Cloud Connector Azure IoT Hub Message Transformation

Since Azure is not a fully fledged MQTT broker, Cloud Connector needs to transform messages coming from standard topics to the topics and messages format that IoT Hub is expecting.

Cloud Connector will transform 3 types of messages with the topic and authentication part of the MQTT message to match what Azure is expecting.

Let’s assume we have a device and endpoint with the following values:

Azure IoT Host: my-iot-hub-name.azure-devices.net
Device Cloud ID: 4601234567890

CONNECT Message

Incoming message:

hasUsername: false
username: someUsername
clientIdentifier: someClientIdentifier

Sent to Azure as:

hasUsername: true
username: my-iot-hub-name.azure-devices.net/4601234567890
clientIdentifier: 4601234567890

Note: Cloud Connector is only modifying three fields hasUsername, username and clientIdentifier, all other fields are sent as they are.

PUBLISH Message

Incoming message:

topic: /my/desired/topic
payload: {"someField":"Some data I want to send"}

Sent to Azure as:

topic: devices/4601234567890/messages/events/my-desired-topic
payload: {"someField":"Some data I want to send"}

Cloud Connector is prepending the only topic format that Azure allows from the incoming topic replaces any / with - and then publishes the message to a property_bag called my-desired-topic under that device in IoT Hub.

Note: Cloud Connector is only modifying one field topic, all other fields are sent as they are.

SUBSCRIBE Message

Incoming message:

topics: /my/desired/topic, /topic/with/wildcard/#

Sent to Azure as:

topics: devices/4601234567890/messages/devicebound/my-desired-topic, devices/4601234567890/messages/devicebound/#

Subscribe messages have 2 conditions:

• When a topic has multi levels like /my/desired/topic, Cloud Connector will transform the same way as publish message but this time to the devicebound topic in IoT Hub
• If subscription topics contains a wildcard (#), Cloud Connector removes anything else from the topic and leaving the wildcard, ending up listening to any property_bags coming to that device.

Note: Cloud Connector is only modifying the topic field, all other fields are sent as they are.