code: func (gcs defaultGCSHandler) Push(c context.Context, i *Client, status isolateservice.HandlersEndpointsV1PreuploadStatus, source Source) error {
  	// GsUploadUrl is signed Google Storage URL that doesn't require additional
  	// authentication. In fact, using authClient causes HTTP 403 because
  	// authClient's tokens don't have Cloud Storage OAuth scope. Use anonymous
  	// client instead.
  	req := lhttp.NewRequest(c, i.anonClient, i.retryFactory, func() (*http.Request, error) {
  		src, err := source()
  		if err != nil {
  			return nil, err
  		}
  
  		request, err := http.NewRequest("PUT", status.GsUploadUrl, nil)
  		if err != nil {
  			src.Close()
  			return nil, err
  		}
  		request.Body = newCompressed(i.namespace, src)
  		request.Header.Set("Content-Type", "application/octet-stream")
  		return request, nil
  	}, func(resp *http.Response) error {
  		_, err4 := io.Copy(ioutil.Discard, resp.Body)
  		err5 := resp.Body.Close()
  		if err4 != nil {
  			return err4
  		}
  		return err5
  	}, nil)
  	_, err := req()
  	return err
  }
docs: // Push uploads content from the provided source to the GCS path specified in
  // the HandlersEndpointsV1PreuploadStatus response.