Enforce a TCP/TLS HTTP timeout on Qt 6.3+

Timeouts for long requests like launch or resume timed the entire
HTTP operation. If the host was no longer reachable, we could
spend 2 minutes sitting there, even though we hadn't even made
successful contact with the host to give it our request yet.

Now we will time out a request if we can't send it in 5 seconds,
regardless of how long we want to wait for the server to respond.

app/backend/nvhttp.cpp

@@ -516,14 +516,35 @@ NvHTTP::openConnection(QUrl baseUrl,
 
     auto sslErrorsConnection = connect(m_Nam, &QNetworkAccessManager::sslErrors, this, &NvHTTP::handleSslErrors);
     QNetworkReply* reply = m_Nam->get(request);
-
-    // Run the request with a timeout if requested
     QEventLoop loop;
+
+    // Connect the quit signals
     connect(reply, &QNetworkReply::finished, &loop, &QEventLoop::quit);
     connect(QCoreApplication::instance(), &QCoreApplication::aboutToQuit, &loop, &QEventLoop::quit);
+
+    // Enforce a transfer timeout if requested
     if (timeoutMs) {
         QTimer::singleShot(timeoutMs, &loop, &QEventLoop::quit);
     }
+
+#if QT_VERSION >= QT_VERSION_CHECK(6, 3, 0)
+    // Time the request to distinguish a slow response from an unreachable host
+    auto* connectTimer = new QTimer(reply);
+    connectTimer->setSingleShot(true);
+    connect(connectTimer, &QTimer::timeout, reply, [reply, logLevel, url]() {
+        if (!reply->isFinished()) {
+            if (logLevel >= NvLogLevel::NVLL_ERROR) {
+                qWarning() << "Aborting timed out connection for" << url.toString();
+            }
+
+            reply->setProperty("timeout_reason", "connection_timeout");
+            reply->abort();
+        }
+    });
+    connect(reply, &QNetworkReply::requestSent, connectTimer, &QTimer::stop);
+    connectTimer->start(REQUEST_TIMEOUT_MS);
+#endif
+
     if (logLevel >= NvLogLevel::NVLL_VERBOSE) {
         qInfo() << "Executing request:" << url.toString();
     }
@@ -559,7 +580,11 @@ NvHTTP::openConnection(QUrl baseUrl,
             throw exception;
         }
         else if (reply->error() == QNetworkReply::OperationCanceledError) {
-            QtNetworkReplyException exception(QNetworkReply::TimeoutError, "Request timed out");
+            QString reason = reply->property("timeout_reason").toString();
+            QtNetworkReplyException exception(QNetworkReply::TimeoutError,
+                                              reason == "connection_timeout" ?
+                                                  "Connection timed out" :
+                                                  "Request timed out");
             delete reply;
             throw exception;
         }
@@ -570,5 +595,11 @@ NvHTTP::openConnection(QUrl baseUrl,
         }
     }
 
+#if QT_VERSION >= QT_VERSION_CHECK(6, 3, 0)
+    // The requestSent signal must have stopped the timer for any successful request,
+    // otherwise we could falsely time out a slow response when we connected fine.
+    Q_ASSERT(!connectTimer->isActive());
+#endif
+
     return reply;
 }