In this set of samples, we will show how to connect and send messages to an Azure IoT Hub without using the Azure IoT SDK. This approach is useful when you use constrained device who don’t have enough memory to support the Azure IoT C SDK. These sample code uses the Eclipse Mosquitto library to send messages directly to the IoTHub via the MQTT Protocol. This repository contains sample for Windows and Linux and a couple of sample command to use with mosquitto_pub tool (tool included in the Mosquitto library package).

Find also a sample using MicroPython and umqtt library, this sample run on ESP32 and demonstrate how to send telemetry message and receive messages from cloud.

Below is the file contents of this repository.

To be able to test these samples you need an Azure IoTHub and installing Eclipse Mosquitto Library.

For MicroPython, follow the steps in this readme file to flash MicroPython on your ESP32 install umqtt library and use it for connecting Azure IoT Hub.

This sample needs an IoT hub and a registered device. If you don't already have an Azure IoT Hub, you can create one following these instructions:

1. Install the Azure CLI (or use the Azure Cloud Shell) and use it to create an Azure IoT Hub.

   az iot hub create --resource-group <your resource group> --name <your IoT Hub name>

   Note that this operation may take a few minutes.

2. Add the IoT Extension to the Azure CLI, and then register a device identity

   az extension add --name azure-cli-iot-ext
   az iot hub device-identity create --hub-name <your IoT Hub name> --device-id <your device id>

3. Retrieve your Device Connection String using the Azure CLI

   az iot hub device-identity connection-string show --device-id <your device id> --hub-name <your IoT Hub name>

   It should be in the format:

   HostName=<your IoT Hub name>.azure-devices.net;DeviceId=<your device id>;SharedAccessKey=<some value>

The Eclipse Mosquitto library and documentation are available at https://mosquitto.org/.

Note: If you use the mosquitto.org installer, only the files (header and lib) are needed for these samples, you can uncheck the service installation.

It is easier to use apt-get on Linux or vcpkg on Windows for installing Eclipse Mosquitto on your machine (see the corresponding readme in Linux and Windows directories).

Once Eclipse Mosquitto is installed correctly on your machine, you will need to provide connection information and a security certificate.

The certificate to use with these samples is located in this repo (IoTHubRootCA_Baltimore.pem)

Server certificates are available here for download.

To get a valid IoT hub SAS Token, run this command in the Azure IoT Command line (see above for installing the Azure IoT extension to the Azure Command line)

az iot hub generate-sas-token -d <DeviceId> -n <MyIoTHub>

Note: That by default the SAS Token is only valid for 60 min. You can use the --du parameter to get the duration you need. You can also use Device Explorer to generate a SAS Token or VSCode Azure Iot Extension.

For more information on how to create SAS Token see here

Then in the code, complete the connection information:

#define IOTHUBNAME <MyIoTHub>
#define DEVICEID <DeviceId>
#define CERTIFICATEFILE "<pathTo>\\IoTHubRootCA_Baltimore.pem"
#define PWD "SharedAccessSignature sr=[yourIoTHub].azure-devices.net%2Fdevices%2F[DeviceId]&sig=[tokengeneratedforyourdevice]"

Note: The SAS token should be used as password see this article for more details on password, username and configuration needed for using MQTT protocol.

IoT Hub under the cover is a MQTT server (but not a full MQTT broker as explained here), so by using the MQTT protocol, we can communicate (send and receive messages) with the IoT Hub without using the Azure IoT SDK.

In order to establish a TLS connection, you may need to download and reference the DigiCert Baltimore Root Certificate. This certificate is the one that Azure uses to secure the connection. You can find this certificate in the Azure-iot-sdk-c repository. More information about these certificates can be found on Digicert's website. The client use the certificate to check that the IoT Hub it's connecting to is indeed legit, by providing the public key of the certificate used by Microsoft to secure IoT Hub connections.

You need to secure the communication and provide a certificate to be accepted by the MQTT broker under the Azure IoTHub.

The information/credential needed by the MQTT broker, are the classic pair: user/password, in the case of Azure IoT Hub the password should be the SAS Token, and the username should have this form:

IOTHUBNAME.azure-devices.net/DEVICEID/?api-version=2018-06-30

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