c# - 对 REST 服务的 WebClient 调用在控制台应用程序中有效，但在 asp.net 中无效

Question

我正在调用一个测试 REST Web 服务，它基本上将字符串作为输入，并将其回显给调用者。我在 C# 控制台应用程序中有以下代码:

static async Task RunAsync()
{
    using (var client = new HttpClient())
    {
    string baseAddress = 
    "http://xxx.xxx.xxx.xxx/Services/OnyxCloudSyncService.svc/pingSync";
    client.BaseAddress = new Uri(baseAddress); 
    client.DefaultRequestHeaders.Accept.Clear();
    client.DefaultRequestHeaders.Accept.Add(new
       MediaTypeWithQualityHeaderValue("application/json"));
    HttpResponseMessage response = await 
               client.GetAsync("?sampleJson={SAMPLEJSON}");           
    if (response.IsSuccessStatusCode)
    {
        string txtBlock = await response.Content.ReadAsStringAsync(); 
        Console.WriteLine(txtBlock);
        Console.ReadKey();
    }
    }
}

这段代码运行完美。但是当我基本上将相同的代码复制到 ASP.NET 页面的代码隐藏时，我在调用服务时超时:

using (var SyncClient = new HttpClient())
  {
   string baseAddress = "http://xxx.xxx.xxx.xxx/Services/OnyxCloudSyncService.svc/pingSync";
   SyncClient.DefaultRequestHeaders.Accept.Clear();
   SyncClient.DefaultRequestHeaders.Accept.Add(new
           MediaTypeWithQualityHeaderValue("application/json"));
   HttpResponseMessage response = await 
          SyncClient.GetAsync("?sampleJson={SAMPLEJSON}");
   if (response.IsSuccessStatusCode)
   {
    string txtBlock = await response.Content.ReadAsStringAsync();
    Response.Write(txtBlock);
    Response.End();
   }
   else
   {
    Response.Write("Error Calling service");
    Response.End();
   }
  }

我从这个页面得到的错误是:

System.Net.Sockets.SocketException: A connection attempt failed because
the connected party did not properly respond after a period of time, or
established connection failed because connected host has failed to respond
xxx.xxx.xxx.xxx:80. 

我是否需要在 WebClient 上设置某种类型的设置或选项，以使其在 ASP 页面中像在控制台应用程序中一样工作？我不知道为什么这会在控制台应用程序而不是 ASP.NET 网页中工作。

Answer 1

您可能遇到问题，因为没有等待结果，解决方案可能在:http://www.hanselman.com/blog/TheMagicOfUsingAsynchronousMethodsInASPNET45PlusAnImportantGotcha.aspx 上找到

我假设您使用的是 .NET 4.5。 将方法编辑为实例，而不是静态的，因为您将无法访问 Response 对象:

async Task RunAsync()
{
    using (var client = new HttpClient())
    {
        string baseAddress =
        "http://74.120.219.166/Services/OnyxCloudSyncService.svc/pingSync";
        client.BaseAddress = new Uri(baseAddress);
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(new
           MediaTypeWithQualityHeaderValue("application/json"));
        HttpResponseMessage response = await
                   client.GetAsync("?sampleJson={SAMPLEJSON}");
        if (response.IsSuccessStatusCode)
        {
            string txtBlock = await response.Content.ReadAsStringAsync();
            Response.Write(txtBlock);
            Response.End();
        }
        else
        {
            Response.Write("Error Calling service");
            Response.End();
        }
    }
}

运行方法如下:RegisterAsyncTask(new PageAsyncTask(RunAsync)); 将 Async="true" 放入 .aspx 页面的 Page 指令中。 我尝试了这种方法，它按预期工作。