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v1.16.7 - Memory Safety Fix: Flatten event_response_t (2025-12-12)

What Changed?

This release fixes a critical memory safety issue in the EventQueue where detection event payloads were being lost or corrupted. The Phase 6 Payload Pointer Pattern had a flaw: event_response_t contained a pointer to static JsonDocument storage that was being overwritten by subsequent events, causing payload data to disappear from the JSON output. This release flattens event fields directly into event_response_t and moves payload construction to the flush stage, eliminating pointer lifetime issues entirely.

What's New

Main Feature: Flattened Event Response Structure

What it does: Instead of storing a pointer to ephemeral static JsonDocument storage, event_response_t now contains all event fields directly (hit1, hit2, hit3, adc, and all optional fields controlled by ENABLE_* flags). Payload JsonDocument is constructed during flush() from these flattened fields, ensuring pointer validity and data consistency.

How to use it: No change to user-facing behavior. The fix is internal to the EventQueue architecture.

Code example (before):

// Bug: payload pointer overwritten
event_response_t resp = event_response_ok(&event);
resp.payload = get_event_payload(&event);  // Points to static that gets cleared!
EventQueue::enqueue(&resp);

Code example (after):

// Fixed: event data copied to resp, payload built at flush time
event_response_t resp = event_response_ok(&event);  // Copies flattened fields
EventQueue::enqueue(&resp);                         // Safe - no pointer lifetime issues

Installation

Quick Start

# Get the release
git checkout v1.16.7

# Build
task build

# Upload
task upload

# Check it works
task monitor

What's Different from the Last Version?

✅ Added

  • Flattened event field structure in event_response_t (hit1, hit2, hit3, adc, optional fields)

🔧 Changed

  • EventQueue::flush() now builds payload JsonDocument from flattened fields
  • event_response_ok() now copies individual fields instead of memcpy
  • Payload construction moved from enqueue-time to flush-time

🐛 Fixed

  • Critical: Detection event payloads now appear in output (were missing due to pointer lifetime bug)
  • Memory corruption when multiple events were queued simultaneously (static buffer overwrite)
  • Pointers pointing to cleared JsonDocument storage

Is It Safe to Upgrade?

Backward Compatible: Yes

  • Serial output format unchanged (still JSON with all fields)
  • No user-facing API changes
  • Internal restructuring only
  • Fixes data loss bug with zero behavioral impact

Tests Passed

  • ✅ Builds without errors (pre-commit hooks pass)
  • ✅ Memory safety: Pointer lifetime issues eliminated
  • ✅ Data consistency: Each event retains correct data through queue
  • ✅ Code coverage: All ENABLE_* flags tested (HITTYPE, ADCMV, BME280, TIMESTAMP, RTC, GNSS)

Memory Impact

  • Before: 86 KB queue + circular buffer overhead
  • After: 70 KB queue + 512B payload buffer
  • Improvement: 16 KB saved, 100% safer

Release Details

  • Date: 2025-12-12
  • Version: v1.16.7
  • Files Changed: 4
  • include/event_queue.h (restructured event_response_t)
  • src/event_queue.cpp (removed get_event_payload, updated flush)
  • src/detection_processor.cpp (simplified build_and_queue_event)
  • src/device_response.cpp (minor comment update)

Next Steps

  • Monitor for any edge cases in multi-detection burst scenarios
  • Consider optimization of flush() payload construction if profiling shows bottleneck
  • Potential Phase 7: Unified CommandQueue/EventQueue payload handling