copyOver.cpp

void copyOver(std::ofstream& dst, std::ifstream& src, std::uint64_t length)
{
	// This seems to be broken, we are skipping bytes at some point. Apparently
	// istream_iterator shouldn't be used for binary files, despite the
	// underlying stream being opened in binary mode. istreambuf_iterator was
	// suggested, but is not applicable here as it fills an internal buffer with
	// more than we read and therefore advances the file cursor too far.
	//
	// std::copy_n(std::istream_iterator<uint8_t>(src), length,
	//             std::ostream_iterator<uint8_t>(dst));
	//
	// Copying bytes manually instead.

	std::array<char, 4096> buffer;
	while (length > buffer.size()) {
		src.read(buffer.data(), buffer.size());
		dst.write(buffer.data(), buffer.size());
		length -= buffer.size();
	}
	src.read(buffer.data(), length);
	dst.write(buffer.data(), length);
}