Catch unhandled SocketException during asynchronous HttpWebResponse read

Question

All the asynchronous calls to HttpWebRequest.BeginGetResponse/EndGetResponse and HttpWebResponse.GetResponseStream().BeginRead/EndRead are made from try/catch blocks, however, these exceptions propagate and do not leave a chance handle them and stop application termination:

Unhandled Exception: System.IO.IOException: Unable to read data from the transport connection: An established connection was aborted by the software in your host machine. ---> System.Net.Sockets.SocketException: An established connection was aborted by the software in your host machine

Unhandled Exception: 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

Unhandled Exception: System.IO.IOException: Unable to read data from the transport connection: An established connection was aborted by the software in your host machine. ---> System.Net.Sockets.SocketException: An established connection was aborted by the software in your host machine
   at System.Net.Sockets.Socket.BeginReceive(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags, AsyncCallback callback, Object state)
   at System.Net.Sockets.NetworkStream.BeginRead(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
   --- End of inner exception stack trace ---
   at System.Net.Sockets.NetworkStream.BeginRead(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
   at System.Net.PooledStream.BeginRead(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
   at System.Net.ConnectStream.BeginReadWithoutValidation(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
   at System.Net.ConnectStream.BeginRead(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
   at System.IO.Compression.DeflateStream.ReadCallback(IAsyncResult baseStreamResult)
   at System.Net.LazyAsyncResult.Complete(IntPtr userToken)
   at System.Net.ContextAwareResult.CompleteCallback(Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Net.ContextAwareResult.Complete(IntPtr userToken)
   at System.Net.LazyAsyncResult.ProtectedInvokeCallback(Object result, IntPtr userToken)
   at System.Net.Sockets.BaseOverlappedAsyncResult.CompletionPortCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped)
   at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP)

Actual code fragments:

public static RequestState StartDownload(string url, string referer, RequestData data, DownloadEventHandler completedHandler, DownloadExceptionHandler failedHandler)
{
    RequestState state = null;

    try
    {
        var request = CreateWebRequest(url, referer, data);
        state = new RequestState(url, data, request)
        {
            DownloadCompleted = completedHandler;
            DownloadFailed = failedHandler;
        }

        state.ResponseAsyncResult = request.BeginGetResponse(WebResponseCallback, state);
        state.AsyncTimeoutHandle = ThreadPool.RegisterWaitForSingleObject(state.CompletedHandle, DownloadTimeoutCallback, state, TimeSpan.FromSeconds(data.DownloadTimeout), true);
    }
    catch(Exception ex)
    {
        Trace.TraceError(ex.ToString());
    }

    return state;
}

private static void DownloadTimeoutCallback(object state, bool timedOut)
{
    var requestState = (RequestState)state;

    try
    {
        requestState.AsyncTimeoutHandle.Unregister(null);

        if(timedOut)
        {
            requestState.Request.Abort();
        }
    }
    catch(Exception ex)
    {
        Trace.TraceError(ex.ToString());
    }
}

private static void WebResponseCallback(IAsyncResult asyncResult)
{
    var state = (RequestState)asyncResult.AsyncState;
    try
    {
        var response = (HttpWebResponse)state.Request.EndGetResponse(asyncResult);
        WebResponse(state, response);
    }
    catch (Exception ex)
    {
        Trace.TraceError(ex.ToString());
    }
}

private static void WebResponse(RequestState state, HttpWebResponse response)
{
    state.ActualUrl = state.Request.Address.ToString();
    state.Response = response;

    BeginRead(state);
}

private static void BeginRead(RequestState state)
{
    var stream = state.Response.GetResponseStream();
    state.ReadAsyncResult = stream.BeginRead(state.Buffer, 0, state.BufferSize, ReadCallBack, state);
}

private static void ReadCallBack(IAsyncResult asyncResult)
{
    var state = (RequestState)asyncResult.AsyncState;

    try
    {
        var stream = state.Response.GetResponseStream();
        var bytesRead = stream.EndRead(asyncResult);

        if (bytesRead > 0)
        {
            //there is still more data to read
            state.AppendResponseData(state.Buffer, 0, bytesRead);
            BeginRead(state);
        }
        else
        {
            state.Response.Close();
            state.InvokeDownloadCompleted();
        }       
    }
    catch(Exception ex)
    {
        Trace.TraceError(ex.ToString());
    }
}

PS: A bug report was filed at Microsoft Connect https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=510564

Answer 1

I think the reason is that the exception raised on a different thread than the one that initiated the BegainGetResponse, and this explains the System.Threading.ExecutionContext.Run call in the call stack. The case might be that you exit the try catch block before the exception gets raised, so it raises with no handler to it, can you please post your part of the code so I can see how we can improve it

Answer 2

This exception is happening on a completion port thread, and therefore there is no chance to catch it, as you dont own the thread on which it is occuring.

What we need to do is to get to the root cause. Can you get a network tracelog as per instructions in http://ferozedaud.blogspot.com/2009/08/tracing-with-systemnet.html and also get a network sniff using Wireshark? That should help us get to the root cause of why the client is aborting the connection.

Answer 3

Posted by Microsoft on 11/16/2009 at 11:14 AM

This issue has been resolved in the .NET 4.0 Framework.

Thank you,

Network Class Library Team

https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=510564