Fix MQTT 3.1.1 session persistence when CleanSession=1 (#1294)

Tests/MQTTnet.Core.Tests/Server/Session_Tests.cs

@@ -1,4 +1,4 @@
-using System.Linq;
+using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
@@ -107,6 +107,58 @@ namespace MQTTnet.Tests.Server
             }
         }
 
+        [TestMethod]
+        public async Task Clean_Session_Persistence()
+        {
+            using (var testEnvironment = new TestEnvironment(TestContext))
+            {
+                // Create server with persistent sessions enabled
+
+                await testEnvironment.StartServer(o => o.WithPersistentSessions());
+
+                const string ClientId = "Client1";
+
+                // Create client with clean session and long session expiry interval
+
+                var client1 = await testEnvironment.ConnectClient(o => o
+                    .WithProtocolVersion(Formatter.MqttProtocolVersion.V311)
+                    .WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
+                    .WithSessionExpiryInterval(9999) // not relevant for v311 but testing impact
+                    .WithCleanSession(true) // start and end with clean session
+                    .WithClientId(ClientId)
+                    .Build()
+                );
+
+                // Disconnect; empty session should be removed from server
+
+                await client1.DisconnectAsync();
+
+                // Simulate some time delay between connections
+
+                await Task.Delay(1000);
+
+                // Reconnect the same client ID without clean session
+
+                var client2 = testEnvironment.CreateClient();
+                var options = testEnvironment.Factory.CreateClientOptionsBuilder()
+                    .WithProtocolVersion(Formatter.MqttProtocolVersion.V311)
+                    .WithTcpServer("127.0.0.1", testEnvironment.ServerPort)
+                    .WithSessionExpiryInterval(9999) // not relevant for v311 but testing impact
+                    .WithCleanSession(false) // see if there is a session
+                    .WithClientId(ClientId)
+                    .Build();
+
+
+                var result = await client2.ConnectAsync(options).ConfigureAwait(false);
+
+                await client2.DisconnectAsync();
+
+                // Session should NOT be present for MQTT v311 and initial CleanSession == true
+
+                Assert.IsTrue(!result.IsSessionPresent, "Session present");
+            }
+        }
+
         async Task<IMqttClient> TryConnect(TestEnvironment testEnvironment, MqttClientOptionsBuilder options)
         {
             try