Easier way to dnstap? (#1496)

* Easier way to dnstap?

* Remove unnecessary function parameter from Tapper

* golint

* golint 2

* Proxy dnstap tests

* README.md & doc

* net.IP

* Proxy test was incorrect

* Small changes

* Update README.md

* Was not reporting dnstap errors + test

* Wasn't working at all, now it's ok

* Thanks Travis

plugin/dnstap/handler_test.go

@@ -1,8 +1,12 @@
 package dnstap
 
 import (
+	"errors"
+	"net"
+	"strings"
 	"testing"
 
+	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/dnstap/test"
 	mwtest "github.com/coredns/coredns/plugin/test"
 
@@ -20,8 +24,8 @@ func testCase(t *testing.T, tapq, tapr *tap.Message, q, r *dns.Msg) {
 
 			return 0, w.WriteMsg(r)
 		}),
-		IO:   &w,
-		Pack: false,
+		IO:             &w,
+		JoinRawMessage: false,
 	}
 	_, err := h.ServeDNS(context.TODO(), &mwtest.ResponseWriter{}, q)
 	if err != nil {
@@ -52,7 +56,62 @@ func TestDnstap(t *testing.T) {
 			mwtest.A("example.org. 3600	IN	A 10.0.0.1"),
 		},
 	}.Msg()
-	tapq := test.TestingData().ToClientQuery()
-	tapr := test.TestingData().ToClientResponse()
+	tapq, _ := test.TestingData().ToClientQuery()
+	tapr, _ := test.TestingData().ToClientResponse()
 	testCase(t, tapq, tapr, q, r)
 }
+
+type noWriter struct {
+}
+
+func (n noWriter) Dnstap(d tap.Dnstap) {
+}
+
+func endWith(c int, err error) plugin.Handler {
+	return mwtest.HandlerFunc(func(_ context.Context, w dns.ResponseWriter, _ *dns.Msg) (int, error) {
+		w.WriteMsg(nil) // trigger plugin dnstap to log client query and response
+		// maybe dnstap should log the client query when no message is written...
+		return c, err
+	})
+}
+
+type badAddr struct {
+}
+
+func (bad badAddr) Network() string {
+	return "bad network"
+}
+func (bad badAddr) String() string {
+	return "bad address"
+}
+
+type badRW struct {
+	dns.ResponseWriter
+}
+
+func (bad *badRW) RemoteAddr() net.Addr {
+	return badAddr{}
+}
+
+func TestError(t *testing.T) {
+	h := Dnstap{
+		Next:           endWith(0, nil),
+		IO:             noWriter{},
+		JoinRawMessage: false,
+	}
+	rw := &badRW{&mwtest.ResponseWriter{}}
+
+	// the dnstap error will show only if there is no plugin error
+	_, err := h.ServeDNS(context.TODO(), rw, nil)
+	if err == nil || !strings.HasPrefix(err.Error(), "plugin/dnstap") {
+		t.Fatal("must return the dnstap error but have:", err)
+	}
+
+	// plugin errors will always overwrite dnstap errors
+	pluginErr := errors.New("plugin error")
+	h.Next = endWith(0, pluginErr)
+	_, err = h.ServeDNS(context.TODO(), rw, nil)
+	if err != pluginErr {
+		t.Fatal("must return the plugin error but have:", err)
+	}
+}