The ESP32 processes HTTP requests sequentially on a single task.
Under load — generating chunked HTML pages, running commands, or
serving sequential stats API calls — it can be slow to send data
or loop back to accept the next request. The previous 2-second
recv/send timeouts were too tight for this: the httpd layer would
drop connections mid-transfer, causing the browser to hang or
show incomplete pages.
Raise recv_wait_timeout and send_wait_timeout from 2 s to 10 s
on both the HTTPS and HTTP-redirect servers, giving the ESP32
enough headroom to finish generating and sending responses without
the transport layer tearing down the connection prematurely.
Set backlog_conn to 0 on both servers. With the previous backlog
of 2, incoming connections completed the TCP handshake and queued
in the kernel while the ESP32 was busy. The browser saw the
connection as open but received no HTTP response, causing it to
freeze indefinitely. With backlog 0 (lwIP minimum), connections
that cannot be immediately accepted are refused outright, giving
the browser a fast, recoverable error instead of a silent hang.
Enable lru_purge_enable on the HTTPS server. Browsers hold
keep-alive connections open for reuse. With max_open_sockets = 2,
both slots can be occupied by idle keep-alive connections from the
same session, blocking a new connection attempt entirely. LRU
purge automatically closes the least-recently-used idle keep-alive
connection to make room, ensuring the single client can always
reconnect without a server restart.
When sending large PROGMEM content in chunks over HTTPS, the lwIP TCP/IP
task (tiT) could monopolize CPU 0 for an extended period without ever
yielding, starving the IDLE0 task and triggering the task watchdog timer.
Add vTaskDelay(1) at the end of each iteration in sendProgmemChunked()
to yield to the scheduler between chunks, allowing the IDLE task to reset
the watchdog and preventing spurious reboots during web panel page loads.
The hardcoded kWebPageChunkSize of 768 bytes caused the task watchdog
to trigger when serving the web panel over HTTPS. Each call to
httpd_resp_send_chunk() results in a separate TLS record encryption
via mbedTLS, which on ESP32-S3 uses DMA-backed AES-GCM (esp_aes_process_dma).
The gdma_disconnect() call inside that path enters a critical section,
blocking the IDLE0 task. With 768-byte chunks, a large page response
requires many such DMA operations in tight succession, starving the IDLE
task long enough to trip the watchdog.
Replacing the hardcoded value with MBEDTLS_SSL_OUT_CONTENT_LEN aligns the
chunk size to the TLS output record buffer, minimising the number of TLS
records (and thus DMA encryption operations) needed to send a full page,
and keeping the httpd task within the watchdog timeout.
Fixes: task_wdt abort in sendProgmemChunked() -> httpd_ssl_send() ->
esp_aes_process_dma() -> gdma_disconnect() on ESP32-S3.
Set task_priority = tskIDLE_PRIORITY + 2 and core_id = 0 for both the
HTTPS server and the HTTP-to-HTTPS redirect server. This keeps web
serving off core 1, which handles radio and application logic, reducing
interference with time-sensitive operations.
Valentin V. Bartenev