Tasmota/lib/libesp32/AsyncHttpClientLight/CODE_ANALYSIS.md

Code Review: USE_BERRY_WEBCLIENT_ASYNC async web client

Status: Not mergeable as-is. Device-crashing/hanging defects present. Scope reviewed:

• lib/libesp32/AsyncHttpClientLight/src/AsyncHttpClientLight.{h,cpp} (~1600 lines)
• tasmota/tasmota_xdrv_driver/xdrv_52_3_berry_webclient.ino (Berry bindings)
• lib/libesp32/berry_tasmota/src/be_webclient_lib.c (class definition)
• Cross-checked against lib/lib_ssl/tls_mini/src/WiFiClientSecureLightBearSSL.{h,cpp}

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What it is

A new, self-contained async HTTP/HTTPS client (AsyncHttpClientLight) by an external contributor (HexaMaster), wired into the existing Berry webclient class as a compile-time alternative to HTTPClientLight. It adds:

• async_get_start(), async_post_start(), async_state(), async_abort()
• TLS public-key pinning: tls_pin_pubkey(), tls_clear_pins(), tls_set_rsa_only()

It is off by default (commented out in my_user_config.h), which is the right call given the state below. Existing sync Berry scripts are meant to remain compatible.

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Architecture concern: a FreeRTOS task per request

Every operation — including synchronous GET/POST/getString/writeToStream — runs by spawning a new FreeRTOS task (WorkerTask, 12 KB stack via ASYNCHTTP_WKR_STACK) and then the caller busy-waits on a semaphore (runJob).

• For sync calls this is pure overhead: the main loop is blocked the whole time anyway (it spins on xSemaphoreTake + delay(0)), so you pay 12 KB stack + task create/teardown per request and gain nothing.
• For async it legitimately offloads blocking I/O to the worker.

The cost model (a fresh 12 KB-stack task for each job, low priority tskIDLE_PRIORITY+1) is heavy for an ESP32 and atypical for Tasmota, which normally does cooperative networking on the main loop / fast_loop. This central design decision deserves a discussion before the feature goes further.

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Critical bugs (blocking)

C1. Use-after-free on destruction while a job is in flight

~AsyncHttpClientLight() calls end() (which does _transport->stop() + _transport.reset()) and deletes _busy/_asyncDone, but it never aborts or joins a running worker task.

If the Berry webclient object is GC'd or deinit'd while async_state() is still RUNNING (script drops its reference, or calls close()/reuses incorrectly), the worker keeps dereferencing self->_transport, self->_asyncBody, and the freed semaphores. Guaranteed crash.

Fix: destructor (and end()/deinit) must set _asyncAbortReq, wait for the worker to exit, then free.

C2. Deadlock if response accessors are called while RUNNING

getString() / writeToStream() only take the fast path when _asyncState == ASYNC_DONE. If called while still RUNNING, they fall through to runJob() → xSemaphoreTake(_busy, portMAX_DELAY). But _busy is only released inside asyncState() on the same (now-blocked) main thread. The main loop hangs forever → WDT reset.

The docs say "don't do this," but a library should not deadlock the device on misuse.

C3. No timeout/abort in the sync body reader → infinite loop

writeToStreamDataBlock() (used by sync getString, writeToStream, get_bytes, write_file, write_flash) loops:

while (_transport && _transport->connected() && (len > 0 || len == -1)) {
  int avail = _transport->available();
  if (avail <= 0) { delay(1); continue; }   // no timeout, no abort check
  ...
}

With an identity response, keep-alive, and no Content-Length (_size == -1), a server that holds the socket open with no further data spins forever. The readme acknowledges this "identity with no data" hazard, but only the async path (readBodyToStreamString) guards it (abort flag + 16 KB cap). The sync path has neither a timeout nor an abort check.

C4. Stale Content-Length on a 302/303 redirect-to-GET

In Job_SendBuf/Job_SendStr, each redirect iteration does not reset _headers; Content-Length is only (re)added when a payload is present. On a 302/303 the code sets payload=nullptr/size=0 and switches to GET, so the previously injected Content-Length: N stays in _headers and is sent on the bodyless GET. The server then waits for a body that never arrives → hang/timeout.

Related: beginInternal() (reached via setURL() for absolute redirect targets) never clears _headers, contradicting the readme's "headers reset after redirect."

C5. Stale async body returned after a later sync call

_asyncState is never reset to IDLE once DONE, and sync GET() doesn't touch it. After one async job, a subsequent sync GET() on the same instance populates _size/transport, but getString() still sees _asyncState == ASYNC_DONE and returns the old _asyncBody.

Fix: any new request (sync or async) must invalidate the DONE fast-path.

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High / medium issues

H1. Async POST from bytes does not copy the payload

asyncPOSTStart(uint8_t*, size) stores the raw pointer; the worker reads it later. The binding guards GC by stashing the bytes object in .__async_hold, but nothing prevents the script from mutating/resizing that bytes while the job runs, which can realloc the buffer → worker reads freed memory. The String overload copies (safe); the buffer overload should too, or the contract must be enforced.

H2. Unbounded RAM growth for chunked sync responses

wc_getstring/wc_getbytes guard with if (sz >= 32767) using getSize(), but a chunked response reports _size == -1, so the guard is bypassed and Job_GetString accumulates the entire body into a StreamString with no cap → OOM on a large chunked download. (The async path is capped at 16 KB; the sync path is not.)

H3. IPv4-only HTTP transport

AsyncTcpAdapter uses sockaddr_in / AF_INET and (in_addr_t)ip. Tasmota supports IPv6; the previous WiFiClient-based path did too. Plain-HTTP async over IPv6 will not work.

M1. TLS transmit buffer effectively 85 bytes

new BearSSL::WiFiClientSecure_light(16384, 0) → setBufferSizes(recv, xmit) yields _iobuf_out_size = 0 + MAX_OUT_OVERHEAD(85). So a 16 KB receive buffer (heavy heap, allocated up front) is paired with a near-zero send buffer (every TLS record carries almost no app data — poor POST throughput). Tasmota normally uses balanced sizes (e.g. 1024/1024). Needs tuning.

M2. SO_LINGER RST-close is unconditional and aggressive

AsyncTcpAdapter::stop() always sets l_onoff=1, l_linger=0, forcing a TCP RST on every close to cut TIME_WAIT. That can discard unread data and surface as connection-reset on the peer. Fine as an option, questionable as an unconditional default.

M3. Default HTTPS is unauthenticated

With no pins, BearSslAdapter calls setPubKeyFingerprint(any, any, allow_all=true) — accepts any server key (MITM-open). This matches existing Tasmota _light behavior, so it is not a regression, but combined with SHA-1 pubkey pinning it should be documented clearly that security requires explicit pinning.

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Code quality / process

• License mismatch: source headers say GPL-3.0-or-later; library.json says "license": "MIT". Must be reconciled before merge.
• library.json description ("Async extension for HttpClientLight by Stephan Hadinger") misattributes authorship, and the authors field is a single object, not the array PlatformIO expects.
• Non-English comments and typos throughout (Slovak/Czech: "telo", "drž payload, aby ho GC nevyhodil kým beží job", "za chunkom"; typos: "wheen", "writin", "succesful", "contetn-length", "metho"). Tasmota upstream is English-only.
• Massive #ifdef USE_BERRY_WEBCLIENT_ASYNC forking in xdrv_52_3 (~20 duplicated wc_getclient blocks). Selecting the client type with a single typedef/helper would remove almost all of it and shrink the diff dramatically.
• asyncState() is declared const but const_casts this to mutate state and free resources — misleading signature.
• Worker task names are fixed strings, so multiple concurrent clients collide (harmless, but indicative).

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What's actually fine

• lwIP non-blocking connect with select() timeout.
• Error-code table mirroring HTTPClientLight.
• Chunked / identity decoding.
• Abort-aware async body reader with a hard 16 KB cap.
• Holding the Berry payload via .__async_hold to prevent GC.
• Cross-thread result handoff is correctly ordered: the worker writes results before xSemaphoreGive, and the main thread reads them after xSemaphoreTake, so the published _asyncHttpCode / _asyncRxBytes / _asyncBody are not racy as long as the documented call sequence is followed.
• Feature is default-off, which is appropriate.