Using a MQTT client to directly connect to IoT Hub

This is a simple example based on instuctions at https://docs.microsoft.com/en-us/azure/iot-hub/iot-hub-mqtt-support#using-the-mqtt-protocol-directly to connect a mqtt client directly to IoT Hub for bidirectional communication.

Using the example

First you install the paho mqtt client using pip:

pip install paho-mqtt

Then change the following variables:

• For the ClientId field, use the deviceId.

• For the Username field, use {iothubhostname}/{device_id}/api-version=2016-11-14, where {iothubhostname} is the full CName of the IoT hub.

  For example, if the name of your IoT hub is contoso.azure-devices.net and if the name of your device is MyDevice01, the full Username field should contain:

  contoso.azure-devices.net/MyDevice01/api-version=2016-11-14

• For the Password field, use a SAS token. The format of the SAS token is the same as for both the HTTPS and AMQP protocols:

  SharedAccessSignature sig={signature-string}&se={expiry}&sr={URL-encoded-resourceURI}

  When testing, you can also use the [device explorer][lnk-device-explorer] tool to quickly generate a SAS token that you can copy and paste into your own code:

  1. Go to the Management tab in Device Explorer.

  2. Click SAS Token (top right).

  3. On SASTokenForm, select your device in the DeviceID drop down. Set your TTL.

  4. Click Generate to create your token.

     The SAS token that's generated has the following structure:

     HostName={your hub name}.azure-devices.net;DeviceId=javadevice;SharedAccessSignature=SharedAccessSignature sr={your hub name}.azure-devices.net%2Fdevices%2FMyDevice01%2Fapi-version%3D2016-11-14&sig=vSgHBMUG.....Ntg%3d&se=1456481802

     The part of this token to use as the Password field to connect using MQTT is:

     SharedAccessSignature sr={your hub name}.azure-devices.net%2Fdevices%2FMyDevice01%2Fapi-version%3D2016-11-14&sig=vSgHBMUG.....Ntg%3d&se=1456481802

Subscribing cloud-to-device messages

To receive messages from IoT Hub, a device should subscribe using devices/{device_id}/messages/devicebound/# as a Topic Filter. The multi-level wildcard # in the Topic Filter is used only to allow the device to receive additional properties in the topic name. IoT Hub does not allow the usage of the # or ? wildcards for filtering of subtopics. Since IoT Hub is not a general-purpose pub-sub messaging broker, it only supports the documented topic names and topic filters.