correct EDNS responses (#96)

Tests updated as well and all the middleware. And Prometheus renamed to
metrics (directive is still prometheus).

middleware/metrics/handler.go

@@ -0,0 +1,42 @@
+package metrics
+
+import (
+	"time"
+
+	"golang.org/x/net/context"
+
+	"github.com/miekg/coredns/middleware"
+	"github.com/miekg/dns"
+)
+
+func (m Metrics) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	state := middleware.State{W: w, Req: r}
+	qname := state.Name()
+	qtype := state.Type()
+	zone := middleware.Zones(m.ZoneNames).Matches(qname)
+	if zone == "" {
+		zone = "."
+	}
+
+	// Record response to get status code and size of the reply.
+	rw := middleware.NewResponseRecorder(w)
+	status, err := m.Next.ServeDNS(ctx, rw, r)
+
+	Report(zone, qtype, rw.Rcode(), rw.Size(), rw.Start())
+
+	return status, err
+}
+
+// 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(start) / time.Second))
+	responseSize.WithLabelValues(zone, qtype).Observe(float64(size))
+	responseRcode.WithLabelValues(zone, rcode, qtype).Inc()
+}