[api] Remove unnecessary string copies from optional access (#9897)

esphome/components/api/api_connection.cpp

@@ -244,21 +244,7 @@ void APIConnection::loop() {
 
 #ifdef USE_API_HOMEASSISTANT_STATES
   if (state_subs_at_ >= 0) {
-    const auto &subs = this->parent_->get_state_subs();
-    if (state_subs_at_ < static_cast<int>(subs.size())) {
-      auto &it = subs[state_subs_at_];
-      SubscribeHomeAssistantStateResponse resp;
-      resp.set_entity_id(StringRef(it.entity_id));
-      // attribute.value() returns temporary - must store it
-      std::string attribute_value = it.attribute.value();
-      resp.set_attribute(StringRef(attribute_value));
-      resp.once = it.once;
-      if (this->send_message(resp, SubscribeHomeAssistantStateResponse::MESSAGE_TYPE)) {
-        state_subs_at_++;
-      }
-    } else {
-      state_subs_at_ = -1;
-    }
+    this->process_state_subscriptions_();
   }
 #endif
 }
@@ -644,17 +630,13 @@ uint16_t APIConnection::try_send_climate_state(EntityBase *entity, APIConnection
   if (traits.get_supports_fan_modes() && climate->fan_mode.has_value())
     resp.fan_mode = static_cast<enums::ClimateFanMode>(climate->fan_mode.value());
   if (!traits.get_supported_custom_fan_modes().empty() && climate->custom_fan_mode.has_value()) {
-    // custom_fan_mode.value() returns temporary - must store it
-    std::string custom_fan_mode = climate->custom_fan_mode.value();
-    resp.set_custom_fan_mode(StringRef(custom_fan_mode));
+    resp.set_custom_fan_mode(StringRef(climate->custom_fan_mode.value()));
   }
   if (traits.get_supports_presets() && climate->preset.has_value()) {
     resp.preset = static_cast<enums::ClimatePreset>(climate->preset.value());
   }
   if (!traits.get_supported_custom_presets().empty() && climate->custom_preset.has_value()) {
-    // custom_preset.value() returns temporary - must store it
-    std::string custom_preset = climate->custom_preset.value();
-    resp.set_custom_preset(StringRef(custom_preset));
+    resp.set_custom_preset(StringRef(climate->custom_preset.value()));
   }
   if (traits.get_supports_swing_modes())
     resp.swing_mode = static_cast<enums::ClimateSwingMode>(climate->swing_mode);
@@ -1843,5 +1825,27 @@ uint16_t APIConnection::try_send_ping_request(EntityBase *entity, APIConnection
   return encode_message_to_buffer(req, PingRequest::MESSAGE_TYPE, conn, remaining_size, is_single);
 }
 
+#ifdef USE_API_HOMEASSISTANT_STATES
+void APIConnection::process_state_subscriptions_() {
+  const auto &subs = this->parent_->get_state_subs();
+  if (this->state_subs_at_ >= static_cast<int>(subs.size())) {
+    this->state_subs_at_ = -1;
+    return;
+  }
+
+  const auto &it = subs[this->state_subs_at_];
+  SubscribeHomeAssistantStateResponse resp;
+  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(""));
+
+  resp.once = it.once;
+  if (this->send_message(resp, SubscribeHomeAssistantStateResponse::MESSAGE_TYPE)) {
+    this->state_subs_at_++;
+  }
+}
+#endif  // USE_API_HOMEASSISTANT_STATES
+
 }  // namespace esphome::api
 #endif

esphome/components/api/api_connection.h

@@ -298,6 +298,10 @@ class APIConnection : public APIServerConnection {
   // Helper function to handle authentication completion
   void complete_authentication_();
 
+#ifdef USE_API_HOMEASSISTANT_STATES
+  void process_state_subscriptions_();
+#endif
+
   // Non-template helper to encode any ProtoMessage
   static uint16_t encode_message_to_buffer(ProtoMessage &msg, uint8_t message_type, APIConnection *conn,
                                            uint32_t remaining_size, bool is_single);

esphome/components/api/proto.h

@@ -35,11 +35,10 @@ namespace esphome::api {
  *
  * Unsafe Patterns (WILL cause crashes/corruption):
  * 1. Temporaries: msg.set_field(StringRef(obj.get_string())) // get_string() returns by value
- * 2. Optional values: msg.set_field(StringRef(optional.value())) // value() returns a copy
- * 3. Concatenation: msg.set_field(StringRef(str1 + str2)) // Result is temporary
+ * 2. Concatenation: msg.set_field(StringRef(str1 + str2)) // Result is temporary
  *
  * For unsafe patterns, store in a local variable first:
- *    std::string temp = optional.value();  // or get_string() or str1 + str2
+ *    std::string temp = get_string();  // or str1 + str2
  *    msg.set_field(StringRef(temp));
  *
  * The send_*_response pattern ensures proper lifetime management by encoding

tests/integration/fixtures/host_mode_many_entities.yaml

@@ -210,6 +210,15 @@ sensor:
     name: "Test Sensor 50"
     lambda: return 50.0;
     update_interval: 0.1s
+  # Temperature sensor for the thermostat
+  - platform: template
+    name: "Temperature Sensor"
+    id: temp_sensor
+    lambda: return 22.5;
+    unit_of_measurement: "°C"
+    device_class: temperature
+    state_class: measurement
+    update_interval: 5s
 
 # Mixed entity types for comprehensive batching test
 binary_sensor:
@@ -285,6 +294,50 @@ valve:
     stop_action:
       - logger.log: "Valve stopping"
 
+output:
+  - platform: template
+    id: heater_output
+    type: binary
+    write_action:
+      - logger.log: "Heater output changed"
+  - platform: template
+    id: cooler_output
+    type: binary
+    write_action:
+      - logger.log: "Cooler output changed"
+
+climate:
+  - platform: thermostat
+    name: "Test Thermostat"
+    sensor: temp_sensor
+    default_preset: Home
+    on_boot_restore_from: default_preset
+    min_heating_off_time: 1s
+    min_heating_run_time: 1s
+    min_cooling_off_time: 1s
+    min_cooling_run_time: 1s
+    min_idle_time: 1s
+    heat_action:
+      - output.turn_on: heater_output
+    cool_action:
+      - output.turn_on: cooler_output
+    idle_action:
+      - output.turn_off: heater_output
+      - output.turn_off: cooler_output
+    preset:
+      - name: Home
+        default_target_temperature_low: 20
+        default_target_temperature_high: 24
+        mode: heat_cool
+      - name: Away
+        default_target_temperature_low: 16
+        default_target_temperature_high: 26
+        mode: heat_cool
+      - name: Sleep
+        default_target_temperature_low: 18
+        default_target_temperature_high: 22
+        mode: heat_cool
+
 alarm_control_panel:
   - platform: template
     name: "Test Alarm"

tests/integration/test_host_mode_many_entities.py

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 import asyncio
 
-from aioesphomeapi import EntityState, SensorState
+from aioesphomeapi import ClimateInfo, EntityState, SensorState
 import pytest
 
 from .types import APIClientConnectedFactory, RunCompiledFunction
@@ -70,3 +70,22 @@ async def test_host_mode_many_entities(
         assert len(sensor_states) >= 50, (
             f"Expected at least 50 sensor states, got {len(sensor_states)}"
         )
+
+        # Get entity info to verify climate entity details
+        entities = await client.list_entities_services()
+        climate_infos = [e for e in entities[0] if isinstance(e, ClimateInfo)]
+        assert len(climate_infos) >= 1, "Expected at least 1 climate entity"
+
+        climate_info = climate_infos[0]
+        # Verify the thermostat has presets
+        assert len(climate_info.supported_presets) > 0, (
+            "Expected climate to have presets"
+        )
+        # The thermostat platform uses standard presets (Home, Away, Sleep)
+        # which should be transmitted properly without string copies
+
+        # Verify specific presets exist
+        preset_names = [p.name for p in climate_info.supported_presets]
+        assert "HOME" in preset_names, f"Expected 'HOME' preset, got {preset_names}"
+        assert "AWAY" in preset_names, f"Expected 'AWAY' preset, got {preset_names}"
+        assert "SLEEP" in preset_names, f"Expected 'SLEEP' preset, got {preset_names}"