HttpClient与ASP.NET Core 2.0 webservice之间的连接关闭错误

Question

[HttpGet()]
public IActionResult Test()
{
    // do some db updates and get data
    var result = DoSomeStuff();
    // serialize data to byte array
    var output = Serialize(result);

    return File(output, "application/octet-stream");
}

我有10个客户。当他们串行调用webservice时，一切都正常工作。当我并行强调webservice和fire客户端时，我几乎总是在其中一些客户端上得到一个错误（通常一两个失败，有时甚至4-5个）。

以下是异常，它是从ReadAsByteArrayAsync调用引发的：

System.AggregateException: One or more errors occurred. ---> System.Net.Http.HttpRequestException: Error while copying content to a stream. ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
   at System.Net.Sockets.Socket.EndReceive(IAsyncResult asyncResult)
   at System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult)
   --- End of inner exception stack trace ---
   at System.Net.ConnectStream.EndRead(IAsyncResult asyncResult)
   at System.IO.Stream.<>c.<BeginEndReadAsync>b__43_1(Stream stream, IAsyncResult asyncResult)
   at System.Threading.Tasks.TaskFactory`1.FromAsyncTrimPromise`1.Complete(TInstance thisRef, Func`3 endMethod, IAsyncResult asyncResult, Boolean requiresSynchronization)
...
---> (Inner Exception #0) System.Net.Http.HttpRequestException: Error while copying content to a stream. ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
   at System.Net.Sockets.Socket.EndReceive(IAsyncResult asyncResult)
   at System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult)
   --- End of inner exception stack trace ---
   at System.Net.ConnectStream.EndRead(IAsyncResult asyncResult)
   at System.IO.Stream.<>c.<BeginEndReadAsync>b__43_1(Stream stream, IAsyncResult asyncResult)
   at System.Threading.Tasks.TaskFactory`1.FromAsyncTrimPromise`1.Complete(TInstance thisRef, Func`3 endMethod, IAsyncResult asyncResult, Boolean requiresSynchronization)
...

我发现了几个与这种异常相关的SO线程（例如这里），所以我最初认为这是一个与客户端相关的问题。建议回答：

null

对我没什么用。我想我在什么地方读到HttpClient中有一些bug（现在找不到源）。我尝试使用NuGet最新的system.net.http包。同样的问题。我创建了.NET核心控制台应用程序，并使用HttpClient的核心版本。同样的问题。我使用了httpwebrequest而不是httpclient。同样的潜在问题。

我在同一台虚拟机上运行webservice和客户端。为了排除一些本地问题，我从其他计算机同时运行客户端。同样的问题。

所以我最后用了以下简化代码（只有一个包含10个线程的应用程序）：

private async void Test_Click(object sender, RoutedEventArgs e)
{
    try
    {
        var tasks = Enumerable.Range(1, 10).Select(async i => await Task.Run(async () => await GetContent(i))).ToList();

        await Task.WhenAll(tasks);

        MessageBox.Show(String.Join(Environment.NewLine, tasks.Select(t => t.Result.ToString())));
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.ToString());
    }
}

private async Task<Int32> GetContent(Int32 id)
{
    using (var httpClient = new HttpClient())
    {
        var url = "http://localhost/TestService/api/test";

        using (var responseMessage = await httpClient.GetAsync(url).ConfigureAwait(false))
        {
            // just read everything and return length
            // ReadAsByteArrayAsync throws sometimes an exception
            var content = await responseMessage.Content.ReadAsByteArrayAsync();
            return content.Length;
        }
    }
}

info: Microsoft.AspNetCore.Server.Kestrel[28]
      Connection id "0HL89D9NUNEOQ", Request id "0HL89D9NUNEOQ:00000001": the connection was closed becuase the response was not read by the client at the specified minimum data rate.
dbug: Microsoft.AspNetCore.Server.Kestrel[10]
      Connection id "0HL89D9NUNEOQ" disconnecting.
...
info: Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv[14]
      Connection id "0HL89D9NUNEOQ" communication error.
Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.Internal.Networking.UvException: Error -4081 ECANCELED operation canceled

<system.applicationHost>
  <webLimits minBytesPerSecond="0"/>
</system.applicationHost>

有什么建议吗？我至少想知道这是服务器还是客户端相关的问题。

Answer 1

您的吞吐量似乎低于最小数据速率。此行为在Kestrel基础知识中进行了描述：

Kestrel每秒检查数据是否以指定的速率（字节/秒）传入。如果速率低于最小值，则连接超时。宽限期是Kestrel为客户端提供的将其发送速率提高到最小的时间量；在此期间不检查费率。宽限期有助于避免由于TCP慢速启动而断开最初以慢速速率发送数据的连接。

默认最小速率为240字节/秒，宽限期为5秒。

var host = new WebHostBuilder() 
    .UseKestrel(options => 
    { 
        options.Limits.MinResponseDataRate = null;
    })