[api] Add zero-copy support for Home Assistant state response messages (#12585)

esphome/components/api/api.proto

@@ -824,9 +824,9 @@ message HomeAssistantStateResponse {
   option (no_delay) = true;
   option (ifdef) = "USE_API_HOMEASSISTANT_STATES";
 
-  string entity_id = 1;
-  string state = 2;
-  string attribute = 3;
+  string entity_id = 1 [(pointer_to_buffer) = true];
+  string state = 2 [(pointer_to_buffer) = true];
+  string attribute = 3 [(pointer_to_buffer) = true];
 }
 
 // ==================== IMPORT TIME ====================

esphome/components/api/api_connection.cpp

@@ -1582,15 +1582,29 @@ 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()) {
-    // 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());
+  // Skip if entity_id is empty (invalid message)
+  if (msg.entity_id_len == 0) {
+    return;
+  }
 
-    if (entity_match && attribute_match) {
-      it.callback(msg.state);
+  for (auto &it : this->parent_->get_state_subs()) {
+    // Compare entity_id: check length matches and content matches
+    size_t entity_id_len = strlen(it.entity_id);
+    if (entity_id_len != msg.entity_id_len || memcmp(it.entity_id, msg.entity_id, msg.entity_id_len) != 0) {
+      continue;
     }
+
+    // Compare attribute: either both have matching attribute, or both have none
+    size_t sub_attr_len = it.attribute != nullptr ? strlen(it.attribute) : 0;
+    if (sub_attr_len != msg.attribute_len ||
+        (sub_attr_len > 0 && memcmp(it.attribute, msg.attribute, sub_attr_len) != 0)) {
+      continue;
+    }
+
+    // Create temporary string for callback (callback takes const std::string &)
+    // Handle empty state (nullptr with len=0)
+    std::string state(msg.state_len > 0 ? reinterpret_cast<const char *>(msg.state) : "", msg.state_len);
+    it.callback(state);
   }
 }
 #endif

esphome/components/api/api_pb2.cpp

@@ -966,15 +966,24 @@ void SubscribeHomeAssistantStateResponse::calculate_size(ProtoSize &size) const
 }
 bool HomeAssistantStateResponse::decode_length(uint32_t field_id, ProtoLengthDelimited value) {
   switch (field_id) {
-    case 1:
-      this->entity_id = value.as_string();
+    case 1: {
+      // Use raw data directly to avoid allocation
+      this->entity_id = value.data();
+      this->entity_id_len = value.size();
       break;
-    case 2:
-      this->state = value.as_string();
+    }
+    case 2: {
+      // Use raw data directly to avoid allocation
+      this->state = value.data();
+      this->state_len = value.size();
       break;
-    case 3:
-      this->attribute = value.as_string();
+    }
+    case 3: {
+      // Use raw data directly to avoid allocation
+      this->attribute = value.data();
+      this->attribute_len = value.size();
       break;
+    }
     default:
       return false;
   }

esphome/components/api/api_pb2.h

@@ -1203,13 +1203,16 @@ class SubscribeHomeAssistantStateResponse final : public ProtoMessage {
 class HomeAssistantStateResponse final : public ProtoDecodableMessage {
  public:
   static constexpr uint8_t MESSAGE_TYPE = 40;
-  static constexpr uint8_t ESTIMATED_SIZE = 27;
+  static constexpr uint8_t ESTIMATED_SIZE = 57;
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *message_name() const override { return "home_assistant_state_response"; }
 #endif
-  std::string entity_id{};
-  std::string state{};
-  std::string attribute{};
+  const uint8_t *entity_id{nullptr};
+  uint16_t entity_id_len{0};
+  const uint8_t *state{nullptr};
+  uint16_t state_len{0};
+  const uint8_t *attribute{nullptr};
+  uint16_t attribute_len{0};
 #ifdef HAS_PROTO_MESSAGE_DUMP
   void dump_to(std::string &out) const override;
 #endif

esphome/components/api/api_pb2_dump.cpp

@@ -1184,9 +1184,15 @@ void SubscribeHomeAssistantStateResponse::dump_to(std::string &out) const {
 }
 void HomeAssistantStateResponse::dump_to(std::string &out) const {
   MessageDumpHelper helper(out, "HomeAssistantStateResponse");
-  dump_field(out, "entity_id", this->entity_id);
-  dump_field(out, "state", this->state);
-  dump_field(out, "attribute", this->attribute);
+  out.append("  entity_id: ");
+  out.append(format_hex_pretty(this->entity_id, this->entity_id_len));
+  out.append("\n");
+  out.append("  state: ");
+  out.append(format_hex_pretty(this->state, this->state_len));
+  out.append("\n");
+  out.append("  attribute: ");
+  out.append(format_hex_pretty(this->attribute, this->attribute_len));
+  out.append("\n");
 }
 #endif
 void GetTimeRequest::dump_to(std::string &out) const { out.append("GetTimeRequest {}"); }

tests/integration/test_api_homeassistant.py

@@ -179,6 +179,12 @@ async def test_api_homeassistant(
         client.send_home_assistant_state("binary_sensor.external_motion", "", "ON")
         client.send_home_assistant_state("weather.home", "condition", "sunny")
 
+        # Test edge cases for zero-copy implementation safety
+        # Empty entity_id should be silently ignored (no crash)
+        client.send_home_assistant_state("", "", "should_be_ignored")
+        # Empty state with valid entity should work (use different entity to not interfere with test)
+        client.send_home_assistant_state("sensor.edge_case_empty_state", "", "")
+
         # List entities and services
         _, services = await client.list_entities_services()