BLE name overiden with "usb_product" name if too long

[spfmoby]

1. flash a T1000e (that's what I have on hand) with any recent bluetooth companion firmware (I tried both 1.12, 1.13 and even a nightly)
2. with the meshcore app, connect to the device, and set a name of 23 chars or longer (just simple alphanum chars are enough to create the problem)
3. reboot the device

Next time when you want to connect to the node, the Bluetooth name displays "T1000-E-BOOT" instead of the "Meshcore-nameofthedevice").
The "T1000-E-BOOT" is the name that is set as "usb_product" in boards/tracker-t1000-e.json

What is really weird is that if you set a device name of 22 chars, the BLE name is correct AND trimmed to its firsts 20 chars.

Suggestion: whatever node name length is set, just use the trimmed name.

[andrewdefilippis]

TL;DR - Need to update firmware to properly truncate the name.

---

Research: T1000-E BLE Device Name Bug

Problem Statement

A user reported that the BLE advertised device name depends on the node name length:

Node name length	BLE name observed
1–20 chars	MeshCore-<nodename> (correct)
21–22 chars	Correct but truncated to show only 20 chars of node name
23+ chars	T1000-E-BOOT (wrong — this is the USB bootloader name)

The problem occurs with any characters (not just special chars).

---

Root Cause

The Nordic SoftDevice S140 v7.3.0 imposes a default maximum GAP device name length of 31 bytes. Any attempt to set a longer name via sd_ble_gap_device_name_set() silently fails (returns NRF_ERROR_DATA_SIZE), and the Bluefruit library's setName() wrapper does not check the return value.

Why 31 bytes?

The SoftDevice has a configurable device name length via BLE_GAP_CFG_DEVICE_NAME, but the Bluefruit library never configures it (the call is commented out in bluefruit.cpp:365–367):

// bluefruit.cpp:364-367
// Device Name
//  varclr(&blecfg);
//  blecfg.gap_cfg.device_name_cfg =
//  VERIFY_STATUS( sd_ble_cfg_set(BLE_GAP_CFG_DEVICE_NAME, &blecfg, ram_start) );

Therefore the SoftDevice uses its default:

// ble_gap.h:541
#define BLE_GAP_DEVNAME_DEFAULT_LEN  31  // Default max device name length

From the Nordic documentation (ble_gap.h:1460–1463):

If the device name is not configured, the default device name will be BLE_GAP_DEVNAME_DEFAULT, the maximum device name length will be BLE_GAP_DEVNAME_DEFAULT_LEN, vloc will be set to BLE_GATTS_VLOC_STACK and the device name will have no write access.

Failure chain (on main branch)

SerialBLEInterface::begin(prefix="MeshCore-", name=<node_name>, pin_code)
│
├─ 1. Bluefruit.begin()
│     └─ sd_ble_gap_device_name_set("T1000-E-BOOT")  ← sets GAP name to USB_PRODUCT (12 chars, succeeds)
│
├─ 2. Bluefruit.setName("MeshCore-<node_name>")
│     └─ sd_ble_gap_device_name_set("MeshCore-<node_name>")
│        ├─ strlen ≤ 31  →  NRF_SUCCESS       →  GAP name = "MeshCore-<node_name>"
│        └─ strlen > 31  →  NRF_ERROR_DATA_SIZE (SILENT FAIL) → GAP name stays "T1000-E-BOOT"
│
├─ 3. Bluefruit.ScanResponse.addName()
│     └─ Bluefruit.getName()  →  reads current GAP name
│        └─ sd_ble_gap_device_name_get() returns whatever the GAP name is
│
└─ Result: scanner sees the GAP name (correct or "T1000-E-BOOT")

Exact thresholds

• BLE_NAME_PREFIX = "MeshCore-" = 9 bytes
• Max GAP device name (SoftDevice default) = 31 bytes
• Max node_name that fits: 31 - 9 = 22 characters
• Node name of 23+ chars: total = 9 + 23 = 32 bytes → exceeds 31-byte limit → sd_ble_gap_device_name_set() fails

This matches the user's report exactly.

Scan response truncation (secondary effect)

The addName() function in the Bluefruit library (BLEAdvertising.cpp:178–195) puts the name in the 31-byte scan response packet. The overhead per AD element is 2 bytes (1 length + 1 type). Since ScanResponse._count = 0 when addName() is called (nothing else is added to ScanResponse), the max name that fits fully is 31 - 2 = 29 bytes.

For node names of 21–22 chars (total 30–31 bytes):

• sd_ble_gap_device_name_set() succeeds (30–31 ≤ 31)
• addName() detects overflow: 0 + 30 + 2 = 32 > 31
• Truncates to 29 bytes and uses BLE_GAP_AD_TYPE_SHORT_LOCAL_NAME
• Result: "MeshCore-" (9) + first 20 chars of node_name = 29 bytes → matches user's "truncated to 20 chars"

// BLEAdvertising.cpp:178-195
bool BLEAdvertisingData::addName(void)
{
  char name[BLE_GAP_ADV_SET_DATA_SIZE_MAX+1];  // 32-byte buffer

  uint8_t type = BLE_GAP_AD_TYPE_COMPLETE_LOCAL_NAME;
  uint8_t len  = Bluefruit.getName(name, sizeof(name));

  if (_count + len + 2 > BLE_GAP_ADV_SET_DATA_SIZE_MAX)  // doesn't fit?
  {
    type = BLE_GAP_AD_TYPE_SHORT_LOCAL_NAME;
    len  = BLE_GAP_ADV_SET_DATA_SIZE_MAX - (_count+2);   // truncate to fit
  }

  VERIFY( addData(type, name, len) );
  return type == BLE_GAP_AD_TYPE_COMPLETE_LOCAL_NAME;
}

---

Key Constants and Limits

Constant	Value	Source
BLE_GAP_DEVNAME_DEFAULT_LEN	31	ble_gap.h:541 (SoftDevice default max GAP name)
BLE_GAP_DEVNAME_MAX_LEN	248	ble_gap.h:542 (absolute max, requires config)
BLE_GAP_ADV_SET_DATA_SIZE_MAX	31	ble_gap.h:246 (max advertising/scan response packet)
CFG_MAX_DEVNAME_LEN	32	bluefruit_common.h:45 (Bluefruit library internal)
node_name[32]	31 chars + NUL	NodePrefs.h:13 (max user-settable node name)
BLE_NAME_PREFIX	"MeshCore-" (9 bytes)	MyMesh.h:67
USB_PRODUCT (T1000-E)	"T1000-E-BOOT" (12 bytes)	boards/tracker-t1000-e.json:16
dev_name buffer	48 bytes (32+16)	SerialBLEInterface.cpp:140

---

Affected Code Paths

1. SerialBLEInterface::begin() (src/helpers/nrf52/SerialBLEInterface.cpp:126)

The BLE initialization function that combines prefix + node_name and sets the BLE device name.

2. Bluefruit::setName() (bluefruit.cpp:523–527)

void AdafruitBluefruit::setName (char const * str)
{
  ble_gap_conn_sec_mode_t sec_mode = BLE_SECMODE_OPEN;
  sd_ble_gap_device_name_set(&sec_mode, (uint8_t const *) str, strlen(str));
  // ^^^ Return value NOT checked! Silent failure for names > 31 bytes.
}

3. Bluefruit::begin() (bluefruit.cpp:461–463)

// Default device name — always overwrites any previously set name
ble_gap_conn_sec_mode_t sec_mode = BLE_SECMODE_OPEN;
VERIFY_STATUS(sd_ble_gap_device_name_set(&sec_mode,
    (uint8_t const *) CFG_DEFAULT_NAME, strlen(CFG_DEFAULT_NAME)), false);

4. BLEAdvertisingData::addName() (BLEAdvertising.cpp:178–195)

Reads the GAP name and adds it to the scan response. Has its own 29-byte truncation logic.

5. Node name validation (src/helpers/CommonCLI.cpp:475–479)

Sets node names via CLI. Uses strncpy with sizeof(_prefs->node_name) = 32. No length validation against BLE limits.

6. ESP32 variant (src/helpers/esp32/SerialBLEInterface.cpp:27)

Uses BLEDevice::init(dev_name) — no SoftDevice constraint. ESP32 BLE stack handles longer names without issue.

---

Summary of Three Distinct Problems

Problem 1: SoftDevice max_len (root cause — names 23+ chars)

sd_ble_gap_device_name_set() fails silently when name > 31 bytes because BLE_GAP_CFG_DEVICE_NAME is not configured and the default max is 31.

Problem 2: Scan response truncation (cosmetic — names 21–22 chars)

BLEAdvertisingData::addName() truncates names longer than 29 bytes to fit the 31-byte scan response packet. This is BLE spec behavior and acceptable, but users may not expect it.

Problem 3: No BLE-aware name validation

CommonCLI allows node names up to 31 chars, but only 22 chars work correctly with the "MeshCore-" prefix over BLE. There is no warning or truncation at the point where the name is set.

---

Related Files

File	Role
src/helpers/nrf52/SerialBLEInterface.cpp	NRF52 BLE initialization
src/helpers/nrf52/SerialBLEInterface.h	NRF52 BLE interface definition
src/helpers/esp32/SerialBLEInterface.cpp	ESP32 BLE initialization (no issue)
examples/companion_radio/main.cpp:154	Calls serial_interface.begin()
examples/companion_radio/MyMesh.h:67	Defines BLE_NAME_PREFIX
examples/companion_radio/NodePrefs.h:13	Defines node_name[32]
src/helpers/CommonCLI.cpp:475	CLI node name setter
boards/tracker-t1000-e.json:16	USB_PRODUCT = "T1000-E-BOOT"
Bluefruit library (read-only):
bluefruit.cpp:365–367	Commented-out BLE_GAP_CFG_DEVICE_NAME config
bluefruit.cpp:461–463	begin() sets name to CFG_DEFAULT_NAME
bluefruit.cpp:523–527	setName() — no return value check
BLEAdvertising.cpp:178–195	addName() — scan response truncation logic
ble_gap.h:541	BLE_GAP_DEVNAME_DEFAULT_LEN = 31

---

Potential Fix Approaches

Approach A: Truncate BLE name to 31 bytes in SerialBLEInterface::begin()

• Simplest fix — truncate dev_name to 31 chars before calling Bluefruit.setName()
• Pro: No library changes needed, works within existing SoftDevice constraints
• Con: Long node names get silently truncated in BLE advertising; the scan response will further truncate to 29 visible chars
• Effective max node name for BLE: 22 chars (31 - 9 prefix)

Approach B: Truncate BLE name + warn/limit in CommonCLI

• Truncate in begin() as in A, plus add a warning or hard limit in the CLI when setting names > 22 chars
• Pro: User gets feedback when setting a name that will be truncated
• Con: Changes validation logic; other platforms (ESP32) don't have this constraint

Approach C: Configure BLE_GAP_CFG_DEVICE_NAME with larger max_len

• Set max_len to 41 (9 prefix + 32 node_name max) via sd_ble_cfg_set() before sd_ble_enable()
• This requires modifying the Bluefruit library or injecting the config before Bluefruit.begin()
• Pro: Supports full node names up to 32 chars at the GAP level; scan response would still truncate to 29 visible chars
• Con: Requires forking/patching the Bluefruit library; uses more SoftDevice RAM

Approach D: Truncate BLE name to 29 bytes (scan response optimized)

• Truncate to 29 chars (the scan response maximum) instead of 31
• Pro: The advertised name is always complete (COMPLETE_LOCAL_NAME type), no SHORT_LOCAL_NAME truncation
• Con: 2 fewer chars than Approach A (max node name: 20 chars instead of 22)
• Effective max node name for BLE: 20 chars (29 - 9 prefix)

Recommended: Approach A with elements of B

• Truncate dev_name to 31 chars in begin() (fixes the crash/fallback)
• Ensure setName() is called AFTER Bluefruit.begin() (restore main branch order)
• Optionally truncate to 29 for cleaner scan response advertising
• Consider a CLI warning for names that will be BLE-truncated (optional, lower priority)

[spfmoby]

The BLE name is not very important, so if it is truncated without any warning, it is not a big deal. The only important thing is that it is properly set with the "MeshCore-" prefix (otherwise for example you can't connect to it with meshcore-open anymore) and that the rest gives information about the node (to differentiate them if you have multiple ones).

[justinormont]

On a Heltec v4 (and likely v3), too long of a name causes the full bluetooth name to be "ESP32".

Secondarily, without the "MeshCore-" prefix, MeshCore-Open (current version of alpha9, and before) filters out (code, code) the device name "ESP32" and doesn't allow you to connect to it.

Next release of MeshCore-Open fixes this by instead searching for the service advertisement by UUID (code, commit), and should let you connect to the misnamed device.

Other client apps, like the web version on Windows/macOS successfully can connect to the misnamed device.

Noted so others don't waste hours attempting to figure out why their MeshCore device is not showing up on their Android/iPhone.

[github-actions]

This issue is stale because it has been open for 60 days with no activity. Remove the stale label or add a comment if this issue is still relevant, otherwise this issue will automatically close in 7 days.

[justinormont]

This issue is stale because it has been open for 60 days with no activity. Remove the stale label or add a comment if this issue is still relevant, otherwise this issue will automatically close in 7 days.

Still an issue.