QNAM HTTP: Do not set cache headers when already set by user

Qt clobbers the cache-control headers set by WebCore when
CacheLoadControlAttribute == QNetworkRequest::AlwaysNetwork.
This causes at least one QtWebKit layout test to fail:
http/tests/misc/refresh-headers.php
Qt needs to detect if the client has already made a cache-control
decision in the headers before overwriting them.
See https://bugs.webkit.org/show_bug.cgi?id=45598

Task-Number: QTBUG-13564
Merge-request: 2472
Reviewed-by: Markus Goetz <Markus.Goetz@nokia.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/src/network/access/qnetworkaccesshttpbackend.cpp b/src/network/access/qnetworkaccesshttpbackend.cpp
index 42dc33d..1d85f3a 100644
--- a/src/network/access/qnetworkaccesshttpbackend.cpp
+++ b/src/network/access/qnetworkaccesshttpbackend.cpp
@@ -353,10 +353,12 @@ void QNetworkAccessHttpBackend::validateCache(QHttpNetworkRequest &httpRequest,
     QNetworkRequest::CacheLoadControl CacheLoadControlAttribute =
         (QNetworkRequest::CacheLoadControl)request().attribute(QNetworkRequest::CacheLoadControlAttribute, QNetworkRequest::PreferNetwork).toInt();
     if (CacheLoadControlAttribute == QNetworkRequest::AlwaysNetwork) {
-        // forced reload from the network
-        // tell any caching proxy servers to reload too
-        httpRequest.setHeaderField("Cache-Control", "no-cache");
-        httpRequest.setHeaderField("Pragma", "no-cache");
+        // If the request does not already specify preferred cache-control
+        // force reload from the network and tell any caching proxy servers to reload too
+        if (!request().rawHeaderList().contains("Cache-Control")) {
+            httpRequest.setHeaderField("Cache-Control", "no-cache");
+            httpRequest.setHeaderField("Pragma", "no-cache");
+        }
         return;
     }