如何将PDF文件从GoogleDrive保存到本地tmp目录？ （c＃asp.net mvc）

Question

我正在玩google drive API和示例DrEdit项目，我想将选择的pdf文件保存到本地目录中。 我目前的步骤

1. 我正在使用DownloadFile方法来获取文件内容流

   public static string DownloadFile(IAuthenticator auth, String downloadUrl)
   {
       string result = "";
       try
       {
           HttpWebRequest request = (HttpWebRequest)WebRequest.Create(new Uri(downloadUrl));
           auth.ApplyAuthenticationToRequest(request);
   
           HttpWebResponse response = (HttpWebResponse)request.GetResponse();
           System.IO.Stream stream = response.GetResponseStream();
           StreamReader reader = new StreamReader(stream);
           return reader.ReadToEnd();
       }
       catch (Exception e)
       {
           Console.WriteLine("An error occurred: " + e.Message);
       }
       return result;
   }
   

2. 然后我将其转换为byte []并尝试保存：

   public static string SaveFileToTmpDir(byte[] fileBytes, string fileName)
   {
       fileName = Path.Combine(Environment.GetEnvironmentVariable("temp"), fileName);
       using (FileStream fs = File.Create(fileName, fileBytes.Length, FileOptions.Asynchronous))
       {
           fs.Write(fileBytes, 0, fileBytes.Length);
       }           
       return fileName;
   }
   

3. 这是我的行动 - ＆gt;我正在从视图到该动作进行ajax调用 - ＆gt;将文件保存在tmp目录中并返回保存文件的路径：

   [HttpPost]
   public JsonResult loadFile(string id)
   {
       IAuthenticator authenticator = Session["authenticator"] as IAuthenticator;
       DriveService service = Session["service"] as DriveService;
   
       if (authenticator == null || service == null)
       {
           Response.Redirect(Utils.GetAuthorizationUrl("", ""));
       }
   
       Google.Apis.Drive.v2.Data.File file = service.Files.Get(id).Fetch();
       string fileStream = Utils.DownloadFile(authenticator, file.DownloadUrl);
       string filePath = Utils.SaveFileToTmpDir(StrToByteArray(fileStream), file.Title);
       return Json(new { filePath = filePath });
   }
   

但在这之后我得到pfd文件完全空白。有任何想法获得精确的副本？