From 5035e7b5fb9a0c08dd10658ef0581c9a3d2c000a Mon Sep 17 00:00:00 2001
From: Mathew Sutcliffe <oktal3700@gmail.com>
Date: Fri, 4 Nov 2016 01:24:19 +0000
Subject: [PATCH] refs #782 CAtomicFile on Windows: flush buffer before
 attempting to rename, and use ReplaceFile to rename if target already exists.

---
 src/blackmisc/atomicfile.cpp | 12 ++++++++++--
 src/blackmisc/atomicfile.h   |  2 ++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/blackmisc/atomicfile.cpp b/src/blackmisc/atomicfile.cpp
index b28bda36f..d94018919 100644
--- a/src/blackmisc/atomicfile.cpp
+++ b/src/blackmisc/atomicfile.cpp
@@ -21,6 +21,7 @@
 #include <errno.h>
 #elif defined(Q_OS_WIN32)
 #include <windows.h>
+#include <io.h>
 #endif
 
 //! \var qt_ntfs_permission_lookup
@@ -73,6 +74,10 @@ namespace BlackMisc
     {
         if (! isOpen()) { return; }
 
+#if defined(Q_OS_WIN32)
+        FlushFileBuffers(reinterpret_cast<HANDLE>(_get_osfhandle(handle())));
+#endif
+
         QFile::close();
 
         if (error() == NoError) { replaceOriginal(); }
@@ -135,13 +140,16 @@ namespace BlackMisc
             const auto prefix = "\\\\?\\"; // support long paths: https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247.aspx#maxpath
             return (prefix + QDir::toNativeSeparators(QDir::cleanPath(QFileInfo(s).absoluteFilePath()))).toStdWString();
         };
-        auto result = MoveFileEx(encode(fileName()).c_str(), encode(m_originalFilename).c_str(), MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH);
+        auto replace = exists(m_originalFilename);
+        auto result = replace
+            ? ReplaceFile(encode(m_originalFilename).c_str(), encode(fileName()).c_str(), nullptr, REPLACEFILE_IGNORE_MERGE_ERRORS, nullptr, nullptr)
+            : MoveFileEx(encode(fileName()).c_str(), encode(m_originalFilename).c_str(), MOVEFILE_WRITE_THROUGH);
         if (! result)
         {
             m_renameError = true;
             wchar_t *s = nullptr;
             FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM, nullptr, GetLastError(), 0, reinterpret_cast<LPWSTR>(&s), 0, nullptr);
-            setErrorString(QString::fromWCharArray(s).simplified());
+            setErrorString((replace ? "ReplaceFile: " : "MoveFileEx: ") + QString::fromWCharArray(s).simplified());
             LocalFree(reinterpret_cast<HLOCAL>(s));
         }
     }
diff --git a/src/blackmisc/atomicfile.h b/src/blackmisc/atomicfile.h
index 126cbd86e..d7b467d6c 100644
--- a/src/blackmisc/atomicfile.h
+++ b/src/blackmisc/atomicfile.h
@@ -27,6 +27,8 @@ namespace BlackMisc
      * when it is closed, so that it overwrites the target file as a single, atomic transaction.
      *
      * If the application crashes while data is still being written, the original file is unchanged.
+     *
+     * \fixme Consider using QSaveFile.
      */
     class BLACKMISC_EXPORT CAtomicFile : public QFile
     {