Using MQTT ManagedClient with ASP NET API, how to? - asp.net-core

Question

I'm currently working on a project that has to rely heavily on MQTT - one of the parts that needs to utilize MQTT is a ASP Net API, but I'm having difficulties receiving messages.
Here is my MQTTHandler:
public MQTTHandler()
{
_mqttUrl = Properties.Resources.mqttURL ?? "";
_mqttPort = Properties.Resources.mqttPort ?? "";
_mqttUsername = Properties.Resources.mqttUsername ?? "";
_mqttPassword = Properties.Resources.mqttUsername ?? "";
_mqttFactory = new MqttFactory();
_tls = false;
}
public async Task<IManagedMqttClient> ConnectClientAsync()
{
var clientID = Guid.NewGuid().ToString();
var messageBuilder = new MqttClientOptionsBuilder()
.WithClientId(clientID)
.WithCredentials(_mqttUsername, _mqttPassword)
.WithTcpServer(_mqttUrl, Convert.ToInt32(_mqttPort));
var options = _tls ? messageBuilder.WithTls().Build() : messageBuilder.Build();
var managedOptions = new ManagedMqttClientOptionsBuilder()
.WithAutoReconnectDelay(TimeSpan.FromSeconds(5))
.WithClientOptions(options)
.Build();
_mqttClient = new MqttFactory().CreateManagedMqttClient();
await _mqttClient.StartAsync(managedOptions);
Console.WriteLine("Klient startet");
return _mqttClient;
}
public async Task PublishAsync(string topic, string payload, bool retainFlag = true, int qos = 1)
{
await _mqttClient.EnqueueAsync(new MqttApplicationMessageBuilder()
.WithTopic(topic)
.WithPayload(payload)
.WithQualityOfServiceLevel((MQTTnet.Protocol.MqttQualityOfServiceLevel)qos)
.WithRetainFlag(retainFlag)
.Build());
Console.WriteLine("Besked published");
}
public async Task SubscribeAsync(string topic, int qos = 1)
{
var topicFilters = new List<MQTTnet.Packets.MqttTopicFilter>
{
new MqttTopicFilterBuilder()
.WithTopic(topic)
.WithQualityOfServiceLevel((MQTTnet.Protocol.MqttQualityOfServiceLevel)(qos))
.Build()
};
await _mqttClient.SubscribeAsync(topicFilters);
}
public Status GetSystemStatus(MqttApplicationMessageReceivedEventArgs e)
{
try
{
var json = Encoding.UTF8.GetString(e.ApplicationMessage.Payload);
var status = JsonSerializer.Deserialize<Status>(json);
if (status != null)
{
return status;
}
else
{
return null;
}
}
catch (Exception)
{
throw;
}
}
The above has been tested with a console app and works as it should.
The reason I need MQTT in the APi is that a POST method has to act on the value of a topic;
In particular I need to check a systems status before allowing the post;
[HttpPost]
public async Task<ActionResult<Order>> PostOrder(Order order)
{
if (_lastStatus != null)
{
if (_lastStatus.OpStatus)
{
return StatusCode(400, "System is busy!");
}
else
{
var response = await _orderManager.AddOrder(order);
return StatusCode(response.StatusCode, response.Message);
}
}
return StatusCode(400, "Something went wrong");
}
So I will need to set up a subscriber for this controller, and set the value of _lastStatus on received messages:
private readonly MQTTHandler _mqttHandler;
private IManagedMqttClient _mqttClient;
private Status _lastStatus;
public OrdersController(OrderManager orderManager)
{
_orderManager = orderManager;
_mqttHandler = new MQTTHandler();
_mqttClient = _mqttHandler.ConnectClientAsync().Result;
_mqttHandler.SubscribeAsync("JSON/Status");
_mqttClient.ApplicationMessageReceivedAsync += e =>
{
_lastStatus = _mqttHandler.GetSystemStatus(e);
return Task.CompletedTask;
};
}
However, it's behaving a little odd and I'm not experienced enough to know why.
The first time I make a POST request, _lastStatus is null - every following POST request seem to have the last retained message.
I'm guessing that I am struggling due to stuff being asynchronous, but not sure, and every attempt I've attempted to make it synchronous have failed.
Anyone have a clue about what I'm doing wrong?