Merge branch 'dev' into 20260210-serial-proxy

CODEOWNERS

@@ -429,6 +429,7 @@ esphome/components/sen21231/* @shreyaskarnik
 esphome/components/sen5x/* @martgras
 esphome/components/sensirion_common/* @martgras
 esphome/components/sensor/* @esphome/core
+esphome/components/serial_proxy/* @kbx81
 esphome/components/sfa30/* @ghsensdev
 esphome/components/sgp40/* @SenexCrenshaw
 esphome/components/sgp4x/* @martgras @SenexCrenshaw

esphome/automation.py

@@ -57,14 +57,8 @@ def maybe_conf(conf, *validators):
     return validate
 
 
-def register_action(
-    name: str,
-    action_type: MockObjClass,
-    schema: cv.Schema,
-    *,
-    deferred: bool = False,
-):
-    return ACTION_REGISTRY.register(name, action_type, schema, deferred=deferred)
+def register_action(name: str, action_type: MockObjClass, schema: cv.Schema):
+    return ACTION_REGISTRY.register(name, action_type, schema)
 
 
 def register_condition(name: str, condition_type: MockObjClass, schema: cv.Schema):
@@ -341,10 +335,7 @@ async def component_is_idle_condition_to_code(
 
 
 @register_action(
-    "delay",
-    DelayAction,
-    cv.templatable(cv.positive_time_period_milliseconds),
-    deferred=True,
+    "delay", DelayAction, cv.templatable(cv.positive_time_period_milliseconds)
 )
 async def delay_action_to_code(
     config: ConfigType,
@@ -454,7 +445,7 @@ _validate_wait_until = cv.maybe_simple_value(
 )
 
 
-@register_action("wait_until", WaitUntilAction, _validate_wait_until, deferred=True)
+@register_action("wait_until", WaitUntilAction, _validate_wait_until)
 async def wait_until_action_to_code(
     config: ConfigType,
     action_id: ID,
@@ -587,26 +578,6 @@ async def build_condition_list(
     return conditions
 
 
-def has_deferred_actions(actions: ConfigType) -> bool:
-    """Check if a validated action list contains any deferred actions.
-
-    Deferred actions (delay, wait_until, script.wait) store trigger args
-    for later execution, making non-owning types like StringRef unsafe.
-    """
-    if isinstance(actions, list):
-        return any(has_deferred_actions(item) for item in actions)
-    if isinstance(actions, dict):
-        for key in actions:
-            if key in ACTION_REGISTRY and ACTION_REGISTRY[key].deferred:
-                return True
-        return any(
-            has_deferred_actions(v)
-            for v in actions.values()
-            if isinstance(v, (list, dict))
-        )
-    return False
-
-
 async def build_automation(
     trigger: MockObj, args: TemplateArgsType, config: ConfigType
 ) -> MockObj:

esphome/components/api/__init__.py

@@ -76,7 +76,7 @@ SERVICE_ARG_NATIVE_TYPES: dict[str, MockObj] = {
     "bool": cg.bool_,
     "int": cg.int32,
     "float": cg.float_,
-    "string": cg.StringRef,
+    "string": cg.std_string,
     "bool[]": cg.FixedVector.template(cg.bool_).operator("const").operator("ref"),
     "int[]": cg.FixedVector.template(cg.int32).operator("const").operator("ref"),
     "float[]": cg.FixedVector.template(cg.float_).operator("const").operator("ref"),
@@ -380,16 +380,9 @@ async def to_code(config: ConfigType) -> None:
                 if is_optional:
                     func_args.append((cg.bool_, "return_response"))
 
-            # Check if action chain has deferred actions that would make
-            # non-owning StringRef dangle (rx_buf_ reused after delay)
-            has_deferred = automation.has_deferred_actions(conf.get(CONF_THEN, []))
-
             service_arg_names: list[str] = []
             for name, var_ in conf[CONF_VARIABLES].items():
                 native = SERVICE_ARG_NATIVE_TYPES[var_]
-                # Fall back to std::string for string args if deferred actions exist
-                if has_deferred and native is cg.StringRef:
-                    native = cg.std_string
                 service_template_args.append(native)
                 func_args.append((native, name))
                 service_arg_names.append(name)

esphome/components/api/api.proto

@@ -69,6 +69,12 @@ service APIConnection {
   rpc zwave_proxy_request(ZWaveProxyRequest) returns (void) {}
 
   rpc infrared_rf_transmit_raw_timings(InfraredRFTransmitRawTimingsRequest) returns (void) {}
+
+  rpc serial_proxy_configure(SerialProxyConfigureRequest) returns (void) {}
+  rpc serial_proxy_write(SerialProxyWriteRequest) returns (void) {}
+  rpc serial_proxy_set_modem_pins(SerialProxySetModemPinsRequest) returns (void) {}
+  rpc serial_proxy_get_modem_pins(SerialProxyGetModemPinsRequest) returns (void) {}
+  rpc serial_proxy_request(SerialProxyRequest) returns (void) {}
 }
 
 
@@ -198,6 +204,17 @@ message DeviceInfo {
   uint32 area_id = 3;
 }
 
+enum SerialProxyPortType {
+  SERIAL_PROXY_PORT_TYPE_TTL = 0;
+  SERIAL_PROXY_PORT_TYPE_RS232 = 1;
+  SERIAL_PROXY_PORT_TYPE_RS485 = 2;
+}
+
+message SerialProxyInfo {
+  string name = 1;                    // Human-readable port name
+  SerialProxyPortType port_type = 2;  // Port type (RS232, RS485)
+}
+
 message DeviceInfoResponse {
   option (id) = 10;
   option (source) = SOURCE_SERVER;
@@ -260,6 +277,9 @@ message DeviceInfoResponse {
   // Indicates if Z-Wave proxy support is available and features supported
   uint32 zwave_proxy_feature_flags = 23 [(field_ifdef) = "USE_ZWAVE_PROXY"];
   uint32 zwave_home_id = 24 [(field_ifdef) = "USE_ZWAVE_PROXY"];
+
+  // Serial proxy instance metadata
+  repeated SerialProxyInfo serial_proxies = 25 [(field_ifdef) = "USE_SERIAL_PROXY", (fixed_array_size_define) = "SERIAL_PROXY_COUNT"];
 }
 
 message ListEntitiesRequest {
@@ -824,7 +844,7 @@ message HomeAssistantStateResponse {
   option (ifdef) = "USE_API_HOMEASSISTANT_STATES";
 
   string entity_id = 1;
-  string state = 2 [(null_terminate) = true];
+  string state = 2;
   string attribute = 3;
 }
 
@@ -882,7 +902,7 @@ message ExecuteServiceArgument {
   bool bool_ = 1;
   int32 legacy_int = 2;
   float float_ = 3;
-  string string_ = 4 [(null_terminate) = true];
+  string string_ = 4;
   // ESPHome 1.14 (api v1.3) make int a signed value
   sint32 int_ = 5;
   repeated bool bool_array = 6 [packed=false, (fixed_vector) = true];
@@ -2488,3 +2508,92 @@ message InfraredRFReceiveEvent {
   fixed32 key = 2;                                    // Key identifying the receiver instance
   repeated sint32 timings = 3 [packed = true, (container_pointer_no_template) = "std::vector<int32_t>"];  // Raw timings in microseconds (zigzag-encoded): alternating mark/space periods
 }
+
+// ==================== SERIAL PROXY ====================
+
+enum SerialProxyParity {
+  SERIAL_PROXY_PARITY_NONE = 0;
+  SERIAL_PROXY_PARITY_EVEN = 1;
+  SERIAL_PROXY_PARITY_ODD = 2;
+}
+
+// Configure UART parameters for a serial proxy instance
+message SerialProxyConfigureRequest {
+  option (id) = 138;
+  option (source) = SOURCE_CLIENT;
+  option (ifdef) = "USE_SERIAL_PROXY";
+
+  uint32 instance = 1;          // Instance index (0-based)
+  uint32 baudrate = 2;          // Baud rate in bits per second
+  bool flow_control = 3;        // Enable hardware flow control
+  SerialProxyParity parity = 4; // Parity setting
+  uint32 stop_bits = 5;         // Number of stop bits (1 or 2)
+  uint32 data_size = 6;         // Number of data bits (5-8)
+}
+
+// Data received from a serial device, forwarded to clients
+message SerialProxyDataReceived {
+  option (id) = 139;
+  option (source) = SOURCE_SERVER;
+  option (ifdef) = "USE_SERIAL_PROXY";
+  option (no_delay) = true;
+
+  uint32 instance = 1;          // Instance index (0-based)
+  bytes data = 2;               // Raw data received from the serial device
+}
+
+// Write data to a serial device
+message SerialProxyWriteRequest {
+  option (id) = 140;
+  option (source) = SOURCE_CLIENT;
+  option (ifdef) = "USE_SERIAL_PROXY";
+  option (no_delay) = true;
+
+  uint32 instance = 1;          // Instance index (0-based)
+  bytes data = 2;               // Raw data to write to the serial device
+}
+
+// Set modem control pin states (RTS and DTR)
+message SerialProxySetModemPinsRequest {
+  option (id) = 141;
+  option (source) = SOURCE_CLIENT;
+  option (ifdef) = "USE_SERIAL_PROXY";
+
+  uint32 instance = 1;          // Instance index (0-based)
+  bool rts = 2;                 // Desired RTS pin state
+  bool dtr = 3;                 // Desired DTR pin state
+}
+
+// Request current modem control pin states
+message SerialProxyGetModemPinsRequest {
+  option (id) = 142;
+  option (source) = SOURCE_CLIENT;
+  option (ifdef) = "USE_SERIAL_PROXY";
+
+  uint32 instance = 1;          // Instance index (0-based)
+}
+
+// Response with current modem control pin states
+message SerialProxyGetModemPinsResponse {
+  option (id) = 143;
+  option (source) = SOURCE_SERVER;
+  option (ifdef) = "USE_SERIAL_PROXY";
+
+  uint32 instance = 1;          // Instance index (0-based)
+  bool rts = 2;                 // Current RTS pin state
+  bool dtr = 3;                 // Current DTR pin state
+}
+
+enum SerialProxyRequestType {
+  SERIAL_PROXY_REQUEST_TYPE_FLUSH = 0;  // Flush the serial port (block until all TX data is sent)
+}
+
+// Generic request message for simple serial proxy operations
+message SerialProxyRequest {
+  option (id) = 144;
+  option (source) = SOURCE_CLIENT;
+  option (ifdef) = "USE_SERIAL_PROXY";
+
+  uint32 instance = 1;                  // Instance index (0-based)
+  SerialProxyRequestType type = 2;      // Request type
+}

esphome/components/api/api_connection.cpp

@@ -1413,6 +1413,73 @@ void APIConnection::send_infrared_rf_receive_event(const InfraredRFReceiveEvent
 }
 #endif
 
+#ifdef USE_SERIAL_PROXY
+void APIConnection::on_serial_proxy_configure_request(const SerialProxyConfigureRequest &msg) {
+  auto &proxies = App.get_serial_proxies();
+  if (msg.instance >= proxies.size()) {
+    ESP_LOGW(TAG, "Serial proxy instance %u out of range (max %u)", msg.instance,
+             static_cast<uint32_t>(proxies.size()));
+    return;
+  }
+  proxies[msg.instance]->configure(msg.baudrate, msg.flow_control, static_cast<uint8_t>(msg.parity), msg.stop_bits,
+                                   msg.data_size);
+}
+
+void APIConnection::on_serial_proxy_write_request(const SerialProxyWriteRequest &msg) {
+  auto &proxies = App.get_serial_proxies();
+  if (msg.instance >= proxies.size()) {
+    ESP_LOGW(TAG, "Serial proxy instance %u out of range", msg.instance);
+    return;
+  }
+  proxies[msg.instance]->write(msg.data, msg.data_len);
+}
+
+void APIConnection::on_serial_proxy_set_modem_pins_request(const SerialProxySetModemPinsRequest &msg) {
+  auto &proxies = App.get_serial_proxies();
+  if (msg.instance >= proxies.size()) {
+    ESP_LOGW(TAG, "Serial proxy instance %u out of range", msg.instance);
+    return;
+  }
+  proxies[msg.instance]->set_modem_pins(msg.rts, msg.dtr);
+}
+
+void APIConnection::on_serial_proxy_get_modem_pins_request(const SerialProxyGetModemPinsRequest &msg) {
+  auto &proxies = App.get_serial_proxies();
+  if (msg.instance >= proxies.size()) {
+    ESP_LOGW(TAG, "Serial proxy instance %u out of range", msg.instance);
+    return;
+  }
+  bool rts, dtr;
+  proxies[msg.instance]->get_modem_pins(rts, dtr);
+
+  SerialProxyGetModemPinsResponse resp{};
+  resp.instance = msg.instance;
+  resp.rts = rts;
+  resp.dtr = dtr;
+  this->send_message(resp, SerialProxyGetModemPinsResponse::MESSAGE_TYPE);
+}
+
+void APIConnection::on_serial_proxy_request(const SerialProxyRequest &msg) {
+  auto &proxies = App.get_serial_proxies();
+  if (msg.instance >= proxies.size()) {
+    ESP_LOGW(TAG, "Serial proxy instance %u out of range", msg.instance);
+    return;
+  }
+  switch (msg.type) {
+    case enums::SERIAL_PROXY_REQUEST_TYPE_FLUSH:
+      proxies[msg.instance]->flush_port();
+      break;
+    default:
+      ESP_LOGW(TAG, "Unknown serial proxy request type: %u", static_cast<uint32_t>(msg.type));
+      break;
+  }
+}
+
+void APIConnection::send_serial_proxy_data(const SerialProxyDataReceived &msg) {
+  this->send_message(msg, SerialProxyDataReceived::MESSAGE_TYPE);
+}
+#endif
+
 #ifdef USE_INFRARED
 uint16_t APIConnection::try_send_infrared_info(EntityBase *entity, APIConnection *conn, uint32_t remaining_size) {
   auto *infrared = static_cast<infrared::Infrared *>(entity);
@@ -1627,6 +1694,16 @@ bool APIConnection::send_device_info_response_() {
   resp.zwave_proxy_feature_flags = zwave_proxy::global_zwave_proxy->get_feature_flags();
   resp.zwave_home_id = zwave_proxy::global_zwave_proxy->get_home_id();
 #endif
+#ifdef USE_SERIAL_PROXY
+  size_t serial_proxy_index = 0;
+  for (auto const &proxy : App.get_serial_proxies()) {
+    if (serial_proxy_index >= SERIAL_PROXY_COUNT)
+      break;
+    auto &info = resp.serial_proxies[serial_proxy_index++];
+    info.name = StringRef(proxy->get_name());
+    info.port_type = proxy->get_port_type();
+  }
+#endif
 #ifdef USE_API_NOISE
   resp.api_encryption_supported = true;
 #endif
@@ -1683,18 +1760,31 @@ void APIConnection::on_home_assistant_state_response(const HomeAssistantStateRes
   }
 
   for (auto &it : this->parent_->get_state_subs()) {
-    if (msg.entity_id != it.entity_id) {
+    // 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.size() ||
+        memcmp(it.entity_id, msg.entity_id.c_str(), msg.entity_id.size()) != 0) {
       continue;
     }
 
     // Compare attribute: either both have matching attribute, or both have none
-    // it.attribute can be nullptr (meaning no attribute filter)
-    if (it.attribute != nullptr ? msg.attribute != it.attribute : !msg.attribute.empty()) {
+    size_t sub_attr_len = it.attribute != nullptr ? strlen(it.attribute) : 0;
+    if (sub_attr_len != msg.attribute.size() ||
+        (sub_attr_len > 0 && memcmp(it.attribute, msg.attribute.c_str(), sub_attr_len) != 0)) {
       continue;
     }
 
-    // msg.state is already null-terminated in-place after protobuf decode
-    it.callback(msg.state);
+    // Create null-terminated state for callback (parse_number needs null-termination)
+    // HA state max length is 255 characters, but attributes can be much longer
+    // Use stack buffer for common case (states), heap fallback for large attributes
+    size_t state_len = msg.state.size();
+    SmallBufferWithHeapFallback<MAX_STATE_LEN + 1> state_buf_alloc(state_len + 1);
+    char *state_buf = reinterpret_cast<char *>(state_buf_alloc.get());
+    if (state_len > 0) {
+      memcpy(state_buf, msg.state.c_str(), state_len);
+    }
+    state_buf[state_len] = '\0';
+    it.callback(StringRef(state_buf, state_len));
   }
 }
 #endif

esphome/components/api/api_connection.h

@@ -182,6 +182,15 @@ class APIConnection final : public APIServerConnectionBase {
   void send_infrared_rf_receive_event(const InfraredRFReceiveEvent &msg);
 #endif
 
+#ifdef USE_SERIAL_PROXY
+  void on_serial_proxy_configure_request(const SerialProxyConfigureRequest &msg) override;
+  void on_serial_proxy_write_request(const SerialProxyWriteRequest &msg) override;
+  void on_serial_proxy_set_modem_pins_request(const SerialProxySetModemPinsRequest &msg) override;
+  void on_serial_proxy_get_modem_pins_request(const SerialProxyGetModemPinsRequest &msg) override;
+  void on_serial_proxy_request(const SerialProxyRequest &msg) override;
+  void send_serial_proxy_data(const SerialProxyDataReceived &msg);
+#endif
+
 #ifdef USE_EVENT
   void send_event(event::Event *event);
 #endif

esphome/components/api/api_frame_helper_noise.cpp

@@ -201,10 +201,9 @@ APIError APINoiseFrameHelper::try_read_frame_() {
     return (state_ == State::DATA) ? APIError::BAD_DATA_PACKET : APIError::BAD_HANDSHAKE_PACKET_LEN;
   }
 
-  // Reserve space for body (+1 for null terminator so protobuf StringRef fields
-  // can be safely null-terminated in-place after decode)
-  if (this->rx_buf_.size() != msg_size + 1) {
-    this->rx_buf_.resize(msg_size + 1);
+  // Reserve space for body
+  if (this->rx_buf_.size() != msg_size) {
+    this->rx_buf_.resize(msg_size);
   }
 
   if (rx_buf_len_ < msg_size) {

esphome/components/api/api_frame_helper_plaintext.cpp

@@ -163,10 +163,9 @@ APIError APIPlaintextFrameHelper::try_read_frame_() {
   }
   // header reading done
 
-  // Reserve space for body (+1 for null terminator so protobuf StringRef fields
-  // can be safely null-terminated in-place after decode)
-  if (this->rx_buf_.size() != this->rx_header_parsed_len_ + 1) {
-    this->rx_buf_.resize(this->rx_header_parsed_len_ + 1);
+  // Reserve space for body
+  if (this->rx_buf_.size() != this->rx_header_parsed_len_) {
+    this->rx_buf_.resize(this->rx_header_parsed_len_);
   }
 
   if (rx_buf_len_ < rx_header_parsed_len_) {

esphome/components/api/api_options.proto

@@ -90,13 +90,4 @@ extend google.protobuf.FieldOptions {
     //   - uint16_t <field>_length_{0};
     //   - uint16_t <field>_count_{0};
     optional bool packed_buffer = 50015 [default=false];
-
-    // null_terminate: Write a null byte after string data in the decode buffer.
-    // When set on a string field in a SOURCE_CLIENT (decodable) message, the
-    // generated decode() override writes '\0' at data[length] after decoding.
-    // This makes the StringRef safe for c_str() usage without copying.
-    // Safe because: (1) frame helpers reserve +1 byte in rx_buf_, and
-    // (2) the overwritten byte was already consumed during decode.
-    // Only mark fields that actually need null-terminated access.
-    optional bool null_terminate = 50016 [default=false];
 }

esphome/components/api/api_pb2.cpp

@@ -65,6 +65,16 @@ void DeviceInfo::calculate_size(ProtoSize &size) const {
   size.add_uint32(1, this->area_id);
 }
 #endif
+#ifdef USE_SERIAL_PROXY
+void SerialProxyInfo::encode(ProtoWriteBuffer buffer) const {
+  buffer.encode_string(1, this->name);
+  buffer.encode_uint32(2, static_cast<uint32_t>(this->port_type));
+}
+void SerialProxyInfo::calculate_size(ProtoSize &size) const {
+  size.add_length(1, this->name.size());
+  size.add_uint32(1, static_cast<uint32_t>(this->port_type));
+}
+#endif
 void DeviceInfoResponse::encode(ProtoWriteBuffer buffer) const {
   buffer.encode_string(2, this->name);
   buffer.encode_string(3, this->mac_address);
@@ -119,6 +129,11 @@ void DeviceInfoResponse::encode(ProtoWriteBuffer buffer) const {
 #ifdef USE_ZWAVE_PROXY
   buffer.encode_uint32(24, this->zwave_home_id);
 #endif
+#ifdef USE_SERIAL_PROXY
+  for (const auto &it : this->serial_proxies) {
+    buffer.encode_message(25, it);
+  }
+#endif
 }
 void DeviceInfoResponse::calculate_size(ProtoSize &size) const {
   size.add_length(1, this->name.size());
@@ -174,6 +189,11 @@ void DeviceInfoResponse::calculate_size(ProtoSize &size) const {
 #ifdef USE_ZWAVE_PROXY
   size.add_uint32(2, this->zwave_home_id);
 #endif
+#ifdef USE_SERIAL_PROXY
+  for (const auto &it : this->serial_proxies) {
+    size.add_message_object_force(2, it);
+  }
+#endif
 }
 #ifdef USE_BINARY_SENSOR
 void ListEntitiesBinarySensorResponse::encode(ProtoWriteBuffer buffer) const {
@@ -953,12 +973,6 @@ bool HomeAssistantStateResponse::decode_length(uint32_t field_id, ProtoLengthDel
   }
   return true;
 }
-void HomeAssistantStateResponse::decode(const uint8_t *buffer, size_t length) {
-  ProtoDecodableMessage::decode(buffer, length);
-  if (!this->state.empty()) {
-    const_cast<char *>(this->state.c_str())[this->state.size()] = '\0';
-  }
-}
 #endif
 bool GetTimeResponse::decode_length(uint32_t field_id, ProtoLengthDelimited value) {
   switch (field_id) {
@@ -1063,9 +1077,6 @@ void ExecuteServiceArgument::decode(const uint8_t *buffer, size_t length) {
   uint32_t count_string_array = ProtoDecodableMessage::count_repeated_field(buffer, length, 9);
   this->string_array.init(count_string_array);
   ProtoDecodableMessage::decode(buffer, length);
-  if (!this->string_.empty()) {
-    const_cast<char *>(this->string_.c_str())[this->string_.size()] = '\0';
-  }
 }
 bool ExecuteServiceRequest::decode_varint(uint32_t field_id, ProtoVarInt value) {
   switch (field_id) {
@@ -3449,5 +3460,111 @@ void InfraredRFReceiveEvent::calculate_size(ProtoSize &size) const {
   }
 }
 #endif
+#ifdef USE_SERIAL_PROXY
+bool SerialProxyConfigureRequest::decode_varint(uint32_t field_id, ProtoVarInt value) {
+  switch (field_id) {
+    case 1:
+      this->instance = value.as_uint32();
+      break;
+    case 2:
+      this->baudrate = value.as_uint32();
+      break;
+    case 3:
+      this->flow_control = value.as_bool();
+      break;
+    case 4:
+      this->parity = static_cast<enums::SerialProxyParity>(value.as_uint32());
+      break;
+    case 5:
+      this->stop_bits = value.as_uint32();
+      break;
+    case 6:
+      this->data_size = value.as_uint32();
+      break;
+    default:
+      return false;
+  }
+  return true;
+}
+void SerialProxyDataReceived::encode(ProtoWriteBuffer buffer) const {
+  buffer.encode_uint32(1, this->instance);
+  buffer.encode_bytes(2, this->data_ptr_, this->data_len_);
+}
+void SerialProxyDataReceived::calculate_size(ProtoSize &size) const {
+  size.add_uint32(1, this->instance);
+  size.add_length(1, this->data_len_);
+}
+bool SerialProxyWriteRequest::decode_varint(uint32_t field_id, ProtoVarInt value) {
+  switch (field_id) {
+    case 1:
+      this->instance = value.as_uint32();
+      break;
+    default:
+      return false;
+  }
+  return true;
+}
+bool SerialProxyWriteRequest::decode_length(uint32_t field_id, ProtoLengthDelimited value) {
+  switch (field_id) {
+    case 2: {
+      this->data = value.data();
+      this->data_len = value.size();
+      break;
+    }
+    default:
+      return false;
+  }
+  return true;
+}
+bool SerialProxySetModemPinsRequest::decode_varint(uint32_t field_id, ProtoVarInt value) {
+  switch (field_id) {
+    case 1:
+      this->instance = value.as_uint32();
+      break;
+    case 2:
+      this->rts = value.as_bool();
+      break;
+    case 3:
+      this->dtr = value.as_bool();
+      break;
+    default:
+      return false;
+  }
+  return true;
+}
+bool SerialProxyGetModemPinsRequest::decode_varint(uint32_t field_id, ProtoVarInt value) {
+  switch (field_id) {
+    case 1:
+      this->instance = value.as_uint32();
+      break;
+    default:
+      return false;
+  }
+  return true;
+}
+void SerialProxyGetModemPinsResponse::encode(ProtoWriteBuffer buffer) const {
+  buffer.encode_uint32(1, this->instance);
+  buffer.encode_bool(2, this->rts);
+  buffer.encode_bool(3, this->dtr);
+}
+void SerialProxyGetModemPinsResponse::calculate_size(ProtoSize &size) const {
+  size.add_uint32(1, this->instance);
+  size.add_bool(1, this->rts);
+  size.add_bool(1, this->dtr);
+}
+bool SerialProxyRequest::decode_varint(uint32_t field_id, ProtoVarInt value) {
+  switch (field_id) {
+    case 1:
+      this->instance = value.as_uint32();
+      break;
+    case 2:
+      this->type = static_cast<enums::SerialProxyRequestType>(value.as_uint32());
+      break;
+    default:
+      return false;
+  }
+  return true;
+}
+#endif
 
 }  // namespace esphome::api

esphome/components/api/api_pb2.h

@@ -12,6 +12,11 @@ namespace esphome::api {
 
 namespace enums {
 
+enum SerialProxyPortType : uint32_t {
+  SERIAL_PROXY_PORT_TYPE_TTL = 0,
+  SERIAL_PROXY_PORT_TYPE_RS232 = 1,
+  SERIAL_PROXY_PORT_TYPE_RS485 = 2,
+};
 enum EntityCategory : uint32_t {
   ENTITY_CATEGORY_NONE = 0,
   ENTITY_CATEGORY_CONFIG = 1,
@@ -311,6 +316,16 @@ enum ZWaveProxyRequestType : uint32_t {
   ZWAVE_PROXY_REQUEST_TYPE_HOME_ID_CHANGE = 2,
 };
 #endif
+#ifdef USE_SERIAL_PROXY
+enum SerialProxyParity : uint32_t {
+  SERIAL_PROXY_PARITY_NONE = 0,
+  SERIAL_PROXY_PARITY_EVEN = 1,
+  SERIAL_PROXY_PARITY_ODD = 2,
+};
+enum SerialProxyRequestType : uint32_t {
+  SERIAL_PROXY_REQUEST_TYPE_FLUSH = 0,
+};
+#endif
 
 }  // namespace enums
 
@@ -471,10 +486,24 @@ class DeviceInfo final : public ProtoMessage {
  protected:
 };
 #endif
+#ifdef USE_SERIAL_PROXY
+class SerialProxyInfo final : public ProtoMessage {
+ public:
+  StringRef name{};
+  enums::SerialProxyPortType port_type{};
+  void encode(ProtoWriteBuffer buffer) const override;
+  void calculate_size(ProtoSize &size) const override;
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *dump_to(DumpBuffer &out) const override;
+#endif
+
+ protected:
+};
+#endif
 class DeviceInfoResponse final : public ProtoMessage {
  public:
   static constexpr uint8_t MESSAGE_TYPE = 10;
-  static constexpr uint8_t ESTIMATED_SIZE = 255;
+  static constexpr uint16_t ESTIMATED_SIZE = 309;
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *message_name() const override { return "device_info_response"; }
 #endif
@@ -526,6 +555,9 @@ class DeviceInfoResponse final : public ProtoMessage {
 #endif
 #ifdef USE_ZWAVE_PROXY
   uint32_t zwave_home_id{0};
+#endif
+#ifdef USE_SERIAL_PROXY
+  std::array<SerialProxyInfo, SERIAL_PROXY_COUNT> serial_proxies{};
 #endif
   void encode(ProtoWriteBuffer buffer) const override;
   void calculate_size(ProtoSize &size) const override;
@@ -1095,7 +1127,6 @@ class HomeAssistantStateResponse final : public ProtoDecodableMessage {
   StringRef entity_id{};
   StringRef state{};
   StringRef attribute{};
-  void decode(const uint8_t *buffer, size_t length) override;
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
@@ -3026,5 +3057,133 @@ class InfraredRFReceiveEvent final : public ProtoMessage {
  protected:
 };
 #endif
+#ifdef USE_SERIAL_PROXY
+class SerialProxyConfigureRequest final : public ProtoDecodableMessage {
+ public:
+  static constexpr uint8_t MESSAGE_TYPE = 138;
+  static constexpr uint8_t ESTIMATED_SIZE = 20;
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *message_name() const override { return "serial_proxy_configure_request"; }
+#endif
+  uint32_t instance{0};
+  uint32_t baudrate{0};
+  bool flow_control{false};
+  enums::SerialProxyParity parity{};
+  uint32_t stop_bits{0};
+  uint32_t data_size{0};
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *dump_to(DumpBuffer &out) const override;
+#endif
+
+ protected:
+  bool decode_varint(uint32_t field_id, ProtoVarInt value) override;
+};
+class SerialProxyDataReceived final : public ProtoMessage {
+ public:
+  static constexpr uint8_t MESSAGE_TYPE = 139;
+  static constexpr uint8_t ESTIMATED_SIZE = 23;
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *message_name() const override { return "serial_proxy_data_received"; }
+#endif
+  uint32_t instance{0};
+  const uint8_t *data_ptr_{nullptr};
+  size_t data_len_{0};
+  void set_data(const uint8_t *data, size_t len) {
+    this->data_ptr_ = data;
+    this->data_len_ = len;
+  }
+  void encode(ProtoWriteBuffer buffer) const override;
+  void calculate_size(ProtoSize &size) const override;
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *dump_to(DumpBuffer &out) const override;
+#endif
+
+ protected:
+};
+class SerialProxyWriteRequest final : public ProtoDecodableMessage {
+ public:
+  static constexpr uint8_t MESSAGE_TYPE = 140;
+  static constexpr uint8_t ESTIMATED_SIZE = 23;
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *message_name() const override { return "serial_proxy_write_request"; }
+#endif
+  uint32_t instance{0};
+  const uint8_t *data{nullptr};
+  uint16_t data_len{0};
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *dump_to(DumpBuffer &out) const override;
+#endif
+
+ protected:
+  bool decode_length(uint32_t field_id, ProtoLengthDelimited value) override;
+  bool decode_varint(uint32_t field_id, ProtoVarInt value) override;
+};
+class SerialProxySetModemPinsRequest final : public ProtoDecodableMessage {
+ public:
+  static constexpr uint8_t MESSAGE_TYPE = 141;
+  static constexpr uint8_t ESTIMATED_SIZE = 8;
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *message_name() const override { return "serial_proxy_set_modem_pins_request"; }
+#endif
+  uint32_t instance{0};
+  bool rts{false};
+  bool dtr{false};
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *dump_to(DumpBuffer &out) const override;
+#endif
+
+ protected:
+  bool decode_varint(uint32_t field_id, ProtoVarInt value) override;
+};
+class SerialProxyGetModemPinsRequest final : public ProtoDecodableMessage {
+ public:
+  static constexpr uint8_t MESSAGE_TYPE = 142;
+  static constexpr uint8_t ESTIMATED_SIZE = 4;
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *message_name() const override { return "serial_proxy_get_modem_pins_request"; }
+#endif
+  uint32_t instance{0};
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *dump_to(DumpBuffer &out) const override;
+#endif
+
+ protected:
+  bool decode_varint(uint32_t field_id, ProtoVarInt value) override;
+};
+class SerialProxyGetModemPinsResponse final : public ProtoMessage {
+ public:
+  static constexpr uint8_t MESSAGE_TYPE = 143;
+  static constexpr uint8_t ESTIMATED_SIZE = 8;
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *message_name() const override { return "serial_proxy_get_modem_pins_response"; }
+#endif
+  uint32_t instance{0};
+  bool rts{false};
+  bool dtr{false};
+  void encode(ProtoWriteBuffer buffer) const override;
+  void calculate_size(ProtoSize &size) const override;
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *dump_to(DumpBuffer &out) const override;
+#endif
+
+ protected:
+};
+class SerialProxyRequest final : public ProtoDecodableMessage {
+ public:
+  static constexpr uint8_t MESSAGE_TYPE = 144;
+  static constexpr uint8_t ESTIMATED_SIZE = 6;
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *message_name() const override { return "serial_proxy_request"; }
+#endif
+  uint32_t instance{0};
+  enums::SerialProxyRequestType type{};
+#ifdef HAS_PROTO_MESSAGE_DUMP
+  const char *dump_to(DumpBuffer &out) const override;
+#endif
+
+ protected:
+  bool decode_varint(uint32_t field_id, ProtoVarInt value) override;
+};
+#endif
 
 }  // namespace esphome::api

esphome/components/api/api_pb2_dump.cpp

@@ -100,6 +100,18 @@ static void dump_bytes_field(DumpBuffer &out, const char *field_name, const uint
   out.append(hex_buf).append("\n");
 }
 
+template<> const char *proto_enum_to_string<enums::SerialProxyPortType>(enums::SerialProxyPortType value) {
+  switch (value) {
+    case enums::SERIAL_PROXY_PORT_TYPE_TTL:
+      return "SERIAL_PROXY_PORT_TYPE_TTL";
+    case enums::SERIAL_PROXY_PORT_TYPE_RS232:
+      return "SERIAL_PROXY_PORT_TYPE_RS232";
+    case enums::SERIAL_PROXY_PORT_TYPE_RS485:
+      return "SERIAL_PROXY_PORT_TYPE_RS485";
+    default:
+      return "UNKNOWN";
+  }
+}
 template<> const char *proto_enum_to_string<enums::EntityCategory>(enums::EntityCategory value) {
   switch (value) {
     case enums::ENTITY_CATEGORY_NONE:
@@ -736,6 +748,28 @@ template<> const char *proto_enum_to_string<enums::ZWaveProxyRequestType>(enums:
   }
 }
 #endif
+#ifdef USE_SERIAL_PROXY
+template<> const char *proto_enum_to_string<enums::SerialProxyParity>(enums::SerialProxyParity value) {
+  switch (value) {
+    case enums::SERIAL_PROXY_PARITY_NONE:
+      return "SERIAL_PROXY_PARITY_NONE";
+    case enums::SERIAL_PROXY_PARITY_EVEN:
+      return "SERIAL_PROXY_PARITY_EVEN";
+    case enums::SERIAL_PROXY_PARITY_ODD:
+      return "SERIAL_PROXY_PARITY_ODD";
+    default:
+      return "UNKNOWN";
+  }
+}
+template<> const char *proto_enum_to_string<enums::SerialProxyRequestType>(enums::SerialProxyRequestType value) {
+  switch (value) {
+    case enums::SERIAL_PROXY_REQUEST_TYPE_FLUSH:
+      return "SERIAL_PROXY_REQUEST_TYPE_FLUSH";
+    default:
+      return "UNKNOWN";
+  }
+}
+#endif
 
 const char *HelloRequest::dump_to(DumpBuffer &out) const {
   MessageDumpHelper helper(out, "HelloRequest");
@@ -785,6 +819,14 @@ const char *DeviceInfo::dump_to(DumpBuffer &out) const {
   return out.c_str();
 }
 #endif
+#ifdef USE_SERIAL_PROXY
+const char *SerialProxyInfo::dump_to(DumpBuffer &out) const {
+  MessageDumpHelper helper(out, "SerialProxyInfo");
+  dump_field(out, "name", this->name);
+  dump_field(out, "port_type", static_cast<enums::SerialProxyPortType>(this->port_type));
+  return out.c_str();
+}
+#endif
 const char *DeviceInfoResponse::dump_to(DumpBuffer &out) const {
   MessageDumpHelper helper(out, "DeviceInfoResponse");
   dump_field(out, "name", this->name);
@@ -845,6 +887,13 @@ const char *DeviceInfoResponse::dump_to(DumpBuffer &out) const {
 #endif
 #ifdef USE_ZWAVE_PROXY
   dump_field(out, "zwave_home_id", this->zwave_home_id);
+#endif
+#ifdef USE_SERIAL_PROXY
+  for (const auto &it : this->serial_proxies) {
+    out.append("  serial_proxies: ");
+    it.dump_to(out);
+    out.append("\n");
+  }
 #endif
   return out.c_str();
 }
@@ -2469,6 +2518,55 @@ const char *InfraredRFReceiveEvent::dump_to(DumpBuffer &out) const {
   return out.c_str();
 }
 #endif
+#ifdef USE_SERIAL_PROXY
+const char *SerialProxyConfigureRequest::dump_to(DumpBuffer &out) const {
+  MessageDumpHelper helper(out, "SerialProxyConfigureRequest");
+  dump_field(out, "instance", this->instance);
+  dump_field(out, "baudrate", this->baudrate);
+  dump_field(out, "flow_control", this->flow_control);
+  dump_field(out, "parity", static_cast<enums::SerialProxyParity>(this->parity));
+  dump_field(out, "stop_bits", this->stop_bits);
+  dump_field(out, "data_size", this->data_size);
+  return out.c_str();
+}
+const char *SerialProxyDataReceived::dump_to(DumpBuffer &out) const {
+  MessageDumpHelper helper(out, "SerialProxyDataReceived");
+  dump_field(out, "instance", this->instance);
+  dump_bytes_field(out, "data", this->data_ptr_, this->data_len_);
+  return out.c_str();
+}
+const char *SerialProxyWriteRequest::dump_to(DumpBuffer &out) const {
+  MessageDumpHelper helper(out, "SerialProxyWriteRequest");
+  dump_field(out, "instance", this->instance);
+  dump_bytes_field(out, "data", this->data, this->data_len);
+  return out.c_str();
+}
+const char *SerialProxySetModemPinsRequest::dump_to(DumpBuffer &out) const {
+  MessageDumpHelper helper(out, "SerialProxySetModemPinsRequest");
+  dump_field(out, "instance", this->instance);
+  dump_field(out, "rts", this->rts);
+  dump_field(out, "dtr", this->dtr);
+  return out.c_str();
+}
+const char *SerialProxyGetModemPinsRequest::dump_to(DumpBuffer &out) const {
+  MessageDumpHelper helper(out, "SerialProxyGetModemPinsRequest");
+  dump_field(out, "instance", this->instance);
+  return out.c_str();
+}
+const char *SerialProxyGetModemPinsResponse::dump_to(DumpBuffer &out) const {
+  MessageDumpHelper helper(out, "SerialProxyGetModemPinsResponse");
+  dump_field(out, "instance", this->instance);
+  dump_field(out, "rts", this->rts);
+  dump_field(out, "dtr", this->dtr);
+  return out.c_str();
+}
+const char *SerialProxyRequest::dump_to(DumpBuffer &out) const {
+  MessageDumpHelper helper(out, "SerialProxyRequest");
+  dump_field(out, "instance", this->instance);
+  dump_field(out, "type", static_cast<enums::SerialProxyRequestType>(this->type));
+  return out.c_str();
+}
+#endif
 
 }  // namespace esphome::api
 

esphome/components/api/api_pb2_service.cpp

@@ -634,6 +634,61 @@ void APIServerConnectionBase::read_message(uint32_t msg_size, uint32_t msg_type,
       this->on_infrared_rf_transmit_raw_timings_request(msg);
       break;
     }
+#endif
+#ifdef USE_SERIAL_PROXY
+    case SerialProxyConfigureRequest::MESSAGE_TYPE: {
+      SerialProxyConfigureRequest msg;
+      msg.decode(msg_data, msg_size);
+#ifdef HAS_PROTO_MESSAGE_DUMP
+      this->log_receive_message_(LOG_STR("on_serial_proxy_configure_request"), msg);
+#endif
+      this->on_serial_proxy_configure_request(msg);
+      break;
+    }
+#endif
+#ifdef USE_SERIAL_PROXY
+    case SerialProxyWriteRequest::MESSAGE_TYPE: {
+      SerialProxyWriteRequest msg;
+      msg.decode(msg_data, msg_size);
+#ifdef HAS_PROTO_MESSAGE_DUMP
+      this->log_receive_message_(LOG_STR("on_serial_proxy_write_request"), msg);
+#endif
+      this->on_serial_proxy_write_request(msg);
+      break;
+    }
+#endif
+#ifdef USE_SERIAL_PROXY
+    case SerialProxySetModemPinsRequest::MESSAGE_TYPE: {
+      SerialProxySetModemPinsRequest msg;
+      msg.decode(msg_data, msg_size);
+#ifdef HAS_PROTO_MESSAGE_DUMP
+      this->log_receive_message_(LOG_STR("on_serial_proxy_set_modem_pins_request"), msg);
+#endif
+      this->on_serial_proxy_set_modem_pins_request(msg);
+      break;
+    }
+#endif
+#ifdef USE_SERIAL_PROXY
+    case SerialProxyGetModemPinsRequest::MESSAGE_TYPE: {
+      SerialProxyGetModemPinsRequest msg;
+      msg.decode(msg_data, msg_size);
+#ifdef HAS_PROTO_MESSAGE_DUMP
+      this->log_receive_message_(LOG_STR("on_serial_proxy_get_modem_pins_request"), msg);
+#endif
+      this->on_serial_proxy_get_modem_pins_request(msg);
+      break;
+    }
+#endif
+#ifdef USE_SERIAL_PROXY
+    case SerialProxyRequest::MESSAGE_TYPE: {
+      SerialProxyRequest msg;
+      msg.decode(msg_data, msg_size);
+#ifdef HAS_PROTO_MESSAGE_DUMP
+      this->log_receive_message_(LOG_STR("on_serial_proxy_request"), msg);
+#endif
+      this->on_serial_proxy_request(msg);
+      break;
+    }
 #endif
     default:
       break;

esphome/components/api/api_pb2_service.h

@@ -224,6 +224,23 @@ class APIServerConnectionBase : public ProtoService {
   virtual void on_infrared_rf_transmit_raw_timings_request(const InfraredRFTransmitRawTimingsRequest &value){};
 #endif
 
+#ifdef USE_SERIAL_PROXY
+  virtual void on_serial_proxy_configure_request(const SerialProxyConfigureRequest &value){};
+#endif
+
+#ifdef USE_SERIAL_PROXY
+  virtual void on_serial_proxy_write_request(const SerialProxyWriteRequest &value){};
+#endif
+#ifdef USE_SERIAL_PROXY
+  virtual void on_serial_proxy_set_modem_pins_request(const SerialProxySetModemPinsRequest &value){};
+#endif
+#ifdef USE_SERIAL_PROXY
+  virtual void on_serial_proxy_get_modem_pins_request(const SerialProxyGetModemPinsRequest &value){};
+#endif
+
+#ifdef USE_SERIAL_PROXY
+  virtual void on_serial_proxy_request(const SerialProxyRequest &value){};
+#endif
  protected:
   void read_message(uint32_t msg_size, uint32_t msg_type, const uint8_t *msg_data) override;
 };

esphome/components/api/api_server.cpp

@@ -382,6 +382,17 @@ void APIServer::send_infrared_rf_receive_event([[maybe_unused]] uint32_t device_
 }
 #endif
 
+#ifdef USE_SERIAL_PROXY
+void APIServer::send_serial_proxy_data(uint32_t instance, const uint8_t *data, size_t len) {
+  SerialProxyDataReceived msg{};
+  msg.instance = instance;
+  msg.set_data(data, len);
+
+  for (auto &c : this->clients_)
+    c->send_serial_proxy_data(msg);
+}
+#endif
+
 #ifdef USE_ALARM_CONTROL_PANEL
 API_DISPATCH_UPDATE(alarm_control_panel::AlarmControlPanel, alarm_control_panel)
 #endif

esphome/components/api/api_server.h

@@ -189,6 +189,10 @@ class APIServer : public Component,
   void send_infrared_rf_receive_event(uint32_t device_id, uint32_t key, const std::vector<int32_t> *timings);
 #endif
 
+#ifdef USE_SERIAL_PROXY
+  void send_serial_proxy_data(uint32_t instance, const uint8_t *data, size_t len);
+#endif
+
   bool is_connected(bool state_subscription_only = false) const;
 
 #ifdef USE_API_HOMEASSISTANT_STATES

esphome/components/api/user_services.cpp

@@ -1,6 +1,5 @@
 #include "user_services.h"
 #include "esphome/core/log.h"
-#include "esphome/core/string_ref.h"
 
 namespace esphome::api {
 
@@ -12,8 +11,6 @@ template<> int32_t get_execute_arg_value<int32_t>(const ExecuteServiceArgument &
 }
 template<> float get_execute_arg_value<float>(const ExecuteServiceArgument &arg) { return arg.float_; }
 template<> std::string get_execute_arg_value<std::string>(const ExecuteServiceArgument &arg) { return arg.string_; }
-// Zero-copy StringRef version for YAML-generated services (string_ is null-terminated after decode)
-template<> StringRef get_execute_arg_value<StringRef>(const ExecuteServiceArgument &arg) { return arg.string_; }
 
 // Legacy std::vector versions for external components using custom_api_device.h - optimized with reserve
 template<> std::vector<bool> get_execute_arg_value<std::vector<bool>>(const ExecuteServiceArgument &arg) {
@@ -64,8 +61,6 @@ template<> enums::ServiceArgType to_service_arg_type<bool>() { return enums::SER
 template<> enums::ServiceArgType to_service_arg_type<int32_t>() { return enums::SERVICE_ARG_TYPE_INT; }
 template<> enums::ServiceArgType to_service_arg_type<float>() { return enums::SERVICE_ARG_TYPE_FLOAT; }
 template<> enums::ServiceArgType to_service_arg_type<std::string>() { return enums::SERVICE_ARG_TYPE_STRING; }
-// Zero-copy StringRef version for YAML-generated services
-template<> enums::ServiceArgType to_service_arg_type<StringRef>() { return enums::SERVICE_ARG_TYPE_STRING; }
 
 // Legacy std::vector versions for external components using custom_api_device.h
 template<> enums::ServiceArgType to_service_arg_type<std::vector<bool>>() { return enums::SERVICE_ARG_TYPE_BOOL_ARRAY; }

esphome/components/script/__init__.py

@@ -219,7 +219,6 @@ async def script_stop_action_to_code(config, action_id, template_arg, args):
     "script.wait",
     ScriptWaitAction,
     maybe_simple_id({cv.Required(CONF_ID): cv.use_id(Script)}),
-    deferred=True,
 )
 async def script_wait_action_to_code(config, action_id, template_arg, args):
     full_id, paren = await cg.get_variable_with_full_id(config[CONF_ID])

esphome/components/serial_proxy/__init__.py

@@ -0,0 +1,80 @@
+"""
+Serial Proxy component for ESPHome.
+
+WARNING: This component is EXPERIMENTAL. The API (both Python configuration
+and C++ interfaces) may change at any time without following the normal
+breaking changes policy. Use at your own risk.
+
+Once the API is considered stable, this warning will be removed.
+
+Provides a proxy to/from a serial interface on the ESPHome device, allowing
+Home Assistant to connect to the serial port and send/receive data to/from
+an arbitrary serial device.
+"""
+
+from esphome import pins
+import esphome.codegen as cg
+from esphome.components import uart
+import esphome.config_validation as cv
+from esphome.const import CONF_ID, CONF_NAME
+
+CODEOWNERS = ["@kbx81"]
+DEPENDENCIES = ["api", "uart"]
+
+MULTI_CONF = True
+
+serial_proxy_ns = cg.esphome_ns.namespace("serial_proxy")
+SerialProxy = serial_proxy_ns.class_("SerialProxy", cg.Component, uart.UARTDevice)
+
+api_enums_ns = cg.esphome_ns.namespace("api").namespace("enums")
+SerialProxyPortType = api_enums_ns.enum("SerialProxyPortType")
+SERIAL_PROXY_PORT_TYPES = {
+    "TTL": SerialProxyPortType.SERIAL_PROXY_PORT_TYPE_TTL,
+    "RS232": SerialProxyPortType.SERIAL_PROXY_PORT_TYPE_RS232,
+    "RS485": SerialProxyPortType.SERIAL_PROXY_PORT_TYPE_RS485,
+}
+
+CONF_DTR_PIN = "dtr_pin"
+CONF_PORT_TYPE = "port_type"
+CONF_RTS_PIN = "rts_pin"
+
+_serial_proxy_count = []
+
+
+CONFIG_SCHEMA = (
+    cv.Schema(
+        {
+            cv.GenerateID(): cv.declare_id(SerialProxy),
+            cv.Required(CONF_NAME): cv.string_strict,
+            cv.Required(CONF_PORT_TYPE): cv.enum(SERIAL_PROXY_PORT_TYPES, upper=True),
+            cv.Optional(CONF_RTS_PIN): pins.gpio_output_pin_schema,
+            cv.Optional(CONF_DTR_PIN): pins.gpio_output_pin_schema,
+        }
+    )
+    .extend(cv.COMPONENT_SCHEMA)
+    .extend(uart.UART_DEVICE_SCHEMA)
+)
+
+
+async def to_code(config):
+    var = cg.new_Pvariable(config[CONF_ID])
+    await cg.register_component(var, config)
+    await uart.register_uart_device(var, config)
+    cg.add(cg.App.register_serial_proxy(var))
+    cg.add(var.set_name(config[CONF_NAME]))
+    cg.add(var.set_port_type(config[CONF_PORT_TYPE]))
+    cg.add_define("USE_SERIAL_PROXY")
+    # Track instance count — last define wins, so the final value is the total count
+    _serial_proxy_count.append(var)
+    cg.add_define("SERIAL_PROXY_COUNT", len(_serial_proxy_count))
+
+    if CONF_RTS_PIN in config:
+        rts_pin = await cg.gpio_pin_expression(config[CONF_RTS_PIN])
+        cg.add(var.set_rts_pin(rts_pin))
+
+    if CONF_DTR_PIN in config:
+        dtr_pin = await cg.gpio_pin_expression(config[CONF_DTR_PIN])
+        cg.add(var.set_dtr_pin(dtr_pin))
+
+    # Request UART to wake the main loop when data arrives for low-latency processing
+    uart.request_wake_loop_on_rx()

esphome/components/serial_proxy/serial_proxy.cpp

@@ -0,0 +1,137 @@
+#include "serial_proxy.h"
+
+#ifdef USE_SERIAL_PROXY
+
+#include "esphome/core/log.h"
+
+#ifdef USE_API
+#include "esphome/components/api/api_server.h"
+#endif
+
+namespace esphome::serial_proxy {
+
+static const char *const TAG = "serial_proxy";
+
+void SerialProxy::setup() {
+  // Set up modem control pins if configured
+  if (this->rts_pin_ != nullptr) {
+    this->rts_pin_->setup();
+    this->rts_pin_->digital_write(this->rts_state_);
+  }
+  if (this->dtr_pin_ != nullptr) {
+    this->dtr_pin_->setup();
+    this->dtr_pin_->digital_write(this->dtr_state_);
+  }
+}
+
+void SerialProxy::loop() {
+  // Read available data from UART and forward to API clients
+  size_t available = this->available();
+  if (available == 0)
+    return;
+
+  // Read in chunks up to SERIAL_PROXY_MAX_READ_SIZE
+  uint8_t buffer[SERIAL_PROXY_MAX_READ_SIZE];
+  size_t to_read = std::min(available, sizeof(buffer));
+
+  if (!this->read_array(buffer, to_read))
+    return;
+
+#ifdef USE_API
+  if (api::global_api_server != nullptr) {
+    api::global_api_server->send_serial_proxy_data(this->instance_index_, buffer, to_read);
+  }
+#endif
+}
+
+void SerialProxy::dump_config() {
+  ESP_LOGCONFIG(TAG,
+                "Serial Proxy [%u]:\n"
+                "  Name: %s\n"
+                "  Port Type: %s\n"
+                "  RTS Pin: %s\n"
+                "  DTR Pin: %s",
+                this->instance_index_, this->name_.c_str(),
+                this->port_type_ == api::enums::SERIAL_PROXY_PORT_TYPE_RS485   ? "RS485"
+                : this->port_type_ == api::enums::SERIAL_PROXY_PORT_TYPE_RS232 ? "RS232"
+                                                                               : "TTL",
+                this->rts_pin_ != nullptr ? "configured" : "not configured",
+                this->dtr_pin_ != nullptr ? "configured" : "not configured");
+}
+
+void SerialProxy::configure(uint32_t baudrate, bool flow_control, uint8_t parity, uint8_t stop_bits,
+                            uint8_t data_size) {
+  ESP_LOGD(TAG, "Configuring serial proxy [%u]: baud=%u, flow_ctrl=%s, parity=%u, stop=%u, data=%u",
+           this->instance_index_, baudrate, YESNO(flow_control), parity, stop_bits, data_size);
+
+  auto *uart_comp = this->parent_;
+  if (uart_comp == nullptr) {
+    ESP_LOGE(TAG, "UART component not available");
+    return;
+  }
+
+  // Apply UART parameters
+  uart_comp->set_baud_rate(baudrate);
+  uart_comp->set_stop_bits(stop_bits);
+  uart_comp->set_data_bits(data_size);
+
+  // Map parity enum to UARTParityOptions
+  switch (parity) {
+    case 0:
+      uart_comp->set_parity(uart::UART_CONFIG_PARITY_NONE);
+      break;
+    case 1:
+      uart_comp->set_parity(uart::UART_CONFIG_PARITY_EVEN);
+      break;
+    case 2:
+      uart_comp->set_parity(uart::UART_CONFIG_PARITY_ODD);
+      break;
+    default:
+      ESP_LOGW(TAG, "Unknown parity value: %u, using NONE", parity);
+      uart_comp->set_parity(uart::UART_CONFIG_PARITY_NONE);
+      break;
+  }
+
+    // Apply the new settings
+    // load_settings() is available on ESP8266 and ESP32 platforms
+#if defined(USE_ESP8266) || defined(USE_ESP32)
+  uart_comp->load_settings(true);
+#endif
+
+  // Note: Hardware flow control configuration is stored but not yet applied
+  // to the UART hardware - this requires additional platform support
+  (void) flow_control;
+}
+
+void SerialProxy::write(const uint8_t *data, size_t len) {
+  if (data == nullptr || len == 0)
+    return;
+  this->write_array(data, len);
+}
+
+void SerialProxy::set_modem_pins(bool rts, bool dtr) {
+  ESP_LOGV(TAG, "Setting modem pins [%u]: RTS=%s, DTR=%s", this->instance_index_, ONOFF(rts), ONOFF(dtr));
+
+  if (this->rts_pin_ != nullptr) {
+    this->rts_state_ = rts;
+    this->rts_pin_->digital_write(rts);
+  }
+  if (this->dtr_pin_ != nullptr) {
+    this->dtr_state_ = dtr;
+    this->dtr_pin_->digital_write(dtr);
+  }
+}
+
+void SerialProxy::get_modem_pins(bool &rts, bool &dtr) const {
+  rts = this->rts_state_;
+  dtr = this->dtr_state_;
+}
+
+void SerialProxy::flush_port() {
+  ESP_LOGV(TAG, "Flushing serial proxy [%u]", this->instance_index_);
+  this->flush();
+}
+
+}  // namespace esphome::serial_proxy
+
+#endif  // USE_SERIAL_PROXY

esphome/components/serial_proxy/serial_proxy.h

@@ -0,0 +1,101 @@
+#pragma once
+
+// WARNING: This component is EXPERIMENTAL. The API may change at any time
+// without following the normal breaking changes policy. Use at your own risk.
+// Once the API is considered stable, this warning will be removed.
+
+#include "esphome/core/defines.h"
+
+#ifdef USE_SERIAL_PROXY
+
+#include "esphome/components/api/api_pb2.h"
+#include "esphome/core/component.h"
+#include "esphome/core/hal.h"
+#include "esphome/components/uart/uart.h"
+
+#include <string>
+
+namespace esphome::serial_proxy {
+
+/// Maximum bytes to read from UART in a single loop iteration
+static constexpr size_t SERIAL_PROXY_MAX_READ_SIZE = 256;
+
+class SerialProxy : public uart::UARTDevice, public Component {
+ public:
+  void setup() override;
+  void loop() override;
+  void dump_config() override;
+  float get_setup_priority() const override { return setup_priority::AFTER_CONNECTION; }
+
+  /// Get the instance index (position in Application's serial_proxies_ vector)
+  uint32_t get_instance_index() const { return this->instance_index_; }
+
+  /// Set the instance index (called by Application::register_serial_proxy)
+  void set_instance_index(uint32_t index) { this->instance_index_ = index; }
+
+  /// Set the human-readable port name (from YAML configuration)
+  void set_name(const std::string &name) { this->name_ = name; }
+
+  /// Get the human-readable port name
+  const std::string &get_name() const { return this->name_; }
+
+  /// Set the port type (from YAML configuration)
+  void set_port_type(api::enums::SerialProxyPortType port_type) { this->port_type_ = port_type; }
+
+  /// Get the port type
+  api::enums::SerialProxyPortType get_port_type() const { return this->port_type_; }
+
+  /// Configure UART parameters and apply them
+  /// @param baudrate Baud rate in bits per second
+  /// @param flow_control True to enable hardware flow control
+  /// @param parity Parity setting (0=none, 1=even, 2=odd)
+  /// @param stop_bits Number of stop bits (1 or 2)
+  /// @param data_size Number of data bits (5-8)
+  void configure(uint32_t baudrate, bool flow_control, uint8_t parity, uint8_t stop_bits, uint8_t data_size);
+
+  /// Write data to the serial device
+  /// @param data Pointer to data buffer
+  /// @param len Number of bytes to write
+  void write(const uint8_t *data, size_t len);
+
+  /// Set modem pin states (RTS and DTR)
+  /// @param rts Desired RTS pin state
+  /// @param dtr Desired DTR pin state
+  void set_modem_pins(bool rts, bool dtr);
+
+  /// Get current modem pin states
+  /// @param[out] rts Current RTS pin state
+  /// @param[out] dtr Current DTR pin state
+  void get_modem_pins(bool &rts, bool &dtr) const;
+
+  /// Flush the serial port (block until all TX data is sent)
+  void flush_port();
+
+  /// Set the RTS GPIO pin (from YAML configuration)
+  void set_rts_pin(GPIOPin *pin) { this->rts_pin_ = pin; }
+
+  /// Set the DTR GPIO pin (from YAML configuration)
+  void set_dtr_pin(GPIOPin *pin) { this->dtr_pin_ = pin; }
+
+ protected:
+  /// Instance index for identifying this proxy in API messages
+  uint32_t instance_index_{0};
+
+  /// Human-readable port name
+  std::string name_;
+
+  /// Port type
+  api::enums::SerialProxyPortType port_type_{api::enums::SERIAL_PROXY_PORT_TYPE_TTL};
+
+  /// Optional GPIO pins for modem control
+  GPIOPin *rts_pin_{nullptr};
+  GPIOPin *dtr_pin_{nullptr};
+
+  /// Current modem pin states
+  bool rts_state_{false};
+  bool dtr_state_{false};
+};
+
+}  // namespace esphome::serial_proxy
+
+#endif  // USE_SERIAL_PROXY

esphome/core/application.h

@@ -94,6 +94,9 @@
 #ifdef USE_INFRARED
 #include "esphome/components/infrared/infrared.h"
 #endif
+#ifdef USE_SERIAL_PROXY
+#include "esphome/components/serial_proxy/serial_proxy.h"
+#endif
 #ifdef USE_EVENT
 #include "esphome/components/event/event.h"
 #endif
@@ -234,6 +237,13 @@ class Application {
   void register_infrared(infrared::Infrared *infrared) { this->infrareds_.push_back(infrared); }
 #endif
 
+#ifdef USE_SERIAL_PROXY
+  void register_serial_proxy(serial_proxy::SerialProxy *proxy) {
+    proxy->set_instance_index(this->serial_proxies_.size());
+    this->serial_proxies_.push_back(proxy);
+  }
+#endif
+
 #ifdef USE_EVENT
   void register_event(event::Event *event) { this->events_.push_back(event); }
 #endif
@@ -473,6 +483,10 @@ class Application {
   GET_ENTITY_METHOD(infrared::Infrared, infrared, infrareds)
 #endif
 
+#ifdef USE_SERIAL_PROXY
+  auto &get_serial_proxies() const { return this->serial_proxies_; }
+#endif
+
 #ifdef USE_EVENT
   auto &get_events() const { return this->events_; }
   GET_ENTITY_METHOD(event::Event, event, events)
@@ -690,6 +704,9 @@ class Application {
 #ifdef USE_INFRARED
   StaticVector<infrared::Infrared *, ESPHOME_ENTITY_INFRARED_COUNT> infrareds_{};
 #endif
+#ifdef USE_SERIAL_PROXY
+  std::vector<serial_proxy::SerialProxy *> serial_proxies_{};
+#endif
 #ifdef USE_UPDATE
   StaticVector<update::UpdateEntity *, ESPHOME_ENTITY_UPDATE_COUNT> updates_{};
 #endif

esphome/core/defines.h

@@ -99,6 +99,7 @@
 #define MDNS_SERVICE_COUNT 3
 #define USE_MDNS_DYNAMIC_TXT
 #define MDNS_DYNAMIC_TXT_COUNT 2
+#define SERIAL_PROXY_COUNT 2
 #define SNTP_SERVER_COUNT 3
 #define USE_MEDIA_PLAYER
 #define USE_NEXTION_TFT_UPLOAD
@@ -109,6 +110,7 @@
 #define USE_SAFE_MODE_CALLBACK
 #define USE_SELECT
 #define USE_SENSOR
+#define USE_SERIAL_PROXY
 #define USE_STATUS_LED
 #define USE_STATUS_SENSOR
 #define USE_SWITCH

esphome/core/string_ref.h

@@ -81,19 +81,6 @@ class StringRef {
 
   operator std::string() const { return str(); }
 
-  /// Compare with a null-terminated C string (compatible with std::string::compare)
-  int compare(const char *s) const {
-    size_t s_len = std::strlen(s);
-    int result = std::memcmp(base_, s, std::min(len_, s_len));
-    if (result != 0)
-      return result;
-    if (len_ < s_len)
-      return -1;
-    if (len_ > s_len)
-      return 1;
-    return 0;
-  }
-
   /// Find first occurrence of substring, returns std::string::npos if not found.
   /// Note: Requires the underlying string to be null-terminated.
   size_type find(const char *s, size_type pos = 0) const {

esphome/util.py

@@ -24,14 +24,11 @@ class RegistryEntry:
         fun: Callable[..., Any],
         type_id: "MockObjClass",
         schema: "Schema",
-        *,
-        deferred: bool = False,
     ):
         self.name = name
         self.fun = fun
         self.type_id = type_id
         self.raw_schema = schema
-        self.deferred = deferred
 
     @property
     def coroutine_fun(self):
@@ -52,16 +49,9 @@ class Registry(dict[str, RegistryEntry]):
         self.base_schema = base_schema or {}
         self.type_id_key = type_id_key
 
-    def register(
-        self,
-        name: str,
-        type_id: "MockObjClass",
-        schema: "Schema",
-        *,
-        deferred: bool = False,
-    ):
+    def register(self, name: str, type_id: "MockObjClass", schema: "Schema"):
         def decorator(fun: Callable[..., Any]):
-            self[name] = RegistryEntry(name, fun, type_id, schema, deferred=deferred)
+            self[name] = RegistryEntry(name, fun, type_id, schema)
             return fun
 
         return decorator

script/api_protobuf/api_protobuf.py

@@ -2020,8 +2020,6 @@ def build_message_type(
 
     # Collect fixed_vector fields for custom decode generation
     fixed_vector_fields = []
-    # Collect fields with (null_terminate) = true option
-    null_terminate_fields = []
 
     for field in desc.field:
         # Skip deprecated fields completely
@@ -2064,10 +2062,6 @@ def build_message_type(
 
         ti = create_field_type_info(field, needs_decode, needs_encode)
 
-        # Collect fields with (null_terminate) = true for post-decode null-termination
-        if needs_decode and get_field_opt(field, pb.null_terminate, False):
-            null_terminate_fields.append(ti.field_name)
-
         # Skip field declarations for fields that are in the base class
         # but include their encode/decode logic
         if field.name not in common_field_names:
@@ -2174,8 +2168,8 @@ def build_message_type(
         prot = "bool decode_64bit(uint32_t field_id, Proto64Bit value) override;"
         protected_content.insert(0, prot)
 
-    # Generate custom decode() override for messages with FixedVector or null_terminate fields
-    if fixed_vector_fields or null_terminate_fields:
+    # Generate custom decode() override for messages with FixedVector fields
+    if fixed_vector_fields:
         # Generate the decode() implementation in cpp
         o = f"void {desc.name}::decode(const uint8_t *buffer, size_t length) {{\n"
         # Count and init each FixedVector field
@@ -2184,13 +2178,6 @@ def build_message_type(
             o += f"  this->{field_name}.init(count_{field_name});\n"
         # Call parent decode to populate the fields
         o += "  ProtoDecodableMessage::decode(buffer, length);\n"
-        # Null-terminate fields marked with (null_terminate) = true in-place.
-        # Safe: decode is complete, byte after string was already parsed (next field tag)
-        # or is the +1 reserved byte at end of rx_buf_.
-        for field_name in null_terminate_fields:
-            o += f"  if (!this->{field_name}.empty()) {{\n"
-            o += f"    const_cast<char *>(this->{field_name}.c_str())[this->{field_name}.size()] = '\\0';\n"
-            o += "  }\n"
         o += "}\n"
         cpp += o
         # Generate the decode() declaration in header (public method)

tests/components/serial_proxy/common.yaml

@@ -0,0 +1,10 @@
+wifi:
+  ssid: MySSID
+  password: password1
+
+api:
+
+serial_proxy:
+  - id: serial_proxy_1
+    name: Test Serial Port
+    port_type: RS232

tests/components/serial_proxy/test.esp32-idf.yaml

@@ -0,0 +1,8 @@
+substitutions:
+  tx_pin: GPIO4
+  rx_pin: GPIO5
+
+packages:
+  uart: !include ../../test_build_components/common/uart/esp32-idf.yaml
+
+<<: !include common.yaml

tests/components/serial_proxy/test.esp8266-ard.yaml

@@ -0,0 +1,8 @@
+substitutions:
+  tx_pin: GPIO0
+  rx_pin: GPIO2
+
+packages:
+  uart: !include ../../test_build_components/common/uart/esp8266-ard.yaml
+
+<<: !include common.yaml

tests/components/serial_proxy/test.rp2040-ard.yaml

@@ -0,0 +1,8 @@
+substitutions:
+  tx_pin: GPIO4
+  rx_pin: GPIO5
+
+packages:
+  uart: !include ../../test_build_components/common/uart/rp2040-ard.yaml
+
+<<: !include common.yaml