Adds the dnstap I/O routines and should fix some issues (#1083)

* adds the dnstap I/O thread and should fix a lot of mistakes

* docs

* -race test

* oops

* docs

plugin/dnstap/dnstapio/io.go

@@ -0,0 +1,69 @@
+package dnstapio
+
+import (
+	"fmt"
+	"io"
+
+	tap "github.com/dnstap/golang-dnstap"
+	"github.com/golang/protobuf/proto"
+)
+
+// DnstapIO wraps the dnstap I/O routine.
+type DnstapIO struct {
+	writer io.WriteCloser
+	queue  chan tap.Dnstap
+	stop   chan bool
+}
+
+// Protocol is either `out.TCP` or `out.Socket`.
+type Protocol interface {
+	// Write takes a single frame at once.
+	Write([]byte) (int, error)
+
+	Close() error
+}
+
+// New dnstap I/O routine from Protocol.
+func New(w Protocol) *DnstapIO {
+	dio := DnstapIO{}
+	dio.writer = w
+	dio.queue = make(chan tap.Dnstap, 10)
+	dio.stop = make(chan bool)
+	go dio.serve()
+	return &dio
+}
+
+// Dnstap enqueues the payload for log.
+func (dio *DnstapIO) Dnstap(payload tap.Dnstap) {
+	select {
+	case dio.queue <- payload:
+	default:
+		fmt.Println("[WARN] Dnstap payload dropped.")
+	}
+}
+
+func (dio *DnstapIO) serve() {
+	for {
+		select {
+		case payload := <-dio.queue:
+			frame, err := proto.Marshal(&payload)
+			if err == nil {
+				dio.writer.Write(frame)
+			} else {
+				fmt.Println("[ERROR] Invalid dnstap payload dropped.")
+			}
+		case <-dio.stop:
+			close(dio.queue)
+			dio.stop <- true
+			return
+		}
+	}
+}
+
+// Close waits until the I/O routine is finished to return.
+func (dio DnstapIO) Close() error {
+	dio.stop <- true
+	<-dio.stop
+	close(dio.stop)
+	return dio.writer.Close()
+}

plugin/dnstap/dnstapio/io_test.go

@@ -0,0 +1,71 @@
+package dnstapio
+
+import (
+	"bytes"
+	"sync"
+	"testing"
+	"time"
+
+	tap "github.com/dnstap/golang-dnstap"
+)
+
+type buf struct {
+	*bytes.Buffer
+	cost time.Duration
+}
+
+func (b buf) Write(frame []byte) (int, error) {
+	time.Sleep(b.cost)
+	return b.Buffer.Write(frame)
+}
+
+func (b buf) Close() error {
+	return nil
+}
+
+func TestRace(t *testing.T) {
+	b := buf{&bytes.Buffer{}, 100 * time.Millisecond}
+	dio := New(b)
+	wg := &sync.WaitGroup{}
+	wg.Add(10)
+	for i := 0; i < 10; i++ {
+		timeout := time.After(time.Second)
+		go func() {
+			for {
+				select {
+				case <-timeout:
+					wg.Done()
+					return
+				default:
+					time.Sleep(50 * time.Millisecond)
+					dio.Dnstap(tap.Dnstap{})
+				}
+			}
+		}()
+	}
+	wg.Wait()
+}
+
+func TestClose(t *testing.T) {
+	done := make(chan bool)
+	var dio *DnstapIO
+	go func() {
+		b := buf{&bytes.Buffer{}, 0}
+		dio = New(b)
+		dio.Close()
+		close(done)
+	}()
+	select {
+	case <-done:
+	case <-time.After(time.Second):
+		t.Fatal("Not closing.")
+	}
+	func() {
+		defer func() {
+			if err := recover(); err == nil {
+				t.Fatal("Send on closed channel.")
+			}
+		}()
+		dio.Dnstap(tap.Dnstap{})
+	}()
+}