Fix event buffer size boundary check (#25234)

* improve event log dump

* Fix event buffer size boundary check

src/app/EventManagement.cpp

@@ -858,6 +858,17 @@ bool CircularEventBuffer::IsFinalDestinationForPriority(PriorityLevel aPriority)
     return !((mpNext != nullptr) && (mpNext->mPriority <= aPriority));
 }
 
+/**
+ * @brief
+ * TLVCircularBuffer::OnInit can modify the state of the buffer, but we don't want that behavior here.
+ * We want to make sure we don't change our state, and just report the currently-available space.
+ */
+CHIP_ERROR CircularEventBuffer::OnInit(TLV::TLVWriter & writer, uint8_t *& bufStart, uint32_t & bufLen)
+{
+    GetCurrentWritableBuffer(bufStart, bufLen);
+    return CHIP_NO_ERROR;
+}
+
 void CircularEventReader::Init(CircularEventBufferWrapper * apBufWrapper)
 {
     CircularEventBuffer * prev;

src/app/EventManagement.h

@@ -109,6 +109,8 @@ class CircularEventBuffer : public TLV::TLVCircularBuffer
                                                       ///< lesser priority are dropped when they get bumped out of this buffer
 
     size_t mRequiredSpaceForEvicted = 0; ///< Required space for previous buffer to evict event to new buffer
+
+    CHIP_ERROR OnInit(TLV::TLVWriter & writer, uint8_t *& bufStart, uint32_t & bufLen) override;
 };
 
 class CircularEventReader;

src/app/tests/TestEventLogging.cpp

@@ -115,12 +115,8 @@ void ENFORCE_FORMAT(1, 2) SimpleDumpWriter(const char * aFormat, ...)
 void PrintEventLog()
 {
     chip::TLV::TLVReader reader;
-    size_t elementCount;
     chip::app::CircularEventBufferWrapper bufWrapper;
-    chip::app::EventManagement::GetInstance().GetEventReader(reader, chip::app::PriorityLevel::Debug, &bufWrapper);
-
-    chip::TLV::Utilities::Count(reader, elementCount, false);
-    printf("Found %u elements\n", static_cast<unsigned int>(elementCount));
+    chip::app::EventManagement::GetInstance().GetEventReader(reader, chip::app::PriorityLevel::Critical, &bufWrapper);
     chip::TLV::Debug::Dump(reader, SimpleDumpWriter);
 }
 

src/lib/core/TLVCircularBuffer.cpp

@@ -194,14 +194,20 @@ CHIP_ERROR TLVCircularBuffer::OnInit(TLVWriter & writer, uint8_t *& bufStart, ui
 
 CHIP_ERROR TLVCircularBuffer::GetNewBuffer(TLVWriter & ioWriter, uint8_t *& outBufStart, uint32_t & outBufLen)
 {
-    uint8_t * tail = QueueTail();
-
     if (mQueueLength >= mQueueSize)
     {
         // Queue is out of space, need to evict an element
         ReturnErrorOnFailure(EvictHead());
     }
 
+    GetCurrentWritableBuffer(outBufStart, outBufLen);
+    return CHIP_NO_ERROR;
+}
+
+void TLVCircularBuffer::GetCurrentWritableBuffer(uint8_t *& outBufStart, uint32_t & outBufLen) const
+{
+    uint8_t * tail = QueueTail();
+
     // set the output values, returned buffer must be contiguous
     outBufStart = tail;
 
@@ -213,8 +219,6 @@ CHIP_ERROR TLVCircularBuffer::GetNewBuffer(TLVWriter & ioWriter, uint8_t *& outB
     {
         outBufLen = static_cast<uint32_t>(mQueueHead - tail);
     }
-
-    return CHIP_NO_ERROR;
 }
 
 /**

src/lib/core/TLVCircularBuffer.h

@@ -128,6 +128,17 @@ class DLL_EXPORT TLVCircularBuffer : public chip::TLV::TLVBackingStore
                                    circular buffer.  See the ProcessEvictedElementFunct type definition on additional information on
                                    implementing the mProcessEvictedElement function. */
 
+protected:
+    /**
+     * @brief
+     *   returns the actual state of what our current available buffer space is
+     *
+     * @param[out] outBufStart The pointer to the current buffer
+     *
+     * @param[out] outBufLen   The available length for writing
+     */
+    void GetCurrentWritableBuffer(uint8_t *& outBufStart, uint32_t & outBufLen) const;
+
 private:
     uint8_t * mQueue;
     uint32_t mQueueSize;