使用AsyncEnumerator实现APM模式时的异常处理

我正在尝试使用Richter的AsyncEnumerator类实现APM模式。目标是实现一个ExtendedSocket类，它来源于Socket，并提供Begin/EndReceiveFixed和Begin/EndSendFixed方法来异步发送或接收固定数量的字节。

代码看起来像这样(我省略了发送部分，因为它基本上与接收相同):

class ExtendedSocket : Socket
{
    public ExtendedSocket(AddressFamily addressFamily, SocketType socketType, ProtocolType protocolType)
        : base(addressFamily, socketType, protocolType)
    {
    }
    public IAsyncResult BeginReceiveFixed(byte[] buffer, SocketFlags socketFlags, AsyncCallback callback, Object state)
    {
        AsyncEnumerator ae = new AsyncEnumerator();
        return ae.BeginExecute(DoReceiveFixed(ae, buffer, socketFlags), callback, state);
    }
    public void EndReceiveFixed(IAsyncResult asyncResult)
    {
        AsyncResult ar = asyncResult as AsyncResult;
        (ar.InitiatingObject as AsyncEnumerator).EndExecute(ar);
    }
    private IEnumerator<Int32> DoReceiveFixed(AsyncEnumerator ae, byte[] buffer, SocketFlags socketFlags)
    {
        int totalReceivedBytes = 0;
        while (totalReceivedBytes < buffer.Length)
        {
            BeginReceive(buffer, totalReceivedBytes, buffer.Length - totalReceivedBytes, socketFlags, ae.End(), null);
            yield return 1;
            totalReceivedBytes += EndReceive(ae.DequeueAsyncResult());
        }
    }
}

这在我的应用程序中非常好，但我不知道如何处理DoReceiveFixed中的异常。我想实现默认的APM行为，当EndReceiveFixed被调用时(重新)抛出异常。

不幸的是，我不能访问DoReceiveFixed内部的AsyncResult对象，所以我不能在AsyncResult对象上异常调用SetAsCompleted。

我目前的解决方法是使用AsyncEnumerator<Exception>代替AsyncEnumerator，像这样:

class ExtendedSocket : Socket
{
    public ExtendedSocket(AddressFamily addressFamily, SocketType socketType, ProtocolType protocolType)
        : base(addressFamily, socketType, protocolType)
    {
    }
    public IAsyncResult BeginReceiveFixed(byte[] buffer, SocketFlags socketFlags, AsyncCallback callback, Object state)
    {
        AsyncEnumerator<Exception> ae = new AsyncEnumerator<Exception>();
        return ae.BeginExecute(DoReceiveFixed(ae, buffer, socketFlags), callback, state);
    }
    public void EndReceiveFixed(IAsyncResult asyncResult)
    {
        AsyncResult ar = asyncResult as AsyncResult;
        AsyncEnumerator<Exception> ae = ar.InitiatingObject as AsyncEnumerator<Exception>;
        ae.EndExecute(ar);
        if (ae.Result != null)
        {
            throw ae.Result;
        }
    }
    private IEnumerator<Int32> DoReceiveFixed(AsyncEnumerator<Exception> ae, byte[] buffer, SocketFlags socketFlags)
    {
        int totalReceivedBytes = 0;
        Exception catchedException = null;
        while (totalReceivedBytes < buffer.Length)
        {
            try
            {
                BeginReceive(buffer, totalReceivedBytes, buffer.Length - totalReceivedBytes, socketFlags, ae.End(), null);
            }
            catch (Exception ex)
            {
                catchedException = ex;
                break;
            }
            yield return 1;
            try
            {
                totalReceivedBytes += EndReceive(ae.DequeueAsyncResult());
            }
            catch (Exception ex)
            {
                catchedException = ex;
                break;
            }
        }
        ae.Result = catchedException;
    }
}

这似乎工作，但我不太喜欢这个解决方案。有更好的方法吗?也许有一种方法可以从DoFixedReceive内部访问AsyncResult对象?