From d93cffedfa2a834e946c4898ec54b494e334502e Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Tue, 20 Jan 2026 13:08:52 -1000
Subject: [PATCH] [mdns] Use stack buffer for txt records on ESP32

---
 esphome/components/mdns/mdns_esp32.cpp |  7 ++++---
 esphome/core/helpers.h                 | 14 ++++++++------
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/esphome/components/mdns/mdns_esp32.cpp b/esphome/components/mdns/mdns_esp32.cpp
index e6b43e59cb..3123f3b604 100644
--- a/esphome/components/mdns/mdns_esp32.cpp
+++ b/esphome/components/mdns/mdns_esp32.cpp
@@ -24,13 +24,14 @@ static void register_esp32(MDNSComponent *comp, StaticVector<MDNSService, MDNS_S
   mdns_instance_name_set(hostname);
 
   for (const auto &service : services) {
-    auto txt_records = std::make_unique<mdns_txt_item_t[]>(service.txt_records.size());
+    // Stack buffer for up to 16 txt records, heap fallback for more
+    SmallBufferWithHeapFallback<16, mdns_txt_item_t> txt_records(service.txt_records.size());
     for (size_t i = 0; i < service.txt_records.size(); i++) {
       const auto &record = service.txt_records[i];
       // key and value are either compile-time string literals in flash or pointers to dynamic_txt_values_
       // Both remain valid for the lifetime of this function, and ESP-IDF makes internal copies
-      txt_records[i].key = MDNS_STR_ARG(record.key);
-      txt_records[i].value = MDNS_STR_ARG(record.value);
+      txt_records.get()[i].key = MDNS_STR_ARG(record.key);
+      txt_records.get()[i].value = MDNS_STR_ARG(record.value);
     }
     uint16_t port = const_cast<TemplatableValue<uint16_t> &>(service.port).value();
     err = mdns_service_add(nullptr, MDNS_STR_ARG(service.service_type), MDNS_STR_ARG(service.proto), port,
diff --git a/esphome/core/helpers.h b/esphome/core/helpers.h
index 7de952a712..eaf3ffb877 100644
--- a/esphome/core/helpers.h
+++ b/esphome/core/helpers.h
@@ -371,13 +371,15 @@ template<typename T> class FixedVector {
 /// @brief Helper class for efficient buffer allocation - uses stack for small sizes, heap for large
 /// This is useful when most operations need a small buffer but occasionally need larger ones.
 /// The stack buffer avoids heap allocation in the common case, while heap fallback handles edge cases.
-template<size_t STACK_SIZE> class SmallBufferWithHeapFallback {
+/// @tparam STACK_SIZE Number of elements in the stack buffer
+/// @tparam T Element type (default: uint8_t)
+template<size_t STACK_SIZE, typename T = uint8_t> class SmallBufferWithHeapFallback {
  public:
   explicit SmallBufferWithHeapFallback(size_t size) {
     if (size <= STACK_SIZE) {
       this->buffer_ = this->stack_buffer_;
     } else {
-      this->heap_buffer_ = new uint8_t[size];
+      this->heap_buffer_ = new T[size];
       this->buffer_ = this->heap_buffer_;
     }
   }
@@ -389,12 +391,12 @@ template<size_t STACK_SIZE> class SmallBufferWithHeapFallback {
   SmallBufferWithHeapFallback(SmallBufferWithHeapFallback &&) = delete;
   SmallBufferWithHeapFallback &operator=(SmallBufferWithHeapFallback &&) = delete;
 
-  uint8_t *get() { return this->buffer_; }
+  T *get() { return this->buffer_; }
 
  private:
-  uint8_t stack_buffer_[STACK_SIZE];
-  uint8_t *heap_buffer_{nullptr};
-  uint8_t *buffer_;
+  T stack_buffer_[STACK_SIZE];
+  T *heap_buffer_{nullptr};
+  T *buffer_;
 };
 
 ///@}