[udp] Keep addresses in a shared flash table (#20085)

esphome/components/udp/__init__.py

@@ -124,7 +124,15 @@ async def to_code(config: ConfigType) -> None:
         cg.add(var.set_broadcast_port(conf_port[CONF_BROADCAST_PORT]))
     if (listen_address := str(config[CONF_LISTEN_ADDRESS])) != "255.255.255.255":
         cg.add(var.set_listen_address(listen_address))
-    cg.add(var.set_addresses([str(addr) for addr in config[CONF_ADDRESSES]]))
+    # Shared flash table ended by nullptr, so the component stores only a pointer.
+    if addresses := [str(addr) for addr in config[CONF_ADDRESSES]]:
+        cg.add(
+            var.set_addresses(
+                cg.shared_progmem_array(
+                    "udp_addresses", cg.const_char_ptr, [*addresses, cg.nullptr]
+                )
+            )
+        )
     for conf in config.get(CONF_ON_RECEIVE, []):
         trigger_id = cg.new_Pvariable(conf[CONF_TRIGGER_ID])
         trigger = await automation.build_automation(trigger_id, trigger_argtype, conf)

esphome/components/udp/udp_component.cpp

@@ -11,7 +11,8 @@ static const char *const TAG = "udp";
 
 void UDPComponent::setup() {
 #if defined(USE_SOCKET_IMPL_BSD_SOCKETS) || defined(USE_SOCKET_IMPL_LWIP_SOCKETS)
-  for (const auto &address : this->addresses_) {
+  for (const char *const *it = this->addresses_; it != nullptr && *it != nullptr; it++) {
+    const char *address = *it;
     struct sockaddr saddr {};
     if (socket::set_sockaddr(&saddr, sizeof(saddr), address, this->broadcast_port_) == 0) {
       ESP_LOGW(TAG, "Invalid address %s", address);
@@ -97,7 +98,8 @@ void UDPComponent::setup() {
 #endif
 #ifdef USE_SOCKET_IMPL_LWIP_TCP
   // 8266 and RP2040 `Duino
-  for (const auto &address : this->addresses_) {
+  for (const char *const *it = this->addresses_; it != nullptr && *it != nullptr; it++) {
+    const char *address = *it;
     auto ipaddr = IPAddress();
     if (!ipaddr.fromString(address)) {
       ESP_LOGW(TAG, "Invalid address %s", address);
@@ -138,7 +140,8 @@ void UDPComponent::dump_config() {
                 "  Listen Port: %u\n"
                 "  Broadcast Port: %u",
                 this->listen_port_, this->broadcast_port_);
-  for (const char *address : this->addresses_) {
+  for (const char *const *it = this->addresses_; it != nullptr && *it != nullptr; it++) {
+    const char *address = *it;
     ESP_LOGCONFIG(TAG, "  Address: %s", address);
   }
   if (this->listen_address_.has_value()) {

esphome/components/udp/udp_component.h

@@ -20,9 +20,8 @@ namespace esphome::udp {
 static const size_t MAX_PACKET_SIZE = 508;
 class UDPComponent final : public Component {
  public:
-  void set_addresses(std::initializer_list<const char *> addresses) { this->addresses_ = addresses; }
-  /// Prevent accidental use of std::string which would dangle
-  void set_addresses(std::initializer_list<std::string> addresses) = delete;
+  /// nullptr-terminated table of addresses; must outlive the component.
+  void set_addresses(const char *const *addresses) { this->addresses_ = addresses; }
   void set_listen_address(const char *listen_addr) { this->listen_address_ = network::IPAddress(listen_addr); }
   void set_listen_port(uint16_t port) { this->listen_port_ = port; }
   void set_broadcast_port(uint16_t port) { this->broadcast_port_ = port; }
@@ -52,7 +51,7 @@ class UDPComponent final : public Component {
   std::vector<IPAddress> ipaddrs_{};
   WiFiUDP udp_client_{};
 #endif
-  FixedVector<const char *> addresses_{};
+  const char *const *addresses_{nullptr};
 
   optional<network::IPAddress> listen_address_{};
 };

tests/component_tests/udp/config/udp_addresses.yaml

@@ -0,0 +1,14 @@
+esphome:
+  name: test
+
+esp8266:
+  board: d1_mini
+
+wifi:
+  ssid: test
+  password: password1
+
+udp:
+  addresses:
+    - 10.0.0.1
+    - 10.0.0.2

tests/component_tests/udp/config/udp_no_addresses.yaml

@@ -0,0 +1,12 @@
+esphome:
+  name: test
+
+esp8266:
+  board: d1_mini
+
+wifi:
+  ssid: test
+  password: password1
+
+udp:
+  addresses: []

tests/component_tests/udp/test_udp_addresses.py

@@ -0,0 +1,29 @@
+"""Tests for the udp component codegen."""
+
+from collections.abc import Callable
+from pathlib import Path
+
+
+def test_addresses_are_a_progmem_table(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    """Addresses live in a nullptr-terminated flash table instead of a heap vector."""
+    main_cpp = generate_main(component_config_path("udp_addresses.yaml"))
+
+    assert (
+        "static constexpr const char * udp_addresses[] PROGMEM = "
+        '{"10.0.0.1", "10.0.0.2", nullptr};' in main_cpp
+    )
+    assert "->set_addresses(udp_addresses);" in main_cpp
+
+
+def test_empty_addresses_emit_no_table(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    """An empty address list leaves the pointer null instead of emitting a table."""
+    main_cpp = generate_main(component_config_path("udp_no_addresses.yaml"))
+
+    assert "udp_addresses" not in main_cpp
+    assert "set_addresses(" not in main_cpp