plugin/dnstap: remove config struct (#4258)

* plugin/dnstap: remove config struct

this struct is an uneeded intermidiate to get a dnstap it can be
removed. Remove the dnstapio subpkg: it's also not needed. Make *many*
functions and structs private now that we can.

Signed-off-by: Miek Gieben <miek@miek.nl>

* correct logging

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/dnstap/encoder.go

@@ -0,0 +1,40 @@
+package dnstap
+
+import (
+	"io"
+	"time"
+
+	tap "github.com/dnstap/golang-dnstap"
+	fs "github.com/farsightsec/golang-framestream"
+	"github.com/golang/protobuf/proto"
+)
+
+// encoder wraps a golang-framestream.Encoder.
+type encoder struct {
+	fs *fs.Encoder
+}
+
+func newEncoder(w io.Writer, timeout time.Duration) (*encoder, error) {
+	fs, err := fs.NewEncoder(w, &fs.EncoderOptions{
+		ContentType:   []byte("protobuf:dnstap.Dnstap"),
+		Bidirectional: true,
+		Timeout:       timeout,
+	})
+	if err != nil {
+		return nil, err
+	}
+	return &encoder{fs}, nil
+}
+
+func (e *encoder) writeMsg(msg *tap.Dnstap) error {
+	buf, err := proto.Marshal(msg)
+	if err != nil {
+		return err
+	}
+
+	_, err = e.fs.Write(buf) // n < len(buf) should return an error?
+	return err
+}
+
+func (e *encoder) flush() error { return e.fs.Flush() }
+func (e *encoder) close() error { return e.fs.Close() }