Cleanup CASESession and PASESession lifetime

The fix in project-chip#12794 means that the CASESession and PASESession objects do
not need to persist for ExchangeMessageDispatch::SendMessage to succeed
at the final ACK of session establishment.  Instead, SendMessage uses the
SessionEstablishmentExchangeDispatch global singleton.

This means we can address 13146 such that CASESession and PASESession may
actually be freed or reused when completion callbacks fire.  This will
only work, however, if these objects clear themselves as delegates for
their exchange contexts when discarding references to these.  This
commit does so.

This commit also reorders all calls to mDelegate->OnSessionEstablished and
mDelegate->OnSessionEstablishmentError to occur last in any given method
in case mDelegate frees or reuses the CASESession or PASESession objects
on execution of these completion callbacks.

With this, we can remove the behavior in the OperationalDeviceProxy which
that was defering release of the CASESession object until after an
iteration of the event loop.  Now when OnSessionEstablished fires, the
CASESession can be reused or discared immediately.

src/app/OperationalDeviceProxy.cpp

@@ -280,22 +280,15 @@ void OperationalDeviceProxy::Clear()
     mInitParams = DeviceProxyInitParams();
 }
 
-void OperationalDeviceProxy::CloseCASESessionTask(System::Layer * layer, void * context)
+void OperationalDeviceProxy::DeferCloseCASESession()
 {
-    OperationalDeviceProxy * device = static_cast<OperationalDeviceProxy *>(context);
-    if (device->mCASEClient)
+    if (this->mCASEClient)
     {
-        device->mInitParams.clientPool->Release(device->mCASEClient);
-        device->mCASEClient = nullptr;
+        this->mInitParams.clientPool->Release(this->mCASEClient);
+        this->mCASEClient = nullptr;
     }
 }
 
-void OperationalDeviceProxy::DeferCloseCASESession()
-{
-    // Defer the release for the pending Ack to be sent
-    mSystemLayer->ScheduleWork(CloseCASESessionTask, this);
-}
-
 void OperationalDeviceProxy::OnSessionReleased(const SessionHandle & session)
 {
     VerifyOrReturn(mSecureSession.Contains(session),

src/protocols/secure_channel/CASESession.cpp

@@ -252,11 +252,13 @@ void CASESession::OnResponseTimeout(ExchangeContext * ec)
     VerifyOrReturn(mExchangeCtxt == ec, ChipLogError(SecureChannel, "CASESession::OnResponseTimeout exchange doesn't match"));
     ChipLogError(SecureChannel, "CASESession timed out while waiting for a response from the peer. Current state was %" PRIu8,
                  mState);
-    mDelegate->OnSessionEstablishmentError(CHIP_ERROR_TIMEOUT);
     // Null out mExchangeCtxt so that Clear() doesn't try closing it.  The
     // exchange will handle that.
+    mExchangeCtxt->SetDelegate(nullptr);
     mExchangeCtxt = nullptr;
     Clear();
+    // Do this last in case the delegate frees us.
+    mDelegate->OnSessionEstablishmentError(CHIP_ERROR_TIMEOUT);
 }
 
 CHIP_ERROR CASESession::DeriveSecureSession(CryptoContext & session, CryptoContext::SessionRole role)
@@ -684,9 +686,11 @@ CHIP_ERROR CASESession::HandleSigma2Resume(System::PacketBufferHandle && msg)
     mCASESessionEstablished = true;
 
     // Forget our exchange, as no additional messages are expected from the peer
+    mExchangeCtxt->SetDelegate(nullptr);
     mExchangeCtxt = nullptr;
 
     // Call delegate to indicate session establishment is successful
+    // Do this last in case the delegate frees us.
     mDelegate->OnSessionEstablished();
 
 exit:
@@ -1118,9 +1122,11 @@ CHIP_ERROR CASESession::HandleSigma3(System::PacketBufferHandle && msg)
     mCASESessionEstablished = true;
 
     // Forget our exchange, as no additional messages are expected from the peer
+    mExchangeCtxt->SetDelegate(nullptr);
     mExchangeCtxt = nullptr;
 
     // Call delegate to indicate session establishment is successful
+    // Do this last in case the delegate frees us.
     mDelegate->OnSessionEstablished();
 
 exit:
@@ -1302,15 +1308,17 @@ void CASESession::OnSuccessStatusReport()
     mCASESessionEstablished = true;
 
     // Forget our exchange, as no additional messages are expected from the peer
+    mExchangeCtxt->SetDelegate(nullptr);
     mExchangeCtxt = nullptr;
 
-    // Call delegate to indicate pairing completion
-    mDelegate->OnSessionEstablished();
-
     mState = kInitialized;
 
     // TODO: Set timestamp on the new session, to allow selecting a least-recently-used session for eviction
     // on running out of session contexts.
+
+    // Call delegate to indicate pairing completion.
+    // Do this last in case the delegate frees us.
+    mDelegate->OnSessionEstablished();
 }
 
 CHIP_ERROR CASESession::OnFailureStatusReport(Protocols::SecureChannel::GeneralStatusCode generalCode, uint16_t protocolCode)
@@ -1524,8 +1532,10 @@ CHIP_ERROR CASESession::OnMessageReceived(ExchangeContext * ec, const PayloadHea
     {
         // Null out mExchangeCtxt so that Clear() doesn't try closing it.  The
         // exchange will handle that.
+        mExchangeCtxt->SetDelegate(nullptr);
         mExchangeCtxt = nullptr;
         Clear();
+        // Do this last in case the delegate frees us.
         mDelegate->OnSessionEstablishmentError(err);
     }
     return err;

src/protocols/secure_channel/PASESession.cpp

@@ -343,11 +343,13 @@ void PASESession::OnResponseTimeout(ExchangeContext * ec)
     ChipLogError(SecureChannel,
                  "PASESession timed out while waiting for a response from the peer. Expected message type was %" PRIu8,
                  to_underlying(mNextExpectedMsg));
-    mDelegate->OnSessionEstablishmentError(CHIP_ERROR_TIMEOUT);
     // Null out mExchangeCtxt so that Clear() doesn't try closing it.  The
     // exchange will handle that.
+    mExchangeCtxt->SetDelegate(nullptr);
     mExchangeCtxt = nullptr;
     Clear();
+    // Do this last in case the delegate frees us.
+    mDelegate->OnSessionEstablishmentError(CHIP_ERROR_TIMEOUT);
 }
 
 CHIP_ERROR PASESession::DeriveSecureSession(CryptoContext & session, CryptoContext::SessionRole role)
@@ -824,9 +826,11 @@ CHIP_ERROR PASESession::HandleMsg3(System::PacketBufferHandle && msg)
     mPairingComplete = true;
 
     // Forget our exchange, as no additional messages are expected from the peer
+    mExchangeCtxt->SetDelegate(nullptr);
     mExchangeCtxt = nullptr;
 
     // Call delegate to indicate pairing completion
+    // Do this last in case the delegate frees us.
     mDelegate->OnSessionEstablished();
 
 exit:
@@ -843,9 +847,11 @@ void PASESession::OnSuccessStatusReport()
     mPairingComplete = true;
 
     // Forget our exchange, as no additional messages are expected from the peer
+    mExchangeCtxt->SetDelegate(nullptr);
     mExchangeCtxt = nullptr;
 
     // Call delegate to indicate pairing completion
+    // Do this last in case the delegate frees us.
     mDelegate->OnSessionEstablished();
 }
 
@@ -938,9 +944,11 @@ CHIP_ERROR PASESession::OnMessageReceived(ExchangeContext * exchange, const Payl
     {
         // Null out mExchangeCtxt so that Clear() doesn't try closing it.  The
         // exchange will handle that.
+        mExchangeCtxt->SetDelegate(nullptr);
         mExchangeCtxt = nullptr;
         Clear();
         ChipLogError(SecureChannel, "Failed during PASE session setup. %s", ErrorStr(err));
+        // Do this last in case the delegate frees us.
         mDelegate->OnSessionEstablishmentError(err);
     }
     return err;