处理网络断开连接 [英] Handling network disconnect

问题描述

我试图做长轮询与HttpWebRequest对象。

I am trying to do "long polling" with an HttpWebRequest object.

在我的C＃应用​​程序，我想提出一个HTTP GET请求，使用HttpWebRequest的。再后来，我等与beginGetResponse响应（）。我使用ThreadPool.RegisterWaitForSingleObject等待响应，或者超时（1分钟后）。

In my C# app, I am making an HTTP GET request, using HttpWebRequest. And then afterwards, I wait for the response with beginGetResponse(). I am using ThreadPool.RegisterWaitForSingleObject to wait for the response, or to timeout (after 1 minute).

我已经设置了目标Web服务器需要很长的时间来响应。所以，我有时间断开网络电缆。

I have set the target web server to take a long time to respond. So that, I have time to disconnect the network cable.

发送请求后，我拉网线。

After sending the request, I pull the network cable.

有没有办法得到一个例外，当这种情况发生？所以我不必等待超时？

Is there a way to get an exception when this happens? So I don't have to wait for the timeout?

而不是一个例外，1分钟超时到期后超时（从RegisterWaitForSingleObject）发生。

Instead of an exception, the timeout (from RegisterWaitForSingleObject) happens after the 1 minute timeout has expired.

有没有办法来确定网络连接去了？目前，这种情况是在Web服务器需要超过1分钟回应的情况下没有区别。

Is there a way to determine that the network connection went down? Currently, this situation is indistinguishable from the case where the web server takes more than 1 minute to respond.

推荐答案

我找到了解决办法

调用beginGetResponse之前，我可以呼吁HttpWebRequest的以下内容：

Before calling beginGetResponse, I can call the following on the HttpWebRequest:

req.ServicePoint.SetTcpKeepAlive( true, 10000, 1000)

我想这意味着，经过闲置10秒，客户端会发送一个TCP保持活动到服务器。这永葆如果网络连接断开，因为网线被拔掉将会失败。

I think this means that after 10 seconds of inactivity, the client will send a TCP "keep alive" over to the server. That keep alive will fail if the network connection is down because the network cable was pulled.

所以，当电缆被拉到，我一个永葆得到10秒内发送（最多），然后为BeginGetResponse回调发生。在回调，我得到和异常时，我打电话req.EndGetResponse（）。

So, when the cable is pulled, I a keep alive gets sent within 10 seconds (at most), and then the callback for BeginGetResponse happens. In the callback, I get and exception when I call req.EndGetResponse().

我想这违背了长轮询的好处之一，虽然。由于我们仍然存在发送数据包。

I guess this defeats one of the benefits of long polling, though. Since we're still sending packets around.

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