[mdns] Skip MDNS.update() while the ESP8266 radio cannot transmit (#18785)

esphome/components/mdns/mdns_esp8266.cpp

@@ -41,7 +41,19 @@ static void register_esp8266(MDNSComponent *, StaticVector<MDNSService, MDNS_SER
 #ifdef USE_MDNS_EVENT_DRIVEN_POLLING
 void MDNSComponent::start_polling_window_() {
   // uint32_t-ID set_interval/set_timeout already does atomic cancel-and-add.
-  this->set_interval(MDNS_POLL_ID, MDNS_UPDATE_INTERVAL_MS, []() { MDNS.update(); });
+  this->set_interval(MDNS_POLL_ID, MDNS_UPDATE_INTERVAL_MS, []() {
+#ifdef USE_MDNS_WIFI_LISTENER
+    // MDNS.update() can suspend the loop in UdpContext::sendTimeout() while a send is
+    // failing (radio off-channel during a roam scan, or mid reconnect); an incoming
+    // packet then re-enters LEAmDNS from lwIP and corrupts shared UdpContext state.
+    // Skip the tick while the radio cannot transmit (#18760), but keep polling while
+    // the AP is serving clients (AP-only or fallback AP with the STA down).
+    auto *wifi = wifi::global_wifi_component;
+    if (wifi->is_roaming() || (!wifi->is_connected() && !wifi->is_ap_active()))
+      return;
+#endif
+    MDNS.update();
+  });
   this->set_timeout(MDNS_POLL_STOP_ID, MDNS_POLL_WINDOW_MS, [this]() { this->cancel_interval(MDNS_POLL_ID); });
 }
 #endif

esphome/components/wifi/wifi_component.cpp

@@ -530,7 +530,7 @@ void WiFiComponent::log_discarded_scan_result_(const char *ssid, const uint8_t *
 #if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE
   // Skip logging during roaming scans to avoid log buffer overflow
   // (roaming scans typically find many networks but only care about same-SSID APs)
-  if (this->roaming_state_ == RoamingState::SCANNING) {
+  if (this->is_roaming_scan_active()) {
     return;
   }
   char bssid_s[MAC_ADDRESS_PRETTY_BUFFER_SIZE];
@@ -835,7 +835,7 @@ void WiFiComponent::loop() {
 
           // Post-connect roaming: check for better AP
           if (this->post_connect_roaming_) {
-            if (this->roaming_state_ == RoamingState::SCANNING) {
+            if (this->is_roaming_scan_active()) {
               if (this->scan_done_) {
                 this->process_roaming_scan_();
               }
@@ -2152,7 +2152,7 @@ void WiFiComponent::retry_connect() {
     // Roam connection failed - transition to reconnecting
     ESP_LOGD(TAG, "Roam failed, reconnecting (attempt %u/%u)", this->roaming_attempts_, ROAMING_MAX_ATTEMPTS);
     this->roaming_state_ = RoamingState::RECONNECTING;
-  } else if (this->roaming_state_ == RoamingState::SCANNING) {
+  } else if (this->is_roaming_scan_active()) {
     // Disconnected during roam scan - transition to RECONNECTING so the attempts
     // counter is preserved when reconnection succeeds (IDLE would reset it)
     ESP_LOGD(TAG, "Disconnected during roam scan (attempt %u/%u)", this->roaming_attempts_, ROAMING_MAX_ATTEMPTS);

esphome/components/wifi/wifi_component.h

@@ -475,6 +475,13 @@ class WiFiComponent final : public Component {
 
   bool is_connected() const { return this->connected_; }
 
+  /// True while a post-connect roaming scan holds the radio off-channel.
+  bool is_roaming_scan_active() const { return this->roaming_state_ == RoamingState::SCANNING; }
+
+  /// True while a post-connect roam is in progress (scanning off-channel, reassociating,
+  /// or recovering from a failed roam).
+  bool is_roaming() const { return this->roaming_state_ != RoamingState::IDLE; }
+
 #ifdef USE_ESP32
   /// esp_netif handle of the station interface, used by network for default-route
   /// arbitration. nullptr until wifi_lazy_init_() has run.

esphome/components/wifi/wifi_component_esp8266.cpp

@@ -717,7 +717,7 @@ bool WiFiComponent::wifi_scan_start_(bool passive) {
   static constexpr uint32_t SCAN_ACTIVE_MAX_DEFAULT_MS = 500;
   static constexpr uint32_t SCAN_ACTIVE_MIN_ROAMING_MS = 100;
   static constexpr uint32_t SCAN_ACTIVE_MAX_ROAMING_MS = 300;
-  bool roaming = this->roaming_state_ == RoamingState::SCANNING;
+  bool roaming = this->is_roaming_scan_active();
   if (passive) {
     config.scan_time.passive = roaming ? SCAN_PASSIVE_ROAMING_MS : SCAN_PASSIVE_DEFAULT_MS;
   } else {

esphome/components/wifi/wifi_component_esp_idf.cpp

@@ -1064,7 +1064,7 @@ bool WiFiComponent::wifi_scan_start_(bool passive) {
   // When scanning while connected (roaming), return to home channel between
   // each scanned channel to maintain the connection (helps with BLE/WiFi coexistence)
 #ifdef CONFIG_SOC_WIFI_SUPPORTED
-  if (this->roaming_state_ == RoamingState::SCANNING) {
+  if (this->is_roaming_scan_active()) {
     config.coex_background_scan = true;
   }
 #endif