Fix for issue/140:

- Removal of RFC2136_ZONE from help text
 - Query nameserver directly to find zone we have to update
 - During insert, make sure the new record is the ONLY challence.
   (I had a few panics, hence 3 challences left. Not good.)

README.md

@@ -97,7 +97,7 @@ GLOBAL OPTIONS:
 									digitalocean: DO_AUTH_TOKEN
 									dnsimple: DNSIMPLE_EMAIL, DNSIMPLE_API_KEY
 									route53: AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_REGION
-									rfc2136: RFC2136_TSIG_KEY, RFC2136_TSIG_SECRET, RFC2136_NAMESERVER, RFC2136_ZONE
+									rfc2136: RFC2136_TSIG_KEY, RFC2136_TSIG_SECRET, RFC2136_NAMESERVER
 									manual: none
    --help, -h								show help
    --version, -v							print the version

acme/dns_challenge_rfc2136.go

@@ -12,26 +12,23 @@ import (
 // uses dynamic DNS updates (RFC 2136) to create TXT records on a nameserver.
 type DNSProviderRFC2136 struct {
 	nameserver    string
-	zone          string
 	tsigAlgorithm string
 	tsigKey       string
 	tsigSecret    string
-	records       map[string]string
+	domain2zone   map[string]string
 }
 
 // NewDNSProviderRFC2136 returns a new DNSProviderRFC2136 instance.
 // To disable TSIG authentication 'tsigAlgorithm, 'tsigKey' and 'tsigSecret' must be set to the empty string.
-// 'nameserver' must be a network address in the the form "host" or "host:port". 'zone' must be the fully
-// qualified name of the zone.
-func NewDNSProviderRFC2136(nameserver, zone, tsigAlgorithm, tsigKey, tsigSecret string) (*DNSProviderRFC2136, error) {
+// 'nameserver' must be a network address in the the form "host" or "host:port".
+func NewDNSProviderRFC2136(nameserver, tsigAlgorithm, tsigKey, tsigSecret string) (*DNSProviderRFC2136, error) {
 	// Append the default DNS port if none is specified.
 	if !strings.Contains(nameserver, ":") {
 		nameserver += ":53"
 	}
 	d := &DNSProviderRFC2136{
-		nameserver: nameserver,
-		zone:       zone,
-		records:    make(map[string]string),
+		nameserver:  nameserver,
+		domain2zone: make(map[string]string),
 	}
 	if tsigAlgorithm == "" {
 		tsigAlgorithm = dns.HmacMD5
@@ -48,18 +45,21 @@ func NewDNSProviderRFC2136(nameserver, zone, tsigAlgorithm, tsigKey, tsigSecret
 // Present creates a TXT record using the specified parameters
 func (r *DNSProviderRFC2136) Present(domain, token, keyAuth string) error {
 	fqdn, value, ttl := DNS01Record(domain, keyAuth)
-	r.records[fqdn] = value
 	return r.changeRecord("INSERT", fqdn, value, ttl)
 }
 
 // CleanUp removes the TXT record matching the specified parameters
 func (r *DNSProviderRFC2136) CleanUp(domain, token, keyAuth string) error {
-	fqdn, _, ttl := DNS01Record(domain, keyAuth)
-	value := r.records[fqdn]
+	fqdn, value, ttl := DNS01Record(domain, keyAuth)
 	return r.changeRecord("REMOVE", fqdn, value, ttl)
 }
 
 func (r *DNSProviderRFC2136) changeRecord(action, fqdn, value string, ttl int) error {
+	zone, err := r.findZone(fqdn)
+	if err != nil {
+		return err
+	}
+
 	// Create RR
 	rr := new(dns.TXT)
 	rr.Hdr = dns.RR_Header{Name: fqdn, Rrtype: dns.TypeTXT, Class: dns.ClassINET, Ttl: uint32(ttl)}
@@ -69,9 +69,11 @@ func (r *DNSProviderRFC2136) changeRecord(action, fqdn, value string, ttl int) e
 
 	// Create dynamic update packet
 	m := new(dns.Msg)
-	m.SetUpdate(dns.Fqdn(r.zone))
+	m.SetUpdate(zone)
 	switch action {
 	case "INSERT":
+		// Always remove old challenge left over from who knows what.
+		m.RemoveRRset(rrs)
 		m.Insert(rrs)
 	case "REMOVE":
 		m.Remove(rrs)
@@ -99,3 +101,55 @@ func (r *DNSProviderRFC2136) changeRecord(action, fqdn, value string, ttl int) e
 
 	return nil
 }
+
+// findZone determines the zone of a qualifying cert DNSname
+func (r *DNSProviderRFC2136) findZone(fqdn string) (string, error) {
+	// Do we have it cached?
+	if val, ok := r.domain2zone[fqdn]; ok {
+		return val, nil
+	}
+
+	// Query the authorative nameserver for a hopefully non-existing SOA record,
+	// in the authority section of the reply it will have the SOA of the
+	// containing zone. rfc2308 has this to say on the subject:
+	//   Name servers authoritative for a zone MUST include the SOA record of
+	//   the zone in the authority section of the response when reporting an
+	//   NXDOMAIN or indicating that no data (NODATA) of the requested type exists
+	m := new(dns.Msg)
+	m.SetQuestion(fqdn, dns.TypeSOA)
+	m.SetEdns0(4096, false)
+	m.RecursionDesired = true
+	m.Authoritative = true
+
+	in, err := dns.Exchange(m, r.nameserver)
+	if err == dns.ErrTruncated {
+		tcp := &dns.Client{Net: "tcp"}
+		in, _, err = tcp.Exchange(m, r.nameserver)
+	}
+	if err != nil {
+		return "", err
+	}
+	if in.Rcode != dns.RcodeNameError {
+		if in.Rcode != dns.RcodeSuccess {
+			return "", fmt.Errorf("DNS Query for zone %q failed", fqdn)
+		}
+		// We have a success, so one of the answers has to be a SOA RR
+		for _, ans := range in.Answer {
+			if ans.Header().Rrtype == dns.TypeSOA {
+				zone := ans.Header().Name
+				r.domain2zone[fqdn] = zone
+				return zone, nil
+			}
+		}
+		// Or it is NODATA, fall through to NXDOMAIN
+	}
+	// Search the authority section for our precious SOA RR
+	for _, ns := range in.Ns {
+		if ns.Header().Rrtype == dns.TypeSOA {
+			zone := ns.Header().Name
+			r.domain2zone[fqdn] = zone
+			return zone, nil
+		}
+	}
+	return "", fmt.Errorf("Expected a SOA record in the authority section")
+}

cli.go

@@ -124,7 +124,7 @@ func main() {
 				"\n\tdigitalocean: DO_AUTH_TOKEN" +
 				"\n\tdnsimple: DNSIMPLE_EMAIL, DNSIMPLE_API_KEY" +
 				"\n\troute53: AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_REGION" +
-				"\n\trfc2136: RFC2136_TSIG_KEY, RFC2136_TSIG_SECRET, RFC2136_NAMESERVER, RFC2136_ZONE" +
+				"\n\trfc2136: RFC2136_TSIG_KEY, RFC2136_TSIG_SECRET, RFC2136_NAMESERVER" +
 				"\n\tmanual: none",
 		},
 	}

cli_handlers.go

@@ -79,12 +79,11 @@ func setup(c *cli.Context) (*Configuration, *Account, *acme.Client) {
 			provider, err = acme.NewDNSProviderRoute53("", "", awsRegion)
 		case "rfc2136":
 			nameserver := os.Getenv("RFC2136_NAMESERVER")
-			zone := os.Getenv("RFC2136_ZONE")
 			tsigAlgorithm := os.Getenv("RFC2136_TSIG_ALGORITHM")
 			tsigKey := os.Getenv("RFC2136_TSIG_KEY")
 			tsigSecret := os.Getenv("RFC2136_TSIG_SECRET")
 
-			provider, err = acme.NewDNSProviderRFC2136(nameserver, zone, tsigAlgorithm, tsigKey, tsigSecret)
+			provider, err = acme.NewDNSProviderRFC2136(nameserver, tsigAlgorithm, tsigKey, tsigSecret)
 		case "manual":
 			provider, err = acme.NewDNSProviderManual()
 		}