refs #545 CAtomicFile used in CValueCache to avoid corruption in case serialization is interrupted.

src/blackmisc/atomicfile.cpp

@@ -0,0 +1,91 @@
+/* Copyright (C) 2015
+ * swift project Community / Contributors
+ *
+ * This file is part of swift project. It is subject to the license terms in the LICENSE file found in the top-level
+ * directory of this distribution and at http://www.swift-project.org/license.html. No part of swift project,
+ * including this file, may be copied, modified, propagated, or distributed except according to the terms
+ * contained in the LICENSE file.
+ */
+
+#include "blackmisc/atomicfile.h"
+#include "blackmisc/algorithm.h"
+#include <QFileInfo>
+#include <QDir>
+#if defined(Q_OS_POSIX)
+#include <stdio.h>
+#elif defined(Q_OS_WIN32)
+#include <windows.h>
+#endif
+
+namespace BlackMisc
+{
+
+    bool CAtomicFile::open(CAtomicFile::OpenMode mode)
+    {
+        Q_ASSERT_X(!(mode & (ReadOnly | Append)), Q_FUNC_INFO, "ReadOnly and Append flags are incompatible with CAtomicFile");
+
+        m_originalFilename = fileName();
+        QFileInfo fileInfo(fileName());
+        setFileName(QFileInfo(fileInfo.dir(), ".tmp." + fileInfo.fileName() + "." + randomSuffix()).filePath());
+        if (exists()) { remove(); }
+
+        bool ok = QFile::open(mode);
+        if (! ok) { setFileName(m_originalFilename); }
+        return ok;
+    }
+
+    void CAtomicFile::close()
+    {
+        if (! isOpen()) { return; }
+
+        QFile::close();
+
+        if (error() == NoError) { replaceOriginal(); }
+        setFileName(m_originalFilename);
+    }
+
+    bool CAtomicFile::checkedClose()
+    {
+        close();
+        return error() == NoError;
+    }
+
+    CAtomicFile::FileError CAtomicFile::error() const
+    {
+        if (m_renameError) { return RenameError; }
+        return QFile::error();
+    }
+
+    void CAtomicFile::unsetError()
+    {
+        m_renameError = false;
+        QFile::unsetError();
+    }
+
+    QString CAtomicFile::randomSuffix()
+    {
+        Q_CONSTEXPR auto max = 2176782335;
+        return QString::number(std::uniform_int_distribution<std::decay<decltype(max)>::type>(0, max)(Private::defaultRandomGenerator()), 36);
+    }
+
+#if defined(Q_OS_POSIX)
+    void CAtomicFile::replaceOriginal()
+    {
+        auto result = ::rename(qPrintable(fileName()), qPrintable(m_originalFilename));
+        if (result < 0) { m_renameError = true; }
+    }
+#elif defined(Q_OS_WIN32)
+    void CAtomicFile::replaceOriginal()
+    {
+        auto result = MoveFileExA(qPrintable(fileName()), qPrintable(m_originalFilename), MOVEFILE_REPLACE_EXISTING);
+        if (! result) { m_renameError = true; }
+    }
+#else
+    void CAtomicFile::replaceOriginal()
+    {
+        if (exists(m_originalFilename)) { remove(m_originalFilename); }
+        rename(m_originalFilename);
+    }
+#endif
+
+}