fixed_vector, bluetooth services

esphome/components/api/api.proto

@@ -1519,7 +1519,7 @@ message BluetoothGATTCharacteristic {
   repeated uint64 uuid = 1 [(fixed_array_size) = 2, (fixed_array_skip_zero) = true];
   uint32 handle = 2;
   uint32 properties = 3;
-  repeated BluetoothGATTDescriptor descriptors = 4;
+  repeated BluetoothGATTDescriptor descriptors = 4 [(fixed_vector) = true];
 
   // New field for efficient UUID (v1.12+)
   // Only one of uuid or short_uuid will be set.
@@ -1531,7 +1531,7 @@ message BluetoothGATTCharacteristic {
 message BluetoothGATTService {
   repeated uint64 uuid = 1 [(fixed_array_size) = 2, (fixed_array_skip_zero) = true];
   uint32 handle = 2;
-  repeated BluetoothGATTCharacteristic characteristics = 3;
+  repeated BluetoothGATTCharacteristic characteristics = 3 [(fixed_vector) = true];
 
   // New field for efficient UUID (v1.12+)
   // Only one of uuid or short_uuid will be set.

esphome/components/api/api_options.proto

@@ -64,4 +64,10 @@ extend google.protobuf.FieldOptions {
     // This is typically done through methods returning const T& or special accessor
     // methods like get_options() or supported_modes_for_api_().
     optional string container_pointer = 50001;
+
+    // fixed_vector: Use FixedVector instead of std::vector for repeated fields
+    // When set, the repeated field will use FixedVector<T> which requires calling
+    // init(size) before adding elements. This eliminates std::vector template overhead
+    // and is ideal when the exact size is known before populating the array.
+    optional bool fixed_vector = 50013 [default=false];
 }

esphome/components/api/api_pb2.h

@@ -1923,7 +1923,7 @@ class BluetoothGATTCharacteristic final : public ProtoMessage {
   std::array<uint64_t, 2> uuid{};
   uint32_t handle{0};
   uint32_t properties{0};
-  std::vector<BluetoothGATTDescriptor> descriptors{};
+  FixedVector<BluetoothGATTDescriptor> descriptors{};
   uint32_t short_uuid{0};
   void encode(ProtoWriteBuffer buffer) const override;
   void calculate_size(ProtoSize &size) const override;
@@ -1937,7 +1937,7 @@ class BluetoothGATTService final : public ProtoMessage {
  public:
   std::array<uint64_t, 2> uuid{};
   uint32_t handle{0};
-  std::vector<BluetoothGATTCharacteristic> characteristics{};
+  FixedVector<BluetoothGATTCharacteristic> characteristics{};
   uint32_t short_uuid{0};
   void encode(ProtoWriteBuffer buffer) const override;
   void calculate_size(ProtoSize &size) const override;

esphome/components/api/proto.h

@@ -749,13 +749,29 @@ class ProtoSize {
   template<typename MessageType>
   inline void add_repeated_message(uint32_t field_id_size, const std::vector<MessageType> &messages) {
     // Skip if the vector is empty
-    if (messages.empty()) {
+    if (!messages.empty()) {
-      return;
+      // Use the force version for all messages in the repeated field
+      for (const auto &message : messages) {
+        add_message_object_force(field_id_size, message);
+      }
     }
+  }
 
-    // Use the force version for all messages in the repeated field
+  /**
-    for (const auto &message : messages) {
+   * @brief Calculates and adds the sizes of all messages in a repeated field to the total message size (FixedVector
-      add_message_object_force(field_id_size, message);
+   * version)
+   *
+   * @tparam MessageType The type of the nested messages in the FixedVector
+   * @param messages FixedVector of message objects
+   */
+  template<typename MessageType>
+  inline void add_repeated_message(uint32_t field_id_size, const FixedVector<MessageType> &messages) {
+    // Skip if the fixed vector is empty
+    if (!messages.empty()) {
+      // Use the force version for all messages in the repeated field
+      for (const auto &message : messages) {
+        add_message_object_force(field_id_size, message);
+      }
     }
   }
 };

esphome/components/bluetooth_proxy/bluetooth_connection.cpp

@@ -230,8 +230,8 @@ void BluetoothConnection::send_service_for_discovery_() {
     service_resp.handle = service_result.start_handle;
 
     if (total_char_count > 0) {
-      // Reserve space and process characteristics
+      // Initialize FixedVector with exact count and process characteristics
-      service_resp.characteristics.reserve(total_char_count);
+      service_resp.characteristics.init(total_char_count);
       uint16_t char_offset = 0;
       esp_gattc_char_elem_t char_result;
       while (true) {  // characteristics
@@ -275,8 +275,8 @@ void BluetoothConnection::send_service_for_discovery_() {
           continue;
         }
 
-        // Reserve space and process descriptors
+        // Initialize FixedVector with exact count and process descriptors
-        characteristic_resp.descriptors.reserve(total_desc_count);
+        characteristic_resp.descriptors.init(total_desc_count);
         uint16_t desc_offset = 0;
         esp_gattc_descr_elem_t desc_result;
         while (true) {  // descriptors

esphome/core/helpers.h

@@ -181,6 +181,31 @@ template<typename T> class FixedVector {
   FixedVector(const FixedVector &) = delete;
   FixedVector &operator=(const FixedVector &) = delete;
 
+  // Enable move semantics for use in containers
+  FixedVector(FixedVector &&other) noexcept : data_(other.data_), size_(other.size_), capacity_(other.capacity_) {
+    other.data_ = nullptr;
+    other.size_ = 0;
+    other.capacity_ = 0;
+  }
+
+  FixedVector &operator=(FixedVector &&other) noexcept {
+    if (this != &other) {
+      // Delete our current data
+      if (data_ != nullptr) {
+        delete[] data_;
+      }
+      // Take ownership of other's data
+      data_ = other.data_;
+      size_ = other.size_;
+      capacity_ = other.capacity_;
+      // Leave other in valid empty state
+      other.data_ = nullptr;
+      other.size_ = 0;
+      other.capacity_ = 0;
+    }
+    return *this;
+  }
+
   // Allocate capacity - can only be called once on empty vector
   void init(size_t n) {
     if (data_ == nullptr && n > 0) {
@@ -199,12 +224,33 @@ template<typename T> class FixedVector {
     }
   }
 
+  /// Construct element in place and return reference
+  /// Caller must ensure sufficient capacity was allocated via init()
+  T &emplace_back() {
+    if (size_ < capacity_) {
+      return data_[size_++];
+    }
+    // Should never happen with proper init() - return last element to avoid crash
+    return data_[capacity_ - 1];
+  }
+
+  /// Access last element
+  T &back() { return data_[size_ - 1]; }
+  const T &back() const { return data_[size_ - 1]; }
+
   size_t size() const { return size_; }
+  bool empty() const { return size_ == 0; }
 
   /// Access element without bounds checking (matches std::vector behavior)
   /// Caller must ensure index is valid (i < size())
   T &operator[](size_t i) { return data_[i]; }
   const T &operator[](size_t i) const { return data_[i]; }
+
+  /// Iterators for range-based for loops
+  T *begin() { return data_; }
+  T *end() { return data_ + size_; }
+  const T *begin() const { return data_; }
+  const T *end() const { return data_ + size_; }
 };
 
 ///@}

script/api_protobuf/api_protobuf.py

@@ -1415,6 +1415,8 @@ class RepeatedTypeInfo(TypeInfo):
         # Check if this is a pointer field by looking for container_pointer option
         self._container_type = get_field_opt(field, pb.container_pointer, "")
         self._use_pointer = bool(self._container_type)
+        # Check if this should use FixedVector instead of std::vector
+        self._use_fixed_vector = get_field_opt(field, pb.fixed_vector, False)
 
         # For repeated fields, we need to get the base type info
         # but we can't call create_field_type_info as it would cause recursion
@@ -1438,6 +1440,8 @@ class RepeatedTypeInfo(TypeInfo):
             if "<" in self._container_type and ">" in self._container_type:
                 return f"const {self._container_type}*"
             return f"const {self._container_type}<{self._ti.cpp_type}>*"
+        if self._use_fixed_vector:
+            return f"FixedVector<{self._ti.cpp_type}>"
         return f"std::vector<{self._ti.cpp_type}>"
 
     @property