mqtt disconnect on non-psram boards

src/core/mqtt.cpp

@@ -313,6 +313,31 @@ void Mqtt::on_publish(uint16_t packetId) const {
     LOG_DEBUG("Packet %d sent successful", packetId);
 }
 
+// gracefully disconnect from the broker by sending a proper MQTT DISCONNECT packet.
+// this is called just before a restart so the broker ends our session cleanly
+// (avoids a lingering session that shows up as "session taken over" on reconnect).
+//
+// the disconnect is deferred inside espMqttClient - the DISCONNECT packet is only
+// queued and actually sent when loop() runs the state machine. On PSRAM boards the
+// client has its own task that keeps pumping loop(), so it flushes on its own. On
+// non-PSRAM boards (UseInternalTask::NO) nothing drives loop() once we're mid-restart,
+// so we pump it here until the client is fully disconnected, bounded by a timeout.
+void Mqtt::disconnect() {
+    if (!mqttClient_) {
+        return;
+    }
+
+    mqttClient_->disconnect(); // graceful - queues the DISCONNECT packet
+
+    if (EMSESP::system_.PSram() == 0) {
+        uint32_t start = uuid::get_uptime();
+        while (!mqttClient_->disconnected() && (uuid::get_uptime() - start) < MQTT_DISCONNECT_TIMEOUT) {
+            mqttClient_->loop();
+            delay(2);
+        }
+    }
+}
+
 // called when MQTT settings have changed via the MQTT Settings or Application Settings Web pages
 void Mqtt::reset_mqtt() {
     if (!enabled()) {

src/core/mqtt.h

@@ -61,8 +61,9 @@ class Mqtt {
     enum Operation : uint8_t { PUBLISH, SUBSCRIBE, UNSUBSCRIBE };
     enum NestedFormat : uint8_t { NESTED = 1, SINGLE };
 
-    static constexpr uint8_t  MQTT_TOPIC_MAX_SIZE = 128; // fixed, not a user setting anymore
-    static constexpr uint16_t MQTT_QUEUE_MAX_SIZE = 300;
+    static constexpr uint8_t  MQTT_TOPIC_MAX_SIZE  = 128; // fixed, not a user setting anymore
+    static constexpr uint16_t MQTT_QUEUE_MAX_SIZE  = 300;
+    static constexpr uint32_t MQTT_DISCONNECT_TIMEOUT = 1000; // max ms to flush a graceful disconnect on non-PSRAM boards
 
     static void on_connect();
     static void on_disconnect(espMqttClientTypes::DisconnectReason reason);
@@ -132,11 +133,7 @@ class Mqtt {
         return mqttClient_ ? mqttClient_->connected() : false;
     }
 
-    static void disconnect() {
-        if (mqttClient_) {
-            mqttClient_->disconnect();
-        };
-    }
+    static void disconnect();
 
     static bool enabled() {
         return mqtt_enabled_;

src/core/system.cpp

@@ -586,7 +586,7 @@ void System::system_restart(const char * partitionname) {
     }
     Serial.flush(); // wait for hardware TX buffer to drain
 
-    Mqtt::disconnect(); // gracefully disconnect MQTT, needed for QOS1
+    Mqtt::disconnect(); // gracefully disconnect MQTT (flushes the DISCONNECT before reboot, needed for QOS1)
     EMSuart::stop();    // stop UART so there is no interference
 #ifndef EMSESP_STANDALONE
     delay(1000);   // wait 1 second