MQTTStudy/MQTTSample/MqttSubscriberApp/Program.cs

using MQTTnet.Client;
using MQTTnet;
using System.Text;

namespace MqttSubscriberApp
{
    internal class Program
    {
        private static IMqttClient _mqttClient;
        private static string CLIENT_ID = $"SubscriberClient_{Random.Shared.Next(1, 1000)}";
        private static string SERVER_IP = "localhost";
        private static readonly int PORT = 1883;
        private static readonly string TOPIC = "home/kitchen/temperature";

        static async Task Main(string[] args)
        {
            var mqttFactory = new MqttFactory();
            _mqttClient = mqttFactory.CreateMqttClient();

            var options = new MqttClientOptionsBuilder()
                .WithClientId(CLIENT_ID)
                .WithTcpServer(SERVER_IP, PORT)
                .Build();

            _mqttClient.ConnectedAsync += MqttClient_ConnectedAsync;
            _mqttClient.ApplicationMessageReceivedAsync += MqttClient_ApplicationMessageReceivedAsync;

            await _mqttClient.ConnectAsync(options);
            Console.ReadLine();
        }

        private static async Task MqttClient_ApplicationMessageReceivedAsync(MqttApplicationMessageReceivedEventArgs arg)
        {
            var message = Encoding.UTF8.GetString(arg.ApplicationMessage.PayloadSegment);
            Console.WriteLine($"Received message: {message}");
        }

        private static async Task MqttClient_ConnectedAsync(MqttClientConnectedEventArgs arg)
        {
            Console.WriteLine($"Connected to broker with ID: [{CLIENT_ID}].");

            await _mqttClient.SubscribeAsync(new MqttTopicFilterBuilder()
                .WithTopic(TOPIC)
                .Build());

            Console.WriteLine($"Subscribed to topic '{TOPIC}'");
        }
    }
}