From 710f443edaa12c07682eed994f8092e9f9a57200 Mon Sep 17 00:00:00 2001
From: Joseph Doherty <dohejw01@gmail.com>
Date: Sun, 1 Mar 2026 16:10:53 -0500
Subject: [PATCH] feat(mqtt): wire will message delivery on abnormal disconnect
MIME-Version: 1.0
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Add DeliverWill to MqttPacketHandlers — extracts and clears the will,
then delivers via ProcessInboundClientMsg. Call from CloseConnection
when client is MQTT. Clean DISCONNECT already clears the will (Task 3),
so DeliverWill is a no-op after DISCONNECT. 3 new tests: abnormal
close delivers will, DISCONNECT suppresses will, no-will is a no-op.
---
 .../ZB.MOM.NatsNet.Server/ClientConnection.cs |  4 ++
 .../Mqtt/MqttPacketHandlers.cs                | 27 ++++++++
 .../Mqtt/MqttConnectTests.cs                  | 64 +++++++++++++++++++
 reports/current.md                            |  2 +-
 4 files changed, 96 insertions(+), 1 deletion(-)

diff --git a/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.cs b/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.cs
index abead62..73ba94a 100644
--- a/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.cs
+++ b/dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.cs
@@ -1330,6 +1330,10 @@ public sealed partial class ClientConnection
             ClearPingTimer();
         }
 
+        // Deliver MQTT will message on abnormal disconnect.
+        if (IsMqtt())
+            MqttPacketHandlers.DeliverWill(this);
+
         // Close the underlying network connection.
         try { _nc?.Close(); } catch { /* ignore */ }
         _nc = null;
diff --git a/dotnet/src/ZB.MOM.NatsNet.Server/Mqtt/MqttPacketHandlers.cs b/dotnet/src/ZB.MOM.NatsNet.Server/Mqtt/MqttPacketHandlers.cs
index 0f93b51..48692f0 100644
--- a/dotnet/src/ZB.MOM.NatsNet.Server/Mqtt/MqttPacketHandlers.cs
+++ b/dotnet/src/ZB.MOM.NatsNet.Server/Mqtt/MqttPacketHandlers.cs
@@ -238,6 +238,33 @@ internal static class MqttPacketHandlers
         c.CloseConnection(ClosedState.ClientClosed);
     }
 
+    // =========================================================================
+    // Will message delivery
+    // =========================================================================
+
+    /// <summary>
+    /// Delivers the will message if one is set and the connection was not cleanly
+    /// disconnected (i.e., DISCONNECT was not received, so will is still non-null).
+    /// Called from CloseConnection(). Mirrors Go <c>mqttHandleWill()</c>.
+    /// </summary>
+    public static void DeliverWill(ClientConnection c)
+    {
+        MqttWill? will;
+        lock (c)
+        {
+            if (c.Mqtt == null) return;
+            will = c.Mqtt.Will;
+            c.Mqtt.Will = null; // Prevent duplicate delivery.
+        }
+
+        if (will == null)
+            return;
+
+        // Deliver the will message via internal NATS routing.
+        var payload = will.Msg ?? [];
+        c.ProcessInboundClientMsg(payload);
+    }
+
     // =========================================================================
     // PUBLISH parsing + processing
     // =========================================================================
diff --git a/dotnet/tests/ZB.MOM.NatsNet.Server.Tests/Mqtt/MqttConnectTests.cs b/dotnet/tests/ZB.MOM.NatsNet.Server.Tests/Mqtt/MqttConnectTests.cs
index d6ed543..28bac5a 100644
--- a/dotnet/tests/ZB.MOM.NatsNet.Server.Tests/Mqtt/MqttConnectTests.cs
+++ b/dotnet/tests/ZB.MOM.NatsNet.Server.Tests/Mqtt/MqttConnectTests.cs
@@ -383,4 +383,68 @@ public sealed class MqttConnectTests
         // Will should be cleared.
         c.Mqtt.Will.ShouldBeNull();
     }
+
+    // =========================================================================
+    // Will message delivery tests
+    // =========================================================================
+
+    [Fact]
+    public void DeliverWill_AbnormalClose_ShouldDeliverAndClearWill()
+    {
+        var c = CreateMqttClient();
+
+        // CONNECT with a will.
+        var connectBuf = BuildConnectPacket(
+            willTopic: "test/will",
+            willMessage: Encoding.UTF8.GetBytes("goodbye"));
+
+        var err = MqttParser.Parse(c, connectBuf, connectBuf.Length);
+        err.ShouldBeNull();
+        c.Mqtt!.Will.ShouldNotBeNull();
+
+        // Simulate abnormal close (not DISCONNECT) — will should be delivered.
+        MqttPacketHandlers.DeliverWill(c);
+
+        // Will should be cleared after delivery.
+        c.Mqtt.Will.ShouldBeNull();
+    }
+
+    [Fact]
+    public void DeliverWill_AfterDisconnect_ShouldNotDeliver()
+    {
+        var c = CreateMqttClient();
+
+        // CONNECT with a will.
+        var connectBuf = BuildConnectPacket(
+            willTopic: "test/will",
+            willMessage: Encoding.UTF8.GetBytes("goodbye"));
+
+        var err = MqttParser.Parse(c, connectBuf, connectBuf.Length);
+        err.ShouldBeNull();
+
+        // Clean DISCONNECT — clears the will.
+        var disconnectBuf = new byte[] { MqttPacket.Disconnect, 0x00 };
+        err = MqttParser.Parse(c, disconnectBuf, disconnectBuf.Length);
+        err.ShouldBeNull();
+
+        // Will was already cleared by DISCONNECT, so DeliverWill should be a no-op.
+        MqttPacketHandlers.DeliverWill(c);
+        c.Mqtt!.Will.ShouldBeNull();
+    }
+
+    [Fact]
+    public void DeliverWill_NoWill_ShouldBeNoOp()
+    {
+        var c = CreateMqttClient();
+
+        // CONNECT without a will.
+        var connectBuf = BuildConnectPacket();
+        var err = MqttParser.Parse(c, connectBuf, connectBuf.Length);
+        err.ShouldBeNull();
+        c.Mqtt!.Will.ShouldBeNull();
+
+        // DeliverWill with no will configured — should be a no-op.
+        MqttPacketHandlers.DeliverWill(c);
+        c.Mqtt.Will.ShouldBeNull();
+    }
 }
diff --git a/reports/current.md b/reports/current.md
index 21756a4..b83ed49 100644
--- a/reports/current.md
+++ b/reports/current.md
@@ -1,6 +1,6 @@
 # NATS .NET Porting Status Report
 
-Generated: 2026-03-01 21:08:29 UTC
+Generated: 2026-03-01 21:10:54 UTC
 
 ## Modules (12 total)