1 files changed, 58 insertions, 0 deletions
diff --git a/plugin/transfer/notify.go b/plugin/transfer/notify.go
new file mode 100644
index 000000000..b024a3aa1
--- /dev/null
+++ b/plugin/transfer/notify.go
@@ -0,0 +1,58 @@
+package transfer
+
+import (
+	"fmt"
+
+	"github.com/coredns/coredns/plugin/pkg/rcode"
+
+	"github.com/miekg/dns"
+)
+
+// Notify will send notifies to all configured to hosts IP addresses. If the zone isn't known
+// to t an error will be returned. The string zone must be lowercased.
+func (t *Transfer) Notify(zone string) error {
+	if t == nil { // t might be nil, mostly expected in tests, so intercept and to a noop in that case
+		return nil
+	}
+
+	m := new(dns.Msg)
+	m.SetNotify(zone)
+	c := new(dns.Client)
+
+	x := longestMatch(t.xfrs, zone)
+	if x == nil {
+		return fmt.Errorf("no such zone registred in the transfer plugin: %s", zone)
+	}
+
+	var err1 error
+	for _, t := range x.to {
+		if t == "*" {
+			continue
+		}
+		if err := sendNotify(c, m, t); err != nil {
+			err1 = err
+		}
+	}
+	log.Debugf("Sent notifies for zone %q to %v", zone, x.to)
+	return err1 // this only captures the last error
+}
+
+func sendNotify(c *dns.Client, m *dns.Msg, s string) error {
+	var err error
+
+	code := dns.RcodeServerFailure
+	for i := 0; i < 3; i++ {
+		ret, _, err := c.Exchange(m, s)
+		if err != nil {
+			continue
+		}
+		code = ret.Rcode
+		if code == dns.RcodeSuccess {
+			return nil
+		}
+	}
+	if err != nil {
+		return fmt.Errorf("notify for zone %q was not accepted by %q: %q", m.Question[0].Name, s, err)
+	}
+	return fmt.Errorf("notify for zone %q was not accepted by %q: rcode was %q", m.Question[0].Name, s, rcode.ToString(code))
+}