Azure IoT Hub Framework 3.5

Question

Are there any good tutorials or guides to using Azure IoT Hub via using the MQTT protocol from devices with framework 3.5? I found the M2MQTT client but it won't work with Azure IoT Hub.

Answer 1

Are you referring to Azure IoT Hub device SDK for .NET, and it working with .NET Framework 3.5 ? As per the GitHub documentation, it seems IoT Hub SDK for .NET supports only .NET Framework 4.5.1 and above only.

Alternatively, Simply using Azure IoT Hub Rest API - then you can make HTTP requests from your legacy .NET Framework 3.5 code

Answer 2

IoT Hub enables devices to communicate with the IoT Hub device endpoints using MQTT v3.1.1 protocol directly. You can take a look at this document. In the document the tutorial is written in python, following code is a full sample for C# using uPLibrary.Networking.M2Mqtt.

C# Example:

    private static string hostName = "<iothub-hosename>";
    private static int port = 8883;
    private static string deviceId = "<deviceid>";
    private static string userName = "";
    private static string password = "";
    private static string certBase64 = "<DigiCert Baltimore Root Certificate>";

    static void Main(string[] args)
    {

        try
        {
            userName = $"{hostName}/{deviceId}/api-version=2016-11-14";
            password = $"SharedAccessSignature sr=<SAS Token>";

            byte[] certBytes = Convert.FromBase64String(certBase64);
            X509Certificate caCert = new X509Certificate(certBytes);

            MqttClient client = new MqttClient(hostName, port, true, caCert, null , MqttSslProtocols.TLSv1_0);
            client.ProtocolVersion = MqttProtocolVersion.Version_3_1_1;

            client.MqttMsgPublishReceived += Client_MqttMsgPublishReceived;
            client.MqttMsgPublished += Client_MqttMsgPublished;
            client.ConnectionClosed += Client_ConnectionClosed;
            client.Connect(deviceId, userName, password);
            if(client.IsConnected)
            {
                //To receive messages from IoT Hub, a device should subscribe using devices/{device_id}/messages/devicebound/# as a Topic Filter. 
                client.Subscribe(new string[] { $"devices/{deviceId}/messages/devicebound/#" }, new byte[] { MqttMsgBase.QOS_LEVEL_AT_LEAST_ONCE });

                //After making a successful connection, a device can send messages to IoT Hub using devices/{device_id}/messages/events/ or devices/{device_id}/messages/events/{property_bag} as a Topic Name. 
                client.Publish($"devices/{deviceid}/messages/events/", System.Text.Encoding.ASCII.GetBytes("{id=123}"), MqttMsgBase.QOS_LEVEL_AT_LEAST_ONCE, false);
            }
        }
        catch(Exception ex)
        {
            Console.Write(ex.Message);
        }

        Console.Read();
    }

    private static void Client_MqttMsgPublished(object sender, MqttMsgPublishedEventArgs e)
    {
        Console.WriteLine("Mqtt Published Message-[MsgId:{0}]:{1}", e.MessageId, e.IsPublished ? "Success": "Failure");
    }

    private static void Client_ConnectionClosed(object sender, EventArgs e)
    {
        Console.WriteLine("ConnectionClosed");
    }

    private static void Client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e)
    {
        Console.WriteLine(System.Text.Encoding.ASCII.GetString(e.Message));
    }

In the code, you may need to copy the DigiCert Baltimore Root Certificate to certBase64 from certs.c as base64 string(remove the lines -----BEGIN CERTIFICATE----- and -----END CERTIFICATE-----, and remove \r\n\).

Update:

How to get SAS token?

You can use Device Explorer to generate SAS tokens,please see the device section of Using IoT Hub security tokens.