Question

情况的简要概要：

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

我目前正在努力实施的解决方案：

本质上，我正在尝试将SslStream（传入）与NetworkStream耦合（传出 - 可能是一个Socket，但我把它放入NetworkStream以匹配传入）并且将读取/写入操作链接到两个。此链接将提供客户端（通过SSL / TLS）和服务（通过不安全的连接）之间的流程。

这是我想出的链接这些Streams的课程：

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：

当客户端完成发送信息并处理SslStream时，服务器没有任何关于是否发生这种情况的指示。这个StreamConnector类愉快地运行到永恒而不会抛出任何类型的错误，我找不到它应该停止的任何指示。（当然，事实上我每次在ReadCallback中都得到0长度，但我需要能够提供长时间运行的连接，所以这不是判断的好方法。）

另一个潜在的问题是，即使没有可用的数据，也会调用ReadCallback。如果我直接使用Socket而不是流来确定是否会有所不同，但是一遍又一遍地运行该代码似乎效率低下。

我的问题：

1）有没有办法判断Stream是否已从客户端关闭？

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。事实证明循环不断被调用，因为我没有关闭Streams（由于不知道如何判断Streams何时需要关闭）。我将包含完整的代码解决方案，以防其他人遇到此问题：

/// <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;
        }
    }
}

Answer 1

您必须尝试读取或写入套接字 - 或基于它的任何内容 - 来检测断开连接。

尝试写入将抛出异常/返回错误（取决于您的语言范例）或者可能只写0个字节。尝试阅读将抛出异常/返回错误（再次取决于您的语言范例）或返回null。

值得注意的是，如果您使用基于选择的服务器模型，断开连接的套接字会显示 - 即返回select - 在断开连接时可读，然后您尝试从中读取并获取错误或{ {1}}。

Answer 2

我不禁想到你的客户应该告诉服务器何时完成某种消息。最好是准备好切断电线或电源故障或拔出插头，但通常你想要终止与某种消息结束标记的连接。保存实际问题的例外情况，而不是正常的对话。

是否可以检测客户端是否已关闭Stream？

2 个答案: