.Hdr.String() + sprintTxt([]string{rr.Address, rr.SubAddress})
+}
+
 // RT RR. See RFC 1183, Section 3.3.
 type RT struct {
 	Hdr        RR_Header