[core] Add a name truncation helper and keep the MAC suffix in the nRF52 BLE name (#19768)

esphome/components/esp32_ble/ble.cpp

@@ -350,19 +350,8 @@ bool ESP32BLE::ble_setup_() {
     }
   } else {
     const auto &app_name = App.get_name();
-    size_t name_len = app_name.length();
-    if (name_len > 20) {
-      if (App.is_name_add_mac_suffix_enabled()) {
-        // Keep first 13 chars and last 7 chars (MAC suffix), remove middle
-        memcpy(name_buffer, app_name.c_str(), 13);
-        memcpy(name_buffer + 13, app_name.c_str() + name_len - 7, 7);
-      } else {
-        memcpy(name_buffer, app_name.c_str(), 20);
-      }
-      name_buffer[20] = '\0';
-    } else {
-      memcpy(name_buffer, app_name.c_str(), name_len + 1);  // Include null terminator
-    }
+    truncate_name_to(name_buffer, sizeof(name_buffer), app_name.c_str(), app_name.length(),
+                     App.is_name_add_mac_suffix_enabled() ? MAC_ADDRESS_SUFFIX_WITH_SEPARATOR_LEN : 0);
     device_name = name_buffer;
   }
 

esphome/components/wifi/wifi_component.cpp

@@ -1048,30 +1048,17 @@ void WiFiComponent::setup_ap_config_() {
     return;
 
   if (this->ap_.ssid_.empty()) {
-    // Build AP SSID from app name without heap allocation
-    // WiFi SSID max is 32 bytes, with MAC suffix we keep first 25 + last 7
+    // Build AP SSID from app name without heap allocation; WiFi SSID max is 32 bytes
     static constexpr size_t AP_SSID_MAX_LEN = 32;
-    static constexpr size_t AP_SSID_PREFIX_LEN = 25;
-    static constexpr size_t AP_SSID_SUFFIX_LEN = 7;
 
     const auto &app_name = App.get_name();
-    const char *name_ptr = app_name.c_str();
-    size_t name_len = app_name.length();
-
-    if (name_len <= AP_SSID_MAX_LEN) {
+    if (app_name.length() <= AP_SSID_MAX_LEN) {
       // Name fits, use directly
-      this->ap_.set_ssid(name_ptr);
+      this->ap_.set_ssid(app_name.c_str());
     } else {
-      // Name too long, need to truncate into stack buffer
       char ssid_buf[AP_SSID_MAX_LEN + 1];
-      if (App.is_name_add_mac_suffix_enabled()) {
-        // Keep first 25 chars and last 7 chars (MAC suffix), remove middle
-        memcpy(ssid_buf, name_ptr, AP_SSID_PREFIX_LEN);
-        memcpy(ssid_buf + AP_SSID_PREFIX_LEN, name_ptr + name_len - AP_SSID_SUFFIX_LEN, AP_SSID_SUFFIX_LEN);
-      } else {
-        memcpy(ssid_buf, name_ptr, AP_SSID_MAX_LEN);
-      }
-      ssid_buf[AP_SSID_MAX_LEN] = '\0';
+      truncate_name_to(ssid_buf, sizeof(ssid_buf), app_name.c_str(), app_name.length(),
+                       App.is_name_add_mac_suffix_enabled() ? MAC_ADDRESS_SUFFIX_WITH_SEPARATOR_LEN : 0);
       this->ap_.set_ssid(ssid_buf);
     }
   }

esphome/components/zephyr_ble_server/ble_server.cpp

@@ -1,6 +1,8 @@
 #ifdef USE_ZEPHYR
 #include "ble_server.h"
+#include "esphome/core/application.h"
 #include "esphome/core/defines.h"
+#include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
 #include <zephyr/bluetooth/bluetooth.h>
 #include <zephyr/settings/settings.h>
@@ -13,13 +15,8 @@ static k_work advertise_work;  // NOLINT(cppcoreguidelines-avoid-non-const-globa
 
 BLEServer *global_ble_server;  // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
 
-#define DEVICE_NAME CONFIG_BT_DEVICE_NAME
-#define DEVICE_NAME_LEN (sizeof(DEVICE_NAME) - 1)
-
-static const bt_data AD[] = {
-    BT_DATA_BYTES(BT_DATA_FLAGS, (BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)),
-    BT_DATA(BT_DATA_NAME_COMPLETE, DEVICE_NAME, DEVICE_NAME_LEN),
-};
+// What the advertisement has left for the name: the flags take 3 bytes and the name header 2
+static constexpr size_t MAX_ADV_NAME_LEN = BT_GAP_ADV_MAX_ADV_DATA_LEN - 3 - 2;
 
 static const bt_data SD[] = {
 #ifdef USE_OTA
@@ -36,7 +33,19 @@ static void advertise(k_work *work) {
     ESP_LOGE(TAG, "Advertising failed to stop (rc %d)", rc);
   }
 
-  rc = bt_le_adv_start(ADV_PARAM, AD, ARRAY_SIZE(AD), SD, ARRAY_SIZE(SD));
+  // Zephyr would cut the end of a long name, which is where the MAC suffix is
+  char name[MAX_ADV_NAME_LEN + 1];
+  const auto &app_name = App.get_name();
+  const size_t name_len =
+      truncate_name_to(name, sizeof(name), app_name.c_str(), app_name.length(),
+                       App.is_name_add_mac_suffix_enabled() ? MAC_ADDRESS_SUFFIX_WITH_SEPARATOR_LEN : 0);
+  const uint8_t name_type = name_len < app_name.length() ? BT_DATA_NAME_SHORTENED : BT_DATA_NAME_COMPLETE;
+  const bt_data ad[] = {
+      BT_DATA_BYTES(BT_DATA_FLAGS, (BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)),
+      BT_DATA(name_type, name, static_cast<uint8_t>(name_len)),
+  };
+
+  rc = bt_le_adv_start(ADV_PARAM, ad, ARRAY_SIZE(ad), SD, ARRAY_SIZE(SD));
   if (rc) {
     ESP_LOGE(TAG, "Advertising failed to start (rc %d)", rc);
     return;

esphome/core/helpers.cpp

@@ -293,6 +293,26 @@ size_t make_name_with_suffix_to(char *buffer, size_t buffer_size, const char *na
   return total_len;
 }
 
+size_t truncate_name_to(char *buffer, size_t buffer_size, const char *name, size_t name_len, size_t keep_suffix_len) {
+  if (buffer_size == 0) {
+    return 0;
+  }
+  const size_t max_len = buffer_size - 1;
+  if (name_len <= max_len) {
+    memcpy(buffer, name, name_len);
+    buffer[name_len] = '\0';
+    return name_len;
+  }
+  if (keep_suffix_len > max_len) {
+    keep_suffix_len = max_len;
+  }
+  const size_t head_len = max_len - keep_suffix_len;
+  memcpy(buffer, name, head_len);
+  memcpy(buffer + head_len, name + name_len - keep_suffix_len, keep_suffix_len);
+  buffer[max_len] = '\0';
+  return max_len;
+}
+
 // Parsing & formatting
 
 size_t parse_hex(const char *str, size_t length, uint8_t *data, size_t count) {

esphome/core/helpers.h

@@ -1256,6 +1256,16 @@ static constexpr size_t MAX_NAME_WITH_SUFFIX_SIZE = 128;
 size_t make_name_with_suffix_to(char *buffer, size_t buffer_size, const char *name, size_t name_len, char sep,
                                 const char *suffix_ptr, size_t suffix_len);
 
+/// Length of the suffix name_add_mac_suffix appends: "-" plus 6 characters of the MAC address
+static constexpr size_t MAC_ADDRESS_SUFFIX_WITH_SEPARATOR_LEN = 7;
+
+/// Copy a name into a buffer, cutting it when it does not fit.
+/// A name that is cut keeps its last keep_suffix_len characters (for example a MAC suffix) and loses
+/// the middle instead; pass 0 to cut the end.
+/// @param buffer Output buffer; holds at most buffer_size - 1 characters plus the null terminator
+/// @return Length written (excluding null terminator)
+size_t truncate_name_to(char *buffer, size_t buffer_size, const char *name, size_t name_len, size_t keep_suffix_len);
+
 ///@}
 
 /// @name Parsing & formatting

tests/components/core/test_helpers.cpp

@@ -7,6 +7,47 @@
 
 namespace esphome::core::testing {
 
+// --- truncate_name_to() ---
+
+TEST(TruncateNameTo, NameThatFitsIsCopied) {
+  char buffer[21];
+  EXPECT_EQ(truncate_name_to(buffer, sizeof(buffer), "kitchen", 7, 7), 7u);
+  EXPECT_STREQ(buffer, "kitchen");
+}
+
+TEST(TruncateNameTo, NameOfExactlyTheLimitIsCopied) {
+  char buffer[8];
+  EXPECT_EQ(truncate_name_to(buffer, sizeof(buffer), "kitchen", 7, 0), 7u);
+  EXPECT_STREQ(buffer, "kitchen");
+}
+
+TEST(TruncateNameTo, CutsTheEndWithoutASuffix) {
+  char buffer[21];
+  const char *name = "a-very-long-device-name-here";
+  EXPECT_EQ(truncate_name_to(buffer, sizeof(buffer), name, strlen(name), 0), 20u);
+  EXPECT_STREQ(buffer, "a-very-long-device-n");
+}
+
+TEST(TruncateNameTo, KeepsTheSuffixAndRemovesTheMiddle) {
+  char buffer[21];
+  const char *name = "a-very-long-device-name-a1b2c3";
+  EXPECT_EQ(truncate_name_to(buffer, sizeof(buffer), name, strlen(name), 7), 20u);
+  EXPECT_STREQ(buffer, "a-very-long-d-a1b2c3");
+}
+
+TEST(TruncateNameTo, SuffixLongerThanTheBufferIsCut) {
+  char buffer[5];
+  const char *name = "name-a1b2c3";
+  EXPECT_EQ(truncate_name_to(buffer, sizeof(buffer), name, strlen(name), 7), 4u);
+  EXPECT_STREQ(buffer, "b2c3");
+}
+
+TEST(TruncateNameTo, ZeroBufferSize) {
+  char buffer[1] = {'x'};
+  EXPECT_EQ(truncate_name_to(buffer, 0, "name", 4, 0), 0u);
+  EXPECT_EQ(buffer[0], 'x');
+}
+
 // --- format_hex_to() ---
 
 TEST(FormatHexTo, Basic) {