private void ReadChunkCrc(PngChunk chunk, byte[] typeBuffer)
{
byte[] crcBuffer = new byte[4];
int numBytes = _stream.Read(crcBuffer, 0, 4);
if (numBytes >= 1 && numBytes <= 3)
{
throw new ImageFormatException("Image stream is not valid!");
}
Array.Reverse(crcBuffer);
chunk.Crc = BitConverter.ToUInt32(crcBuffer, 0);
Crc32 crc = new Crc32();
crc.Update(typeBuffer);
crc.Update(chunk.Data);
if (crc.Value != chunk.Crc)
{
throw new ImageFormatException("CRC Error. PNG Image chunk is corrupt!");
}
}
private void WriteChunk(Stream stream, string type, byte[] data, int offset, int length)
{
WriteInteger(stream, length);
byte[] typeArray = new byte[4];
typeArray[0] = (byte)type[0];
typeArray[1] = (byte)type[1];
typeArray[2] = (byte)type[2];
typeArray[3] = (byte)type[3];
stream.Write(typeArray, 0, 4);
if (data != null)
{
stream.Write(data, offset, length);
}
Crc32 crc32 = new Crc32();
crc32.Update(typeArray);
if (data != null)
{
crc32.Update(data, offset, length);
}
WriteInteger(stream, (uint)crc32.Value);
}
