flutter - 我必须在服务器上传 multipartData 时打电话，但我遇到了这个问题

Question

这是我的代码，但我收到此错误：

[错误：flutter/lib/ui/ui_dart_state.cc(186)] 未处理的异常：内容大小超过指定的 contentLength。写入 17282 字节，而预期为 398。

 uploadFile(File imageFile,String id,LoginResponseModel responseModel) async {
 var stream = new http.ByteStream(DelegatingStream.typed(imageFile.openRead()));

 var length = await imageFile.length();

 var uri = Uri.parse(BASE_URL+"/jobs/"+id+"/signatures/");

 Map<String, String> headers = { "Accept": "application/json",
   "content-type": "application/json",
   "Authorization": "Bearer " + responseModel.access};

 var request = new http.MultipartRequest("POST", uri);

 request.headers.addAll(headers);

 request.fields['name'] = 'test';

 var multipartFile = new http.MultipartFile('signature', stream, length,
     filename: basename(imageFile.path));

 request.files.add(multipartFile);


 var response = await request.send();

 print(response.statusCode);

 response.stream.transform(utf8.decoder).listen((value) {
 });

   }