Conversion between IPv4 addresses and their network-order wire bytes.

This module reads an address straight out of a packet buffer and writes it straight back into one, with no string round-trip. It is the byte-form counterpart of the ipv4 submodule: addressv4FromBytes is to parseAddressv4 what addressv4ToBytes is to stringifyAddressv4.

Addresses keep the numeric representation of the rest of the package — a number holding a 32-bit unsigned integer. Bytes are a conversion, not a second representation.

Byte order

Always network order (big-endian), on both the read and the write side. There is no option, because an IP address has exactly one wire order.

Widths and offsets

Both functions are fixed at 4 bytes, and offset selects where in the buffer that span sits, never how wide it is. A span that runs past the end of the buffer throws a RangeError rather than reading undefined and quietly decoding as 0.0.0.0.

For IPv6 see bytesv6; for the version-detecting pair see bytes.

import { assertEquals } from "@std/assert";
import { addressv4FromBytes } from "@hertzg/ip/bytesv4";
import { stringifyAddressv4 } from "@hertzg/ip/addressv4";

// deno-fmt-ignore
const packet = new Uint8Array([
  0x45, 0x00, 0x00, 0x54, 0x1c, 0x46, 0x40, 0x00,
  0x40, 0x06, 0x00, 0x00,
  10, 0, 0, 1,
  192, 168, 1, 1,
]);

assertEquals(stringifyAddressv4(addressv4FromBytes(packet, 12)), "10.0.0.1");
assertEquals(stringifyAddressv4(addressv4FromBytes(packet, 16)), "192.168.1.1");

import { assertEquals } from "@std/assert";
import { addressv4ToBytes } from "@hertzg/ip/bytesv4";
import { parseAddressv4 } from "@hertzg/ip/addressv4";

const frame = new Uint8Array(20);
addressv4ToBytes(parseAddressv4("10.0.0.1").address, frame, 12);
addressv4ToBytes(parseAddressv4("192.168.1.1").address, frame, 16);

assertEquals(frame.slice(12), new Uint8Array([10, 0, 0, 1, 192, 168, 1, 1]));