code: func NewRequestReaderWithInitialResponse(c *http.Client, r *http.Request, maxfail uint32, totalsize int64, initialResponse *http.Response) io.ReadCloser {
  	return &requestReader{client: c, request: r, maxFailures: maxfail, totalSize: totalsize, currentResponse: initialResponse, waitDuration: 5 * time.Second}
  }
docs: // NewRequestReaderWithInitialResponse makes it possible to resume
  // reading the body of an already initiated request.