fixed parsing issue and added test

MQTTnet.sln

@@ -45,6 +45,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Benchmarks", "Tests
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Extensions.ManagedClient", "Source\MQTTnet.Extensions.ManagedClient\MQTTnet.Extensions.ManagedClient.csproj", "{C400533A-8EBA-4F0B-BF4D-295C3708604B}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.AspNetCore.Tests", "Tests\MQTTnet.AspNetCore.Tests\MQTTnet.AspNetCore.Tests.csproj", "{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -208,6 +210,22 @@ Global
 		{C400533A-8EBA-4F0B-BF4D-295C3708604B}.Release|x64.Build.0 = Release|Any CPU
 		{C400533A-8EBA-4F0B-BF4D-295C3708604B}.Release|x86.ActiveCfg = Release|Any CPU
 		{C400533A-8EBA-4F0B-BF4D-295C3708604B}.Release|x86.Build.0 = Release|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Debug|ARM.ActiveCfg = Debug|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Debug|ARM.Build.0 = Debug|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Debug|x64.Build.0 = Debug|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Debug|x86.Build.0 = Debug|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Release|Any CPU.Build.0 = Release|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Release|ARM.ActiveCfg = Release|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Release|ARM.Build.0 = Release|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Release|x64.ActiveCfg = Release|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Release|x64.Build.0 = Release|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Release|x86.ActiveCfg = Release|Any CPU
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -222,6 +240,7 @@ Global
 		{C444E9C8-95FA-430E-9126-274129DE16CD} = {12816BCC-AF9E-44A9-9AE5-C246AF2A0587}
 		{998D04DD-7CB0-45F5-A393-E2495C16399E} = {9248C2E1-B9D6-40BF-81EC-86004D7765B4}
 		{C400533A-8EBA-4F0B-BF4D-295C3708604B} = {12816BCC-AF9E-44A9-9AE5-C246AF2A0587}
+		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E} = {9248C2E1-B9D6-40BF-81EC-86004D7765B4}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {07536672-5CBC-4BE3-ACE0-708A431A7894}

Source/MQTTnet.AspnetCore/ReaderExtensions.cs

@@ -26,6 +26,11 @@ namespace MQTTnet.AspNetCore
                 return false;
             }
 
+            if (copy.Length < bodyLength)
+            {
+                return false;
+            }
+
             var bodySlice = copy.Slice(0, bodyLength);
             packet = serializer.Deserialize(new ReceivedMqttPacket(fixedheader, new MqttPacketBodyReader(bodySlice.GetArray(), 0)));
             consumed = bodySlice.End;

Tests/MQTTnet.AspNetCore.Tests/MQTTnet.AspNetCore.Tests.csproj

@@ -0,0 +1,19 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp2.1</TargetFramework>
+
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.7.0" />
+    <PackageReference Include="MSTest.TestAdapter" Version="1.2.1" />
+    <PackageReference Include="MSTest.TestFramework" Version="1.2.1" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\Source\MQTTnet.AspnetCore\MQTTnet.AspNetCore.csproj" />
+  </ItemGroup>
+
+</Project>

Tests/MQTTnet.AspNetCore.Tests/ReaderExtensionsTest.cs

@@ -0,0 +1,45 @@
+using System.Buffers;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.AspNetCore;
+using MQTTnet.Packets;
+using MQTTnet.Serializer;
+
+namespace MQTTnet.AspNetCore.Tests
+{
+    [TestClass]
+    public class ReaderExtensionsTest
+    {
+        [TestMethod]
+        public void TestTryDeserialize()
+        {
+            var serializer = new MqttPacketSerializer();
+
+            var buffer = serializer.Serialize(new MqttPublishPacket() {Topic = "a", Payload = new byte[5]});
+
+            var sequence = new ReadOnlySequence<byte>(buffer.Array, buffer.Offset, buffer.Count);
+
+            var part = sequence;
+            MqttBasePacket packet;
+            var consumed = part.Start;
+            var observed = part.Start;
+            var result = false;
+
+            part = sequence.Slice(sequence.Start, 0); // empty message should fail
+            result = serializer.TryDeserialize(part, out packet, out consumed, out observed);
+            Assert.IsFalse(result);
+
+
+            part = sequence.Slice(sequence.Start, 1); // partial fixed header should fail
+            result = serializer.TryDeserialize(part, out packet, out consumed, out observed);
+            Assert.IsFalse(result);
+
+            part = sequence.Slice(sequence.Start, 4); // partial body should fail
+            result = serializer.TryDeserialize(part, out packet, out consumed, out observed);
+            Assert.IsFalse(result);
+
+            part = sequence; // complete msg should work
+            result = serializer.TryDeserialize(part, out packet, out consumed, out observed);
+            Assert.IsTrue(result);
+        }
+    }
+}