From e6c1626deeb1f81f0c3abc2b15802499579b06ec Mon Sep 17 00:00:00 2001
From: Lukasz Michalski <lm@zork.pl>
Date: Mon, 30 Dec 2024 19:51:11 +0100
Subject: [PATCH] fixed bug when non recent change was published if topic was
 updated as part of poll group read

---
 libmodmqttsrv/mqttclient.cpp            |  7 +++-
 libmodmqttsrv/mqttobject.hpp            |  2 ++
 unittests/mqtt_publish_retain_tests.cpp | 44 +++++++++++++++++++++++++
 3 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/libmodmqttsrv/mqttclient.cpp b/libmodmqttsrv/mqttclient.cpp
index ed3f150..d01f4ad 100644
--- a/libmodmqttsrv/mqttclient.cpp
+++ b/libmodmqttsrv/mqttclient.cpp
@@ -151,6 +151,7 @@ MqttClient::processRegisterValues(const std::string& pModbusNetworkName, const M
 
     for (std::shared_ptr<MqttObject>& obj: *affectedObjects) {
         AvailableFlag oldAvail = obj->getAvailableFlag();
+        bool hadValue = obj->hasValue();
         obj->updateRegisterValues(pModbusNetworkName, pSlaveData);
         AvailableFlag newAvail = obj->getAvailableFlag();
 
@@ -163,8 +164,12 @@ MqttClient::processRegisterValues(const std::string& pModbusNetworkName, const M
                     publishState(*obj, true);
                 } else {
                     // delete retained message
-                    if (oldAvail == AvailableFlag::NotSet)
+                    if (oldAvail == AvailableFlag::NotSet) {
                         mMqttImpl->publish(obj->getStateTopic().c_str(), 0, NULL, true);
+                        // remember initial payload for comparsion with subsequent modbus data updates
+                        if (!obj->getRetain())
+                            obj->setLastPublishedPayload(MqttPayload::generate(*obj));
+                    }
                     if (obj->getPublishMode() == PublishMode::EVERY_POLL)
                         publishState(*obj, true);
                 }
diff --git a/libmodmqttsrv/mqttobject.hpp b/libmodmqttsrv/mqttobject.hpp
index 0197a60..e72844e 100644
--- a/libmodmqttsrv/mqttobject.hpp
+++ b/libmodmqttsrv/mqttobject.hpp
@@ -195,6 +195,8 @@ class MqttObject {
         void setAvailableValue(const MqttValue& pValue) { mAvailability.setAvailableValue(pValue); }
         AvailableFlag getAvailableFlag() const { return mIsAvailable; }
 
+        bool hasValue() const { return mState.hasAllValues(); }
+
         void setLastPublishedPayload(const std::string& pVal) { mLastPublishedPayload = pVal; }
         const std::string& getLastPublishedPayload() const { return mLastPublishedPayload; }
 
diff --git a/unittests/mqtt_publish_retain_tests.cpp b/unittests/mqtt_publish_retain_tests.cpp
index 774d6ce..7077af9 100644
--- a/unittests/mqtt_publish_retain_tests.cpp
+++ b/unittests/mqtt_publish_retain_tests.cpp
@@ -100,3 +100,47 @@ TestConfig config(R"(
     }
 }
 
+TEST_CASE ("When retain topic is a part of poll group") {
+
+TestConfig config(R"(
+modbus:
+  networks:
+    - name: tcptest
+      address: localhost
+      port: 501
+      slaves:
+        - address: 1
+          poll_groups:
+            - register: 2
+              register_type: holding
+              count: 2
+mqtt:
+  client_id: mqtt_test
+  refresh: 50ms
+  broker:
+    host: localhost
+  objects:
+    - topic: test_sensor
+      retain: false
+      state:
+        register: tcptest.1.2
+    - topic: other_sensor
+      state:
+        register: tcptest.1.3
+)");
+
+    SECTION("its value should be ignored if related register value is not changed") {
+        MockedModMqttServerThread server(config.toString());
+        server.setModbusRegisterValue("tcptest", 1, 2, modmqttd::RegisterType::HOLDING, 2);
+        server.setModbusRegisterValue("tcptest", 1, 3, modmqttd::RegisterType::HOLDING, 3);
+
+        server.start();
+        server.waitForPublish("other_sensor/state");
+
+        //this caused test_sensor value change due to null -> 3
+        server.setModbusRegisterValue("tcptest", 1, 3, modmqttd::RegisterType::HOLDING, 33);
+        server.waitForPublish("other_sensor/state");
+
+        server.requirePublishCount("test_sensor/state", 1);
+    }
+}