QNAM should prepend Host header to the header list instead of appending

When original QNetworkRequest is missing "Host" header (which is the most
common case), it is provided automatically from request URL. However,
resulting header is appended to the list, i.e. after all headers specified
by user, which may include a big bunch of cookies.

To the contrary, RFC 7230 suggests: "However, it is good practice to send
header fields that contain control data first, such as Host on requests
and Date on responses, so that implementations can decide when not to
handle a message as early as possible". Many other user agents are
following this suggestion.

Task-number: QTBUG-51557
Change-Id: I1448ed3ae124f5ce86a8ca8ff35f5d05476a005d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

src/network/access/qhttpnetworkconnection.cpp

@@ -355,7 +355,7 @@ void QHttpNetworkConnectionPrivate::prepareRequest(HttpMessagePair &messagePair)
             host += QByteArray::number(port);
         }
 
-        request.setHeaderField("Host", host);
+        request.prependHeaderField("Host", host);
     }
 
     reply->d_func()->requestIsPrepared = true;

src/network/access/qhttpnetworkheader.cpp

@@ -114,6 +114,11 @@ void QHttpNetworkHeaderPrivate::setHeaderField(const QByteArray &name, const QBy
     fields.append(qMakePair(name, data));
 }
 
+void QHttpNetworkHeaderPrivate::prependHeaderField(const QByteArray &name, const QByteArray &data)
+{
+    fields.prepend(qMakePair(name, data));
+}
+
 bool QHttpNetworkHeaderPrivate::operator==(const QHttpNetworkHeaderPrivate &other) const
 {
    return (url == other.url);

src/network/access/qhttpnetworkheader_p.h

@@ -92,6 +92,7 @@ public:
     QByteArray headerField(const QByteArray &name, const QByteArray &defaultValue = QByteArray()) const;
     QList<QByteArray> headerFieldValues(const QByteArray &name) const;
     void setHeaderField(const QByteArray &name, const QByteArray &data);
+    void prependHeaderField(const QByteArray &name, const QByteArray &data);
     bool operator==(const QHttpNetworkHeaderPrivate &other) const;
 
 };

src/network/access/qhttpnetworkrequest.cpp

@@ -279,6 +279,11 @@ void QHttpNetworkRequest::setHeaderField(const QByteArray &name, const QByteArra
     d->setHeaderField(name, data);
 }
 
+void QHttpNetworkRequest::prependHeaderField(const QByteArray &name, const QByteArray &data)
+{
+    d->prependHeaderField(name, data);
+}
+
 QHttpNetworkRequest &QHttpNetworkRequest::operator=(const QHttpNetworkRequest &other)
 {
     d = other.d;

src/network/access/qhttpnetworkrequest_p.h

@@ -102,6 +102,7 @@ public:
     QList<QPair<QByteArray, QByteArray> > header() const Q_DECL_OVERRIDE;
     QByteArray headerField(const QByteArray &name, const QByteArray &defaultValue = QByteArray()) const Q_DECL_OVERRIDE;
     void setHeaderField(const QByteArray &name, const QByteArray &data) Q_DECL_OVERRIDE;
+    void prependHeaderField(const QByteArray &name, const QByteArray &data);
 
     Operation operation() const;
     void setOperation(Operation operation);