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Close the session when the MQTT client does not take a subscription; name the root topic when the broker refuses one

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Two error lines of 8ea7778 did not help the reader act.

"the MQTT client refused to subscribe (N bytes of heap free): no directives until it reconnects": nothing reconnected. The session stayed open without subscriptions and the state SUBSCRIBING for good, because the reconnect only acts on a session that has ended. The free heap was beside the point: AsyncMqttClient 0.9.0 returns 0 from subscribe() only when its session is not open. The bridge now prints "the MQTT client did not take the subscriptions: closing the session, the next one subscribes again" and calls disconnect(), which queues the DISCONNECT packet; the end of the session then starts the reconnect.

"the broker refused the subscription to <topic>": it did not say what to check. The usual cause is a root topic that does not belong to the account, so the line ends with ": check the root topic passed to begin()". The session stays open and the state SUBSCRIBING, since the broker would refuse the same topic again; the comment says so.

Measured with the bridge built for the host against a fake MQTT client (not in the repository): subscribe() returning 0 leads to one disconnect() and, after the session has ended, to one connect() within 7 s and a session that reaches CONNECTED; a SUBACK with 0x80 prints the new line and leaves the session open.

examples/basicLight.cpp for d1_mini, static RAM / flash in bytes: 34,452 / 337,401 -> 34,452 / 337,461, no warnings. 41 host tests pass.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
This commit is contained in:
David 2026-09-28 16:01:25 +00:00
parent c5b4802d65
commit 5b090a43dd
2 changed files with 9 additions and 5 deletions
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8
src/Alex2ESP.cpp
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@ -195,7 +195,10 @@ void Alex2ESP::onMqttConnect(bool sessionPresent)
directiveSubscription = mqttClient.subscribe(directiveFilter.c_str(), 1);
if (discoverSubscription == 0 || directiveSubscription == 0)
{
ALEX2ESP_LOGE("the MQTT client refused to subscribe (%u bytes of heap free): no directives until it reconnects", (unsigned)ESP.getFreeHeap());
// The client takes a subscription whenever its session is open, so this one is not. Without the
// subscriptions the board would stay deaf: the session is closed, and the next one subscribes again.
ALEX2ESP_LOGE("the MQTT client did not take the subscriptions: closing the session, the next one subscribes again");
mqttClient.disconnect();
return;
}
ALEX2ESP_LOGI("connected to %s, subscribing", MQTT_SERVER);
@ -210,7 +213,8 @@ void Alex2ESP::onSubscribe(uint16_t packetId, uint8_t qos)
const String &topic = (packetId == discoverSubscription) ? discoverTopic : directiveFilter;
if (qos == SUBSCRIPTION_REFUSED)
{
ALEX2ESP_LOGE("the broker refused the subscription to %s", topic.c_str());
// The session stays open and the state SUBSCRIBING: the broker would refuse the same topic again
ALEX2ESP_LOGE("the broker refused the subscription to %s: check the root topic passed to begin()", topic.c_str());
return;
}