MultiStream.cs

using System.Collections.Generic;
using System.IO;
using System.Text;

public class MultiStream : Stream
{
    IList<Stream> _streamList = new List<Stream>();

    long position = 0;
    public override bool CanRead
    {
        get { return true; }
    }

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

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

    public override long Length
    {
        get
        {
            long result = 0;
            foreach (Stream stream in _streamList)
            {
                result += stream.Length;
            }
            return result;
        }
    }

    public override long Position
    {
        get { return position; }
        set { Seek(value, SeekOrigin.Begin); }
    }

    public override void Flush() { }

    public override long Seek(long offset, SeekOrigin origin)
    {
        long len = Length;
        switch (origin)
        {
            case SeekOrigin.Begin:
                position = offset;
                break;
            case SeekOrigin.Current:
                position += offset;
                break;
            case SeekOrigin.End:
                position = len + offset;
                break;
        }
        if (position > len)
        {
            position = len;
        }
        if (position < 0)
        {
            position = 0;
        }
        return position;
    }

    public override void SetLength(long value) { }

    public void AddStream(Stream stream)
    {
        _streamList.Add(stream);
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        long len = 0;
        int result = 0;
        int buf_pos = offset;
        int bytesRead;
        foreach (Stream stream in _streamList)
        {
            if (position < (len + stream.Length))
            {
                stream.Position = position - len;
                bytesRead = stream.Read(buffer, buf_pos, count);
                result += bytesRead;
                buf_pos += bytesRead;
                position += bytesRead;
                if (bytesRead < count)
                {
                    count -= bytesRead;
                }
                else
                {
                    break;
                }
            }
            len += stream.Length;
        }
        return result;
    }

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