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[mqtt] Restore ESP8266 on_message defer to prevent stack overflow (#13648)

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This commit is contained in:
J. Nick Koston
2026-01-30 12:49:14 -06:00
committed by GitHub
parent a1a60c44da
commit 4e96b20b46
1 changed files with 28 additions and 4 deletions
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32
esphome/components/mqtt/mqtt_client.cpp
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@@ -643,10 +643,34 @@ static bool topic_match(const char *message, const char *subscription) {
}
void MQTTClientComponent::on_message(const std::string &topic, const std::string &payload) {
for (auto &subscription : this->subscriptions_) {
if (topic_match(topic.c_str(), subscription.topic.c_str()))
subscription.callback(topic, payload);
}
#ifdef USE_ESP8266
// IMPORTANT: This defer is REQUIRED to prevent stack overflow crashes on ESP8266.
//
// On ESP8266, this callback is invoked directly from the lwIP/AsyncTCP network stack
// which runs in the "sys" context with a very limited stack (~4KB). By the time we
// reach this function, the stack is already partially consumed by the network
// processing chain: tcp_input -> AsyncClient::_recv -> AsyncMqttClient::_onMessage -> here.
//
// MQTT subscription callbacks can trigger arbitrary user actions (automations, HTTP
// requests, sensor updates, etc.) which may have deep call stacks of their own.
// For example, an HTTP request action requires: DNS lookup -> TCP connect -> TLS
// handshake (if HTTPS) -> request formatting. This easily overflows the remaining
// system stack space, causing a LoadStoreAlignmentCause exception or silent corruption.
//
// By deferring to the main loop, we ensure callbacks execute with a fresh, full-size
// stack in the normal application context rather than the constrained network task.
//
// DO NOT REMOVE THIS DEFER without understanding the above. It may appear to work
// in simple tests but will cause crashes with complex automations.
this->defer([this, topic, payload]() {
#endif
for (auto &subscription : this->subscriptions_) {
if (topic_match(topic.c_str(), subscription.topic.c_str()))
subscription.callback(topic, payload);
}
#ifdef USE_ESP8266
});
#endif
}
// Setters