[wifi] Eliminate heap allocations in dump_config logging (#12664)

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

esphome/components/wifi/wifi_component.cpp

@@ -899,12 +899,20 @@ void WiFiComponent::print_connect_params_() {
     ESP_LOGCONFIG(TAG, "  Disabled");
     return;
   }
+  // Use stack buffers for IP address formatting to avoid heap allocations
+  char ip_buf[network::IP_ADDRESS_BUFFER_SIZE];
   for (auto &ip : wifi_sta_ip_addresses()) {
     if (ip.is_set()) {
-      ESP_LOGCONFIG(TAG, "  IP Address: %s", ip.str().c_str());
+      ESP_LOGCONFIG(TAG, "  IP Address: %s", ip.str_to(ip_buf));
     }
   }
   int8_t rssi = wifi_rssi();
+  // Use stack buffers for SSID and all IP addresses to avoid heap allocations
+  char ssid_buf[SSID_BUFFER_SIZE];
+  char subnet_buf[network::IP_ADDRESS_BUFFER_SIZE];
+  char gateway_buf[network::IP_ADDRESS_BUFFER_SIZE];
+  char dns1_buf[network::IP_ADDRESS_BUFFER_SIZE];
+  char dns2_buf[network::IP_ADDRESS_BUFFER_SIZE];
   ESP_LOGCONFIG(TAG,
                 "  SSID: " LOG_SECRET("'%s'") "\n"
                                               "  BSSID: " LOG_SECRET("%s") "\n"
@@ -915,9 +923,9 @@ void WiFiComponent::print_connect_params_() {
                                                                            "  Gateway: %s\n"
                                                                            "  DNS1: %s\n"
                                                                            "  DNS2: %s",
-                wifi_ssid().c_str(), bssid_s, App.get_name().c_str(), rssi, LOG_STR_ARG(get_signal_bars(rssi)),
+                wifi_ssid_to(ssid_buf), bssid_s, App.get_name().c_str(), rssi, LOG_STR_ARG(get_signal_bars(rssi)),
-                get_wifi_channel(), wifi_subnet_mask_().str().c_str(), wifi_gateway_ip_().str().c_str(),
+                get_wifi_channel(), wifi_subnet_mask_().str_to(subnet_buf), wifi_gateway_ip_().str_to(gateway_buf),
-                wifi_dns_ip_(0).str().c_str(), wifi_dns_ip_(1).str().c_str());
+                wifi_dns_ip_(0).str_to(dns1_buf), wifi_dns_ip_(1).str_to(dns2_buf));
 #ifdef ESPHOME_LOG_HAS_VERBOSE
   if (const WiFiAP *config = this->get_selected_sta_(); config && config->has_bssid()) {
     ESP_LOGV(TAG, "  Priority: %d", this->get_sta_priority(config->get_bssid()));

esphome/components/wifi/wifi_component.h

@@ -61,6 +61,9 @@ namespace esphome::wifi {
 /// Sentinel value for RSSI when WiFi is not connected
 static constexpr int8_t WIFI_RSSI_DISCONNECTED = -127;
 
+/// Buffer size for SSID (IEEE 802.11 max 32 bytes + null terminator)
+static constexpr size_t SSID_BUFFER_SIZE = 33;
+
 struct SavedWifiSettings {
   char ssid[33];
   char password[65];
@@ -408,6 +411,9 @@ class WiFiComponent : public Component {
 
   network::IPAddresses wifi_sta_ip_addresses();
   std::string wifi_ssid();
+  /// Write SSID to buffer without heap allocation.
+  /// Returns pointer to buffer, or empty string if not connected.
+  const char *wifi_ssid_to(std::span<char, SSID_BUFFER_SIZE> buffer);
   bssid_t wifi_bssid();
 
   int8_t wifi_rssi();

esphome/components/wifi/wifi_component_esp8266.cpp

@@ -913,6 +913,18 @@ bssid_t WiFiComponent::wifi_bssid() {
   return bssid;
 }
 std::string WiFiComponent::wifi_ssid() { return WiFi.SSID().c_str(); }
+const char *WiFiComponent::wifi_ssid_to(std::span<char, SSID_BUFFER_SIZE> buffer) {
+  struct station_config conf {};
+  if (!wifi_station_get_config(&conf)) {
+    buffer[0] = '\0';
+    return buffer.data();
+  }
+  // conf.ssid is uint8[32], not null-terminated if full
+  size_t len = strnlen(reinterpret_cast<const char *>(conf.ssid), sizeof(conf.ssid));
+  memcpy(buffer.data(), conf.ssid, len);
+  buffer[len] = '\0';
+  return buffer.data();
+}
 int8_t WiFiComponent::wifi_rssi() {
   if (WiFi.status() != WL_CONNECTED)
     return WIFI_RSSI_DISCONNECTED;

esphome/components/wifi/wifi_component_esp_idf.cpp

@@ -1086,6 +1086,19 @@ std::string WiFiComponent::wifi_ssid() {
   size_t len = strnlen(ssid_s, sizeof(info.ssid));
   return {ssid_s, len};
 }
+const char *WiFiComponent::wifi_ssid_to(std::span<char, SSID_BUFFER_SIZE> buffer) {
+  wifi_ap_record_t info{};
+  esp_err_t err = esp_wifi_sta_get_ap_info(&info);
+  if (err != ESP_OK) {
+    buffer[0] = '\0';
+    return buffer.data();
+  }
+  // info.ssid is uint8[33], but only 32 bytes are SSID data
+  size_t len = strnlen(reinterpret_cast<const char *>(info.ssid), 32);
+  memcpy(buffer.data(), info.ssid, len);
+  buffer[len] = '\0';
+  return buffer.data();
+}
 int8_t WiFiComponent::wifi_rssi() {
   wifi_ap_record_t info;
   esp_err_t err = esp_wifi_sta_get_ap_info(&info);

esphome/components/wifi/wifi_component_libretiny.cpp

@@ -554,6 +554,14 @@ bssid_t WiFiComponent::wifi_bssid() {
   return bssid;
 }
 std::string WiFiComponent::wifi_ssid() { return WiFi.SSID().c_str(); }
+const char *WiFiComponent::wifi_ssid_to(std::span<char, SSID_BUFFER_SIZE> buffer) {
+  // TODO: Find direct LibreTiny API to avoid Arduino String allocation
+  String ssid = WiFi.SSID();
+  size_t len = std::min(static_cast<size_t>(ssid.length()), SSID_BUFFER_SIZE - 1);
+  memcpy(buffer.data(), ssid.c_str(), len);
+  buffer[len] = '\0';
+  return buffer.data();
+}
 int8_t WiFiComponent::wifi_rssi() { return WiFi.status() == WL_CONNECTED ? WiFi.RSSI() : WIFI_RSSI_DISCONNECTED; }
 int32_t WiFiComponent::get_wifi_channel() { return WiFi.channel(); }
 network::IPAddress WiFiComponent::wifi_subnet_mask_() { return {WiFi.subnetMask()}; }

esphome/components/wifi/wifi_component_pico_w.cpp

@@ -214,6 +214,14 @@ bssid_t WiFiComponent::wifi_bssid() {
   return bssid;
 }
 std::string WiFiComponent::wifi_ssid() { return WiFi.SSID().c_str(); }
+const char *WiFiComponent::wifi_ssid_to(std::span<char, SSID_BUFFER_SIZE> buffer) {
+  // TODO: Find direct CYW43 API to avoid Arduino String allocation
+  String ssid = WiFi.SSID();
+  size_t len = std::min(static_cast<size_t>(ssid.length()), SSID_BUFFER_SIZE - 1);
+  memcpy(buffer.data(), ssid.c_str(), len);
+  buffer[len] = '\0';
+  return buffer.data();
+}
 int8_t WiFiComponent::wifi_rssi() { return WiFi.status() == WL_CONNECTED ? WiFi.RSSI() : WIFI_RSSI_DISCONNECTED; }
 int32_t WiFiComponent::get_wifi_channel() { return WiFi.channel(); }