/// <summary> Called after setting data, before writing to os </summary>
int ComputeCrc()
{
Zlib.CRC32 crcengine = PngHelperInternal.GetCRC();
crcengine.Reset();
crcengine.Update(IdBytes, 0, 4);
if (Len > 0)
{
crcengine.Update(Data, 0, Len);
}
return((int)crcengine.GetValue());
}
public override void Close() => base.Close(); // nothing
void EndChunkGoForNext()
{
// Called after readging the last byte of chunk
// Checks CRC, and read ID from next CHUNK
// Those values are left in idLastChunk / lenLastChunk
// Skips empty IDATS
do
{
int crc = PngHelperInternal.ReadInt4(inputStream);
offset += 4;
if (checkCrc)
{
int crccalc = (int)crcEngine.GetValue();
if (lenLastChunk > 0 && crc != crccalc)
{
throw new System.Exception($"error reading idat; offset: {offset}");
}
crcEngine.Reset();
}
lenLastChunk = PngHelperInternal.ReadInt4(inputStream);
if (lenLastChunk < 0)
{
throw new System.IO.IOException($"invalid len for chunk: {lenLastChunk}");
}
toReadThisChunk = lenLastChunk;
PngHelperInternal.ReadBytes(inputStream, idLastChunk, 0, 4);
offset += 8;
ended = !PngCsUtils.UnSafeEquals(idLastChunk, Chunks.ChunkHelper.b_IDAT);
if (!ended)
{
foundChunksInfo.Add(new PngIDatChunkInputStream.IdatChunkInfo(lenLastChunk, offset - 8));
if (checkCrc)
{
crcEngine.Update(idLastChunk, 0, 4);
}
}
// PngHelper.logdebug("IDAT ended. next len= " + lenLastChunk + " idat?" +
// (!ended));
}while(lenLastChunk == 0 && !ended);
// rarely condition is true (empty IDAT ??)
}
