C# HttpWebRequest 在两次服务器 500 错误后超时

Question

在我创建两个因“(500) 内部服务器错误 500”而抛出异常的 C# HttpWebRequest 之后，第三次尝试抛出超时异常。为什么它不抛出另一个 (500) Internal Server Error 异常？

当我重新启动我的应用程序时，它会抛出两个 500 错误，然后再次开始超时。

这是我的代码:

GetPages GetPages = new GetPages();
string test = GetPages.GetPage(); /* Exception: (500) Internal Server Error */
GetPages.Dispose();

GetPages GetPages = new GetPages();
string test = GetPages.GetPage();  /* Exception: (500) Internal Server Error */
GetPages.Dispose();

GetPages GetPages = new GetPages();
string test = GetPages.GetPage();  /* Exception: time out, why? */
GetPages.Dispose();

这是 GetPages 类和 GetPage 方法:

namespace MyNamespace
{
    class GetPages
    {
        public string GetPage()
        {
            this.httpRequest = (HttpWebRequest)WebRequest.Create("http://myurl");

            try
            {
                StringBuilder postData = new StringBuilder(100);
                postData.Append("test=test");
                byte[] dataArray = Encoding.UTF8.GetBytes(postData.ToString());

                httpRequest.CachePolicy = new HttpRequestCachePolicy(HttpRequestCacheLevel.NoCacheNoStore);
                httpRequest.KeepAlive = false;
                httpRequest.Proxy = null;
                httpRequest.Method = "POST";
                httpRequest.Timeout = 10;
                httpRequest.ContentType = "application/x-www-form-urlencoded";

                httpRequest.ContentLength = dataArray.Length;

                using (this.requestStream = httpRequest.GetRequestStream())
                {
                    requestStream.Write(dataArray, 0, dataArray.Length);
                    requestStream.Flush();
                    requestStream.Close();

                    this.webResponse = (HttpWebResponse)httpRequest.GetResponse();

                    Stream responseStream = webResponse.GetResponseStream();
                    StreamReader responseReader = new System.IO.StreamReader(responseStream, Encoding.UTF8);
                    String responseString = responseReader.ReadToEnd();


                    MessageBox.Show(responseString);
                    return responseString;
                }
            }

            catch (Exception e)
            {
                MessageBox.Show(e.Message);
                return "FAIL";
            }
        }

        public void Dispose()
        {
            System.GC.SuppressFinalize(this);
        }
    }
}

更新

谢谢大家的帮助。我没能解决这个问题。

dispose 方法现在消失了。

我已经在本地创建了 HttpWebRequest httpRequest、HttpWebResponse webResponse 和 Stream requestStream，并且正在使用以下 using 语句:

using (webResponse = (HttpWebResponse)httpRequest.GetResponse())
{
    using (Stream responseStream = webResponse.GetResponseStream())
    {
        using (StreamReader responseReader = new System.IO.StreamReader(responseStream, Encoding.UTF8))
        {
            responseString = responseReader.ReadToEnd();
        }
    }
}

另一个更新

现在这是整个 GetPage 方法:

public string GetPage()
{
    HttpWebRequest httpRequest;
    HttpWebResponse webResponse;
    Stream requestStream;

    try
    {
        StringBuilder postData = new StringBuilder(100);
        postData.Append("test=test");
        byte[] dataArray = Encoding.UTF8.GetBytes(postData.ToString());

        httpRequest = (HttpWebRequest)WebRequest.Create("http://myurl");

        httpRequest.Proxy = null;
        httpRequest.Method = "POST";
        httpRequest.Timeout = 10;
        httpRequest.ContentType = "application/x-www-form-urlencoded";

        httpRequest.ContentLength = dataArray.Length;

        using (requestStream = httpRequest.GetRequestStream())
        {
            /* this is never reached when the time out exception starts 
            so the error seems to be related to too many GetRequestStreams */

            requestStream.Write(dataArray, 0, dataArray.Length);

            webResponse = (HttpWebResponse)httpRequest.GetResponse();

            /* this is never reached when the 500 server error occurs */

            String responseString = "";
            using (Stream responseStream = webResponse.GetResponseStream())
            {
                using (StreamReader responseReader = new System.IO.StreamReader(responseStream, Encoding.UTF8))
                {
                    responseString = responseReader.ReadToEnd();
                    return responseString;
                }
            }
        }
    }

    catch (Exception e)
    {
        return "FAIL";
    }

    return "...";
}

** 解决了!! ** httpRequest 没有被中止()。在 catch() block 中，我添加了 httpRequest.abort()，现在它可以正常工作了。

Answer 1

我怀疑这是问题所在:

this.webResponse = (HttpWebResponse)httpRequest.GetResponse();
Stream responseStream = webResponse.GetResponseStream();
StreamReader responseReader = new StreamReader(responseStream, Encoding.UTF8);
String responseString = responseReader.ReadToEnd();

您不会处理任何这些一次性元素。这意味着与 Web 服务器的连接将一直保持到最终确定，因此连接池(每个服务器两个连接)将不允许任何其他请求。

我建议:

• 您将 GetResponse 调用从请求流的 using 语句中移出
• 您删除了对请求流的 Flush 和 Close 的显式调用(处理它就足够了)
• 您制作 webResponse 和 webRequest 局部变量而不是实例变量，除非您以后真的需要它们，在这种情况下您应该处理它们在您的 Dispose 方法中。
• 您对WebResponse、Stream 和StreamReader 使用using 语句。 (最后一个不是绝对必要的，因为处理流就足够了。)
• 你让 GetPages 不实现 IDisposable，除非你真的需要它。