Enable monitoring for non middleware

If monitoring is enabled for one zone, also enable it for when the

server reports REFUSED. Normally the metrics are only enabled if

you enter the middleware, with this you'll see REFUSED queries.

Each of these are reported agains the root zone otherwise

middleware/prometheus/handler.go

@@ -22,14 +22,21 @@ func (m Metrics) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
 	rw := middleware.NewResponseRecorder(w)
 	status, err := m.Next.ServeDNS(ctx, rw, r)
 
-	m.Report(zone, qtype, rw)
+	Report(zone, qtype, rw.Rcode(), rw.Size(), rw.Start())
 
 	return status, err
 }
 
-func (m Metrics) Report(zone, qtype string, rw *middleware.ResponseRecorder) {
+// Report is a plain reporting function that the server can use for REFUSED and other
+// queries that are turned down because they don't match any middleware.
+func Report(zone, qtype, rcode string, size int, start time.Time) {
+	if requestCount == nil {
+		// no metrics are enabled
+		return
+	}
+
 	requestCount.WithLabelValues(zone, qtype).Inc()
-	requestDuration.WithLabelValues(zone, qtype).Observe(float64(time.Since(rw.Start()) / time.Second))
-	responseSize.WithLabelValues(zone, qtype).Observe(float64(rw.Size()))
-	responseRcode.WithLabelValues(zone, rw.Rcode(), qtype).Inc()
+	requestDuration.WithLabelValues(zone, qtype).Observe(float64(time.Since(start) / time.Second))
+	responseSize.WithLabelValues(zone, qtype).Observe(float64(size))
+	responseRcode.WithLabelValues(zone, rcode, qtype).Inc()
 }

server/server.go

@@ -12,12 +12,15 @@ import (
 	"net"
 	"os"
 	"runtime"
+	"strconv"
 	"sync"
 	"time"
 
 	"golang.org/x/net/context"
 
+	"github.com/miekg/coredns/middleware"
 	"github.com/miekg/coredns/middleware/chaos"
+	"github.com/miekg/coredns/middleware/prometheus"
 	"github.com/miekg/dns"
 )
 
@@ -329,8 +332,18 @@ func (s *Server) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
 // DefaultErrorFunc responds to an HTTP request with a simple description
 // of the specified HTTP status code.
 func DefaultErrorFunc(w dns.ResponseWriter, r *dns.Msg, rcode int) {
+	// this code is duplicated a few times, TODO(miek)
+	rc := dns.RcodeToString[rcode]
+	if rc == "" {
+		rc = "RCODE" + strconv.Itoa(rcode)
+	}
 	answer := new(dns.Msg)
 	answer.SetRcode(r, rcode)
+
+	state := middleware.State{W: w, Req: r}
+	// Default zone to "." here to not blow up this metric
+	metrics.Report(".", state.Type(), rc, answer.Len(), time.Now())
+
 	w.WriteMsg(answer)
 }