From 93b28447ee3532313e7f6dc29a1ef2c4dc7e1ed0 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 4 Aug 2025 15:13:55 -1000
Subject: [PATCH] [bluetooth_proxy] Optimize memory usage with fixed-size array
 and const string references (#10015)

---
 .../bluetooth_proxy/bluetooth_proxy.cpp           | 15 +++++++++------
 .../components/bluetooth_proxy/bluetooth_proxy.h  | 14 +++++++++-----
 .../components/esp32_ble_client/ble_client_base.h |  2 +-
 3 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/esphome/components/bluetooth_proxy/bluetooth_proxy.cpp b/esphome/components/bluetooth_proxy/bluetooth_proxy.cpp
index a59a33117a..97b0884dda 100644
--- a/esphome/components/bluetooth_proxy/bluetooth_proxy.cpp
+++ b/esphome/components/bluetooth_proxy/bluetooth_proxy.cpp
@@ -35,8 +35,8 @@ void BluetoothProxy::setup() {
   // Don't pre-allocate pool - let it grow only if needed in busy environments
   // Many devices in quiet areas will never need the overflow pool
 
-  this->connections_free_response_.limit = this->connections_.size();
-  this->connections_free_response_.free = this->connections_.size();
+  this->connections_free_response_.limit = BLUETOOTH_PROXY_MAX_CONNECTIONS;
+  this->connections_free_response_.free = BLUETOOTH_PROXY_MAX_CONNECTIONS;
 
   this->parent_->add_scanner_state_callback([this](esp32_ble_tracker::ScannerState state) {
     if (this->api_connection_ != nullptr) {
@@ -134,12 +134,13 @@ void BluetoothProxy::dump_config() {
   ESP_LOGCONFIG(TAG,
                 "  Active: %s\n"
                 "  Connections: %d",
-                YESNO(this->active_), this->connections_.size());
+                YESNO(this->active_), this->connection_count_);
 }
 
 void BluetoothProxy::loop() {
   if (!api::global_api_server->is_connected() || this->api_connection_ == nullptr) {
-    for (auto *connection : this->connections_) {
+    for (uint8_t i = 0; i < this->connection_count_; i++) {
+      auto *connection = this->connections_[i];
       if (connection->get_address() != 0 && !connection->disconnect_pending()) {
         connection->disconnect();
       }
@@ -162,7 +163,8 @@ esp32_ble_tracker::AdvertisementParserType BluetoothProxy::get_advertisement_par
 }
 
 BluetoothConnection *BluetoothProxy::get_connection_(uint64_t address, bool reserve) {
-  for (auto *connection : this->connections_) {
+  for (uint8_t i = 0; i < this->connection_count_; i++) {
+    auto *connection = this->connections_[i];
     if (connection->get_address() == address)
       return connection;
   }
@@ -170,7 +172,8 @@ BluetoothConnection *BluetoothProxy::get_connection_(uint64_t address, bool rese
   if (!reserve)
     return nullptr;
 
-  for (auto *connection : this->connections_) {
+  for (uint8_t i = 0; i < this->connection_count_; i++) {
+    auto *connection = this->connections_[i];
     if (connection->get_address() == 0) {
       connection->send_service_ = DONE_SENDING_SERVICES;
       connection->set_address(address);
diff --git a/esphome/components/bluetooth_proxy/bluetooth_proxy.h b/esphome/components/bluetooth_proxy/bluetooth_proxy.h
index 70deef1ebd..d367dad438 100644
--- a/esphome/components/bluetooth_proxy/bluetooth_proxy.h
+++ b/esphome/components/bluetooth_proxy/bluetooth_proxy.h
@@ -2,6 +2,7 @@
 
 #ifdef USE_ESP32
 
+#include <array>
 #include <map>
 #include <vector>
 
@@ -63,8 +64,10 @@ class BluetoothProxy : public esp32_ble_tracker::ESPBTDeviceListener, public Com
   esp32_ble_tracker::AdvertisementParserType get_advertisement_parser_type() override;
 
   void register_connection(BluetoothConnection *connection) {
-    this->connections_.push_back(connection);
-    connection->proxy_ = this;
+    if (this->connection_count_ < BLUETOOTH_PROXY_MAX_CONNECTIONS) {
+      this->connections_[this->connection_count_++] = connection;
+      connection->proxy_ = this;
+    }
   }
 
   void bluetooth_device_request(const api::BluetoothDeviceRequest &msg);
@@ -138,8 +141,8 @@ class BluetoothProxy : public esp32_ble_tracker::ESPBTDeviceListener, public Com
   // Group 1: Pointers (4 bytes each, naturally aligned)
   api::APIConnection *api_connection_{nullptr};
 
-  // Group 2: Container types (typically 12 bytes on 32-bit)
-  std::vector<BluetoothConnection *> connections_{};
+  // Group 2: Fixed-size array of connection pointers
+  std::array<BluetoothConnection *, BLUETOOTH_PROXY_MAX_CONNECTIONS> connections_{};
 
   // BLE advertisement batching
   std::vector<api::BluetoothLERawAdvertisement> advertisement_pool_;
@@ -154,7 +157,8 @@ class BluetoothProxy : public esp32_ble_tracker::ESPBTDeviceListener, public Com
   // Group 4: 1-byte types grouped together
   bool active_;
   uint8_t advertisement_count_{0};
-  // 2 bytes used, 2 bytes padding
+  uint8_t connection_count_{0};
+  // 3 bytes used, 1 byte padding
 };
 
 extern BluetoothProxy *global_bluetooth_proxy;  // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
diff --git a/esphome/components/esp32_ble_client/ble_client_base.h b/esphome/components/esp32_ble_client/ble_client_base.h
index b30e9cd444..93260b1c15 100644
--- a/esphome/components/esp32_ble_client/ble_client_base.h
+++ b/esphome/components/esp32_ble_client/ble_client_base.h
@@ -66,7 +66,7 @@ class BLEClientBase : public espbt::ESPBTClient, public Component {
                        (uint8_t) (this->address_ >> 0) & 0xff);
     }
   }
-  std::string address_str() const { return this->address_str_; }
+  const std::string &address_str() const { return this->address_str_; }
 
   BLEService *get_service(espbt::ESPBTUUID uuid);
   BLEService *get_service(uint16_t uuid);