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In scenarios where you want to extend functionality of a simple System.IO.Stream instance, it is convenient to have a decorator. Neither the original stream or the client instance will have to know anything about the extension as it is still just a Stream.
This can be used to add position tracking or to manage lifetime. For instance you might want to dispose a System.Net.HttpWebResponse instance that created the stream when the stream is being closed.
The most straightforward way to achieve this is to copy/paste the code below and inherit that class to create your stream extender. Of course you could also have done this with a dynamic proxy plus interceptor.

abstract class DecoratorStream : Stream
{
    Stream m_stream;

    protected DecoratorStream(Stream stream)
    {
        m_stream = stream;
    }

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

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

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

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

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

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

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

    public override bool CanTimeout
    {
        get
        {
            return m_stream.CanTimeout;
        }
    }

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

    public override void Close()
    {
        m_stream.Close();
    }

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

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

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

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

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

    public override int ReadTimeout
    {
        get
        {
            return m_stream.ReadTimeout;
        }
        set
        {
            m_stream.ReadTimeout = value;
        }
    }

    protected override void Dispose(bool disposing)
    {
        try
        {
            m_stream.Dispose();
        }
        finally
        {
            base.Dispose(disposing);
        }
    }

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

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

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

    public override int WriteTimeout
    {
        get
        {
            return m_stream.WriteTimeout;
        }
        set
        {
            m_stream.WriteTimeout = value;
        }
    }
}