code: func (c *Client) download(path string, in interface{}, r io.Reader) (io.ReadCloser, int64, error) {
  	url := "https://content.dropboxapi.com/2" + path
  
  	body, err := json.Marshal(in)
  	if err != nil {
  		return nil, 0, err
  	}
  
  	req, err := http.NewRequest("POST", url, r)
  	if err != nil {
  		return nil, 0, err
  	}
  	req.Header.Set("Authorization", "Bearer "+c.AccessToken)
  	req.Header.Set("Dropbox-API-Arg", string(body))
  
  	if r != nil {
  		req.Header.Set("Content-Type", "application/octet-stream")
  	}
  
  	return c.do(req)
  }
docs: // download style endpoint.