From c0c0a423626b66abc5e35dbe6c02e116c566328d Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Sun, 3 Aug 2025 16:37:47 -1000
Subject: [PATCH] [api] Use static allocation for areas and devices in
 DeviceInfoResponse (#10038)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>
---
 esphome/components/api/api.proto          |  4 ++--
 esphome/components/api/api_connection.cpp | 12 ++++++++----
 esphome/components/api/api_pb2.cpp        | 12 ++++++++----
 esphome/components/api/api_pb2.h          |  6 +++---
 4 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/esphome/components/api/api.proto b/esphome/components/api/api.proto
index e0b2c19a21..67e91cc8e3 100644
--- a/esphome/components/api/api.proto
+++ b/esphome/components/api/api.proto
@@ -250,8 +250,8 @@ message DeviceInfoResponse {
   // Supports receiving and saving api encryption key
   bool api_encryption_supported = 19 [(field_ifdef) = "USE_API_NOISE"];
 
-  repeated DeviceInfo devices = 20 [(field_ifdef) = "USE_DEVICES"];
-  repeated AreaInfo areas = 21 [(field_ifdef) = "USE_AREAS"];
+  repeated DeviceInfo devices = 20 [(field_ifdef) = "USE_DEVICES", (fixed_array_size_define) = "ESPHOME_DEVICE_COUNT"];
+  repeated AreaInfo areas = 21 [(field_ifdef) = "USE_AREAS", (fixed_array_size_define) = "ESPHOME_AREA_COUNT"];
 
   // Top-level area info to phase out suggested_area
   AreaInfo area = 22 [(field_ifdef) = "USE_AREAS"];
diff --git a/esphome/components/api/api_connection.cpp b/esphome/components/api/api_connection.cpp
index 5fff270c99..cdeabb5cac 100644
--- a/esphome/components/api/api_connection.cpp
+++ b/esphome/components/api/api_connection.cpp
@@ -1462,18 +1462,22 @@ bool APIConnection::send_device_info_response(const DeviceInfoRequest &msg) {
   resp.api_encryption_supported = true;
 #endif
 #ifdef USE_DEVICES
+  size_t device_index = 0;
   for (auto const &device : App.get_devices()) {
-    resp.devices.emplace_back();
-    auto &device_info = resp.devices.back();
+    if (device_index >= ESPHOME_DEVICE_COUNT)
+      break;
+    auto &device_info = resp.devices[device_index++];
     device_info.device_id = device->get_device_id();
     device_info.set_name(StringRef(device->get_name()));
     device_info.area_id = device->get_area_id();
   }
 #endif
 #ifdef USE_AREAS
+  size_t area_index = 0;
   for (auto const &area : App.get_areas()) {
-    resp.areas.emplace_back();
-    auto &area_info = resp.areas.back();
+    if (area_index >= ESPHOME_AREA_COUNT)
+      break;
+    auto &area_info = resp.areas[area_index++];
     area_info.area_id = area->get_area_id();
     area_info.set_name(StringRef(area->get_name()));
   }
diff --git a/esphome/components/api/api_pb2.cpp b/esphome/components/api/api_pb2.cpp
index 8c14153155..5dddc79b49 100644
--- a/esphome/components/api/api_pb2.cpp
+++ b/esphome/components/api/api_pb2.cpp
@@ -115,12 +115,12 @@ void DeviceInfoResponse::encode(ProtoWriteBuffer buffer) const {
   buffer.encode_bool(19, this->api_encryption_supported);
 #endif
 #ifdef USE_DEVICES
-  for (auto &it : this->devices) {
+  for (const auto &it : this->devices) {
     buffer.encode_message(20, it, true);
   }
 #endif
 #ifdef USE_AREAS
-  for (auto &it : this->areas) {
+  for (const auto &it : this->areas) {
     buffer.encode_message(21, it, true);
   }
 #endif
@@ -167,10 +167,14 @@ void DeviceInfoResponse::calculate_size(ProtoSize &size) const {
   size.add_bool(2, this->api_encryption_supported);
 #endif
 #ifdef USE_DEVICES
-  size.add_repeated_message(2, this->devices);
+  for (const auto &it : this->devices) {
+    size.add_message_object_force(2, it);
+  }
 #endif
 #ifdef USE_AREAS
-  size.add_repeated_message(2, this->areas);
+  for (const auto &it : this->areas) {
+    size.add_message_object_force(2, it);
+  }
 #endif
 #ifdef USE_AREAS
   size.add_message_object(2, this->area);
diff --git a/esphome/components/api/api_pb2.h b/esphome/components/api/api_pb2.h
index 0bc75ef00b..d43d3c61b7 100644
--- a/esphome/components/api/api_pb2.h
+++ b/esphome/components/api/api_pb2.h
@@ -490,7 +490,7 @@ class DeviceInfo : public ProtoMessage {
 class DeviceInfoResponse : public ProtoMessage {
  public:
   static constexpr uint8_t MESSAGE_TYPE = 10;
-  static constexpr uint8_t ESTIMATED_SIZE = 211;
+  static constexpr uint8_t ESTIMATED_SIZE = 247;
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *message_name() const override { return "device_info_response"; }
 #endif
@@ -543,10 +543,10 @@ class DeviceInfoResponse : public ProtoMessage {
   bool api_encryption_supported{false};
 #endif
 #ifdef USE_DEVICES
-  std::vector<DeviceInfo> devices{};
+  std::array<DeviceInfo, ESPHOME_DEVICE_COUNT> devices{};
 #endif
 #ifdef USE_AREAS
-  std::vector<AreaInfo> areas{};
+  std::array<AreaInfo, ESPHOME_AREA_COUNT> areas{};
 #endif
 #ifdef USE_AREAS
   AreaInfo area{};