private void CheckSignatures()
{
if (_image.Length < ImageMarkup.HeaderLength)
{
throw new IncorrectSignatureException("Header is not present");
}
var dataLength = 2 * _bitConverter.ReadInt(_image, ImageMarkup.DataLengthOffset);
if (_image.Length < dataLength + ImageMarkup.HeaderLength)
{
throw new IncorrectSignatureException("Data length is bigger than file size");
}
Checksum = _bitConverter.ReadInt(_image, ImageMarkup.CheckSumOffset);
var actualChecksum = _checkSumCalculator.Calculate(_image, ImageMarkup.HeaderLength, dataLength);
if (actualChecksum != Checksum || actualChecksum % 256 != ImageMarkup.ChecksumLittleByte)
{
throw new IncorrectSignatureException("Checksum fault");
}
if (_image.Length < ImageMarkup.CopyrightString.Count + ImageMarkup.CopyrightOffset)
{
throw new IncorrectSignatureException("Copyright is not present");
}
for (var i = 0; i < ImageMarkup.CopyrightString.Count; ++i)
{
if (_image[ImageMarkup.CopyrightOffset + i] == ImageMarkup.CopyrightString[i])
{
continue;
}
if (i == ImageMarkup.CopyrightString.Count - 2 && _image[ImageMarkup.CopyrightOffset + i] == 0)
{
//Image was already patched
break;
}
throw new IncorrectSignatureException("Can't find copyright string");
}
}
