cloud.py

import machine
import esp32
from third_party import string
import network
import socket
import os
import utime
import ssl
from third_party import rsa
from umqtt.simple import MQTTClient
from ubinascii import b2a_base64
from machine import RTC, Pin
import ntptime
import ujson
import config

sta_if = network.WLAN(network.STA_IF)
led_pin = machine.Pin(
    config.device_config['led_pin'], Pin.OUT)  # built-in LED pin
led_pin.value(1)


def on_message(topic, message):
    print((topic, message))


def connect():
    if not sta_if.isconnected():
        print('connecting to network...')
        sta_if.active(True)
        sta_if.connect(config.wifi_config['ssid'],
                       config.wifi_config['password'])
        while not sta_if.isconnected():
            pass
    print('network config: {}'.format(sta_if.ifconfig()))


def set_time():
    ntptime.settime()
    tm = utime.localtime()
    tm = tm[0:3] + (0,) + tm[3:6] + (0,)
    machine.RTC().datetime(tm)
    print('current time: {}'.format(utime.localtime()))


def b42_urlsafe_encode(payload):
    return string.translate(b2a_base64(payload)[:-1].decode('utf-8'), {ord('+'): '-', ord('/'): '_'})


def create_jwt(project_id, private_key, algorithm, token_ttl):
    print("Creating JWT...")
    private_key = rsa.PrivateKey(*private_key)

    # Epoch_offset is needed because micropython epoch is 2000-1-1 and unix is 1970-1-1. Adding 946684800 (30 years)
    epoch_offset = 946684800
    claims = {
        # The time that the token was issued at
        'iat': utime.time() + epoch_offset,
        # The time the token expires.
        'exp': utime.time() + epoch_offset + token_ttl,
        # The audience field should always be set to the GCP project id.
        'aud': project_id
    }

    #This only supports RS256 at this time.
    header = {"alg": algorithm, "typ": "JWT"}
    content = b42_urlsafe_encode(ujson.dumps(header).encode('utf-8'))
    content = content + '.' + \
        b42_urlsafe_encode(ujson.dumps(claims).encode('utf-8'))
    signature = b42_urlsafe_encode(rsa.sign(content, private_key, 'SHA-256'))
    return content + '.' + signature  # signed JWT


def get_mqtt_client(project_id, cloud_region, registry_id, device_id, jwt):
    """Create our MQTT client. The client_id is a unique string that identifies
    this device. For Google Cloud IoT Core, it must be in the format below."""
    client_id = 'projects/{}/locations/{}/registries/{}/devices/{}'.format(
        project_id, cloud_region, registry_id, device_id)
    print('Sending message with password {}'.format(jwt))
    client = MQTTClient(client_id.encode('utf-8'), server=config.google_cloud_config['mqtt_bridge_hostname'],
                        port=config.google_cloud_config['mqtt_bridge_port'], user=b'ignored', password=jwt.encode('utf-8'), ssl=True)
    client.set_callback(on_message)
    client.connect()
    client.subscribe('/devices/{}/config'.format(device_id), 1)
    client.subscribe('/devices/{}/commands/#'.format(device_id), 1)
    return client


connect()
#Need to be connected to the internet before setting the local RTC.
set_time()

jwt = create_jwt(config.google_cloud_config['project_id'], config.jwt_config['private_key'],
                 config.jwt_config['algorithm'], config.jwt_config['token_ttl'])
client = get_mqtt_client(config.google_cloud_config['project_id'], config.google_cloud_config['cloud_region'],
                         config.google_cloud_config['registry_id'], config.google_cloud_config['device_id'], jwt)

while True:
    message = {
        "device_id": config.google_cloud_config['device_id'],
        "temp": esp32.raw_temperature()
    }
    print("Publishing message "+str(ujson.dumps(message)))
    led_pin.value(1)
    mqtt_topic = '/devices/{}/{}'.format(
        config.google_cloud_config['device_id'], 'events')
    client.publish(mqtt_topic.encode('utf-8'),
                   ujson.dumps(message).encode('utf-8'))
    led_pin.value(0)

    client.check_msg()  # Check for new messages on subscription
    utime.sleep(10)  # Delay for 10 seconds.