ha-meshtastic-addon/meshtastic_receiver/receiver.py

#!/usr/bin/env python3
"""Receive Meshtastic mesh text messages over MQTT and expose them in Home Assistant.

Flow:
  1. Subscribe to a Meshtastic gateway's MQTT topic (public server or local broker).
  2. Decrypt channel packets (AES-CTR) using the channel PSK.
  3. Publish the latest text message and parsed Temperature/Humidity values to
     Home Assistant via MQTT Discovery (so entities appear automatically).
"""

import base64
import json
import os
import re
import sys
import time

import paho.mqtt.client as mqtt
import requests
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from meshtastic.protobuf import mesh_pb2, mqtt_pb2, portnums_pb2


def log(msg):
    print(msg, file=sys.stdout, flush=True)


# --- Add-on options (written by the Supervisor) ------------------------------
with open("/data/options.json", encoding="utf-8") as fh:
    OPTS = json.load(fh)

SRC_BROKER = OPTS["source_broker"]
SRC_PORT = int(OPTS.get("source_port", 1883))
SRC_USER = OPTS.get("source_username", "") or ""
SRC_PASS = OPTS.get("source_password", "") or ""
SRC_TLS = bool(OPTS.get("source_tls", False))
REGION = OPTS.get("region", "+") or "+"
CHANNEL_NAME = OPTS["channel_name"]
CHANNEL_PSK = OPTS.get("channel_psk", "AQ==")
MATCH_PREFIX = OPTS.get("match_prefix", "") or ""
DEVICE_NAME = OPTS.get("device_name", "Meshtastic Mesh")
DISCOVERY_PREFIX = OPTS.get("discovery_prefix", "homeassistant")
SENSORS = OPTS.get("sensors", [])

DEVICE_UID = re.sub(r"[^a-z0-9_]", "_", DEVICE_NAME.lower()) or "meshtastic_mesh"
BASE_TOPIC = f"meshtastic_receiver/{DEVICE_UID}"
AVAIL_TOPIC = f"{BASE_TOPIC}/status"

# --- PSK handling ------------------------------------------------------------
# "AQ==" (byte 0x01) is Meshtastic's shorthand for this well-known default key.
_DEFAULT_KEY = base64.b64decode("1PG7OiApB1nwvP+rz05pAQ==")


def expand_psk(psk_b64):
    raw = base64.b64decode(psk_b64)
    return _DEFAULT_KEY if raw == b"\x01" else raw


CHANNEL_KEY = expand_psk(CHANNEL_PSK)

# Matches "T1:20.8", "H2:54.4", "P:1013" etc. (unit suffix is ignored here).
PAIR_RE = re.compile(r"([A-Za-z][A-Za-z0-9_]*)\s*:\s*(-?\d+(?:\.\d+)?)")

# Set once the HA broker client is connected.
ha_client = None


# --- Decryption --------------------------------------------------------------
def decrypt_packet(encrypted, key, from_id, packet_id):
    """AES-CTR decrypt. Nonce = packetId(uint64 LE) | fromNode(uint32 LE) | 0*4."""
    try:
        nonce = (
            packet_id.to_bytes(4, "little")
            + b"\x00" * 4
            + from_id.to_bytes(4, "little")
            + b"\x00" * 4
        )
        cipher = Cipher(
            algorithms.AES(key), modes.CTR(nonce), backend=default_backend()
        )
        d = cipher.decryptor()
        return d.update(encrypted) + d.finalize()
    except Exception as exc:  # noqa: BLE001
        log(f"[warn] decryption error: {exc}")
        return None


# --- Home Assistant MQTT broker resolution (via Supervisor service) ----------
def resolve_ha_mqtt():
    token = os.environ.get("SUPERVISOR_TOKEN")
    if not token:
        return None
    try:
        r = requests.get(
            "http://supervisor/services/mqtt",
            headers={"Authorization": f"Bearer {token}"},
            timeout=10,
        )
        if r.status_code == 200:
            d = r.json()["data"]
            return {
                "host": d["host"],
                "port": int(d["port"]),
                "username": d.get("username") or None,
                "password": d.get("password") or None,
                "ssl": bool(d.get("ssl", False)),
            }
        log(f"[warn] supervisor mqtt service returned HTTP {r.status_code}")
    except Exception as exc:  # noqa: BLE001
        log(f"[warn] could not resolve HA MQTT via supervisor: {exc}")
    return None


# --- MQTT Discovery ----------------------------------------------------------
def device_block():
    return {
        "identifiers": [DEVICE_UID],
        "name": DEVICE_NAME,
        "manufacturer": "Meshtastic",
        "model": "MQTT Mesh Receiver",
    }


def publish_discovery():
    # Latest text message (with from/to/time as attributes).
    cfg = {
        "name": "Last Message",
        "unique_id": f"{DEVICE_UID}_last_message",
        "state_topic": f"{BASE_TOPIC}/last_message",
        "json_attributes_topic": f"{BASE_TOPIC}/last_message/attributes",
        "icon": "mdi:message-text",
        "availability_topic": AVAIL_TOPIC,
        "device": device_block(),
    }
    ha_client.publish(
        f"{DISCOVERY_PREFIX}/sensor/{DEVICE_UID}/last_message/config",
        json.dumps(cfg),
        retain=True,
    )

    for s in SENSORS:
        label = s["label"]
        cfg = {
            "name": s.get("name", label),
            "unique_id": f"{DEVICE_UID}_{label}",
            "state_topic": f"{BASE_TOPIC}/{label}",
            "availability_topic": AVAIL_TOPIC,
            "device": device_block(),
        }
        if s.get("unit"):
            cfg["unit_of_measurement"] = s["unit"]
        if s.get("device_class"):
            cfg["device_class"] = s["device_class"]
            cfg["state_class"] = "measurement"
        ha_client.publish(
            f"{DISCOVERY_PREFIX}/sensor/{DEVICE_UID}/{label}/config",
            json.dumps(cfg),
            retain=True,
        )
    log(f"[ha] published discovery for last_message + {len(SENSORS)} sensors")


# --- Message handling --------------------------------------------------------
def handle_text(text, from_id, to_id):
    # HA sensor states are limited to 255 chars.
    ha_client.publish(f"{BASE_TOPIC}/last_message", text[:255], retain=True)
    ha_client.publish(
        f"{BASE_TOPIC}/last_message/attributes",
        json.dumps(
            {
                "from": f"!{from_id:08x}",
                "to": f"!{to_id:08x}",
                "received": time.strftime("%Y-%m-%dT%H:%M:%S%z"),
                "full_text": text,
            }
        ),
        retain=True,
    )

    if MATCH_PREFIX and MATCH_PREFIX not in text:
        return

    known = {s["label"] for s in SENSORS}
    published = []
    for label, value in PAIR_RE.findall(text):
        if label in known:
            ha_client.publish(f"{BASE_TOPIC}/{label}", value, retain=True)
            published.append(f"{label}={value}")
    if published:
        log(f"[parse] {' '.join(published)}")


# --- Source MQTT callbacks ---------------------------------------------------
def on_src_connect(client, userdata, flags, reason_code, properties=None):
    if reason_code == 0:
        topic = f"msh/{REGION}/2/e/{CHANNEL_NAME}/#"
        client.subscribe(topic)
        log(f"[source] connected; subscribed to {topic}")
    else:
        log(f"[source] connection refused: reason_code={reason_code}")


def on_src_message(client, userdata, msg):
    try:
        env = mqtt_pb2.ServiceEnvelope()
        env.ParseFromString(msg.payload)
    except Exception as exc:  # noqa: BLE001
        log(f"[warn] could not parse ServiceEnvelope: {exc}")
        return

    mp = env.packet
    from_id = getattr(mp, "from")

    if mp.HasField("decoded"):
        data = mp.decoded
    elif mp.HasField("encrypted"):
        plain = decrypt_packet(mp.encrypted, CHANNEL_KEY, from_id, mp.id)
        if plain is None:
            return
        data = mesh_pb2.Data()
        try:
            data.ParseFromString(plain)
        except Exception:  # noqa: BLE001
            return  # wrong PSK or not for this channel
    else:
        return

    if data.portnum == portnums_pb2.PortNum.TEXT_MESSAGE_APP:
        text = data.payload.decode("utf-8", errors="replace")
        log(f"[rx] !{from_id:08x}: {text}")
        handle_text(text, from_id, mp.to)


# --- Entry point -------------------------------------------------------------
def main():
    global ha_client

    ha = resolve_ha_mqtt()
    if ha is None:
        log(
            "[fatal] No MQTT broker available. Install and start the Mosquitto "
            "broker add-on, then restart this add-on."
        )
        sys.exit(1)
    log(f"[ha] using MQTT broker {ha['host']}:{ha['port']}")

    ha_client = mqtt.Client(
        mqtt.CallbackAPIVersion.VERSION2, client_id="meshtastic_receiver"
    )
    if ha["username"]:
        ha_client.username_pw_set(ha["username"], ha["password"])
    if ha["ssl"]:
        ha_client.tls_set()
    ha_client.will_set(AVAIL_TOPIC, "offline", retain=True)

    def on_ha_connect(client, userdata, flags, reason_code, properties=None):
        if reason_code == 0:
            log("[ha] connected")
            client.publish(AVAIL_TOPIC, "online", retain=True)
            publish_discovery()
        else:
            log(f"[ha] connection refused: reason_code={reason_code}")

    ha_client.on_connect = on_ha_connect
    ha_client.connect(ha["host"], ha["port"], keepalive=60)
    ha_client.loop_start()

    src = mqtt.Client(mqtt.CallbackAPIVersion.VERSION2)
    if SRC_USER:
        src.username_pw_set(SRC_USER, SRC_PASS)
    if SRC_TLS:
        src.tls_set()
    src.on_connect = on_src_connect
    src.on_message = on_src_message
    log(f"[source] connecting to {SRC_BROKER}:{SRC_PORT} …")
    src.connect(SRC_BROKER, SRC_PORT, keepalive=60)

    try:
        src.loop_forever()
    except KeyboardInterrupt:
        pass
    finally:
        ha_client.publish(AVAIL_TOPIC, "offline", retain=True)
        ha_client.loop_stop()


if __name__ == "__main__":
    main()