ESPSomfy-RTS/docs/KNOWN_ISSUES.md

Known Issues

Concurrent mutation during chunked /controller response

Status: open Introduced: 2026-04-19, alongside the chunked-response conversion of /controller (see ControllerChunker in src/Web.cpp and the original crash report about cbuf::resize aborting async_tcp).

Summary

The chunked streaming of /controller lazily reads somfy.rooms, somfy.shades, somfy.groups, and somfy.repeaters across many async_tcp callback invocations as the client's TCP send window opens. If another task mutates those arrays mid-stream, the rendered JSON can be internally inconsistent.

Why this is strictly worse than the pre-chunked code

The old handleController ran the serializers synchronously inside a single request-handler invocation, so the full JSON was built in memory before any bytes were sent. Window of exposure: a few milliseconds.

The new ControllerChunker reads state as the response drains. On a slow link or under backpressure, that window is hundreds of ms to seconds.

Concrete failure modes

1. A shade is deleted mid-stream (e.g. via /deleteShade) — it may appear in the shades array but be missing from a later group's linkedShades, or vice versa.
2. lastRollingCode / position fields change between the shades pass and a later group's linkedShades pass — the client sees two values for the same shade in one document.
3. A group's linkedShades list is mutated while the chunker iterates inside S_GROUPS — an entry is skipped or emitted twice.

Fix options (pick one later)

• (a) Document and accept. In practice users rarely mutate shades while the config UI is loading. Zero code change.
• (b) FreeRTOS mutex around somfy reads/writes. Acquire for the full duration of the chunked response and in every mutating path (RF RX, MQTT, web handlers). Cleanest but wide-reaching.
• (c) Up-front snapshot. At handler start, copy the subset of somfy state the response will serialize into the ControllerChunker. Defeats part of the memory benefit — a full snapshot of shades + groups is close in size to the old growing cbuf. Could be reduced by snapshotting only minimal fields (IDs, names, rolling codes) and reading the rest live.

Related

• Same exposure exists in any other endpoint converted to chunked responses next (/discovery, /shades). Resolve this issue before expanding the pattern.

• Other handlers on the web server task still change the shade model that loop() owns:

  • /addRoom, /saveRoom, /deleteRoom, /addShade, /saveShade, /deleteShade, /addGroup, /saveGroup and /deleteGroup add, change and remove rooms, shades and groups.
  • /linkRemote and /unlinkRemote change a shade's linked remotes. /linkRemote also sets a linked remote's rolling code, which loop() updates whenever it receives a frame from that remote: the last write wins, so a received frame can undo the code just set.
  • /linkToGroup and /unlinkFromGroup change a group's linked shades.
  • /setPaired sets paired.

  Shade commands, set-My, unpair, /setRollingCode, a shades restore and /updateShadeConfig already go through the web command queue to loop().

• /controller leaves out a room, shade, group or linked shade that doesn't fit in its chunk buffer, see Oversized /controller items are left out.

Oversized /controller items are left out

Status: open Location: ControllerChunker::overflowed in src/Web.cpp.

Summary

ControllerChunker builds each room, shade, group and linked shade into a 3 KB buffer before sending it. When one doesn't fit, the chunker logs an ESP_LOGE line, skips that item and carries on, so the document stays valid JSON. The client gets no sign that anything is missing: the item just isn't in the list.

A shade with every linked remote populated is about 1.5 KB today, so nothing overflows yet. It becomes a silent loss as soon as a change to the shade, room or group fields pushes an item past 3 KB.

Concrete failure modes

1. A shade is left out after a firmware change adds fields to it. It is missing from the config UI, and Home Assistant doesn't create an entity for it.
2. A group whose linkedShades entry doesn't fit loses that shade from its list.

Fix options (pick one later)

• (a) Fail loud. Add a list of the skipped item ids to the end of the document, and show a warning in the UI.
• (b) Check the size at build time. Work out the worst case for each item from the field limits and static_assert that it fits the buffer, so a change that breaks it doesn't build.

Related

• The same "lost without telling the client" problem as Large websocket events are dropped.

Large websocket events are dropped

Status: open Location: JsonSockEvent in src/WResp.cpp, buffer g_response[MAX_SOCK_RESPONSE] (2048 bytes) in src/Sockets.cpp.

Summary

Socket events are built into a fixed 2 KB static buffer. When a value doesn't fit, JsonSockEvent::_safecat marks the event as overflowed, and endEvent logs an error and doesn't send it. Clients never see malformed JSON. The event is simply lost, and the client isn't told.

Unlike the /controller HTTP crash, this path does not abort — there is no growing cbuf and no new[] on the send path. Per-client frame allocations inside AsyncWebSocket are bounded by the 2 KB buffer size and have their own overflow guard (queue drop / client disconnect).

Concrete failure modes

1. A single event serializing a fully-populated shade (~1.3–1.5 KB for a shade with all SOMFY_MAX_LINKED_REMOTES = 7 populated) gets close to the 2 KB limit. Any additional fields or long names push it over, and that shade's state update never reaches the clients.
2. Any event that loops over a collection (e.g. frequency-scan results in Transceiver.cpp, batch emits in SomfyEvents.cpp) can exceed 2 KB depending on size, with no indication to the client beyond the ESP-side ESP_LOGE line.

Fix options (pick one later)

• (a) Fail loud. Send a small error event in place of the dropped one so the client knows to reload the state.
• (b) Split large events across frames. Use the socket.io ack/chunk pattern to send an event in multiple frames when it wouldn't fit. Requires matching client-side reassembly.
• (c) Raise MAX_SOCK_RESPONSE. Cheapest, but just pushes the limit — doesn't eliminate the failure mode.

Related

• Not the same code path as the /controller crash. Solve independently.
• Worth grepping for JsonSockEvent usages that iterate collections (see references in SomfyEvents.cpp, Transceiver.cpp, ESPNetwork.cpp, GitOTA.cpp) to identify the most at-risk events.