Close socket descriptor when QBluetoothSocketBluez is destroyed

There are two private QBluetoothSocket backends on Linux:
- QBluetoothSocketBluez is native linux socket implementation
  It is always used by the linux QBluetoothServer, and by
  QBluetoothSocket if Bluez version is < 5.46
- QBluetoothSocketBluezDbus used by QBluetoothSocket when
  Bluez >= 5.46

Leaving the native socket unclosed leaks the resource and eventually
we may run out of descriptors. This is reproducible by creating and
destroying QBluetoothServer instances in a loop.

As a related drive-by:
- Fix bluetooth socket autotest version check. DBus socket is used
  with bluez 5.46+ (for clarity: DBus lowenergycontroller
  is used with bluez 5.42+). This is needed for the test to pass
  with Bluez < 5.46
- Add a clarifying comment on socket close()

Fixes: QTBUG-103067
Change-Id: Idc38c743be09e559ea82bf09c2f9e44e4b80d666
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>
(cherry picked from commit 3aafe9d5ce)

src/bluetooth/qbluetoothsocket.cpp

@@ -791,6 +791,9 @@ void QBluetoothSocket::close()
   Set the socket to use \a socketDescriptor with a type of \a socketType,
   which is in state, \a socketState, and mode, \a openMode.
 
+  The set socket descriptor is considered owned by the QBluetoothSocket
+  and may be e.g. closed once finished.
+
   Returns true on success
 */
 

src/bluetooth/qbluetoothsocket_bluez.cpp

@@ -75,6 +75,10 @@ QBluetoothSocketPrivateBluez::~QBluetoothSocketPrivateBluez()
     readNotifier = nullptr;
     delete connectWriteNotifier;
     connectWriteNotifier = nullptr;
+
+    // If the socket wasn't closed/aborted make sure we free the socket file descriptor
+    if (socket != -1)
+        QT_CLOSE(socket);
 }
 
 bool QBluetoothSocketPrivateBluez::ensureNativeSocket(QBluetoothServiceInfo::Protocol type)
@@ -658,6 +662,8 @@ qint64 QBluetoothSocketPrivateBluez::readData(char *data, qint64 maxSize)
 
 void QBluetoothSocketPrivateBluez::close()
 {
+    // If we have pending data on the write buffer, wait until it has been written,
+    // after which this close() will be called again
     if (txBuffer.size() > 0)
         connectWriteNotifier->setEnabled(true);
     else

tests/auto/qbluetoothsocket/tst_qbluetoothsocket.cpp

@@ -511,7 +511,7 @@ void tst_QBluetoothSocket::tst_preferredSecurityFlags()
 #elif QT_CONFIG(bluez)
     // The bluezdbus socket uses "NoSecurity" by default, whereas the non-dbus bluez
     // socket uses "Authorization" by default
-    if (bluetoothdVersion() >= QVersionNumber(5, 42))
+    if (bluetoothdVersion() >= QVersionNumber(5, 46))
         QCOMPARE(socket.preferredSecurityFlags(), QBluetooth::Security::NoSecurity);
     else
         QCOMPARE(socket.preferredSecurityFlags(), QBluetooth::Security::Authorization);
@@ -577,4 +577,3 @@ void tst_QBluetoothSocket::tst_unsupportedProtocolError()
 QTEST_MAIN(tst_QBluetoothSocket)
 
 #include "tst_qbluetoothsocket.moc"
-