From 85420b0606db4d585fcd303aac81c41b6c0048eb Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Tue, 14 Oct 2025 14:50:40 -1000
Subject: [PATCH] [web_server_idf] Use std::vector instead of std::set for SSE
 sessions (#11233)

---
 .../components/web_server_idf/web_server_idf.cpp    | 13 +++++++------
 esphome/components/web_server_idf/web_server_idf.h  |  6 ++++--
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/esphome/components/web_server_idf/web_server_idf.cpp b/esphome/components/web_server_idf/web_server_idf.cpp
index d90efd18bc..c3ba7ddc2b 100644
--- a/esphome/components/web_server_idf/web_server_idf.cpp
+++ b/esphome/components/web_server_idf/web_server_idf.cpp
@@ -380,24 +380,25 @@ void AsyncEventSource::handleRequest(AsyncWebServerRequest *request) {
   if (this->on_connect_) {
     this->on_connect_(rsp);
   }
-  this->sessions_.insert(rsp);
+  this->sessions_.push_back(rsp);
 }
 
 void 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
-  auto it = this->sessions_.begin();
-  while (it != this->sessions_.end()) {
-    auto *ses = *it;
+  for (size_t i = 0; i < this->sessions_.size();) {
+    auto *ses = this->sessions_[i];
     // If the session has a dead socket (marked by destroy callback)
     if (ses->fd_.load() == 0) {
       ESP_LOGD(TAG, "Removing dead event source session");
-      it = this->sessions_.erase(it);
       delete ses;  // NOLINT(cppcoreguidelines-owning-memory)
+      // Remove by swapping with last element (O(1) removal, order doesn't matter for sessions)
+      this->sessions_[i] = this->sessions_.back();
+      this->sessions_.pop_back();
     } else {
       ses->loop();
-      ++it;
+      ++i;
     }
   }
 }
diff --git a/esphome/components/web_server_idf/web_server_idf.h b/esphome/components/web_server_idf/web_server_idf.h
index bf93dcbd34..5ec6fec009 100644
--- a/esphome/components/web_server_idf/web_server_idf.h
+++ b/esphome/components/web_server_idf/web_server_idf.h
@@ -8,7 +8,6 @@
 #include <functional>
 #include <list>
 #include <map>
-#include <set>
 #include <string>
 #include <utility>
 #include <vector>
@@ -315,7 +314,10 @@ class AsyncEventSource : public AsyncWebHandler {
 
  protected:
   std::string url_;
-  std::set<AsyncEventSourceResponse *> sessions_;
+  // Use vector instead of set: SSE sessions are typically 1-5 connections (browsers, dashboards).
+  // Linear search is faster than red-black tree overhead for this small dataset.
+  // Only operations needed: add session, remove session, iterate sessions - no need for sorted order.
+  std::vector<AsyncEventSourceResponse *> sessions_;
   connect_handler_t on_connect_{};
   esphome::web_server::WebServer *web_server_;
 };