src/client/admin.go
func (c APIClient) ExtractWriter(objects bool, w io.Writer) error {
	writer := pbutil.NewWriter(w)
	return c.Extract(objects, func(op *admin.Op) error {
		_, err := writer.Write(op)
		return err
	})
}
func (c APIClient) ExtractWriter(objects bool, w io.Writer) error {
	writer := pbutil.NewWriter(w)
	return c.Extract(objects, func(op *admin.Op) error {
		_, err := writer.Write(op)
		return err
	})
}
// ExtractWriter extracts all cluster state and marshals it to w.