From 52c8f00ef866a832a6983b7e5e2b31a6f3e129e9 Mon Sep 17 00:00:00 2001
From: Suhas Holla Karkada Chandrashekar
 <51073384+suhashollakc@users.noreply.github.com>
Date: Sun, 21 Jun 2026 10:19:45 -0400
Subject: [PATCH] Fix keep alive ping send timeout disconnect handling (#2253)

Fix keep alive ping send timeout disconnect
---
 .../Clients/MqttClient/MqttClient_Tests.cs    | 114 +++++++++++++++++-
 Source/MQTTnet/MqttClient.cs                  |   9 +-
 2 files changed, 120 insertions(+), 3 deletions(-)

diff --git a/Source/MQTTnet.Tests/Clients/MqttClient/MqttClient_Tests.cs b/Source/MQTTnet.Tests/Clients/MqttClient/MqttClient_Tests.cs
index 4b478427..a14c5afa 100644
--- a/Source/MQTTnet.Tests/Clients/MqttClient/MqttClient_Tests.cs
+++ b/Source/MQTTnet.Tests/Clients/MqttClient/MqttClient_Tests.cs
@@ -5,8 +5,12 @@
 using System.Buffers;
 using System.Diagnostics;
 using System.Globalization;
+using System.Net;
 using System.Net.Sockets;
+using System.Security.Cryptography.X509Certificates;
 using System.Text;
+using MQTTnet.Adapter;
+using MQTTnet.Diagnostics.Logger;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
 using MQTTnet.Internal;
@@ -454,6 +458,34 @@ public sealed class MqttClient_Tests : BaseTestClass
         }
     }
 
+    [TestMethod]
+    public async Task KeepAlive_Ping_Send_Timeout_Raises_Disconnected()
+    {
+        var adapterFactory = new KeepAliveTimeoutAdapterFactory();
+        var disconnected = new TaskCompletionSource<MqttClientDisconnectedEventArgs>(TaskCreationOptions.RunContinuationsAsynchronously);
+
+        using var client = new MqttClientFactory().CreateMqttClient(adapterFactory);
+        client.DisconnectedAsync += eventArgs =>
+        {
+            disconnected.TrySetResult(eventArgs);
+            return CompletedTask.Instance;
+        };
+
+        var options = new MqttClientOptionsBuilder()
+            .WithTcpServer("localhost")
+            .WithKeepAlivePeriod(TimeSpan.FromSeconds(1))
+            .Build();
+
+        await client.ConnectAsync(options);
+
+        await adapterFactory.Adapter.PingRequestReceived.Task.WaitAsync(TimeSpan.FromSeconds(3));
+        var disconnectedEventArgs = await disconnected.Task.WaitAsync(TimeSpan.FromSeconds(3));
+
+        Assert.IsTrue(disconnectedEventArgs.ClientWasConnected);
+        Assert.IsInstanceOfType<OperationCanceledException>(disconnectedEventArgs.Exception);
+        Assert.IsFalse(client.IsConnected);
+    }
+
     [TestMethod]
     public async Task Publish_QoS_1_In_ApplicationMessageReceiveHandler()
     {
@@ -975,4 +1007,84 @@ public sealed class MqttClient_Tests : BaseTestClass
         Assert.IsTrue(publisher.IsConnected);
         Assert.AreEqual(Threads * MessagesPerThread, receivedCount);
     }
-}
\ No newline at end of file
+
+    sealed class KeepAliveTimeoutAdapterFactory : IMqttClientAdapterFactory
+    {
+        public KeepAliveTimeoutAdapter Adapter { get; private set; }
+
+        public IMqttChannelAdapter CreateClientAdapter(MqttClientOptions options, MqttPacketInspector packetInspector, IMqttNetLogger logger)
+        {
+            Adapter = new KeepAliveTimeoutAdapter(options.ProtocolVersion, options.WriterBufferSize, options.WriterBufferSizeMax);
+            return Adapter;
+        }
+    }
+
+    sealed class KeepAliveTimeoutAdapter : IMqttChannelAdapter
+    {
+        int _connAckReturned;
+
+        public KeepAliveTimeoutAdapter(MqttProtocolVersion protocolVersion, int writerBufferSize, int writerBufferSizeMax)
+        {
+            PacketFormatterAdapter = new MqttPacketFormatterAdapter(protocolVersion, new MqttBufferWriter(writerBufferSize, writerBufferSizeMax));
+        }
+
+        public long BytesReceived { get; }
+
+        public long BytesSent { get; }
+
+        public X509Certificate2 ClientCertificate { get; }
+
+        public EndPoint RemoteEndPoint { get; } = new DnsEndPoint("localhost", 1883);
+
+        public EndPoint LocalEndPoint { get; } = new DnsEndPoint("localhost", 0);
+
+        public bool IsSecureConnection { get; }
+
+        public MqttPacketFormatterAdapter PacketFormatterAdapter { get; }
+
+        public TaskCompletionSource PingRequestReceived { get; } = new(TaskCreationOptions.RunContinuationsAsynchronously);
+
+        public Task ConnectAsync(CancellationToken cancellationToken)
+        {
+            return CompletedTask.Instance;
+        }
+
+        public Task DisconnectAsync(CancellationToken cancellationToken)
+        {
+            return CompletedTask.Instance;
+        }
+
+        public void Dispose()
+        {
+        }
+
+        public async Task<MqttPacket> ReceivePacketAsync(CancellationToken cancellationToken)
+        {
+            if (Interlocked.Exchange(ref _connAckReturned, 1) == 0)
+            {
+                return new MqttConnAckPacket
+                {
+                    ReturnCode = MqttConnectReturnCode.ConnectionAccepted
+                };
+            }
+
+            await Task.Delay(Timeout.InfiniteTimeSpan, cancellationToken);
+            return null;
+        }
+
+        public void ResetStatistics()
+        {
+        }
+
+        public Task SendPacketAsync(MqttPacket packet, CancellationToken cancellationToken)
+        {
+            if (packet is MqttPingReqPacket)
+            {
+                PingRequestReceived.TrySetResult();
+                return Task.Delay(Timeout.InfiniteTimeSpan, cancellationToken);
+            }
+
+            return CompletedTask.Instance;
+        }
+    }
+}
diff --git a/Source/MQTTnet/MqttClient.cs b/Source/MQTTnet/MqttClient.cs
index a9231ddb..b7a81790 100644
--- a/Source/MQTTnet/MqttClient.cs
+++ b/Source/MQTTnet/MqttClient.cs
@@ -1064,7 +1064,12 @@ public sealed class MqttClient : Disposable, IMqttClient
             switch (exception)
             {
                 case OperationCanceledException:
-                    return;
+                    if (cancellationToken.IsCancellationRequested)
+                    {
+                        return;
+                    }
+
+                    break;
                 case MqttCommunicationException:
                     _logger.Warning(exception, "Communication error while sending/receiving keep alive packets");
                     break;
@@ -1080,4 +1085,4 @@ public sealed class MqttClient : Disposable, IMqttClient
             _logger.Verbose("Stopped sending keep alive packets");
         }
     }
-}
\ No newline at end of file
+}