Zero-Copy Streaming & Memory

Serving dynamic web interfaces and real-time graphs on a microcontroller often leads to severe heap fragmentation and Out-Of-Memory (OOM) crashes. The ESP32-SwitchBot avoids heap exhaustion through chunked HTTP streaming and memory segregation.

Chunked HTTP Streaming Engine (`sendWrappedPageStream`)

Traditional Arduino web servers construct entire HTML documents into dynamic String objects on the heap before calling server.send(). For complex pages containing JavaScript and SVG graphics (8–20 KB), this causes frequent allocations, moves, and heap fragmentation.

The ESP32-SwitchBot uses an optimized lambda-based chunked streaming pipeline:

cpp

template <typename F>
inline void sendWrappedPageStream(WebServer &server, const char* title, const char* icon, F bodyWriter, const char* extraScript = "", bool centered = false) {
  server.sendHeader("Connection", "close");
  server.setContentLength(CONTENT_LENGTH_UNKNOWN);
  server.send(200, "text/html; charset=utf-8", "");

  char headBuf[600];
  // Format standard <head> and container on the stack
  server.sendContent(headBuf);

  // Stream dynamic body content via closure callback
  bodyWriter();

  server.sendContent(F("</div>"));
  if (extraScript && extraScript[0]) {
    server.sendContent(extraScript);
  }
  server.sendContent(F("</body></html>"));
  server.sendContent(""); // Terminate chunked transfer
}

Advantages:

Zero Dynamic Heap Allocations: Small stack buffers (snprintf) format each HTML card, which is transmitted directly into the network buffer via server.sendContent().
Infinite Payload Scalability: Pages of any size can be delivered without consuming RAM.
No Truncation: Large embedded scripts (such as the 8 KB calibration JavaScript bundle) stream completely to the browser without risk of buffer clipping.

Memory Segregation (Internal SRAM vs. Octal PSRAM)

The ESP32-S3 (N16R8) combines ~360 KB of ultra-fast internal SRAM with 8 MB of Octal SPI PSRAM (MALLOC_CAP_SPIRAM):

Internal SRAM: Reserved exclusively for high-frequency FreeRTOS kernel stacks, Wi-Fi DMA packet buffers, and the WebServer task.
Octal PSRAM: Utilized by microlink and WireGuard for large crypto buffers, packet queues, and TLS handshake states.
Heap Threshold (CONFIG_SPIRAM_MALLOC_ALWAYSINTERNAL=4096): Allocations smaller than 4 KB always stay in internal SRAM for maximum execution speed, while large buffers automatically spill into PSRAM.

Zero-Copy Streaming & Memory ​

Chunked HTTP Streaming Engine (sendWrappedPageStream) ​

Advantages: ​

Memory Segregation (Internal SRAM vs. Octal PSRAM) ​

Zero-Copy Streaming & Memory

Chunked HTTP Streaming Engine (`sendWrappedPageStream`)

Advantages:

Memory Segregation (Internal SRAM vs. Octal PSRAM)