More efficient message marshaling

message.go

@@ -3,7 +3,6 @@ package main
 import (
 	"bytes"
 	"encoding/binary"
-	"log"
 )
 
 // VailMessage is a single Vail message.
@@ -19,31 +18,25 @@ type Message struct {
 	Duration []uint8
 }
 
+// Marshaling presumes something else is keeping track of lengths
 func (m Message) MarshalBinary() ([]byte, error) {
 	var w bytes.Buffer
 	if err := binary.Write(&w, binary.BigEndian, m.Timestamp); err != nil {
 		return nil, err
 	}
-	dlen := uint16(len(m.Duration))
-	if err := binary.Write(&w, binary.BigEndian, dlen); err != nil {
-		return nil, err
-	}
 	if err := binary.Write(&w, binary.BigEndian, m.Duration); err != nil {
 		return nil, err
 	}
 	return w.Bytes(), nil
 }
 
+// Unmarshaling presumes something else is keeping track of lengths
 func (m *Message) UnmarshalBinary(data []byte) error {
 	r := bytes.NewReader(data)
 	if err := binary.Read(r, binary.BigEndian, &m.Timestamp); err != nil {
 		return err
 	}
-	log.Printf("timestamp %x", m.Timestamp)
+	dlen := r.Len()
-	var dlen uint16
-	if err := binary.Read(r, binary.BigEndian, &dlen); err != nil {
-		return err
-	}
 	m.Duration = make([]uint8, dlen)
 	if err := binary.Read(r, binary.BigEndian, &m.Duration); err != nil {
 		return err

message_test.go

@@ -23,7 +23,7 @@ func TestMessage(t *testing.T) {
 	if err != nil {
 		t.Error(err)
 	}
-	if ! bytes.Equal(bm, []byte("\x11\x22\x33\x44\x55\x66\x77\x88\x00\x03\xaa\xbb\xcc")) {
+	if ! bytes.Equal(bm, []byte("\x11\x22\x33\x44\x55\x66\x77\x88\xaa\xbb\xcc")) {
 		t.Error("Encoded wrong:", bm)
 	}