我正在构建一个执行对NodeJS Server的HTTP请求的应用程序，但是当我执行HTTP请求时，结果如下：

Access to XMLHttpRequest at 'http://127.0.0.1:8000/' from origin 'http://127.0.0.1:8080' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

和

Uncaught (in promise) Error: XMLHttpRequest error.
    dart:sdk_internal 41864:30                                    get current
package:http/src/packages/http/src/browser_client.dart 84:22  <fn>
dart:sdk_internal 99587:96                                    <fn>


    at Object.dart.createErrorWithStack (dart_sdk.js:4617)
    at Object.async._rethrow (dart_sdk.js:28723)
    at async._AsyncCallbackEntry.new.callback (dart_sdk.js:28719)
    at Object.async._microtaskLoop (dart_sdk.js:25352)
    at async._startMicrotaskLoop (dart_sdk.js:25358)
    at dart_sdk.js:25433

这是我使用以下命令发出HTTP请求的代码'package:http/http.dart' as http;：

void requestGet(String endpoint, Callback cb) async {
    return await http.get(Uri.encodeFull(url + endpoint),
        headers: {"Accept": "application/json"}).then((http.Response response) {
      print(response.body);
    });
  }

  void requestPost(String endpoint, Map data, Callback cb) async {
    return await http.post(Uri.encodeFull(url + endpoint),
        body: data,
        headers: {"Accept": "application/json"}).then((http.Response response) {
      print(response.body);
    });
  }