[ICD] Add OnPeerTypeChange for dynamic ICD

src/app/InteractionModelEngine.cpp

@@ -995,6 +995,22 @@ void InteractionModelEngine::OnActiveModeNotification(ScopedNodeId aPeer)
     }
 }
 
+void InteractionModelEngine::OnPeerTypeChange(ScopedNodeId aPeer, ReadClient::PeerType aType)
+{
+    // TODO: Follow up to use a iterator function to avoid copy/paste here.
+    for (ReadClient * pListItem = mpActiveReadClientList; pListItem != nullptr;)
+    {
+        // It is possible that pListItem is destroyed by the app in OnPeerTypeChange.
+        // Get the next item before invoking `OnPeerTypeChange`.
+        auto pNextItem = pListItem->GetNextClient();
+        if (ScopedNodeId(pListItem->GetPeerNodeId(), pListItem->GetFabricIndex()) == aPeer)
+        {
+            pListItem->OnPeerTypeChange(aType);
+        }
+        pListItem = pNextItem;
+    }
+}
+
 void InteractionModelEngine::AddReadClient(ReadClient * apReadClient)
 {
     apReadClient->SetNextClient(mpActiveReadClientList);

src/app/InteractionModelEngine.h

@@ -247,6 +247,14 @@ class InteractionModelEngine : public Messaging::UnsolicitedMessageHandler,
      */
     void OnActiveModeNotification(ScopedNodeId aPeer);
 
+    /**
+     *  Used to notify whether a peer becomes LIT ICD or vice versa.
+     *
+     *  When the app knows that the peer becoms LIT ICD, it is expected to call this method with PeerType::kLITICD and when
+     * the peer is nolonger a LIT ICD, it is expected to call this method with PeerType::kNormal.
+     */
+    void OnPeerTypeChange(ScopedNodeId aPeer, ReadClient::PeerType aType);
+
     /**
      * Add a read client to the internally tracked list of weak references. This list is used to
      * correctly dispatch unsolicited reports to the right matching handler by subscription ID.

src/app/ReadClient.cpp

@@ -451,6 +451,19 @@ void ReadClient::OnActiveModeNotification()
     TriggerResubscriptionForLivenessTimeout(CHIP_ERROR_TIMEOUT);
 }
 
+void ReadClient::OnPeerTypeChange(PeerType aType)
+{
+    VerifyOrDie(mpImEngine->InActiveReadClientList(this));
+
+    mIsPeerLIT = (aType == PeerType::kLITICD);
+
+    // If the peer is nolonger LIT, try to wake up the subscription and do resubsribe when necessary.
+    if (!mIsPeerLIT)
+    {
+        OnActiveModeNotification();
+    }
+}
+
 CHIP_ERROR ReadClient::OnMessageReceived(Messaging::ExchangeContext * apExchangeContext, const PayloadHeader & aPayloadHeader,
                                          System::PacketBufferHandle && aPayload)
 {

src/app/ReadClient.h

@@ -292,6 +292,11 @@ class ReadClient : public Messaging::ExchangeDelegate
         Subscribe,
     };
 
+    enum class PeerType : uint8_t {
+        kNormal,
+        kLITICD,
+    };
+
     /**
      *
      *  Constructor.
@@ -350,6 +355,16 @@ class ReadClient : public Messaging::ExchangeDelegate
      */
     void OnActiveModeNotification();
 
+    /**
+     *  Used to notify whether a peer becomes LIT ICD or vice versa.
+     *
+     *  When the app knows that the peer becoms LIT ICD, it is expected to call this method with PeerType::kLITICD and when
+     * the peer is nolonger a LIT ICD, it is expected to call this method with PeerType::kNormal.
+     *
+     *  Users should call InteractionModelEngine::OnPeerTypeChange instead of this function.  
+     */
+    void OnPeerTypeChange(PeerType aType);
+
     void OnUnsolicitedReportData(Messaging::ExchangeContext * apExchangeContext, System::PacketBufferHandle && aPayload);
 
     void OnUnsolicitedMessageFromPublisher()