https://www.haxibami.net/blog/posts/migrate-to-controld

index.ts

// Run this with [Bun](https://bun.sh)
const CF_IP_PREFIX = "2606:4700::";
const ipv4 = Bun.argv[2]?.split(".").map(Number);
if (
    !ipv4 ||
    ipv4.length !== 4 ||
    ipv4.some((n) => Number.isNaN(n) || n < 0 || n > 255)
) {
    console.log("Usage: bun run index.ts <ipv4>");
    process.exit(1);
}
const ipv6 = CF_IP_PREFIX + ipv4
.map((n, i) => (i === 2 ? ":" : "") + n.toString(16).padStart(2, "0"))
.join("");
console.log(ipv6);