Encoding and crypto

import { DAAP, NSKeyedArchiver, NTP, OPack, Plist, RTI, TLV8 } from '@corewire/core/encoding';
import { AES, ChaCha20, Curve25519, Ed25519, HKDF } from '@corewire/core/crypto';

Each codec and each cipher is a namespace. Acronyms stay in capitals in their names. They work on Buffer and Uint8Array and have no dependencies.

Codecs

Namespace	Format	Used by
TLV8	Type-length-value with 8-bit types, as HAP pairing uses it	Pairing
OPack	Apple's compact binary object format	Companion Link messages
Plist	Binary property lists	AirPlay SETUP, /info, play queue commands, data channel framing
DAAP	DMAP tags	RAOP metadata
NTP	NTP timestamps and packets	Audio timing
NSKeyedArchiver	Keyed archives	Artwork URLs and metadata in MRP, Companion Link text input
RTI	Remote text input sessions	Text input over AirPlay

TLV8

import { TLV8 } from '@corewire/core/encoding';

const payload = TLV8.encode([
    [TLV8.Value.State, 1],
    [TLV8.Value.Method, 0]
]);

const fields = TLV8.decode(payload);
console.log(fields.get(TLV8.Value.State));

encode(entries) splits values over 255 bytes into fragments. decode(buffer) joins adjacent fragments again into a Map of type to value. When a type comes back after another type, the map keeps the first value. For a list in which a type repeats, decodeEntries(buffer) returns every [type, value] in order, with adjacent fragments joined. bail(fields) throws a TLV8PairingError (a PairingError from @corewire/core, with the TLV8 error code) when a pairing reply carries an error or a back-off. Value, State, Method, Flags and ErrorCode name the HAP constants.

OPack

import { OPack } from '@corewire/core/encoding';

const bytes = OPack.encode({_i: '_launchApp', _c: {_bundleID: 'com.apple.TVMusic'}, _x: OPack.int(42)});
const message = OPack.decode(bytes);

console.log(message._i);

encode() picks the smallest encoding for a number. A negative number gets 8 bytes. OPack.int(value), OPack.float(value) and OPack.sizedInteger(value, size) force a type when the device expects one. Integers are signed. decode() returns a sized integer as sizedInteger, holding a bigint when the value falls outside the safe number range. Dates travel as Date.

A repeated value becomes a reference to its first occurrence. That holds for strings, byte strings of 2 bytes or more, dates, floats and integers outside -1 to 39. Arrays and objects are always written in full. A value may sit at most 32 containers deep. decode() throws a TypeError on deeper nesting, a truncated buffer, a reference to a value that does not exist and a tag OPack does not define.

Plist

import { Plist } from '@corewire/core/encoding';

const bytes = Plist.serialize({deviceID: 'AA:BB:CC:DD:EE:FF', streams: [{type: 130}]});
const value = Plist.parse(bytes as ArrayBuffer);

console.log(value);

serialize(value) writes a binary plist and parse(buffer) reads one. Integers of 1, 2 and 4 bytes read as unsigned, an 8-byte integer comes back as a bigint, and a date as a Date.

NTP

NTP.now() returns the current time as a 64-bit NTP timestamp from the wall clock. NTP.parts(timestamp) splits it into seconds and fraction. encode() and decode() handle a timing packet.

Crypto

Export	Contents
ChaCha20	encrypt(key, nonce, aad, plaintext) and decrypt(key, nonce, aad, ciphertext, authTag) with ChaCha20-Poly1305; padNonce()
Ed25519	generateKeyPair(), sign(), verify()
Curve25519	generateKeyPair(), generateSharedSecKey()
AES	encrypt() and decrypt() with AES-128-CTR
HKDF	derive(options): HKDF (RFC 5869) with the hash you pass, such as sha512. deriveEncryptionKeys(sharedSecret, salt, readInfo, writeInfo): read and write keys from a shared secret

import { randomBytes } from 'node:crypto';
import { ChaCha20 } from '@corewire/core/crypto';

const key = randomBytes(32);
const nonce = ChaCha20.padNonce(Buffer.from([1, 0, 0, 0, 0, 0, 0, 0]));

const {ciphertext, authTag} = ChaCha20.encrypt(key, nonce, null, Buffer.from('hello'));
const plaintext = ChaCha20.decrypt(key, nonce, null, ciphertext, authTag);

console.log(plaintext.toString());

A wrong key, nonce or tag throws DecryptionError, an EncryptionError from @corewire/core.