SubStream.Write C# (CSharp) Method

    public override void Write(byte[] buffer, int offset, int count)
    {
        if (Position + count > Length)
            throw new Exception("Write operation passes end of stream");
        stream.Position = Position + streamOffset;
        stream.Write(buffer, offset, count);
        Position = Position + count;
        if (Position > Length)
            Position = Length;
    }

 private void LoadDescriptor(Stream s)
 {
     s.Position = 0;
     byte[] header = Utilities.ReadFully(s, (int)Math.Min(Sizes.Sector, s.Length));
     if (header.Length < Sizes.Sector || Utilities.ToUInt32LittleEndian(header, 0) != HostedSparseExtentHeader.VmdkMagicNumber)
     {
         s.Position  = 0;
         _descriptor = new DescriptorFile(s);
         if (_access != FileAccess.Read)
         {
             _descriptor.ContentId = (uint)_rng.Next();
             s.Position            = 0;
             _descriptor.Write(s);
             s.SetLength(s.Position);
         }
     }
     else
     {
         // This is a sparse disk extent, hopefully with embedded descriptor...
         HostedSparseExtentHeader hdr = HostedSparseExtentHeader.Read(header, 0);
         if (hdr.DescriptorOffset != 0)
         {
             Stream descriptorStream = new SubStream(s, hdr.DescriptorOffset * Sizes.Sector, hdr.DescriptorSize * Sizes.Sector);
             _descriptor = new DescriptorFile(descriptorStream);
             if (_access != FileAccess.Read)
             {
                 _descriptor.ContentId     = (uint)_rng.Next();
                 descriptorStream.Position = 0;
                 _descriptor.Write(descriptorStream);
                 byte[] blank = new byte[descriptorStream.Length - descriptorStream.Position];
                 descriptorStream.Write(blank, 0, blank.Length);
             }
         }
     }
 }