Add secondary support

Allow specifying a primary server and retrieve the zone's content.

Add tests and an Expired bool to zone struct, to stop server zones

that are expired. The zone is retrieved on Startup, no updates of

changed content are done. We also don't respond to notifies yet.

middleware/file/secondary.go

@@ -0,0 +1,63 @@
+package file
+
+import (
+	"log"
+
+	"github.com/miekg/dns"
+)
+
+// TransferIn retrieves the zone from the masters, parses it and sets it live.
+func (z *Zone) TransferIn() error {
+	if len(z.TransferFrom) == 0 {
+		return nil
+	}
+	t := new(dns.Transfer)
+	m := new(dns.Msg)
+	m.SetAxfr(z.name)
+	/*
+	   t.TsigSecret = map[string]string{"axfr.": "so6ZGir4GPAqINNh9U5c3A=="}
+	   m.SetTsig("axfr.", dns.HmacMD5, 300, time.Now().Unix())
+	*/
+
+	var Err error
+Transfer:
+	for _, tr := range z.TransferFrom {
+		c, err := t.In(m, tr)
+		if err != nil {
+			log.Printf("[ERROR] failed to setup transfer %s with %s: %v", z.name, z.TransferFrom[0], err)
+			Err = err
+			continue Transfer
+		}
+		for env := range c {
+			if env.Error != nil {
+				log.Printf("[ERROR] failed to parse transfer %s: %v", z.name, env.Error)
+				Err = env.Error
+				continue Transfer
+			}
+			for _, rr := range env.RR {
+				if rr.Header().Rrtype == dns.TypeSOA {
+					z.SOA = rr.(*dns.SOA)
+					continue
+				}
+				if rr.Header().Rrtype == dns.TypeRRSIG {
+					if x, ok := rr.(*dns.RRSIG); ok && x.TypeCovered == dns.TypeSOA {
+						z.SIG = append(z.SIG, x)
+					}
+				}
+				z.Insert(rr)
+			}
+		}
+	}
+	return Err
+}
+
+/*
+
+				28800      ; refresh (8 hours)
+				7200       ; retry (2 hours)
+				604800     ; expire (1 week)
+				3600       ; minimum (1 hour)
+// Check SOA
+// Just check every refresh hours, if fail set to retry until succeeds
+// expire is need: to give SERVFAIL.
+*/