Add a means to specify the protocol type, to aid websockets over proxy

When a PAC script is used on macOS, it will only allow connections for
http/https, although a proxy can be used for ws/wss. Therefore we need
to add a means of setting the protocol type for this sort of connection
so that we can pass on the necessary information to the PAC script.

Change-Id: I3fa29fa85a529bd88d9565daa58fe9d748b61a92
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

src/network/socket/qabstractsocket.cpp

@@ -914,7 +914,7 @@ void QAbstractSocketPrivate::resolveProxy(const QString &hostname, quint16 port)
         proxies << proxy;
     } else {
         // try the application settings instead
-        QNetworkProxyQuery query(hostname, port, QString(),
+        QNetworkProxyQuery query(hostname, port, protocolTag,
                                  socketType == QAbstractSocket::TcpSocket ?
                                  QNetworkProxyQuery::TcpSocket :
                                  socketType == QAbstractSocket::SctpSocket ?
@@ -2959,6 +2959,38 @@ QNetworkProxy QAbstractSocket::proxy() const
     Q_D(const QAbstractSocket);
     return d->proxy;
 }
+
+/*!
+    \since 5.13
+
+    Returns the protocol tag for this socket.
+    If the protocol tag is set then this is passed to QNetworkProxyQuery
+    when this is created internally to indicate the protocol tag to be
+    used.
+
+    \sa setProtocolTag(), QNetworkProxyQuery
+*/
+
+QString QAbstractSocket::protocolTag() const
+{
+    Q_D(const QAbstractSocket);
+    return d->protocolTag;
+}
+
+/*!
+    \since 5.13
+
+    Sets the protocol tag for this socket to \a tag.
+
+    \sa protocolTag()
+*/
+
+void QAbstractSocket::setProtocolTag(const QString &tag)
+{
+    Q_D(QAbstractSocket);
+    d->protocolTag = tag;
+}
+
 #endif // QT_NO_NETWORKPROXY
 
 #ifndef QT_NO_DEBUG_STREAM

src/network/socket/qabstractsocket.h

@@ -197,6 +197,8 @@ public:
 #ifndef QT_NO_NETWORKPROXY
     void setProxy(const QNetworkProxy &networkProxy);
     QNetworkProxy proxy() const;
+    QString protocolTag() const;
+    void setProtocolTag(const QString &tag);
 #endif
 
 Q_SIGNALS:

src/network/socket/qabstractsocket_p.h

@@ -124,6 +124,7 @@ public:
 #ifndef QT_NO_NETWORKPROXY
     QNetworkProxy proxy;
     QNetworkProxy proxyInUse;
+    QString protocolTag;
     void resolveProxy(const QString &hostName, quint16 port);
 #else
     inline void resolveProxy(const QString &, quint16) { }

src/network/ssl/qsslsocket.cpp

@@ -1977,6 +1977,7 @@ void QSslSocket::connectToHost(const QString &hostName, quint16 port, OpenMode o
         d->createPlainSocket(openMode);
     }
 #ifndef QT_NO_NETWORKPROXY
+    d->plainSocket->setProtocolTag(d->protocolTag);
     d->plainSocket->setProxy(proxy());
 #endif
     QIODevice::open(openMode);