QAbstractSocket::flush(): remove manual polymorphism

... by making a function in the private class virtual.

Change-Id: I45c25c6c59511a8e8821ca96b0cf28cbf1b2f267
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Markus Goetz (Woboq GmbH) <markus@woboq.com>

src/network/socket/qabstractsocket.cpp

@@ -2397,15 +2397,7 @@ bool QAbstractSocket::atEnd() const
 // Note! docs copied to QSslSocket::flush()
 bool QAbstractSocket::flush()
 {
-    Q_D(QAbstractSocket);
-#ifndef QT_NO_SSL
-    // Manual polymorphism; flush() isn't virtual, but QSslSocket overloads
-    // it.
-    if (QSslSocket *socket = qobject_cast<QSslSocket *>(this))
-        return socket->flush();
-#endif
-    Q_CHECK_SOCKETENGINE(false);
-    return d->flush();
+    return d_func()->flush();
 }
 
 /*! \reimp

src/network/socket/qabstractsocket_p.h

@@ -129,7 +129,7 @@ public:
     inline void resolveProxy(quint16 port) { resolveProxy(QString(), port); }
 
     void resetSocketLayer();
-    bool flush();
+    virtual bool flush();
 
     bool initSocketLayer(QAbstractSocket::NetworkLayerProtocol protocol);
     virtual void configureCreatedSocket();

src/network/ssl/qsslsocket.cpp

@@ -834,15 +834,7 @@ bool QSslSocket::atEnd() const
 // Note! docs copied from QAbstractSocket::flush()
 bool QSslSocket::flush()
 {
-    Q_D(QSslSocket);
-#ifdef QSSLSOCKET_DEBUG
-    qCDebug(lcSsl) << "QSslSocket::flush()";
-#endif
-    if (d->mode != UnencryptedMode)
-        // encrypt any unencrypted bytes in our buffer
-        d->transmit();
-
-    return d->plainSocket ? d->plainSocket->flush() : false;
+    return d_func()->flush();
 }
 
 /*!
@@ -2579,6 +2571,22 @@ QByteArray QSslSocketPrivate::peek(qint64 maxSize)
     }
 }
 
+/*!
+    \internal
+*/
+bool QSslSocketPrivate::flush()
+{
+#ifdef QSSLSOCKET_DEBUG
+    qCDebug(lcSsl) << "QSslSocketPrivate::flush()";
+#endif
+    if (mode != QSslSocket::UnencryptedMode) {
+        // encrypt any unencrypted bytes in our buffer
+        transmit();
+    }
+
+    return plainSocket && plainSocket->flush();
+}
+
 /*!
     \internal
 */

src/network/ssl/qsslsocket.h

@@ -116,7 +116,7 @@ public:
     bool canReadLine() const Q_DECL_OVERRIDE;
     void close() Q_DECL_OVERRIDE;
     bool atEnd() const Q_DECL_OVERRIDE;
-    bool flush();
+    bool flush(); // ### Qt6: remove me (implementation moved to private flush())
     void abort();
 
     // From QAbstractSocket:

src/network/ssl/qsslsocket_p.h

@@ -191,6 +191,7 @@ public:
 
     virtual qint64 peek(char *data, qint64 maxSize) Q_DECL_OVERRIDE;
     virtual QByteArray peek(qint64 maxSize) Q_DECL_OVERRIDE;
+    bool flush() Q_DECL_OVERRIDE;
 
     // Platform specific functions
     virtual void startClientEncryption() = 0;