Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

plugin/dnstap/taprw/writer_test.go

@@ -0,0 +1,82 @@
+package taprw
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/coredns/coredns/plugin/dnstap/msg"
+	"github.com/coredns/coredns/plugin/dnstap/test"
+	mwtest "github.com/coredns/coredns/plugin/test"
+
+	tap "github.com/dnstap/golang-dnstap"
+	"github.com/miekg/dns"
+)
+
+type TapFailer struct {
+}
+
+func (TapFailer) TapMessage(*tap.Message) error {
+	return errors.New("failed")
+}
+func (TapFailer) TapBuilder() msg.Builder {
+	return msg.Builder{Full: true}
+}
+
+func TestDnstapError(t *testing.T) {
+	rw := ResponseWriter{
+		Query:          new(dns.Msg),
+		ResponseWriter: &mwtest.ResponseWriter{},
+		Tapper:         TapFailer{},
+	}
+	if err := rw.WriteMsg(new(dns.Msg)); err != nil {
+		t.Errorf("dnstap error during Write: %s", err)
+	}
+	if rw.DnstapError() == nil {
+		t.Fatal("no dnstap error")
+	}
+}
+
+func testingMsg() (m *dns.Msg) {
+	m = new(dns.Msg)
+	m.SetQuestion("example.com.", dns.TypeA)
+	m.SetEdns0(4097, true)
+	return
+}
+
+func TestClientQueryResponse(t *testing.T) {
+	trapper := test.TrapTapper{Full: true}
+	m := testingMsg()
+	rw := ResponseWriter{
+		Query:          m,
+		Tapper:         &trapper,
+		ResponseWriter: &mwtest.ResponseWriter{},
+	}
+	d := test.TestingData()
+
+	// will the wire-format msg be reported?
+	bin, err := m.Pack()
+	if err != nil {
+		t.Fatal(err)
+		return
+	}
+	d.Packed = bin
+
+	if err := rw.WriteMsg(m); err != nil {
+		t.Fatal(err)
+		return
+	}
+	if l := len(trapper.Trap); l != 2 {
+		t.Fatalf("%d msg trapped", l)
+		return
+	}
+	want := d.ToClientQuery()
+	have := trapper.Trap[0]
+	if !test.MsgEqual(want, have) {
+		t.Fatalf("query: want: %v\nhave: %v", want, have)
+	}
+	want = d.ToClientResponse()
+	have = trapper.Trap[1]
+	if !test.MsgEqual(want, have) {
+		t.Fatalf("response: want: %v\nhave: %v", want, have)
+	}
+}