HttpWebRequest随机失败并异步并等待

本文介绍了HttpWebRequest随机失败并异步并等待的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我想进行服务器POST请求。

I would like to do serveral POST-Request.

我的问题是应用程序在 Task< ...>中随机崩溃; do_POST（）-在 async void bt_publishPath_Click（） -Event中 await 期间的功能。

My problem is that the Application crashes randomly in the Task<...> do_POST()-Function during await in my async void bt_publishPath_Click()-Event.

我可以执行一些POST请求（一切正常），有时 await 会阻塞，应用崩溃与 System.NullReferenceException （经过长时间的等待）。我不明白为什么会这样，因为它是第一次工作。

I can do some POST-Requests (everything's working fine) and sometime the await will block and the app crashes with a System.NullReferenceException (after a long time of waiting). I don't understand why this is happing because the first times it is working.

这是我到目前为止所得到的：

我已注释掉所有不重要的功能。我已经测试了没有这些代码行的代码，并且也发生了错误。

// MainWindow private async void bt_publishPath_Click(object sender, RoutedEventArgs e) { // gr_spinner.Visibility = Visibility.Visible; ApiResponse res = await ApiCall.do_POST( "/path", getBasicAuthString(), flink.getJsonString() ); // gr_spinner.Visibility = Visibility.Collapsed; // Globals.errorHandling(res.Statuscode, res.Parameters[0]); } // ApiCall static Class public static Task<ApiResponse> do_POST(string apiPath, string auth, string json) { return Task.Run(() => { int statuscode = 0; HttpWebResponse response = null; try { // HEADER HttpWebRequest request = (HttpWebRequest)WebRequest.Create(apiBase + apiPath); request.Method = "POST"; request.ContentType = "application/json"; request.Headers.Add("Authorization", auth); // DATA byte[] data = Encoding.ASCII.GetBytes(json); request.ContentLength = data.Length; Stream requestStream = request.GetRequestStream(); requestStream.Write(data, 0, data.Length); requestStream.Close(); // SEND AND GET RESPONSE /* * It seems to be that GetResponse() isn't called correctly. * The Backend doesn't receive a POST-request and the reponse stays null. */ response = (HttpWebResponse)request.GetResponse(); statuscode = (int)response.StatusCode; } catch (WebException ex) { statuscode = (int)((HttpWebResponse)ex.Response).StatusCode; } return new ApiResponse(statuscode, null, new String[] { apiPath }); }); }

其他信息：

在使用异步并等待之前，我尝试使用BackgroundWorker解决此问题。在这种情况下，我有一个类似的问题：有时上一个POST的backgroundWorker仍然很忙，并且该程序无法启动一个新的（死锁）。

Before doing this with async and await I tried to solve this issue by using a BackgroundWorker. In this case I had a similar problem: Sometimes the backgroundWorker of the previous POST was still busy and the program wasn't able to start a new one (deadlock).

此外，我发现了一些有趣的东西： async await任务空引用异常

Furthermore I have found something interesting: async await Task null reference exception

• 但是在这种情况下，它是一个ASP.NET应用程序。我正在开发Windows桌面客户端-而不是服务器应用程序。

谢谢您的帮助！

推荐答案

在您的catch块中，您有（HttpWebResponse）ex.Response 。

In your catch block you have (HttpWebResponse)ex.Response.

来自 MSDN ：

如果Internet资源有响应，则为WebResponse实例，其中包含Internet资源的错误响应；

If a response is available from the Internet resource, a WebResponse instance that contains the error response from an Internet resource; otherwise, null.

所以您的问题是服务器没有响应，并且错误处理出错。 但是不要解决此问题，请查找HttpClient并编写一个新的 async Task<>。 DoPost（...）。

So your problem is a non-responsive server and an error in your error handling. But don't fix this, look up the HttpClient and write a new async Task<> DoPost(...).