如何捕获从 HttpWebRequest.GetResponseAsync 抛出的异常？

Question

I have the following method:

private static async void SendRequest()
{
    HttpWebRequest httpWebRequest = (HttpWebRequest)WebRequest.Create("http://google.com");
    httpWebRequest.KeepAlive = false;
    httpWebRequest.Proxy = null;
    httpWebRequest.Timeout = 1;
    try
    {
        await httpWebRequest.GetResponseAsync();
        Console.WriteLine("GetResponse Finished");
    }
    catch (Exception ex)
    {
        Console.WriteLine("Exception thrown="+ex);
    }
}

This throws an exception in case of failure to resolve name, but it never seems to throw an exception in case of timeout. If I use GetResponse with the unrealistic timeout of 1 ms, it always throws an timeout exception, but this doesn't seem to happen with GetResponseAsync.

Any idea how I can get Timeout exceptions to be thrown and handled like the synchronous method ?

Answer 1

As noted in the documentation , HttpWebRequest.Timeout does not apply to asynchronous requests. You have to write your own timeout code in that case.

Or you could upgrade to HttpClient , which does a lot of that work for you.

Answer 2

Use Wait() for async method to complete. Change void to Task in SendRequest()

   static void Main()
   {
      SendRequest().Wait()
   }

    private static async **Task** SendRequest()
    {
        HttpWebRequest httpWebRequest = (HttpWebRequest)WebRequest.Create("http://google.com");
        httpWebRequest.KeepAlive = false;
        httpWebRequest.Proxy = null;
        httpWebRequest.Timeout = 1;
        try
        {
            await httpWebRequest.GetResponseAsync();
            Console.WriteLine("GetResponse Finished");
        }
        catch (Exception ex)
        {
            Console.WriteLine("Exception thrown="+ex);
        }
    }