[modbus] Use stack buffer instead of heap vector in send()

Replace std::vector<uint8_t> with a fixed stack buffer in Modbus::send()
to eliminate a heap allocation on every Modbus frame transmission. The
maximum frame size is 264 bytes (bounded by the uint8_t payload_len
parameter), so a 270-byte stack buffer is sufficient.

esphome/codegen.py

@@ -87,7 +87,6 @@ from esphome.cpp_types import (  # noqa: F401
     size_t,
     std_ns,
     std_shared_ptr,
-    std_span,
     std_string,
     std_string_ref,
     std_vector,

esphome/components/api/proto.h

@@ -112,12 +112,8 @@ class ProtoVarInt {
     uint64_t result = buffer[0] & 0x7F;
     uint8_t bitpos = 7;
 
-    // A 64-bit varint is at most 10 bytes (ceil(64/7)). Reject overlong encodings
-    // to avoid undefined behavior from shifting uint64_t by >= 64 bits.
-    uint32_t max_len = std::min(len, uint32_t(10));
-
     // Start from the second byte since we've already processed the first
-    for (uint32_t i = 1; i < max_len; i++) {
+    for (uint32_t i = 1; i < len; i++) {
       uint8_t val = buffer[i];
       result |= uint64_t(val & 0x7F) << uint64_t(bitpos);
       bitpos += 7;

esphome/components/modbus/modbus.cpp

@@ -219,39 +219,50 @@ void Modbus::send(uint8_t address, uint8_t function_code, uint16_t start_address
     return;
   }
 
-  std::vector<uint8_t> data;
-  data.push_back(address);
-  data.push_back(function_code);
+  static constexpr size_t ADDR_SIZE = 1;
+  static constexpr size_t FC_SIZE = 1;
+  static constexpr size_t START_ADDR_SIZE = 2;
+  static constexpr size_t NUM_ENTITIES_SIZE = 2;
+  static constexpr size_t BYTE_COUNT_SIZE = 1;
+  static constexpr size_t MAX_PAYLOAD_SIZE = std::numeric_limits<uint8_t>::max();
+  static constexpr size_t CRC_SIZE = 2;
+  static constexpr size_t MAX_FRAME_SIZE =
+      ADDR_SIZE + FC_SIZE + START_ADDR_SIZE + NUM_ENTITIES_SIZE + BYTE_COUNT_SIZE + MAX_PAYLOAD_SIZE + CRC_SIZE;
+  uint8_t data[MAX_FRAME_SIZE];
+  size_t pos = 0;
+
+  data[pos++] = address;
+  data[pos++] = function_code;
   if (this->role == ModbusRole::CLIENT) {
-    data.push_back(start_address >> 8);
-    data.push_back(start_address >> 0);
+    data[pos++] = start_address >> 8;
+    data[pos++] = start_address >> 0;
     if (function_code != ModbusFunctionCode::WRITE_SINGLE_COIL &&
         function_code != ModbusFunctionCode::WRITE_SINGLE_REGISTER) {
-      data.push_back(number_of_entities >> 8);
-      data.push_back(number_of_entities >> 0);
+      data[pos++] = number_of_entities >> 8;
+      data[pos++] = number_of_entities >> 0;
     }
   }
 
   if (payload != nullptr) {
     if (this->role == ModbusRole::SERVER || function_code == ModbusFunctionCode::WRITE_MULTIPLE_COILS ||
         function_code == ModbusFunctionCode::WRITE_MULTIPLE_REGISTERS) {  // Write multiple
-      data.push_back(payload_len);                                        // Byte count is required for write
+      data[pos++] = payload_len;                                          // Byte count is required for write
     } else {
       payload_len = 2;  // Write single register or coil
     }
     for (int i = 0; i < payload_len; i++) {
-      data.push_back(payload[i]);
+      data[pos++] = payload[i];
     }
   }
 
-  auto crc = crc16(data.data(), data.size());
-  data.push_back(crc >> 0);
-  data.push_back(crc >> 8);
+  auto crc = crc16(data, pos);
+  data[pos++] = crc >> 0;
+  data[pos++] = crc >> 8;
 
   if (this->flow_control_pin_ != nullptr)
     this->flow_control_pin_->digital_write(true);
 
-  this->write_array(data);
+  this->write_array(data, pos);
   this->flush();
 
   if (this->flow_control_pin_ != nullptr)
@@ -261,7 +272,7 @@ void Modbus::send(uint8_t address, uint8_t function_code, uint16_t start_address
 #if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE
   char hex_buf[format_hex_pretty_size(MODBUS_MAX_LOG_BYTES)];
 #endif
-  ESP_LOGV(TAG, "Modbus write: %s", format_hex_pretty_to(hex_buf, data.data(), data.size()));
+  ESP_LOGV(TAG, "Modbus write: %s", format_hex_pretty_to(hex_buf, data, pos));
 }
 
 // Helper function for lambdas

esphome/components/packet_transport/packet_transport.cpp

@@ -396,9 +396,9 @@ static bool process_rolling_code(Provider &provider, PacketDecoder &decoder) {
 /**
  * Process a received packet
  */
-void PacketTransport::process_(std::span<const uint8_t> data) {
+void PacketTransport::process_(const std::vector<uint8_t> &data) {
   auto ping_key_seen = !this->ping_pong_enable_;
-  PacketDecoder decoder(data.data(), data.size());
+  PacketDecoder decoder((data.data()), data.size());
   char namebuf[256]{};
   uint8_t byte;
   FuData rdata{};

esphome/components/packet_transport/packet_transport.h

@@ -9,9 +9,8 @@
 #include "esphome/components/binary_sensor/binary_sensor.h"
 #endif
 
-#include <map>
-#include <span>
 #include <vector>
+#include <map>
 
 /**
  * Providing packet encoding functions for exchanging data with a remote host.
@@ -114,7 +113,7 @@ class PacketTransport : public PollingComponent {
   virtual bool should_send() { return true; }
 
   // to be called by child classes when a data packet is received.
-  void process_(std::span<const uint8_t> data);
+  void process_(const std::vector<uint8_t> &data);
   void send_data_(bool all);
   void flush_();
   void add_data_(uint8_t key, const char *id, float data);

esphome/components/udp/__init__.py

@@ -13,7 +13,7 @@ from esphome.components.packet_transport import (
 import esphome.config_validation as cv
 from esphome.const import CONF_DATA, CONF_ID, CONF_PORT, CONF_TRIGGER_ID
 from esphome.core import ID
-from esphome.cpp_generator import MockObj
+from esphome.cpp_generator import literal
 
 CODEOWNERS = ["@clydebarrow"]
 DEPENDENCIES = ["network"]
@@ -23,12 +23,8 @@ MULTI_CONF = True
 udp_ns = cg.esphome_ns.namespace("udp")
 UDPComponent = udp_ns.class_("UDPComponent", cg.Component)
 UDPWriteAction = udp_ns.class_("UDPWriteAction", automation.Action)
-trigger_argname = "data"
-# Listener callback type (non-owning span from UDP component)
-listener_args = cg.std_span.template(cg.uint8.operator("const"))
-listener_argtype = [(listener_args, trigger_argname)]
-# Automation/trigger type (owned vector, safe for deferred actions like delay)
 trigger_args = cg.std_vector.template(cg.uint8)
+trigger_argname = "data"
 trigger_argtype = [(trigger_args, trigger_argname)]
 
 CONF_ADDRESSES = "addresses"
@@ -122,13 +118,7 @@ async def to_code(config):
             trigger_id, trigger_argtype, on_receive
         )
         trigger_lambda = await cg.process_lambda(
-            trigger.trigger(
-                cg.std_vector.template(cg.uint8)(
-                    MockObj(trigger_argname).begin(),
-                    MockObj(trigger_argname).end(),
-                )
-            ),
-            listener_argtype,
+            trigger.trigger(literal(trigger_argname)), trigger_argtype
         )
         cg.add(var.add_listener(trigger_lambda))
         cg.add(var.set_should_listen())

esphome/components/udp/packet_transport/udp_transport.cpp

@@ -12,7 +12,7 @@ bool UDPTransport::should_send() { return network::is_connected(); }
 void UDPTransport::setup() {
   PacketTransport::setup();
   if (!this->providers_.empty() || this->is_encrypted_()) {
-    this->parent_->add_listener([this](std::span<const uint8_t> data) { this->process_(data); });
+    this->parent_->add_listener([this](std::vector<uint8_t> &buf) { this->process_(buf); });
   }
 }
 

esphome/components/udp/udp_component.cpp

@@ -103,8 +103,8 @@ void UDPComponent::setup() {
 }
 
 void UDPComponent::loop() {
+  auto buf = std::vector<uint8_t>(MAX_PACKET_SIZE);
   if (this->should_listen_) {
-    std::array<uint8_t, MAX_PACKET_SIZE> buf;
     for (;;) {
 #if defined(USE_SOCKET_IMPL_BSD_SOCKETS) || defined(USE_SOCKET_IMPL_LWIP_SOCKETS)
       auto len = this->listen_socket_->read(buf.data(), buf.size());
@@ -116,9 +116,9 @@ void UDPComponent::loop() {
 #endif
       if (len <= 0)
         break;
-      size_t packet_len = static_cast<size_t>(len);
-      ESP_LOGV(TAG, "Received packet of length %zu", packet_len);
-      this->packet_listeners_.call(std::span<const uint8_t>(buf.data(), packet_len));
+      buf.resize(len);
+      ESP_LOGV(TAG, "Received packet of length %zu", len);
+      this->packet_listeners_.call(buf);
     }
   }
 }

esphome/components/udp/udp_component.h

@@ -10,9 +10,7 @@
 #ifdef USE_SOCKET_IMPL_LWIP_TCP
 #include <WiFiUdp.h>
 #endif
-#include <array>
 #include <initializer_list>
-#include <span>
 #include <vector>
 
 namespace esphome::udp {
@@ -28,7 +26,7 @@ class UDPComponent : public Component {
   void set_broadcast_port(uint16_t port) { this->broadcast_port_ = port; }
   void set_should_broadcast() { this->should_broadcast_ = true; }
   void set_should_listen() { this->should_listen_ = true; }
-  void add_listener(std::function<void(std::span<const uint8_t>)> &&listener) {
+  void add_listener(std::function<void(std::vector<uint8_t> &)> &&listener) {
     this->packet_listeners_.add(std::move(listener));
   }
   void setup() override;
@@ -43,7 +41,7 @@ class UDPComponent : public Component {
   uint16_t broadcast_port_{};
   bool should_broadcast_{};
   bool should_listen_{};
-  CallbackManager<void(std::span<const uint8_t>)> packet_listeners_{};
+  CallbackManager<void(std::vector<uint8_t> &)> packet_listeners_{};
 
 #if defined(USE_SOCKET_IMPL_BSD_SOCKETS) || defined(USE_SOCKET_IMPL_LWIP_SOCKETS)
   std::unique_ptr<socket::Socket> broadcast_socket_ = nullptr;

esphome/cpp_types.py

@@ -12,7 +12,6 @@ std_shared_ptr = std_ns.class_("shared_ptr")
 std_string = std_ns.class_("string")
 std_string_ref = std_ns.namespace("string &")
 std_vector = std_ns.class_("vector")
-std_span = std_ns.class_("span")
 uint8 = global_ns.namespace("uint8_t")
 uint16 = global_ns.namespace("uint16_t")
 uint32 = global_ns.namespace("uint32_t")

tests/integration/test_udp.py

@@ -93,34 +93,23 @@ async def udp_listener(port: int = 0) -> AsyncGenerator[tuple[int, UDPReceiver]]
         sock.close()
 
 
-def _get_free_udp_port() -> int:
-    """Get a free UDP port by binding to port 0 and releasing."""
-    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
-    sock.bind(("127.0.0.1", 0))
-    port = sock.getsockname()[1]
-    sock.close()
-    return port
-
-
 @pytest.mark.asyncio
 async def test_udp_send_receive(
     yaml_config: str,
     run_compiled: RunCompiledFunction,
     api_client_connected: APIClientConnectedFactory,
 ) -> None:
-    """Test UDP component can send and receive messages."""
+    """Test UDP component can send messages with multiple addresses configured."""
+    # Track log lines to verify dump_config output
     log_lines: list[str] = []
-    receive_event = asyncio.Event()
 
     def on_log_line(line: str) -> None:
         log_lines.append(line)
-        if "Received UDP:" in line:
-            receive_event.set()
 
-    async with udp_listener() as (broadcast_port, receiver):
-        listen_port = _get_free_udp_port()
-        config = yaml_config.replace("UDP_LISTEN_PORT_PLACEHOLDER", str(listen_port))
-        config = config.replace("UDP_BROADCAST_PORT_PLACEHOLDER", str(broadcast_port))
+    async with udp_listener() as (udp_port, receiver):
+        # Replace placeholders in the config
+        config = yaml_config.replace("UDP_LISTEN_PORT_PLACEHOLDER", str(udp_port + 1))
+        config = config.replace("UDP_BROADCAST_PORT_PLACEHOLDER", str(udp_port))
 
         async with (
             run_compiled(config, line_callback=on_log_line),
@@ -180,19 +169,3 @@ async def test_udp_send_receive(
             assert "Address: 127.0.0.2" in log_text, (
                 f"Address 127.0.0.2 not found in dump_config. Log: {log_text[-2000:]}"
             )
-
-            # Test receiving a UDP packet (exercises on_receive with std::span)
-            test_payload = b"TEST_RECEIVE_UDP"
-            send_sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
-            try:
-                send_sock.sendto(test_payload, ("127.0.0.1", listen_port))
-            finally:
-                send_sock.close()
-
-            try:
-                await asyncio.wait_for(receive_event.wait(), timeout=5.0)
-            except TimeoutError:
-                pytest.fail(
-                    f"on_receive did not fire. Expected 'Received UDP:' in logs. "
-                    f"Last log lines: {log_lines[-20:]}"
-                )