Don't send the default SETTINGS_INITIAL_WINDOW_SIZE

And don't set non-default large value in QNetworkRequest's constructor.
Some servers consider those values as 'flow control error'.

Pick-to: 6.2
Fixes: QTBUG-97384
Change-Id: I801b7c83fe7e7392a02ba653c36dfa8a22c21d1e
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

3 files changed, 14 insertions, 13 deletions

diff --git a/src/network/access/http2/http2protocol.cpp b/src/network/access/http2/http2protocol.cpp
index 31da6fd616..baae68bc30 100644
--- a/src/network/access/http2/http2protocol.cpp
+++ b/src/network/access/http2/http2protocol.cpp
@@ -71,9 +71,12 @@ Frame configurationToSettingsFrame(const QHttp2Configuration &config)
     // Server push:
     builder.append(Settings::ENABLE_PUSH_ID);
     builder.append(int(config.serverPushEnabled()));
-    // Stream receive window size:
-    builder.append(Settings::INITIAL_WINDOW_SIZE_ID);
-    builder.append(config.streamReceiveWindowSize());
+
+    // Stream receive window size (if it's a default value, don't include):
+    if (config.streamReceiveWindowSize() != defaultSessionWindowSize) {
+        builder.append(Settings::INITIAL_WINDOW_SIZE_ID);
+        builder.append(config.streamReceiveWindowSize());
+    }
 
     if (config.maxFrameSize() != minPayloadLimit) {
         builder.append(Settings::MAX_FRAME_SIZE_ID);
diff --git a/src/network/access/qhttp2configuration.cpp b/src/network/access/qhttp2configuration.cpp
index 4facfd7776..626a564fff 100644
--- a/src/network/access/qhttp2configuration.cpp
+++ b/src/network/access/qhttp2configuration.cpp
@@ -98,9 +98,6 @@ class QHttp2ConfigurationPrivate : public QSharedData
 {
 public:
     unsigned sessionWindowSize = Http2::defaultSessionWindowSize;
-    // The size below is quite a limiting default value, QNetworkRequest
-    // by default sets a larger number, an application can change this using
-    // QNetworkRequest::setHttp2Configuration.
     unsigned streamWindowSize = Http2::defaultSessionWindowSize;
 
     unsigned maxFrameSize = Http2::minPayloadLimit; // Initial (default) value of 16Kb.
@@ -256,7 +253,7 @@ bool QHttp2Configuration::setStreamReceiveWindowSize(unsigned size)
 /*!
     Returns the window size for stream-level flow control.
     The default value QNetworkAccessManager will be using is
-    21474836 octets.
+    65535 octets (see \l {https://httpwg.org/specs/rfc7540.html#SettingValues}{RFC 7540}).
 */
 unsigned QHttp2Configuration::streamReceiveWindowSize() const
 {
diff --git a/src/network/access/qnetworkrequest.cpp b/src/network/access/qnetworkrequest.cpp
index 688c29935c..3e9c12ae9e 100644
--- a/src/network/access/qnetworkrequest.cpp
+++ b/src/network/access/qnetworkrequest.cpp
@@ -492,13 +492,14 @@ public:
 QNetworkRequest::QNetworkRequest()
     : d(new QNetworkRequestPrivate)
 {
-
 #if QT_CONFIG(http)
-    // Initial values proposed by RFC 7540 are quite draconian,
-    // so unless an application will set its own parameters, we
-    // make stream window size larger and increase (via WINDOW_UPDATE)
-    // the session window size. These are our 'defaults':
-    d->h2Configuration.setStreamReceiveWindowSize(Http2::qtDefaultStreamReceiveWindowSize);
+    // Initial values proposed by RFC 7540 are quite draconian, but we
+    // know about servers configured with this value as maximum possible,
+    // rejecting our SETTINGS frame and sending us a GOAWAY frame with the
+    // flow control error set. Unless an application sets its own parameters,
+    // we don't send SETTINGS_INITIAL_WINDOW_SIZE, but increase
+    // (via WINDOW_UPDATE) the session window size. These are our 'defaults':
+    d->h2Configuration.setStreamReceiveWindowSize(Http2::defaultSessionWindowSize);
     d->h2Configuration.setSessionReceiveWindowSize(Http2::maxSessionReceiveWindowSize);
     d->h2Configuration.setServerPushEnabled(false);
 #endif // QT_CONFIG(http)