处理 XmlWriter 而不发送未完成的结束元素

Question

我正在使用 XmlWriter 发送 XMPP (Jingle) 流。 XMPP 协议在协商 TLS 时替换了 XML 流，这意味着 XML 最终的结果如下：

<stream>
 <features>
  ...
 </features>

 ...TLS gets negotiated...

<stream>
 ...
</stream>

XML 最终格式不正确，因为有两个流开始标记。

我想做的是在 TLS 协商之前扔掉我正在使用的 XmlWriter 并创建一个全新的，它可以让我更好地模块化我的代码。但是，当我调用 myXmlWriter.Close() 来确保它被处理时，它将发送关闭流结束元素，这会破坏 XMPP 协议。

无论如何，我是否可以关闭 XmlWriter 而不发送未完成的结束元素？

Answer 1

创建一个中间流，可用于断开 XmlWriter 与基本流的连接。

这不是最优雅的解决方案，下面的代码需要工作，因此在将其投入生产之前对其进行测试，但是这是关于想法的。

public class DummyStream : Stream
{
    public DummyStream(Stream baseStream)
    {
        if (baseStream == null)
            throw new ArgumentNullException("baseStream");

        BaseStream = baseStream;
    }

    public Stream BaseStream { get; private set; }

    public void DisconnectBaseStream()
    {
        BaseStream = null;
    }

    private Stream GetBaseStream()
    {
        return BaseStream ?? Stream.Null;
    }

    public override IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback callback, object state)
    {
        return GetBaseStream().BeginRead(buffer, offset, count, callback, state);
    }

    public override IAsyncResult BeginWrite(byte[] buffer, int offset, int count, AsyncCallback callback, object state)
    {
        return GetBaseStream().BeginWrite(buffer, offset, count, callback, state);
    }

    public override bool CanRead
    {
        get { return GetBaseStream().CanRead; }
    }

    public override bool CanSeek
    {
        get { return GetBaseStream().CanSeek; }
    }

    public override bool CanTimeout
    {
        get { return GetBaseStream().CanTimeout; }
    }

    public override bool CanWrite
    {
        get { return GetBaseStream().CanWrite; }
    }

    public override void Close()
    {
        // We do not close the BaseStream because this stream
        // is just a wrapper.

        // GetBaseStream().Close();
    }

    public override ObjRef CreateObjRef(Type requestedType)
    {
        return GetBaseStream().CreateObjRef(requestedType);
    }

    protected override void Dispose(bool disposing)
    {
        base.Dispose(disposing);

        // We do not dispose the BaseStream because this stream
        // is just a wrapper.
    }

    public override int EndRead(IAsyncResult asyncResult)
    {
        return GetBaseStream().EndRead(asyncResult);
    }

    public override void EndWrite(IAsyncResult asyncResult)
    {
        GetBaseStream().EndWrite(asyncResult);
    }

    public override bool Equals(object obj)
    {
        return GetBaseStream().Equals(obj);
    }

    public override void Flush()
    {
        GetBaseStream().Flush();
    }

    public override int GetHashCode()
    {
        return GetBaseStream().GetHashCode();
    }

    public override object InitializeLifetimeService()
    {
        return GetBaseStream().InitializeLifetimeService();
    }

    public override long Length
    {
        get { return GetBaseStream().Length; }
    }

    public override long Position
    {
        get { return GetBaseStream().Position; }
        set { GetBaseStream().Position = value; }
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        return GetBaseStream().Read(buffer, offset, count);
    }

    public override int ReadByte()
    {
        return GetBaseStream().ReadByte();
    }

    public override int ReadTimeout
    {
        get { return GetBaseStream().ReadTimeout; }
        set { GetBaseStream().ReadTimeout = value; }
    }

    public override long Seek(long offset, SeekOrigin origin)
    {
        return GetBaseStream().Seek(offset, origin);
    }

    public override void SetLength(long value)
    {
        GetBaseStream().SetLength(value);
    }

    public override string ToString()
    {
        return GetBaseStream().ToString();
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        GetBaseStream().Write(buffer, offset, count);
    }

    public override void WriteByte(byte value)
    {
        GetBaseStream().WriteByte(value);
    }

    public override int WriteTimeout
    {
        get { return GetBaseStream().WriteTimeout; }
        set { GetBaseStream().WriteTimeout = value; }
    }
}

此类旨在用作 XmlWriter 和 XmlWriter 输出到的流之间的流。该类只是将所有来自 XmlWriter 的调用转发到基本流，但是一旦调用 DisconnectBaseStream，它就会停止转发它们，并且 XmlWriter 无法控制不再是基础流了。

您可以像这样使用此类：

using (var stream = /* stream used to communicate with */)
{
    using (var wrapperStream = new DummyStream(stream))
    using (var writer = XmlWriter.Create(wrapperStream))
    {
        // Do you work here.

        // Now, disconnect the dummy stream so that the XML writer
        // cannot send more data.

        wrapperStream.DisconnectBaseStream();

        // End of the using block will close the XmlWriter and it
        // cannot send more data to the base stream.
    }

    // Perform TLS negotiation etc...
}

同样，DummyStream 是一个起点，需要一些工作。例如，您需要确保 XmlWriter 在断开连接后不会进行会崩溃的调用，因此您需要使用 Write 方法进行一些检查BaseStream 是否为 null，如果是，则跳过调用。