Function RandomBytesWithFallback

src/core/random_func.cpp:94–130

* Fill the given buffer with random bytes. * * This function will attempt to use a cryptographically-strong random * generator, but will fall back to a weaker random generator if none is * available. * * In the end, the buffer will always be filled with some form of random * bytes when this function returns. * * @param buf The buffer to fill with random bytes. */

 * @param buf The buffer to fill with random bytes.
 */
void RandomBytesWithFallback(std::span<uint8_t> buf)
{
#if defined(_WIN32)
	auto res = BCryptGenRandom(nullptr, static_cast<PUCHAR>(buf.data()), static_cast<ULONG>(buf.size()), BCRYPT_USE_SYSTEM_PREFERRED_RNG);
	if (res >= 0) return;
#elif defined(__APPLE__) || defined(__NetBSD__) || defined(__FreeBSD__) || defined(__OpenBSD__)
	arc4random_buf(buf.data(), buf.size());
	return;
#elif defined(__GLIBC__) && ((__GLIBC__ > 2) || ((__GLIBC__ == 2) && (__GLIBC_MINOR__ >= 25)))
	auto res = getrandom(buf.data(), buf.size(), 0);
	if (res > 0 && static_cast<size_t>(res) == buf.size()) return;
#elif defined(__EMSCRIPTEN__)
	auto res = EM_ASM_INT({
		var buf = $0;
		var bytes = $1;

		var crypto = window.crypto;
		if (crypto === undefined || crypto.getRandomValues === undefined) {
			return -1;
		}

		crypto.getRandomValues(Module.HEAPU8.subarray(buf, buf + bytes));
		return 1;
	}, buf.data(), buf.size());
	if (res > 0) return;
#else
#	warning "No cryptographically-strong random generator available; using a fallback instead"
#endif

	static bool warned_once = false;
	Debug(misc, warned_once ? 1 : 0, "Cryptographically-strong random generator unavailable; using fallback");
	warned_once = true;

	for (uint i = 0; i < buf.size(); i++) {
		buf[i] = static_cast<uint8_t>(InteractiveRandom());
	}
}