如果状态 ！= 200，则 HttpWebRequest 返回空值

Question

我正在创建一个函数来测试给定的网址并获取状态代码，问题是 HttpWebRequest 变量将返回 NULL - 如代码中注释的那样 - 如果状态为 tineOut 或无法访问 url，而它应该返回 408 进行超时。

try
{
    request = (HttpWebRequest)WebRequest.Create(url); //set http request
    request.Timeout = timeOut * 1000;
    request.ContinueTimeout = timeOut * 1000;
    stopwatch.Start(); //start timer
    response = (HttpWebResponse)request.GetResponse(); //this will return NULL if URL is timedOut or not reachable
    response.Close(); //close session 
    stopwatch.Stop(); //Stop timer
    statusCode = (int)response.StatusCode; //save status code as int
    info[0] = stopwatch.Elapsed.TotalMilliseconds.ToString(); //store Latency to info
    info[1] = statusCode.ToString(); //store status code
    info[2] = response.StatusDescription; //store status description 
}
catch (WebException err) //catch timeOut case
{
    stopwatch.Stop();
    var responseObj = err.Response as HttpWebResponse; //err.Response is NULL as well.
    info[0] = stopwatch.Elapsed.TotalMilliseconds.ToString(); //store Latency to info
    info[1] = (int)responseObj.StatusCode + "";//store status code
    info[2] = responseObj.StatusDescription; //store status description 
}

最后，我

无法将这两个解决方案应用于我当前的代码，因为它们似乎与我的问题相同。
如何为 HttpWebRequest 定义更激进的超时？
捕获 HttpWebRequest 超时

如果需要任何澄清，请通知我。

Answer 1

请求。GetResponse(( 返回来自您尝试与之通信的 Web 服务器的响应。

现在，当您遇到超时或错误的 URL 时，来自 Web 服务器的响应将为 NULL，因为您没有从该服务器获得任何信息。

您可以使用从 WebException 获得的状态来检测超时。

这是您的 http 通信的通用捕获块。请注意，您的 408 实际上是不正确的，任何其他与 http 无关的问题最终都将以 -1 结束。

catch (WebException wbEx)
{
    if (wbEx.Status == WebExceptionStatus.ProtocolError)
    {
        if (wbEx.Response is HttpWebResponse response)
        {
            returnStatusCode = (int) response.StatusCode;
        }
        else // should not happen
        {
            returnStatusCode = -1;
        }
    }
    else
    {
        if (wbEx.Status == WebExceptionStatus.Timeout)
        {
            returnStatusCode = 408; // now this is not right because this is CLIENT timeout.
        }
    }
}
catch
{
    returnStatusCode =  -1;
}