As I’m testing my Message Queue Telemetry Transport(MQTT) LoRa gateway I’m building a proof of concept(PoC) .Net core console application for each IoT platform I would like to support.
This PoC was to confirm that I could connect to the Losant MQTT API then format the topics and payloads correctly. The Losant screen designer has “Blocks” which generate commands for devices so I extended the test client to see how well this worked.
The MQTT broker, username, password, and client ID 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;
static void Main(string[] args)
{
MqttFactory factory = new MqttFactory();
mqttClient = factory.CreateMqttClient();
bool heatPumpOn = false;
if (args.Length != 4)
{
Console.WriteLine("[MQTT Server] [UserName] [Password] [ClientID]");
Console.WriteLine("Press <enter> to exit");
Console.ReadLine();
}
server = args[0];
username = args[1];
password = args[2];
clientId = args[3];
Console.WriteLine($"MQTT Server:{server} Username:{username} ClientID:{clientId}");
mqttOptions = new MqttClientOptionsBuilder()
.WithTcpServer(server)
.WithCredentials(username, password)
.WithClientId(clientId)
.WithTls()
.Build();
mqttClient.ApplicationMessageReceived += MqttClient_ApplicationMessageReceived;
mqttClient.Disconnected += MqttClient_Disconnected;
mqttClient.ConnectAsync(mqttOptions).Wait();
// Setup a subscription for commands sent to client
string commandTopic = $"losant/{clientId}/command";
mqttClient.SubscribeAsync(commandTopic);
// Losant formatted client state update topic
string stateTopic = $"losant/{clientId}/state";
while (true)
{
string payloadText;
double temperature = 22.0 + +(DateTime.UtcNow.Millisecond / 1000.0);
double humidity = 50 + +(DateTime.UtcNow.Millisecond / 1000.0);
Console.WriteLine($"Topic:{stateTopic} Temperature:{temperature} Humidity:{humidity} HeatPumpOn:{heatPumpOn}");
// First attempt which worked
//payloadText = @"{""data"":{ ""OfficeTemperature"":22.5}}";
// Second attempt to work out data format with "real" values injected
payloadText = @"{""data"":{ ""OfficeTemperature"":"+ temperature.ToString("f1") + @",""OfficeHumidity"":" + humidity.ToString("F0") + @"}}";
// Third attempt with Jobject which sort of worked but number serialisation is sub optimal
//JObject payloadJObject = new JObject();
//payloadJObject.Add("time", DateTime.UtcNow.ToString("u")); // This field is optional and can be commented out
//JObject data = new JObject();
//data.Add("OfficeTemperature", temperature.ToString("F1"));
//data.Add("OfficeHumidity", humidity.ToString("F0"));
//data.Add("HeatPumpOn", heatPumpOn);
//heatPumpOn = !heatPumpOn;
//payloadJObject.Add( "data", data);
//payloadText = JsonConvert.SerializeObject(payloadJObject);
// Forth attempt with JOBject and gps info https://docs.losant.com/devices/state/
//JObject payloadJObject = new JObject();
//payloadJObject.Add("time", DateTime.UtcNow.ToString("u")); // This field is optional and can be commented out
//JObject data = new JObject();
//data.Add("GPS", "-43.5309325, 172.637119"); // Christchurch Cathederal
//payloadJObject.Add("data", data);
//payloadText = JsonConvert.SerializeObject(payloadJObject);
var message = new MqttApplicationMessageBuilder()
.WithTopic(stateTopic)
.WithPayload(payloadText)
.WithQualityOfServiceLevel(global::MQTTnet.Protocol.MqttQualityOfServiceLevel.AtLeastOnce)
//.WithExactlyOnceQoS() With Losant this caused the publish to hang
.WithAtLeastOnceQoS()
//.WithRetainFlag() Losant doesn't allow this flag
.Build();
Console.WriteLine("PublishAsync start");
mqttClient.PublishAsync(message).Wait();
Console.WriteLine("PublishAsync finish");
Thread.Sleep(30100);
}
}
private static void MqttClient_ApplicationMessageReceived(object sender, MqttApplicationMessageReceivedEventArgs e)
{
Console.WriteLine($"ClientId:{e.ClientId} Topic:{e.ApplicationMessage.Topic} Payload:{e.ApplicationMessage.ConvertPayloadToString()}");
}
private static async void MqttClient_Disconnected(object sender, MqttClientDisconnectedEventArgs e)
{
Debug.WriteLine("Disconnected");
await Task.Delay(TimeSpan.FromSeconds(5));
try
{
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 initial configuration went really smoothly, I found the dragging of blocks onto the dashboard and configuring them worked well.
Losant .Net Core V2 client uploading simulated sensor readings
The device log made bring up a new device easy and the error messages displayed when I had badly formatted payloads were helpful (unlike many other packages I have used).
I put a button block on the overview screen, associated it with a command publication and my client reliably received messages when the button was pressed
Overall the Losant experience was pretty good and I’m going to spend some more time working with the application designer, devices recipes, webhooks, integrations and workflows etc. to see how well it works for a “real-world” project.
