add Utils::SaveFile: class for atomic saving of files

inspired by KSaveFile

src/libs/utils/savefile.cpp

@@ -0,0 +1,106 @@
+/**************************************************************************
+**
+** This file is part of Qt Creator
+**
+** Copyright (c) 2011 Nokia Corporation and/or its subsidiary(-ies).
+**
+** Contact: Nokia Corporation (info@qt.nokia.com)
+**
+**
+** GNU Lesser General Public License Usage
+**
+** This file may be used under the terms of the GNU Lesser General Public
+** License version 2.1 as published by the Free Software Foundation and
+** appearing in the file LICENSE.LGPL included in the packaging of this file.
+** Please review the following information to ensure the GNU Lesser General
+** Public License version 2.1 requirements will be met:
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Nokia gives you certain additional
+** rights. These rights are described in the Nokia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** Other Usage
+**
+** Alternatively, this file may be used in accordance with the terms and
+** conditions contained in a signed written agreement between you and Nokia.
+**
+** If you have questions regarding the use of this file, please contact
+** Nokia at qt-info@nokia.com.
+**
+**************************************************************************/
+
+#include "savefile.h"
+
+#include "qtcassert.h"
+
+#include <QtCore/QFileInfo>
+#include <QtCore/QTemporaryFile>
+
+namespace Utils {
+
+SaveFile::SaveFile(const QString &filename)
+{
+    m_finalFileName = filename;
+    m_finalized = false;
+    m_backup = false;
+}
+
+SaveFile::~SaveFile()
+{
+    QTC_ASSERT(m_finalized, rollback());
+}
+
+bool SaveFile::open(OpenMode flags)
+{
+    QTC_ASSERT(!m_finalFileName.isEmpty() && fileName().isEmpty(), return false);
+
+    QFile ofi(m_finalFileName);
+    // Check whether the existing file is writable
+    if (ofi.exists() && !ofi.open(QIODevice::ReadWrite)) {
+        setErrorString(ofi.errorString());
+        return false;
+    }
+
+    setAutoRemove(false);
+    setFileTemplate(m_finalFileName);
+    if (!QTemporaryFile::open(flags))
+        return false;
+
+    if (ofi.exists())
+        setPermissions(ofi.permissions()); // Ignore errors
+
+    return true;
+}
+
+void SaveFile::rollback()
+{
+    remove();
+    m_finalized = true;
+}
+
+bool SaveFile::commit()
+{
+    QTC_ASSERT(!m_finalized, return false);
+    m_finalized = true;
+
+    close();
+    if (error() != NoError) {
+        remove();
+        return false;
+    }
+
+    QString bakname = m_finalFileName + QLatin1Char('~');
+    QFile::remove(bakname); // Kill old backup
+    QFile::rename(m_finalFileName, bakname); // Backup current file
+    if (!rename(m_finalFileName)) { // Replace current file
+        QFile::rename(bakname, m_finalFileName); // Rollback to current file
+        return false;
+    }
+    if (!m_backup)
+        QFile::remove(bakname);
+
+    return true;
+}
+
+} // namespace Utils