archive/zip: remove WriterOptions and replace with SetOffset method

Change-Id: I0a8b972c33e80c750ff1d63717177a5a3294a112
Reviewed-on: https://go-review.googlesource.com/7445Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Geert-Johan Riemer <gjr19912@gmail.com>
Reviewed-by: Andrew Gerrand <adg@golang.org>

src/archive/zip/writer.go

@@ -29,29 +29,20 @@ type header struct {
 	offset uint64
 }
 
-// WriterOptions contains configuration options for a zip.Writer.
-type WriterOptions struct {
-	// Offset modifies the initial zip offset.
-	// This is useful when the zip is appended to other data such as a binary executable.
-	Offset int64
-}
-
 // NewWriter returns a new Writer writing a zip file to w.
 func NewWriter(w io.Writer) *Writer {
-	return NewWriterWithOptions(w, nil)
+	return &Writer{cw: &countWriter{w: bufio.NewWriter(w)}}
 }
 
-// NewWriterWithOptions returns a new Writer writing a zip file to w and uses the given options.
-func NewWriterWithOptions(w io.Writer, options *WriterOptions) *Writer {
-	writer := &Writer{
-		cw: &countWriter{
-			w: bufio.NewWriter(w),
-		},
-	}
-	if options != nil {
-		writer.cw.count = options.Offset
+// SetOffset sets the offset of the beginning of the zip data within the
+// underlying writer. It should be used when the zip data is appended to an
+// existing file, such as a binary executable.
+// It must be called before any data is written.
+func (w *Writer) SetOffset(n int64) {
+	if w.cw.count != 0 {
+		panic("zip: SetOffset called after data was written")
 	}
-	return writer
+	w.cw.count = n
 }
 
 // Flush flushes any buffered data to the underlying writer.

src/archive/zip/writer_test.go

@@ -87,7 +87,7 @@ func TestWriter(t *testing.T) {
 	}
 }
 
-func TestWriterOffsetOption(t *testing.T) {
+func TestWriterOffset(t *testing.T) {
 	largeData := make([]byte, 1<<17)
 	for i := range largeData {
 		largeData[i] = byte(rand.Int())
@@ -101,7 +101,8 @@ func TestWriterOffsetOption(t *testing.T) {
 	buf := new(bytes.Buffer)
 	existingData := []byte{1, 2, 3, 1, 2, 3, 1, 2, 3}
 	n, _ := buf.Write(existingData)
-	w := NewWriterWithOptions(buf, &WriterOptions{Offset: int64(n)})
+	w := NewWriter(buf)
+	w.SetOffset(int64(n))
 
 	for _, wt := range writeTests {
 		testCreate(t, w, &wt)