Add middleware reverse (#452)

middleware/reverse/reverse.go

@@ -0,0 +1,114 @@
+package reverse
+
+import (
+	"net"
+
+	"github.com/miekg/coredns/request"
+	"github.com/miekg/coredns/middleware"
+	"github.com/miekg/coredns/middleware/pkg/dnsutil"
+
+	"github.com/miekg/dns"
+	"golang.org/x/net/context"
+)
+
+// Reverse provides dynamic reverse dns and the related forward rr
+type Reverse struct {
+	Next     middleware.Handler
+	Networks networks
+}
+
+// ServeDNS implements the middleware.Handler interface.
+func (reverse Reverse) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	var rr dns.RR
+	nextHandler := true
+
+	state := request.Request{W: w, Req: r}
+	m := new(dns.Msg)
+	m.SetReply(r)
+	m.Authoritative, m.RecursionAvailable, m.Compress = true, true, true
+
+	switch state.QType(){
+	case dns.TypePTR:
+		address := dnsutil.ExtractAddressFromReverse(state.Name())
+
+		if address == "" {
+			// Not an reverse lookup, but can still be an pointer for an domain
+			break
+		}
+
+		ip := net.ParseIP(address)
+		// loop through the configured networks
+		for _, n := range reverse.Networks {
+			if (n.IPnet.Contains(ip)) {
+				nextHandler = n.Fallthrough
+				rr = &dns.PTR{
+					Hdr:  dns.RR_Header{Name: state.QName(), Rrtype: dns.TypePTR, Class: dns.ClassINET, Ttl: n.TTL},
+					Ptr: n.ipToHostname(ip),
+				}
+				break
+			}
+		}
+
+	case dns.TypeA:
+		for _, n := range reverse.Networks {
+			if dns.IsSubDomain(n.Zone, state.Name()) {
+				nextHandler = n.Fallthrough
+
+				// skip if requesting an v4 address and network is not v4
+				if n.IPnet.IP.To4() == nil {
+					continue
+				}
+
+				result := n.hostnameToIP(state.Name())
+				if result != nil {
+					rr = &dns.A{
+						Hdr:  dns.RR_Header{Name: state.QName(), Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: n.TTL},
+						A: result,
+					}
+					break
+				}
+			}
+		}
+
+	case dns.TypeAAAA:
+		for _, n := range reverse.Networks {
+			if dns.IsSubDomain(n.Zone, state.Name()) {
+				nextHandler = n.Fallthrough
+
+				// Do not use To16 which tries to make v4 in v6
+				if n.IPnet.IP.To4() != nil {
+					continue
+				}
+
+				result := n.hostnameToIP(state.Name())
+				if result != nil {
+					rr = &dns.AAAA{
+						Hdr:  dns.RR_Header{Name: state.QName(), Rrtype: dns.TypeAAAA, Class: dns.ClassINET, Ttl: n.TTL},
+						AAAA: result,
+					}
+					break
+				}
+			}
+		}
+
+	}
+
+	if rr == nil {
+		if reverse.Next == nil || !nextHandler {
+			// could not resolv
+			w.WriteMsg(m)
+			return dns.RcodeNameError, nil
+		}
+		return reverse.Next.ServeDNS(ctx, w, r)
+	}
+
+	m.Answer = append(m.Answer, rr)
+	state.SizeAndDo(m)
+	w.WriteMsg(m)
+	return dns.RcodeSuccess, nil
+}
+
+// Name implements the Handler interface.
+func (reverse Reverse) Name() string {
+	return "reverse"
+}