Prefer previously used channels in QHttpNetworkConnection

When IPv4 and IPv6 are supported by a server, QHttpNetworkConnection
will start up two connections and pick the network layer of the one
that finish first. In this case the channel with index 1 is used for
IPv6. When IPv6 wins, there is no channel at index 0. This situation
needs to be respected and we should try to use existing channels first
when there is a next request.

This is especially important when TLS session resumption is used.
Creating a new channel will cause to lose the ephemeralServerKey
used in the first connection.

Fixes: QTBUG-93295
Pick-to: 5.15 6.1
Change-Id: Ic9dc6a24ef793a29c2652ad37bc11120e2e6ceef
Reviewed-by: Mårten Nordheim <[email protected]>

src/network/access/qhttpnetworkconnection.cpp

@@ -1117,31 +1117,50 @@ void QHttpNetworkConnectionPrivate::_q_startNextRequest()
         int normalRequests = queuedRequests - preConnectRequests;
         neededOpenChannels = qMax(normalRequests, preConnectRequests);
     }
+
+    if (neededOpenChannels <= 0)
+        return;
+
+    QQueue<int> channelsToConnect;
+
+    // use previously used channels first
     for (int i = 0; i < activeChannelCount && neededOpenChannels > 0; ++i) {
-        bool connectChannel = false;
-        if (channels[i].socket) {
-            if ((channels[i].socket->state() == QAbstractSocket::ConnectingState)
-                    || (channels[i].socket->state() == QAbstractSocket::HostLookupState)
-                    || channels[i].pendingEncrypt) // pendingEncrypt == "EncryptingState"
-                neededOpenChannels--;
-
-            if (neededOpenChannels <= 0)
-                break;
-            if (!channels[i].reply && !channels[i].isSocketBusy() && (channels[i].socket->state() == QAbstractSocket::UnconnectedState))
-                connectChannel = true;
-        } else { // not previously used channel
-            connectChannel = true;
+        if (!channels[i].socket)
+            continue;
+
+        if ((channels[i].socket->state() == QAbstractSocket::ConnectingState)
+            || (channels[i].socket->state() == QAbstractSocket::HostLookupState)
+            || channels[i].pendingEncrypt) { // pendingEncrypt == "EncryptingState"
+            neededOpenChannels--;
+            continue;
         }
 
-        if (connectChannel) {
-            if (networkLayerState == IPv4)
-                channels[i].networkLayerPreference = QAbstractSocket::IPv4Protocol;
-            else if (networkLayerState == IPv6)
-                channels[i].networkLayerPreference = QAbstractSocket::IPv6Protocol;
-            channels[i].ensureConnection();
+        if (!channels[i].reply && !channels[i].isSocketBusy()
+            && (channels[i].socket->state() == QAbstractSocket::UnconnectedState)) {
+            channelsToConnect.enqueue(i);
             neededOpenChannels--;
         }
     }
+
+    // use other channels
+    for (int i = 0; i < activeChannelCount && neededOpenChannels > 0; ++i) {
+        if (channels[i].socket)
+            continue;
+
+        channelsToConnect.enqueue(i);
+        neededOpenChannels--;
+    }
+
+    while (!channelsToConnect.isEmpty()) {
+        const int channel = channelsToConnect.dequeue();
+
+        if (networkLayerState == IPv4)
+            channels[channel].networkLayerPreference = QAbstractSocket::IPv4Protocol;
+        else if (networkLayerState == IPv6)
+            channels[channel].networkLayerPreference = QAbstractSocket::IPv6Protocol;
+
+        channels[channel].ensureConnection();
+    }
 }