C# 流管道（流间谍）

Question

我有一个输入流和一个流 reader 组件。这工作正常，但现在我想记录所有流量（在文件中保存一份副本）。所以我需要监视流。我正在考虑的一个解决方案是流管道（管道）或流包装器，它将流作为输入，然后让我首先了解流量。像这样：

    void Init(System.Net.Sockets.NetworkStream stream)
    {
        System.IO.Stream wrappedStream = new MyWrapper(stream);
        wrappedStream.ReadSpy = MyMethod;
        XmlReader reader = XmlReader.Create(wrappedStream);
    }

    // This will get called after some bytes have been read from a stream,
    // but before they get passed to the XmlReader
    byte[] MyMethod(byte[] buffer)
    {
        m_Writer.Write(buffer); // write to a file 
        return buffer; // Give to XmlReader 
    }

Answer 1

你要的就是装饰器模式。这是一种动态 adding/modifying 行为的技术：

为此，您需要使用接受另一个 Stream 实例的工厂构造函数来实现抽象 class Stream。您为抽象 class 的每个 method/overload 提供一个实现，它在修饰的 Stream 上调用相同的 method/overload，并执行您需要的任何额外工作。

完成此操作并用新装饰器装饰 Stream 后，它可以与接受 Stream 的任何其他东西互换使用，包括其他类似的装饰器：装饰器甚至可以是嵌套，就像洋葱层一样组成你需要的行为。

像这样：

class StreamInterceptor : Stream
{

  public Stream DecoratedInstance { get; set; }

  public event Action<byte[]> BytesRead;
  public event Action<byte[]> BytesWritten;

  public StreamInterceptor( Stream instance )
  {
    if ( instance == null ) throw new ArgumentNullException("instance");
    this.DecoratedInstance = instance ;
    return ;
  }

  public override bool CanRead
  {
    get { return DecoratedInstance.CanRead; }
  }

  public override bool CanSeek
  {
    get { return DecoratedInstance.CanSeek; }
  }

  public override bool CanWrite
  {
    get { return DecoratedInstance.CanWrite; }
  }

  public override void Flush()
  {
    DecoratedInstance.Flush();
    return;
  }

  public override long Length
  {
    get { return DecoratedInstance.Length; }
  }

  public override long Position
  {
    get { return DecoratedInstance.Position; }
    set { DecoratedInstance.Position = value; }
  }

  public override int Read( byte[] buffer , int offset , int count )
  {
    int bytesRead = DecoratedInstance.Read(buffer, offset, count);

    // raise the bytes read event
    byte[] temp = new byte[bytesRead];
    Array.Copy(buffer,offset,temp,0,bytesRead);
    BytesRead(temp);

    return bytesRead;
  }

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

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

  public override void Write( byte[] buffer , int offset , int count )
  {

    // raise the bytes written event
    byte[] temp = new byte[count];
    Array.Copy(buffer,offset,temp,0,count);
    BytesWritten(temp);

    DecoratedInstance.Write(buffer, offset, count);
    return;
  }

}

一旦你知道了，你可以这样说：

static void Main()
{
  StreamInterceptor si = new StreamInterceptor(File.Open("foo.bar.txt",FileMode.Open,FileAccess.ReadWrite,FileShare.Read));

  si.BytesRead    += (bytes) => { Console.WriteLine("{0} bytes read", bytes.Length); } ;
  si.BytesWritten += (bytes) => { Console.WriteLine("{0} bytes written", bytes.Length); } ;

  Stream s = (Stream) si ;
  DoSomethingUseful(s);

}

只要有人从流中读取或写入，就会调用您的事件处理程序。

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