Using QBluetoothSocket() to connect to multiple Rfcomm devices failes for second device

tmre

I'm trying to use QBluetoothSocket to open (client-) connections to two BT Classic SPP Servers. The SPP Servers run on two separate ESP32 devices which are paired with the PC already.

I wrote a Class to handle a SPP connection to a device with a known Bluetooth address. This works fine as long as I'm only trying to connect to a single device. If I try to start a connection to a second device with QBluetoothSocket::connectToService() the PC connects to the device ( connection is reported correctly on ESP32 side ).

The problem is that the QBluetoothSocket stays in the "ConnectingState" and never calls the QBluetoothSocket::connected() signal for the second device.

I'm on a Linux system ( Ubuntu 20.04 ) running BlueZ ( 5.5.3 ) with QT v6.2.4

Has anyone experienced this problem before?

For reference, this is the implementation of the Class handling the connection:

#include <QtCore/qmetaobject.h>

#include "bclassichandler.h"

BTClassicHandler::BTClassicHandler( QObject *parent ) : QObject{ parent } {}

BTClassicHandler::~BTClassicHandler() {}

void BTClassicHandler::connect( const QBluetoothAddress &btAddr )
{
    if ( m_socket ) return;

    m_socket = new QBluetoothSocket( QBluetoothServiceInfo::RfcommProtocol );
    qDebug() << "Created Socket for " << btAddr.toString();

    qDebug() << "Connecting to SPP on " << btAddr.toString();

    QObject::connect( m_socket, &QBluetoothSocket::readyRead, this,
                      &BTClassicHandler::onSocketRead );
    QObject::connect( m_socket, &QBluetoothSocket::connected, this,
                      &BTClassicHandler::onSocketConnected );
    QObject::connect( m_socket, &QBluetoothSocket::disconnected, this,
                      &BTClassicHandler::onSocketDisconnected );
    QObject::connect( m_socket, &QBluetoothSocket::errorOccurred, this,
                      &BTClassicHandler::onSocketError );
    QObject::connect( m_socket, &QBluetoothSocket::stateChanged, this,
                      &BTClassicHandler::onStateChanged );

    setAddress( btAddr );

    m_socket->connectToService( btAddr, QBluetoothUuid::ServiceClassUuid::SerialPort );
}

void BTClassicHandler::disconnect()
{
    delete m_socket;
    m_socket = nullptr;
}

/* Private Slots */

void BTClassicHandler::onSocketConnected() // <<<<< THIS IS NEVER CALLED FOR THE SECOND DEVICE !!!!
{
    qDebug() << "Connected to " << m_btAddr.toString();
    emit sig_BTConnected( m_btAddr );
}

void BTClassicHandler::onSocketDisconnected()
{
    qDebug() << "Disconnected from " << m_btAddr.toString();
}

void BTClassicHandler::onSocketRead() {}

void BTClassicHandler::onSocketError( QBluetoothSocket::SocketError error )
{
    QMetaEnum metaEnum = QMetaEnum::fromType<QBluetoothSocket::SocketError>();
    QString errorString = metaEnum.valueToKey( static_cast<int>( error ) );

    qDebug() << "Socket Error " << m_btAddr.toString() << " :" << errorString;
}

void BTClassicHandler::onStateChanged( QBluetoothSocket::SocketState state )
{
    QMetaEnum metaEnum = QMetaEnum::fromType<QBluetoothSocket::SocketState>();
    QString stateString = metaEnum.valueToKey( static_cast<int>( state ) );

    qDebug() << "State Changed " << m_btAddr.toString() << " : " << stateString;
}

( I also tried to get help here: https://stackoverflow.com/questions/72965275/problem-connecting-qbluetoothsocket-to-multiple-devices )