QNAM: Enable HTTP/2 by default

It has been in Qt for some years now and 6.0 marks a good point to
enable it by default. The exception is connectToHostEncrypted where we
still require the users to enable it explicitly since there's no logical
way to disable it.

[ChangeLog][QtNetwork][QNetworkAccessManager] HTTP/2 is now enabled by
default.

Fixes: QTBUG-85902
Change-Id: Ia029a045727cc593d77df9eb3a5888522ad19199
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

src/network/access/qhttpnetworkrequest.cpp

@@ -45,7 +45,7 @@ QT_BEGIN_NAMESPACE
 QHttpNetworkRequestPrivate::QHttpNetworkRequestPrivate(QHttpNetworkRequest::Operation op,
         QHttpNetworkRequest::Priority pri, const QUrl &newUrl)
     : QHttpNetworkHeaderPrivate(newUrl), operation(op), priority(pri), uploadByteDevice(nullptr),
-      autoDecompress(false), pipeliningAllowed(false), http2Allowed(false),
+      autoDecompress(false), pipeliningAllowed(false), http2Allowed(true),
       http2Direct(false), withCredentials(true), preConnect(false), redirectCount(0),
       redirectPolicy(QNetworkRequest::ManualRedirectPolicy)
 {

src/network/access/qnetworkaccessmanager.cpp

@@ -931,9 +931,9 @@ QNetworkReply *QNetworkAccessManager::deleteResource(const QNetworkRequest &requ
     \a sslConfiguration. This function is useful to complete the TCP and SSL handshake
     to a host before the HTTPS request is made, resulting in a lower network latency.
 
-    \note Preconnecting a SPDY connection can be done by calling setAllowedNextProtocols()
+    \note Preconnecting a HTTP/2 connection can be done by calling setAllowedNextProtocols()
-    on \a sslConfiguration with QSslConfiguration::NextProtocolSpdy3_0 contained in
+    on \a sslConfiguration with QSslConfiguration::ALPNProtocolHTTP2 contained in
-    the list of allowed protocols. When using SPDY, one single connection per host is
+    the list of allowed protocols. When using HTTP/2, one single connection per host is
     enough, i.e. calling this method multiple times per host will not result in faster
     network transactions.
 
@@ -957,9 +957,9 @@ void QNetworkAccessManager::connectToHostEncrypted(const QString &hostName, quin
     validation. This function is useful to complete the TCP and SSL handshake
     to a host before the HTTPS request is made, resulting in a lower network latency.
 
-    \note Preconnecting a SPDY connection can be done by calling setAllowedNextProtocols()
+    \note Preconnecting a HTTP/2 connection can be done by calling setAllowedNextProtocols()
-    on \a sslConfiguration with QSslConfiguration::NextProtocolSpdy3_0 contained in
+    on \a sslConfiguration with QSslConfiguration::ALPNProtocolHTTP2 contained in
-    the list of allowed protocols. When using SPDY, one single connection per host is
+    the list of allowed protocols. When using HTTP/2, one single connection per host is
     enough, i.e. calling this method multiple times per host will not result in faster
     network transactions.
 
@@ -980,10 +980,10 @@ void QNetworkAccessManager::connectToHostEncrypted(const QString &hostName, quin
     if (sslConfiguration != QSslConfiguration::defaultConfiguration())
         request.setSslConfiguration(sslConfiguration);
 
-    // There is no way to enable HTTP2 via a request, so we need to check
+    // There is no way to enable HTTP2 via a request after having established the connection,
-    // the ssl configuration whether HTTP2 is allowed here.
+    // so we need to check the ssl configuration whether HTTP2 is allowed here.
-    if (sslConfiguration.allowedNextProtocols().contains(QSslConfiguration::ALPNProtocolHTTP2))
+    if (!sslConfiguration.allowedNextProtocols().contains(QSslConfiguration::ALPNProtocolHTTP2))
-        request.setAttribute(QNetworkRequest::Http2AllowedAttribute, true);
+        request.setAttribute(QNetworkRequest::Http2AllowedAttribute, false);
 
     request.setPeerVerifyName(peerName);
     get(request);

src/network/access/qnetworkreplyhttpimpl.cpp

@@ -755,8 +755,10 @@ void QNetworkReplyHttpImplPrivate::postRequest(const QNetworkRequest &newHttpReq
     if (newHttpRequest.attribute(QNetworkRequest::HttpPipeliningAllowedAttribute).toBool())
         httpRequest.setPipeliningAllowed(true);
 
-    if (request.attribute(QNetworkRequest::Http2AllowedAttribute).toBool())
+    if (auto allowed = request.attribute(QNetworkRequest::Http2AllowedAttribute);
-        httpRequest.setHTTP2Allowed(true);
+        allowed.isValid() && allowed.canConvert<bool>()) {
+        httpRequest.setHTTP2Allowed(allowed.value<bool>());
+    }
 
     if (request.attribute(QNetworkRequest::Http2DirectAttribute).toBool()) {
         // Intentionally mutually exclusive - cannot be both direct and 'allowed'

src/network/access/qnetworkrequest.cpp

@@ -269,7 +269,7 @@ QT_BEGIN_NAMESPACE
         to different policies.
 
     \value Http2AllowedAttribute
-        Requests only, type: QMetaType::Bool (default: false)
+        Requests only, type: QMetaType::Bool (default: true)
         Indicates whether the QNetworkAccessManager code is
         allowed to use HTTP/2 with this request. This applies
         to SSL requests or 'cleartext' HTTP/2.

tests/manual/qnetworkreply/main.cpp

@@ -386,7 +386,6 @@ void tst_qnetworkreply::npnWithEmptyList() // QTBUG-40714
 
     QUrl url(QStringLiteral("https://www.ossifrage.net/"));
     QNetworkRequest request(url);
-    request.setAttribute(QNetworkRequest::Http2AllowedAttribute, QVariant(true));
     QNetworkReply *reply = m_manager.get(request);
     QObject::connect(reply, SIGNAL(finished()), &QTestEventLoop::instance(), SLOT(exitLoop()));