Merge pull request #3462 from reubenmiller/fix-mqtt-topic-sub-without-session

fix: subscribe to topics on reconnection when session persistence is not enabled or broken

Author: reubenmiller

crates/common/mqtt_channel/src/connection.rs

@@ -271,9 +271,10 @@ impl Connection {
                                 .await?;
                         }
 
-                        if config.session_name.is_none() {
+                        if config.session_name.is_none() || !ack.session_present {
                             // Workaround for  https://github.com/bytebeamio/rumqtt/issues/250
-                            // If session_name is not provided, then re-subscribe
+                            // If session_name is not provided or if the broker session persistence
+                            // is not enabled or working, then re-subscribe
 
                             let subscriptions = config.subscriptions.filters();
                             // Need check here otherwise it will hang waiting for a SubAck, and none will come when there is no subscription.

tests/RobotFramework/tests/mqtt/session_persistence.robot

@@ -0,0 +1,30 @@
+*** Settings ***
+Resource            ../../resources/common.resource
+Library             Cumulocity
+Library             ThinEdgeIO
+
+Test Setup          Custom Setup
+Test Teardown       Get Logs
+
+Test Tags           theme:mqtt    theme:c8y
+
+
+*** Test Cases ***
+Agent Processes Operations After Local MQTT Broker Disconnects Without Mosquitto Persistence Settings
+    # Force tedge-agent to disconnect by restarting mosquitto
+    Restart Service    mosquitto
+    ${operation}=    Cumulocity.Get Configuration    tedge-configuration-plugin
+    Operation Should Be SUCCESSFUL    ${operation}
+
+
+*** Keywords ***
+Custom Setup
+    ${DEVICE_SN}=    Setup
+    Set Suite Variable    $DEVICE_SN
+    Device Should Exist    ${DEVICE_SN}
+    # Remove mosquitto persistence settings
+    Execute Command    sed -i '/^persistence.*/d' /etc/mosquitto/mosquitto.conf
+
+    # Restart mosquitto to start again ignoring pre-existing persisted data
+    # Note: Tests should not rely on the mosquitto service restarting in the test setup
+    Restart Service    mosquitto