M2Mqtt in C# is not connected, doesn't give data

Question

I have a project creating a websocket client side (Subscriber) to a MQTT publisher. I am quite new to C# and MQTT protocol. I follow some youtube video to make finish my very first lines connecting to this MQTT publisher to get all the train going in and out Helsinki station.

• broker: "rata.digitraffic.fi"
• Port: 80
• Topic: trains-by-station/HKI (HKI abbr for Helsinki)

I use M2Mqtt library in dotnet to build the subscriber, somehow the client_MqttMsgPublishReceived function is never triggered. the client.IsConnected always returned false value! You can find info of this mqtt protocol in the url below.

https://www.digitraffic.fi/rautatieliikenne/#websocket-mqtt

It gives me example in JavaScripts and it seems to run fine with the example of each MQTT. But when I tried to do it with my PC, it doesn't give me any thing, but

Hello World!!!
False

and the cmd window on hold. SOOOO FRUSTRATING right now. it would be much appreciate if anyone can help me out. BTW, I am using win10, I tried with dotnet 4/5/6 and m2mqtt 4.3.0.

using System.Text;
using uPLibrary.Networking.M2Mqtt;
using uPLibrary.Networking.M2Mqtt.Messages;
using System;

namespace m2qttSubscriber
{
    internal class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!!!!");
            MqttClient client = new MqttClient("rata.digitraffic.fi", 
                                               80,
                                               false,
                                               MqttSslProtocols.None,
                                               null,
                                               null);

            client.MqttMsgPublishReceived += client_MqttMsgPublishReceived;

            string clientID = "myclientid_" + RandomDigits(4);
            client.Connect(clientID);
            Console.WriteLine(client.IsConnected);
            client.Subscribe(new string[] { "trains-by-station/HKI" },
                             new byte[] { MqttMsgBase.QOS_LEVEL_AT_MOST_ONCE}) ;
        }
        static void client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e)
        {
            Console.WriteLine("SOme thing is received");
            string payload = Encoding.Default.GetString(e.Message);
            Console.WriteLine("Recevied {0} from", payload);
        }
        static public string RandomDigits(int length)
        {
            var random = new Random();

            string s = string.Empty;
            for (int i = 0; i < length; i++)
                s = String.Concat(s, random.Next(10).ToString());
            return s;
        }
    }
}

Answer 1

As per the comments the library used (uPLibrary.Networking.M2Mqtt) does not support MQTT over Websockets (which is what rata.digitraffic.fi:80 offers).

If you are able to use standard MQTT (over TCP/IP) then rata-mqtt.digitraffic.fi:1883 works (OP succeeded with MqttClient client = new MqttClient("rata-mqtt.digitraffic.fi", 1883, false, MqttSslProtocols.None, null, null);) and this is generally preferable to using WebSockets (there are some situations where you have to use WebSockets; e.g. code running in a browser or to bypass some filters/proxies).

Alternatively there are other libraries that do offer support for MQTT over Websockets.