[api] Default response only string fields to a null StringRef

A StringRef field that is only ever encoded is skipped when empty before its pointer is
read, and the dump helper checks empty() first, so pointing it at "" buys nothing while
costing one store per field in every message constructor. Fields that are decoded or force
encoded keep the empty string default.

esphome/components/api/api_pb2.h

@@ -377,7 +377,7 @@ class InfoResponseProtoMessage : public ProtoMessage {
   StringRef name{};
   bool disabled_by_default{false};
 #ifdef USE_ENTITY_ICON
-  StringRef icon{};
+  StringRef icon{nullptr, 0};
 #endif
   enums::EntityCategory entity_category{};
 #ifdef USE_DEVICES
@@ -549,7 +549,7 @@ class DeviceInfo final : public ProtoMessage {
 #ifdef USE_SERIAL_PROXY
 class SerialProxyInfo final : public ProtoMessage {
  public:
-  StringRef name{};
+  StringRef name{nullptr, 0};
   enums::SerialProxyPortType port_type{};
   uint32_t configured_line_states{0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
@@ -744,7 +744,7 @@ class ListEntitiesBinarySensorResponse final : public InfoResponseProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("list_entities_binary_sensor_response"); }
 #endif
-  StringRef device_class{};
+  StringRef device_class{nullptr, 0};
   bool is_status_binary_sensor{false};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
@@ -791,7 +791,7 @@ class ListEntitiesCoverResponse final : public InfoResponseProtoMessage {
   bool assumed_state{false};
   bool supports_position{false};
   bool supports_tilt{false};
-  StringRef device_class{};
+  StringRef device_class{nullptr, 0};
   bool supports_stop{false};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
@@ -883,7 +883,7 @@ class FanStateResponse final : public StateResponseProtoMessage {
   bool oscillating{false};
   enums::FanDirection direction{};
   int32_t speed_level{0};
-  StringRef preset_mode{};
+  StringRef preset_mode{nullptr, 0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -963,7 +963,7 @@ class LightStateResponse final : public StateResponseProtoMessage {
   float color_temperature{0.0f};
   float cold_white{0.0f};
   float warm_white{0.0f};
-  StringRef effect{};
+  StringRef effect{nullptr, 0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -1025,10 +1025,10 @@ class ListEntitiesSensorResponse final : public InfoResponseProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("list_entities_sensor_response"); }
 #endif
-  StringRef unit_of_measurement{};
+  StringRef unit_of_measurement{nullptr, 0};
   int32_t accuracy_decimals{0};
   bool force_update{false};
-  StringRef device_class{};
+  StringRef device_class{nullptr, 0};
   enums::SensorStateClass state_class{};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
@@ -1073,7 +1073,7 @@ class ListEntitiesSwitchResponse final : public InfoResponseProtoMessage {
   const LogString *message_name() const override { return LOG_STR("list_entities_switch_response"); }
 #endif
   bool assumed_state{false};
-  StringRef device_class{};
+  StringRef device_class{nullptr, 0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -1130,7 +1130,7 @@ class ListEntitiesTextSensorResponse final : public InfoResponseProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("list_entities_text_sensor_response"); }
 #endif
-  StringRef device_class{};
+  StringRef device_class{nullptr, 0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -1150,7 +1150,7 @@ class TextSensorStateResponse final : public StateResponseProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("text_sensor_state_response"); }
 #endif
-  StringRef state{};
+  StringRef state{nullptr, 0};
   bool missing_state{false};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
@@ -1248,8 +1248,8 @@ class NoiseEncryptionSetKeyResponse final : public ProtoMessage {
 #ifdef USE_API_HOMEASSISTANT_SERVICES
 class HomeassistantServiceMap final : public ProtoMessage {
  public:
-  StringRef key{};
-  StringRef value{};
+  StringRef key{nullptr, 0};
+  StringRef value{nullptr, 0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -1269,7 +1269,7 @@ class HomeassistantActionRequest final : public ProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("homeassistant_action_request"); }
 #endif
-  StringRef service{};
+  StringRef service{nullptr, 0};
   FixedVector<HomeassistantServiceMap> data{};
   FixedVector<HomeassistantServiceMap> data_template{};
   FixedVector<HomeassistantServiceMap> variables{};
@@ -1281,7 +1281,7 @@ class HomeassistantActionRequest final : public ProtoMessage {
   bool wants_response{false};
 #endif
 #ifdef USE_API_HOMEASSISTANT_ACTION_RESPONSES_JSON
-  StringRef response_template{};
+  StringRef response_template{nullptr, 0};
 #endif
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
@@ -1327,8 +1327,8 @@ class SubscribeHomeAssistantStateResponse final : public ProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("subscribe_home_assistant_state_response"); }
 #endif
-  StringRef entity_id{};
-  StringRef attribute{};
+  StringRef entity_id{nullptr, 0};
+  StringRef attribute{nullptr, 0};
   bool once{false};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
@@ -1421,13 +1421,13 @@ class GetTimeResponse final : public ProtoDecodableMessage {
 #ifdef USE_API_USER_DEFINED_ACTIONS
 class ListEntitiesServicesArgument final : public ProtoMessage {
  public:
-  StringRef name{};
+  StringRef name{nullptr, 0};
   enums::ServiceArgType type{};
 #ifdef USE_API_USER_DEFINED_ACTION_METADATA
-  StringRef description{};
+  StringRef description{nullptr, 0};
 #endif
 #ifdef USE_API_USER_DEFINED_ACTION_METADATA
-  StringRef example{};
+  StringRef example{nullptr, 0};
 #endif
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
@@ -1448,12 +1448,12 @@ class ListEntitiesServicesResponse final : public ProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("list_entities_services_response"); }
 #endif
-  StringRef name{};
+  StringRef name{nullptr, 0};
   uint32_t key{0};
   FixedVector<ListEntitiesServicesArgument> args{};
   enums::SupportsResponseType supports_response{};
 #ifdef USE_API_USER_DEFINED_ACTION_METADATA
-  StringRef description{};
+  StringRef description{nullptr, 0};
 #endif
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
@@ -1520,7 +1520,7 @@ class ExecuteServiceResponse final : public ProtoMessage {
 #endif
   uint32_t call_id{0};
   bool success{false};
-  StringRef error_message{};
+  StringRef error_message{nullptr, 0};
 #ifdef USE_API_USER_DEFINED_ACTION_RESPONSES_JSON
   const uint8_t *response_data{nullptr};
   uint16_t response_data_len{0};
@@ -1655,9 +1655,9 @@ class ClimateStateResponse final : public StateResponseProtoMessage {
   enums::ClimateAction action{};
   enums::ClimateFanMode fan_mode{};
   enums::ClimateSwingMode swing_mode{};
-  StringRef custom_fan_mode{};
+  StringRef custom_fan_mode{nullptr, 0};
   enums::ClimatePreset preset{};
-  StringRef custom_preset{};
+  StringRef custom_preset{nullptr, 0};
   float current_humidity{0.0f};
   float target_humidity{0.0f};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
@@ -1790,9 +1790,9 @@ class ListEntitiesNumberResponse final : public InfoResponseProtoMessage {
   float min_value{0.0f};
   float max_value{0.0f};
   float step{0.0f};
-  StringRef unit_of_measurement{};
+  StringRef unit_of_measurement{nullptr, 0};
   enums::NumberMode mode{};
-  StringRef device_class{};
+  StringRef device_class{nullptr, 0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -1870,7 +1870,7 @@ class SelectStateResponse final : public StateResponseProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("select_state_response"); }
 #endif
-  StringRef state{};
+  StringRef state{nullptr, 0};
   bool missing_state{false};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
@@ -1977,7 +1977,7 @@ class ListEntitiesLockResponse final : public InfoResponseProtoMessage {
   bool assumed_state{false};
   bool supports_open{false};
   bool requires_code{false};
-  StringRef code_format{};
+  StringRef code_format{nullptr, 0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -2036,7 +2036,7 @@ class ListEntitiesButtonResponse final : public InfoResponseProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("list_entities_button_response"); }
 #endif
-  StringRef device_class{};
+  StringRef device_class{nullptr, 0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -2067,7 +2067,7 @@ class ButtonCommandRequest final : public CommandProtoMessage {
 #ifdef USE_MEDIA_PLAYER
 class MediaPlayerSupportedFormat final : public ProtoMessage {
  public:
-  StringRef format{};
+  StringRef format{nullptr, 0};
   uint32_t sample_rate{0};
   uint32_t num_channels{0};
   enums::MediaPlayerFormatPurpose purpose{};
@@ -2727,10 +2727,10 @@ class VoiceAssistantRequest final : public ProtoMessage {
   const LogString *message_name() const override { return LOG_STR("voice_assistant_request"); }
 #endif
   bool start{false};
-  StringRef conversation_id{};
+  StringRef conversation_id{nullptr, 0};
   uint32_t flags{0};
   VoiceAssistantAudioSettings audio_settings{};
-  StringRef wake_word_phrase{};
+  StringRef wake_word_phrase{nullptr, 0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -2871,8 +2871,8 @@ class VoiceAssistantAnnounceFinished final : public ProtoMessage {
 };
 class VoiceAssistantWakeWord final : public ProtoMessage {
  public:
-  StringRef id{};
-  StringRef wake_word{};
+  StringRef id{nullptr, 0};
+  StringRef wake_word{nullptr, 0};
   std::vector<std::string> trained_languages{};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
@@ -3025,7 +3025,7 @@ class ListEntitiesTextResponse final : public InfoResponseProtoMessage {
 #endif
   uint32_t min_length{0};
   uint32_t max_length{0};
-  StringRef pattern{};
+  StringRef pattern{nullptr, 0};
   enums::TextMode mode{};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
@@ -3046,7 +3046,7 @@ class TextStateResponse final : public StateResponseProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("text_state_response"); }
 #endif
-  StringRef state{};
+  StringRef state{nullptr, 0};
   bool missing_state{false};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
@@ -3206,7 +3206,7 @@ class ListEntitiesEventResponse final : public InfoResponseProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("list_entities_event_response"); }
 #endif
-  StringRef device_class{};
+  StringRef device_class{nullptr, 0};
   const FixedVector<const char *> *event_types{};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
@@ -3227,7 +3227,7 @@ class EventResponse final : public StateResponseProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("event_response"); }
 #endif
-  StringRef event_type{};
+  StringRef event_type{nullptr, 0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -3249,7 +3249,7 @@ class ListEntitiesValveResponse final : public InfoResponseProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("list_entities_valve_response"); }
 #endif
-  StringRef device_class{};
+  StringRef device_class{nullptr, 0};
   bool assumed_state{false};
   bool supports_position{false};
   bool supports_stop{false};
@@ -3369,7 +3369,7 @@ class ListEntitiesUpdateResponse final : public InfoResponseProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("list_entities_update_response"); }
 #endif
-  StringRef device_class{};
+  StringRef device_class{nullptr, 0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -3393,11 +3393,11 @@ class UpdateStateResponse final : public StateResponseProtoMessage {
   bool in_progress{false};
   bool has_progress{false};
   float progress{0.0f};
-  StringRef current_version{};
-  StringRef latest_version{};
-  StringRef title{};
-  StringRef release_summary{};
-  StringRef release_url{};
+  StringRef current_version{nullptr, 0};
+  StringRef latest_version{nullptr, 0};
+  StringRef title{nullptr, 0};
+  StringRef release_summary{nullptr, 0};
+  StringRef release_url{nullptr, 0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -3735,7 +3735,7 @@ class SerialProxyRequestResponse final : public ProtoMessage {
   uint32_t instance{0};
   enums::SerialProxyRequestType type{};
   enums::SerialProxyStatus status{};
-  StringRef error_message{};
+  StringRef error_message{nullptr, 0};
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);

script/api_protobuf/api_protobuf.py

@@ -576,7 +576,7 @@ def create_field_type_info(
 
     # Special handling for string fields - use StringRef for zero-copy
     if field.type == 9:
-        return PointerToStringBufferType(field, None)
+        return PointerToStringBufferType(field, needs_decode)
 
     validate_field_type(field.type, field.name)
     if field.type == 11:
@@ -1215,12 +1215,22 @@ class PointerToStringBufferType(PointerToBufferTypeBase):
     reference_type = "StringRef &"
     const_reference_type = "const StringRef &"
 
+    def __init__(
+        self, field: descriptor.FieldDescriptorProto, needs_decode: bool
+    ) -> None:
+        super().__init__(field, None)
+        self._needs_decode = needs_decode
+
     @classmethod
     def can_use_dump_field(cls) -> bool:
         return True
 
     @property
     def public_content(self) -> list[str]:
+        # A field that is only ever encoded and skipped when empty never has its pointer read, so a
+        # null default lets the whole message construct as one zero fill
+        if not self._needs_decode and not self.force:
+            return [f"StringRef {self.field_name}{{nullptr, 0}};"]
         return [f"StringRef {self.field_name}{{}};"]
 
     @property