Introducing esp32-mqtt

15 Jun 2023

esp32-mqtt

esp32-mqtt is a sandbox to explore the MQTT capabilities of the ESP32, for example:

• connect to AWS IoT broker using ssl transport with client certificate
• connect to local broker using ssl transport with PSK

ESP-MQTT SSL sample application (mutual authentication)

This example connects to the AWS IoT broker using ssl transport with client certificate and as a demonstration subscribes/unsubscribes and sends a message on certain topic.

It uses ESP-MQTT library which implements mqtt client to connect to mqtt broker.

How to use the example

Hardware required

This example can be executed on any ESP32 board, the only required interface is WiFi and connection to the internet.

Configure the project

• Open the project configuration menu (idf.py menuconfig)
• Configure Wi-Fi under “Example Connection Configuration” menu.
• Add your AWS endpoint to app_main.c:

  static void mqtt_app_start(void)
  {
  ...
    .broker.address.uri = "mqtts://<your-aws-endpoint>:8883",
  ...
  }
  

Configure AWS IoT

• Create a simple thing (device) at https://aws.amazon.com/ and download the device certificate, device private key and server (root) certificate.
• Copy the content of the device certificate to client.crt, the content of the device private key to client.key and the content of the root certificate to amazonaws.com.crt.
• Add a custom rule which will republish from topic esp32/sensors/temp to esp32/warn if out temperature value is too high:

• Subscribe to topic esp32/sensors/temp and to topic esp32/warn:

Build and flash

$ idf.py build
$ idf.py flash

Example output

$ sudo screen /dev/ttyUSB0 115200
...
I (5646) MQTTS_EXAMPLE: [APP] Free memory: 234868 bytes
I (5656) MQTTS_EXAMPLE: Other event id:7
I (5666) main_task: Returned from app_main()
I (7316) MQTTS_EXAMPLE: MQTT_EVENT_CONNECTED
I (7316) MQTTS_EXAMPLE: sent subscribe successful, msg_id=39078
I (7326) MQTTS_EXAMPLE: sent subscribe successful, msg_id=26176
I (7326) MQTTS_EXAMPLE: sent publish successful, msg_id=0
I (7336) MQTTS_EXAMPLE: sent publish successful, msg_id=0
I (7526) MQTTS_EXAMPLE: MQTT_EVENT_SUBSCRIBED, msg_id=39078
I (8476) MQTTS_EXAMPLE: MQTT_EVENT_DATA
TOPIC=esp32/sensors/temp
DATA={
  "T": 91
}
I (8476) MQTTS_EXAMPLE: MQTT_EVENT_DATA
TOPIC=esp32/sensors/temp
DATA={
  "T": 90
}
I (8516) MQTTS_EXAMPLE: MQTT_EVENT_SUBSCRIBED, msg_id=26176
I (8556) MQTTS_EXAMPLE: MQTT_EVENT_DATA
TOPIC=esp32/warn
DATA={
  "T": 91
}

ESP-MQTT SSL example with PSK verification

This example connects to a local broker configured to PSK authentication.

How to use the example

Hardware required

This example can be executed on any ESP32 board, the only required interface is WiFi to connect to a MQTT broker with preconfigured PSK verification method.

Mosquitto broker settings

$ sudo dnf install -y mosquitto
$ sudo systemctl enable mosquitto.service
$ sudo systemctl start mosquitto.service
$ systemctl status mosquitto.service
$ sudo nano /etc/mosquitto/mosquitto.conf
$ sudo cat /etc/mosquitto/mosquitto.conf
listener 8883
psk_hint hint
psk_file /etc/mosquitto/psk
allow_anonymous true
$ sudo nano /etc/mosquitto/psk
$ sudo cat /etc/mosquitto/psk
hint:BAD123
$ sudo systemctl restart mosquitto.service

Note that the PSK file has to contain pairs of hints and keys. Keys are stored as text hexadecimal values in PSK file, while the example code stores key as plain binary as required by MQTT API. (See the example source for details: "BAD123" -> 0xBA, 0xD1, 0x23)

Configure the project

• Run idf.py menuconfig
• Configure Wi-Fi or Ethernet under “Example Connection Configuration” menu.
• Add your broker IP to app_main.c:

  #define EXAMPLE_BROKER_URI "mqtts://192.168.2.157"
  

Build and flash

$ idf.py build
$ idf.py flash

Example output

$ sudo screen /dev/ttyUSB0 115200
...
I (5647) MQTTS_EXAMPLE: [APP] Free memory: 234728 bytes
I (5657) MQTTS_EXAMPLE: Other event id:7
I (5667) main_task: Returned from app_main()
I (6117) MQTTS_EXAMPLE: MQTT_EVENT_CONNECTED
I (6117) MQTTS_EXAMPLE: sent subscribe successful, msg_id=32194
I (6127) MQTTS_EXAMPLE: sent publish successful, msg_id=0
I (6137) MQTTS_EXAMPLE: MQTT_EVENT_SUBSCRIBED, msg_id=32194
I (6137) MQTTS_EXAMPLE: MQTT_EVENT_DATA
TOPIC=esp32/sensors/temp
DATA=data
I (755127) MQTTS_EXAMPLE: MQTT_EVENT_DATA
TOPIC=esp32/sensors/temp
DATA=other_data

$ mosquitto_pub -h localhost -p 8883 --psk BAD123 --psk-identity hint -t "esp32/sensors/temp" -m "other_data" -q 1

$ mosquitto_sub -h localhost -p 8883 --psk BAD123 --psk-identity hint -t "esp32/sensors/temp" -v

esp32/sensors/temp data