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.
Browsers negotiate ECDHE cipher suites by default. On ESP32-S3 the
hardware RSA accelerator handles RSA key exchange efficiently, but
there is no ECP hardware accelerator. ECDHE requires the server to
compute an ephemeral key pair: ecp_precompute_comb() builds a comb
table through many sequential ECP point doublings, each dispatched
to the hardware bignum unit (esp_bignum.c), but the ECP layer has
no RTOS yield points between iterations. The entire computation runs
to completion on CPU 0 without ever resetting the task watchdog.
A single handshake does not exceed the watchdog timeout on its own,
but two consecutive handshakes (e.g. a browser retry after a failed
attempt) accumulate enough uninterrupted runtime to starve IDLE0:
E (54924) esp-tls-mbedtls: mbedtls_ssl_handshake returned -0x0050
E (57208) esp-tls-mbedtls: mbedtls_ssl_handshake returned -0x7280
E (57638) task_wdt: Task watchdog got triggered.
E (57638) task_wdt: - IDLE0 (CPU 0)
E (57638) task_wdt: Tasks currently running:
E (57638) task_wdt: CPU 0: httpd
The crash occurs in ecp_precompute_comb() → ecp_double_jac() →
mbedtls_mpi_mul_mpi() during the ServerKeyExchange step.
Fix by wrapping mbedtls_ssl_config_defaults() via the linker --wrap
mechanism. The wrapper intercepts server-side SSL config init
(MBEDTLS_SSL_IS_SERVER) and replaces the cipher suite list with
RSA key exchange only, routing handshakes through the hardware RSA
accelerator and eliminating the ECDH path entirely. MQTT connections
(MBEDTLS_SSL_IS_CLIENT) are unaffected.
Also switch the self-signed cert generator from EC (prime256v1) to
RSA 2048 so the generated certificate matches the restricted cipher
suites.
Changes:
- arch/esp32/tls_cipher_restrict.c: new file implementing the
mbedtls_ssl_config_defaults wrap; restricts server cipher suites
to RSA_WITH_AES_{128,256}_{GCM,CBC}_SHA{256,384}
- platformio.ini: add -Wl,--wrap=mbedtls_ssl_config_defaults and
include tls_cipher_restrict.c in the esp32_base build
- arch/esp32/extra_scripts/generate_web_panel_cert.py: switch key
generation from `openssl ecparam -name prime256v1` to `openssl
genrsa 2048`
On dual-core ESP32-S3 (ARDUINO_RUNNING_CORE=1), the Arduino loop and
LoRa processing run exclusively on core 1. ESP-IDF v4 creates mqtt_task
with tskNO_AFFINITY, meaning FreeRTOS may schedule them on core 1 under
load, preempting the LoRa loop.
ESP-IDF v4 provides no public API to change a task's core affinity after
creation (vTaskCoreAffinitySet is IDF v5+ only), and the esp_mqtt_client
config struct has no task_core_id field. The precompiled Arduino-ESP32
framework cannot be patched via sdkconfig.
Instead, use the GCC/LD --wrap linker mechanism to intercept every call
to xTaskCreatePinnedToCore. Any task created with tskNO_AFFINITY is
redirected to core 0. Tasks that are already explicitly pinned (Wi-Fi
driver, LwIP, httpd, esp_timer, ipc0/ipc1) are passed through unchanged.
We intentionally do not filter by task name. Pinning all unpinned tasks
makes the approach robust against internal ESP-IDF task name changes and
catches any future tasks that may be added with tskNO_AFFINITY.
Verified task layout after the change:
loopTask pri=1 core=1 (Arduino loop / LoRa — unchanged)
mqtt_task pri=5 core=0 (was tskNO_AFFINITY, now pinned)
httpd pri=2 core=0 (core_id set explicitly in WebPanelServer)
tiT pri=18 core=0 (LwIP, already pinned by ESP-IDF)
wifi pri=23 core=0 (Wi-Fi driver, already pinned)
esp_timer pri=22 core=0 (already pinned)
ipc0/ipc1 pri=24 core=0/1 (IPC, already pinned per-core)
The -Wl,--wrap flag and arch/esp32/task_pinning.c are added only to
[esp32_base] (IDF v4). The ESP32-C6 pioarduino target (IDF v5) is
unaffected and can use vTaskCoreAffinitySet() if needed in the future.
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.
_have_time_sync is reset to false whenever WiFi disconnects, even
though the ESP32 RTC continues to hold accurate time after a
successful SNTP sync. This caused hasTimeSync() to return false
during transient WiFi outages, unnecessarily tearing down MQTT
broker connections and suppressing packet publishing.
Introduce _last_time_sync to record the wall-clock time of the
most recent confirmed sync. Move hasTimeSync() out of the header
into NetworkService.cpp and extend its logic: in addition to the
existing _have_time_sync flag, return true if the system clock is
still sane (>= kMinSaneEpoch) and no more than kMaxOutOfSync (24h)
has elapsed since the last confirmed sync.
This makes the MQTT uplink resilient to brief WiFi dropouts without
requiring any changes to callers of hasTimeSync().
Also bump kMinSaneEpoch from 2025-01-01 to 2026-01-01.
There's no known reason why additional firmware build of this board
with serial logging enabled was needed.
So, removing it for now to optimize building process and cleanup
firmware list.
When the MQTT WebSocket handshake fails before a connection is fully
established (e.g. "Sec-WebSocket-Accept not found"), the IDF v4
transport teardown path writes only 3 of the 4 bytes of the heap block
tail canary (expected 0xbaad5678, actual 0xbaad5600). The subsequent
esp_mqtt_client_destroy() call frees that block, causing multi_heap_free
to detect the broken canary and abort:
CORRUPT HEAP: Bad tail at 0x3fcb42a4. Expected 0xbaad5678 got 0xbaad5600
assert failed: multi_heap_free multi_heap_poisoning.c:259 (head != NULL)
The fix is to check heap integrity with heap_caps_check_integrity_all(false)
between esp_mqtt_client_stop() and esp_mqtt_client_destroy(). If corruption
is detected, scan internal SRAM (0x3FC00000–0x3FD00000) for the truncated
canary pattern and restore it to the correct value before
destroy() runs.
The scan is a no-op when the heap is clean and is compiled out entirely
on IDF v5+, where the underlying bug does not exist.
This fixes crash-on-reconnect observed with ESP32-S3 + IDF v4 + WSS transport.
