plugin/dnstap: don't spam Travis + valid dnstap payload (#1121)

* don't spam Travis + valid dnstap payload

* log instead of fmt

* Revert "log instead of fmt"

This reverts commit 88f09c3939.

* log the right way

* log the final way

* minor enhancements

plugin/dnstap/dnstapio/io.go

@@ -1,8 +1,7 @@
 package dnstapio
 
 import (
-	"fmt"
-	"io"
+	"log"
 
 	tap "github.com/dnstap/golang-dnstap"
 	"github.com/golang/protobuf/proto"
@@ -10,9 +9,9 @@ import (
 
 // DnstapIO wraps the dnstap I/O routine.
 type DnstapIO struct {
-	writer io.WriteCloser
-	queue  chan tap.Dnstap
-	stop   chan bool
+	protocol Protocol
+	queue    chan tap.Dnstap
+	stop     chan bool
 }
 
 // Protocol is either `out.TCP` or `out.Socket`.
@@ -26,7 +25,7 @@ type Protocol interface {
 // New dnstap I/O routine from Protocol.
 func New(w Protocol) *DnstapIO {
 	dio := DnstapIO{}
-	dio.writer = w
+	dio.protocol = w
 	dio.queue = make(chan tap.Dnstap, 10)
 	dio.stop = make(chan bool)
 	go dio.serve()
@@ -38,7 +37,7 @@ func (dio *DnstapIO) Dnstap(payload tap.Dnstap) {
 	select {
 	case dio.queue <- payload:
 	default:
-		fmt.Println("[WARN] Dnstap payload dropped.")
+		log.Println("[WARN] Dnstap payload dropped.")
 	}
 }
 
@@ -48,9 +47,9 @@ func (dio *DnstapIO) serve() {
 		case payload := <-dio.queue:
 			frame, err := proto.Marshal(&payload)
 			if err == nil {
-				dio.writer.Write(frame)
+				dio.protocol.Write(frame)
 			} else {
-				fmt.Println("[ERROR] Invalid dnstap payload dropped.")
+				log.Printf("[ERROR] Invalid dnstap payload dropped: %s\n", err)
 			}
 		case <-dio.stop:
 			close(dio.queue)
@@ -65,5 +64,5 @@ func (dio DnstapIO) Close() error {
 	dio.stop <- true
 	<-dio.stop
 	close(dio.stop)
-	return dio.writer.Close()
+	return dio.protocol.Close()
 }