From 541c697a42e5ff46434a3f4fdcf4e8e1cb6c6777 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Mon, 13 Oct 2025 18:52:49 -1000
Subject: [PATCH] [mdns] Use FixedVector for txt_records to reduce flash usage

---
 esphome/components/mdns/mdns_component.cpp | 4 ++--
 esphome/components/mdns/mdns_component.h   | 2 +-
 esphome/core/helpers.h                     | 9 +++++++++
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/esphome/components/mdns/mdns_component.cpp b/esphome/components/mdns/mdns_component.cpp
index fea3ced99f..ef585db51b 100644
--- a/esphome/components/mdns/mdns_component.cpp
+++ b/esphome/components/mdns/mdns_component.cpp
@@ -83,7 +83,7 @@ void MDNSComponent::compile_records_(StaticVector<MDNSService, MDNS_SERVICE_COUN
 #endif
 
     auto &txt_records = service.txt_records;
-    txt_records.reserve(txt_count);
+    txt_records.init(txt_count);
 
     if (!friendly_name_empty) {
       txt_records.push_back({MDNS_STR(TXT_FRIENDLY_NAME), MDNS_STR(friendly_name.c_str())});
@@ -171,7 +171,7 @@ void MDNSComponent::compile_records_(StaticVector<MDNSService, MDNS_SERVICE_COUN
   fallback_service.service_type = MDNS_STR(SERVICE_HTTP);
   fallback_service.proto = MDNS_STR(SERVICE_TCP);
   fallback_service.port = USE_WEBSERVER_PORT;
-  fallback_service.txt_records.push_back({MDNS_STR(TXT_VERSION), MDNS_STR(VALUE_VERSION)});
+  fallback_service.txt_records = {{MDNS_STR(TXT_VERSION), MDNS_STR(VALUE_VERSION)}};
 #endif
 
 #ifdef USE_MDNS_STORE_SERVICES
diff --git a/esphome/components/mdns/mdns_component.h b/esphome/components/mdns/mdns_component.h
index 62476e9504..35371fd739 100644
--- a/esphome/components/mdns/mdns_component.h
+++ b/esphome/components/mdns/mdns_component.h
@@ -38,7 +38,7 @@ struct MDNSService {
   // as defined in RFC6763 Section 7, like "_tcp" or "_udp"
   const MDNSString *proto;
   TemplatableValue<uint16_t> port;
-  std::vector<MDNSTXTRecord> txt_records;
+  FixedVector<MDNSTXTRecord> txt_records;
 };
 
 class MDNSComponent : public Component {
diff --git a/esphome/core/helpers.h b/esphome/core/helpers.h
index e352c9c415..b94826629f 100644
--- a/esphome/core/helpers.h
+++ b/esphome/core/helpers.h
@@ -197,6 +197,15 @@ template<typename T> class FixedVector {
  public:
   FixedVector() = default;
 
+  /// Constructor from initializer list - allocates exact size needed
+  /// This enables brace initialization: FixedVector<int> v = {1, 2, 3};
+  FixedVector(std::initializer_list<T> init) {
+    init(init.size());
+    for (const auto &item : init) {
+      push_back(item);
+    }
+  }
+
   ~FixedVector() { cleanup_(); }
 
   // Disable copy operations (avoid accidental expensive copies)