Add validation for topics before publishing.

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClient.cs

@@ -127,6 +127,8 @@ namespace MQTTnet.Extensions.ManagedClient
         {
             if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
 
+            MqttTopicValidator.ThrowIfInvalid(applicationMessage.ApplicationMessage.Topic);
+
             ManagedMqttApplicationMessage removedMessage = null;
             ApplicationMessageSkippedEventArgs applicationMessageSkippedEventArgs = null;
 

Source/MQTTnet/Client/MqttClient.cs

@@ -166,6 +166,8 @@ namespace MQTTnet.Client
         {
             if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
 
+            MqttTopicValidator.ThrowIfInvalid(applicationMessage.Topic);
+
             ThrowIfNotConnected();
 
             var publishPacket = _adapter.PacketFormatterAdapter.DataConverter.CreatePublishPacket(applicationMessage);

Source/MQTTnet/Internal/AsyncAutoResetEvent.cs

@@ -74,8 +74,11 @@ namespace MQTTnet.Internal
             Task winner;
             if (timeout == Timeout.InfiniteTimeSpan)
             {
-                await tcs.Task.ConfigureAwait(false);
-                winner = tcs.Task;
+                using (cancellationToken.Register(() => { tcs.TrySetCanceled(); }))
+                {
+                    await tcs.Task.ConfigureAwait(false);
+                    winner = tcs.Task;
+                }               
             }
             else
             {
@@ -122,7 +125,7 @@ namespace MQTTnet.Internal
                 }
             }
 
-            toRelease?.SetResult(true);
+            toRelease?.TrySetResult(true);
         }
     }
 }

Source/MQTTnet/Protocol/MqttTopicValidator.cs

@@ -0,0 +1,25 @@
+using MQTTnet.Exceptions;
+
+namespace MQTTnet.Protocol
+{
+    public static class MqttTopicValidator
+    {
+        public static void ThrowIfInvalid(string topic)
+        {
+            if (string.IsNullOrEmpty(topic))
+            {
+                throw new MqttProtocolViolationException("Topic should not be empty.");
+            }
+
+            if (topic.Contains("+"))
+            {
+                throw new MqttProtocolViolationException("The character '+' is not allowed in topics.");
+            }
+
+            if (topic.Contains("#"))
+            {
+                throw new MqttProtocolViolationException("The character '#' is not allowed in topics.");
+            }
+        }
+    }
+}

Source/MQTTnet/Server/MqttServer.cs

@@ -7,6 +7,7 @@ using MQTTnet.Adapter;
 using MQTTnet.Client.Publishing;
 using MQTTnet.Client.Receiving;
 using MQTTnet.Diagnostics;
+using MQTTnet.Protocol;
 using MQTTnet.Server.Status;
 
 namespace MQTTnet.Server
@@ -101,6 +102,8 @@ namespace MQTTnet.Server
         {
             if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
 
+            MqttTopicValidator.ThrowIfInvalid(applicationMessage.Topic);
+
             if (_cancellationTokenSource == null) throw new InvalidOperationException("The server is not started.");
 
             _clientSessionsManager.DispatchApplicationMessage(applicationMessage, null);