[esp32_ble] Optimize name storage to reduce RAM and eliminate heap allocations (#12071)

esphome/components/esp32_ble/ble.cpp

@@ -256,29 +256,38 @@ bool ESP32BLE::ble_setup_() {
   }
 #endif
 
-  std::string name;
-  if (this->name_.has_value()) {
-    name = this->name_.value();
+  const char *device_name;
+  std::string name_with_suffix;
+
+  if (this->name_ != nullptr) {
     if (App.is_name_add_mac_suffix_enabled()) {
+      // MAC address length: 12 hex chars + null terminator
+      constexpr size_t mac_address_len = 13;
       // MAC address suffix length (last 6 characters of 12-char MAC address string)
       constexpr size_t mac_address_suffix_len = 6;
-      const std::string mac_addr = get_mac_address();
-      const char *mac_suffix_ptr = mac_addr.c_str() + mac_address_suffix_len;
-      name = make_name_with_suffix(name, '-', mac_suffix_ptr, mac_address_suffix_len);
+      char mac_addr[mac_address_len];
+      get_mac_address_into_buffer(mac_addr);
+      const char *mac_suffix_ptr = mac_addr + mac_address_suffix_len;
+      name_with_suffix =
+          make_name_with_suffix(this->name_, strlen(this->name_), '-', mac_suffix_ptr, mac_address_suffix_len);
+      device_name = name_with_suffix.c_str();
+    } else {
+      device_name = this->name_;
     }
   } else {
-    name = App.get_name();
-    if (name.length() > 20) {
+    name_with_suffix = App.get_name();
+    if (name_with_suffix.length() > 20) {
       if (App.is_name_add_mac_suffix_enabled()) {
         // Keep first 13 chars and last 7 chars (MAC suffix), remove middle
-        name.erase(13, name.length() - 20);
+        name_with_suffix.erase(13, name_with_suffix.length() - 20);
       } else {
-        name.resize(20);
+        name_with_suffix.resize(20);
       }
     }
+    device_name = name_with_suffix.c_str();
   }
 
-  err = esp_ble_gap_set_device_name(name.c_str());
+  err = esp_ble_gap_set_device_name(device_name);
   if (err != ESP_OK) {
     ESP_LOGE(TAG, "esp_ble_gap_set_device_name failed: %d", err);
     return false;

esphome/components/esp32_ble/ble.h

@@ -112,7 +112,7 @@ class ESP32BLE : public Component {
   void loop() override;
   void dump_config() override;
   float get_setup_priority() const override;
-  void set_name(const std::string &name) { this->name_ = name; }
+  void set_name(const char *name) { this->name_ = name; }
 
 #ifdef USE_ESP32_BLE_ADVERTISING
   void advertising_start();
@@ -191,13 +191,11 @@ class ESP32BLE : public Component {
   esphome::LockFreeQueue<BLEEvent, MAX_BLE_QUEUE_SIZE> ble_events_;
   esphome::EventPool<BLEEvent, MAX_BLE_QUEUE_SIZE> ble_event_pool_;
 
-  // optional<string> (typically 16+ bytes on 32-bit, aligned to 4 bytes)
-  optional<std::string> name_;
-
   // 4-byte aligned members
 #ifdef USE_ESP32_BLE_ADVERTISING
   BLEAdvertising *advertising_{};  // 4 bytes (pointer)
 #endif
+  const char *name_{nullptr};                 // 4 bytes (pointer to string literal in flash)
   esp_ble_io_cap_t io_cap_{ESP_IO_CAP_NONE};  // 4 bytes (enum)
   uint32_t advertising_cycle_time_{};         // 4 bytes
 

esphome/core/application.h

@@ -105,11 +105,13 @@ class Application {
     arch_init();
     this->name_add_mac_suffix_ = name_add_mac_suffix;
     if (name_add_mac_suffix) {
+      // MAC address length: 12 hex chars + null terminator
+      constexpr size_t mac_address_len = 13;
       // MAC address suffix length (last 6 characters of 12-char MAC address string)
       constexpr size_t mac_address_suffix_len = 6;
-      const std::string mac_addr = get_mac_address();
-      // Use pointer + offset to avoid substr() allocation
-      const char *mac_suffix_ptr = mac_addr.c_str() + mac_address_suffix_len;
+      char mac_addr[mac_address_len];
+      get_mac_address_into_buffer(mac_addr);
+      const char *mac_suffix_ptr = mac_addr + mac_address_suffix_len;
       this->name_ = make_name_with_suffix(name, '-', mac_suffix_ptr, mac_address_suffix_len);
       if (!friendly_name.empty()) {
         this->friendly_name_ = make_name_with_suffix(friendly_name, ' ', mac_suffix_ptr, mac_address_suffix_len);

esphome/core/helpers.cpp

@@ -238,9 +238,9 @@ std::string str_sprintf(const char *fmt, ...) {
 // Maximum size for name with suffix: 120 (max friendly name) + 1 (separator) + 6 (MAC suffix) + 1 (null term)
 static constexpr size_t MAX_NAME_WITH_SUFFIX_SIZE = 128;
 
-std::string make_name_with_suffix(const std::string &name, char sep, const char *suffix_ptr, size_t suffix_len) {
+std::string make_name_with_suffix(const char *name, size_t name_len, char sep, const char *suffix_ptr,
+                                  size_t suffix_len) {
   char buffer[MAX_NAME_WITH_SUFFIX_SIZE];
-  size_t name_len = name.size();
   size_t total_len = name_len + 1 + suffix_len;
 
   // Silently truncate if needed: prioritize keeping the full suffix
@@ -252,13 +252,17 @@ std::string make_name_with_suffix(const std::string &name, char sep, const char
     total_len = name_len + 1 + suffix_len;
   }
 
-  memcpy(buffer, name.c_str(), name_len);
+  memcpy(buffer, name, name_len);
   buffer[name_len] = sep;
   memcpy(buffer + name_len + 1, suffix_ptr, suffix_len);
   buffer[total_len] = '\0';
   return std::string(buffer, total_len);
 }
 
+std::string make_name_with_suffix(const std::string &name, char sep, const char *suffix_ptr, size_t suffix_len) {
+  return make_name_with_suffix(name.c_str(), name.size(), sep, suffix_ptr, suffix_len);
+}
+
 // Parsing & formatting
 
 size_t parse_hex(const char *str, size_t length, uint8_t *data, size_t count) {

esphome/core/helpers.h

@@ -512,6 +512,17 @@ std::string __attribute__((format(printf, 1, 2))) str_sprintf(const char *fmt, .
 /// @return The concatenated string: name + sep + suffix
 std::string make_name_with_suffix(const std::string &name, char sep, const char *suffix_ptr, size_t suffix_len);
 
+/// Optimized string concatenation: name + separator + suffix (const char* overload)
+/// Uses a fixed stack buffer to avoid heap allocations.
+/// @param name The base name string
+/// @param name_len Length of the name
+/// @param sep Single character separator
+/// @param suffix_ptr Pointer to the suffix characters
+/// @param suffix_len Length of the suffix
+/// @return The concatenated string: name + sep + suffix
+std::string make_name_with_suffix(const char *name, size_t name_len, char sep, const char *suffix_ptr,
+                                  size_t suffix_len);
+
 ///@}
 
 /// @name Parsing & formatting