Fixes and clean the new topic matcher from israellot

Tests/MQTTnet.Benchmarks/MQTTnet.Benchmarks.csproj

@@ -147,6 +147,7 @@
     </Reference>
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="TopicFilterComparerBenchmark.cs" />
     <Compile Include="LoggerBenchmark.cs" />
     <Compile Include="MessageProcessingBenchmark.cs" />
     <Compile Include="Program.cs" />

Tests/MQTTnet.Benchmarks/Program.cs

@@ -12,6 +12,7 @@ namespace MQTTnet.Benchmarks
             Console.WriteLine("1 = MessageProcessingBenchmark");
             Console.WriteLine("2 = SerializerBenchmark");
             Console.WriteLine("3 = LoggerBenchmark");
+            Console.WriteLine("4 = TopicFilterComparerBenchmark");
 
             var pressedKey = Console.ReadKey(true);
             switch (pressedKey.KeyChar)
@@ -25,6 +26,9 @@ namespace MQTTnet.Benchmarks
                 case '3':
                     BenchmarkRunner.Run<LoggerBenchmark>();
                     break;
+                case '4':
+                    BenchmarkRunner.Run<TopicFilterComparerBenchmark>();
+                    break;
             }
 
             Console.ReadLine();

Tests/MQTTnet.Benchmarks/TopicFilterComparerBenchmark.cs

@@ -0,0 +1,91 @@
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Attributes.Exporters;
+using BenchmarkDotNet.Attributes.Jobs;
+using MQTTnet.Server;
+using System;
+
+namespace MQTTnet.Benchmarks
+{
+    [ClrJob]
+    [RPlotExporter]
+    [MemoryDiagnoser]
+    public class TopicFilterComparerBenchmark
+    {
+        private static readonly char[] TopicLevelSeparator = { '/' };
+
+        [GlobalSetup]
+        public void Setup()
+        {
+        }
+
+        [Benchmark]
+        public void MqttTopicFilterComparer_10000_StringSplitMethod()
+        {
+            for (var i = 0; i < 10000; i++)
+            {
+                LegacyMethodByStringSplit("sport/tennis/player1", "sport/#");
+                LegacyMethodByStringSplit("sport/tennis/player1/ranking", "sport/#/ranking");
+                LegacyMethodByStringSplit("sport/tennis/player1/score/wimbledon", "sport/+/player1/#");
+                LegacyMethodByStringSplit("sport/tennis/player1", "sport/tennis/+");
+                LegacyMethodByStringSplit("/finance", "+/+");
+                LegacyMethodByStringSplit("/finance", "/+");
+                LegacyMethodByStringSplit("/finance", "+");
+            }
+        }
+
+        [Benchmark]
+        public void MqttTopicFilterComparer_10000_LoopMethod()
+        {
+            for (var i = 0; i < 10000; i++)
+            {
+                MqttTopicFilterComparer.IsMatch("sport/tennis/player1", "sport/#");
+                MqttTopicFilterComparer.IsMatch("sport/tennis/player1/ranking", "sport/#/ranking");
+                MqttTopicFilterComparer.IsMatch("sport/tennis/player1/score/wimbledon", "sport/+/player1/#");
+                MqttTopicFilterComparer.IsMatch("sport/tennis/player1", "sport/tennis/+");
+                MqttTopicFilterComparer.IsMatch("/finance", "+/+");
+                MqttTopicFilterComparer.IsMatch("/finance", "/+");
+                MqttTopicFilterComparer.IsMatch("/finance", "+");
+            }
+        }
+
+        private static bool LegacyMethodByStringSplit(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(TopicLevelSeparator, StringSplitOptions.None);
+            var fragmentsFilter = filter.Split(TopicLevelSeparator, StringSplitOptions.None);
+
+            // # > In either case it MUST be the last character specified in the Topic Filter [MQTT-4.7.1-2].
+            for (var i = 0; i < fragmentsFilter.Length; i++)
+            {
+                if (fragmentsFilter[i] == "+")
+                {
+                    continue;
+                }
+
+                if (fragmentsFilter[i] == "#")
+                {
+                    return true;
+                }
+
+                if (i >= fragmentsTopic.Length)
+                {
+                    return false;
+                }
+
+                if (!string.Equals(fragmentsFilter[i], fragmentsTopic[i], StringComparison.Ordinal))
+                {
+                    return false;
+                }
+            }
+
+            return fragmentsTopic.Length == fragmentsFilter.Length;
+        }
+    }
+}