prevent updating files when that would result in invalid mtime

ensure that we never try to sync a file with a sync that would result in
setting it up to an invalid mtime

test a recovery scenario with plain old sync folder and virtual files

Signed-off-by: Matthieu Gallien <matthieu.gallien@nextcloud.com>

6 files changed, 280 insertions, 36 deletions

diff --git a/src/libsync/discovery.cpp b/src/libsync/discovery.cpp
index c9a3b1d53..cb6ce2755 100644
--- a/src/libsync/discovery.cpp
+++ b/src/libsync/discovery.cpp
@@ -848,6 +848,12 @@ void ProcessDirectoryJob::processFileAnalyzeLocalInfo(
         if (_queryLocal != NormalQuery && _queryServer != NormalQuery)
             recurse = false;
 
+        if ((item->_direction == SyncFileItem::Down || item->_instruction == CSYNC_INSTRUCTION_CONFLICT) && (item->_modtime <= 0 || item->_modtime >= 0xFFFFFFFF)) {
+            item->_instruction = CSYNC_INSTRUCTION_ERROR;
+            item->_errorString = tr("Cannot sync due to invalid modification time");
+            item->_status = SyncFileItem::Status::NormalError;
+        }
+
         auto recurseQueryLocal = _queryLocal == ParentNotChanged ? ParentNotChanged : localEntry.isDirectory || item->_instruction == CSYNC_INSTRUCTION_RENAME ? NormalQuery : ParentDontExist;
         processFileFinalize(item, path, recurse, recurseQueryLocal, recurseQueryServer);
     };
@@ -875,14 +881,14 @@ void ProcessDirectoryJob::processFileAnalyzeLocalInfo(
         }
         path._original = originalPath;
         item->_originalFile = path._original;
-        item->_modtime = base._modtime;
-        item->_inode = base._inode;
+        item->_modtime = base.isValid() ? base._modtime : localEntry.modtime;
+        item->_inode = base.isValid() ? base._inode : localEntry.inode;
         item->_instruction = CSYNC_INSTRUCTION_RENAME;
         item->_direction = direction;
-        item->_fileId = base._fileId;
-        item->_remotePerm = base._remotePerm;
-        item->_etag = base._etag;
-        item->_type = base._type;
+        item->_fileId = base.isValid() ? base._fileId : QByteArray{};
+        item->_remotePerm = base.isValid() ? base._remotePerm : RemotePermissions{};
+        item->_etag = base.isValid() ? base._etag : QByteArray{};
+        item->_type = base.isValid() ? base._type : localEntry.type;
     };
 
     if (!localEntry.isValid()) {
@@ -1002,7 +1008,7 @@ void ProcessDirectoryJob::processFileAnalyzeLocalInfo(
             item->_type = localEntry.isDirectory ? ItemTypeDirectory : ItemTypeFile;
             _childModified = true;
         } else if (dbEntry._modtime > 0 && localEntry.modtime <= 0) {
-            item->_instruction = CSYNC_INSTRUCTION_SYNC;
+            item->_instruction = CSYNC_INSTRUCTION_UPDATE_METADATA;
             item->_direction = SyncFileItem::Down;
             item->_size = localEntry.size > 0 ? localEntry.size : dbEntry._fileSize;
             item->_modtime = dbEntry._modtime;
diff --git a/test/syncenginetestutils.cpp b/test/syncenginetestutils.cpp
index a5eaaaaf7..1d813e3ff 100644
--- a/test/syncenginetestutils.cpp
+++ b/test/syncenginetestutils.cpp
@@ -188,6 +188,13 @@ void FileInfo::setModTime(const QString &relativePath, const QDateTime &modTime)
     file->lastModified = modTime;
 }
 
+void FileInfo::setModTimeKeepEtag(const QString &relativePath, const QDateTime &modTime)
+{
+    FileInfo *file = find(relativePath);
+    Q_ASSERT(file);
+    file->lastModified = modTime;
+}
+
 FileInfo *FileInfo::find(PathComponents pathComponents, const bool invalidateEtags)
 {
     if (pathComponents.isEmpty()) {
diff --git a/test/syncenginetestutils.h b/test/syncenginetestutils.h
index c434925cc..8abe50848 100644
--- a/test/syncenginetestutils.h
+++ b/test/syncenginetestutils.h
@@ -128,6 +128,8 @@ public:
 
     void setModTime(const QString &relativePath, const QDateTime &modTime) override;
 
+    void setModTimeKeepEtag(const QString &relativePath, const QDateTime &modTime);
+
     FileInfo *find(PathComponents pathComponents, const bool invalidateEtags = false);
 
     FileInfo *createDir(const QString &relativePath);
diff --git a/test/testlocaldiscovery.cpp b/test/testlocaldiscovery.cpp
index 448d2d2b6..fa714129d 100644
--- a/test/testlocaldiscovery.cpp
+++ b/test/testlocaldiscovery.cpp
@@ -387,8 +387,11 @@ private slots:
         QCOMPARE(fakeFolder.currentRemoteState(), expectedState);
     }
 
-    void testInvalidMtimeRecovery()
+    void testBlockInvalidMtimeSyncRemote()
     {
+        constexpr auto INVALID_MODTIME1 = 0;
+        constexpr auto INVALID_MODTIME2 = -3600;
+
         FakeFolder fakeFolder{FileInfo{}};
         QCOMPARE(fakeFolder.currentLocalState(), fakeFolder.currentRemoteState());
         const QString fooFileRootFolder("foo");
@@ -408,44 +411,177 @@ private slots:
 
         QVERIFY(fakeFolder.syncOnce());
 
-        fakeFolder.remoteModifier().setModTime(fooFileRootFolder, QDateTime::fromSecsSinceEpoch(0));
-        fakeFolder.remoteModifier().setModTime(barFileRootFolder, QDateTime::fromSecsSinceEpoch(0));
-        fakeFolder.remoteModifier().setModTime(blaFileRootFolder, QDateTime::fromSecsSinceEpoch(0));
-        fakeFolder.remoteModifier().setModTime(fooFileSubFolder, QDateTime::fromSecsSinceEpoch(0));
-        fakeFolder.remoteModifier().setModTime(barFileSubFolder, QDateTime::fromSecsSinceEpoch(0));
-        fakeFolder.remoteModifier().setModTime(blaFileSubFolder, QDateTime::fromSecsSinceEpoch(0));
-        fakeFolder.localModifier().setModTime(fooFileRootFolder, QDateTime::fromSecsSinceEpoch(0));
-        fakeFolder.localModifier().setModTime(barFileRootFolder, QDateTime::fromSecsSinceEpoch(0));
-        fakeFolder.localModifier().setModTime(blaFileRootFolder, QDateTime::fromSecsSinceEpoch(0));
-        fakeFolder.localModifier().setModTime(fooFileSubFolder, QDateTime::fromSecsSinceEpoch(0));
-        fakeFolder.localModifier().setModTime(barFileSubFolder, QDateTime::fromSecsSinceEpoch(0));
-        fakeFolder.localModifier().setModTime(blaFileSubFolder, QDateTime::fromSecsSinceEpoch(0));
+        fakeFolder.remoteModifier().setModTime(fooFileRootFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME1));
+        fakeFolder.remoteModifier().setModTime(barFileRootFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME1));
+        fakeFolder.remoteModifier().setModTime(blaFileRootFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME1));
+        fakeFolder.remoteModifier().setModTime(fooFileSubFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME1));
+        fakeFolder.remoteModifier().setModTime(barFileSubFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME1));
+        fakeFolder.remoteModifier().setModTime(blaFileSubFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME1));
+
+        QVERIFY(!fakeFolder.syncOnce());
+
+        QVERIFY(!fakeFolder.syncOnce());
+
+        fakeFolder.remoteModifier().setModTime(fooFileRootFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME2));
+        fakeFolder.remoteModifier().setModTime(barFileRootFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME2));
+        fakeFolder.remoteModifier().setModTime(blaFileRootFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME2));
+        fakeFolder.remoteModifier().setModTime(fooFileSubFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME2));
+        fakeFolder.remoteModifier().setModTime(barFileSubFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME2));
+        fakeFolder.remoteModifier().setModTime(blaFileSubFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME2));
+
+        QVERIFY(!fakeFolder.syncOnce());
+
+        QVERIFY(!fakeFolder.syncOnce());
+    }
+
+    void testBlockInvalidMtimeSyncLocal()
+    {
+        constexpr auto INVALID_MODTIME1 = 0;
+        constexpr auto INVALID_MODTIME2 = -3600;
+
+        FakeFolder fakeFolder{FileInfo{}};
+
+        int nGET = 0;
+        fakeFolder.setServerOverride([&](QNetworkAccessManager::Operation op, const QNetworkRequest &, QIODevice *) {
+            if (op == QNetworkAccessManager::GetOperation)
+                ++nGET;
+            return nullptr;
+        });
+
+        QCOMPARE(fakeFolder.currentLocalState(), fakeFolder.currentRemoteState());
+        const QString fooFileRootFolder("foo");
+        const QString barFileRootFolder("bar");
+        const QString blaFileRootFolder("bla");
+        const QString fooFileSubFolder("subfolder/foo");
+        const QString barFileSubFolder("subfolder/bar");
+        const QString blaFileSubFolder("subfolder/bla");
+
+        fakeFolder.remoteModifier().insert(fooFileRootFolder);
+        fakeFolder.remoteModifier().insert(barFileRootFolder);
+        fakeFolder.remoteModifier().insert(blaFileRootFolder);
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("subfolder"));
+        fakeFolder.remoteModifier().insert(fooFileSubFolder);
+        fakeFolder.remoteModifier().insert(barFileSubFolder);
+        fakeFolder.remoteModifier().insert(blaFileSubFolder);
 
         QVERIFY(fakeFolder.syncOnce());
+        nGET = 0;
+
+        fakeFolder.localModifier().setModTime(fooFileRootFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME1));
+        fakeFolder.localModifier().setModTime(barFileRootFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME1));
+        fakeFolder.localModifier().setModTime(blaFileRootFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME1));
+        fakeFolder.localModifier().setModTime(fooFileSubFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME1));
+        fakeFolder.localModifier().setModTime(barFileSubFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME1));
+        fakeFolder.localModifier().setModTime(blaFileSubFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME1));
 
         QVERIFY(fakeFolder.syncOnce());
+        QCOMPARE(nGET, 0);
 
-        auto expectedState = fakeFolder.currentLocalState();
-        QCOMPARE(fakeFolder.currentRemoteState(), expectedState);
+        QVERIFY(fakeFolder.syncOnce());
+        QCOMPARE(nGET, 0);
 
-        fakeFolder.remoteModifier().setModTime(fooFileRootFolder, QDateTime::fromSecsSinceEpoch(-3600));
-        fakeFolder.remoteModifier().setModTime(barFileRootFolder, QDateTime::fromSecsSinceEpoch(-3600));
-        fakeFolder.remoteModifier().setModTime(blaFileRootFolder, QDateTime::fromSecsSinceEpoch(-3600));
-        fakeFolder.remoteModifier().setModTime(fooFileSubFolder, QDateTime::fromSecsSinceEpoch(-3600));
-        fakeFolder.remoteModifier().setModTime(barFileSubFolder, QDateTime::fromSecsSinceEpoch(-3600));
-        fakeFolder.remoteModifier().setModTime(blaFileSubFolder, QDateTime::fromSecsSinceEpoch(-3600));
-        fakeFolder.localModifier().setModTime(fooFileRootFolder, QDateTime::fromSecsSinceEpoch(-3600));
-        fakeFolder.localModifier().setModTime(barFileRootFolder, QDateTime::fromSecsSinceEpoch(-3600));
-        fakeFolder.localModifier().setModTime(blaFileRootFolder, QDateTime::fromSecsSinceEpoch(-3600));
-        fakeFolder.localModifier().setModTime(fooFileSubFolder, QDateTime::fromSecsSinceEpoch(-3600));
-        fakeFolder.localModifier().setModTime(barFileSubFolder, QDateTime::fromSecsSinceEpoch(-3600));
-        fakeFolder.localModifier().setModTime(blaFileSubFolder, QDateTime::fromSecsSinceEpoch(-3600));
+        fakeFolder.localModifier().setModTime(fooFileRootFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME2));
+        fakeFolder.localModifier().setModTime(barFileRootFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME2));
+        fakeFolder.localModifier().setModTime(blaFileRootFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME2));
+        fakeFolder.localModifier().setModTime(fooFileSubFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME2));
+        fakeFolder.localModifier().setModTime(barFileSubFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME2));
+        fakeFolder.localModifier().setModTime(blaFileSubFolder, QDateTime::fromSecsSinceEpoch(INVALID_MODTIME2));
 
-        QVERIFY(!fakeFolder.syncOnce());
+        QVERIFY(fakeFolder.syncOnce());
+        QCOMPARE(nGET, 0);
+
+        QVERIFY(fakeFolder.syncOnce());
+        QCOMPARE(nGET, 0);
+    }
+
+    void testDoNotSyncInvalidFutureMtime()
+    {
+        constexpr auto FUTURE_MTIME = 0xFFFFFFFF;
+        constexpr auto CURRENT_MTIME = 1646057277;
+
+        FakeFolder fakeFolder{FileInfo{}};
+        QCOMPARE(fakeFolder.currentLocalState(), fakeFolder.currentRemoteState());
+
+        const QString fooFileRootFolder("foo");
+        const QString barFileRootFolder("bar");
+        const QString fooFileSubFolder("subfolder/foo");
+        const QString barFileSubFolder("subfolder/bar");
+        const QString fooFileAaaSubFolder("aaa/subfolder/foo");
+        const QString barFileAaaSubFolder("aaa/subfolder/bar");
+
+        fakeFolder.remoteModifier().insert(fooFileRootFolder);
+        fakeFolder.remoteModifier().insert(barFileRootFolder);
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("subfolder"));
+        fakeFolder.remoteModifier().insert(fooFileSubFolder);
+        fakeFolder.remoteModifier().insert(barFileSubFolder);
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("aaa"));
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("aaa/subfolder"));
+        fakeFolder.remoteModifier().insert(fooFileAaaSubFolder);
+        fakeFolder.remoteModifier().insert(barFileAaaSubFolder);
+
+        QVERIFY(fakeFolder.syncOnce());
+
+        fakeFolder.remoteModifier().setModTime(fooFileRootFolder, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.remoteModifier().setModTime(barFileRootFolder, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.remoteModifier().setModTime(fooFileSubFolder, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.remoteModifier().setModTime(barFileSubFolder, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.remoteModifier().setModTime(fooFileAaaSubFolder, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.remoteModifier().setModTime(barFileAaaSubFolder, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.localModifier().setModTime(fooFileRootFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.localModifier().setModTime(barFileRootFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.localModifier().setModTime(fooFileSubFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.localModifier().setModTime(barFileSubFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.localModifier().setModTime(fooFileAaaSubFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.localModifier().setModTime(barFileAaaSubFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
 
         QVERIFY(!fakeFolder.syncOnce());
+    }
+
+    void testInvalidFutureMtimeRecovery()
+    {
+        constexpr auto FUTURE_MTIME = 0xFFFFFFFF;
+        constexpr auto CURRENT_MTIME = 1646057277;
+
+        FakeFolder fakeFolder{FileInfo{}};
+        QCOMPARE(fakeFolder.currentLocalState(), fakeFolder.currentRemoteState());
 
-        expectedState = fakeFolder.currentLocalState();
+        const QString fooFileRootFolder("foo");
+        const QString barFileRootFolder("bar");
+        const QString fooFileSubFolder("subfolder/foo");
+        const QString barFileSubFolder("subfolder/bar");
+        const QString fooFileAaaSubFolder("aaa/subfolder/foo");
+        const QString barFileAaaSubFolder("aaa/subfolder/bar");
+
+        fakeFolder.remoteModifier().insert(fooFileRootFolder);
+        fakeFolder.remoteModifier().insert(barFileRootFolder);
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("subfolder"));
+        fakeFolder.remoteModifier().insert(fooFileSubFolder);
+        fakeFolder.remoteModifier().insert(barFileSubFolder);
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("aaa"));
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("aaa/subfolder"));
+        fakeFolder.remoteModifier().insert(fooFileAaaSubFolder);
+        fakeFolder.remoteModifier().insert(barFileAaaSubFolder);
+
+        QVERIFY(fakeFolder.syncOnce());
+
+        fakeFolder.remoteModifier().setModTimeKeepEtag(fooFileRootFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.remoteModifier().setModTimeKeepEtag(barFileRootFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.remoteModifier().setModTimeKeepEtag(fooFileSubFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.remoteModifier().setModTimeKeepEtag(barFileSubFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.remoteModifier().setModTimeKeepEtag(fooFileAaaSubFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.remoteModifier().setModTimeKeepEtag(barFileAaaSubFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.localModifier().setModTime(fooFileRootFolder, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.localModifier().setModTime(barFileRootFolder, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.localModifier().setModTime(fooFileSubFolder, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.localModifier().setModTime(barFileSubFolder, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.localModifier().setModTime(fooFileAaaSubFolder, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.localModifier().setModTime(barFileAaaSubFolder, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+
+        QVERIFY(fakeFolder.syncOnce());
+
+        QVERIFY(fakeFolder.syncOnce());
+
+        auto expectedState = fakeFolder.currentLocalState();
         QCOMPARE(fakeFolder.currentRemoteState(), expectedState);
     }
 };
diff --git a/test/testsyncengine.cpp b/test/testsyncengine.cpp
index 1ec461aa1..bc6125616 100644
--- a/test/testsyncengine.cpp
+++ b/test/testsyncengine.cpp
@@ -1129,6 +1129,34 @@ private slots:
 
         QCOMPARE(fakeFolder.currentLocalState(), fakeFolder.currentRemoteState());
     }
+
+    void testFolderWithFilesInError()
+    {
+        FakeFolder fakeFolder{FileInfo{}};
+
+        fakeFolder.setServerOverride([&](QNetworkAccessManager::Operation op, const QNetworkRequest &request, QIODevice *outgoingData) -> QNetworkReply * {
+            Q_UNUSED(outgoingData)
+
+            if (op == QNetworkAccessManager::GetOperation) {
+                const auto fileName = getFilePathFromUrl(request.url());
+                if (fileName == QStringLiteral("aaa/subfolder/foo")) {
+                    return new FakeErrorReply(op, request, &fakeFolder.syncEngine(), 403);
+                }
+            }
+            return nullptr;
+        });
+
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("aaa"));
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("aaa/subfolder"));
+        fakeFolder.remoteModifier().insert(QStringLiteral("aaa/subfolder/bar"));
+
+        QVERIFY(fakeFolder.syncOnce());
+
+        fakeFolder.remoteModifier().insert(QStringLiteral("aaa/subfolder/foo"));
+        QVERIFY(!fakeFolder.syncOnce());
+
+        QVERIFY(!fakeFolder.syncOnce());
+    }
 };
 
 QTEST_GUILESS_MAIN(TestSyncEngine)
diff --git a/test/testsyncvirtualfiles.cpp b/test/testsyncvirtualfiles.cpp
index 882879c7b..e45fc7d58 100644
--- a/test/testsyncvirtualfiles.cpp
+++ b/test/testsyncvirtualfiles.cpp
@@ -1517,6 +1517,71 @@ private slots:
         QCOMPARE(fakeFolder.currentLocalState().find("A/hello" DVSUFFIX)->size, 222);
         QCOMPARE(fakeFolder.currentLocalState().find("A/igno" DVSUFFIX)->size, 123);
     }
+
+    void testUpdateMetadataErrorManagement()
+    {
+        FakeFolder fakeFolder{FileInfo{}};
+        setupVfs(fakeFolder);
+        QCOMPARE(fakeFolder.currentLocalState(), fakeFolder.currentRemoteState());
+
+        // Existing files are propagated just fine in both directions
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("aaa"));
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("aaa/subfolder"));
+        fakeFolder.remoteModifier().insert(QStringLiteral("aaa/subfolder/bar"));
+        QVERIFY(fakeFolder.syncOnce());
+
+        // New files on the remote create virtual files
+        fakeFolder.remoteModifier().setModTime(QStringLiteral("aaa/subfolder/bar"), QDateTime::fromSecsSinceEpoch(0));
+        QVERIFY(!fakeFolder.syncOnce());
+
+        QVERIFY(!fakeFolder.syncOnce());
+    }
+
+    void testInvalidFutureMtimeRecovery()
+    {
+        constexpr auto FUTURE_MTIME = 0xFFFFFFFF;
+        constexpr auto CURRENT_MTIME = 1646057277;
+
+        FakeFolder fakeFolder{FileInfo{}};
+        setupVfs(fakeFolder);
+        QCOMPARE(fakeFolder.currentLocalState(), fakeFolder.currentRemoteState());
+
+        const QString fooFileRootFolder("foo");
+        const QString barFileRootFolder("bar");
+        const QString fooFileSubFolder("subfolder/foo");
+        const QString barFileSubFolder("subfolder/bar");
+        const QString fooFileAaaSubFolder("aaa/subfolder/foo");
+        const QString barFileAaaSubFolder("aaa/subfolder/bar");
+
+        fakeFolder.remoteModifier().insert(fooFileRootFolder);
+        fakeFolder.remoteModifier().insert(barFileRootFolder);
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("subfolder"));
+        fakeFolder.remoteModifier().insert(fooFileSubFolder);
+        fakeFolder.remoteModifier().insert(barFileSubFolder);
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("aaa"));
+        fakeFolder.remoteModifier().mkdir(QStringLiteral("aaa/subfolder"));
+        fakeFolder.remoteModifier().insert(fooFileAaaSubFolder);
+        fakeFolder.remoteModifier().insert(barFileAaaSubFolder);
+
+        QVERIFY(fakeFolder.syncOnce());
+
+        fakeFolder.remoteModifier().setModTimeKeepEtag(fooFileRootFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.remoteModifier().setModTimeKeepEtag(barFileRootFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.remoteModifier().setModTimeKeepEtag(fooFileSubFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.remoteModifier().setModTimeKeepEtag(barFileSubFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.remoteModifier().setModTimeKeepEtag(fooFileAaaSubFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.remoteModifier().setModTimeKeepEtag(barFileAaaSubFolder, QDateTime::fromSecsSinceEpoch(CURRENT_MTIME));
+        fakeFolder.localModifier().setModTime(fooFileRootFolder + DVSUFFIX, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.localModifier().setModTime(barFileRootFolder + DVSUFFIX, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.localModifier().setModTime(fooFileSubFolder + DVSUFFIX, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.localModifier().setModTime(barFileSubFolder + DVSUFFIX, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.localModifier().setModTime(fooFileAaaSubFolder + DVSUFFIX, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+        fakeFolder.localModifier().setModTime(barFileAaaSubFolder + DVSUFFIX, QDateTime::fromSecsSinceEpoch(FUTURE_MTIME));
+
+        QVERIFY(fakeFolder.syncOnce());
+
+        QVERIFY(fakeFolder.syncOnce());
+    }
 };
 
 QTEST_GUILESS_MAIN(TestSyncVirtualFiles)