是否可以检测流是否已被客户端关闭

情况简介：

我有一个服务，可以接收信息并通过套接字发送回复。连接不安全。我想设置另一个可以为这些连接提供TLS的服务——这个新服务将提供一个端口，并根据提供的客户端证书分发连接。我不想使用stunnel有两个原因，一个是每个接收端口需要一个转发端口。

我目前正在尝试实现的解决方案：

本质上，我试图将SslStream（传入）与NetworkStream（传出-可能是Socket，但我将其放入NetworkStream中以匹配传入）相耦合，并将两者的读/写操作链接起来。该链接将提供客户端（通过SSL/TLS）和服务（通过不安全的连接）之间的流。

这是我想出的链接这些流的类：

public class StreamConnector
{
    public StreamConnector(Stream s1, Stream s2)
    {
        StreamConnectorState state1 = new StreamConnectorState(s1, s2);
        StreamConnectorState state2 = new StreamConnectorState(s2, s1);
        s1.BeginRead(state1.Buffer, 0, state1.Buffer.Length, new AsyncCallback(ReadCallback), state1);
        s2.BeginRead(state2.Buffer, 0, state2.Buffer.Length, new AsyncCallback(ReadCallback), state2);
    }
    private void ReadCallback(IAsyncResult result)
    {
        // Get state object.
        StreamConnectorState state = (StreamConnectorState)result.AsyncState;
        // Finish reading data.
        int length = state.InStream.EndRead(result);
        // Write data.
        state.OutStream.Write(state.Buffer, 0, length);
        // Wait for new data.
        state.InStream.BeginRead(state.Buffer, 0, state.Buffer.Length, new AsyncCallback(ReadCallback), state);
    }
}
public class StreamConnectorState
{
    private const int BYTE_ARRAY_SIZE = 4096;
    public byte[] Buffer { get; set; }
    public Stream InStream { get; set; }
    public Stream OutStream { get; set; }
    public StreamConnectorState(Stream inStream, Stream outStream)
    {
        Buffer = new byte[BYTE_ARRAY_SIZE];
        InStream = inStream;
        OutStream = outStream;
    }
}

问题：

当客户端发送完信息并处理了SslStream时，服务器没有任何关于这种情况是否发生的指示。这个StreamConnector类愉快地一直运行到永恒，没有抛出任何错误，我找不到任何应该停止的指标。（当然，我每次在ReadCallback中都会得到0的长度，但我需要能够提供长时间运行的连接，所以这不是一个好的判断方法。）

另一个潜在的问题是，即使没有可用的数据，ReadCallback也会被调用。如果我直接使用Socket而不是流，我不确定这是否会有所不同，但一遍又一遍地运行代码似乎效率很低。

我的问题：

1） 有没有一种方法可以判断流是否已经从客户端关闭？

2） 有没有更好的方法来做我想做的事情？

2a）是否有更有效的方法来运行异步读/写循环？

编辑：谢谢，罗伯特。事实证明，循环一直被调用，因为我没有关闭Streams（因为不知道如何判断何时需要关闭Streams）。我包括完整的代码解决方案，以防其他人遇到这个问题：

/// <summary>
/// Connects the read/write operations of two provided streams
/// so long as both of the streams remain open.
/// Disposes of both streams when either of them disconnect.
/// </summary>
public class StreamConnector
{
    public StreamConnector(Stream s1, Stream s2)
    {
        StreamConnectorState state1 = new StreamConnectorState(s1, s2);
        StreamConnectorState state2 = new StreamConnectorState(s2, s1);
        s1.BeginRead(state1.Buffer, 0, state1.Buffer.Length, new AsyncCallback(ReadCallback), state1);
        s2.BeginRead(state2.Buffer, 0, state2.Buffer.Length, new AsyncCallback(ReadCallback), state2);
    }
    private void ReadCallback(IAsyncResult result)
    {
        // Get state object.
        StreamConnectorState state = (StreamConnectorState)result.AsyncState;
        // Check to make sure Streams are still connected before processing.
        if (state.InStream.IsConnected() && state.OutStream.IsConnected())
        {
            // Finish reading data.
            int length = state.InStream.EndRead(result);
            // Write data.
            state.OutStream.Write(state.Buffer, 0, length);
            // Wait for new data.
            state.InStream.BeginRead(state.Buffer, 0, state.Buffer.Length, new AsyncCallback(ReadCallback), state);
        }
        else
        {
            // Dispose of both streams if either of them is no longer connected.
            state.InStream.Dispose();
            state.OutStream.Dispose();
        }
    }
}
public class StreamConnectorState
{
    private const int BYTE_ARRAY_SIZE = 4096;
    public byte[] Buffer { get; set; }
    public Stream InStream { get; set; }
    public Stream OutStream { get; set; }
    public StreamConnectorState(Stream inStream, Stream outStream)
    {
        Buffer = new byte[BYTE_ARRAY_SIZE];
        InStream = inStream;
        OutStream = outStream;
    }
}
public static class StreamExtensions
{
    private static readonly byte[] POLLING_BYTE_ARRAY = new byte[0];
    public static bool IsConnected(this Stream stream)
    {
        try
        {
            // Twice because the first time will return without issue but
            // cause the Stream to become closed (if the Stream is actually
            // closed.)
            stream.Write(POLLING_BYTE_ARRAY, 0, POLLING_BYTE_ARRAY.Length);
            stream.Write(POLLING_BYTE_ARRAY, 0, POLLING_BYTE_ARRAY.Length);
            return true;
        }
        catch (ObjectDisposedException)
        {
            // Since we're disposing of both Streams at the same time, one
            // of the streams will be checked after it is disposed.
            return false;
        }
        catch (IOException)
        {
            // This will be thrown on the second stream.Write when the Stream
            // is closed on the client side.
            return false;
        }
    }
}