plugin/k8s_external: implement zone transfers (#4977)

Implement transfer for k8s_external. Notifies not supported.

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

plugin/k8s_external/transfer.go

@@ -0,0 +1,97 @@
+package external
+
+import (
+	"context"
+
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/etcd/msg"
+	"github.com/coredns/coredns/plugin/transfer"
+	"github.com/coredns/coredns/request"
+
+	"github.com/miekg/dns"
+)
+
+// Transfer implements transfer.Transferer
+func (e *External) Transfer(zone string, serial uint32) (<-chan []dns.RR, error) {
+	z := plugin.Zones(e.Zones).Matches(zone)
+	if z != zone {
+		return nil, transfer.ErrNotAuthoritative
+	}
+
+	ctx := context.Background()
+	ch := make(chan []dns.RR, 2)
+	if zone == "." {
+		zone = ""
+	}
+	state := request.Request{Zone: zone}
+
+	// SOA
+	soa := e.soa(state)
+	ch <- []dns.RR{soa}
+	if serial != 0 && serial >= soa.Serial {
+		close(ch)
+		return ch, nil
+	}
+
+	go func() {
+		// Add NS
+		nsName := "ns1." + e.apex + "." + zone
+		nsHdr := dns.RR_Header{Name: zone, Rrtype: dns.TypeNS, Ttl: e.ttl, Class: dns.ClassINET}
+		ch <- []dns.RR{&dns.NS{Hdr: nsHdr, Ns: nsName}}
+
+		// Add Nameserver A/AAAA records
+		nsRecords := e.externalAddrFunc(state)
+		for i := range nsRecords {
+			// externalAddrFunc returns incomplete header names, correct here
+			nsRecords[i].Header().Name = nsName
+			nsRecords[i].Header().Ttl = e.ttl
+			ch <- []dns.RR{nsRecords[i]}
+		}
+
+		svcs := e.externalServicesFunc(zone)
+		srvSeen := make(map[string]struct{})
+		for i := range svcs {
+			name := msg.Domain(svcs[i].Key)
+			if svcs[i].TargetStrip == 0 {
+				// Add Service A/AAAA records
+				s := request.Request{Req: &dns.Msg{Question: []dns.Question{{Name: name}}}}
+				as := e.a(ctx, []msg.Service{svcs[i]}, s)
+				if len(as) > 0 {
+					ch <- as
+				}
+				aaaas := e.aaaa(ctx, []msg.Service{svcs[i]}, s)
+				if len(aaaas) > 0 {
+					ch <- aaaas
+				}
+				// Add bare SRV record, ensuring uniqueness
+				recs, _ := e.srv(ctx, []msg.Service{svcs[i]}, s)
+				for _, srv := range recs {
+					if !nameSeen(srvSeen, srv) {
+						ch <- []dns.RR{srv}
+					}
+				}
+				continue
+			}
+			// Add full SRV record, ensuring uniqueness
+			s := request.Request{Req: &dns.Msg{Question: []dns.Question{{Name: name}}}}
+			recs, _ := e.srv(ctx, []msg.Service{svcs[i]}, s)
+			for _, srv := range recs {
+				if !nameSeen(srvSeen, srv) {
+					ch <- []dns.RR{srv}
+				}
+			}
+		}
+		ch <- []dns.RR{soa}
+		close(ch)
+	}()
+
+	return ch, nil
+}
+
+func nameSeen(namesSeen map[string]struct{}, rr dns.RR) bool {
+	if _, duplicate := namesSeen[rr.Header().Name]; duplicate {
+		return true
+	}
+	namesSeen[rr.Header().Name] = struct{}{}
+	return false
+}