From c47b981a56414379a6964ae3dac609eaae88f33d Mon Sep 17 00:00:00 2001
From: sledgehammer999 <hammered999@gmail.com>
Date: Sun, 29 Jun 2025 22:25:34 +0300
Subject: [PATCH] Add fallback to update mechanism

This brings a fallback version check to the update mechanism,
which should be as stable as it can be.
It will allow migrating to another primary mechanism without
having to have updated the older primary mechanism too.
---
 src/gui/programupdater.cpp | 72 ++++++++++++++++++++++++++++++++------
 src/gui/programupdater.h   |  8 ++++-
 2 files changed, 69 insertions(+), 11 deletions(-)

diff --git a/src/gui/programupdater.cpp b/src/gui/programupdater.cpp
index 063bc5473..58b1d47b0 100644
--- a/src/gui/programupdater.cpp
+++ b/src/gui/programupdater.cpp
@@ -35,10 +35,13 @@
 #include <QtSystemDetection>
 #include <QDebug>
 #include <QDesktopServices>
+#include <QJsonDocument>
+#include <QJsonValue>
 #include <QRegularExpression>
 #include <QXmlStreamReader>
 
 #include "base/global.h"
+#include "base/logger.h"
 #include "base/net/downloadmanager.h"
 #include "base/preferences.h"
 #include "base/utils/version.h"
@@ -82,30 +85,34 @@ namespace
 
 void ProgramUpdater::checkForUpdates() const
 {
+    const auto USER_AGENT = QStringLiteral("qBittorrent/" QBT_VERSION_2 " ProgramUpdater (www.qbittorrent.org)");
     const auto RSS_URL = u"https://www.fosshub.com/feed/5b8793a7f9ee5a5c3e97a3b2.xml"_s;
+    const auto FALLBACK_URL = u"https://www.qbittorrent.org/versions.json"_s;
+
     // Don't change this User-Agent. In case our updater goes haywire,
     // the filehost can identify it and contact us.
-    Net::DownloadManager::instance()->download(
-            Net::DownloadRequest(RSS_URL).userAgent(QStringLiteral("qBittorrent/" QBT_VERSION_2 " ProgramUpdater (www.qbittorrent.org)"))
+    Net::DownloadManager::instance()->download(Net::DownloadRequest(RSS_URL).userAgent(USER_AGENT)
             , Preferences::instance()->useProxyForGeneralPurposes(), this, &ProgramUpdater::rssDownloadFinished);
+    Net::DownloadManager::instance()->download(Net::DownloadRequest(FALLBACK_URL).userAgent(USER_AGENT)
+            , Preferences::instance()->useProxyForGeneralPurposes(), this, &ProgramUpdater::fallbackDownloadFinished);
+
+    m_hasCompletedOneReq = false;
 }
 
 QString ProgramUpdater::getNewVersion() const
 {
-    return m_newVersion;
+    return shouldUseFallback() ? m_fallbackRemoteVersion : m_remoteVersion;
 }
 
 void ProgramUpdater::rssDownloadFinished(const Net::DownloadResult &result)
 {
     if (result.status != Net::DownloadStatus::Success)
     {
-        qDebug() << "Downloading the new qBittorrent updates RSS failed:" << result.errorString;
-        emit updateCheckFinished();
+        LogMsg(tr("Failed to download the update info. URL: %1. Error: %2").arg(result.url, result.errorString) , Log::WARNING);
+        handleFinishedRequest();
         return;
     }
 
-    qDebug("Finished downloading the new qBittorrent updates RSS");
-
     const auto getStringValue = [](QXmlStreamReader &xml) -> QString
     {
         xml.readNext();
@@ -148,7 +155,7 @@ void ProgramUpdater::rssDownloadFinished(const Net::DownloadResult &result)
                         qDebug("Detected version is %s", qUtf8Printable(version));
                         if (isVersionMoreRecent(version))
                         {
-                            m_newVersion = version;
+                            m_remoteVersion = version;
                             m_updateURL = updateLink;
                         }
                     }
@@ -163,10 +170,55 @@ void ProgramUpdater::rssDownloadFinished(const Net::DownloadResult &result)
         }
     }
 
-    emit updateCheckFinished();
+    handleFinishedRequest();
+}
+
+void ProgramUpdater::fallbackDownloadFinished(const Net::DownloadResult &result)
+{
+    if (result.status != Net::DownloadStatus::Success)
+    {
+        LogMsg(tr("Failed to download the update info. URL: %1. Error: %2").arg(result.url, result.errorString) , Log::WARNING);
+        handleFinishedRequest();
+        return;
+    }
+
+    const auto json = QJsonDocument::fromJson(result.data);
+
+#if defined(Q_OS_MACOS)
+    const QString platformKey = u"macos"_s;
+#elif defined(Q_OS_WIN)
+    const QString platformKey = u"win"_s;
+#endif
+
+    if (const QJsonValue verJSON = json[platformKey][u"version"_s]; verJSON.isString())
+    {
+        const auto ver = verJSON.toString();
+        if (isVersionMoreRecent(ver))
+            m_fallbackRemoteVersion = ver;
+    }
+
+    handleFinishedRequest();
 }
 
 bool ProgramUpdater::updateProgram() const
 {
-    return QDesktopServices::openUrl(m_updateURL);
+    return QDesktopServices::openUrl(shouldUseFallback() ? u"https://www.qbittorrent.org/download"_s : m_updateURL);
+}
+
+void ProgramUpdater::handleFinishedRequest()
+{
+    if (m_hasCompletedOneReq)
+        emit updateCheckFinished();
+    else
+        m_hasCompletedOneReq = true;
+}
+
+bool ProgramUpdater::shouldUseFallback() const
+{
+    using Version = Utils::Version<4, 3>;
+
+    const auto remote = Version::fromString(m_remoteVersion);
+    const auto fallback = Version::fromString(m_fallbackRemoteVersion);
+
+    return fallback > remote;
 }
diff --git a/src/gui/programupdater.h b/src/gui/programupdater.h
index 88d41985f..3d046f853 100644
--- a/src/gui/programupdater.h
+++ b/src/gui/programupdater.h
@@ -55,8 +55,14 @@ signals:
 
 private slots:
     void rssDownloadFinished(const Net::DownloadResult &result);
+    void fallbackDownloadFinished(const Net::DownloadResult &result);
 
 private:
-    QString m_newVersion;
+    void handleFinishedRequest();
+    bool shouldUseFallback() const;
+
+    mutable bool m_hasCompletedOneReq = false;
+    QString m_remoteVersion;
+    QString m_fallbackRemoteVersion;
     QUrl m_updateURL;
 };