public class ResponseFilter : System.IO.Stream
{
    public ResponseFilter(System.IO.Stream sink, string _str)
    {
        _sink = sink;
        //
        // TODO: 在此处添加构造函数逻辑
        //
        this.str = _str;
    }
    private string str = "";
    private System.IO.Stream _sink;
    private long _position;
    private System.Text.Encoding end = System.Text.Encoding.GetEncoding("GB18030");
    private System.Text.StringBuilder oOutput = new System.Text.StringBuilder();
    // The following members of Stream must be overriden.
    public override bool CanRead
    {
        get { return true; }
    }

    public override bool CanSeek
    {
        get { return true; }
    }

    public override bool CanWrite
    {
        get { return true; }
    }

    public override long Length
    {
        get { return 0; }
    }

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

    public override long Seek(long offset, System.IO.SeekOrigin direction)
    {
        return _sink.Seek(offset, direction);
    }

    public override void SetLength(long length)
    {
        _sink.SetLength(length);
    }