middleware/proxy: dnstap (#786)

* experimental dnstap support into proxy

* proxy reports dnstap errors

* refactoring

* add a message builder for less dnstap code

* msg lint

* context

* proxy by DNS: dnstap comments

* TapBuilder

* resolves conflict

* dnstap into ServeDNS

* testing

* more tests

* `go lint`

* doc update

middleware/proxy/dnstap_test.go

@@ -0,0 +1,57 @@
+package proxy
+
+import (
+	"testing"
+
+	"github.com/coredns/coredns/middleware/dnstap/msg"
+	"github.com/coredns/coredns/middleware/dnstap/test"
+	mwtest "github.com/coredns/coredns/middleware/test"
+	"github.com/coredns/coredns/request"
+
+	tap "github.com/dnstap/golang-dnstap"
+	"github.com/miekg/dns"
+	"golang.org/x/net/context"
+)
+
+func testCase(t *testing.T, ex Exchanger, q, r *dns.Msg, datq, datr *msg.Data) {
+	tapq := datq.ToOutsideQuery(tap.Message_FORWARDER_QUERY)
+	tapr := datr.ToOutsideResponse(tap.Message_FORWARDER_RESPONSE)
+	ctx := test.Context{}
+	err := toDnstap(&ctx, "10.240.0.1:40212", ex,
+		request.Request{W: &mwtest.ResponseWriter{}, Req: q}, r, 0, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(ctx.Trap) != 2 {
+		t.Fatalf("messages: %d", len(ctx.Trap))
+	}
+	if !test.MsgEqual(ctx.Trap[0], tapq) {
+		t.Errorf("want: %v\nhave: %v", tapq, ctx.Trap[0])
+	}
+	if !test.MsgEqual(ctx.Trap[1], tapr) {
+		t.Errorf("want: %v\nhave: %v", tapr, ctx.Trap[1])
+	}
+}
+
+func TestDnstap(t *testing.T) {
+	q := mwtest.Case{Qname: "example.org", Qtype: dns.TypeA}.Msg()
+	r := mwtest.Case{
+		Qname: "example.org.", Qtype: dns.TypeA,
+		Answer: []dns.RR{
+			mwtest.A("example.org. 3600	IN	A 10.0.0.1"),
+		},
+	}.Msg()
+	tapq, tapr := test.TestingData(), test.TestingData()
+	testCase(t, newDNSEx(), q, r, tapq, tapr)
+	tapq.SocketProto = tap.SocketProtocol_TCP
+	tapr.SocketProto = tap.SocketProtocol_TCP
+	testCase(t, newDNSExWithOption(Options{ForceTCP: true}), q, r, tapq, tapr)
+	testCase(t, newGoogle("", []string{"8.8.8.8:53", "8.8.4.4:53"}), q, r, tapq, tapr)
+}
+
+func TestNoDnstap(t *testing.T) {
+	err := toDnstap(context.TODO(), "", nil, request.Request{}, nil, 0, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+}