WIP: middleware/dnstap (#711)

middleware/dnstap add

middleware/dnstap/taprw/writer.go

@@ -0,0 +1,84 @@
+// Package taprw takes a query and intercepts the response.
+// It will log both after the response is written.
+package taprw
+
+import (
+	"fmt"
+
+	"github.com/coredns/coredns/middleware/dnstap/msg"
+	"github.com/coredns/coredns/request"
+
+	tap "github.com/dnstap/golang-dnstap"
+	"github.com/miekg/dns"
+)
+
+type Taper interface {
+	TapMessage(m *tap.Message) error
+}
+
+// Single request use.
+type ResponseWriter struct {
+	queryData msg.Data
+	Query     *dns.Msg
+	dns.ResponseWriter
+	Taper
+	Pack bool
+	err  error
+}
+
+// Check if a dnstap error occured.
+// Set during ResponseWriter.Write.
+func (w ResponseWriter) DnstapError() error {
+	return w.err
+}
+
+// To be called as soon as possible.
+func (w *ResponseWriter) QueryEpoch() {
+	w.queryData.Epoch()
+}
+
+// Write back the response to the client and THEN work on logging the request
+// and response to dnstap.
+// Dnstap errors to be checked by DnstapError.
+func (w *ResponseWriter) WriteMsg(resp *dns.Msg) error {
+	writeErr := w.ResponseWriter.WriteMsg(resp)
+
+	if err := tapQuery(w); err != nil {
+		w.err = fmt.Errorf("client query: %s", err)
+		// don't forget to call DnstapError later
+	}
+
+	if writeErr == nil {
+		if err := tapResponse(w, resp); err != nil {
+			w.err = fmt.Errorf("client response: %s", err)
+		}
+	}
+
+	return writeErr
+}
+func tapQuery(w *ResponseWriter) error {
+	req := request.Request{W: w.ResponseWriter, Req: w.Query}
+	if err := w.queryData.FromRequest(req); err != nil {
+		return err
+	}
+	if w.Pack {
+		if err := w.queryData.Pack(w.Query); err != nil {
+			return fmt.Errorf("pack: %s", err)
+		}
+	}
+	return w.Taper.TapMessage(w.queryData.ToClientQuery())
+}
+func tapResponse(w *ResponseWriter, resp *dns.Msg) error {
+	d := &msg.Data{}
+	d.Epoch()
+	req := request.Request{W: w, Req: resp}
+	if err := d.FromRequest(req); err != nil {
+		return err
+	}
+	if w.Pack {
+		if err := d.Pack(resp); err != nil {
+			return fmt.Errorf("pack: %s", err)
+		}
+	}
+	return w.Taper.TapMessage(d.ToClientResponse())
+}