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[mdns] Drive MDNS.update() polling from WiFi IP state events on ESP8266/RP2040

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The Arduino LEAmDNS library only has meaningful timer-driven work during the
~9 s probe+announce phase following MDNS.begin() or _restart(): 3 probes at
250 ms + 8 announcements at 1000 ms, then all internal timeouts are set to
resetToNeverExpires(). Incoming packets are handled via the lwIP UDP RX
callback independently of update(). ESPHome does not issue service queries,
so the query cache path is always a no-op.

The previous implementation ran set_interval(50) forever — ~20 dispatches/sec,
1200+ scheduler calls per minute of pure overhead once probing completed.

This PR arms a bounded MDNS_POLL_WINDOW_MS (12 s) polling window driven by
WiFiIPStateListener events. A fresh window covers each probe/announce cycle
(boot, wifi reconnect, or internal _restart() triggered by netif changes);
outside the window there are zero scheduler dispatches and the scheduler
heap contains no mDNS items.

ESP8266 is WiFi-only in the Arduino build so the path is unconditional.
RP2040 supports W5500 ethernet without WiFi, so the listener is requested
only when WiFi is in the config; ethernet-only RP2040 builds keep the
legacy polling loop.

Scheduler IDs use uint32_t (MDNS_POLL_ID / MDNS_POLL_STOP_ID) to avoid the
name-hash/strcmp cost of string-named timers on the cancel + re-arm paths.
This commit is contained in:
J. Nick Koston
2026-04-23 19:19:29 -05:00
parent ddf1426f86
commit bf7083c501
5 changed files with 153 additions and 29 deletions
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esphome/components/mdns/mdns_component.cpp
+14
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@@ -190,6 +190,20 @@ void MDNSComponent::compile_records_(StaticVector<MDNSService, MDNS_SERVICE_COUN
#endif
}
#ifdef USE_MDNS_EVENT_DRIVEN_POLLING
void MDNSComponent::start_polling_window_() {
// Re-arming replaces the previous window; cancel any active schedulers first.
this->cancel_polling_window_();
this->set_interval(MDNS_POLL_ID, MDNS_UPDATE_INTERVAL_MS, mdns_pump_update);
this->set_timeout(MDNS_POLL_STOP_ID, MDNS_POLL_WINDOW_MS, [this]() { this->cancel_interval(MDNS_POLL_ID); });
}
void MDNSComponent::cancel_polling_window_() {
this->cancel_interval(MDNS_POLL_ID);
this->cancel_timeout(MDNS_POLL_STOP_ID);
}
#endif
void MDNSComponent::dump_config() {
ESP_LOGCONFIG(TAG,
"mDNS:\n"