Azure IoT Hub, EventHub and Functions

Question

I have an IoTHub with a route that points to an EventHub which triggers a Functions.

I'm having problem getting the DeviceId and other IoT Hub properties from the event object without adding those explicitly to the payload.

If I set the input type to a string (or a custom type):

public static void Run(string iotMessage, TraceWriter log) {
    log.Info($"C# Event Hub trigger function processed a message: {iotMessage}");
}

I only get the payload without any other IoT Hub properties like DeviceId, CorrelationId or MessageId.

I tried to set the type to EventData instead:

public static void Run(EventData iotMessage, TraceWriter log) {
    log.Info($"C# Event Hub trigger function processed a message: {JsonConvert.SerializeObject(iotMessage)}");
}

Now I can access the IoT Hub properties via two getters: Properties and SystemProperties. For example I can access DeviceId like this iotMessage.SystemProperties["iothub-connection-device-id"]. But it does not expose the payload.

So how do I access both IoT Hub properties and the payload?

Answer 1

I missed a thing in the documentation for EventData. It has a method called GetBytes() and returns the body as a byte array. Example of getting both the IoT Hub properties and the body:

public static async void Run(EventData telemetryMessage, TraceWriter log)
{
    var deviceId = GetDeviceId(telemetryMessage);
    var payload = GetPayload(telemetryMessage.GetBytes());

    log.Info($"C# Event Hub trigger function processed a message.  deviceId: { deviceId }, payload: { JsonConvert.SerializeObject(payload) }");
}

private static Payload GetPayload(byte[] body)
{
    var json = System.Text.Encoding.UTF8.GetString(body);
    return JsonConvert.DeserializeObject<Payload>(json);
}

private static string GetDeviceId(EventData message)
{
    return message.SystemProperties["iothub-connection-device-id"].ToString();
}