Address comments and apply suggestions from code review

Co-authored-by: Boris Zbarsky <bzbarsky@apple.com>

Author: pidarped

src/app/ReadHandler.cpp

@@ -921,11 +921,11 @@ void ReadHandler::ClearStateFlag(ReadHandlerFlags aFlag)
 
 size_t ReadHandler::GetReportBufferMaxSize()
 {
-    size_t maxBufSize                  = chip::app::kMaxSecureSduLengthBytes;
+    size_t maxBufSize                  = kMaxSecureSduLengthBytes;
     Transport::SecureSession * session = GetSession();
     if (session && session->AllowsLargePayload())
     {
-        maxBufSize = chip::app::kMaxLargeSecureSduLengthBytes;
+        maxBufSize = kMaxLargeSecureSduLengthBytes;
     }
 
     return maxBufSize;

src/app/ReadHandler.h

@@ -335,9 +335,10 @@ class ReadHandler : public Messaging::ExchangeDelegate
 
     /*
      * Get the appropriate size of a packet buffer to allocate for encoding a Report message.
-     * Depending on the underlying session, which may or may not support large
-     * payloads, a buffer with the corresponding max size would be allocated.
+     * This size might depend on the underlying session used by the ReadHandler.
      *
+     * The size returned here is the size not including the various prepended headers
+     * (what System::PacketBuffer calls the "available size").
      */
     size_t GetReportBufferMaxSize();
 

src/app/reporting/Engine.cpp

@@ -496,7 +496,7 @@ CHIP_ERROR Engine::BuildAndSendSingleReportData(ReadHandler * apReadHandler)
     uint16_t reservedSize                      = 0;
     bool hasMoreChunks                         = false;
     bool needCloseReadHandler                  = false;
-    size_t maxSduSize                          = 0;
+    size_t reportBufferMaxSize                 = 0;
 
     // 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;
@@ -514,16 +514,14 @@ CHIP_ERROR Engine::BuildAndSendSingleReportData(ReadHandler * apReadHandler)
     VerifyOrExit(apReadHandler != nullptr, err = CHIP_ERROR_INVALID_ARGUMENT);
     VerifyOrExit(apReadHandler->GetSession() != nullptr, err = CHIP_ERROR_INCORRECT_STATE);
 
-    // Depending on whether the session supports large payload or not, the
-    // appropriate  max size would be returned for the Report buffer.
-    maxSduSize = apReadHandler->GetReportBufferMaxSize();
+    reportBufferMaxSize = apReadHandler->GetReportBufferMaxSize();
 
-    bufHandle = System::PacketBufferHandle::New(maxSduSize);
+    bufHandle = System::PacketBufferHandle::New(reportBufferMaxSize);
     VerifyOrExit(!bufHandle.IsNull(), err = CHIP_ERROR_NO_MEMORY);
 
-    if (bufHandle->AvailableDataLength() > maxSduSize)
+    if (bufHandle->AvailableDataLength() > reportBufferMaxSize)
     {
-        reservedSize = static_cast<uint16_t>(bufHandle->AvailableDataLength() - maxSduSize);
+        reservedSize = static_cast<uint16_t>(bufHandle->AvailableDataLength() - reportBufferMaxSize);
     }
 
     reportDataWriter.Init(std::move(bufHandle));
@@ -532,8 +530,8 @@ CHIP_ERROR Engine::BuildAndSendSingleReportData(ReadHandler * apReadHandler)
     reportDataWriter.ReserveBuffer(mReservedSize);
 #endif
 
-    // Always limit the size of the generated packet to fit within kMaxSecureSduLengthBytes regardless of the available buffer
-    // capacity.
+    // Always limit the size of the generated packet to fit within the max size returned by the ReadHandler regardless
+    // of the available buffer capacity.
     // Also, we need to reserve some extra space for the MIC field.
     reportDataWriter.ReserveBuffer(static_cast<uint32_t>(reservedSize + chip::Crypto::CHIP_CRYPTO_AEAD_MIC_LENGTH_BYTES));