Allow setting up an auto-resubscribe ReadClient with just a peer id.

src/app/ReadClient.cpp

@@ -940,6 +940,19 @@ CHIP_ERROR ReadClient::SendAutoResubscribeRequest(ReadPrepareParams && aReadPrep
     return err;
 }
 
+CHIP_ERROR ReadClient::SendAutoResubscribeRequest(const ScopedNodeId & aPublisherId, ReadPrepareParams && aReadPrepareParams)
+{
+    mPeer              = aPublisherId;
+    mReadPrepareParams = std::move(aReadPrepareParams);
+    CHIP_ERROR err     = EstablishSessionToPeer();
+    if (err != CHIP_NO_ERROR)
+    {
+        // Make sure we call our callback's OnDeallocatePaths.
+        StopResubscription();
+    }
+    return err;
+}
+
 CHIP_ERROR ReadClient::SendSubscribeRequest(const ReadPrepareParams & aReadPrepareParams)
 {
     VerifyOrReturnError(aReadPrepareParams.mMinIntervalFloorSeconds <= aReadPrepareParams.mMaxIntervalCeilingSeconds,
@@ -1118,12 +1131,8 @@ void ReadClient::OnResubscribeTimerCallback(System::Layer * /* If this starts be
     {
         // We don't have an active CASE session.  We need to go ahead and set
         // one up, if we can.
-        ChipLogProgress(DataManagement, "Trying to establish a CASE session");
-        auto * caseSessionManager = InteractionModelEngine::GetInstance()->GetCASESessionManager();
-        if (caseSessionManager)
+        if (_this->EstablishSessionToPeer() == CHIP_NO_ERROR)
         {
-            caseSessionManager->FindOrEstablishSession(_this->mPeer, &_this->mOnConnectedCallback,
-                                                       &_this->mOnConnectionFailureCallback);
             return;
         }
 
@@ -1209,5 +1218,14 @@ Optional<System::Clock::Timeout> ReadClient::GetSubscriptionTimeout()
     return MakeOptional(timeout);
 }
 
+CHIP_ERROR ReadClient::EstablishSessionToPeer()
+{
+    ChipLogProgress(DataManagement, "Trying to establish a CASE session for subscription");
+    auto * caseSessionManager = InteractionModelEngine::GetInstance()->GetCASESessionManager();
+    VerifyOrReturnError(caseSessionManager != nullptr, CHIP_ERROR_INCORRECT_STATE);
+    caseSessionManager->FindOrEstablishSession(mPeer, &mOnConnectedCallback, &mOnConnectionFailureCallback);
+    return CHIP_NO_ERROR;
+}
+
 } // namespace app
 } // namespace chip

src/app/ReadClient.h

@@ -352,12 +352,22 @@ class ReadClient : public Messaging::ExchangeDelegate
      *  OnDeallocatePaths. Note: At a given time in the system, you can either have a single subscription with re-sub enabled that
      *  has mKeepSubscriptions = false, OR, multiple subs with re-sub enabled with mKeepSubscriptions = true. You shall not
      *  have a mix of both simultaneously. If SendAutoResubscribeRequest is called at all, it guarantees that it will call
-     *  OnDeallocatePaths when OnDone is called. SendAutoResubscribeRequest is the only case that calls OnDeallocatePaths, since
-     *  that's the only case when the consumer moved a ReadParams into the client.
+     *  OnDeallocatePaths (either befor returning error, or when OnDone is called). SendAutoResubscribeRequest is the only case
+     *  that calls OnDeallocatePaths, since that's the only case when the consumer moved a ReadParams into the client.
      *
      */
     CHIP_ERROR SendAutoResubscribeRequest(ReadPrepareParams && aReadPrepareParams);
 
+    /**
+     * Like SendAutoResubscribeRequest above, but without a session being
+     * available in the ReadPrepareParams.  When this is used, the ReadClient is
+     * responsible for setting up the CASE session itself.
+     *
+     * When using this version of SendAutoResubscribeRequest, any session to
+     * which ReadPrepareParams has a reference will be ignored.
+     */
+    CHIP_ERROR SendAutoResubscribeRequest(const ScopedNodeId & aPublisherId, ReadPrepareParams && aReadPrepareParams);
+
     /**
      *   This provides a standard re-subscription policy implementation that given a termination cause, does the following:
      *   - Calculates the time till next subscription with fibonacci back-off (implemented by ComputeTimeTillNextSubscription()).
@@ -538,6 +548,13 @@ class ReadClient : public Messaging::ExchangeDelegate
 
     CHIP_ERROR GetMinEventNumber(const ReadPrepareParams & aReadPrepareParams, Optional<EventNumber> & aEventMin);
 
+    /**
+     * Start setting up a CASE session to our peer, if we can locate a
+     * CASESessionManager.  Returns error if we did not even manage to kick off
+     * a CASE attempt.
+     */
+    CHIP_ERROR EstablishSessionToPeer();
+
     Messaging::ExchangeManager * mpExchangeMgr = nullptr;
     Messaging::ExchangeHolder mExchange;
     Callback & mpCallback;