Move the RPC topic validation to the topic generation strategy.

Source/MQTTnet.Extensions.Rpc/Options/MqttRpcClientOptions.cs

@@ -2,7 +2,7 @@
 
 namespace MQTTnet.Extensions.Rpc.Options
 {
-    public class MqttRpcClientOptions : IMqttRpcClientOptions
+    public sealed class MqttRpcClientOptions : IMqttRpcClientOptions
     {
         public IMqttRpcClientTopicGenerationStrategy TopicGenerationStrategy { get; set; } = new DefaultMqttRpcClientTopicGenerationStrategy();
     }

Source/MQTTnet.Extensions.Rpc/Options/MqttRpcClientOptionsBuilder.cs

@@ -3,7 +3,7 @@ using System;
 
 namespace MQTTnet.Extensions.Rpc.Options
 {
-    public class MqttRpcClientOptionsBuilder
+    public sealed class MqttRpcClientOptionsBuilder
     {
         IMqttRpcClientTopicGenerationStrategy _topicGenerationStrategy = new DefaultMqttRpcClientTopicGenerationStrategy();
 

Source/MQTTnet.Extensions.Rpc/Options/MqttRpcTopicPair.cs

@@ -1,6 +1,6 @@
 namespace MQTTnet.Extensions.Rpc.Options
 {
-    public class MqttRpcTopicPair
+    public sealed class MqttRpcTopicPair
     {
         public string RequestTopic { get; set; }
 

Source/MQTTnet.Extensions.Rpc/Options/TopicGeneration/DefaultMqttRpcClientTopicGenerationStrategy.cs

@@ -2,10 +2,15 @@
 
 namespace MQTTnet.Extensions.Rpc.Options.TopicGeneration
 {
-    public class DefaultMqttRpcClientTopicGenerationStrategy : IMqttRpcClientTopicGenerationStrategy
+    public sealed class DefaultMqttRpcClientTopicGenerationStrategy : IMqttRpcClientTopicGenerationStrategy
     {
         public MqttRpcTopicPair CreateRpcTopics(TopicGenerationContext context)
         {
+            if (context.MethodName.Contains("/") || context.MethodName.Contains("+") || context.MethodName.Contains("#"))
+            {
+                throw new ArgumentException("The method name cannot contain /, + or #.");
+            }
+            
             var requestTopic = $"MQTTnet.RPC/{Guid.NewGuid():N}/{context.MethodName}";
             var responseTopic = requestTopic + "/response";
 

Source/MQTTnet.Extensions.Rpc/Options/TopicGeneration/TopicGenerationContext.cs

@@ -3,7 +3,7 @@ using MQTTnet.Protocol;
 
 namespace MQTTnet.Extensions.Rpc.Options.TopicGeneration
 {
-    public class TopicGenerationContext
+    public sealed class TopicGenerationContext
     {
         public string MethodName { get; set; }