simplify

esphome/components/api/api_connection.cpp

@@ -1535,8 +1535,13 @@ bool APIConnection::send_device_info_response(const DeviceInfoRequest &msg) {
 #ifdef USE_API_HOMEASSISTANT_STATES
 void APIConnection::on_home_assistant_state_response(const HomeAssistantStateResponse &msg) {
   for (auto &it : this->parent_->get_state_subs()) {
-    if (it.entity_id == msg.entity_id && it.attribute.value() == msg.attribute) {
-      it.callback(msg.state);
+    // Compare entity_id and attribute with message fields
+    bool entity_match = (strcmp(it.entity_id_, msg.entity_id.c_str()) == 0);
+    bool attribute_match = (it.attribute_ != nullptr && strcmp(it.attribute_, msg.attribute.c_str()) == 0) ||
+                           (it.attribute_ == nullptr && msg.attribute.empty());
+
+    if (entity_match && attribute_match) {
+      it.callback_(msg.state);
     }
   }
 }
@@ -1873,12 +1878,12 @@ void APIConnection::process_state_subscriptions_() {
 
   const auto &it = subs[this->state_subs_at_];
   SubscribeHomeAssistantStateResponse resp;
-  resp.set_entity_id(StringRef(it.entity_id));
+  resp.set_entity_id(StringRef(it.entity_id_));
 
-  // Avoid string copy by directly using the optional's value if it exists
-  resp.set_attribute(it.attribute.has_value() ? StringRef(it.attribute.value()) : StringRef(""));
+  // Avoid string copy by using the const char* pointer if it exists
+  resp.set_attribute(it.attribute_ != nullptr ? StringRef(it.attribute_) : StringRef(""));
 
-  resp.once = it.once;
+  resp.once = it.once_;
   if (this->send_message(resp, SubscribeHomeAssistantStateResponse::MESSAGE_TYPE)) {
     this->state_subs_at_++;
   }

esphome/components/api/api_server.cpp

@@ -431,25 +431,56 @@ void APIServer::handle_action_response(uint32_t call_id, bool success, const std
 #endif  // USE_API_HOMEASSISTANT_SERVICES
 
 #ifdef USE_API_HOMEASSISTANT_STATES
+// Helper to add subscription (reduces duplication)
+void APIServer::add_state_subscription_(const char *entity_id, const char *attribute,
+                                        std::function<void(std::string)> f, bool once) {
+  this->state_subs_.push_back(HomeAssistantStateSubscription{
+      .entity_id_ = entity_id, .attribute_ = attribute, .callback_ = std::move(f), .once_ = once,
+      // entity_id_copy_ and attribute_copy_ remain nullptr (no heap allocation)
+  });
+}
+
+// Helper to add subscription with heap-allocated strings (reduces duplication)
+void APIServer::add_state_subscription_(std::string entity_id, optional<std::string> attribute,
+                                        std::function<void(std::string)> f, bool once) {
+  HomeAssistantStateSubscription sub;
+  // Allocate heap storage for the strings
+  sub.entity_id_copy_ = std::make_unique<std::string>(std::move(entity_id));
+  sub.entity_id_ = sub.entity_id_copy_->c_str();
+
+  if (attribute.has_value()) {
+    sub.attribute_copy_ = std::make_unique<std::string>(std::move(attribute.value()));
+    sub.attribute_ = sub.attribute_copy_->c_str();
+  } else {
+    sub.attribute_ = nullptr;
+  }
+
+  sub.callback_ = std::move(f);
+  sub.once_ = once;
+  this->state_subs_.push_back(std::move(sub));
+}
+
+// New const char* overload (for internal components - zero allocation)
+void APIServer::subscribe_home_assistant_state(const char *entity_id, const char *attribute,
+                                               std::function<void(std::string)> f) {
+  this->add_state_subscription_(entity_id, attribute, std::move(f), false);
+}
+
+void APIServer::get_home_assistant_state(const char *entity_id, const char *attribute,
+                                         std::function<void(std::string)> f) {
+  this->add_state_subscription_(entity_id, attribute, std::move(f), true);
+}
+
+// Existing std::string overload (for custom_api_device.h - heap allocation)
 void APIServer::subscribe_home_assistant_state(std::string entity_id, optional<std::string> attribute,
                                                std::function<void(std::string)> f) {
-  this->state_subs_.push_back(HomeAssistantStateSubscription{
-      .entity_id = std::move(entity_id),
-      .attribute = std::move(attribute),
-      .callback = std::move(f),
-      .once = false,
-  });
+  this->add_state_subscription_(std::move(entity_id), std::move(attribute), std::move(f), false);
 }
 
 void APIServer::get_home_assistant_state(std::string entity_id, optional<std::string> attribute,
                                          std::function<void(std::string)> f) {
-  this->state_subs_.push_back(HomeAssistantStateSubscription{
-      .entity_id = std::move(entity_id),
-      .attribute = std::move(attribute),
-      .callback = std::move(f),
-      .once = true,
-  });
-};
+  this->add_state_subscription_(std::move(entity_id), std::move(attribute), std::move(f), true);
+}
 
 const std::vector<APIServer::HomeAssistantStateSubscription> &APIServer::get_state_subs() const {
   return this->state_subs_;

esphome/components/api/api_server.h

@@ -154,16 +154,27 @@ class APIServer : public Component, public Controller {
 
 #ifdef USE_API_HOMEASSISTANT_STATES
   struct HomeAssistantStateSubscription {
-    std::string entity_id;
-    optional<std::string> attribute;
-    std::function<void(std::string)> callback;
-    bool once;
+    const char *entity_id_;  // Pointer to flash (internal) or heap (external)
+    const char *attribute_;  // Pointer to flash or nullptr (nullptr means no attribute)
+    std::function<void(std::string)> callback_;
+    bool once_;
+
+    // Storage for external components using std::string API (custom_api_device.h)
+    // These are only allocated when using the std::string overload
+    std::unique_ptr<std::string> entity_id_copy_;
+    std::unique_ptr<std::string> attribute_copy_;
   };
 
+  // New const char* overload (for internal components - zero allocation)
+  void subscribe_home_assistant_state(const char *entity_id, const char *attribute, std::function<void(std::string)> f);
+  void get_home_assistant_state(const char *entity_id, const char *attribute, std::function<void(std::string)> f);
+
+  // Existing std::string overload (for custom_api_device.h - heap allocation)
   void subscribe_home_assistant_state(std::string entity_id, optional<std::string> attribute,
                                       std::function<void(std::string)> f);
   void get_home_assistant_state(std::string entity_id, optional<std::string> attribute,
                                 std::function<void(std::string)> f);
+
   const std::vector<HomeAssistantStateSubscription> &get_state_subs() const;
 #endif
 #ifdef USE_API_SERVICES
@@ -185,6 +196,13 @@ class APIServer : public Component, public Controller {
   bool update_noise_psk_(const SavedNoisePsk &new_psk, const LogString *save_log_msg, const LogString *fail_log_msg,
                          const psk_t &active_psk, bool make_active);
 #endif  // USE_API_NOISE
+#ifdef USE_API_HOMEASSISTANT_STATES
+  // Helper methods to reduce code duplication
+  void add_state_subscription_(const char *entity_id, const char *attribute, std::function<void(std::string)> f,
+                               bool once);
+  void add_state_subscription_(std::string entity_id, optional<std::string> attribute,
+                               std::function<void(std::string)> f, bool once);
+#endif  // USE_API_HOMEASSISTANT_STATES
   // Pointers and pointer-like types first (4 bytes each)
   std::unique_ptr<socket::Socket> socket_ = nullptr;
 #ifdef USE_API_CLIENT_CONNECTED_TRIGGER

esphome/components/homeassistant/binary_sensor/homeassistant_binary_sensor.cpp

@@ -19,11 +19,10 @@ void HomeassistantBinarySensor::setup() {
           case PARSE_ON:
           case PARSE_OFF:
             bool new_state = val == PARSE_ON;
-            if (this->attribute_.has_value()) {
-              ESP_LOGD(TAG, "'%s::%s': Got attribute state %s", this->entity_id_.c_str(),
-                       this->attribute_.value().c_str(), ONOFF(new_state));
+            if (this->attribute_ != nullptr) {
+              ESP_LOGD(TAG, "'%s::%s': Got attribute state %s", this->entity_id_, this->attribute_, ONOFF(new_state));
             } else {
-              ESP_LOGD(TAG, "'%s': Got state %s", this->entity_id_.c_str(), ONOFF(new_state));
+              ESP_LOGD(TAG, "'%s': Got state %s", this->entity_id_, ONOFF(new_state));
             }
             if (this->initial_) {
               this->publish_initial_state(new_state);
@@ -37,9 +36,9 @@ void HomeassistantBinarySensor::setup() {
 }
 void HomeassistantBinarySensor::dump_config() {
   LOG_BINARY_SENSOR("", "Homeassistant Binary Sensor", this);
-  ESP_LOGCONFIG(TAG, "  Entity ID: '%s'", this->entity_id_.c_str());
-  if (this->attribute_.has_value()) {
-    ESP_LOGCONFIG(TAG, "  Attribute: '%s'", this->attribute_.value().c_str());
+  ESP_LOGCONFIG(TAG, "  Entity ID: '%s'", this->entity_id_);
+  if (this->attribute_ != nullptr) {
+    ESP_LOGCONFIG(TAG, "  Attribute: '%s'", this->attribute_);
   }
 }
 float HomeassistantBinarySensor::get_setup_priority() const { return setup_priority::AFTER_WIFI; }

esphome/components/homeassistant/binary_sensor/homeassistant_binary_sensor.h

@@ -8,15 +8,15 @@ namespace homeassistant {
 
 class HomeassistantBinarySensor : public binary_sensor::BinarySensor, public Component {
  public:
-  void set_entity_id(const std::string &entity_id) { entity_id_ = entity_id; }
-  void set_attribute(const std::string &attribute) { attribute_ = attribute; }
+  void set_entity_id(const char *entity_id) { this->entity_id_ = entity_id; }
+  void set_attribute(const char *attribute) { this->attribute_ = attribute; }
   void setup() override;
   void dump_config() override;
   float get_setup_priority() const override;
 
  protected:
-  std::string entity_id_;
-  optional<std::string> attribute_;
+  const char *entity_id_{nullptr};
+  const char *attribute_{nullptr};
   bool initial_{true};
 };
 

esphome/components/homeassistant/number/homeassistant_number.cpp

@@ -12,21 +12,21 @@ static const char *const TAG = "homeassistant.number";
 void HomeassistantNumber::state_changed_(const std::string &state) {
   auto number_value = parse_number<float>(state);
   if (!number_value.has_value()) {
-    ESP_LOGW(TAG, "'%s': Can't convert '%s' to number!", this->entity_id_.c_str(), state.c_str());
+    ESP_LOGW(TAG, "'%s': Can't convert '%s' to number!", this->entity_id_, state.c_str());
     this->publish_state(NAN);
     return;
   }
   if (this->state == number_value.value()) {
     return;
   }
-  ESP_LOGD(TAG, "'%s': Got state %s", this->entity_id_.c_str(), state.c_str());
+  ESP_LOGD(TAG, "'%s': Got state %s", this->entity_id_, state.c_str());
   this->publish_state(number_value.value());
 }
 
 void HomeassistantNumber::min_retrieved_(const std::string &min) {
   auto min_value = parse_number<float>(min);
   if (!min_value.has_value()) {
-    ESP_LOGE(TAG, "'%s': Can't convert 'min' value '%s' to number!", this->entity_id_.c_str(), min.c_str());
+    ESP_LOGE(TAG, "'%s': Can't convert 'min' value '%s' to number!", this->entity_id_, min.c_str());
     return;
   }
   ESP_LOGD(TAG, "'%s': Min retrieved: %s", get_name().c_str(), min.c_str());
@@ -36,7 +36,7 @@ void HomeassistantNumber::min_retrieved_(const std::string &min) {
 void HomeassistantNumber::max_retrieved_(const std::string &max) {
   auto max_value = parse_number<float>(max);
   if (!max_value.has_value()) {
-    ESP_LOGE(TAG, "'%s': Can't convert 'max' value '%s' to number!", this->entity_id_.c_str(), max.c_str());
+    ESP_LOGE(TAG, "'%s': Can't convert 'max' value '%s' to number!", this->entity_id_, max.c_str());
     return;
   }
   ESP_LOGD(TAG, "'%s': Max retrieved: %s", get_name().c_str(), max.c_str());
@@ -46,7 +46,7 @@ void HomeassistantNumber::max_retrieved_(const std::string &max) {
 void HomeassistantNumber::step_retrieved_(const std::string &step) {
   auto step_value = parse_number<float>(step);
   if (!step_value.has_value()) {
-    ESP_LOGE(TAG, "'%s': Can't convert 'step' value '%s' to number!", this->entity_id_.c_str(), step.c_str());
+    ESP_LOGE(TAG, "'%s': Can't convert 'step' value '%s' to number!", this->entity_id_, step.c_str());
     return;
   }
   ESP_LOGD(TAG, "'%s': Step Retrieved %s", get_name().c_str(), step.c_str());
@@ -55,22 +55,19 @@ void HomeassistantNumber::step_retrieved_(const std::string &step) {
 
 void HomeassistantNumber::setup() {
   api::global_api_server->subscribe_home_assistant_state(
-      this->entity_id_, nullopt, std::bind(&HomeassistantNumber::state_changed_, this, std::placeholders::_1));
+      this->entity_id_, nullptr, std::bind(&HomeassistantNumber::state_changed_, this, std::placeholders::_1));
 
   api::global_api_server->get_home_assistant_state(
-      this->entity_id_, optional<std::string>("min"),
-      std::bind(&HomeassistantNumber::min_retrieved_, this, std::placeholders::_1));
+      this->entity_id_, "min", std::bind(&HomeassistantNumber::min_retrieved_, this, std::placeholders::_1));
   api::global_api_server->get_home_assistant_state(
-      this->entity_id_, optional<std::string>("max"),
-      std::bind(&HomeassistantNumber::max_retrieved_, this, std::placeholders::_1));
+      this->entity_id_, "max", std::bind(&HomeassistantNumber::max_retrieved_, this, std::placeholders::_1));
   api::global_api_server->get_home_assistant_state(
-      this->entity_id_, optional<std::string>("step"),
-      std::bind(&HomeassistantNumber::step_retrieved_, this, std::placeholders::_1));
+      this->entity_id_, "step", std::bind(&HomeassistantNumber::step_retrieved_, this, std::placeholders::_1));
 }
 
 void HomeassistantNumber::dump_config() {
   LOG_NUMBER("", "Homeassistant Number", this);
-  ESP_LOGCONFIG(TAG, "  Entity ID: '%s'", this->entity_id_.c_str());
+  ESP_LOGCONFIG(TAG, "  Entity ID: '%s'", this->entity_id_);
 }
 
 float HomeassistantNumber::get_setup_priority() const { return setup_priority::AFTER_CONNECTION; }

esphome/components/homeassistant/number/homeassistant_number.h

@@ -11,7 +11,7 @@ namespace homeassistant {
 
 class HomeassistantNumber : public number::Number, public Component {
  public:
-  void set_entity_id(const std::string &entity_id) { this->entity_id_ = entity_id; }
+  void set_entity_id(const char *entity_id) { this->entity_id_ = entity_id; }
 
   void setup() override;
   void dump_config() override;
@@ -25,7 +25,7 @@ class HomeassistantNumber : public number::Number, public Component {
 
   void control(float value) override;
 
-  std::string entity_id_;
+  const char *entity_id_{nullptr};
 };
 }  // namespace homeassistant
 }  // namespace esphome

esphome/components/homeassistant/sensor/homeassistant_sensor.cpp

@@ -12,25 +12,24 @@ void HomeassistantSensor::setup() {
       this->entity_id_, this->attribute_, [this](const std::string &state) {
         auto val = parse_number<float>(state);
         if (!val.has_value()) {
-          ESP_LOGW(TAG, "'%s': Can't convert '%s' to number!", this->entity_id_.c_str(), state.c_str());
+          ESP_LOGW(TAG, "'%s': Can't convert '%s' to number!", this->entity_id_, state.c_str());
           this->publish_state(NAN);
           return;
         }
 
-        if (this->attribute_.has_value()) {
-          ESP_LOGD(TAG, "'%s::%s': Got attribute state %.2f", this->entity_id_.c_str(),
-                   this->attribute_.value().c_str(), *val);
+        if (this->attribute_ != nullptr) {
+          ESP_LOGD(TAG, "'%s::%s': Got attribute state %.2f", this->entity_id_, this->attribute_, *val);
         } else {
-          ESP_LOGD(TAG, "'%s': Got state %.2f", this->entity_id_.c_str(), *val);
+          ESP_LOGD(TAG, "'%s': Got state %.2f", this->entity_id_, *val);
         }
         this->publish_state(*val);
       });
 }
 void HomeassistantSensor::dump_config() {
   LOG_SENSOR("", "Homeassistant Sensor", this);
-  ESP_LOGCONFIG(TAG, "  Entity ID: '%s'", this->entity_id_.c_str());
-  if (this->attribute_.has_value()) {
-    ESP_LOGCONFIG(TAG, "  Attribute: '%s'", this->attribute_.value().c_str());
+  ESP_LOGCONFIG(TAG, "  Entity ID: '%s'", this->entity_id_);
+  if (this->attribute_ != nullptr) {
+    ESP_LOGCONFIG(TAG, "  Attribute: '%s'", this->attribute_);
   }
 }
 float HomeassistantSensor::get_setup_priority() const { return setup_priority::AFTER_CONNECTION; }

esphome/components/homeassistant/sensor/homeassistant_sensor.h

@@ -8,15 +8,15 @@ namespace homeassistant {
 
 class HomeassistantSensor : public sensor::Sensor, public Component {
  public:
-  void set_entity_id(const std::string &entity_id) { entity_id_ = entity_id; }
-  void set_attribute(const std::string &attribute) { attribute_ = attribute; }
+  void set_entity_id(const char *entity_id) { this->entity_id_ = entity_id; }
+  void set_attribute(const char *attribute) { this->attribute_ = attribute; }
   void setup() override;
   void dump_config() override;
   float get_setup_priority() const override;
 
  protected:
-  std::string entity_id_;
-  optional<std::string> attribute_;
+  const char *entity_id_{nullptr};
+  const char *attribute_{nullptr};
 };
 
 }  // namespace homeassistant

esphome/components/homeassistant/switch/homeassistant_switch.cpp

@@ -10,7 +10,7 @@ static const char *const TAG = "homeassistant.switch";
 using namespace esphome::switch_;
 
 void HomeassistantSwitch::setup() {
-  api::global_api_server->subscribe_home_assistant_state(this->entity_id_, nullopt, [this](const std::string &state) {
+  api::global_api_server->subscribe_home_assistant_state(this->entity_id_, nullptr, [this](const std::string &state) {
     auto val = parse_on_off(state.c_str());
     switch (val) {
       case PARSE_NONE:
@@ -20,7 +20,7 @@ void HomeassistantSwitch::setup() {
       case PARSE_ON:
       case PARSE_OFF:
         bool new_state = val == PARSE_ON;
-        ESP_LOGD(TAG, "'%s': Got state %s", this->entity_id_.c_str(), ONOFF(new_state));
+        ESP_LOGD(TAG, "'%s': Got state %s", this->entity_id_, ONOFF(new_state));
         this->publish_state(new_state);
         break;
     }
@@ -29,7 +29,7 @@ void HomeassistantSwitch::setup() {
 
 void HomeassistantSwitch::dump_config() {
   LOG_SWITCH("", "Homeassistant Switch", this);
-  ESP_LOGCONFIG(TAG, "  Entity ID: '%s'", this->entity_id_.c_str());
+  ESP_LOGCONFIG(TAG, "  Entity ID: '%s'", this->entity_id_);
 }
 
 float HomeassistantSwitch::get_setup_priority() const { return setup_priority::AFTER_CONNECTION; }

esphome/components/homeassistant/switch/homeassistant_switch.h

@@ -8,14 +8,14 @@ namespace homeassistant {
 
 class HomeassistantSwitch : public switch_::Switch, public Component {
  public:
-  void set_entity_id(const std::string &entity_id) { this->entity_id_ = entity_id; }
+  void set_entity_id(const char *entity_id) { this->entity_id_ = entity_id; }
   void setup() override;
   void dump_config() override;
   float get_setup_priority() const override;
 
  protected:
   void write_state(bool state) override;
-  std::string entity_id_;
+  const char *entity_id_{nullptr};
 };
 
 }  // namespace homeassistant

esphome/components/homeassistant/text_sensor/homeassistant_text_sensor.cpp

@@ -10,20 +10,19 @@ static const char *const TAG = "homeassistant.text_sensor";
 void HomeassistantTextSensor::setup() {
   api::global_api_server->subscribe_home_assistant_state(
       this->entity_id_, this->attribute_, [this](const std::string &state) {
-        if (this->attribute_.has_value()) {
-          ESP_LOGD(TAG, "'%s::%s': Got attribute state '%s'", this->entity_id_.c_str(),
-                   this->attribute_.value().c_str(), state.c_str());
+        if (this->attribute_ != nullptr) {
+          ESP_LOGD(TAG, "'%s::%s': Got attribute state '%s'", this->entity_id_, this->attribute_, state.c_str());
         } else {
-          ESP_LOGD(TAG, "'%s': Got state '%s'", this->entity_id_.c_str(), state.c_str());
+          ESP_LOGD(TAG, "'%s': Got state '%s'", this->entity_id_, state.c_str());
         }
         this->publish_state(state);
       });
 }
 void HomeassistantTextSensor::dump_config() {
   LOG_TEXT_SENSOR("", "Homeassistant Text Sensor", this);
-  ESP_LOGCONFIG(TAG, "  Entity ID: '%s'", this->entity_id_.c_str());
-  if (this->attribute_.has_value()) {
-    ESP_LOGCONFIG(TAG, "  Attribute: '%s'", this->attribute_.value().c_str());
+  ESP_LOGCONFIG(TAG, "  Entity ID: '%s'", this->entity_id_);
+  if (this->attribute_ != nullptr) {
+    ESP_LOGCONFIG(TAG, "  Attribute: '%s'", this->attribute_);
   }
 }
 float HomeassistantTextSensor::get_setup_priority() const { return setup_priority::AFTER_CONNECTION; }

esphome/components/homeassistant/text_sensor/homeassistant_text_sensor.h

@@ -8,15 +8,15 @@ namespace homeassistant {
 
 class HomeassistantTextSensor : public text_sensor::TextSensor, public Component {
  public:
-  void set_entity_id(const std::string &entity_id) { entity_id_ = entity_id; }
-  void set_attribute(const std::string &attribute) { attribute_ = attribute; }
+  void set_entity_id(const char *entity_id) { this->entity_id_ = entity_id; }
+  void set_attribute(const char *attribute) { this->attribute_ = attribute; }
   void setup() override;
   void dump_config() override;
   float get_setup_priority() const override;
 
  protected:
-  std::string entity_id_;
-  optional<std::string> attribute_;
+  const char *entity_id_{nullptr};
+  const char *attribute_{nullptr};
 };
 
 }  // namespace homeassistant

tests/integration/fixtures/api_custom_services.yaml

@@ -5,6 +5,7 @@ host:
 # This is required for CustomAPIDevice to work
 api:
   custom_services: true
+  homeassistant_states: true
   # Also test that YAML services still work
   actions:
     - action: test_yaml_service

tests/integration/fixtures/external_components/custom_api_device_component/custom_api_device_component.cpp

@@ -17,6 +17,10 @@ void CustomAPIDeviceComponent::setup() {
   // Test array types
   register_service(&CustomAPIDeviceComponent::on_service_with_arrays, "custom_service_with_arrays",
                    {"bool_array", "int_array", "float_array", "string_array"});
+
+  // Test Home Assistant state subscription using std::string API (custom_api_device.h)
+  // This tests the backward compatibility of the std::string overloads
+  subscribe_homeassistant_state(&CustomAPIDeviceComponent::on_ha_state_changed, std::string("sensor.custom_test"));
 }
 
 void CustomAPIDeviceComponent::on_test_service() { ESP_LOGI(TAG, "Custom test service called!"); }
@@ -48,6 +52,11 @@ void CustomAPIDeviceComponent::on_service_with_arrays(std::vector<bool> bool_arr
   }
 }
 
+void CustomAPIDeviceComponent::on_ha_state_changed(std::string entity_id, std::string state) {
+  ESP_LOGI(TAG, "Home Assistant state changed for %s: %s", entity_id.c_str(), state.c_str());
+  ESP_LOGI(TAG, "This subscription uses std::string API for backward compatibility");
+}
+
 }  // namespace custom_api_device_component
 }  // namespace esphome
 #endif  // USE_API

tests/integration/fixtures/external_components/custom_api_device_component/custom_api_device_component.h

@@ -22,6 +22,9 @@ class CustomAPIDeviceComponent : public Component, public CustomAPIDevice {
 
   void on_service_with_arrays(std::vector<bool> bool_array, std::vector<int32_t> int_array,
                               std::vector<float> float_array, std::vector<std::string> string_array);
+
+  // Test Home Assistant state subscription with std::string API
+  void on_ha_state_changed(std::string entity_id, std::string state);
 };
 
 }  // namespace custom_api_device_component

tests/integration/test_api_custom_services.py

@@ -38,6 +38,7 @@ async def test_api_custom_services(
     custom_service_future = loop.create_future()
     custom_args_future = loop.create_future()
     custom_arrays_future = loop.create_future()
+    ha_state_future = loop.create_future()
 
     # Patterns to match in logs
     yaml_service_pattern = re.compile(r"YAML service called")
@@ -50,6 +51,9 @@ async def test_api_custom_services(
     custom_arrays_pattern = re.compile(
         r"Array service called with 2 bools, 3 ints, 2 floats, 2 strings"
     )
+    ha_state_pattern = re.compile(
+        r"This subscription uses std::string API for backward compatibility"
+    )
 
     def check_output(line: str) -> None:
         """Check log output for expected messages."""
@@ -65,6 +69,8 @@ async def test_api_custom_services(
             custom_args_future.set_result(True)
         elif not custom_arrays_future.done() and custom_arrays_pattern.search(line):
             custom_arrays_future.set_result(True)
+        elif not ha_state_future.done() and ha_state_pattern.search(line):
+            ha_state_future.set_result(True)
 
     # Run with log monitoring
     async with (
@@ -198,3 +204,8 @@ async def test_api_custom_services(
             },
         )
         await asyncio.wait_for(custom_arrays_future, timeout=5.0)
+
+        # Test Home Assistant state subscription (std::string API backward compatibility)
+        # This verifies that custom_api_device.h can still use std::string overloads
+        client.send_home_assistant_state("sensor.custom_test", "", "42.5")
+        await asyncio.wait_for(ha_state_future, timeout=5.0)