[SOLVED] Qt 5.7 QBluetooth LE GATT Server Example with Raspberry Pi 3 and BlueZ 5.39

I am trying to run the Qt 5.7 beta QBluetooth GATT Server example ( https://doc-snapshots.qt.io/qt5-dev/qtbluetooth-heartrate-server-example.html ) on a Raspberry Pi 3 with it's integrated Broadcom Bluetooth chip.

Bluetooth works great on my Pi 3 and the hci0 interface is "UP RUNNING" after a fresh boot:

root@raspberrypi:~/bluez-5.39# hciconfig -a
hci0:   Type: BR/EDR  Bus: UART
    BD Address: B8:27:EB:6F:71:A7  ACL MTU: 1021:8  SCO MTU: 64:1
    UP RUNNING PSCAN 
    RX bytes:2316 acl:0 sco:0 events:99 errors:0
    TX bytes:2676 acl:0 sco:0 commands:99 errors:0
    Features: 0xbf 0xfe 0xcf 0xfe 0xdb 0xff 0x7b 0x87
    Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3 
    Link policy: RSWITCH SNIFF 
    Link mode: SLAVE ACCEPT 
    Name: 'raspberrypi'
    Class: 0x000000
    Service Classes: Unspecified
    Device Class: Miscellaneous, 
    HCI Version: 4.1 (0x7)  Revision: 0xb6
    LMP Version: 4.1 (0x7)  Subversion: 0x2209
    Manufacturer: Broadcom Corporation (15)

I successfully downloaded, compiled, and installed the latest BlueZ 5.39, which contains a complete DBus interface to the BlueZ BLE functionality:

http://www.kernel.org/pub/linux/bluetooth/bluez-5.39.tar.xz

I've confirmed that the versions picked up in the path are the right version:

[bluetooth]# version
Version 5.39

I used buildroot to cross compile Qt 5.7 and deployed it's libraries to the Pi. I can successfully build on my host machine and run the resulting executable on the Pi.

The GATT example from Qt is very simple and I only added 2 "qDebug" lines to see some console ouput. I'll paste it here for completeness:

#include <QtBluetooth/qlowenergyadvertisingdata.h>
#include <QtBluetooth/qlowenergyadvertisingparameters.h>
#include <QtBluetooth/qlowenergycharacteristic.h>
#include <QtBluetooth/qlowenergycharacteristicdata.h>
#include <QtBluetooth/qlowenergydescriptordata.h>
#include <QtBluetooth/qlowenergycontroller.h>
#include <QtBluetooth/qlowenergyservice.h>
#include <QtBluetooth/qlowenergyservicedata.h>
#include <QtCore/qbytearray.h>
#include <QtCore/qcoreapplication.h>
#include <QtCore/qlist.h>
#include <QtCore/qscopedpointer.h>
#include <QtCore/qtimer.h>

#include <QDebug>

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);

    QLowEnergyAdvertisingData advertisingData;
    advertisingData.setDiscoverability(QLowEnergyAdvertisingData::DiscoverabilityGeneral);
    advertisingData.setIncludePowerLevel(true);
    advertisingData.setLocalName("BlueZ 5 GATT Server");
    advertisingData.setServices(QList<QBluetoothUuid>() << QBluetoothUuid::HeartRate);

    QLowEnergyCharacteristicData charData;
    charData.setUuid(QBluetoothUuid::HeartRateMeasurement);
    charData.setValue(QByteArray(2, 0));
    charData.setProperties(QLowEnergyCharacteristic::Notify);
    const QLowEnergyDescriptorData clientConfig(QBluetoothUuid::ClientCharacteristicConfiguration,
                                                QByteArray(2, 0));
    charData.addDescriptor(clientConfig);

    QLowEnergyServiceData serviceData;
    serviceData.setType(QLowEnergyServiceData::ServiceTypePrimary);
    serviceData.setUuid(QBluetoothUuid::HeartRate);
    serviceData.addCharacteristic(charData);

    const QScopedPointer<QLowEnergyController> leController(QLowEnergyController::createPeripheral());
    const QScopedPointer<QLowEnergyService> service(leController->addService(serviceData));
    qDebug() << "Beginning to advertise...";
    leController->startAdvertising(QLowEnergyAdvertisingParameters(), advertisingData,
                                   advertisingData);

    QTimer heartbeatTimer;
    quint8 currentHeartRate = 60;
    enum ValueChange { ValueUp, ValueDown } valueChange = ValueUp;
    const auto heartbeatProvider = [&service, &currentHeartRate, &valueChange]() {
        QByteArray value;
        value.append(char(0)); // Flags that specify the format of the value.
        value.append(char(currentHeartRate)); // Actual value.
        QLowEnergyCharacteristic characteristic
                = service->characteristic(QBluetoothUuid::HeartRateMeasurement);
        Q_ASSERT(characteristic.isValid());
        qDebug() << "Changing characteristic to: " << value;
        service->writeCharacteristic(characteristic, value); // Potentially causes notification.
        if (currentHeartRate == 60)
            valueChange = ValueUp;
        else if (currentHeartRate == 100)
            valueChange = ValueDown;
        if (valueChange == ValueUp)
            ++currentHeartRate;
        else
            --currentHeartRate;
    };
    QObject::connect(&heartbeatTimer, &QTimer::timeout, heartbeatProvider);
    heartbeatTimer.start(1000);

    auto reconnect = [&leController, advertisingData]() {
        leController->startAdvertising(QLowEnergyAdvertisingParameters(), advertisingData,
                                       advertisingData);
    };
    QObject::connect(leController.data(), &QLowEnergyController::disconnected, reconnect);

    return app.exec();
}

Pro file:

TEMPLATE = app
TARGET = qt-gatt

QT += bluetooth
CONFIG += c++11

SOURCES += main.cpp

## Install directory
target.path = /home/pi
INSTALLS += target

When I run the app on the Pi as root after a fresh boot - it runs and outputs my print messages:

root@raspberrypi:/home/pi# ./qt-gatt 
Beginning to advertise...
Changing characteristic to:  "\x00<"
Changing characteristic to:  "\x00="
Changing characteristic to:  "\x00>"
Changing characteristic to:  "\x00?"

There are no errors or warnings displayed - but none of my devices can see it. My iPhone and Mac can see other BLE devices, but not the Pi. The code sets the Pi as "discoverable".

How can I make this work / What am I doing wrong?