This commit resolves critical stability issues causing WiFi file transfer
crashes in STA mode and adds aggressive performance optimizations for
maximum upload/download throughput.
CRITICAL BUG FIXES:
1. Fix use-after-free race condition in handleClient()
- Added atomic operations and mutex protection for server pointer
- Prevents store access fault crashes when stop() is called during handleClient()
- Root cause of the Guru Meditation Error in crash logs
- Location: src/network/CrossPointWebServer.cpp:135-158
2. Fix JSON buffer overflow in handleFileListData()
- Replaced 512-byte static buffer with dynamic allocation
- Safely handles 500-character filenames with JSON escaping
- Prevents stack corruption from oversized file entries
- Location: src/network/CrossPointWebServer.cpp:253-306
3. Convert static upload variables to thread-safe instance variables
- Moved uploadFile, uploadFileName, uploadPath, etc. to class members
- Added mutex protection to prevent concurrent access corruption
- Eliminates race conditions during uploads
- Location: src/network/CrossPointWebServer.h:44-54, CrossPointWebServer.cpp:311-313
4. Add yield() to handleClient loop
- Prevents WiFi stack starvation in STA mode
- Allows LWIP to process incoming packets and prevent buffer overflow
- Critical for stability during file transfers
- Location: src/activities/network/CrossPointWebServerActivity.cpp:304-311
5. Fix heap exhaustion with String pre-allocation
- Pre-allocate String capacities to avoid reallocations during upload
- Add heap threshold check (50KB minimum) before accepting uploads
- Reduces memory fragmentation
- Location: src/network/CrossPointWebServer.cpp:323-376
ROBUSTNESS IMPROVEMENTS:
6. Increase task stack size from 2KB to 6KB
- Prevents stack overflow during rendering + network operations
- Aligns with other display+network activity stack sizes
- Location: src/activities/network/CrossPointWebServerActivity.cpp:51
PERFORMANCE OPTIMIZATIONS:
7. Add LWIP TCP/IP stack optimizations
- Increased TCP MSS to 1436 bytes (optimized for WiFi)
- Increased send/receive buffers to 5744 bytes (4x MSS)
- Enlarged TCP/IP mailbox sizes for better packet handling
- Increased retransmission timeout to 3000ms (accommodates SD writes)
- Location: platformio.ini:31-49
8. Add WiFi performance optimizations
- Increased WiFi RX/TX buffer counts for better throughput
- Configured dynamic buffer allocation for optimal memory usage
- Enabled TCP window scaling and oversizing
- Location: platformio.ini:41-49
9. Maximize WiFi TX power
- Set WiFi TX power to maximum (19.5dBm) for best signal strength
- Improves throughput, especially at distance
- Applied to both STA and AP modes
- Location: src/network/CrossPointWebServer.cpp:58,
src/activities/network/CrossPointWebServerActivity.cpp:152,192
EXPECTED IMPACT:
- Eliminates WiFi file transfer crashes in STA mode
- Improves upload/download speeds by 2-3x through TCP optimizations
- Increases stability during large file transfers (>100MB)
- Better performance on weak WiFi signals
- Reduces heap fragmentation and memory pressure
TESTING RECOMMENDATIONS:
1. Test large file uploads (>50MB) in both STA and AP modes
2. Verify system stability during concurrent uploads
3. Monitor heap usage during file transfers
4. Test with long filenames (400+ characters)
5. Verify performance improvement with speed tests
Fixes: WiFi lockup bug causing Guru Meditation Errors during file transfer
## Summary
* **What is the goal of this PR?** Adds WiFi Access Point (AP) mode
support for File Transfer, allowing the device to create its own WiFi
network that users can connect to directly - useful when no existing
WiFi network is available. And in my experience is faster when the
device is right next to your laptop (but maybe further from your wifi)
* **What changes are included?**
- New `NetworkModeSelectionActivity` - an interstitial screen asking
users to choose between:
- "Join a Network" - connects to an existing WiFi network (existing
behavior)
- "Create Hotspot" - creates a WiFi access point named
"CrossPoint-Reader"
- Modified `CrossPointWebServerActivity` to:
- Launch the network mode selection screen before proceeding
- Support starting an Access Point with mDNS (`crosspoint.local`) and
DNS server for captive portal behavior
- Display appropriate connection info for both modes
- Modified `CrossPointWebServer` to support starting when WiFi is in AP
mode (not just STA connected mode)
## Additional Context
* **AP Mode Details**: The device creates an open WiFi network named
"CrossPoint-Reader". Once connected, users can access the file transfer
page at `http://crosspoint.local/` or `http://192.168.4.1/`
* **DNS Captive Portal**: A DNS server redirects all domain requests to
the device's IP, enabling captive portal behavior on some devices
* **mDNS**: Hostname resolution via `crosspoint.local` is enabled for
both AP and STA modes
* **No breaking changes**: The "Join a Network" option preserves the
existing WiFi connection flow
* **Memory impact**: Minimal - the AP mode uses roughly the same
resources as STA mode
## Summary
* HTML files are now static, streamed directly to the client without
modification
* For any dynamic values, load via JSON APIs
* For files page, we stream the JSON content as we scan the directory to
avoid holding onto too much data
## Additional details
* We were previously building up a very large string all generated on
the X4 directly, we should be leveraging the browser
* Fixes https://github.com/daveallie/crosspoint-reader/issues/94
