How to expose a sub section of my stream to a user

Smith325_46810 0
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I have a stream that contains many pieces of data. I want to expose just a piece of that data in another stream. The piece of data I want to extract can often be over 100mb. Since I already have stream with the data in it it seems like a waste to copy that data to another stream and return that. What im looking for is a way to reference the data in the first stream while controlling how much of it the second stream can reference. Is this possible

filestream stream c#
5 Answers

I also needed a substream so that I could work on a ZIP archive inside of another file, the other answer didn't implement seeking though so here's one with seeking; be aware it will not dispose the original stream when disposed:

public class SubStream : Stream
{
    Stream Vector;
    long Offset, _Length, _Position = 0;
    public SubStream(Stream vector, long offset, long length)
    {
        if (length < 1) throw new ArgumentException("Length must be greater than zero.");

        this.Vector = vector;
        this.Offset = offset;
        this._Length = length;

        vector.Seek(offset, SeekOrigin.Begin);
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        CheckDisposed();
        long remaining = _Length - _Position;
        if (remaining <= 0) return 0;
        if (remaining < count) count = (int)remaining;
        int read = Vector.Read(buffer, offset, count);
        _Position += read;
        return read;
    }

    private void CheckDisposed()
    {
        if (Vector == null) throw new ObjectDisposedException(GetType().Name);
    }

    public override long Seek(long offset, SeekOrigin origin)
    {
        long pos = _Position;

        if (origin == SeekOrigin.Begin)
            pos = offset;
        else if (origin == SeekOrigin.End)
            pos = _Length + offset;
        else if (origin == SeekOrigin.Current)
            pos += offset;

        if (pos < 0) pos = 0;
        else if (pos >= _Length) pos = _Length - 1;

        _Position = Vector.Seek(this.Offset + pos, SeekOrigin.Begin) - this.Offset;

        return pos;
    }

    public override bool CanRead => true;

    public override bool CanSeek => true;

    public override bool CanWrite => false;

    public override long Length => _Length;

    public override long Position { get => _Position; set { _Position = this.Seek(value, SeekOrigin.Begin); } }

    public override void Flush()
    {
        throw new NotImplementedException();
    }

    public override void SetLength(long value)
    {
        throw new NotImplementedException();
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        throw new NotImplementedException();
    }
}
user_14816990
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