Automatic-Parking/Source/ProofOfConcept/Services/MQTTServer.cs

using System.Net;
using System.Text;
using Microsoft.Extensions.Options;
using MQTTnet.Protocol;
using MQTTnet.Server;

namespace ProofOfConcept.Services;

public class MQTTServer : IHostedService
{
    private readonly ILogger<MQTTServer> logger;
    private readonly MQTTServerConfiguration configuration;

    private readonly MqttServer server;
    
    public MQTTServer(ILogger<MQTTServer> logger, IOptions<MQTTServerConfiguration> options)
    {
        this.logger = logger;
        this.configuration = options.Value;

        MqttServerOptions mqttServerOptions = new MqttServerOptionsBuilder().WithDefaultEndpoint().WithDefaultEndpointPort(this.configuration.Port).WithKeepAlive().Build();
        this.server = new MqttServerFactory().CreateMqttServer(mqttServerOptions);

        this.server.ClientConnectedAsync += (e) =>
        {
            logger.LogInformation("Client connected from: {IPAddress}. ClientID: {ClientID}", e.RemoteEndPoint.ToString(), e.ClientId);
            return Task.CompletedTask;
        };

        this.server.ClientDisconnectedAsync += (e) =>
        {
            logger.LogInformation("Client {ClientID} disconnected from: {IPAddress}. Reason: {ReasonString} ({ReasonCode})", e.ClientId, e.RemoteEndPoint.ToString(), e.ReasonString, e.ReasonCode);
            return Task.CompletedTask;
        };
        
        this.server.ClientSubscribedTopicAsync += (e) =>
        {
            logger.LogInformation("Client {ClientID} subscribed to topic: {Topic}", e.ClientId, e.TopicFilter.Topic);
            return Task.CompletedTask;
        };

        this.server.ClientUnsubscribedTopicAsync += (e) =>
        {
            logger.LogInformation("Client {ClientID} unsubscribed from topic: {Topic}", e.ClientId, e.TopicFilter);
            return Task.CompletedTask;
        };

        this.server.InterceptingPublishAsync += (e) =>
        {
            if (e.ApplicationMessage.Topic == "telemetry" && e.ClientId != this.configuration.TelemetryClient.ClientID)
            {
                logger.LogWarning("Client {ClientID} tried to publish to telemetry topic", e.ClientId);
                
                e.Response.ReasonCode = MqttPubAckReasonCode.NotAuthorized;
                return Task.CompletedTask;
            }

            logger.LogInformation("Client {ClientID} published message to topic: {Topic}: {Message}", e.ClientId, e.ApplicationMessage.Topic, Encoding.UTF8.GetString(e.ApplicationMessage.Payload));
            return Task.CompletedTask;
        };

        this.server.ValidatingConnectionAsync += (e) =>
        {
            //Local client (by clientID)
            if (e.ClientId == this.configuration.LocalClient.ClientID)
            {
                //Not local connection (IP is not loopback)
                if (e.RemoteEndPoint is IPEndPoint ipEndPoint && !IPAddress.IsLoopback(ipEndPoint.Address))
                {
                    logger.LogWarning("Local client tried to connect from non-loopback address: {IPAddress}", ipEndPoint.ToString());
                    e.ReasonCode = MqttConnectReasonCode.NotAuthorized;
                }
                
                //Invalid username or password
                else if (e.UserName != configuration.LocalClient.Username || e.Password != configuration.LocalClient.Password)
                {
                    logger.LogWarning("Local client tried to connect with invalid credentials");
                    e.ReasonCode = MqttConnectReasonCode.NotAuthorized;
                }
            }
            
            //Telemetry client
            else if (e.ClientId == this.configuration.TelemetryClient.ClientID)
            {
                if (e.UserName != configuration.TelemetryClient.Username || e.Password != configuration.TelemetryClient.Password)
                {
                    logger.LogWarning("Telemetry client tried to connect with invalid credentials");
                    e.ReasonCode = MqttConnectReasonCode.NotAuthorized;
                }
            }
            
            //Observer
            else if ((this.configuration.Observer.ClientID is not null && e.ClientId == this.configuration.Observer.ClientID) || this.configuration.Observer.ClientID is null)
            {
                if (e.UserName != configuration.Observer.Username || e.Password != configuration.Observer.Password)
                {
                    logger.LogWarning("Observer tried to connect with invalid credentials: {Username} / {Password} from {RemoteIP}", e.UserName, e.Password, e.RemoteEndPoint is IPEndPoint ipEndPoint ? ipEndPoint.ToString() : e.RemoteEndPoint.GetType().FullName);
                    e.ReasonCode = MqttConnectReasonCode.NotAuthorized;
                }
            }

            else
                e.ReasonCode = MqttConnectReasonCode.Banned;
            
            return Task.CompletedTask;
        };
    }

    public async Task StartAsync(CancellationToken cancellationToken)
    {
        this.logger.LogTrace("Starting MQTT Server...");

        await this.server.StartAsync();
       
        this.logger.LogInformation("MQTT Server started");
    }

    public async Task StopAsync(CancellationToken cancellationToken)
    {
        this.logger.LogTrace("Stopping MQTT Server...");

        await this.server.StopAsync();
        
        this.logger.LogInformation("MQTT Server stopped");
    }
}

public class MQTTServerConfiguration
{
    public ushort Port { get; set; } = 1883;
    public MQTTAuthenticationData TelemetryClient { get; set; } = new MQTTAuthenticationData("telemetry", "fleet", "9R0FXNs5NEIEbI4"); //Must have a known client id
    public MQTTAuthenticationData LocalClient { get; set; } = new MQTTAuthenticationData("local", "client", "xuhvoc-parrox-xuzsE4"); //Must have a known client id
    public MQTTAuthenticationData Observer { get; set; } = new MQTTAuthenticationData("observer", "JC740d4c4E9dveh");
}

public class MQTTAuthenticationData
{
    public string? ClientID { get; set; }
    public string Username { get; set; }
    public string Password { get; set; }

    public MQTTAuthenticationData(string clientId, string username, string password)
    {
        ClientID = clientId;
        Username = username;
        Password = password;
    }
    
    public MQTTAuthenticationData(string username, string password)
    {
        ClientID = null;
        Username = username;
        Password = password;
    }
}