HttpWebRequest随机失败并异步并等待 [英] HttpWebRequest randomly fails with async and await

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(...).

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