HTTP2: Delay any communication until encrypted() can be responded to

We have the encrypted() signal that lets users do extra checks on the
established connection. It is emitted as BlockingQueued, so the HTTP
thread stalls until it is done emitting. Users can potentially call
abort() on the QNetworkReply at that point, which is passed as a Queued
call back to the HTTP thread. That means that any currently queued
signal emission will be processed before the abort() call is processed.

In the case of HTTP2 it is a little special since it is multiplexed and
the code is built to start requests as they are available. This means
that, while the code worked fine for HTTP1, since one connection only
has one request, it is not working for HTTP2, since we try to send more
requests in-between the encrypted() signal and the abort() call.

This patch changes the code to delay any communication until the
encrypted() signal has been emitted and processed, for HTTP2 only.
It's done by adding a few booleans, both to know that we have to return
early and so we can keep track of what events arose and what we need to
resume once enough time has passed that any abort() call must have been
processed.

Fixes: QTBUG-126610
Pick-to: 6.8 6.7 6.5 6.2 5.15 5.12
Change-Id: Ic25a600c278203256e35f541026f34a8783235ae
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/network/access/qhttp2protocolhandler.cpp

@@ -304,12 +304,12 @@ bool QHttp2ProtocolHandler::sendRequest()
         }
     }
 
-    if (!prefaceSent && !sendClientPreface())
-        return false;
-
     if (!requests.size())
         return true;
 
+    if (!prefaceSent && !sendClientPreface())
+        return false;
+
     m_channel->state = QHttpNetworkConnectionChannel::WritingState;
     // Check what was promised/pushed, maybe we do not have to send a request
     // and have a response already?

src/network/access/qhttpnetworkconnectionchannel.cpp

@@ -220,6 +220,10 @@ void QHttpNetworkConnectionChannel::abort()
 bool QHttpNetworkConnectionChannel::sendRequest()
 {
     Q_ASSERT(protocolHandler);
+    if (waitingForPotentialAbort) {
+        needInvokeSendRequest = true;
+        return false; // this return value is unused
+    }
     return protocolHandler->sendRequest();
 }
 
@@ -232,21 +236,28 @@ bool QHttpNetworkConnectionChannel::sendRequest()
 void QHttpNetworkConnectionChannel::sendRequestDelayed()
 {
     QMetaObject::invokeMethod(this, [this] {
-        Q_ASSERT(protocolHandler);
         if (reply)
-            protocolHandler->sendRequest();
+            sendRequest();
     }, Qt::ConnectionType::QueuedConnection);
 }
 
 void QHttpNetworkConnectionChannel::_q_receiveReply()
 {
     Q_ASSERT(protocolHandler);
+    if (waitingForPotentialAbort) {
+        needInvokeReceiveReply = true;
+        return;
+    }
     protocolHandler->_q_receiveReply();
 }
 
 void QHttpNetworkConnectionChannel::_q_readyRead()
 {
     Q_ASSERT(protocolHandler);
+    if (waitingForPotentialAbort) {
+        needInvokeReadyRead = true;
+        return;
+    }
     protocolHandler->_q_readyRead();
 }
 
@@ -1270,7 +1281,18 @@ void QHttpNetworkConnectionChannel::_q_encrypted()
         if (!h2RequestsToSend.isEmpty()) {
             // Similar to HTTP/1.1 counterpart below:
             const auto &pair = std::as_const(h2RequestsToSend).first();
+            waitingForPotentialAbort = true;
             emit pair.second->encrypted();
+
+            // We don't send or handle any received data until any effects from
+            // emitting encrypted() have been processed. This is necessary
+            // because the user may have called abort(). We may also abort the
+            // whole connection if the request has been aborted and there is
+            // no more requests to send.
+            QMetaObject::invokeMethod(this,
+                                      &QHttpNetworkConnectionChannel::checkAndResumeCommunication,
+                                      Qt::QueuedConnection);
+
             // In case our peer has sent us its settings (window size, max concurrent streams etc.)
             // let's give _q_receiveReply a chance to read them first ('invokeMethod', QueuedConnection).
         }
@@ -1288,6 +1310,28 @@ void QHttpNetworkConnectionChannel::_q_encrypted()
     QMetaObject::invokeMethod(connection, "_q_startNextRequest", Qt::QueuedConnection);
 }
 
+
+void QHttpNetworkConnectionChannel::checkAndResumeCommunication()
+{
+    Q_ASSERT(connection->connectionType() == QHttpNetworkConnection::ConnectionTypeHTTP2
+             || connection->connectionType() == QHttpNetworkConnection::ConnectionTypeHTTP2Direct);
+
+    // Because HTTP/2 requires that we send a SETTINGS frame as the first thing we do, and respond
+    // to a SETTINGS frame with an ACK, we need to delay any handling until we can ensure that any
+    // effects from emitting encrypted() have been processed.
+    // This function is called after encrypted() was emitted, so check for changes.
+
+    if (!reply && h2RequestsToSend.isEmpty())
+        abort();
+    waitingForPotentialAbort = false;
+    if (needInvokeReadyRead)
+        _q_readyRead();
+    if (needInvokeReceiveReply)
+        _q_receiveReply();
+    if (needInvokeSendRequest)
+        sendRequest();
+}
+
 void QHttpNetworkConnectionChannel::requeueHttp2Requests()
 {
     const auto h2RequestsToSendCopy = std::exchange(h2RequestsToSend, {});

src/network/access/qhttpnetworkconnectionchannel_p.h

@@ -75,6 +75,10 @@ public:
     QIODevice *socket;
     bool ssl;
     bool isInitialized;
+    bool waitingForPotentialAbort = false;
+    bool needInvokeReceiveReply = false;
+    bool needInvokeReadyRead = false;
+    bool needInvokeSendRequest = false;
     ChannelState state;
     QHttpNetworkRequest request; // current request, only used for HTTP
     QHttpNetworkReply *reply; // current reply for this request, only used for HTTP
@@ -147,6 +151,8 @@ public:
     void closeAndResendCurrentRequest();
     void resendCurrentRequest();
 
+    void checkAndResumeCommunication();
+
     bool isSocketBusy() const;
     bool isSocketWriting() const;
     bool isSocketWaiting() const;

tests/auto/network/access/http2/tst_http2.cpp

@@ -108,6 +108,8 @@ private slots:
 
     void duplicateRequestsWithAborts();
 
+    void abortOnEncrypted();
+
 protected slots:
     // Slots to listen to our in-process server:
     void serverStarted(quint16 port);
@@ -1545,6 +1547,48 @@ void tst_Http2::duplicateRequestsWithAborts()
     QCOMPARE(finishedCount, ExpectedSuccessfulRequests);
 }
 
+void tst_Http2::abortOnEncrypted()
+{
+#if !QT_CONFIG(ssl)
+    QSKIP("TLS support is needed for this test");
+#else
+    clearHTTP2State();
+    serverPort = 0;
+
+    ServerPtr targetServer(newServer(defaultServerSettings, H2Type::h2Direct));
+
+    QMetaObject::invokeMethod(targetServer.data(), "startServer", Qt::QueuedConnection);
+    runEventLoop();
+
+    nRequests = 1;
+    nSentRequests = 0;
+
+    const auto url = requestUrl(H2Type::h2Direct);
+    QNetworkRequest request(url);
+    request.setAttribute(QNetworkRequest::Http2DirectAttribute, true);
+
+    std::unique_ptr<QNetworkReply> reply{manager->get(request)};
+    reply->ignoreSslErrors();
+    connect(reply.get(), &QNetworkReply::encrypted, reply.get(), [reply = reply.get()](){
+        reply->abort();
+    });
+    connect(reply.get(), &QNetworkReply::errorOccurred, this, &tst_Http2::replyFinishedWithError);
+
+    runEventLoop();
+    STOP_ON_FAILURE
+
+    QCOMPARE(nRequests, 0);
+    QCOMPARE(reply->error(), QNetworkReply::OperationCanceledError);
+
+    const bool res = QTest::qWaitFor(
+            [this, server = targetServer.get()]() {
+                return serverGotSettingsACK || prefaceOK || nSentRequests > 0;
+            },
+            500);
+    QVERIFY(!res);
+#endif // QT_CONFIG(ssl)
+}
+
 void tst_Http2::serverStarted(quint16 port)
 {
     serverPort = port;