Feature/cloud sync : add cloud sync support for dropbox and nextcloud with conflict resolution

src/CMakeLists.txt

@@ -293,7 +293,13 @@ if(KPXC_FEATURE_NETWORK)
             networking/UpdateChecker.cpp
             gui/UpdateCheckDialog.cpp
             gui/IconDownloader.cpp
-            gui/IconDownloaderDialog.cpp)
+            gui/IconDownloaderDialog.cpp
+            gui/remote/CloudSyncPage.cpp
+            gui/remote/dropbox/DropboxCloudSyncPage.cpp
+            gui/remote/nextcloud/NextcloudCloudSyncPage.cpp
+            gui/remote/nextcloud/NextcloudCloudSyncPage.h
+            gui/remote/nextcloud/NextcloudCloudSyncPage.ui
+            gui/remote/DatabaseSettingsWidgetCloudSync.cpp)
 endif()
 
 add_subdirectory(cli)
@@ -320,6 +326,11 @@ if(KPXC_FEATURE_FDOSECRETS)
     set(fdosecrets_LIB fdosecrets)
 endif()
 
+add_subdirectory(remotesync)
+# remotesync's foundation (provider abstraction + engine + command provider)
+# is always built.
+set(remotesync_LIB remotesync)
+
 configure_file(config-keepassx.h.cmake ${CMAKE_CURRENT_BINARY_DIR}/config-keepassx.h)
 configure_file(git-info.h.cmake ${CMAKE_CURRENT_BINARY_DIR}/git-info.h)
 
@@ -352,7 +363,8 @@ target_link_libraries(keepassxc_gui
         ${browser_LIB}
         ${fdosecrets_LIB}
         ${keeshare_LIB}
-        ${sshagent_LIB})
+        ${sshagent_LIB}
+        ${remotesync_LIB})
 
 if(APPLE)
     target_link_libraries(keepassxc_gui "-framework Foundation -framework AppKit -framework Carbon -framework Security -framework LocalAuthentication -framework ScreenCaptureKit")

src/core/Database.cpp

@@ -565,6 +565,7 @@ void Database::releaseData()
 
     m_data.clear();
     m_metadata->clear();
+    m_syncPreviousKey.reset();
 
     // Reset and delete the root group
     auto oldGroup = setRootGroup(new Group());
@@ -959,6 +960,27 @@ bool Database::setKey(const QSharedPointer<const CompositeKey>& key,
     return true;
 }
 
+void Database::setSyncPreviousKey(const QSharedPointer<const CompositeKey>& key)
+{
+    // Don't overwrite an existing snapshot: if the user does A->B->C without
+    // an intervening successful sync, the remote still holds A and that's
+    // the key we need to keep.
+    if (m_syncPreviousKey) {
+        return;
+    }
+    m_syncPreviousKey = key;
+}
+
+QSharedPointer<const CompositeKey> Database::syncPreviousKey() const
+{
+    return m_syncPreviousKey;
+}
+
+void Database::clearSyncPreviousKey()
+{
+    m_syncPreviousKey.reset();
+}
+
 QString Database::keyError()
 {
     return m_keyError;

src/core/Database.h

@@ -151,6 +151,13 @@ class Database : public ModifiableObject
                 bool updateChangedTime = true,
                 bool updateTransformSalt = false,
                 bool transformKey = true);
+    /// Snapshot of the master key prior to a change-key, kept transiently so
+    /// the cloud-sync engine can unlock the remote DB (which still holds the
+    /// old key) and migrate it to the new key. Cleared on successful sync
+    /// upload, on releaseData (lock/close), and on destruction. Not persisted.
+    void setSyncPreviousKey(const QSharedPointer<const CompositeKey>& key);
+    QSharedPointer<const CompositeKey> syncPreviousKey() const;
+    void clearSyncPreviousKey();
     QString keyError();
     QByteArray challengeResponseKey() const;
     bool challengeMasterSeed(const QByteArray& masterSeed);
@@ -253,6 +260,7 @@ public slots:
     bool m_hasNonDataChange = false;
     QString m_keyError;
     bool m_isTemporaryDatabase = false;
+    QSharedPointer<const CompositeKey> m_syncPreviousKey;
 
     QStringList m_commonUsernames;
     QStringList m_tagList;