LengthWriter.cs

/////////////////////////////////////////////////////////////////////////////////
//
// ABR FileType Plugin for Paint.NET
// 
// This software is provided under the MIT License:
//   Copyright (c) 2012-2017 Nicholas Hayes
//
// See LICENSE.txt for complete licensing and attribution information.
//
/////////////////////////////////////////////////////////////////////////////////

// Portions of this file has been adapted from:
/////////////////////////////////////////////////////////////////////////////////
//
// Photoshop PSD FileType Plugin for Paint.NET
// http://psdplugin.codeplex.com/
//
// This software is provided under the MIT License:
//   Copyright (c) 2006-2007 Frank Blumenberg
//   Copyright (c) 2010-2011 Tao Yue
//
// Portions of this file are provided under the BSD 3-clause License:
//   Copyright (c) 2006, Jonas Beckeman
//
// See LICENSE.txt for complete licensing and attribution information.
//
/////////////////////////////////////////////////////////////////////////////////

using System;

namespace AbrFileTypePlugin
{
    internal sealed class LengthWriter : IDisposable
    {
        private readonly long lengthFieldOffset;
        private readonly long startPosition;
        private BinaryReverseWriter writer;
        private bool disposed;

        public LengthWriter(BinaryReverseWriter writer)
        {
            this.writer = writer;
            // we will write the correct length later, so remember 
            // the position
            this.lengthFieldOffset = writer.BaseStream.Position;
            writer.Write(0xFEEDFEED);

            // remember the start  position for calculation Image 
            // resources length
            this.startPosition = writer.BaseStream.Position;
            this.disposed = false;
        }

        public void Dispose()
        {
            if (!this.disposed)
            {
                long endPosition = this.writer.BaseStream.Position;
                long length = endPosition - this.startPosition;

                writer.BaseStream.Position = this.lengthFieldOffset;
                writer.Write((uint)length);

                writer.BaseStream.Position = endPosition;

                this.disposed = true;
            }
        }
    }
}