[web_server] Disable loop when no SSE clients are connected (#15428)

esphome/components/web_server/web_server.cpp

@@ -286,10 +286,11 @@ void DeferredUpdateEventSource::try_send_nodefer(const char *message, const char
   this->send(message, event, id, reconnect);
 }
 
-void DeferredUpdateEventSourceList::loop() {
+bool DeferredUpdateEventSourceList::loop() {
   for (DeferredUpdateEventSource *dues : *this) {
     dues->loop();
   }
+  return !this->empty();
 }
 
 void DeferredUpdateEventSourceList::deferrable_send_state(void *source, const char *event_type,
@@ -318,6 +319,7 @@ void DeferredUpdateEventSourceList::add_new_client(WebServer *ws, AsyncWebServer
   es->onDisconnect([this, es](AsyncEventSourceClient *client) { this->on_client_disconnect_(es); });
 
   es->handleRequest(request);
+  ws->enable_loop_soon_any_context();
 }
 
 void DeferredUpdateEventSourceList::on_client_connect_(DeferredUpdateEventSource *source) {
@@ -413,13 +415,24 @@ void WebServer::setup() {
   // doesn't need defer functionality - if the queue is full, the client JS knows it's alive because it's clearly
   // getting a lot of events
   this->set_interval(10000, [this]() {
+    if (this->events_.empty())
+      return;
     char buf[32];
     auto uptime = static_cast<uint32_t>(millis_64() / 1000);
     buf_append_printf(buf, sizeof(buf), 0, "{\"uptime\":%" PRIu32 "}", uptime);
     this->events_.try_send_nodefer(buf, "ping", millis(), 30000);
   });
 }
-void WebServer::loop() { this->events_.loop(); }
+void WebServer::loop() {
+  // No SSE clients connected; stop looping until a new client connects via
+  // enable_loop_soon_any_context(). This is safe because:
+  // - set_interval/set_timeout/defer run via the Scheduler, independent of loop()
+  // - deferrable_send_state early-outs when no clients are connected
+  // - try_send_nodefer (log, ping) iterates sessions which are empty
+  // - REST API handlers use defer() which runs via the Scheduler
+  if (!this->events_.loop())
+    this->disable_loop();
+}
 
 #ifdef USE_LOGGER
 void WebServer::on_log(uint8_t level, const char *tag, const char *message, size_t message_len) {

esphome/components/web_server/web_server.h

@@ -169,7 +169,8 @@ class DeferredUpdateEventSourceList final : public std::list<DeferredUpdateEvent
   void on_client_disconnect_(DeferredUpdateEventSource *source);
 
  public:
-  void loop();
+  /// Returns true if there are event sources remaining (including pending cleanup).
+  bool loop();
 
   void deferrable_send_state(void *source, const char *event_type, message_generator_t *message_generator);
   void try_send_nodefer(const char *message, const char *event = nullptr, uint32_t id = 0, uint32_t reconnect = 0);

esphome/components/web_server_idf/web_server_idf.cpp

@@ -484,9 +484,12 @@ void AsyncEventSource::handleRequest(AsyncWebServerRequest *request) {
     this->on_connect_(rsp);
   }
   this->sessions_.push_back(rsp);
+  // Wake up WebServer::loop() to drain deferred event queues for this client.
+  // Safe from httpd task context via the pending_enable_loop_ flag.
+  this->web_server_->enable_loop_soon_any_context();
 }
 
-void AsyncEventSource::loop() {
+bool AsyncEventSource::loop() {
   // Clean up dead sessions safely
   // This follows the ESP-IDF pattern where free_ctx marks resources as dead
   // and the main loop handles the actual cleanup to avoid race conditions
@@ -504,6 +507,7 @@ void AsyncEventSource::loop() {
       ++i;
     }
   }
+  return !this->sessions_.empty();
 }
 
 void AsyncEventSource::try_send_nodefer(const char *message, const char *event, uint32_t id, uint32_t reconnect) {

esphome/components/web_server_idf/web_server_idf.h

@@ -340,7 +340,8 @@ class AsyncEventSource : public AsyncWebHandler {
 
   void try_send_nodefer(const char *message, const char *event = nullptr, uint32_t id = 0, uint32_t reconnect = 0);
   void deferrable_send_state(void *source, const char *event_type, message_generator_t *message_generator);
-  void loop();
+  /// Returns true if there are sessions remaining (including pending cleanup).
+  bool loop();
   bool empty() { return this->count() == 0; }
 
   size_t count() const { return this->sessions_.size(); }