code: func gsUploader(ctx context.Context, size int64, uploadURL string) io.Writer {
  	// Authentication is handled through the tokens in the upload session URL.
  	tr, err := auth.GetRPCTransport(ctx, auth.NoAuth)
  	if err != nil {
  		panic(errors.Annotate(err, "failed to get the RPC transport").Err())
  	}
  	return &gs.Uploader{
  		Context:   ctx,
  		Client:    &http.Client{Transport: tr},
  		UploadURL: uploadURL,
  		FileSize:  size,
  	}
  }
docs: ////////////////////////////////////////////////////////////////////////////////