>>>
httpClient.getUrl(url)
  .then((HttpClientRequest request) {
    print('have request');
    return request.close();
  })
  .then((HttpClientResponse response) {
    body;
  });
<<<
httpClient.getUrl(url).then((HttpClientRequest request) {
  print('have request');
  return request.close();
}).then((HttpClientResponse response) {
  body;
});