/// <summary>
/// Creates an FDAT Chunk from an IDAT Chunk.
/// </summary>
/// <returns>The FDAT chunk.</returns>
/// <param name="idatChunk">IDAT chunk.</param>
/// <param name="sequenceNumber">Sequence number.</param>
public static fdATChunk FromIDATChunk(IDATChunk idatChunk, uint sequenceNumber)
{
uint newCrc;
byte[] frameData;
fdATChunk fdat = null;
using (var msCrc = new MemoryStream())
{
msCrc.WriteBytes(new[] { (byte)'f', (byte)'d', (byte)'A', (byte)'T' });
byte[] seqNum = BitConverter.GetBytes(Helper.ConvertEndian(sequenceNumber));
frameData = new byte[seqNum.Length + idatChunk.ChunkData.Length];
Buffer.BlockCopy(seqNum, 0, frameData, 0, seqNum.Length);
Buffer.BlockCopy(idatChunk.ChunkData, 0, frameData, seqNum.Length, idatChunk.ChunkData.Length);
msCrc.WriteBytes(frameData);
newCrc = CrcHelper.Calculate(msCrc.ToArray());
}
using (var ms = new MemoryStream())
{
ms.WriteUInt32((uint)Helper.ConvertEndian(idatChunk.ChunkData.Length + 4));
ms.WriteBytes(new[] { (byte)'f', (byte)'d', (byte)'A', (byte)'T' });
ms.WriteBytes(frameData);
ms.WriteUInt32(Helper.ConvertEndian(newCrc));
ms.Position = 0;
fdat = new fdATChunk(ms);
}
return(fdat);
}
/// <summary>
/// Modify the ChunkData part.
/// </summary>
public void ModifyChunkData(int postion, byte[] newData)
{
Array.Copy(newData, 0, ChunkData, postion, newData.Length);
using (var msCrc = new MemoryStream())
{
msCrc.WriteBytes(Encoding.ASCII.GetBytes(ChunkType));
msCrc.WriteBytes(ChunkData);
Crc = CrcHelper.Calculate(msCrc.ToArray());
}
}
/// <summary>
/// Converts an FDAT Chunk to an IDAT Chunk.
/// </summary>
/// <returns>The IDAT chunk.</returns>
public IDATChunk ToIDATChunk()
{
uint newCrc;
using (var msCrc = new MemoryStream())
{
msCrc.WriteBytes(new[] { (byte)'I', (byte)'D', (byte)'A', (byte)'T' });
msCrc.WriteBytes(FrameData);
newCrc = CrcHelper.Calculate(msCrc.ToArray());
}
using (var ms = new MemoryStream())
{
ms.WriteUInt32(Helper.ConvertEndian(Length - 4));
ms.WriteBytes(new[] { (byte)'I', (byte)'D', (byte)'A', (byte)'T' });
ms.WriteBytes(FrameData);
ms.WriteUInt32(Helper.ConvertEndian(newCrc));
ms.Position = 0;
return(new IDATChunk(ms));
}
}