MQTTnet/Source/MQTTnet/Server/Internal/MqttClientConnection.cs

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using MQTTnet.Adapter;
using MQTTnet.Client;
using MQTTnet.Diagnostics;
using MQTTnet.Exceptions;
using MQTTnet.Formatter;
using MQTTnet.Internal;
using MQTTnet.PacketDispatcher;
using MQTTnet.Packets;
using MQTTnet.Protocol;

namespace MQTTnet.Server
{
    public sealed class MqttClientConnection : IDisposable
    {
        readonly Dictionary<ushort, string> _topicAlias = new Dictionary<ushort, string>();
        readonly MqttPacketDispatcher _packetDispatcher = new MqttPacketDispatcher();
        readonly MqttPacketFactories _packetFactories = new MqttPacketFactories();
        readonly MqttApplicationMessageFactory _applicationMessageFactory = new MqttApplicationMessageFactory();
        
        readonly MqttClientSessionsManager _sessionsManager;
        readonly MqttNetSourceLogger _logger;
        
        readonly MqttApplicationMessageInterceptorInvoker _applicationMessageInterceptorInvoker;
        
        readonly MqttServerOptions _serverOptions;
        readonly MqttServerEventContainer _eventContainer;
        readonly MqttConnectPacket _connectPacket;

        CancellationTokenSource _cancellationToken;
        
        public MqttClientConnection(
            MqttConnectPacket connectPacket,
            IMqttChannelAdapter channelAdapter,
            MqttClientSession session,
            MqttServerOptions serverOptions,
            MqttServerEventContainer eventContainer,
            MqttClientSessionsManager sessionsManager,
            IMqttNetLogger logger)
        {
            _serverOptions = serverOptions ?? throw new ArgumentNullException(nameof(serverOptions));
            _eventContainer = eventContainer;
            _sessionsManager = sessionsManager ?? throw new ArgumentNullException(nameof(sessionsManager));

            ChannelAdapter = channelAdapter ?? throw new ArgumentNullException(nameof(channelAdapter));
            Endpoint = channelAdapter.Endpoint;

            Session = session ?? throw new ArgumentNullException(nameof(session));
            _connectPacket = connectPacket ?? throw new ArgumentNullException(nameof(connectPacket));

            _applicationMessageInterceptorInvoker = new MqttApplicationMessageInterceptorInvoker(eventContainer, Id, Session.Items);
            
            if (logger == null) throw new ArgumentNullException(nameof(logger));
            _logger = logger.WithSource(nameof(MqttClientConnection));
        }

        public string Id => _connectPacket.ClientId;

        public string Endpoint { get; }

        public IMqttChannelAdapter ChannelAdapter { get; }

        public MqttClientConnectionStatistics Statistics { get; } = new MqttClientConnectionStatistics();

        public bool IsRunning { get; private set; }

        public ushort KeepAlivePeriod => _connectPacket.KeepAlivePeriod;

        public MqttClientSession Session { get; }

        public bool IsTakenOver { get; set; }

        public bool IsCleanDisconnect { get; private set; }

        public async Task StopAsync(MqttClientDisconnectReason reason)
        {
            IsRunning = false;

            if (reason == MqttClientDisconnectReason.SessionTakenOver || reason == MqttClientDisconnectReason.KeepAliveTimeout)
            {
                // Is is very important to send the DISCONNECT packet here BEFORE cancelling the
                // token because the entire connection is closed (disposed) as soon as the cancellation
                // token is cancelled. To there is no chance that the DISCONNECT packet will ever arrive
                // at the client!
                await TrySendDisconnectPacket(reason).ConfigureAwait(false);
            }

            StopInternal();
        }

        public void ResetStatistics()
        {
            ChannelAdapter.ResetStatistics();
        }

        public void Dispose()
        {
            _cancellationToken.Dispose();
        }

        public async Task RunAsync()
        {
            _logger.Info("Client '{0}': Session started.", Id);

            Session.LatestConnectPacket = _connectPacket;
            Session.WillMessageSent = false;

            using (var cancellationToken = new CancellationTokenSource())
            {
                _cancellationToken = cancellationToken;

                try
                {
                    Task.Run(() => SendPacketsLoop(cancellationToken.Token), cancellationToken.Token).RunInBackground(_logger);
                    
                    IsRunning = true;

                    await ReceivePackagesLoop(cancellationToken.Token).ConfigureAwait(false);
                }
                finally
                {
                    IsRunning = false;

                    cancellationToken.Cancel();
                    _cancellationToken = null;
                }
            }

            _packetDispatcher.CancelAll();

            if (!IsTakenOver && !IsCleanDisconnect && Session.LatestConnectPacket.WillFlag && !Session.WillMessageSent)
            {
                var willPublishPacket = _packetFactories.Publish.Create(Session.LatestConnectPacket);
                var willApplicationMessage = _applicationMessageFactory.Create(willPublishPacket);
                
                _= _sessionsManager.DispatchPublishPacket(Id, willApplicationMessage);
                Session.WillMessageSent = true;
                
                _logger.Info("Client '{0}': Published will message.", Id);
            }

            _logger.Info("Client '{0}': Connection stopped.", Id);
        }

        public async Task SendPacketAsync(MqttBasePacket packet, CancellationToken cancellationToken)
        {
            var interceptingPacketEventArgs = new InterceptingPacketEventArgs
            {
                ClientId = Id,
                Endpoint = Endpoint,
                Packet = packet,
                CancellationToken = cancellationToken
            };
            
            await _eventContainer.InterceptingOutboundPacketEvent.InvokeAsync(interceptingPacketEventArgs).ConfigureAwait(false);
            packet = interceptingPacketEventArgs.Packet;

            if (!interceptingPacketEventArgs.ProcessPacket || packet == null)
            {
                return;
            }

            await ChannelAdapter.SendPacketAsync(packet, cancellationToken).ConfigureAwait(false);
            Statistics.HandleSentPacket(packet);
        }

        async Task ReceivePackagesLoop(CancellationToken cancellationToken)
        {
            try
            {
                // We do not listen for the cancellation token here because the internal buffer might still
                // contain data to be read even if the TCP connection was already dropped. So we rely on an
                // own exception in the reading loop!
                while (!cancellationToken.IsCancellationRequested)
                {
                    var packet = await ChannelAdapter.ReceivePacketAsync(cancellationToken).ConfigureAwait(false);

                    if (packet == null)
                    {
                        return;
                    }
                    
                    var interceptingPacketEventArgs = new InterceptingPacketEventArgs
                    {
                        ClientId = Id,
                        Endpoint = Endpoint,
                        Packet = packet,
                        CancellationToken = cancellationToken
                    };
                    
                    await _eventContainer.InterceptingInboundPacketEvent.InvokeAsync(interceptingPacketEventArgs).ConfigureAwait(false);
                    packet = interceptingPacketEventArgs.Packet;
                    
                    if (!interceptingPacketEventArgs.ProcessPacket || packet == null)
                    {
                        // Restart the receiving process to get the next packet ignoring the current one..
                        continue;
                    }

                    Statistics.HandleReceivedPacket(packet);

                    if (packet is MqttPublishPacket publishPacket)
                    {
                        await HandleIncomingPublishPacket(publishPacket, cancellationToken).ConfigureAwait(false);
                    }
                    else if (packet is MqttPubAckPacket pubAckPacket)
                    {
                        Session.AcknowledgePublishPacket(pubAckPacket.PacketIdentifier);
                    }
                    else if (packet is MqttPubCompPacket pubCompPacket)
                    {
                        Session.AcknowledgePublishPacket(pubCompPacket.PacketIdentifier);
                    }
                    else if (packet is MqttPubRecPacket pubRecPacket)
                    {
                        HandleIncomingPubRecPacket(pubRecPacket);
                    }
                    else if (packet is MqttPubRelPacket pubRelPacket)
                    {
                        HandleIncomingPubRelPacket(pubRelPacket);
                    }
                    else if (packet is MqttSubscribePacket subscribePacket)
                    {
                        await HandleIncomingSubscribePacket(subscribePacket, cancellationToken).ConfigureAwait(false);
                    }
                    else if (packet is MqttUnsubscribePacket unsubscribePacket)
                    {
                        await HandleIncomingUnsubscribePacket(unsubscribePacket, cancellationToken).ConfigureAwait(false);
                    }
                    else if (packet is MqttPingReqPacket)
                    {
                        // See: The Server MUST send a PINGRESP packet in response to a PINGREQ packet [MQTT-3.12.4-1].
                        //await SendPacketAsync(MqttPingRespPacket.Instance, cancellationToken).ConfigureAwait(false);
                        Session.EnqueuePacket(new MqttPacketBusItem(MqttPingRespPacket.Instance));
                    }
                    else if (packet is MqttPingRespPacket)
                    {
                        throw new MqttProtocolViolationException("A PINGRESP Packet is sent by the Server to the Client in response to a PINGREQ Packet only.");
                    }
                    else if (packet is MqttDisconnectPacket)
                    {
                        IsCleanDisconnect = true;
                        return;
                    }
                    else
                    {
                        if (!_packetDispatcher.TryDispatch(packet))
                        {
                            throw new MqttProtocolViolationException($"Received packet '{packet}' at an unexpected time.");
                        }
                    }
                }
            }
            catch (OperationCanceledException)
            {
            }
            catch (Exception exception)
            {
                if (exception is MqttCommunicationException)
                {
                    _logger.Warning(exception, "Client '{0}': Communication exception while receiving client packets.", Id);
                }
                else
                {
                    _logger.Error(exception, "Client '{0}': Error while receiving client packets.", Id);
                }
            }
        }

        async Task SendPacketsLoop(CancellationToken cancellationToken)
        {
            MqttPacketBusItem packetBusItem = null;

            try
            {
                while (!cancellationToken.IsCancellationRequested)
                {
                    packetBusItem = await Session.DequeuePacketAsync(cancellationToken).ConfigureAwait(false);

                    // Also check the cancellation token here because the dequeue is blocking and may take some time.
                    if (cancellationToken.IsCancellationRequested)
                    {
                        return;
                    }

                    try
                    {
                        await SendPacketAsync(packetBusItem.Packet, cancellationToken).ConfigureAwait(false);
                        packetBusItem.MarkAsDelivered();
                    }
                    catch (OperationCanceledException)
                    {
                        packetBusItem.MarkAsCancelled();
                    }
                    catch (Exception exception)
                    {
                        packetBusItem.MarkAsFailed(exception);
                    }
                }
            }
            catch (OperationCanceledException)
            {
            }
            catch (Exception exception)
            {
                if (exception is MqttCommunicationTimedOutException)
                {
                    _logger.Warning(exception, "Client '{0}': Sending publish packet failed: Timeout.", Id);
                }
                else if (exception is MqttCommunicationException)
                {
                    _logger.Warning(exception, "Client '{0}': Sending publish packet failed: Communication exception.", Id);
                }
                else
                {
                    _logger.Error(exception, "Client '{0}': Sending publish packet failed.", Id);
                }

                if (packetBusItem?.Packet is MqttPublishPacket publishPacket)
                {
                    if (publishPacket.QualityOfServiceLevel > MqttQualityOfServiceLevel.AtMostOnce)
                    {
                        publishPacket.Dup = true;
                        Session.EnqueuePacket(new MqttPacketBusItem(publishPacket));
                    }
                }

                StopInternal();
            }
        }
        
        void StopInternal()
        {
            _cancellationToken?.Cancel();
        }

        void HandleIncomingPubRecPacket(MqttPubRecPacket pubRecPacket)
        {
            var pubRelPacket = _packetFactories.PubRel.Create(pubRecPacket, MqttApplicationMessageReceivedReasonCode.Success);
            Session.EnqueuePacket(new MqttPacketBusItem(pubRelPacket));
        }

        void HandleIncomingPubRelPacket(MqttPubRelPacket pubRelPacket)
        {
            var pubCompPacket = _packetFactories.PubComp.Create(pubRelPacket, MqttApplicationMessageReceivedReasonCode.Success);
            Session.EnqueuePacket(new MqttPacketBusItem(pubCompPacket));
        }

        async Task HandleIncomingSubscribePacket(MqttSubscribePacket subscribePacket, CancellationToken cancellationToken)
        {
            var subscribeResult = await Session.SubscriptionsManager.Subscribe(subscribePacket, cancellationToken).ConfigureAwait(false);

            var subAckPacket = _packetFactories.SubAck.Create(subscribePacket, subscribeResult);

            Session.EnqueuePacket(new MqttPacketBusItem(subAckPacket));

            if (subscribeResult.CloseConnection)
            {
                StopInternal();
                return;
            }

            foreach (var retainedApplicationMessage in subscribeResult.RetainedApplicationMessages)
            {
                var publishPacket = _packetFactories.Publish.Create(retainedApplicationMessage.ApplicationMessage);
                Session.EnqueuePacket(new MqttPacketBusItem(publishPacket));
            }
        }

        async Task HandleIncomingUnsubscribePacket(MqttUnsubscribePacket unsubscribePacket, CancellationToken cancellationToken)
        {
            var unsubscribeResult = await Session.SubscriptionsManager.Unsubscribe(unsubscribePacket, cancellationToken).ConfigureAwait(false);

            var unsubAckPacket = _packetFactories.UnsubAck.Create(unsubscribePacket, unsubscribeResult);

            Session.EnqueuePacket(new MqttPacketBusItem(unsubAckPacket));

            if (unsubscribeResult.CloseConnection)
            {
                StopInternal();
            }
        }
       
        async Task HandleIncomingPublishPacket(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
        {
            HandleTopicAlias(publishPacket);

            var applicationMessage = new MqttApplicationMessageFactory().Create(publishPacket);

            await _applicationMessageInterceptorInvoker.Invoke(applicationMessage, cancellationToken).ConfigureAwait(false);

            applicationMessage = _applicationMessageInterceptorInvoker.ApplicationMessage;
            
            if (_applicationMessageInterceptorInvoker.CloseConnection)
            {
                await StopAsync(MqttClientDisconnectReason.UnspecifiedError);
                return;
            }

            if (_applicationMessageInterceptorInvoker.ProcessPublish)
            {
                await _sessionsManager.DispatchPublishPacket(Id, applicationMessage).ConfigureAwait(false);    
            }
            
            switch (publishPacket.QualityOfServiceLevel)
            {
                case MqttQualityOfServiceLevel.AtMostOnce:
                {
                    // Do nothing since QoS 0 has no ack at all!
                    break;
                }
                case MqttQualityOfServiceLevel.AtLeastOnce:
                {
                    var pubAckPacket = _packetFactories.PubAck.Create(publishPacket, _applicationMessageInterceptorInvoker.Response);
                    Session.EnqueuePacket(new MqttPacketBusItem(pubAckPacket));
                    break;
                }
                case MqttQualityOfServiceLevel.ExactlyOnce:
                {
                    var pubRecPacket = _packetFactories.PubRec.Create(publishPacket, _applicationMessageInterceptorInvoker.Response);
                    Session.EnqueuePacket(new MqttPacketBusItem(pubRecPacket));
                    break;
                }
                default:
                {
                    throw new MqttCommunicationException("Received a not supported QoS level.");
                }
            }
        }

        void HandleTopicAlias(MqttPublishPacket publishPacket)
        {
            if (publishPacket.Properties?.TopicAlias == null)
            {
                return;
            }

            var topicAlias = publishPacket.Properties.TopicAlias.Value;

            lock (_topicAlias)
            {
                if (!string.IsNullOrEmpty(publishPacket.Topic))
                {
                    _topicAlias[topicAlias] = publishPacket.Topic;
                }
                else
                {
                    if (_topicAlias.TryGetValue(topicAlias, out var topic))
                    {
                        publishPacket.Topic = topic;
                    }
                    else
                    {
                        _logger.Warning("Client '{0}': Received invalid topic alias ({1}).", Id, publishPacket.Properties.TopicAlias);
                    }
                }
            }
        }

        async Task TrySendDisconnectPacket(MqttClientDisconnectReason reason)
        {
            try
            {
                var disconnectOptions = new MqttClientDisconnectOptions
                {
                    Reason = reason,
                    ReasonString = reason.ToString()
                };

                var disconnectPacket = _packetFactories.Disconnect.Create(disconnectOptions);

                using (var timeout = new CancellationTokenSource(_serverOptions.DefaultCommunicationTimeout))
                {
                    await SendPacketAsync(disconnectPacket, timeout.Token).ConfigureAwait(false);
                }
            }
            catch (Exception exception)
            {
                _logger.Warning(exception, "Client '{0}': Error while sending DISCONNECT packet (Reason = {1}).", Id, reason);
            }
        }
    }
}