Support logging to dnstap in forward plugin (#2703)

plugin/forward/dnstap.go

@@ -0,0 +1,61 @@
+package forward
+
+import (
+	"context"
+	"time"
+
+	"github.com/coredns/coredns/plugin/dnstap"
+	"github.com/coredns/coredns/plugin/dnstap/msg"
+	"github.com/coredns/coredns/request"
+
+	tap "github.com/dnstap/golang-dnstap"
+	"github.com/miekg/dns"
+)
+
+func toDnstap(ctx context.Context, host string, f *Forward, state request.Request, reply *dns.Msg, start time.Time) error {
+	tapper := dnstap.TapperFromContext(ctx)
+	if tapper == nil {
+		return nil
+	}
+	// Query
+	b := msg.New().Time(start).HostPort(host)
+	opts := f.opts
+	t := ""
+	switch {
+	case opts.forceTCP: // TCP flag has precedence over UDP flag
+		t = "tcp"
+	case opts.preferUDP:
+		t = "udp"
+	default:
+		t = state.Proto()
+	}
+
+	if t == "tcp" {
+		b.SocketProto = tap.SocketProtocol_TCP
+	} else {
+		b.SocketProto = tap.SocketProtocol_UDP
+	}
+
+	if tapper.Pack() {
+		b.Msg(state.Req)
+	}
+	m, err := b.ToOutsideQuery(tap.Message_FORWARDER_QUERY)
+	if err != nil {
+		return err
+	}
+	tapper.TapMessage(m)
+
+	// Response
+	if reply != nil {
+		if tapper.Pack() {
+			b.Msg(reply)
+		}
+		m, err := b.Time(time.Now()).ToOutsideResponse(tap.Message_FORWARDER_RESPONSE)
+		if err != nil {
+			return err
+		}
+		tapper.TapMessage(m)
+	}
+
+	return nil
+}