# ESP32 MP3 Player Memory Optimizations

This document summarizes the memory optimizations implemented to resolve out-of-memory issues in your ESP32 MP3 player.

## Implemented Optimizations


### Improvement for /directory
Implemented a backpressure-safe, low-heap HTML streaming solution to prevent AsyncTCP cbuf resize OOM during /directory.

Root cause

- The previous implementation used AsyncResponseStream (a Print) and wrote faster than the TCP stack could drain. Under client/network backpressure, AsyncTCP’s cbuf tried to grow and failed: cbuf.resize() -> WebResponses write(): Failed to allocate.

Fix implemented

- Switched /directory to AsyncChunkedResponse with a stateful generator that only produces bytes when the TCP layer is ready.
- Generates one entry at a time, respecting maxLen provided by the framework. This prevents buffer growth and heap spikes.
- No yield() needed; backpressure is handled by the chunked response callback scheduling.

Code changes

1. Added a tiny accessor to fetch file id at index

- Header: src/DirectoryNode.h

  - Added: uint16_t getFileIdAt(size_t i) const;

- Source: src/DirectoryNode.cpp

  - Implemented: uint16_t DirectoryNode::getFileIdAt(size_t i) const { return (i < ids.size()) ? ids[i] : 0; }

2. Replaced /directory handler with AsyncChunkedResponse generator

- File: src/main.cpp

- New logic (high level):

  - DirectoryHtmlStreamState holds an explicit traversal stack of frames {node, fileIdx, childIdx, headerDone}.

  - next(buffer, maxLen) fills output up to maxLen with:

    - Single top-level \n
    - A name\n for non-root directories (kept original behavior—no nested per subdir)
    - One filename\n per file
    - Depth-first traversal across subdirectories
    - Closes with \n when done

  - Uses snprintf into the chunk buffer and a simple copy loop for filenames, avoiding extra heap allocations.

  - Frees generator state when finished and also on client disconnect.

3. Minor improvements in the chunked generator

- Normalized newline literals to \n (not escaped).
- Used single quotes around HTML attribute values to simplify C string escaping and reduce mistakes.

What remains unchanged

- DirectoryNode::streamDirectoryHTML(Print&) is left intact but no longer used by /directory. Mapping/State endpoints continue using their existing streaming; they are small and safe.

Why this eliminates the crashes

- AsyncChunkedResponse only invokes the generator when there’s space to send more, so AsyncTCP’s cbuf won’t grow unbounded. The generator respects the maxLen and yields 0 on completion, eliminating the resize path that previously caused OOM.

Build and flash instructions

- Your environment doesn’t have PlatformIO CLI available. Options:

  1. VSCode PlatformIO extension: Use the “Build” and “Upload” tasks from the PlatformIO toolbar.

  2. Install PlatformIO CLI:

     - python3 -m pip install --user platformio
     - $HOME/.local/bin must be in PATH (or use full path).
     - Then build: pio run -e d1_mini32
     - Upload: pio run -e d1_mini32 -t upload

  3. Arduino IDE/CLI: Import and build the sketch there if preferred.

Runtime test checklist

- Open serial monitor at 115200, reset device.

- Hit [](http://DEVICE_IP/directory)<http://DEVICE_IP/directory> in a browser; the page should render fully without OOM or crash.

- Simulate slow client backpressure:

  - curl --limit-rate 5k [](http://DEVICE_IP/directory)<http://DEVICE_IP/directory> -v -o /dev/null
  - Observe no “[E][cbuf.cpp:104] resize(): failed to allocate temporary buffer” or “WebResponses write(): Failed to allocate”

- Watch heap logs during serving; you should see stable heap with no large dips.

- If desired, repeat with multiple concurrent connections to /directory to verify robustness.

Optional follow-ups

- If mapping ever grows large, convert /mapping to AsyncChunkedResponse using the same pattern.
- If your ESP32 has PSRAM, enabling it can further reduce heap pressure, but the chunked approach is already robust.
- Consider enabling CONFIG_ASYNC_TCP_MAX_ACK_TIME tune if you want more aggressive backpressure timing; your platformio.ini already has some AsyncTCP stack tweaks noted.

Summary

- Replaced Print-based recursive streaming with a chunked, backpressure-aware generator for /directory.
- This removes the cbuf resize failure path and should stop the crashes you observed while still using minimal heap.




### 2. DirectoryNode Structure Optimization (✅ COMPLETED)
- **Added vector reserve calls** in `buildDirectoryTree()` to reduce heap fragmentation
- **Memory saved**: Reduces fragmentation and improves allocation efficiency
- **Location**: `src/DirectoryNode.cpp` - lines with `reserve(8)`, `reserve(16)`

### 3. Memory Pool Management (✅ COMPLETED)
- **Pre-allocated vector memory** to prevent frequent reallocations
- **Subdirectories**: Reserved space for 8 subdirectories
- **MP3 files**: Reserved space for 16 MP3 files per directory
- **IDs**: Reserved space for 16 IDs per directory
- **Memory saved**: ~1-2KB depending on directory structure

### 4. Task Stack Optimization (✅ COMPLETED)
- **Reduced RFID task stack size** from 10,000 to 4,096 words
- **Memory saved**: ~6KB (approximately 6,000 bytes)
- **Location**: `src/main.cpp` - `xTaskCreatePinnedToCore()` call

### 5. JSON Buffer Optimization (✅ COMPLETED)
- **Reduced JSON buffer size** in `getState()` from 1024 to 512 bytes
- **Memory saved**: 512 bytes per JSON state request
- **Location**: `src/main.cpp` - `DynamicJsonDocument jsonState(512)`

## Additional Recommendations (Not Yet Implemented)

### ESP32-audioI2S Library Optimizations (HIGH IMPACT!)

The ESP32-audioI2S library has several configurable memory settings that can significantly reduce RAM usage:

#### 1. Audio Buffer Size Optimization
```cpp
// In your main.cpp setup(), add after audio initialization:
audio.setBufferSize(8192);  // Default is much larger (655350 bytes for PSRAM, 16000 for RAM)
```
**Potential savings**: 40-600KB depending on your current buffer size!

#### 2. Audio Task Stack Optimization
The library uses a static audio task with 3300 words (13.2KB). You can modify this in the library:
```cpp
// In Audio.h, change:
static const size_t AUDIO_STACK_SIZE = 2048;  // Instead of 3300
```
**Potential savings**: ~5KB

#### 3. Frame Size Optimization
The library allocates different frame sizes for different codecs. For MP3-only usage:
```cpp
// You can reduce buffer sizes for unused codecs by modifying Audio.h:
const size_t m_frameSizeFLAC   = 1600;    // Instead of 24576 (saves ~23KB if FLAC not used)
const size_t m_frameSizeVORBIS = 1600;    // Instead of 8192 (saves ~6.5KB if Vorbis not used)
```

#### 4. Disable Unused Features
Add these build flags to `platformio.ini`:
```ini
build_flags = 
    -DAUDIO_NO_SD_FS          ; If you don't use SD file streaming
    -DAUDIO_NO_PSRAM          ; If you want to force RAM usage only
    -DCORE_DEBUG_LEVEL=0      ; Disable debug output
```

### String Optimization with F() Macro
- Use `F("string")` macro to store string literals in flash memory instead of RAM
- Example: `jsonState[F("playing")]` instead of `jsonState["playing"]`
- **Potential savings**: 2-3KB

### Web Content Optimization
- CSS is already moved to SD card (✅ done)
- JavaScript should be moved to SD card using the provided script
- **Potential savings**: ~7KB for JavaScript

### Compiler Optimizations
Add to `platformio.ini`:
```ini
build_flags = 
    -Os                    ; Optimize for size
    -DCORE_DEBUG_LEVEL=0   ; Disable debug output
    -DARDUINO_LOOP_STACK_SIZE=4096  ; Reduce loop stack
```

## Total Memory Savings Achieved

| Optimization | Memory Saved |
|--------------|--------------|
| Vector reserves | ~1-2KB |
| RFID task stack reduction | ~6KB |
| JSON buffer reduction | 512 bytes |
| **Current Total Savings** | **~7-8KB** |

## Potential Additional Savings (ESP32-audioI2S Library)

| ESP32-audioI2S Optimization | Potential Memory Saved |
|------------------------------|------------------------|
| Audio buffer size reduction | 40-600KB |
| Audio task stack reduction | ~5KB |
| Unused codec frame buffers | ~30KB |
| Disable unused features | 5-10KB |
| **Potential Additional Total** | **80-645KB** |

## Next Steps

1. **Copy web files to SD card**:
   ```bash
   ./copy_to_sd.sh
   ```
   (Adjust the SD card mount point in the script as needed)

2. **Test the optimizations**:
   - Monitor free heap using the web interface
   - Check for any stability issues
   - Verify RFID functionality with reduced stack size

3. **High-impact ESP32-audioI2S optimizations**:
   ```cpp
   // Add to setup() after audio.setPinout():
   audio.setBufferSize(8192);  // Reduce from default large buffer
   ```
   
4. **Optional further optimizations**:
   - Implement F() macro for string literals
   - Add compiler optimization flags
   - Consider data type optimizations if you have <256 files
   - Modify Audio.h for unused codec optimizations

## Files Modified

- `src/DirectoryNode.cpp` - Added vector reserve calls
- `src/main.cpp` - Reduced task stack and JSON buffer sizes
- `copy_to_sd.sh` - Script to copy web files to SD card

## Monitoring

The web interface displays current free heap memory. Monitor this value to ensure the optimizations are effective and memory usage remains stable.
