Adafruit MQTT with MQTTnet

Before building the Message Queue Telemetry Transport(MQTT) gateway I built a proof of concept(PoC) .Net core console application. This was to confirm that I could connect to the Adafruit.IO MQTT broker and format the topic (with and without group name) and payload correctly. The Adafruit IO MQTT documentation suggests an approach for naming topics which allows a bit more structure for feed names than the REST API.

The MQTT broker, username, API key, client ID, optional group name (to keep MQTT aligned with REST API terminology) and feed name are command line options.

class Program
	private static IMqttClient mqttClient = null;
	private static IMqttClientOptions mqttOptions = null;
	private static string server;
	private static string username;
	private static string password;
	private static string clientId;
	private static string groupname;
	private static string feedname;

	static void Main(string[] args)
		MqttFactory factory = new MqttFactory();
		mqttClient = factory.CreateMqttClient();

		if ((args.Length != 5) && (args.Length != 6))
			Console.WriteLine("[MQTT Server] [UserName] [Password] [ClientID] [GroupName] [FeedName]");
			Console.WriteLine("[MQTT Server] [UserName] [Password] [ClientID] [FeedName]");
			Console.WriteLine("Press <enter> to exit");

		server = args[0];
		username = args[1];
		password = args[2];
		clientId = args[3];
		if (args.Length == 5)
			feedname = args[4].ToLower();
			Console.WriteLine($"MQTT Server:{server} Username:{username} ClientID:{clientId} Feedname:{feedname}");

		if (args.Length == 6)
			groupname = args[4].ToLower();
			feedname = args[5].ToLower();
			Console.WriteLine($"MQTT Server:{server} Username:{username} ClientID:{clientId} Groupname:{groupname} Feedname:{feedname}");

		mqttOptions = new MqttClientOptionsBuilder()
			.WithCredentials(username, password)

		mqttClient.Disconnected += MqttClient_Disconnected;

		// Adafruit.IO format for topics which are called feeds
		string topic = string.Empty;

		if (args.Length == 5)
			topic = $"{args[1]}/feeds/{feedname}";

		if (args.Length == 6)
			topic = $"{args[1]}/feeds/{groupname}.{feedname}";

		while (true)
			string value = "22." + DateTime.UtcNow.Millisecond.ToString();
			Console.WriteLine($"Topic:{topic} Value:{value}");

			var message = new MqttApplicationMessageBuilder()

			Console.WriteLine("PublishAsync start");
			Console.WriteLine("PublishAsync finish");


	private static async void MqttClient_Disconnected(object sender, MqttClientDisconnectedEventArgs e)
		await Task.Delay(TimeSpan.FromSeconds(5));

			await mqttClient.ConnectAsync(mqttOptions);
		catch (Exception ex)
			Debug.WriteLine("Reconnect failed {0}", ex.Message);

For this PoC I used the MQTTnet package which is available via NuGet. It appeared to be reasonably well supported and has had recent updates.

Overall the process went pretty well, I found that looking at the topic names in the Adafruit IO feed setup screens helped a lot. A couple of times I was tripped up by mixed case in my text fields.

.Net Core 2 client with group name
Adafruit IO feed setup with group name
Console client without group name
Adafruit IO feed setup without group name

I am also going to try building some clients with the Eclipse Paho project .net client so I can compare a couple of different libraries.

One thought on “Adafruit MQTT with MQTTnet

  1. Pingback: Adafruit MQTT Cloud to Device Messaging | devMobile's blog

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