Allow QSettings to synchronize non-atomically

This is required so that one can use QSettings in situations that
temporary files or renaming may not work.

[ChangeLog][QtCore][QSettings] Added setAtomicSyncRequired(), which
allows one to use QSettings with config files in unwriteable directories
or in Alternate Data Streams on NTFS on Windows. This used to work
before Qt 5.4, but remains a non-default behavior due to the potential
of data corruption.

Task-number: QTBUG-47379
Change-Id: I81480fdb578d4d43b3fcfffd14d4f77112f0402f
Reviewed-by: Jesus Fernandez <Jesus.Fernandez@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Kai Koehne <kai.koehne@qt.io>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

1 files changed, 76 insertions, 0 deletions

diff --git a/tests/auto/corelib/io/qsettings/tst_qsettings.cpp b/tests/auto/corelib/io/qsettings/tst_qsettings.cpp
index 332c2dcc01..012ce5f2f5 100644
--- a/tests/auto/corelib/io/qsettings/tst_qsettings.cpp
+++ b/tests/auto/corelib/io/qsettings/tst_qsettings.cpp
@@ -118,6 +118,10 @@ private slots:
     void remove();
     void contains();
     void sync();
+    void syncNonWriteableDir();
+#ifdef Q_OS_WIN
+    void syncAlternateDataStream();
+#endif
     void setFallbacksEnabled();
     void setFallbacksEnabled_data();
     void fromFile_data();
@@ -1750,6 +1754,78 @@ void tst_QSettings::sync()
     QCOMPARE(settings1.allKeys().count(), 11);
 }
 
+void tst_QSettings::syncNonWriteableDir()
+{
+    QTemporaryDir tempDir;
+    QVERIFY2(tempDir.isValid(), qUtf8Printable(tempDir.errorString()));
+
+    // first, create a file
+    QString filename = tempDir.path() + "/config.ini";
+    {
+        QFile f(filename);
+        QVERIFY2(f.open(QIODevice::WriteOnly), qUtf8Printable(f.errorString()));
+    }
+
+    // second, make the dir unwriteable
+    QVERIFY(QFile::setPermissions(tempDir.path(), QFile::ReadUser | QFile::ExeUser));
+    struct UndoSetPermissions {
+        QString name;
+        UndoSetPermissions(const QString &name) : name(name) {}
+        ~UndoSetPermissions()
+        { QFile::setPermissions(name, QFile::ReadUser | QFile::WriteUser | QFile::ExeUser); }
+    };
+    UndoSetPermissions undo(tempDir.path());    // otherwise, QTemporaryDir will fail
+
+    {
+        QSettings settings(filename, QSettings::IniFormat);
+        QVERIFY(settings.isAtomicSyncRequired());
+        settings.setAtomicSyncRequired(false);
+        settings.setValue("alpha/beta", 1);
+        settings.sync();
+        QCOMPARE(settings.status(), QSettings::NoError);
+    }
+
+    QVERIFY(QFileInfo(filename).size() != 0);
+    QSettings settings(filename, QSettings::IniFormat);
+    QCOMPARE(settings.value("alpha/beta"), QVariant(1));
+}
+
+#ifdef Q_OS_WIN
+void tst_QSettings::syncAlternateDataStream()
+{
+    QTemporaryDir tempDir;
+    QVERIFY2(tempDir.isValid(), qUtf8Printable(tempDir.errorString()));
+
+    // first, create a file
+    QString filename = tempDir.path() + "/file";
+    {
+        QFile f(filename);
+        QVERIFY2(f.open(QIODevice::WriteOnly), qUtf8Printable(f.errorString()));
+    }
+
+    // then create an ADS
+    filename += ":config.ini";
+    {
+        QFile f(filename);
+        if (!f.open(QIODevice::WriteOnly))
+            QSKIP("Could not create ADS file (" + f.errorString().toUtf8() + ") - FAT drive?");
+    }
+
+    {
+        QSettings settings(filename, QSettings::IniFormat);
+        QVERIFY(settings.isAtomicSyncRequired());
+        settings.setAtomicSyncRequired(false);
+        settings.setValue("alpha/beta", 1);
+        settings.sync();
+        QCOMPARE(settings.status(), QSettings::NoError);
+    }
+
+    QVERIFY(QFileInfo(filename).size() != 0);
+    QSettings settings(filename, QSettings::IniFormat);
+    QCOMPARE(settings.value("alpha/beta"), QVariant(1));
+}
+#endif
+
 void tst_QSettings::setFallbacksEnabled_data()
 {
     populateWithFormats();