[helpers] Add get_mac_address_into_buffer() (#11700)

esphome/core/helpers.cpp

@@ -643,6 +643,12 @@ std::string get_mac_address_pretty() {
   return format_mac_address_pretty(mac);
 }
 
+void get_mac_address_into_buffer(std::span<char, 13> buf) {
+  uint8_t mac[6];
+  get_mac_address_raw(mac);
+  format_mac_addr_lower_no_sep(mac, buf.data());
+}
+
 #ifndef USE_ESP32
 bool has_custom_mac_address() { return false; }
 #endif

esphome/core/helpers.h

@@ -8,6 +8,7 @@
 #include <iterator>
 #include <limits>
 #include <memory>
+#include <span>
 #include <string>
 #include <type_traits>
 #include <vector>
@@ -1027,6 +1028,10 @@ std::string get_mac_address();
 /// Get the device MAC address as a string, in colon-separated uppercase hex notation.
 std::string get_mac_address_pretty();
 
+/// Get the device MAC address into the given buffer, in lowercase hex notation.
+/// Assumes buffer length is 13 (12 digits for hexadecimal representation followed by null terminator).
+void get_mac_address_into_buffer(std::span<char, 13> buf);
+
 #ifdef USE_ESP32
 /// Set the MAC address to use from the provided byte array (6 bytes).
 void set_mac_address(uint8_t *mac);