Update QTBUG-17223 for Qt 4.8

In Qt 4.7, http network requests are assigned to http connection
channels before connecting the channel.
In Qt 4.8, channels are connected "blind" as this gives a performance
improvement in certain circumstances.

On the assumption that User-Agent should be the same for all the
requests being sent to the server in a given burst, we use the first
queued request to set the user agent for a http proxy.

Task-number: QTBUG-17223
Reviewed-by: Markus Goetz
Reviewed-by: Martin Petersson

src/network/access/qhttpnetworkconnection.cpp

@@ -520,6 +520,15 @@ bool QHttpNetworkConnectionPrivate::dequeueRequest(QAbstractSocket *socket)
     return false;
 }
 
+QHttpNetworkRequest QHttpNetworkConnectionPrivate::predictNextRequest()
+{
+    if (!highPriorityQueue.isEmpty())
+        return highPriorityQueue.last().first;
+    if (!lowPriorityQueue.isEmpty())
+        return lowPriorityQueue.last().first;
+    return QHttpNetworkRequest();
+}
+
 // this is called from _q_startNextRequest and when a request has been sent down a socket from the channel
 void QHttpNetworkConnectionPrivate::fillPipeline(QAbstractSocket *socket)
 {

src/network/access/qhttpnetworkconnection_p.h

@@ -169,6 +169,7 @@ public:
     void requeueRequest(const HttpMessagePair &pair); // e.g. after pipeline broke
     bool dequeueRequest(QAbstractSocket *socket);
     void prepareRequest(HttpMessagePair &request);
+    QHttpNetworkRequest predictNextRequest();
 
     void fillPipeline(QAbstractSocket *socket);
     bool fillPipeline(QList<HttpMessagePair> &queue, QHttpNetworkConnectionChannel &channel);

src/network/access/qhttpnetworkconnectionchannel.cpp

@@ -581,7 +581,12 @@ bool QHttpNetworkConnectionChannel::ensureConnection()
         }
         if (socket->proxy().type() == QNetworkProxy::HttpProxy) {
             // Make user-agent field available to HTTP proxy socket engine (QTBUG-17223)
-            QByteArray value = request.headerField("user-agent");
+            QByteArray value;
+            // ensureConnection is called before any request has been assigned, but can also be called again if reconnecting
+            if (request.url().isEmpty())
+                value = connection->d_func()->predictNextRequest().headerField("user-agent");
+            else
+                value = request.headerField("user-agent");
             if (!value.isEmpty())
                 socket->setProperty("_q_user-agent", value);
         }