Add server implementation

MQTTnet.Core/Adapter/IMqttCommunicationAdapter.cs

@@ -0,0 +1,18 @@
+using System;
+using System.Threading.Tasks;
+using MQTTnet.Core.Client;
+using MQTTnet.Core.Packets;
+
+namespace MQTTnet.Core.Adapter
+{
+    public interface IMqttCommunicationAdapter
+    {
+        Task ConnectAsync(MqttClientOptions options, TimeSpan timeout);
+
+        Task DisconnectAsync();
+
+        Task SendPacketAsync(MqttBasePacket packet, TimeSpan timeout);
+
+        Task<MqttBasePacket> ReceivePacketAsync(TimeSpan timeout);
+    }
+}

MQTTnet.Core/Adapter/IMqttServerAdapter.cs

@@ -0,0 +1,14 @@
+using System;
+using MQTTnet.Core.Server;
+
+namespace MQTTnet.Core.Adapter
+{
+    public interface IMqttServerAdapter
+    {
+        event EventHandler<MqttClientConnectedEventArgs> ClientConnected;
+
+        void Start(MqttServerOptions options);
+
+        void Stop();
+    }
+}

MQTTnet.Core/Adapter/MqttChannelCommunicationAdapter.cs

@@ -0,0 +1,88 @@
+using System;
+using System.Threading.Tasks;
+using MQTTnet.Core.Channel;
+using MQTTnet.Core.Client;
+using MQTTnet.Core.Diagnostics;
+using MQTTnet.Core.Exceptions;
+using MQTTnet.Core.Packets;
+using MQTTnet.Core.Serializer;
+
+namespace MQTTnet.Core.Adapter
+{
+    public class MqttChannelCommunicationAdapter : IMqttCommunicationAdapter
+    {
+        private readonly IMqttPacketSerializer _serializer;
+        private readonly IMqttCommunicationChannel _channel;
+
+        public MqttChannelCommunicationAdapter(IMqttCommunicationChannel channel, IMqttPacketSerializer serializer)
+        {
+            _channel = channel ?? throw new ArgumentNullException(nameof(channel));
+            _serializer = serializer ?? throw new ArgumentNullException(nameof(serializer));
+        }
+
+        public async Task ConnectAsync(MqttClientOptions options, TimeSpan timeout)
+        {
+            var task = _channel.ConnectAsync(options);
+            if (await Task.WhenAny(Task.Delay(timeout), task) != task)
+            {
+                throw new MqttCommunicationTimedOutException();
+            }
+        }
+
+        public async Task DisconnectAsync()
+        {
+            await _channel.DisconnectAsync();
+        }
+
+        public async Task SendPacketAsync(MqttBasePacket packet, TimeSpan timeout)
+        {
+            MqttTrace.Information(nameof(MqttChannelCommunicationAdapter), $"TX >>> {packet} [Timeout={timeout}]");
+
+            bool hasTimeout;
+            try
+            {
+                var task = _serializer.SerializeAsync(packet, _channel);
+                hasTimeout = await Task.WhenAny(Task.Delay(timeout), task) != task;
+            }
+            catch (Exception exception)
+            {
+                throw new MqttCommunicationException(exception);
+            }
+
+            if (hasTimeout)
+            {
+                throw new MqttCommunicationTimedOutException();
+            }
+        }
+
+        public async Task<MqttBasePacket> ReceivePacketAsync(TimeSpan timeout)
+        {
+            MqttBasePacket packet;
+            if (timeout > TimeSpan.Zero)
+            {
+                var workerTask = _serializer.DeserializeAsync(_channel);
+                var timeoutTask = Task.Delay(timeout);
+                var hasTimeout = Task.WhenAny(timeoutTask, workerTask) == timeoutTask;
+
+                if (hasTimeout)
+                {
+                    throw new MqttCommunicationTimedOutException();
+                }
+
+                packet = workerTask.Result;
+            }
+            else
+            {
+                packet = await _serializer.DeserializeAsync(_channel);
+            }
+
+            if (packet == null)
+            {
+                throw new MqttProtocolViolationException("Received malformed packet.");
+            }
+
+            MqttTrace.Information(nameof(MqttChannelCommunicationAdapter), $"RX <<< {packet}");
+            return packet;
+        }
+    }
+}

MQTTnet.Core/Adapter/MqttClientConnectedEventArgs.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace MQTTnet.Core.Adapter
+{
+    public class MqttClientConnectedEventArgs : EventArgs
+    {
+        public MqttClientConnectedEventArgs(string identifier, IMqttCommunicationAdapter clientAdapter)
+        {
+            Identifier = identifier ?? throw new ArgumentNullException(nameof(identifier));
+            ClientAdapter = clientAdapter ?? throw new ArgumentNullException(nameof(clientAdapter));
+        }
+
+        public string Identifier { get; }
+
+        public IMqttCommunicationAdapter ClientAdapter { get; }
+    }
+}

MQTTnet.Core/Adapter/MqttConnectingFailedException.cs

@@ -0,0 +1,16 @@
+using MQTTnet.Core.Exceptions;
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Adapter
+{
+    public class MqttConnectingFailedException : MqttCommunicationException
+    {
+        public MqttConnectingFailedException(MqttConnectReturnCode returnCode) 
+            : base($"Connecting with MQTT server failed ({returnCode}).")
+        {
+            ReturnCode = returnCode;
+        }
+
+        public MqttConnectReturnCode ReturnCode { get; }
+    }
+}

MQTTnet.Core/Channel/IMqttCommunicationChannel.cs

@@ -0,0 +1,16 @@
+using System.Threading.Tasks;
+using MQTTnet.Core.Client;
+
+namespace MQTTnet.Core.Channel
+{
+    public interface IMqttCommunicationChannel
+    {
+        Task ConnectAsync(MqttClientOptions options);
+
+        Task DisconnectAsync();
+
+        Task WriteAsync(byte[] buffer);
+
+        Task ReadAsync(byte[] buffer);
+    }
+}

MQTTnet.Core/Client/MqttClient.cs

@@ -0,0 +1,374 @@
+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using MQTTnet.Core.Adapter;
+using MQTTnet.Core.Diagnostics;
+using MQTTnet.Core.Exceptions;
+using MQTTnet.Core.Internal;
+using MQTTnet.Core.Packets;
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Client
+{
+    public class MqttClient
+    {
+        private readonly ConcurrentDictionary<ushort, MqttPublishPacket> _pendingExactlyOncePublishPackets = new ConcurrentDictionary<ushort, MqttPublishPacket>();
+        private readonly HashSet<ushort> _processedPublishPackets = new HashSet<ushort>();
+
+        private readonly MqttPacketDispatcher _packetDispatcher = new MqttPacketDispatcher();
+        private readonly MqttClientOptions _options;
+        private readonly IMqttCommunicationAdapter _adapter;
+
+        private int _latestPacketIdentifier;
+        private CancellationTokenSource _cancellationTokenSource;
+
+        public MqttClient(MqttClientOptions options, IMqttCommunicationAdapter adapter)
+        {
+            _options = options ?? throw new ArgumentNullException(nameof(options));
+            _adapter = adapter ?? throw new ArgumentNullException(nameof(adapter));
+        }
+
+        public event EventHandler Connected;
+
+        public event EventHandler Disconnected;
+
+        public event EventHandler<MqttApplicationMessageReceivedEventArgs> ApplicationMessageReceived;
+
+        public bool IsConnected { get; private set; }
+
+        public async Task ConnectAsync(MqttApplicationMessage willApplicationMessage = null)
+        {
+            MqttTrace.Verbose(nameof(MqttClient), "Trying to connect.");
+
+            if (IsConnected)
+            {
+                throw new MqttProtocolViolationException("It is not allowed to connect with a server after the connection is established.");
+            }
+
+            var connectPacket = new MqttConnectPacket
+            {
+                ClientId = _options.ClientId,
+                Username = _options.UserName,
+                Password = _options.Password,
+                KeepAlivePeriod = (ushort)_options.KeepAlivePeriod.TotalSeconds,
+                WillMessage = willApplicationMessage
+            };
+
+            await _adapter.ConnectAsync(_options, _options.DefaultCommunicationTimeout);
+            MqttTrace.Verbose(nameof(MqttClient), "Connection with server established.");
+
+            _cancellationTokenSource = new CancellationTokenSource();
+            _latestPacketIdentifier = 0;
+            _processedPublishPackets.Clear();
+            _packetDispatcher.Reset();
+            IsConnected = true;
+
+            Task.Run(async () => await ReceivePackets(_cancellationTokenSource.Token), _cancellationTokenSource.Token).Forget();
+
+            var response = await SendAndReceiveAsync<MqttConnAckPacket>(connectPacket);
+            if (response.ConnectReturnCode != MqttConnectReturnCode.ConnectionAccepted)
+            {
+                throw new MqttConnectingFailedException(response.ConnectReturnCode);
+            }
+
+            if (_options.KeepAlivePeriod != TimeSpan.Zero)
+            {
+                Task.Run(async () => await SendKeepAliveMessagesAsync(_cancellationTokenSource.Token), _cancellationTokenSource.Token).Forget();
+            }
+
+            Connected?.Invoke(this, EventArgs.Empty);
+        }
+
+        public async Task DisconnectAsync()
+        {
+            await SendAsync(new MqttDisconnectPacket());
+            await DisconnectInternalAsync();
+        }
+
+        public async Task<IList<MqttSubscribeResult>> SubscribeAsync(params TopicFilter[] topicFilters)
+        {
+            if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));
+
+            return await SubscribeAsync(topicFilters.ToList());
+        }
+
+        public async Task<IList<MqttSubscribeResult>> SubscribeAsync(IList<TopicFilter> topicFilters)
+        {
+            if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));
+            if (!topicFilters.Any()) throw new MqttProtocolViolationException("At least one topic filter must be set [MQTT-3.8.3-3].");
+            ThrowIfNotConnected();
+
+            var subscribePacket = new MqttSubscribePacket
+            {
+                PacketIdentifier = GetNewPacketIdentifier(),
+                TopicFilters = topicFilters
+            };
+
+            var response = await SendAndReceiveAsync<MqttSubAckPacket>(subscribePacket);
+
+            if (response.SubscribeReturnCodes.Count != topicFilters.Count)
+            {
+                throw new MqttProtocolViolationException("The return codes are not matching the topic filters [MQTT-3.9.3-1].");
+            }
+
+            var result = new List<MqttSubscribeResult>();
+            for (var i = 0; i < topicFilters.Count; i++)
+            {
+                result.Add(new MqttSubscribeResult(topicFilters[i], response.SubscribeReturnCodes[i]));
+            }
+
+            return result;
+        }
+
+        public async Task Unsubscribe(params string[] topicFilters)
+        {
+            if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));
+
+            await Unsubscribe(topicFilters.ToList());
+        }
+
+        public async Task Unsubscribe(IList<string> topicFilters)
+        {
+            if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));
+            if (!topicFilters.Any()) throw new MqttProtocolViolationException("At least one topic filter must be set [MQTT-3.10.3-2].");
+            ThrowIfNotConnected();
+
+            var unsubscribePacket = new MqttUnsubscribePacket
+            {
+                PacketIdentifier = GetNewPacketIdentifier(),
+                TopicFilters = topicFilters
+            };
+
+            await SendAndReceiveAsync<MqttUnsubAckPacket>(unsubscribePacket);
+        }
+
+        public async Task PublishAsync(MqttApplicationMessage applicationMessage)
+        {
+            if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
+            ThrowIfNotConnected();
+
+            var publishPacket = applicationMessage.ToPublishPacket();
+
+            if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
+            {
+                await SendAsync(publishPacket);
+            }
+            else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtLeastOnce)
+            {
+                publishPacket.PacketIdentifier = GetNewPacketIdentifier();
+                await SendAndReceiveAsync<MqttPubAckPacket>(publishPacket);
+            }
+            else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
+            {
+                publishPacket.PacketIdentifier = GetNewPacketIdentifier();
+                await SendAndReceiveAsync<MqttPubRecPacket>(publishPacket);
+                await SendAsync(publishPacket.CreateResponse<MqttPubCompPacket>());
+            }
+        }
+
+        private void ThrowIfNotConnected()
+        {
+            if (!IsConnected) throw new MqttCommunicationException("The client is not connected.");
+        }
+
+        private async Task DisconnectInternalAsync()
+        {
+            try
+            {
+                await _adapter.DisconnectAsync();
+            }
+            catch
+            {
+            }
+            finally
+            {
+                _cancellationTokenSource?.Cancel();
+                IsConnected = false;
+                Disconnected?.Invoke(this, EventArgs.Empty);
+            }
+        }
+
+        private async void ProcessReceivedPacket(MqttBasePacket mqttPacket)
+        {
+            try
+            {
+                if (mqttPacket is MqttPingReqPacket)
+                {
+                    await SendAsync(new MqttPingRespPacket());
+                    return;
+                }
+
+                if (mqttPacket is MqttDisconnectPacket)
+                {
+                    await DisconnectAsync();
+                    return;
+                }
+
+                var publishPacket = mqttPacket as MqttPublishPacket;
+                if (publishPacket != null)
+                {
+                    await ProcessReceivedPublishPacket(publishPacket);
+                    return;
+                }
+
+                var pubRelPacket = mqttPacket as MqttPubRelPacket;
+                if (pubRelPacket != null)
+                {
+                    await ProcessReceivedPubRelPacket(pubRelPacket);
+                    return;
+                }
+
+                _packetDispatcher.Dispatch(mqttPacket);
+            }
+            catch (Exception exception)
+            {
+                MqttTrace.Error(nameof(MqttClient), exception, "Error while processing received packet.");
+            }
+        }
+
+        private void FireApplicationMessageReceivedEvent(MqttPublishPacket publishPacket)
+        {
+            if (publishPacket.QualityOfServiceLevel != MqttQualityOfServiceLevel.AtMostOnce)
+            {
+                _processedPublishPackets.Add(publishPacket.PacketIdentifier);
+            }
+
+            var applicationMessage = new MqttApplicationMessage(
+                publishPacket.Topic,
+                publishPacket.Payload,
+                publishPacket.QualityOfServiceLevel,
+                publishPacket.Retain
+            );
+
+            ApplicationMessageReceived?.Invoke(this, new MqttApplicationMessageReceivedEventArgs(applicationMessage));
+        }
+
+        private async Task ProcessReceivedPublishPacket(MqttPublishPacket publishPacket)
+        {
+            if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
+            {
+                FireApplicationMessageReceivedEvent(publishPacket);
+            }
+            else
+            {
+                if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtLeastOnce)
+                {
+                    FireApplicationMessageReceivedEvent(publishPacket);
+                    await SendAsync(new MqttPubAckPacket { PacketIdentifier = publishPacket.PacketIdentifier });
+                }
+                else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
+                {
+                    _pendingExactlyOncePublishPackets[publishPacket.PacketIdentifier] = publishPacket;
+                    await SendAsync(new MqttPubRecPacket { PacketIdentifier = publishPacket.PacketIdentifier });
+                }
+            }
+        }
+
+        private async Task ProcessReceivedPubRelPacket(MqttPubRelPacket pubRelPacket)
+        {
+            MqttPublishPacket originalPublishPacket;
+            if (!_pendingExactlyOncePublishPackets.TryRemove(pubRelPacket.PacketIdentifier, out originalPublishPacket))
+            {
+                throw new MqttCommunicationException();
+            }
+
+            await SendAsync(originalPublishPacket.CreateResponse<MqttPubCompPacket>());
+
+            FireApplicationMessageReceivedEvent(originalPublishPacket);
+        }
+
+        private async Task SendAsync(MqttBasePacket packet)
+        {
+            await _adapter.SendPacketAsync(packet, _options.DefaultCommunicationTimeout);
+        }
+
+        private async Task<TResponsePacket> SendAndReceiveAsync<TResponsePacket>(MqttBasePacket requestPacket) where TResponsePacket : MqttBasePacket
+        {
+            Func<MqttBasePacket, bool> responsePacketSelector = p =>
+            {
+                var p1 = p as TResponsePacket;
+                if (p1 == null)
+                {
+                    return false;
+                }
+
+                var pi1 = requestPacket as IPacketWithIdentifier;
+                var pi2 = p as IPacketWithIdentifier;
+
+                if (pi1 != null && pi2 != null)
+                {
+                    if (pi1.PacketIdentifier != pi2.PacketIdentifier)
+                    {
+                        return false;
+                    }
+                }
+
+                return true;
+            };
+
+            await _adapter.SendPacketAsync(requestPacket, _options.DefaultCommunicationTimeout);
+            return (TResponsePacket)await _packetDispatcher.WaitForPacketAsync(responsePacketSelector, _options.DefaultCommunicationTimeout);
+        }
+
+        private ushort GetNewPacketIdentifier()
+        {
+            return (ushort)Interlocked.Increment(ref _latestPacketIdentifier);
+        }
+
+        private async Task SendKeepAliveMessagesAsync(CancellationToken cancellationToken)
+        {
+            MqttTrace.Information(nameof(MqttClient), "Start sending keep alive packets.");
+
+            try
+            {
+                while (!cancellationToken.IsCancellationRequested)
+                {
+                    await Task.Delay(_options.KeepAlivePeriod, cancellationToken);
+                    await SendAndReceiveAsync<MqttPingRespPacket>(new MqttPingReqPacket());
+                }
+            }
+            catch (MqttCommunicationException)
+            {
+            }
+            catch (Exception exception)
+            {
+                MqttTrace.Warning(nameof(MqttClient), exception, "Error while sending/receiving keep alive packets.");
+            }
+            finally
+            {
+                MqttTrace.Information(nameof(MqttClient), "Stopped sending keep alive packets.");
+                await DisconnectInternalAsync();
+            }
+        }
+
+        private async Task ReceivePackets(CancellationToken cancellationToken)
+        {
+            MqttTrace.Information(nameof(MqttClient), "Start receiving packets.");
+            try
+            {
+                while (!cancellationToken.IsCancellationRequested)
+                {
+                    var mqttPacket = await _adapter.ReceivePacketAsync(TimeSpan.Zero);
+                    MqttTrace.Information(nameof(MqttClient), $"Received <<< {mqttPacket}");
+
+                    Task.Run(() => ProcessReceivedPacket(mqttPacket), cancellationToken).Forget();
+                }
+            }
+            catch (MqttCommunicationException)
+            {
+            }
+            catch (Exception exception)
+            {
+                MqttTrace.Error(nameof(MqttClient), exception, "Error while receiving packets.");
+            }
+            finally
+            {
+                MqttTrace.Information(nameof(MqttClient), "Stopped receiving packets.");
+                await DisconnectInternalAsync();
+            }
+        }
+    }
+}

MQTTnet.Core/Client/MqttClientOptions.cs

@@ -0,0 +1,21 @@
+using System;
+
+namespace MQTTnet.Core.Client
+{
+    public class MqttClientOptions
+    {
+        public string Server { get; set; }
+
+        public int Port { get; set; } = 1883;
+
+        public string UserName { get; set; }
+
+        public string Password { get; set; }
+
+        public string ClientId { get; set; } = Guid.NewGuid().ToString().Replace("-", string.Empty);
+
+        public TimeSpan KeepAlivePeriod { get; set; } = TimeSpan.FromSeconds(5);
+
+        public TimeSpan DefaultCommunicationTimeout { get; set; } = TimeSpan.FromSeconds(10);
+    }
+}

MQTTnet.Core/Client/MqttPacketAwaiter.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Threading.Tasks;
+using MQTTnet.Core.Packets;
+
+namespace MQTTnet.Core.Client
+{
+    public class MqttPacketAwaiter : TaskCompletionSource<MqttBasePacket>
+    {
+        public MqttPacketAwaiter(Func<MqttBasePacket, bool> packetSelector)
+        {
+            PacketSelector = packetSelector ?? throw new ArgumentNullException(nameof(packetSelector));
+        }
+
+        public Func<MqttBasePacket, bool> PacketSelector { get; }
+    }
+}

MQTTnet.Core/Client/MqttPacketDispatcher.cs

@@ -0,0 +1,112 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using MQTTnet.Core.Diagnostics;
+using MQTTnet.Core.Exceptions;
+using MQTTnet.Core.Packets;
+
+namespace MQTTnet.Core.Client
+{
+    public class MqttPacketDispatcher
+    {
+        private readonly object _syncRoot = new object();
+        private readonly List<MqttBasePacket> _receivedPackets = new List<MqttBasePacket>();
+        private readonly List<MqttPacketAwaiter> _packetAwaiters = new List<MqttPacketAwaiter>();
+
+        public async Task<MqttBasePacket> WaitForPacketAsync(Func<MqttBasePacket, bool> selector, TimeSpan timeout)
+        {
+            if (selector == null) throw new ArgumentNullException(nameof(selector));
+
+            var packetAwaiter = AddPacketAwaiter(selector);
+            DispatchPendingPackets();
+
+            var hasTimeout = await Task.WhenAny(Task.Delay(timeout), packetAwaiter.Task) != packetAwaiter.Task;
+            RemovePacketAwaiter(packetAwaiter);
+
+            if (hasTimeout)
+            {
+                MqttTrace.Warning(nameof(MqttPacketDispatcher), "Timeout while waiting for packet.");
+                throw new MqttCommunicationTimedOutException();
+            }
+
+            return packetAwaiter.Task.Result;
+        }
+
+        public void Dispatch(MqttBasePacket packet)
+        {
+            if (packet == null) throw new ArgumentNullException(nameof(packet));
+
+            var packetDispatched = false;
+            foreach (var packetAwaiter in GetPacketAwaiters())
+            {
+                if (packetAwaiter.PacketSelector(packet))
+                {
+                    packetAwaiter.SetResult(packet);
+                    packetDispatched = true;
+                    break;
+                }
+            }
+
+            lock (_syncRoot)
+            {
+                if (!packetDispatched)
+                {
+                    _receivedPackets.Add(packet);
+                }
+                else
+                {
+                    _receivedPackets.Remove(packet);
+                }
+            }
+        }
+
+        public void Reset()
+        {
+            lock (_syncRoot)
+            {
+                _packetAwaiters.Clear();
+                _receivedPackets.Clear();
+            }
+        }
+
+        private List<MqttPacketAwaiter> GetPacketAwaiters()
+        {
+            lock (_packetAwaiters)
+            {
+                return new List<MqttPacketAwaiter>(_packetAwaiters);
+            }
+        }
+
+        private MqttPacketAwaiter AddPacketAwaiter(Func<MqttBasePacket, bool> selector)
+        {
+            lock (_syncRoot)
+            {
+                var packetAwaiter = new MqttPacketAwaiter(selector);
+                _packetAwaiters.Add(packetAwaiter);
+                return packetAwaiter;
+            }
+        }
+
+        private void RemovePacketAwaiter(MqttPacketAwaiter packetAwaiter)
+        {
+            lock (_syncRoot)
+            {
+                _packetAwaiters.Remove(packetAwaiter);
+            }
+        }
+
+        private void DispatchPendingPackets()
+        {
+            List<MqttBasePacket> receivedPackets;
+            lock (_syncRoot)
+            {
+                receivedPackets = new List<MqttBasePacket>(_receivedPackets);
+            }
+
+            foreach (var pendingPacket in receivedPackets)
+            {
+                Dispatch(pendingPacket);
+            }
+        }
+    }
+}

MQTTnet.Core/Client/MqttSubscribeResult.cs

@@ -0,0 +1,18 @@
+using MQTTnet.Core.Packets;
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Client
+{
+    public class MqttSubscribeResult
+    {
+        public MqttSubscribeResult(TopicFilter topicFilter, MqttSubscribeReturnCode returnCode)
+        {
+            TopicFilter = topicFilter;
+            ReturnCode = returnCode;
+        }
+
+        public TopicFilter TopicFilter { get; }
+
+        public MqttSubscribeReturnCode ReturnCode { get; }
+    }
+}

MQTTnet.Core/Diagnostics/MqttTrace.cs

@@ -0,0 +1,44 @@
+using System;
+
+namespace MQTTnet.Core.Diagnostics
+{
+    public static class MqttTrace
+    {
+        public static event EventHandler<MqttTraceMessagePublishedEventArgs> TraceMessagePublished;
+
+        public static void Verbose(string source, string message)
+        {
+            Publish(source, MqttTraceLevel.Verbose, null, message);
+        }
+
+        public static void Information(string source, string message)
+        {
+            Publish(source, MqttTraceLevel.Information, null, message);
+        }
+
+        public static void Warning(string source, string message)
+        {
+            Publish(source, MqttTraceLevel.Warning, null, message);
+        }
+
+        public static void Warning(string source, Exception exception, string message)
+        {
+            Publish(source, MqttTraceLevel.Warning, exception, message);
+        }
+
+        public static void Error(string source, string message)
+        {
+            Publish(source, MqttTraceLevel.Error, null, message);
+        }
+
+        public static void Error(string source, Exception exception, string message)
+        {
+            Publish(source, MqttTraceLevel.Error, exception, message);
+        }
+
+        private static void Publish(string source, MqttTraceLevel traceLevel, Exception exception, string message)
+        {
+            TraceMessagePublished?.Invoke(null, new MqttTraceMessagePublishedEventArgs(Environment.CurrentManagedThreadId, source, traceLevel, message, exception));
+        }
+    }
+}

MQTTnet.Core/Diagnostics/MqttTraceLevel.cs

@@ -0,0 +1,10 @@
+namespace MQTTnet.Core.Diagnostics
+{
+    public enum  MqttTraceLevel
+    {
+        Verbose,
+        Information,
+        Warning,
+        Error
+    }
+}

MQTTnet.Core/Diagnostics/MqttTraceMessagePublishedEventArgs.cs

@@ -0,0 +1,26 @@
+using System;
+
+namespace MQTTnet.Core.Diagnostics
+{
+    public class MqttTraceMessagePublishedEventArgs : EventArgs
+    {
+        public MqttTraceMessagePublishedEventArgs(int threadId, string source, MqttTraceLevel level, string message, Exception exception)
+        {
+            ThreadId = threadId;
+            Source = source;
+            Level = level;
+            Message = message;
+            Exception = exception;
+        }
+
+        public int ThreadId { get; }
+
+        public string Source { get; }
+
+        public MqttTraceLevel Level { get; }
+
+        public string Message { get; }
+
+        public Exception Exception { get; }
+    }
+}

MQTTnet.Core/Exceptions/MqttCommunicationException.cs

@@ -0,0 +1,21 @@
+using System;
+
+namespace MQTTnet.Core.Exceptions
+{
+    public class MqttCommunicationException : Exception
+    {
+        public MqttCommunicationException()
+        {
+        }
+
+        public MqttCommunicationException(Exception innerException)
+            : base(innerException.Message, innerException)
+        {
+        }
+
+        public MqttCommunicationException(string message)
+            : base(message)
+        {
+        }
+    }
+}

MQTTnet.Core/Exceptions/MqttCommunicationTimedOutException.cs

@@ -0,0 +1,6 @@
+namespace MQTTnet.Core.Exceptions
+{
+    public class MqttCommunicationTimedOutException : MqttCommunicationException
+    {
+    }
+}

MQTTnet.Core/Exceptions/MqttProtocolViolationException.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace MQTTnet.Core.Exceptions
+{
+    public class MqttProtocolViolationException : Exception
+    {
+        public MqttProtocolViolationException(string message) 
+            : base(message)
+        {
+        }
+    }
+}

MQTTnet.Core/Internal/MqttApplicationMessageExtensions.cs

@@ -0,0 +1,24 @@
+using MQTTnet.Core.Packets;
+
+namespace MQTTnet.Core.Internal
+{
+    internal static class MqttApplicationMessageExtensions
+    {
+        public static MqttPublishPacket ToPublishPacket(this MqttApplicationMessage applicationMessage)
+        {
+            if (applicationMessage == null)
+            {
+                return null;
+            }
+
+            return new MqttPublishPacket
+            {
+                Topic = applicationMessage.Topic,
+                Payload = applicationMessage.Payload,
+                QualityOfServiceLevel = applicationMessage.QualityOfServiceLevel,
+                Retain = applicationMessage.Retain,
+                Dup = false
+            };
+        }
+    }
+}

MQTTnet.Core/Internal/TaskExtensions.cs

@@ -0,0 +1,11 @@
+using System.Threading.Tasks;
+
+namespace MQTTnet.Core.Internal
+{
+    internal static class TaskExtensions
+    {
+        public static void Forget(this Task task)
+        {
+        }
+    }
+}

MQTTnet.Core/MQTTnet.Core.csproj

@@ -0,0 +1,107 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
+  <PropertyGroup>
+    <MinimumVisualStudioVersion>10.0</MinimumVisualStudioVersion>
+    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
+    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
+    <ProjectGuid>{99C884F3-B4B9-417D-AA92-DC7DD1C4CFEE}</ProjectGuid>
+    <OutputType>Library</OutputType>
+    <AppDesignerFolder>Properties</AppDesignerFolder>
+    <RootNamespace>MQTTnet.Core</RootNamespace>
+    <AssemblyName>MQTTnet.Core</AssemblyName>
+    <DefaultLanguage>en-US</DefaultLanguage>
+    <FileAlignment>512</FileAlignment>
+    <ProjectTypeGuids>{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
+    <TargetFrameworkProfile>Profile111</TargetFrameworkProfile>
+    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
+    <DebugSymbols>true</DebugSymbols>
+    <DebugType>full</DebugType>
+    <Optimize>false</Optimize>
+    <OutputPath>bin\Debug\</OutputPath>
+    <DefineConstants>DEBUG;TRACE</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <WarningLevel>4</WarningLevel>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
+    <DebugType>pdbonly</DebugType>
+    <Optimize>true</Optimize>
+    <OutputPath>bin\Release\</OutputPath>
+    <DefineConstants>TRACE</DefineConstants>
+    <ErrorReport>prompt</ErrorReport>
+    <WarningLevel>4</WarningLevel>
+  </PropertyGroup>
+  <ItemGroup>
+    <!-- A reference to the entire .NET Framework is automatically included -->
+  </ItemGroup>
+  <ItemGroup>
+    <Compile Include="Adapter\IMqttCommunicationAdapter.cs" />
+    <Compile Include="Adapter\IMqttServerAdapter.cs" />
+    <Compile Include="Adapter\MqttClientConnectedEventArgs.cs" />
+    <Compile Include="Adapter\MqttConnectingFailedException.cs" />
+    <Compile Include="Adapter\MqttChannelCommunicationAdapter.cs" />
+    <Compile Include="Channel\IMqttCommunicationChannel.cs" />
+    <Compile Include="Client\MqttPacketDispatcher.cs" />
+    <Compile Include="Client\MqttSubscribeResult.cs" />
+    <Compile Include="Client\MqttPacketAwaiter.cs" />
+    <Compile Include="Diagnostics\MqttTrace.cs" />
+    <Compile Include="Diagnostics\MqttTraceLevel.cs" />
+    <Compile Include="Diagnostics\MqttTraceMessagePublishedEventArgs.cs" />
+    <Compile Include="Exceptions\MqttCommunicationException.cs" />
+    <Compile Include="Exceptions\MqttCommunicationTimedOutException.cs" />
+    <Compile Include="Exceptions\MqttProtocolViolationException.cs" />
+    <Compile Include="Internal\MqttApplicationMessageExtensions.cs" />
+    <Compile Include="MqttApplicationMessageReceivedEventArgs.cs" />
+    <Compile Include="Packets\IPacketWithPacketIdentifier.cs" />
+    <Compile Include="Packets\MqttConnAckPacket.cs" />
+    <Compile Include="Packets\MqttBasePacket.cs" />
+    <Compile Include="Packets\MqttConnectPacket.cs" />
+    <Compile Include="Packets\MqttDisconnectPacket.cs" />
+    <Compile Include="MqttApplicationMessage.cs" />
+    <Compile Include="Client\MqttClient.cs" />
+    <Compile Include="Client\MqttClientOptions.cs" />
+    <Compile Include="Packets\MqttPingReqPacket.cs" />
+    <Compile Include="Packets\MqttPubCompPacket.cs" />
+    <Compile Include="Packets\MqttBasePublishPacket.cs" />
+    <Compile Include="Packets\MqttUnsubAckPacket.cs" />
+    <Compile Include="Packets\MqttSubAckPacket.cs" />
+    <Compile Include="Packets\MqttPubRelPacket.cs" />
+    <Compile Include="Packets\MqttPingRespPacket.cs" />
+    <Compile Include="Packets\MqttPubAckPacket.cs" />
+    <Compile Include="Packets\MqttPublishPacket.cs" />
+    <Compile Include="Packets\MqttPubRecPacket.cs" />
+    <Compile Include="Packets\MqttUnsubscribe.cs" />
+    <Compile Include="Packets\MqttSubscribePacket.cs" />
+    <Compile Include="Packets\TopicFilter.cs" />
+    <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="Protocol\MqttConnectReturnCode.cs" />
+    <Compile Include="Protocol\MqttControlPacketType.cs" />
+    <Compile Include="Protocol\MqttQualityOfServiceLevel.cs" />
+    <Compile Include="Protocol\MqttSubscribeReturnCode.cs" />
+    <Compile Include="Serializer\ByteReader.cs" />
+    <Compile Include="Serializer\ByteWriter.cs" />
+    <Compile Include="Serializer\DefaultMqttV311PacketSerializer.cs" />
+    <Compile Include="Serializer\IMqttPacketSerializer.cs" />
+    <Compile Include="Serializer\MqttPacketReader.cs" />
+    <Compile Include="Serializer\MqttPacketWriter.cs" />
+    <Compile Include="Server\MqttClientSession.cs" />
+    <Compile Include="Server\MqttClientSessionManager.cs" />
+    <Compile Include="Server\MqttOutgoingPublicationsManager.cs" />
+    <Compile Include="Server\MqttServer.cs" />
+    <Compile Include="Server\MqttServerOptions.cs" />
+    <Compile Include="Server\MqttClientPublishPacketContext.cs" />
+    <Compile Include="Server\MqttTopicFilterComparer.cs" />
+    <Compile Include="Server\MqttClientSubscriptionsManager.cs" />
+    <Compile Include="Internal\TaskExtensions.cs" />
+  </ItemGroup>
+  <Import Project="$(MSBuildExtensionsPath32)\Microsoft\Portable\$(TargetFrameworkVersion)\Microsoft.Portable.CSharp.targets" />
+  <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
+       Other similar extension points exist, see Microsoft.Common.targets.
+  <Target Name="BeforeBuild">
+  </Target>
+  <Target Name="AfterBuild">
+  </Target>
+  -->
+</Project>

MQTTnet.Core/MqttApplicationMessage.cs

@@ -0,0 +1,24 @@
+using System;
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core
+{
+    public class MqttApplicationMessage
+    {
+        public MqttApplicationMessage(string topic, byte[] payload, MqttQualityOfServiceLevel qualityOfServiceLevel, bool retain)
+        {
+            Topic = topic ?? throw new ArgumentNullException(nameof(topic));
+            Payload = payload ?? throw new ArgumentNullException(nameof(payload));
+            QualityOfServiceLevel = qualityOfServiceLevel;
+            Retain = retain;
+        }
+
+        public string Topic { get; }
+
+        public byte[] Payload { get; }
+
+        public MqttQualityOfServiceLevel QualityOfServiceLevel { get; }
+
+        public bool Retain { get; }
+    }
+}

MQTTnet.Core/MqttApplicationMessageReceivedEventArgs.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace MQTTnet.Core
+{
+    public class MqttApplicationMessageReceivedEventArgs : EventArgs
+    {
+        public MqttApplicationMessageReceivedEventArgs(MqttApplicationMessage applicationMessage)
+        {
+            ApplicationMessage = applicationMessage ?? throw new ArgumentNullException(nameof(applicationMessage));
+        }
+
+        public MqttApplicationMessage ApplicationMessage { get; }
+    }
+}

MQTTnet.Core/Packets/IPacketWithPacketIdentifier.cs

@@ -0,0 +1,7 @@
+namespace MQTTnet.Core.Packets
+{
+    public interface IPacketWithIdentifier
+    {
+        ushort PacketIdentifier { get; set; }
+    }
+}

MQTTnet.Core/Packets/MqttBasePacket.cs

@@ -0,0 +1,25 @@
+using System;
+
+namespace MQTTnet.Core.Packets
+{
+    public abstract class MqttBasePacket
+    {
+        public TResponsePacket CreateResponse<TResponsePacket>()
+        {
+            var responsePacket = Activator.CreateInstance<TResponsePacket>();
+            var responsePacketWithIdentifier = responsePacket as IPacketWithIdentifier;
+            if (responsePacketWithIdentifier != null)
+            {
+                var requestPacketWithIdentifier = this as IPacketWithIdentifier;
+                if (requestPacketWithIdentifier == null)
+                {
+                    throw new InvalidOperationException("Response packet has PacketIdentifier but request packet does not.");
+                }
+
+                responsePacketWithIdentifier.PacketIdentifier = requestPacketWithIdentifier.PacketIdentifier;
+            }
+
+            return responsePacket;
+        }
+    }
+}

MQTTnet.Core/Packets/MqttBasePublishPacket.cs

@@ -0,0 +1,7 @@
+namespace MQTTnet.Core.Packets
+{
+    public class MqttBasePublishPacket : MqttBasePacket, IPacketWithIdentifier
+    {
+        public ushort PacketIdentifier { get; set; }
+    }
+}

MQTTnet.Core/Packets/MqttConnAckPacket.cs

@@ -0,0 +1,16 @@
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Packets
+{
+    public class MqttConnAckPacket : MqttBasePacket
+    {
+        public bool IsSessionPresent { get; set; }
+
+        public MqttConnectReturnCode ConnectReturnCode { get; set; }
+
+        public override string ToString()
+        {
+            return $"{nameof(MqttConnAckPacket)}: [ConnectReturnCode={ConnectReturnCode}] [IsSessionPresent={IsSessionPresent}]";
+        }
+    }
+}

MQTTnet.Core/Packets/MqttConnectPacket.cs

@@ -0,0 +1,22 @@
+namespace MQTTnet.Core.Packets
+{
+    public class MqttConnectPacket: MqttBasePacket
+    {
+        public string ClientId { get; set; }
+
+        public string Username { get; set; }
+
+        public string Password { get; set; }
+
+        public ushort KeepAlivePeriod { get; set; }
+
+        public bool CleanSession { get; set; }
+
+        public MqttApplicationMessage WillMessage { get; set; }
+
+        public override string ToString()
+        {
+            return $"{nameof(MqttConnectPacket)} [ClientId={ClientId}] [Username={Username}] [Password={Password}] [KeepAlivePeriod={KeepAlivePeriod}] [CleanSession={CleanSession}]";
+        }
+    }
+}

MQTTnet.Core/Packets/MqttDisconnectPacket.cs

@@ -0,0 +1,6 @@
+namespace MQTTnet.Core.Packets
+{
+    public class MqttDisconnectPacket : MqttBasePacket
+    {
+    }
+}

MQTTnet.Core/Packets/MqttPingReqPacket.cs

@@ -0,0 +1,10 @@
+namespace MQTTnet.Core.Packets
+{
+    public class MqttPingReqPacket : MqttBasePacket
+    {
+        public override string ToString()
+        {
+            return nameof(MqttPingReqPacket);
+        }
+    }
+}

MQTTnet.Core/Packets/MqttPingRespPacket.cs

@@ -0,0 +1,10 @@
+namespace MQTTnet.Core.Packets
+{
+    public class MqttPingRespPacket : MqttBasePacket
+    {
+        public override string ToString()
+        {
+            return nameof(MqttPingRespPacket);
+        }
+    }
+}

MQTTnet.Core/Packets/MqttPubAckPacket.cs

@@ -0,0 +1,6 @@
+namespace MQTTnet.Core.Packets
+{
+    public class MqttPubAckPacket : MqttBasePublishPacket
+    {
+    }
+}

MQTTnet.Core/Packets/MqttPubCompPacket.cs

@@ -0,0 +1,6 @@
+namespace MQTTnet.Core.Packets
+{
+    public class MqttPubCompPacket : MqttBasePublishPacket
+    {
+    }
+}

MQTTnet.Core/Packets/MqttPubRecPacket.cs

@@ -0,0 +1,6 @@
+namespace MQTTnet.Core.Packets
+{
+    public class MqttPubRecPacket : MqttBasePublishPacket
+    {
+    }
+}

MQTTnet.Core/Packets/MqttPubRelPacket.cs

@@ -0,0 +1,6 @@
+namespace MQTTnet.Core.Packets
+{
+    public class MqttPubRelPacket : MqttBasePublishPacket
+    {
+    }
+}

MQTTnet.Core/Packets/MqttPublishPacket.cs

@@ -0,0 +1,24 @@
+using System.Text;
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Packets
+{
+    public class MqttPublishPacket : MqttBasePublishPacket
+    {
+        public bool Retain { get; set; }
+
+        public MqttQualityOfServiceLevel QualityOfServiceLevel { get; set; }
+
+        public bool Dup { get; set; }
+
+        public string Topic { get; set; }
+
+        public byte[] Payload { get; set; }
+
+        public override string ToString()
+        {
+            return
+                $"{nameof(MqttPublishPacket)} [Topic={Topic}] [Payload={Encoding.UTF8.GetString(Payload, 0, Payload.Length)}] [QoSLevel={QualityOfServiceLevel}] [Dup={Dup}] [Retain={Retain}] [PacketIdentifier={PacketIdentifier}]";
+        }
+    }
+}

MQTTnet.Core/Packets/MqttSubAckPacket.cs

@@ -0,0 +1,20 @@
+using System.Collections.Generic;
+using System.Linq;
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Packets
+{
+    public class MqttSubAckPacket : MqttBasePacket, IPacketWithIdentifier
+    {
+        public ushort PacketIdentifier { get; set; }
+
+        public IList<MqttSubscribeReturnCode> SubscribeReturnCodes { get; set; } = new List<MqttSubscribeReturnCode>();
+
+        public override string ToString()
+        {
+            var subscribeReturnCodesText = string.Join(",", SubscribeReturnCodes.Select(f => f.ToString()));
+            return
+                $"{nameof(MqttSubAckPacket)} [PacketIdentifier={PacketIdentifier}] [SubscribeReturnCodes={subscribeReturnCodesText}]";
+        }
+    }
+}

MQTTnet.Core/Packets/MqttSubscribePacket.cs

@@ -0,0 +1,19 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace MQTTnet.Core.Packets
+{
+    public class MqttSubscribePacket : MqttBasePacket, IPacketWithIdentifier
+    {
+        public ushort PacketIdentifier { get; set; }
+        
+        public IList<TopicFilter> TopicFilters { get; set; } = new List<TopicFilter>();
+
+        public override string ToString()
+        {
+            var topicFiltersText = string.Join(",", TopicFilters.Select(f => $"{f.Topic}@{f.QualityOfServiceLevel}"));
+            return
+                $"{nameof(MqttSubscribePacket)} [PacketIdentifier={PacketIdentifier}] [TopicFilters={topicFiltersText}]";
+        }
+    }
+}

MQTTnet.Core/Packets/MqttUnsubAckPacket.cs

@@ -0,0 +1,7 @@
+namespace MQTTnet.Core.Packets
+{
+    public class MqttUnsubAckPacket : MqttBasePacket, IPacketWithIdentifier
+    {
+        public ushort PacketIdentifier { get; set; }
+    }
+}

MQTTnet.Core/Packets/MqttUnsubscribe.cs

@@ -0,0 +1,11 @@
+using System.Collections.Generic;
+
+namespace MQTTnet.Core.Packets
+{
+    public class MqttUnsubscribePacket : MqttBasePacket, IPacketWithIdentifier
+    {
+        public ushort PacketIdentifier { get; set; }
+        
+        public IList<string> TopicFilters { get; set; } = new List<string>();
+    }
+}

MQTTnet.Core/Packets/TopicFilter.cs

@@ -0,0 +1,17 @@
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Packets
+{
+    public class TopicFilter
+    {
+        public TopicFilter(string topic, MqttQualityOfServiceLevel qualityOfServiceLevel)
+        {
+            Topic = topic;
+            QualityOfServiceLevel = qualityOfServiceLevel;
+        }
+
+        public string Topic { get; }
+
+        public MqttQualityOfServiceLevel QualityOfServiceLevel { get; }
+    }
+}

MQTTnet.Core/Properties/AssemblyInfo.cs

@@ -0,0 +1,15 @@
+using System.Reflection;
+using System.Runtime.InteropServices;
+
+[assembly: AssemblyTitle("MQTTnet")]
+[assembly: AssemblyDescription("The core library of MQTTnet")]
+[assembly: AssemblyConfiguration("")]
+[assembly: AssemblyCompany("Christian Kratky")]
+[assembly: AssemblyProduct("MQTTnet")]
+[assembly: AssemblyCopyright("Copyright © Christian Kratky 2016-2017")]
+[assembly: AssemblyTrademark("")]
+[assembly: AssemblyCulture("")]
+[assembly: ComVisible(false)]
+[assembly: Guid("0e10d0ea-8e4b-4903-ab9e-93a187d07922")]
+[assembly: AssemblyVersion("2.1.0.4")]
+[assembly: AssemblyFileVersion("2.1.0.4")]

MQTTnet.Core/Protocol/MqttConnectReturnCode.cs

@@ -0,0 +1,12 @@
+namespace MQTTnet.Core.Protocol
+{
+    public enum MqttConnectReturnCode
+    {
+        ConnectionAccepted = 0x00,
+        ConnectionRefusedUnacceptableProtocolVersion = 0x01,
+        ConnectionRefusedIdentifierRejected = 0x02,
+        ConnectionRefusedServerUnavailable = 0x03,
+        ConnectionRefusedBadUsernameOrPassword = 0x04,
+        ConnectionRefusedNotAuthorized = 0x05
+    }
+}

MQTTnet.Core/Protocol/MqttControlPacketType.cs

@@ -0,0 +1,20 @@
+namespace MQTTnet.Core.Protocol
+{
+    public enum MqttControlPacketType
+    {
+        Connect = 1,
+        ConnAck = 2,
+        Publish = 3,
+        PubAck = 4,
+        PubRec = 5,
+        PubRel = 6,
+        PubComp = 7,
+        Subscribe = 8,
+        SubAck = 9,
+        Unsubscibe = 10,
+        UnsubAck = 11,
+        PingReq = 12,
+        PingResp = 13,
+        Disconnect = 14
+    }
+}

MQTTnet.Core/Protocol/MqttQualityOfServiceLevel.cs

@@ -0,0 +1,9 @@
+namespace MQTTnet.Core.Protocol
+{
+    public enum MqttQualityOfServiceLevel
+    {
+        AtMostOnce = 0x00,
+        AtLeastOnce = 0x01,
+        ExactlyOnce = 0x02
+    }
+}

MQTTnet.Core/Protocol/MqttSubscribeReturnCode.cs

@@ -0,0 +1,10 @@
+namespace MQTTnet.Core.Protocol
+{
+    public enum MqttSubscribeReturnCode
+    {
+        SuccessMaximumQoS0 = 0x00,
+        SuccessMaximumQoS1 = 0x01,
+        SuccessMaximumQoS2 = 0x02,
+        Failure = 0x80
+    }
+}

MQTTnet.Core/Serializer/ByteReader.cs

@@ -0,0 +1,42 @@
+using System;
+
+namespace MQTTnet.Core.Serializer
+{
+    public class ByteReader
+    {
+        private int _index;
+        private readonly int _byte;
+
+        public ByteReader(byte @byte)
+        {
+            _byte = @byte;
+        }
+
+        public bool Read()
+        {
+            if (_index >= 8)
+            {
+                throw new InvalidOperationException("End of the byte reached.");
+            }
+
+            var result = ((1 << _index) & _byte) > 0;
+            _index++;
+
+            return result;
+        }
+
+        public byte Read(int count)
+        {
+            var result = 0;
+            for (var i = 0; i < count; i++)
+            {
+                if (Read())
+                {
+                    result |= 1 << i;
+                }
+            }
+
+            return (byte)result;
+        }
+    }
+}

MQTTnet.Core/Serializer/ByteWriter.cs

@@ -0,0 +1,36 @@
+using System;
+
+namespace MQTTnet.Core.Serializer
+{
+    public class ByteWriter
+    {
+        private int _index;
+        private int _byte;
+
+        public byte Value => (byte)_byte;
+
+        public void Write(byte @byte, int count)
+        {
+            for (var i = 0; i < count; i++)
+            {
+                var value = ((1 << i) & @byte) > 0;
+                Write(value);
+            }
+        }
+
+        public void Write(bool bit)
+        {
+            if (_index >= 8)
+            {
+                throw new InvalidOperationException("End of the byte reached.");
+            }
+
+            if (bit)
+            {
+                _byte |= 1 << _index;
+            }
+
+            _index++;
+        }
+    }
+}

MQTTnet.Core/Serializer/DefaultMqttV311PacketSerializer.cs

@@ -0,0 +1,632 @@
+using System;
+using System.Linq;
+using System.Net;
+using System.Text;
+using System.Text.RegularExpressions;
+using System.Threading.Tasks;
+using MQTTnet.Core.Channel;
+using MQTTnet.Core.Exceptions;
+using MQTTnet.Core.Packets;
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Serializer
+{
+    public class DefaultMqttV311PacketSerializer : IMqttPacketSerializer
+    {
+        public async Task SerializeAsync(MqttBasePacket packet, IMqttCommunicationChannel destination)
+        {
+            if (packet == null) throw new ArgumentNullException(nameof(packet));
+            if (destination == null) throw new ArgumentNullException(nameof(destination));
+
+            var connectPacket = packet as MqttConnectPacket;
+            if (connectPacket != null)
+            {
+                await SerializeAsync(connectPacket, destination);
+                return;
+            }
+
+            var connAckPacket = packet as MqttConnAckPacket;
+            if (connAckPacket != null)
+            {
+                await SerializeAsync(connAckPacket, destination);
+                return;
+            }
+
+            var disconnectPacket = packet as MqttDisconnectPacket;
+            if (disconnectPacket != null)
+            {
+                await SerializeAsync(disconnectPacket, destination);
+                return;
+            }
+
+            var pingReqPacket = packet as MqttPingReqPacket;
+            if (pingReqPacket != null)
+            {
+                await SerializeAsync(pingReqPacket, destination);
+                return;
+            }
+
+            var pingRespPacket = packet as MqttPingRespPacket;
+            if (pingRespPacket != null)
+            {
+                await SerializeAsync(pingRespPacket, destination);
+                return;
+            }
+
+            var publishPacket = packet as MqttPublishPacket;
+            if (publishPacket != null)
+            {
+                await SerializeAsync(publishPacket, destination);
+                return;
+            }
+
+            var pubAckPacket = packet as MqttPubAckPacket;
+            if (pubAckPacket != null)
+            {
+                await SerializeAsync(pubAckPacket, destination);
+                return;
+            }
+
+            var pubRecPacket = packet as MqttPubRecPacket;
+            if (pubRecPacket != null)
+            {
+                await SerializeAsync(pubRecPacket, destination);
+                return;
+            }
+
+            var pubRelPacket = packet as MqttPubRelPacket;
+            if (pubRelPacket != null)
+            {
+                await SerializeAsync(pubRelPacket, destination);
+                return;
+            }
+
+            var pubCompPacket = packet as MqttPubCompPacket;
+            if (pubCompPacket != null)
+            {
+                await SerializeAsync(pubCompPacket, destination);
+                return;
+            }
+
+            var subscribePacket = packet as MqttSubscribePacket;
+            if (subscribePacket != null)
+            {
+                await SerializeAsync(subscribePacket, destination);
+                return;
+            }
+
+            var subAckPacket = packet as MqttSubAckPacket;
+            if (subAckPacket != null)
+            {
+                await SerializeAsync(subAckPacket, destination);
+                return;
+            }
+
+            var unsubscribePacket = packet as MqttUnsubscribePacket;
+            if (unsubscribePacket != null)
+            {
+                await SerializeAsync(unsubscribePacket, destination);
+                return;
+            }
+
+            var unsubAckPacket = packet as MqttUnsubAckPacket;
+            if (unsubAckPacket != null)
+            {
+                await SerializeAsync(unsubAckPacket, destination);
+                return;
+            }
+
+            throw new MqttProtocolViolationException("Packet type invalid.");
+        }
+
+        public async Task<MqttBasePacket> DeserializeAsync(IMqttCommunicationChannel source)
+        {
+            if (source == null) throw new ArgumentNullException(nameof(source));
+
+            using (var mqttPacketReader = new MqttPacketReader(source))
+            {
+                await mqttPacketReader.ReadToEndAsync();
+
+                switch (mqttPacketReader.ControlPacketType)
+                {
+                    case MqttControlPacketType.Connect:
+                        {
+                            return await DeserializeConnectAsync(mqttPacketReader);
+                        }
+
+                    case MqttControlPacketType.ConnAck:
+                        {
+                            return await DeserializeConnAck(mqttPacketReader);
+                        }
+
+                    case MqttControlPacketType.Disconnect:
+                        {
+                            return new MqttDisconnectPacket();
+                        }
+
+                    case MqttControlPacketType.Publish:
+                        {
+                            return await DeserializePublishAsync(mqttPacketReader);
+                        }
+
+                    case MqttControlPacketType.PubAck:
+                        {
+                            return new MqttPubAckPacket
+                            {
+                                PacketIdentifier = await mqttPacketReader.ReadRemainingDataUShortAsync()
+                            };
+                        }
+
+                    case MqttControlPacketType.PubRec:
+                        {
+                            return new MqttPubRecPacket
+                            {
+                                PacketIdentifier = await mqttPacketReader.ReadRemainingDataUShortAsync()
+                            };
+                        }
+
+                    case MqttControlPacketType.PubRel:
+                        {
+                            return new MqttPubRelPacket
+                            {
+                                PacketIdentifier = await mqttPacketReader.ReadRemainingDataUShortAsync()
+                            };
+                        }
+
+                    case MqttControlPacketType.PubComp:
+                        {
+                            return new MqttPubCompPacket
+                            {
+                                PacketIdentifier = await mqttPacketReader.ReadRemainingDataUShortAsync()
+                            };
+                        }
+
+                    case MqttControlPacketType.PingReq:
+                        {
+                            return new MqttPingReqPacket();
+                        }
+
+                    case MqttControlPacketType.PingResp:
+                        {
+                            return new MqttPingRespPacket();
+                        }
+
+                    case MqttControlPacketType.Subscribe:
+                        {
+                            return await DeserializeSubscribeAsync(mqttPacketReader);
+                        }
+
+                    case MqttControlPacketType.SubAck:
+                        {
+                            return await DeserializeSubAck(mqttPacketReader);
+                        }
+
+                    case MqttControlPacketType.Unsubscibe:
+                        {
+                            return await DeserializeUnsubscribeAsync(mqttPacketReader);
+                        }
+
+                    case MqttControlPacketType.UnsubAck:
+                        {
+                            return new MqttUnsubAckPacket
+                            {
+                                PacketIdentifier = await mqttPacketReader.ReadRemainingDataUShortAsync()
+                            };
+                        }
+
+                    default:
+                        {
+                            throw new ProtocolViolationException();
+                        }
+                }
+            }
+        }
+
+        private async Task<MqttBasePacket> DeserializeUnsubscribeAsync(MqttPacketReader reader)
+        {
+            var packet = new MqttUnsubscribePacket
+            {
+                PacketIdentifier = await reader.ReadRemainingDataUShortAsync(),
+            };
+
+            while (!reader.EndOfRemainingData)
+            {
+                packet.TopicFilters.Add(await reader.ReadRemainingDataStringWithLengthPrefixAsync());
+            }
+
+            return packet;
+        }
+
+        private async Task<MqttBasePacket> DeserializeSubscribeAsync(MqttPacketReader reader)
+        {
+            var packet = new MqttSubscribePacket
+            {
+                PacketIdentifier = await reader.ReadRemainingDataUShortAsync(),
+            };
+
+            while (!reader.EndOfRemainingData)
+            {
+                packet.TopicFilters.Add(new TopicFilter(
+                    await reader.ReadRemainingDataStringWithLengthPrefixAsync(),
+                    (MqttQualityOfServiceLevel)await reader.ReadRemainingDataByteAsync()));
+            }
+
+            return packet;
+        }
+
+        private async Task<MqttBasePacket> DeserializePublishAsync(MqttPacketReader reader)
+        {
+            var fixedHeader = new ByteReader(reader.FixedHeader);
+            var retain = fixedHeader.Read();
+            var qualityOfServiceLevel = (MqttQualityOfServiceLevel)fixedHeader.Read(2);
+            var dup = fixedHeader.Read();
+
+            var topic = await reader.ReadRemainingDataStringWithLengthPrefixAsync();
+
+            ushort packetIdentifier = 0;
+            if (qualityOfServiceLevel > MqttQualityOfServiceLevel.AtMostOnce)
+            {
+                packetIdentifier = await reader.ReadRemainingDataUShortAsync();
+            }
+
+            var packet = new MqttPublishPacket
+            {
+                Retain = retain,
+                QualityOfServiceLevel = qualityOfServiceLevel,
+                Dup = dup,
+                Topic = topic,
+                Payload = await reader.ReadRemainingDataAsync(),
+                PacketIdentifier = packetIdentifier
+            };
+
+            return packet;
+        }
+
+        private async Task<MqttBasePacket> DeserializeConnectAsync(MqttPacketReader reader)
+        {
+            var packet = new MqttConnectPacket();
+
+            await reader.ReadRemainingDataByteAsync();
+            await reader.ReadRemainingDataByteAsync();
+            var protocolName = await reader.ReadRemainingDataAsync(4);
+
+            if (Encoding.UTF8.GetString(protocolName, 0, protocolName.Length) != "MQTT")
+            {
+                throw new ProtocolViolationException("Protocol name is not 'MQTT'.");
+            }
+
+            var protocolLevel = await reader.ReadRemainingDataByteAsync();
+            var connectFlags = await reader.ReadRemainingDataByteAsync();
+
+            var connectFlagsReader = new ByteReader(connectFlags);
+            connectFlagsReader.Read(); // Reserved.
+            packet.CleanSession = connectFlagsReader.Read();
+            var willFlag = connectFlagsReader.Read();
+            var willQoS = connectFlagsReader.Read(2);
+            var willRetain = connectFlagsReader.Read();
+            var passwordFlag = connectFlagsReader.Read();
+            var usernameFlag = connectFlagsReader.Read();
+
+            packet.KeepAlivePeriod = await reader.ReadRemainingDataUShortAsync();
+            packet.ClientId = await reader.ReadRemainingDataStringWithLengthPrefixAsync();
+
+            if (willFlag)
+            {
+                packet.WillMessage = new MqttApplicationMessage(
+                    await reader.ReadRemainingDataStringWithLengthPrefixAsync(),
+                    await reader.ReadRemainingDataWithLengthPrefixAsync(),
+                    (MqttQualityOfServiceLevel)willQoS,
+                    willRetain);
+            }
+
+            if (usernameFlag)
+            {
+                packet.Username = await reader.ReadRemainingDataStringWithLengthPrefixAsync();
+            }
+
+            if (passwordFlag)
+            {
+                packet.Password = await reader.ReadRemainingDataStringWithLengthPrefixAsync();
+            }
+
+            ValidateConnectPacket(packet);
+            return packet;
+        }
+
+        private async Task<MqttBasePacket> DeserializeSubAck(MqttPacketReader reader)
+        {
+            var packet = new MqttSubAckPacket
+            {
+                PacketIdentifier = await reader.ReadRemainingDataUShortAsync()
+            };
+
+            while (!reader.EndOfRemainingData)
+            {
+                packet.SubscribeReturnCodes.Add((MqttSubscribeReturnCode)await reader.ReadRemainingDataByteAsync());
+            }
+
+            return packet;
+        }
+
+        private async Task<MqttBasePacket> DeserializeConnAck(MqttPacketReader reader)
+        {
+            var variableHeader1 = await reader.ReadRemainingDataByteAsync();
+            var variableHeader2 = await reader.ReadRemainingDataByteAsync();
+
+            var packet = new MqttConnAckPacket
+            {
+                IsSessionPresent = new ByteReader(variableHeader1).Read(),
+                ConnectReturnCode = (MqttConnectReturnCode)variableHeader2
+            };
+
+            return packet;
+        }
+
+        private void ValidateConnectPacket(MqttConnectPacket packet)
+        {
+            if (string.IsNullOrEmpty(packet.ClientId) && !packet.CleanSession)
+            {
+                throw new ProtocolViolationException("CleanSession must be set if ClientId is empty [MQTT-3.1.3-7].");
+            }
+
+            if (!string.IsNullOrEmpty(packet.ClientId) && !Regex.IsMatch(packet.ClientId, "^[a-zA-Z0-9]*$"))
+            {
+                throw new ProtocolViolationException("ClientId contains invalid characters [MQTT-3.1.3-5].");
+            }
+        }
+
+        private void ValidatePublishPacket(MqttPublishPacket packet)
+        {
+            if (packet.QualityOfServiceLevel == 0 && packet.Dup)
+            {
+                throw new ProtocolViolationException("Dup flag must be false for QoS 0 packets [MQTT-3.3.1-2].");
+            }
+        }
+
+        private async Task SerializeAsync(MqttConnectPacket packet, IMqttCommunicationChannel destination)
+        {
+            ValidateConnectPacket(packet);
+
+            using (var output = new MqttPacketWriter())
+            {
+                // Write variable header
+                output.Write(0x00); // 3.1.2.1 Protocol Name
+                output.Write(0x04); // ""
+                output.Write('M');
+                output.Write('Q');
+                output.Write('T');
+                output.Write('T');
+                output.Write(0x04); // 3.1.2.2 Protocol Level
+
+                var connectFlags = new ByteWriter(); // 3.1.2.3 Connect Flags
+                connectFlags.Write(false); // Reserved
+                connectFlags.Write(packet.CleanSession);
+                connectFlags.Write(packet.WillMessage != null);
+
+                if (packet.WillMessage != null)
+                {
+                    connectFlags.Write((byte)packet.WillMessage.QualityOfServiceLevel, 2);
+                    connectFlags.Write(packet.WillMessage.Retain);
+                }
+                else
+                {
+                    connectFlags.Write(0, 2);
+                    connectFlags.Write(false);
+                }
+
+                connectFlags.Write(packet.Password != null);
+                connectFlags.Write(packet.Username != null);
+
+                output.Write(connectFlags);
+                output.Write(packet.KeepAlivePeriod);
+                output.WriteWithLengthPrefix(packet.ClientId);
+
+                if (packet.WillMessage != null)
+                {
+                    output.WriteWithLengthPrefix(packet.WillMessage.Topic);
+                    output.WriteWithLengthPrefix(packet.WillMessage.Payload);
+                }
+
+                if (packet.Username != null)
+                {
+                    output.WriteWithLengthPrefix(packet.Username);
+                }
+
+                if (packet.Password != null)
+                {
+                    output.WriteWithLengthPrefix(packet.Password);
+                }
+
+                output.InjectFixedHeader(MqttControlPacketType.Connect);
+                await output.WriteToAsync(destination);
+            }
+        }
+
+        private async Task SerializeAsync(MqttConnAckPacket packet, IMqttCommunicationChannel destination)
+        {
+            using (var output = new MqttPacketWriter())
+            {
+                var connectAcknowledgeFlags = new ByteWriter();
+                connectAcknowledgeFlags.Write(packet.IsSessionPresent);
+
+                output.Write(connectAcknowledgeFlags);
+                output.Write((byte)packet.ConnectReturnCode);
+
+                output.InjectFixedHeader(MqttControlPacketType.ConnAck);
+                await output.WriteToAsync(destination);
+            }
+        }
+
+        private async Task SerializeAsync(MqttDisconnectPacket packet, IMqttCommunicationChannel destination)
+        {
+            await SerializeEmptyPacketAsync(MqttControlPacketType.Disconnect, destination);
+        }
+
+        private async Task SerializeAsync(MqttPingReqPacket packet, IMqttCommunicationChannel destination)
+        {
+            await SerializeEmptyPacketAsync(MqttControlPacketType.PingReq, destination);
+        }
+
+        private async Task SerializeAsync(MqttPingRespPacket packet, IMqttCommunicationChannel destination)
+        {
+            await SerializeEmptyPacketAsync(MqttControlPacketType.PingResp, destination);
+        }
+
+        private async Task SerializeAsync(MqttPublishPacket packet, IMqttCommunicationChannel destination)
+        {
+            ValidatePublishPacket(packet);
+
+            using (var output = new MqttPacketWriter())
+            {
+                output.WriteWithLengthPrefix(packet.Topic);
+
+                if (packet.QualityOfServiceLevel > MqttQualityOfServiceLevel.AtMostOnce)
+                {
+                    output.Write(packet.PacketIdentifier);
+                }
+                else
+                {
+                    if (packet.PacketIdentifier > 0)
+                    {
+                        throw new MqttProtocolViolationException("Packet identifier must be empty if QoS == 0 [MQTT-2.3.1-5].");
+                    }
+                }
+
+                if (packet.Payload?.Length > 0)
+                {
+                    output.Write(packet.Payload);
+                }
+
+                var fixedHeader = new ByteWriter();
+                fixedHeader.Write(packet.Retain);
+                fixedHeader.Write((byte)packet.QualityOfServiceLevel, 2);
+                fixedHeader.Write(packet.Dup);
+
+                output.InjectFixedHeader(MqttControlPacketType.Publish, fixedHeader.Value);
+                await output.WriteToAsync(destination);
+            }
+        }
+
+        private async Task SerializeAsync(MqttPubAckPacket packet, IMqttCommunicationChannel destination)
+        {
+            using (var output = new MqttPacketWriter())
+            {
+                output.Write(packet.PacketIdentifier);
+
+                output.InjectFixedHeader(MqttControlPacketType.PubAck);
+                await output.WriteToAsync(destination);
+            }
+        }
+
+        private async Task SerializeAsync(MqttPubRecPacket packet, IMqttCommunicationChannel destination)
+        {
+            using (var output = new MqttPacketWriter())
+            {
+                output.Write(packet.PacketIdentifier);
+
+                output.InjectFixedHeader(MqttControlPacketType.PubRec);
+                await output.WriteToAsync(destination);
+            }
+        }
+
+        private async Task SerializeAsync(MqttPubRelPacket packet, IMqttCommunicationChannel destination)
+        {
+            using (var output = new MqttPacketWriter())
+            {
+                output.Write(packet.PacketIdentifier);
+
+                output.InjectFixedHeader(MqttControlPacketType.PubRel, 0x02);
+                await output.WriteToAsync(destination);
+            }
+        }
+
+        private async Task SerializeAsync(MqttPubCompPacket packet, IMqttCommunicationChannel destination)
+        {
+            using (var output = new MqttPacketWriter())
+            {
+                output.Write(packet.PacketIdentifier);
+
+                output.InjectFixedHeader(MqttControlPacketType.PubComp);
+                await output.WriteToAsync(destination);
+            }
+        }
+
+        private async Task SerializeAsync(MqttSubscribePacket packet, IMqttCommunicationChannel destination)
+        {
+            using (var output = new MqttPacketWriter())
+            {
+                output.Write(packet.PacketIdentifier);
+
+                if (packet.TopicFilters?.Any() == true)
+                {
+                    foreach (var topicFilter in packet.TopicFilters)
+                    {
+                        output.WriteWithLengthPrefix(topicFilter.Topic);
+                        output.Write((byte)topicFilter.QualityOfServiceLevel);
+                    }
+                }
+
+                output.InjectFixedHeader(MqttControlPacketType.Subscribe, 0x02);
+                await output.WriteToAsync(destination);
+            }
+        }
+
+        private async Task SerializeAsync(MqttSubAckPacket packet, IMqttCommunicationChannel destination)
+        {
+            using (var output = new MqttPacketWriter())
+            {
+                output.Write(packet.PacketIdentifier);
+
+                if (packet.SubscribeReturnCodes?.Any() == true)
+                {
+                    foreach (var packetSubscribeReturnCode in packet.SubscribeReturnCodes)
+                    {
+                        output.Write((byte)packetSubscribeReturnCode);
+                    }
+                }
+
+                output.InjectFixedHeader(MqttControlPacketType.SubAck);
+                await output.WriteToAsync(destination);
+            }
+        }
+
+        private async Task SerializeAsync(MqttUnsubscribePacket packet, IMqttCommunicationChannel destination)
+        {
+            using (var output = new MqttPacketWriter())
+            {
+                output.Write(packet.PacketIdentifier);
+
+                if (packet.TopicFilters?.Any() == true)
+                {
+                    foreach (var topicFilter in packet.TopicFilters)
+                    {
+                        output.WriteWithLengthPrefix(topicFilter);
+                    }
+                }
+
+                output.InjectFixedHeader(MqttControlPacketType.Unsubscibe, 0x02);
+                await output.WriteToAsync(destination);
+            }
+        }
+
+        private async Task SerializeAsync(MqttUnsubAckPacket packet, IMqttCommunicationChannel destination)
+        {
+            using (var output = new MqttPacketWriter())
+            {
+                output.Write(packet.PacketIdentifier);
+
+                output.InjectFixedHeader(MqttControlPacketType.UnsubAck);
+                await output.WriteToAsync(destination);
+            }
+        }
+
+        private async Task SerializeEmptyPacketAsync(MqttControlPacketType type, IMqttCommunicationChannel destination)
+        {
+            using (var output = new MqttPacketWriter())
+            {
+                output.InjectFixedHeader(type);
+                await output.WriteToAsync(destination);
+            }
+        }
+    }
+}

MQTTnet.Core/Serializer/IMqttPacketSerializer.cs

@@ -0,0 +1,13 @@
+using System.Threading.Tasks;
+using MQTTnet.Core.Channel;
+using MQTTnet.Core.Packets;
+
+namespace MQTTnet.Core.Serializer
+{
+    public interface IMqttPacketSerializer
+    {
+        Task SerializeAsync(MqttBasePacket mqttPacket, IMqttCommunicationChannel destination);
+
+        Task<MqttBasePacket> DeserializeAsync(IMqttCommunicationChannel source);
+    }
+}

MQTTnet.Core/Serializer/MqttPacketReader.cs

@@ -0,0 +1,127 @@
+using System;
+using System.IO;
+using System.Text;
+using System.Threading.Tasks;
+using MQTTnet.Core.Channel;
+using MQTTnet.Core.Exceptions;
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Serializer
+{
+    public sealed class MqttPacketReader : IDisposable
+    {
+        private readonly MemoryStream _remainingData = new MemoryStream();
+        private readonly IMqttCommunicationChannel _source;
+
+        public MqttPacketReader(IMqttCommunicationChannel source)
+        {
+            _source = source ?? throw new ArgumentNullException(nameof(source));
+        }
+
+        public MqttControlPacketType ControlPacketType { get; private set; }
+
+        public byte FixedHeader { get; private set; }
+
+        public int RemainingLength { get; private set; }
+
+        public bool EndOfRemainingData => _remainingData.Position == _remainingData.Length;
+
+        public async Task ReadToEndAsync()
+        {
+            await ReadFixedHeaderAsync();
+            await ReadRemainingLengthAsync();
+
+            if (RemainingLength == 0)
+            {
+                return;
+            }
+
+            var buffer = new byte[RemainingLength];
+            await _source.ReadAsync(buffer);
+
+            _remainingData.Write(buffer, 0, buffer.Length);
+            _remainingData.Position = 0;
+        }
+
+        private async Task ReadFixedHeaderAsync()
+        {
+            FixedHeader = await ReadStreamByteAsync();
+
+            var byteReader = new ByteReader(FixedHeader);
+            byteReader.Read(4);
+            ControlPacketType = (MqttControlPacketType)byteReader.Read(4);
+        }
+
+        private async Task<byte> ReadStreamByteAsync()
+        {
+            var buffer = new byte[1];
+            await _source.ReadAsync(buffer);
+            return buffer[0];
+        }
+
+        private async Task ReadRemainingLengthAsync()
+        {
+            // Alorithm taken from http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html.
+            var multiplier = 1;
+            var value = 0;
+            byte encodedByte;
+            do
+            {
+                encodedByte = await ReadStreamByteAsync();
+                value += (encodedByte & 127) * multiplier;
+                multiplier *= 128;
+                if (multiplier > 128 * 128 * 128)
+                {
+                    throw new MqttProtocolViolationException("Remaining length is ivalid.");
+                }
+            } while ((encodedByte & 128) != 0);
+
+            RemainingLength = value;
+        }
+
+        public async Task<byte> ReadRemainingDataByteAsync()
+        {
+            return (await ReadRemainingDataAsync(1))[0];
+        }
+
+        public async Task<ushort> ReadRemainingDataUShortAsync()
+        {
+            var buffer = await ReadRemainingDataAsync(2);
+
+            var temp = buffer[0];
+            buffer[0] = buffer[1];
+            buffer[1] = temp;
+
+            return BitConverter.ToUInt16(buffer, 0);
+        }
+
+        public async Task<string> ReadRemainingDataStringWithLengthPrefixAsync()
+        {
+            var buffer = await ReadRemainingDataWithLengthPrefixAsync();
+            return Encoding.UTF8.GetString(buffer, 0, buffer.Length);
+        }
+
+        public async Task<byte[]> ReadRemainingDataWithLengthPrefixAsync()
+        {
+            var length = await ReadRemainingDataUShortAsync();
+            return await ReadRemainingDataAsync(length);
+        }
+
+        public async Task<byte[]> ReadRemainingDataAsync()
+        {
+            return await ReadRemainingDataAsync(RemainingLength - (int)_remainingData.Position);
+        }
+
+        public async Task<byte[]> ReadRemainingDataAsync(int length)
+        {
+            var buffer = new byte[length];
+            await _remainingData.ReadAsync(buffer, 0, buffer.Length);
+            return buffer;
+        }
+
+        public void Dispose()
+        {
+            _remainingData?.Dispose();
+        }
+    }
+}

MQTTnet.Core/Serializer/MqttPacketWriter.cs

@@ -0,0 +1,107 @@
+using System;
+using System.IO;
+using System.Text;
+using System.Threading.Tasks;
+using MQTTnet.Core.Channel;
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Serializer
+{
+    public sealed class MqttPacketWriter : IDisposable
+    {
+        private readonly MemoryStream _buffer = new MemoryStream();
+
+        public void InjectFixedHeader(byte fixedHeader)
+        {
+            if (_buffer.Length == 0)
+            {
+                Write(fixedHeader);
+                Write(0);
+                return;
+            }
+
+            var remainingLength = (int)_buffer.Length;
+            using (var buffer = new MemoryStream())
+            {
+                _buffer.WriteTo(buffer);
+                _buffer.SetLength(0);
+
+                _buffer.WriteByte(fixedHeader);
+
+                // Alorithm taken from http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html.
+                var x = remainingLength;
+                do
+                {
+                    var encodedByte = (byte)(x % 128);
+                    x = x / 128;
+                    if (x > 0)
+                    {
+                        encodedByte = (byte)(encodedByte | 128);
+                    }
+
+                    _buffer.WriteByte(encodedByte);
+                } while (x > 0);
+
+                buffer.Position = 0;
+                buffer.WriteTo(_buffer);
+            }
+        }
+
+        public void InjectFixedHeader(MqttControlPacketType packetType, byte flags = 0)
+        {
+            var fixedHeader = (byte)((byte)packetType << 4);
+            fixedHeader |= flags;
+            InjectFixedHeader(fixedHeader);
+        }
+
+        public void Write(byte value)
+        {
+            _buffer.WriteByte(value);
+        }
+
+        public void Write(char value)
+        {
+            _buffer.WriteByte((byte)value);
+        }
+
+        public void Write(ushort value)
+        {
+            var buffer = BitConverter.GetBytes(value);
+            _buffer.WriteByte(buffer[1]);
+            _buffer.WriteByte(buffer[0]);
+        }
+
+        public void Write(ByteWriter value)
+        {
+            _buffer.WriteByte(value.Value);
+        }
+
+        public void Write(byte[] value)
+        {
+            _buffer.Write(value, 0, value.Length);
+        }
+
+        public void WriteWithLengthPrefix(string value)
+        {
+            WriteWithLengthPrefix(Encoding.UTF8.GetBytes(value ?? string.Empty));
+        }
+
+        public void WriteWithLengthPrefix(byte[] value)
+        {
+            var length = (ushort)value.Length;
+
+            Write(length);
+            Write(value);
+        }
+
+        public void Dispose()
+        {
+            _buffer?.Dispose();
+        }
+
+        public async Task WriteToAsync(IMqttCommunicationChannel destination)
+        {
+            await destination.WriteAsync(_buffer.ToArray());
+        }
+    }
+}

MQTTnet.Core/Server/MqttClientPublishPacketContext.cs

@@ -0,0 +1,22 @@
+using System;
+using MQTTnet.Core.Packets;
+
+namespace MQTTnet.Core.Server
+{
+    public class MqttClientPublishPacketContext
+    {
+        public MqttClientPublishPacketContext(MqttClientSession senderClientSession, MqttPublishPacket publishPacket)
+        {
+            SenderClientSession = senderClientSession ?? throw new ArgumentNullException(nameof(senderClientSession));
+            PublishPacket = publishPacket ?? throw new ArgumentNullException(nameof(publishPacket));
+        }
+
+        public MqttClientSession SenderClientSession { get; }
+
+        public MqttPublishPacket PublishPacket { get; }
+
+        public int SendTries { get; set; }
+
+        public bool IsSent { get; set; }
+    }
+}

MQTTnet.Core/Server/MqttClientSession.cs

@@ -0,0 +1,179 @@
+using System;
+using System.Collections.Concurrent;
+using System.Threading;
+using System.Threading.Tasks;
+using MQTTnet.Core.Adapter;
+using MQTTnet.Core.Diagnostics;
+using MQTTnet.Core.Exceptions;
+using MQTTnet.Core.Internal;
+using MQTTnet.Core.Packets;
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Server
+{
+    public class MqttClientSession
+    {
+        private readonly ConcurrentDictionary<ushort, MqttPublishPacket> _pendingIncomingPublications = new ConcurrentDictionary<ushort, MqttPublishPacket>();
+
+        private readonly MqttClientSubscriptionsManager _subscriptionsManager = new MqttClientSubscriptionsManager();
+        private readonly MqttOutgoingPublicationsManager _outgoingPublicationsManager;
+        private readonly Action<MqttClientSession, MqttPublishPacket> _publishPacketReceivedCallback;
+        private readonly MqttServerOptions _options;
+
+        private CancellationTokenSource _cancellationTokenSource;
+        private IMqttCommunicationAdapter _adapter;
+        private string _identifier;
+        private MqttApplicationMessage _willApplicationMessage;
+        
+        public MqttClientSession(MqttServerOptions options, Action<MqttClientSession, MqttPublishPacket> publishPacketReceivedCallback)
+        {
+            _options = options ?? throw new ArgumentNullException(nameof(options));
+            _publishPacketReceivedCallback = publishPacketReceivedCallback ?? throw new ArgumentNullException(nameof(publishPacketReceivedCallback));
+            
+            _outgoingPublicationsManager = new MqttOutgoingPublicationsManager(options);
+        }
+
+        public async Task RunAsync(string identifier, MqttApplicationMessage willApplicationMessage, IMqttCommunicationAdapter adapter)
+        {
+            if (adapter == null) throw new ArgumentNullException(nameof(adapter));
+
+            _willApplicationMessage = willApplicationMessage;
+
+            try
+            {
+                _identifier = identifier;
+                _adapter = adapter;
+                _cancellationTokenSource = new CancellationTokenSource();
+
+                _outgoingPublicationsManager.Start(adapter);
+                while (!_cancellationTokenSource.IsCancellationRequested)
+                {
+                    var packet = await adapter.ReceivePacketAsync(TimeSpan.Zero);
+                    await HandleIncomingPacketAsync(packet);
+                }
+            }
+            catch (MqttCommunicationException)
+            {
+            }
+            catch (Exception exception)
+            {
+                MqttTrace.Error(nameof(MqttClientSession), exception, $"Client '{_identifier}': Unhandled exception while processing client packets.");
+            }
+            finally
+            {
+                if (willApplicationMessage != null)
+                {
+                    _publishPacketReceivedCallback(this, _willApplicationMessage.ToPublishPacket());
+                }
+                
+                _outgoingPublicationsManager.Stop();
+                _cancellationTokenSource.Cancel();
+                _adapter = null;
+
+                MqttTrace.Information(nameof(MqttClientSession), $"Client '{_identifier}': Disconnected.");
+            }
+        }
+
+        public void DispatchPublishPacket(MqttClientSession senderClientSession, MqttPublishPacket publishPacket)
+        {
+            if (senderClientSession == null) throw new ArgumentNullException(nameof(senderClientSession));
+            if (publishPacket == null) throw new ArgumentNullException(nameof(publishPacket));
+
+            if (!_subscriptionsManager.IsTopicSubscribed(publishPacket))
+            {
+                return;
+            }
+
+            _outgoingPublicationsManager.Enqueue(senderClientSession, publishPacket);
+            MqttTrace.Verbose(nameof(MqttClientSession), $"Client '{_identifier}: Enqueued pending publish packet.");
+        }
+
+        private async Task HandleIncomingPacketAsync(MqttBasePacket packet)
+        {
+            var subscribePacket = packet as MqttSubscribePacket;
+            if (subscribePacket != null)
+            {
+                await _adapter.SendPacketAsync(_subscriptionsManager.Subscribe(subscribePacket), _options.DefaultCommunicationTimeout);
+                return;
+            }
+
+            var unsubscribePacket = packet as MqttUnsubscribePacket;
+            if (unsubscribePacket != null)
+            {
+                await _adapter.SendPacketAsync(_subscriptionsManager.Unsubscribe(unsubscribePacket), _options.DefaultCommunicationTimeout);
+                return;
+            }
+
+            var publishPacket = packet as MqttPublishPacket;
+            if (publishPacket != null)
+            {
+                await HandleIncomingPublishPacketAsync(publishPacket);
+                return;
+            }
+
+            var pubRelPacket = packet as MqttPubRelPacket;
+            if (pubRelPacket != null)
+            {
+                await HandleIncomingPubRelPacketAsync(pubRelPacket);
+                return;
+            }
+
+            var pubAckPacket = packet as MqttPubAckPacket;
+            if (pubAckPacket != null)
+            {
+                await HandleIncomingPubAckPacketAsync(pubAckPacket);
+                return;
+            }
+
+            if (packet is MqttPingReqPacket)
+            {
+                await _adapter.SendPacketAsync(new MqttPingRespPacket(), _options.DefaultCommunicationTimeout);
+                return;
+            }
+
+            if (packet is MqttDisconnectPacket || packet is MqttConnectPacket)
+            {
+                _cancellationTokenSource.Cancel();
+                return;
+            }
+
+            MqttTrace.Warning(nameof(MqttClientSession), $"Client '{_identifier}': Received not supported packet ({packet}). Closing connection.");
+            _cancellationTokenSource.Cancel();
+        }
+
+        private async Task HandleIncomingPubAckPacketAsync(MqttPubAckPacket pubAckPacket)
+        {
+            await Task.FromResult(0);
+        }
+
+        private async Task HandleIncomingPublishPacketAsync(MqttPublishPacket publishPacket)
+        {
+            if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
+            {
+                _publishPacketReceivedCallback(this, publishPacket);
+            }
+            else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtLeastOnce)
+            {
+                await _adapter.SendPacketAsync(new MqttPubAckPacket { PacketIdentifier = publishPacket.PacketIdentifier }, _options.DefaultCommunicationTimeout);
+                _publishPacketReceivedCallback(this, publishPacket);
+            }
+            else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
+            {
+                _pendingIncomingPublications[publishPacket.PacketIdentifier] = publishPacket;
+                await _adapter.SendPacketAsync(new MqttPubRecPacket { PacketIdentifier = publishPacket.PacketIdentifier }, _options.DefaultCommunicationTimeout);
+            }
+        }
+
+        private async Task HandleIncomingPubRelPacketAsync(MqttPubRelPacket pubRelPacket)
+        {
+            MqttPublishPacket publishPacket;
+            if (!_pendingIncomingPublications.TryRemove(pubRelPacket.PacketIdentifier, out publishPacket))
+            {
+                return;
+            }
+
+            await _adapter.SendPacketAsync(new MqttPubCompPacket { PacketIdentifier = publishPacket.PacketIdentifier }, _options.DefaultCommunicationTimeout);
+            _publishPacketReceivedCallback(this, publishPacket);
+        }
+    }
+}

MQTTnet.Core/Server/MqttClientSessionManager.cs

@@ -0,0 +1,93 @@
+using System;
+using System.Collections.Concurrent;
+using System.Linq;
+using System.Threading.Tasks;
+using MQTTnet.Core.Adapter;
+using MQTTnet.Core.Diagnostics;
+using MQTTnet.Core.Exceptions;
+using MQTTnet.Core.Packets;
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Server
+{
+    public class MqttClientSessionManager
+    {
+        private readonly ConcurrentDictionary<string, MqttClientSession> _clientSessions = new ConcurrentDictionary<string, MqttClientSession>();
+        private readonly MqttServerOptions _options;
+
+        public MqttClientSessionManager(MqttServerOptions options)
+        {
+            _options = options ?? throw new ArgumentNullException(nameof(options));
+        }
+
+        public async Task RunClientSessionAsync(MqttClientConnectedEventArgs eventArgs)
+        {
+            try
+            {
+                var connectPacket = await eventArgs.ClientAdapter.ReceivePacketAsync(_options.DefaultCommunicationTimeout) as MqttConnectPacket;
+                if (connectPacket == null)
+                {
+                    throw new MqttProtocolViolationException("The first packet from a client must be a 'Connect' packet [MQTT-3.1.0-1].");
+                }
+
+                var connectReturnCode = MqttConnectReturnCode.ConnectionAccepted;
+                if (_options.ConnectionValidator != null)
+                {
+                    connectReturnCode = _options.ConnectionValidator(connectPacket);
+                }
+
+                MqttClientSession clientSession = null;
+                var isSessionPresent = _clientSessions.ContainsKey(connectPacket.ClientId);
+                if (isSessionPresent && connectPacket.CleanSession)
+                {
+                    MqttClientSession _;
+                    _clientSessions.TryRemove(connectPacket.ClientId, out _);
+                }
+                else if (!connectPacket.CleanSession)
+                {
+                    _clientSessions.TryGetValue(connectPacket.ClientId, out clientSession);
+                }
+
+                await eventArgs.ClientAdapter.SendPacketAsync(new MqttConnAckPacket
+                {
+                    ConnectReturnCode = connectReturnCode,
+                    IsSessionPresent = clientSession != null
+                }, _options.DefaultCommunicationTimeout);
+
+                if (connectReturnCode != MqttConnectReturnCode.ConnectionAccepted)
+                {
+                    return;
+                }
+
+                if (clientSession == null)
+                {
+                    clientSession = new MqttClientSession(_options, DispatchPublishPacket);
+                    _clientSessions.TryAdd(connectPacket.ClientId, clientSession);
+                }
+
+                await clientSession.RunAsync(eventArgs.Identifier, connectPacket.WillMessage, eventArgs.ClientAdapter);
+            }
+            catch (Exception exception)
+            {
+                MqttTrace.Error(nameof(MqttServer), exception, exception.Message);
+            }
+            finally
+            {
+                await eventArgs.ClientAdapter.DisconnectAsync();
+            }
+        }
+
+        public void Clear()
+        {
+            _clientSessions.Clear();
+        }
+
+        private void DispatchPublishPacket(MqttClientSession senderClientSession, MqttPublishPacket publishPacket)
+        {
+            foreach (var clientSession in _clientSessions.Values.ToList())
+            {
+                clientSession.DispatchPublishPacket(senderClientSession, publishPacket);
+            }
+        }
+    }
+}

MQTTnet.Core/Server/MqttClientSubscriptionsManager.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Concurrent;
+using MQTTnet.Core.Packets;
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Server
+{
+    public class MqttClientSubscriptionsManager
+    {
+        private readonly ConcurrentDictionary<string, MqttQualityOfServiceLevel> _subscribedTopics = new ConcurrentDictionary<string, MqttQualityOfServiceLevel>();
+
+        public MqttSubAckPacket Subscribe(MqttSubscribePacket subscribePacket)
+        {
+            if (subscribePacket == null) throw new ArgumentNullException(nameof(subscribePacket));
+
+            var responsePacket = subscribePacket.CreateResponse<MqttSubAckPacket>();
+            foreach (var topicFilter in subscribePacket.TopicFilters)
+            {
+                _subscribedTopics[topicFilter.Topic] = topicFilter.QualityOfServiceLevel;
+                responsePacket.SubscribeReturnCodes.Add(MqttSubscribeReturnCode.SuccessMaximumQoS1); // TODO: Add support for QoS 2.
+            }
+
+            return responsePacket;
+        }
+
+        public MqttUnsubAckPacket Unsubscribe(MqttUnsubscribePacket unsubscribePacket)
+        {
+            if (unsubscribePacket == null) throw new ArgumentNullException(nameof(unsubscribePacket));
+
+            foreach (var topicFilter in unsubscribePacket.TopicFilters)
+            {
+                MqttQualityOfServiceLevel _;
+                _subscribedTopics.TryRemove(topicFilter, out _);
+            }
+
+            return unsubscribePacket.CreateResponse<MqttUnsubAckPacket>();
+        }
+
+        public bool IsTopicSubscribed(MqttPublishPacket publishPacket)
+        {
+            if (publishPacket == null) throw new ArgumentNullException(nameof(publishPacket));
+
+            foreach (var subscribedTopic in _subscribedTopics)
+            {
+                if (!MqttTopicFilterComparer.IsMatch(publishPacket.Topic, subscribedTopic.Key))
+                {
+                    continue;
+                }
+
+                if (subscribedTopic.Value < publishPacket.QualityOfServiceLevel)
+                {
+                    continue;
+                }
+
+                return true;
+            }
+
+            return false;
+        }
+    }
+}

MQTTnet.Core/Server/MqttOutgoingPublicationsManager.cs

@@ -0,0 +1,129 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using MQTTnet.Core.Adapter;
+using MQTTnet.Core.Diagnostics;
+using MQTTnet.Core.Exceptions;
+using MQTTnet.Core.Internal;
+using MQTTnet.Core.Packets;
+
+namespace MQTTnet.Core.Server
+{
+    public class MqttOutgoingPublicationsManager
+    {
+        private readonly AutoResetEvent _resetEvent = new AutoResetEvent(false);
+        private readonly List<MqttClientPublishPacketContext> _pendingPublishPackets = new List<MqttClientPublishPacketContext>();
+
+        private readonly MqttServerOptions _options;
+        private CancellationTokenSource _cancellationTokenSource;
+        private IMqttCommunicationAdapter _adapter;
+
+        public MqttOutgoingPublicationsManager(MqttServerOptions options)
+        {
+            _options = options ?? throw new ArgumentNullException(nameof(options));
+        }
+
+        public void Start(IMqttCommunicationAdapter adapter)
+        {
+            if (_cancellationTokenSource != null)
+            {
+                throw new InvalidOperationException($"{nameof(MqttOutgoingPublicationsManager)} already started.");
+            }
+
+            _adapter = adapter ?? throw new ArgumentNullException(nameof(adapter));
+            _cancellationTokenSource = new CancellationTokenSource();
+
+            Task.Run(async () => await SendPendingPublishPacketsAsync(_cancellationTokenSource.Token)).Forget();
+        }
+
+        public void Stop()
+        {
+            _cancellationTokenSource?.Cancel();
+            _cancellationTokenSource = null;
+        }
+
+        public void Enqueue(MqttClientSession senderClientSession, MqttPublishPacket publishPacket)
+        {
+            if (senderClientSession == null) throw new ArgumentNullException(nameof(senderClientSession));
+            if (publishPacket == null) throw new ArgumentNullException(nameof(publishPacket));
+
+            lock (_pendingPublishPackets)
+            {
+                _pendingPublishPackets.Add(new MqttClientPublishPacketContext(senderClientSession, publishPacket));
+                _resetEvent.Set();
+            }
+        }
+
+        private async Task SendPendingPublishPacketsAsync(CancellationToken cancellationToken)
+        {
+            while (!cancellationToken.IsCancellationRequested)
+            {
+                try
+                {
+                    _resetEvent.WaitOne();
+                    if (cancellationToken.IsCancellationRequested)
+                    {
+                        return;
+                    }
+
+                    List<MqttClientPublishPacketContext> pendingPublishPackets;
+                    lock (_pendingPublishPackets)
+                    {
+                        pendingPublishPackets = _pendingPublishPackets.ToList();
+                    }
+
+                    foreach (var publishPacket in pendingPublishPackets)
+                    {
+                        await TrySendPendingPublishPacketAsync(publishPacket);
+                    }
+                }
+                catch (Exception e)
+                {
+                    MqttTrace.Error(nameof(MqttOutgoingPublicationsManager), e, "Error while sending pending publish packets.");
+                }
+                finally
+                {
+                    Cleanup();
+                }               
+            }
+        }
+
+        private async Task TrySendPendingPublishPacketAsync(MqttClientPublishPacketContext publishPacketContext)
+        {
+            try
+            {
+                if (_adapter == null)
+                {
+                    return;
+                }
+
+                publishPacketContext.PublishPacket.Dup = publishPacketContext.SendTries > 0;
+                await _adapter.SendPacketAsync(publishPacketContext.PublishPacket, _options.DefaultCommunicationTimeout);
+
+                publishPacketContext.IsSent = true;
+            }
+            catch (MqttCommunicationException exception)
+            {
+                MqttTrace.Warning(nameof(MqttOutgoingPublicationsManager), exception, "Sending publish packet failed.");
+            }
+            catch (Exception exception)
+            {
+                MqttTrace.Error(nameof(MqttOutgoingPublicationsManager), exception, "Sending publish packet failed.");
+            }
+            finally
+            {
+                publishPacketContext.SendTries++;
+            }
+        }
+
+        private void Cleanup()
+        {
+            lock (_pendingPublishPackets)
+            {
+                _pendingPublishPackets.RemoveAll(p => p.IsSent);
+            }
+        }
+    }
+}

MQTTnet.Core/Server/MqttServer.cs

@@ -0,0 +1,67 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using MQTTnet.Core.Adapter;
+using MQTTnet.Core.Diagnostics;
+using MQTTnet.Core.Internal;
+
+namespace MQTTnet.Core.Server
+{
+    public class MqttServer
+    {
+        private readonly MqttClientSessionManager _clientSessionManager;
+        private readonly IMqttServerAdapter _adapter;
+        private readonly MqttServerOptions _options;
+
+        private CancellationTokenSource _cancellationTokenSource;
+
+        public MqttServer(MqttServerOptions options, IMqttServerAdapter adapter)
+        {
+            _options = options ?? throw new ArgumentNullException(nameof(options));
+            _adapter = adapter ?? throw new ArgumentNullException(nameof(adapter));
+            
+            _clientSessionManager = new MqttClientSessionManager(options);
+        }
+
+        public void InjectClient(string identifier, IMqttCommunicationAdapter adapter)
+        {
+            if (adapter == null) throw new ArgumentNullException(nameof(adapter));
+
+            OnClientConnected(this, new MqttClientConnectedEventArgs(identifier, adapter));
+        }
+
+        public void Start()
+        {
+            if (_cancellationTokenSource != null)
+            {
+                throw new InvalidOperationException("The server is already started.");
+            }
+
+            _cancellationTokenSource = new CancellationTokenSource();
+
+            _adapter.ClientConnected += OnClientConnected;
+            _adapter.Start(_options);
+
+            MqttTrace.Information(nameof(MqttServer), "Started.");
+        }
+
+        public void Stop()
+        {
+            _cancellationTokenSource?.Cancel();
+            _cancellationTokenSource = null;
+
+            _adapter.ClientConnected -= OnClientConnected;
+            _adapter.Stop();
+
+            _clientSessionManager.Clear();
+
+            MqttTrace.Information(nameof(MqttServer), "Stopped.");
+        }
+
+        private void OnClientConnected(object sender, MqttClientConnectedEventArgs eventArgs)
+        {
+            MqttTrace.Information(nameof(MqttServer), $"Client '{eventArgs.Identifier}': Connected.");
+            Task.Run(async () => await _clientSessionManager.RunClientSessionAsync(eventArgs), _cancellationTokenSource.Token).Forget();
+        }
+    }
+}

MQTTnet.Core/Server/MqttServerOptions.cs

@@ -0,0 +1,17 @@
+using System;
+using MQTTnet.Core.Packets;
+using MQTTnet.Core.Protocol;
+
+namespace MQTTnet.Core.Server
+{
+    public class MqttServerOptions
+    {
+        public int Port { get; set; } = 1883;
+
+        public int ConnectionBacklog { get; set; } = 10;
+
+        public TimeSpan DefaultCommunicationTimeout { get; set; } = TimeSpan.FromSeconds(10);
+
+        public Func<MqttConnectPacket, MqttConnectReturnCode> ConnectionValidator { get; set; }
+    }
+}

MQTTnet.Core/Server/MqttTopicFilterComparer.cs

@@ -0,0 +1,53 @@
+using System;
+
+namespace MQTTnet.Core.Server
+{
+    public static class MqttTopicFilterComparer
+    {
+        private const char TopicLevelSeparator = '/';
+
+        public static bool IsMatch(string topic, string filter)
+        {
+            if (topic == null) throw new ArgumentNullException(nameof(topic));
+            if (filter == null) throw new ArgumentNullException(nameof(filter));
+
+            if (string.Equals(topic, filter, StringComparison.Ordinal))
+            {
+                return true;
+            }
+
+            var fragmentsTopic = topic.Split(new[] { TopicLevelSeparator }, StringSplitOptions.None);
+            var fragmentsFilter = filter.Split(new[] { TopicLevelSeparator }, StringSplitOptions.None);
+
+            for (var i = 0; i < fragmentsFilter.Length; i++)
+            {
+                if (fragmentsFilter[i] == "+")
+                {
+                    continue;
+                }
+
+                if (fragmentsFilter[i] == "#" && i == fragmentsFilter.Length - 1)
+                {
+                    return true;
+                }
+
+                if (i >= fragmentsTopic.Length)
+                {
+                    return false;
+                }
+
+                if (!string.Equals(fragmentsFilter[i], fragmentsTopic[i]))
+                {
+                    return false;
+                }
+            }
+
+            if (fragmentsTopic.Length > fragmentsFilter.Length)
+            {
+                return false;
+            }
+
+            return true;
+        }
+    }
+}