plugin/template : add support for extended DNS errors (#5659)

* plugin/template : add support for extended DNS errors

Signed-off-by: Ondřej Benkovský <ondrej.benkovsky@jamf.com>

plugin/template/template.go

@@ -33,10 +33,16 @@ type template struct {
 	authority  []*gotmpl.Template
 	qclass     uint16
 	qtype      uint16
+	ederror    *ederror
 	fall       fall.F
 	upstream   Upstreamer
 }
 
+type ederror struct {
+	code   uint16
+	reason string
+}
+
 // Upstreamer looks up targets of CNAME templates
 type Upstreamer interface {
 	Lookup(ctx context.Context, state request.Request, name string, typ uint16) (*dns.Msg, error)
@@ -125,6 +131,12 @@ func (h Handler) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
 			msg.Ns = append(msg.Ns, rr)
 		}
 
+		if template.ederror != nil {
+			msg = msg.SetEdns0(4096, true)
+			ede := dns.EDNS0_EDE{InfoCode: template.ederror.code, ExtraText: template.ederror.reason}
+			msg.IsEdns0().Option = append(msg.IsEdns0().Option, &ede)
+		}
+
 		w.WriteMsg(msg)
 		return template.rcode, nil
 	}