Function getNat64EmbeddedIpv4

server/modules/outboundTargetPolicy.js:140–150

(address)

NAT64_BLOCKLIST.addSubnet("64:ff9b:1::", 48, "ipv6");

function getNat64EmbeddedIpv4(address) {
  if (net.isIP(address) !== 6) return null;
  if (!NAT64_BLOCKLIST.check(address, "ipv6")) return null;

  // Expand to full hextets and read the trailing 32 bits as IPv4 octets.
  const groups = expandIpv6(address);
  if (!groups) return null;
  const lo = (groups[6] << 16) | groups[7]; // last two 16-bit groups = 32-bit IPv4
  const ipv4 = [(lo >>> 24) & 0xff, (lo >>> 16) & 0xff, (lo >>> 8) & 0xff, lo & 0xff].join(".");
  return net.isIP(ipv4) === 4 ? ipv4 : null;
}

function expandIpv6(address) {
  // Returns an array of 8 numeric hextets, or null if not a valid IPv6 literal.