ReadHandler changes for large payloads

When sending reports, if the session established with the peer
supports large payloads, the ReadHandler will allocate a large
buffer to, potentially, fit more attribute and event data.

Author: pidarped

src/app/InteractionModelEngine.cpp

@@ -853,6 +853,11 @@ Protocols::InteractionModel::Status InteractionModelEngine::OnReadInitialRequest
         return Status::ResourceExhausted;
     }
 
+    if (apExchangeContext->GetSessionHandle()->AllowsLargePayload())
+    {
+        handler->UseLargePayloadBuffer();
+    }
+
     handler->OnInitialRequest(std::move(aPayload));
 
     return Status::Success;

src/app/ReadHandler.h

@@ -491,6 +491,10 @@ class ReadHandler : public Messaging::ExchangeDelegate
     /// @param aFlag Flag to clear
     void ClearStateFlag(ReadHandlerFlags aFlag);
 
+
+    void UseLargePayloadBuffer() { mUseLargePayloadBuffer = true; }
+    bool ShouldUseLargePayloadBuffer() { return mUseLargePayloadBuffer; }
+
     AttributePathExpandIterator mAttributePathExpandIterator = AttributePathExpandIterator(nullptr);
 
     // The current generation of the reporting engine dirty set the last time we were notified that a path we're interested in was
@@ -572,6 +576,8 @@ class ReadHandler : public Messaging::ExchangeDelegate
 
     // TODO (#27675): Merge all observers into one and that one will dispatch the callbacks to the right place.
     Observer * mObserver = nullptr;
+
+    bool mUseLargePayloadBuffer = false;
 };
 } // namespace app
 } // namespace chip

src/app/StatusResponse.h

@@ -27,6 +27,7 @@
 namespace chip {
 namespace app {
 static constexpr size_t kMaxSecureSduLengthBytes = kMaxAppMessageLen + kMaxTagLen;
+static constexpr size_t kMaxLargeSecureSduLengthBytes = kMaxLargeAppMessageLen + kMaxTagLen;
 
 class StatusResponse
 {

src/app/reporting/Engine.cpp

@@ -492,10 +492,11 @@ CHIP_ERROR Engine::BuildAndSendSingleReportData(ReadHandler * apReadHandler)
     CHIP_ERROR err = CHIP_NO_ERROR;
     chip::System::PacketBufferTLVWriter reportDataWriter;
     ReportDataMessage::Builder reportDataBuilder;
-    chip::System::PacketBufferHandle bufHandle = System::PacketBufferHandle::New(chip::app::kMaxSecureSduLengthBytes);
-    uint16_t reservedSize                      = 0;
-    bool hasMoreChunks                         = false;
-    bool needCloseReadHandler                  = false;
+    size_t maxSduSize                           = chip::app::kMaxSecureSduLengthBytes;
+    chip::System::PacketBufferHandle bufHandle  = nullptr;
+    uint16_t reservedSize                       = 0;
+    bool hasMoreChunks                          = false;
+    bool needCloseReadHandler                   = false;
 
     // Reserved size for the MoreChunks boolean flag, which takes up 1 byte for the control tag and 1 byte for the context tag.
     const uint32_t kReservedSizeForMoreChunksFlag = 1 + 1;
@@ -512,11 +513,18 @@ CHIP_ERROR Engine::BuildAndSendSingleReportData(ReadHandler * apReadHandler)
 
     VerifyOrExit(apReadHandler != nullptr, err = CHIP_ERROR_INVALID_ARGUMENT);
     VerifyOrExit(apReadHandler->GetSession() != nullptr, err = CHIP_ERROR_INCORRECT_STATE);
+
+    if (apReadHandler->ShouldUseLargePayloadBuffer())
+    {
+        maxSduSize = chip::app::kMaxLargeSecureSduLengthBytes;
+    }
+
+    bufHandle = System::PacketBufferHandle::New(maxSduSize);
     VerifyOrExit(!bufHandle.IsNull(), err = CHIP_ERROR_NO_MEMORY);
 
-    if (bufHandle->AvailableDataLength() > kMaxSecureSduLengthBytes)
+    if (bufHandle->AvailableDataLength() > maxSduSize)
     {
-        reservedSize = static_cast<uint16_t>(bufHandle->AvailableDataLength() - kMaxSecureSduLengthBytes);
+        reservedSize = static_cast<uint16_t>(bufHandle->AvailableDataLength() - maxSduSize);
     }
 
     reportDataWriter.Init(std::move(bufHandle));