Move nonwriter to mw/pkg/nonwriter (#948)

Make it its own package as shared between autopath and federation.

Fixes #933

middleware/autopath/autopath.go

@@ -36,6 +36,7 @@ import (
 
 	"github.com/coredns/coredns/middleware"
 	"github.com/coredns/coredns/middleware/pkg/dnsutil"
+	"github.com/coredns/coredns/middleware/pkg/nonwriter"
 	"github.com/coredns/coredns/request"
 
 	"github.com/miekg/dns"
@@ -101,7 +102,7 @@ func (a *AutoPath) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Ms
 	for i, s := range searchpath {
 		newQName := base + "." + s
 		ar.Question[0].Name = newQName
-		nw := NewNonWriter(w)
+		nw := nonwriter.New(w)
 
 		rcode, err := middleware.NextOrFailure(a.Name(), a.Next, ctx, nw, ar)
 		if err != nil {

middleware/autopath/nonwriter.go

@@ -1,22 +0,0 @@
-package autopath
-
-import (
-	"github.com/miekg/dns"
-)
-
-// NonWriter is a type of ResponseWriter that captures the message, but never writes to the client.
-type NonWriter struct {
-	dns.ResponseWriter
-	Msg *dns.Msg
-}
-
-// NewNonWriter makes and returns a new NonWriter.
-func NewNonWriter(w dns.ResponseWriter) *NonWriter { return &NonWriter{ResponseWriter: w} }
-
-// WriteMsg records the message, but doesn't write it itself.
-func (r *NonWriter) WriteMsg(res *dns.Msg) error {
-	r.Msg = res
-	return nil
-}
-
-func (r *NonWriter) Write(buf []byte) (int, error) { return len(buf), nil }

middleware/federation/federation.go

@@ -17,6 +17,7 @@ import (
 	"github.com/coredns/coredns/middleware"
 	"github.com/coredns/coredns/middleware/etcd/msg"
 	"github.com/coredns/coredns/middleware/pkg/dnsutil"
+	"github.com/coredns/coredns/middleware/pkg/nonwriter"
 	"github.com/coredns/coredns/request"
 
 	"github.com/miekg/dns"
@@ -67,7 +68,7 @@ func (f *Federation) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.
 
 	// Start the next middleware, but with a nowriter, capture the result, if NXDOMAIN
 	// perform federation, otherwise just write the result.
-	nw := NewNonWriter(w)
+	nw := nonwriter.New(w)
 	ret, err := middleware.NextOrFailure(f.Name(), f.Next, ctx, nw, r)
 
 	if !middleware.ClientWrite(ret) {

middleware/federation/nonwriter.go

@@ -1,22 +0,0 @@
-package federation
-
-import (
-	"github.com/miekg/dns"
-)
-
-// NonWriter is a type of ResponseWriter that captures the message, but never writes to the client.
-type NonWriter struct {
-	dns.ResponseWriter
-	Msg *dns.Msg
-}
-
-// NewNonWriter makes and returns a new NonWriter.
-func NewNonWriter(w dns.ResponseWriter) *NonWriter { return &NonWriter{ResponseWriter: w} }
-
-// WriteMsg records the message, but doesn't write it itself.
-func (r *NonWriter) WriteMsg(res *dns.Msg) error {
-	r.Msg = res
-	return nil
-}
-
-func (r *NonWriter) Write(buf []byte) (int, error) { return len(buf), nil }

middleware/pkg/nonwriter/nonwriter.go

@@ -0,0 +1,23 @@
+// Package nonwriter implements a dns.ResponseWriter that never writes, but captures the dns.Msg being written.
+package nonwriter
+
+import (
+	"github.com/miekg/dns"
+)
+
+// Writer is a type of ResponseWriter that captures the message, but never writes to the client.
+type Writer struct {
+	dns.ResponseWriter
+	Msg *dns.Msg
+}
+
+// New makes and returns a new NonWriter.
+func New(w dns.ResponseWriter) *Writer { return &Writer{ResponseWriter: w} }
+
+// WriteMsg records the message, but doesn't write it itself.
+func (w *Writer) WriteMsg(res *dns.Msg) error {
+	w.Msg = res
+	return nil
+}
+
+func (w *Writer) Write(buf []byte) (int, error) { return len(buf), nil }

middleware/pkg/nonwriter/nonwriter_test.go

@@ -0,0 +1,19 @@
+package nonwriter
+
+import (
+	"testing"
+
+	"github.com/miekg/dns"
+)
+
+func TestNonWriter(t *testing.T) {
+	nw := New(nil)
+	m := new(dns.Msg)
+	m.SetQuestion("example.org.", dns.TypeA)
+	if err := nw.WriteMsg(m); err != nil {
+		t.Errorf("Got error when writing to nonwriter: %s", err)
+	}
+	if x := nw.Msg.Question[0].Name; x != "example.org." {
+		t.Errorf("Expacted 'example.org.' got %q:", x)
+	}
+}