Add / update comments

src/app/InteractionModelEngine.h

@@ -330,6 +330,11 @@ class InteractionModelEngine : public Messaging::UnsolicitedMessageHandler,
     bool SubjectHasPersistedSubscription(FabricIndex aFabricIndex, NodeId subjectID) override;
 
 #if CHIP_CONFIG_PERSIST_SUBSCRIPTIONS
+    /**
+     * @brief Function decrements the number of subscriptions to resume counter - mNumOfSubscriptionsToResume.
+     *        This should be called after we have completed a re-subscribe attempt on a persisted subscription wether the attempt
+     *        was succesful or not.
+     */
     void DecrementNumSubscriptionsToResume();
 #endif // CHIP_CONFIG_PERSIST_SUBSCRIPTIONS
 
@@ -681,6 +686,12 @@ class InteractionModelEngine : public Messaging::UnsolicitedMessageHandler,
 #endif // CONFIG_BUILD_FOR_HOST_UNIT_TEST
 
 #if CHIP_CONFIG_PERSIST_SUBSCRIPTIONS
+    /**
+     * mNumOfSubscriptionsToResume tracks the number of subscriptions that the device will try to resume at its next resumption
+     * attempt. At boot up, the attempt will be at the highest min interval of all the subscriptions to resume.
+     * When the subscription timeout resumption feature is present, after the boot up attempt, the next attempt will be determined
+     * by ComputeTimeSecondsTillNextSubscriptionResumption.
+     */
     int8_t mNumOfSubscriptionsToResume = 0;
 #if CHIP_CONFIG_SUBSCRIPTION_TIMEOUT_RESUMPTION
     bool HasSubscriptionsToResume();

src/app/SubscriptionResumptionSessionEstablisher.cpp

@@ -91,7 +91,9 @@ void SubscriptionResumptionSessionEstablisher::HandleDeviceConnected(void * cont
     SubscriptionResumptionStorage::SubscriptionInfo & subscriptionInfo = establisher->mSubscriptionInfo;
     InteractionModelEngine * imEngine                                  = InteractionModelEngine::GetInstance();
 
-    // Decrement the number of subscriptions to resume
+    // Decrement the number of subscriptions to resume since we have completed our retry attempt for a given subscription.
+    // We do this before the readHandler creation since we do not care if the subscription has successfully been resumed or
+    // not. Counter only tracks the number of individual subscriptions we will try to resume.
     imEngine->DecrementNumSubscriptionsToResume();
 
     if (!imEngine->EnsureResourceForSubscription(subscriptionInfo.mFabricIndex, subscriptionInfo.mAttributePaths.AllocatedSize(),
@@ -129,7 +131,9 @@ void SubscriptionResumptionSessionEstablisher::HandleDeviceConnectionFailure(voi
     ChipLogError(DataManagement, "Failed to establish CASE for subscription-resumption with error '%" CHIP_ERROR_FORMAT "'",
                  error.Format());
 
-    // Decrement the number of subscriptions to resume
+    // Decrement the number of subscriptions to resume since we have completed our retry attempt for a given subscription.
+    // We do this here since we were not able to connect to the subscriber thus we have completed our resumption attempt.
+    // Counter only tracks the number of individual subscriptions we will try to resume.
     imEngine->DecrementNumSubscriptionsToResume();
 
     auto * subscriptionResumptionStorage = imEngine->GetSubscriptionResumptionStorage();

src/app/icd/server/ICDManager.cpp

@@ -260,6 +260,12 @@ bool ICDManager::CheckInMessagesWouldBeSent(const std::function<ShouldCheckInMsg
  * @brief Implementation for when the persistent subscription and subscription timeout resumption feature are present.
  *        Function checks that there are no active or persisted subscriptions for a given fabricIndex or subjectID.
  *
+ * @note When the persistent subscription and subscription timeout resumption feature are present, we need to check for
+ *       persisted subscription at each transition to ActiveMode since there will be persisted subscriptions during normal
+ *       operation for the subscription timeout resumption feature. Once we have finished all our subscription resumption attempts
+ *       for a given subscription, the entry is deleted from persisted storage which will enable us to send Check-In messages for
+ *       the client registration. This logic avoids the device sending a Check-In message while trying to resume subscriptions.
+ *
  * @param aFabricIndex
  * @param subjectID subjectID to check. Can be an operational node id or a CAT
  *
@@ -307,6 +313,9 @@ bool ICDManager::ShouldCheckInMsgsBeSentAtActiveModeFunction(FabricIndex aFabric
  * @brief Implementation for when neither the persistent subscription nor the subscription timeout resumption features are present.
  *        Function checks that there no active sbuscriptions for a given fabricIndex and subjectId combination.
  *
+ * @note When neither the persistent subscription nor the subscription timeout resumption features are present, we only need to
+ *       check for active subscription since we will never have any persisted subscription.
+ *
  * @param aFabricIndex
  * @param subjectID subjectID to check. Can be an opperationnal node id or a CAT
  *