Method Sample

src/cripts/Connections.cc:176–219

}

bool
IP::Sample(double rate, uint32_t seed, unsigned ipv4_cidr, unsigned ipv6_cidr)
{
  CAssert(rate >= 0.0 && rate <= 1.0); // For detecting bugs in a Cript, 0.0 and 1.0 are valid though

  if (_sampler == 0) {
    // This only works until 2038
    uint32_t now = (Time::Local::Now().Epoch() / NORMALIZED_TIME_QUANTUM) * NORMALIZED_TIME_QUANTUM;

    if (is_ip4()) {
      auto      addr = this->_addr._ip4.network_order();
      in_addr_t ip   = addr & htonl(UINT32_MAX << (32 - ipv4_cidr));

      _sampler = (ip >> 16) ^ (ip & 0x00ff); // Fold them to 16 bits, mixing net and host

    } else if (is_ip6()) {
      unsigned int v6_zero_bytes = (128 - ipv6_cidr) / 8;
      int          v6_mask       = 0xff >> ((128 - ipv6_cidr) % 8);
      auto         addr          = this->_addr._ip6.network_order();

      if (v6_zero_bytes > 0) {
        memset(&addr.s6_addr[16 - v6_zero_bytes], 0, v6_zero_bytes);
      }
      if (v6_mask != 0xff) {
        addr.s6_addr[16 - v6_zero_bytes] &= v6_mask;
      }

      _sampler = *reinterpret_cast<uint16_t const *>(addr.s6_addr) ^
                 *reinterpret_cast<uint16_t const *>(addr.s6_addr + sizeof(uint16_t)) ^
                 *reinterpret_cast<uint16_t const *>(addr.s6_addr + 2 * sizeof(uint16_t)) ^
                 *reinterpret_cast<uint16_t const *>(addr.s6_addr + 3 * sizeof(uint16_t));
    } else {
      // Clearly this shouldn't happen, but lets not assert
    }

    _sampler ^= (now >> 16) ^ (now & 0x00ff); // Fold in the hourly normalized timestamp
    if (seed) {
      _sampler ^= (seed >> 16) ^ (seed & 0x00ff); // Fold in the seed as well
    }
  }

  // To avoid picking sequential folded IPs bucketize them with a modulo of the sampler (just in case)
  return (_sampler % static_cast<uint16_t>(rate * UINT16_MAX)) == _sampler;
}

Client::Connection &
Client::Connection::_get(cripts::Context *context)