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mosquitto_pub -h mqtt.iotaps.com -p 8883 --capath /etc/ssl/certs \
  -V mqttv5 -q 1 -i "$DEVICE_ID" -u "$CREDENTIAL_ID" -P "$SECRET" \
  -t "$TOPIC" \
  -m "{\"schema_version\":1,\"message_id\":\"$(uuidgen)\",
       \"metrics\":{\"temperature_c\":21.5}}"

import json, time, uuid
import paho.mqtt.client as mqtt  # pip install paho-mqtt (2.x)

client = mqtt.Client(mqtt.CallbackAPIVersion.VERSION2,
                     client_id=DEVICE_ID, protocol=mqtt.MQTTv5)
client.username_pw_set(CREDENTIAL_ID, SECRET)
client.tls_set()  # system CA store, hostname verification on
client.connect("mqtt.iotaps.com", 8883, keepalive=60)
client.loop_start()

while True:
    message = {
        "schema_version": 1,
        "message_id": str(uuid.uuid4()),  # reuse only when retrying
        "metrics": {"temperature_c": 21.5, "fan_on": True},
    }
    client.publish(TOPIC, json.dumps(message), qos=1).wait_for_publish()
    time.sleep(10)

import mqtt from "mqtt";  // npm install mqtt (5.x)
import { randomUUID } from "node:crypto";

const client = mqtt.connect("mqtts://mqtt.iotaps.com:8883", {
  clientId: DEVICE_ID,
  username: CREDENTIAL_ID,
  password: SECRET,
  protocolVersion: 5,
});

client.on("connect", () => {
  setInterval(() => {
    const message = {
      schema_version: 1,
      message_id: randomUUID(),
      metrics: { temperature_c: 21.5 },
    };
    client.publish(TOPIC, JSON.stringify(message), { qos: 1 });
  }, 10_000);
});

#include <WiFi.h>
#include <WiFiClientSecure.h>
#include <PubSubClient.h>  // MQTT 3.1.1, publishes with QoS 0

// ISRG Root X1 (PEM) from letsencrypt.org/certificates
extern const char ISRG_ROOT_X1[];

WiFiClientSecure net;
PubSubClient mqtt(net);

void setup() {
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  while (WiFi.status() != WL_CONNECTED) delay(250);
  net.setCACert(ISRG_ROOT_X1);
  mqtt.setServer("mqtt.iotaps.com", 8883);
  mqtt.setBufferSize(512);
}

void loop() {
  if (!mqtt.connected()) mqtt.connect(DEVICE_ID, CREDENTIAL_ID, SECRET);
  char id[17], payload[192];
  // Random IDs survive reboots; a counter restarting at 0 would be deduplicated.
  snprintf(id, sizeof id, "%08lx%08lx",
           (unsigned long) esp_random(), (unsigned long) esp_random());
  snprintf(payload, sizeof payload,
           "{\"schema_version\":1,\"message_id\":\"%s\","
           "\"metrics\":{\"temperature_c\":%.2f}}",
           id, readTemperature());
  mqtt.publish(TOPIC, payload);
  mqtt.loop();
  delay(10000);
}