Minimum viable POC for mDNS to support HomeKit Accessory Protocol in CircuitPython 9.x with mDNS TXT record support

hap.py

class Accessory:
    aid: int
    services: list = []


class Service:
    type: str
    iid: int
    characteristics: list = []
    hidden: bool
    primary: bool
    linked: list = []


class Characteristic:
    type: str
    iid: int
    value: any
    perms: list = []
    ev: bool
    description: str
    format: str
    unit: str
    minValue: any
    maxValue: any
    minStep: any
    maxLen: int
    maxDataLen: int
    valid_values: list
    valid_values_range: list
    TTL: int
    pid: int


class ServiceDiscoveryConfig:
    configuration_number: int
    feature_flags: int
    id: str
    model_name: str
    protocol_version: str = "1.0"
    state_number: int = 1
    status_flags: int = 0
    accessory_catalog_identifier: int
    setup_hash: str

    def __init__(
        self,
        configuration_number: int,
        feature_flags: int,
        id: str,
        model_name: str,
        accessory_catalog_identifier: int,
        setup_hash: str,
        protocol_version: str = "1.0",
        state_number: int = 1,
        status_flags: int = 0,
    ) -> None:
        self.configuration_number = configuration_number
        self.feature_flags = feature_flags
        self.id = id
        self.model_name = model_name
        self.accessory_catalog_identifier = accessory_catalog_identifier
        self.setup_hash = setup_hash
        self.protocol_version = protocol_version
        self.state_number = state_number
        self.status_flags = status_flags

    def to_txt_record(self) -> list:
        pairs = [
            f"c#={self.configuration_number}",
            f"id={self.id}",
            f"md={self.model_name}",
            f"pv={self.protocol_version}",
            f"s#={self.state_number}",
            f"sf={self.status_flags}",
            f"ci={self.accessory_catalog_identifier}",
            f"sh={self.setup_hash}",
        ]
        if self.feature_flags > 0:
            pairs.append(f"ff={self.feature_flags}")
        return pairs

main.py

import board
import digitalio
import hap
import mdns
import os
import time
import wifi

ssid = os.getenv("WIFI_SSID")
password = os.getenv("WIFI_PASSWORD")

print("Connecting to", ssid)
wifi.radio.connect(ssid, password)
print("Connected to", ssid)

mac = ":".join([f"{i:02x}" for i in wifi.radio.mac_address])
model_name = os.getenv("MODEL_NAME", "Pico")
setup_hash = os.getenv("SETUP_HASH", "336699198")
print(f"MAC: {mac}")

service_discovery_config = hap.ServiceDiscoveryConfig(
    configuration_number=3,
    feature_flags=0,
    id=mac,
    model_name=model_name,
    status_flags=1,
    accessory_catalog_identifier=5,  # HACK: 5 is lighting
    setup_hash=setup_hash,
)

print(service_discovery_config.to_txt_record())

mdns_server = mdns.Server(wifi.radio)
mdns_server.hostname = "pico"
mdns_server.instance_name = service_discovery_config.model_name
mdns_server.advertise_service(
    service_type="_hap",
    protocol="_tcp",
    port=80,
    txt_records=service_discovery_config.to_txt_record(),
)


led = digitalio.DigitalInOut(board.LED)
led.direction = digitalio.Direction.OUTPUT

on = False
while True:
    on = not on
    led.value = on
    time.sleep(0.25)

settings.toml

WIFI_SSID="your_ssid"
WIFI_PASSWORD="your_password"