plugin/dnstap: some cleanup (#1172)

Some cleanup in proxy and dnstap:
* just use time pkg directly and side step the indirection for Epoch
* Use Set in SetQueryEpoch to be more Go like. (Looked like a reader)
* Don't maintain two sets of time, we already track start, so use that.
* Use time.Time and convert when needed
* dedent the toDnstap function and put in a separate file

plugin/dnstap/handler.go

@@ -79,7 +79,7 @@ func (h Dnstap) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
 	newCtx := context.WithValue(ctx, DnstapSendOption, &sendOption)
 
 	rw := &taprw.ResponseWriter{ResponseWriter: w, Tapper: &h, Query: r, Send: &sendOption}
-	rw.QueryEpoch()
+	rw.SetQueryEpoch()
 
 	code, err := plugin.NextOrFailure(h.Name(), h.Next, tapContext{newCtx, h}, rw, r)
 	if err != nil {

plugin/dnstap/msg/msg.go

@@ -5,7 +5,6 @@ import (
 	"errors"
 	"net"
 	"strconv"
-	"time"
 
 	tap "github.com/dnstap/golang-dnstap"
 	"github.com/miekg/dns"
@@ -103,16 +102,6 @@ func (d *Data) Pack(m *dns.Msg) error {
 	return nil
 }
 
-// Epoch returns the epoch time in seconds.
-func Epoch() uint64 {
-	return uint64(time.Now().Unix())
-}
-
-// Epoch sets the dnstap message epoch.
-func (d *Data) Epoch() {
-	d.TimeSec = Epoch()
-}
-
 // ToClientResponse transforms Data into a client response message.
 func (d *Data) ToClientResponse() *tap.Message {
 	t := tap.Message_CLIENT_RESPONSE

plugin/dnstap/taprw/writer.go

@@ -4,6 +4,7 @@ package taprw
 
 import (
 	"fmt"
+	"time"
 
 	"github.com/coredns/coredns/plugin/dnstap/msg"
 
@@ -41,9 +42,9 @@ func (w ResponseWriter) DnstapError() error {
 	return w.err
 }
 
-// QueryEpoch sets the query epoch as reported by dnstap.
-func (w *ResponseWriter) QueryEpoch() {
-	w.queryEpoch = msg.Epoch()
+// SetQueryEpoch sets the query epoch as reported by dnstap.
+func (w *ResponseWriter) SetQueryEpoch() {
+	w.queryEpoch = uint64(time.Now().Unix())
 }
 
 // WriteMsg writes back the response to the client and THEN works on logging the request
@@ -51,7 +52,7 @@ func (w *ResponseWriter) QueryEpoch() {
 // Dnstap errors are to be checked by DnstapError.
 func (w *ResponseWriter) WriteMsg(resp *dns.Msg) (writeErr error) {
 	writeErr = w.ResponseWriter.WriteMsg(resp)
-	writeEpoch := msg.Epoch()
+	writeEpoch := uint64(time.Now().Unix())
 
 	b := w.TapBuilder()
 	b.TimeSec = w.queryEpoch