Universal reverse DNS pointer names for IP addresses.

This module provides addressToArpa, which picks the IP version from the shape of its argument and delegates to the version-specific function. The name it builds is where a PTR record for the address lives: the four IPv4 octets reversed under in-addr.arpa (RFC 1035 §3.5), or all 32 IPv6 nibbles reversed under ip6.arpa (RFC 3596 §2.5).

For version-specific functions, see:

• arpav4: addressv4ToArpa
• arpav6: addressv6ToArpa

The names are relative

No trailing dot. 1.0.168.192.in-addr.arpa, not 1.0.168.192.in-addr.arpa. — the dot is DNS wire-format framing, and every other stringifier in this package emits a bare canonical form without it. Callers handing the name to a resolver that requires an absolute name append "." themselves. See ADR 0009.

Addresses only

There is no prefix or zone form. The reverse zone name of a CIDR block is only well defined on a byte (IPv4) or nibble (IPv6) boundary, and the RFC 2317 classless-delegation name is a different construct again; if either is ever wanted it gets its own name. There is no inverse direction either — nothing in this package parses DNS names.

import { assertEquals } from "@std/assert";
import { addressToArpa } from "@hertzg/ip/arpa";
import { parseAddress } from "@hertzg/ip/address";

assertEquals(addressToArpa(parseAddress("8.8.8.8").address), "8.8.8.8.in-addr.arpa");
assertEquals(
  addressToArpa(parseAddress("2001:4860:4860::8888").address),
  "8.8.8.8.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.6.8.4.0.6.8.4.1.0.0.2.ip6.arpa",
);