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esphome/components/esp32/preferences.cpp

@@ -19,16 +19,7 @@ static constexpr size_t KEY_BUFFER_SIZE = 12;
 
 struct NVSData {
   uint32_t key;
-  std::unique_ptr<uint8_t[]> data;
-  size_t len;
-
-  void set_data(const uint8_t *src, size_t size) {
-    if (!this->data || this->len != size) {
-      this->data = std::make_unique<uint8_t[]>(size);
-      this->len = size;
-    }
-    memcpy(this->data.get(), src, size);
-  }
+  SmallInlineBuffer<8> data;  // Most prefs fit in 8 bytes (covers fan, cover, select, etc.)
 };
 
 static std::vector<NVSData> s_pending_save;  // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
@@ -41,14 +32,14 @@ class ESP32PreferenceBackend : public ESPPreferenceBackend {
     // try find in pending saves and update that
     for (auto &obj : s_pending_save) {
       if (obj.key == this->key) {
-        obj.set_data(data, len);
+        obj.data.set(data, len);
         return true;
       }
     }
     NVSData save{};
     save.key = this->key;
-    save.set_data(data, len);
-    s_pending_save.emplace_back(std::move(save));
+    save.data.set(data, len);
+    s_pending_save.push_back(std::move(save));
     ESP_LOGVV(TAG, "s_pending_save: key: %" PRIu32 ", len: %zu", this->key, len);
     return true;
   }
@@ -56,11 +47,11 @@ class ESP32PreferenceBackend : public ESPPreferenceBackend {
     // try find in pending saves and load from that
     for (auto &obj : s_pending_save) {
       if (obj.key == this->key) {
-        if (obj.len != len) {
+        if (obj.data.size() != len) {
           // size mismatch
           return false;
         }
-        memcpy(data, obj.data.get(), len);
+        memcpy(data, obj.data.data(), len);
         return true;
       }
     }
@@ -136,10 +127,10 @@ class ESP32Preferences : public ESPPreferences {
       snprintf(key_str, sizeof(key_str), "%" PRIu32, save.key);
       ESP_LOGVV(TAG, "Checking if NVS data %s has changed", key_str);
       if (this->is_changed_(this->nvs_handle, save, key_str)) {
-        esp_err_t err = nvs_set_blob(this->nvs_handle, key_str, save.data.get(), save.len);
-        ESP_LOGV(TAG, "sync: key: %s, len: %zu", key_str, save.len);
+        esp_err_t err = nvs_set_blob(this->nvs_handle, key_str, save.data.data(), save.data.size());
+        ESP_LOGV(TAG, "sync: key: %s, len: %zu", key_str, save.data.size());
         if (err != 0) {
-          ESP_LOGV(TAG, "nvs_set_blob('%s', len=%zu) failed: %s", key_str, save.len, esp_err_to_name(err));
+          ESP_LOGV(TAG, "nvs_set_blob('%s', len=%zu) failed: %s", key_str, save.data.size(), esp_err_to_name(err));
           failed++;
           last_err = err;
           last_key = save.key;
@@ -147,7 +138,7 @@ class ESP32Preferences : public ESPPreferences {
         }
         written++;
       } else {
-        ESP_LOGV(TAG, "NVS data not changed skipping %" PRIu32 "  len=%zu", save.key, save.len);
+        ESP_LOGV(TAG, "NVS data not changed skipping %" PRIu32 "  len=%zu", save.key, save.data.size());
         cached++;
       }
       s_pending_save.erase(s_pending_save.begin() + i);
@@ -178,7 +169,7 @@ class ESP32Preferences : public ESPPreferences {
       return true;
     }
     // Check size first before allocating memory
-    if (actual_len != to_save.len) {
+    if (actual_len != to_save.data.size()) {
       return true;
     }
     auto stored_data = std::make_unique<uint8_t[]>(actual_len);
@@ -187,7 +178,7 @@ class ESP32Preferences : public ESPPreferences {
       ESP_LOGV(TAG, "nvs_get_blob('%s') failed: %s", key_str, esp_err_to_name(err));
       return true;
     }
-    return memcmp(to_save.data.get(), stored_data.get(), to_save.len) != 0;
+    return memcmp(to_save.data.data(), stored_data.get(), to_save.data.size()) != 0;
   }
 
   bool reset() override {

esphome/components/libretiny/preferences.cpp

@@ -18,16 +18,7 @@ static constexpr size_t KEY_BUFFER_SIZE = 12;
 
 struct NVSData {
   uint32_t key;
-  std::unique_ptr<uint8_t[]> data;
-  size_t len;
-
-  void set_data(const uint8_t *src, size_t size) {
-    if (!this->data || this->len != size) {
-      this->data = std::make_unique<uint8_t[]>(size);
-      this->len = size;
-    }
-    memcpy(this->data.get(), src, size);
-  }
+  SmallInlineBuffer<8> data;  // Most prefs fit in 8 bytes (covers fan, cover, select, etc.)
 };
 
 static std::vector<NVSData> s_pending_save;  // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
@@ -42,14 +33,14 @@ class LibreTinyPreferenceBackend : public ESPPreferenceBackend {
     // try find in pending saves and update that
     for (auto &obj : s_pending_save) {
       if (obj.key == this->key) {
-        obj.set_data(data, len);
+        obj.data.set(data, len);
         return true;
       }
     }
     NVSData save{};
     save.key = this->key;
-    save.set_data(data, len);
-    s_pending_save.emplace_back(std::move(save));
+    save.data.set(data, len);
+    s_pending_save.push_back(std::move(save));
     ESP_LOGVV(TAG, "s_pending_save: key: %" PRIu32 ", len: %zu", this->key, len);
     return true;
   }
@@ -58,11 +49,11 @@ class LibreTinyPreferenceBackend : public ESPPreferenceBackend {
     // try find in pending saves and load from that
     for (auto &obj : s_pending_save) {
       if (obj.key == this->key) {
-        if (obj.len != len) {
+        if (obj.data.size() != len) {
           // size mismatch
           return false;
         }
-        memcpy(data, obj.data.get(), len);
+        memcpy(data, obj.data.data(), len);
         return true;
       }
     }
@@ -126,11 +117,11 @@ class LibreTinyPreferences : public ESPPreferences {
       snprintf(key_str, sizeof(key_str), "%" PRIu32, save.key);
       ESP_LOGVV(TAG, "Checking if FDB data %s has changed", key_str);
       if (this->is_changed_(&this->db, save, key_str)) {
-        ESP_LOGV(TAG, "sync: key: %s, len: %zu", key_str, save.len);
-        fdb_blob_make(&this->blob, save.data.get(), save.len);
+        ESP_LOGV(TAG, "sync: key: %s, len: %zu", key_str, save.data.size());
+        fdb_blob_make(&this->blob, save.data.data(), save.data.size());
         fdb_err_t err = fdb_kv_set_blob(&this->db, key_str, &this->blob);
         if (err != FDB_NO_ERR) {
-          ESP_LOGV(TAG, "fdb_kv_set_blob('%s', len=%zu) failed: %d", key_str, save.len, err);
+          ESP_LOGV(TAG, "fdb_kv_set_blob('%s', len=%zu) failed: %d", key_str, save.data.size(), err);
           failed++;
           last_err = err;
           last_key = save.key;
@@ -138,7 +129,7 @@ class LibreTinyPreferences : public ESPPreferences {
         }
         written++;
       } else {
-        ESP_LOGD(TAG, "FDB data not changed; skipping %" PRIu32 "  len=%zu", save.key, save.len);
+        ESP_LOGD(TAG, "FDB data not changed; skipping %" PRIu32 "  len=%zu", save.key, save.data.size());
         cached++;
       }
       s_pending_save.erase(s_pending_save.begin() + i);
@@ -162,7 +153,7 @@ class LibreTinyPreferences : public ESPPreferences {
     }
 
     // Check size first - if different, data has changed
-    if (kv.value_len != to_save.len) {
+    if (kv.value_len != to_save.data.size()) {
       return true;
     }
 
@@ -176,7 +167,7 @@ class LibreTinyPreferences : public ESPPreferences {
     }
 
     // Compare the actual data
-    return memcmp(to_save.data.get(), stored_data.get(), kv.value_len) != 0;
+    return memcmp(to_save.data.data(), stored_data.get(), kv.value_len) != 0;
   }
 
   bool reset() override {

esphome/core/helpers.h

@@ -132,6 +132,78 @@ template<typename T> class ConstVector {
   size_t size_;
 };
 
+/// Small buffer optimization - stores data inline when small, heap-allocates for large data
+/// This avoids heap fragmentation for common small allocations while supporting arbitrary sizes.
+/// Memory management is encapsulated - callers just use set() and data().
+template<size_t InlineSize = 8> class SmallInlineBuffer {
+ public:
+  SmallInlineBuffer() = default;
+  ~SmallInlineBuffer() {
+    if (!this->is_inline_())
+      delete[] this->heap_;
+  }
+
+  // Move constructor
+  SmallInlineBuffer(SmallInlineBuffer &&other) noexcept : len_(other.len_) {
+    if (other.is_inline_()) {
+      memcpy(this->inline_, other.inline_, this->len_);
+    } else {
+      this->heap_ = other.heap_;
+      other.heap_ = nullptr;
+    }
+    other.len_ = 0;
+  }
+
+  // Move assignment
+  SmallInlineBuffer &operator=(SmallInlineBuffer &&other) noexcept {
+    if (this != &other) {
+      if (!this->is_inline_())
+        delete[] this->heap_;
+      this->len_ = other.len_;
+      if (other.is_inline_()) {
+        memcpy(this->inline_, other.inline_, this->len_);
+      } else {
+        this->heap_ = other.heap_;
+        other.heap_ = nullptr;
+      }
+      other.len_ = 0;
+    }
+    return *this;
+  }
+
+  // Disable copy (would need deep copy of heap data)
+  SmallInlineBuffer(const SmallInlineBuffer &) = delete;
+  SmallInlineBuffer &operator=(const SmallInlineBuffer &) = delete;
+
+  /// Set buffer contents, allocating heap if needed
+  void set(const uint8_t *src, size_t size) {
+    // Free existing heap allocation if switching from heap to inline or different heap size
+    if (!this->is_inline_() && (size <= InlineSize || size != this->len_)) {
+      delete[] this->heap_;
+      this->heap_ = nullptr;  // Defensive: prevent use-after-free if logic changes
+    }
+    // Allocate new heap buffer if needed
+    if (size > InlineSize && (this->is_inline_() || size != this->len_)) {
+      this->heap_ = new uint8_t[size];  // NOLINT(cppcoreguidelines-owning-memory)
+    }
+    this->len_ = size;
+    memcpy(this->data(), src, size);
+  }
+
+  uint8_t *data() { return this->is_inline_() ? this->inline_ : this->heap_; }
+  const uint8_t *data() const { return this->is_inline_() ? this->inline_ : this->heap_; }
+  size_t size() const { return this->len_; }
+
+ protected:
+  bool is_inline_() const { return this->len_ <= InlineSize; }
+
+  size_t len_{0};
+  union {
+    uint8_t inline_[InlineSize]{};  // Zero-init ensures clean initial state
+    uint8_t *heap_;
+  };
+};
+
 /// Minimal static vector - saves memory by avoiding std::vector overhead
 template<typename T, size_t N> class StaticVector {
  public: