return errors when translating DNSRR->dns.RR (#15)

* add new method that returns error
* log failures to translate records
* deprecate old method

fixes #13

handler.go

@@ -44,22 +44,9 @@ func (h *Handler) Handle(w dns.ResponseWriter, r *dns.Msg) {
 	}
 
 	// Parse google RRs to DNS RRs
-	answers := []dns.RR{}
-	for _, a := range dnsResp.Answer {
-		answers = append(answers, a.RR())
-	}
-
-	// Parse google RRs to DNS RRs
-	authorities := []dns.RR{}
-	for _, ns := range dnsResp.Authority {
-		authorities = append(authorities, ns.RR())
-	}
-
-	// Parse google RRs to DNS RRs
-	extras := []dns.RR{}
-	for _, extra := range dnsResp.Extra {
-		authorities = append(authorities, extra.RR())
-	}
+	answers := transformRR(dnsResp.Answer, "answer")
+	authorities := transformRR(dnsResp.Authority, "authority")
+	extras := transformRR(dnsResp.Extra, "extra")
 
 	resp := dns.Msg{
 		MsgHdr: dns.MsgHdr{
@@ -87,3 +74,18 @@ func (h *Handler) Handle(w dns.ResponseWriter, r *dns.Msg) {
 		log.Errorln("Error writing DNS response:", err)
 	}
 }
+
+// for a given []DNSRR, transform to dns.RR, logging if any errors occur
+func transformRR(rrs []DNSRR, logType string) []dns.RR {
+	var t []dns.RR
+
+	for _, r := range rrs {
+		if rr, err := r.DNSRR(); err != nil {
+			log.Errorln("unable to translate record rr", logType, r, err)
+		} else {
+			t = append(t, rr)
+		}
+	}
+
+	return t
+}

provider.go

@@ -18,14 +18,27 @@ type DNSRR struct {
 	Data string `json:"data,omitempty"`
 }
 
-// RR transforms a DNSRR to a dns.RR.
+// RR is deprecated as of 2.2.0, use DNSRR instead
 func (r DNSRR) RR() dns.RR {
 	hdr := dns.RR_Header{Name: r.Name, Rrtype: r.Type, Class: dns.ClassINET, Ttl: r.TTL}
 	str := hdr.String() + r.Data
 	rr, _ := dns.NewRR(str)
 	return rr
 }
 
+// DNSRR transforms a DNSRR to a dns.RR; returns `nil` if an RR could not be
+// created from the record.
+func (r DNSRR) DNSRR() (dns.RR, error) {
+	hdr := dns.RR_Header{Name: r.Name, Rrtype: r.Type, Class: dns.ClassINET, Ttl: r.TTL}
+	str := hdr.String() + r.Data
+	return dns.NewRR(str)
+}
+
+func (r DNSRR) String() string {
+	hdr := dns.RR_Header{Name: r.Name, Rrtype: r.Type, Class: dns.ClassINET, Ttl: r.TTL}
+	return hdr.String()
+}
+
 // DNSResponse represents a complete DNS server response, to be served by the
 // DNS server handler.
 type DNSResponse struct {

provider_test.go

@@ -17,7 +17,10 @@ func TestDNSRRTypeA(t *testing.T) {
 		Data: "10.10.10.1",
 	}
 
-	rr = r.RR()
+	rr, err := r.DNSRR()
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	v, ok := rr.(*dns.A)
 	if !ok {
@@ -46,7 +49,10 @@ func TestDNSRRTypeMX(t *testing.T) {
 		Data: "10 mail.who.wut.co.jp",
 	}
 
-	rr = r.RR()
+	rr, err := r.DNSRR()
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	v, ok := rr.(*dns.MX)
 	if !ok {
@@ -78,7 +84,10 @@ func TestDNSRRTypeCNAME(t *testing.T) {
 		Data: "omg.wtf.bbq",
 	}
 
-	rr = r.RR()
+	rr, err := r.DNSRR()
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	v, ok := rr.(*dns.CNAME)
 	if !ok {
@@ -107,7 +116,10 @@ func TestDNSRRTypeAAAA(t *testing.T) {
 		Data: "::1",
 	}
 
-	rr = r.RR()
+	rr, err := r.DNSRR()
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	v, ok := rr.(*dns.AAAA)
 	if !ok {