[fan] Add zero-copy support for API preset mode commands (#12404)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

esphome/components/api/api.proto

@@ -477,7 +477,7 @@ message FanCommandRequest {
   bool has_speed_level = 10;
   int32 speed_level = 11;
   bool has_preset_mode = 12;
-  string preset_mode = 13;
+  string preset_mode = 13 [(pointer_to_buffer) = true];
   uint32 device_id = 14 [(field_ifdef) = "USE_DEVICES"];
 }
 

esphome/components/api/api_connection.cpp

@@ -447,7 +447,7 @@ void APIConnection::fan_command(const FanCommandRequest &msg) {
   if (msg.has_direction)
     call.set_direction(static_cast<fan::FanDirection>(msg.direction));
   if (msg.has_preset_mode)
-    call.set_preset_mode(msg.preset_mode);
+    call.set_preset_mode(reinterpret_cast<const char *>(msg.preset_mode), msg.preset_mode_len);
   call.perform();
 }
 #endif

esphome/components/api/api_pb2.cpp

@@ -447,9 +447,12 @@ bool FanCommandRequest::decode_varint(uint32_t field_id, ProtoVarInt value) {
 }
 bool FanCommandRequest::decode_length(uint32_t field_id, ProtoLengthDelimited value) {
   switch (field_id) {
-    case 13:
-      this->preset_mode = value.as_string();
+    case 13: {
+      // Use raw data directly to avoid allocation
+      this->preset_mode = value.data();
+      this->preset_mode_len = value.size();
       break;
+    }
     default:
       return false;
   }

esphome/components/api/api_pb2.h

@@ -765,7 +765,7 @@ class FanStateResponse final : public StateResponseProtoMessage {
 class FanCommandRequest final : public CommandProtoMessage {
  public:
   static constexpr uint8_t MESSAGE_TYPE = 31;
-  static constexpr uint8_t ESTIMATED_SIZE = 38;
+  static constexpr uint8_t ESTIMATED_SIZE = 48;
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *message_name() const override { return "fan_command_request"; }
 #endif
@@ -778,7 +778,8 @@ class FanCommandRequest final : public CommandProtoMessage {
   bool has_speed_level{false};
   int32_t speed_level{0};
   bool has_preset_mode{false};
-  std::string preset_mode{};
+  const uint8_t *preset_mode{nullptr};
+  uint16_t preset_mode_len{0};
 #ifdef HAS_PROTO_MESSAGE_DUMP
   void dump_to(std::string &out) const override;
 #endif

esphome/components/api/api_pb2_dump.cpp

@@ -923,7 +923,9 @@ void FanCommandRequest::dump_to(std::string &out) const {
   dump_field(out, "has_speed_level", this->has_speed_level);
   dump_field(out, "speed_level", this->speed_level);
   dump_field(out, "has_preset_mode", this->has_preset_mode);
-  dump_field(out, "preset_mode", this->preset_mode);
+  out.append("  preset_mode: ");
+  out.append(format_hex_pretty(this->preset_mode, this->preset_mode_len));
+  out.append("\n");
 #ifdef USE_DEVICES
   dump_field(out, "device_id", this->device_id);
 #endif

esphome/components/fan/fan.cpp

@@ -19,22 +19,28 @@ const LogString *fan_direction_to_string(FanDirection direction) {
   }
 }
 
-FanCall &FanCall::set_preset_mode(const std::string &preset_mode) { return this->set_preset_mode(preset_mode.c_str()); }
+FanCall &FanCall::set_preset_mode(const std::string &preset_mode) {
+  return this->set_preset_mode(preset_mode.data(), preset_mode.size());
+}
 
 FanCall &FanCall::set_preset_mode(const char *preset_mode) {
-  if (preset_mode == nullptr || strlen(preset_mode) == 0) {
+  return this->set_preset_mode(preset_mode, preset_mode ? strlen(preset_mode) : 0);
+}
+
+FanCall &FanCall::set_preset_mode(const char *preset_mode, size_t len) {
+  if (preset_mode == nullptr || len == 0) {
     this->preset_mode_ = nullptr;
     return *this;
   }
 
   // Find and validate pointer from traits immediately
   auto traits = this->parent_.get_traits();
-  const char *validated_mode = traits.find_preset_mode(preset_mode);
+  const char *validated_mode = traits.find_preset_mode(preset_mode, len);
   if (validated_mode != nullptr) {
     this->preset_mode_ = validated_mode;  // Store pointer from traits
   } else {
     // Preset mode not found in traits - log warning and don't set
-    ESP_LOGW(TAG, "%s: Preset mode '%s' not supported", this->parent_.get_name().c_str(), preset_mode);
+    ESP_LOGW(TAG, "%s: Preset mode '%.*s' not supported", this->parent_.get_name().c_str(), (int) len, preset_mode);
     this->preset_mode_ = nullptr;
   }
   return *this;
@@ -140,7 +146,13 @@ FanCall Fan::turn_off() { return this->make_call().set_state(false); }
 FanCall Fan::toggle() { return this->make_call().set_state(!this->state); }
 FanCall Fan::make_call() { return FanCall(*this); }
 
-const char *Fan::find_preset_mode_(const char *preset_mode) { return this->get_traits().find_preset_mode(preset_mode); }
+const char *Fan::find_preset_mode_(const char *preset_mode) {
+  return this->find_preset_mode_(preset_mode, preset_mode ? strlen(preset_mode) : 0);
+}
+
+const char *Fan::find_preset_mode_(const char *preset_mode, size_t len) {
+  return this->get_traits().find_preset_mode(preset_mode, len);
+}
 
 bool Fan::set_preset_mode_(const char *preset_mode) {
   if (preset_mode == nullptr) {

esphome/components/fan/fan.h

@@ -72,6 +72,7 @@ class FanCall {
   optional<FanDirection> get_direction() const { return this->direction_; }
   FanCall &set_preset_mode(const std::string &preset_mode);
   FanCall &set_preset_mode(const char *preset_mode);
+  FanCall &set_preset_mode(const char *preset_mode, size_t len);
   const char *get_preset_mode() const { return this->preset_mode_; }
   bool has_preset_mode() const { return this->preset_mode_ != nullptr; }
 
@@ -152,6 +153,7 @@ class Fan : public EntityBase {
   void clear_preset_mode_();
   /// Find and return the matching preset mode pointer from traits, or nullptr if not found.
   const char *find_preset_mode_(const char *preset_mode);
+  const char *find_preset_mode_(const char *preset_mode, size_t len);
 
   CallbackManager<void()> state_callback_{};
   ESPPreferenceObject rtc_;

esphome/components/fan/fan_traits.h

@@ -47,10 +47,13 @@ class FanTraits {
   bool supports_preset_modes() const { return !this->preset_modes_.empty(); }
   /// Find and return the matching preset mode pointer from supported modes, or nullptr if not found.
   const char *find_preset_mode(const char *preset_mode) const {
-    if (preset_mode == nullptr)
+    return this->find_preset_mode(preset_mode, preset_mode ? strlen(preset_mode) : 0);
+  }
+  const char *find_preset_mode(const char *preset_mode, size_t len) const {
+    if (preset_mode == nullptr || len == 0)
       return nullptr;
     for (const char *mode : this->preset_modes_) {
-      if (strcmp(mode, preset_mode) == 0) {
+      if (strncmp(mode, preset_mode, len) == 0 && mode[len] == '\0') {
         return mode;  // Return pointer from traits
       }
     }