Make sure QDBusConnection::connect() returns false if already connected

QDBusConnection::connect() behaves like QObject::connect with a
connection type of Qt::UniqueConnection | Qt::QueuedConnection. So
return false if it's already connected.

[ChangeLog][QtDBus][QDBusConnection] Fixed a bug that would cause
QDBusConnection::connect() to return true if a slot was already
connected to the same D-Bus signal. QtDBus does not support multiple
connections.

Change-Id: I87e17314d8b24ae983b1fffd1453aef5a7c9ad0b
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/dbus/qdbusconnection_p.h

@@ -280,7 +280,7 @@ public slots:
     void socketWrite(int);
     void objectDestroyed(QObject *o);
     void relaySignal(QObject *obj, const QMetaObject *, int signalId, const QVariantList &args);
-    void addSignalHook(const QString &key, const SignalHook &hook);
+    bool addSignalHook(const QString &key, const SignalHook &hook);
     bool removeSignalHook(const QString &key, const SignalHook &hook);
 
 private slots:
@@ -293,7 +293,7 @@ signals:
     void dispatchStatusChanged();
     void spyHooksFinished(const QDBusMessage &msg);
     void messageNeedsSending(QDBusPendingCallPrivate *pcall, void *msg, int timeout = -1);
-    void signalNeedsConnecting(const QString &key, const QDBusConnectionPrivate::SignalHook &hook);
+    bool signalNeedsConnecting(const QString &key, const QDBusConnectionPrivate::SignalHook &hook);
     bool signalNeedsDisconnecting(const QString &key, const QDBusConnectionPrivate::SignalHook &hook);
     void serviceOwnerChanged(const QString &name, const QString &oldOwner, const QString &newOwner);
     void callWithCallbackFailed(const QDBusError &error, const QDBusMessage &message);

src/dbus/qdbusintegrator.cpp

@@ -2187,20 +2187,16 @@ bool QDBusConnectionPrivate::connectSignal(const QString &service,
     // check the slot
     QDBusConnectionPrivate::SignalHook hook;
     QString key;
-    QString name2 = name;
-    if (name2.isNull())
-        name2.detach();
 
     hook.signature = signature;
     if (!prepareHook(hook, key, service, path, interface, name, argumentMatch, receiver, slot, 0, false))
         return false;           // don't connect
 
     Q_ASSERT(thread() != QThread::currentThread());
-    emit signalNeedsConnecting(key, hook);
-    return true;
+    return emit signalNeedsConnecting(key, hook);
 }
 
-void QDBusConnectionPrivate::addSignalHook(const QString &key, const SignalHook &hook)
+bool QDBusConnectionPrivate::addSignalHook(const QString &key, const SignalHook &hook)
 {
     QDBusWriteLocker locker(ConnectAction, this);
 
@@ -2216,7 +2212,7 @@ void QDBusConnectionPrivate::addSignalHook(const QString &key, const SignalHook
             entry.midx == hook.midx &&
             entry.argumentMatch == hook.argumentMatch) {
             // no need to compare the parameters if it's the same slot
-            return;        // already there
+            return false;     // already there
         }
     }
 
@@ -2228,7 +2224,7 @@ void QDBusConnectionPrivate::addSignalHook(const QString &key, const SignalHook
 
     if (mit != matchRefCounts.end()) { // Match already present
         mit.value() = mit.value() + 1;
-        return;
+        return true;
     }
 
     matchRefCounts.insert(hook.matchRule, 1);
@@ -2255,6 +2251,7 @@ void QDBusConnectionPrivate::addSignalHook(const QString &key, const SignalHook
             }
         }
     }
+    return true;
 }
 
 bool QDBusConnectionPrivate::disconnectSignal(const QString &service,

tests/auto/dbus/qdbusconnection/tst_qdbusconnection.cpp

@@ -1087,6 +1087,16 @@ void tst_QDBusConnection::connectSignal()
     QTest::qWait(100);
     QCOMPARE(recv.argumentReceived, signal.arguments().at(0).toString());
     QCOMPARE(recv.signalsReceived, 1);
+
+    // confirm that we are, indeed, a unique connection
+    recv.argumentReceived.clear();
+    recv.signalsReceived = 0;
+    QVERIFY(!con.connect(con.baseService(), signal.path(), signal.interface(),
+                        signal.member(), "s", &recv, SLOT(oneSlot(QString))));
+    QVERIFY(con.send(signal));
+    QTest::qWait(100);
+    QCOMPARE(recv.argumentReceived, signal.arguments().at(0).toString());
+    QCOMPARE(recv.signalsReceived, 1);
 }
 
 void tst_QDBusConnection::slotsWithLessParameters()
@@ -1118,6 +1128,15 @@ void tst_QDBusConnection::slotsWithLessParameters()
     QTest::qWait(100);
     QCOMPARE(recv.argumentReceived, QString());
     QCOMPARE(recv.signalsReceived, 1);
+
+    // confirm that we are, indeed, a unique connection
+    recv.signalsReceived = 0;
+    QVERIFY(!con.connect(con.baseService(), signal.path(), signal.interface(),
+                         signal.member(), "s", &recv, SLOT(oneSlot())));
+    QVERIFY(con.send(signal));
+    QTest::qWait(100);
+    QCOMPARE(recv.argumentReceived, QString());
+    QCOMPARE(recv.signalsReceived, 1);
 }
 
 void SignalReceiver::secondCallWithCallback()