Fix QFile append on windows

1. make windows file engine seek to end on open to match unix/symbian
2. make qfile forcibly seek the file engine in case a custom file
   engine has the same bug.

Task-number: QTBUG-25906
Change-Id: I62a26519a9401e547ff77bd8a71027cb361dc671
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>

2 files changed, 10 insertions, 2 deletions

diff --git a/src/corelib/io/qfile.cpp b/src/corelib/io/qfile.cpp
index c4bc612..8eea244 100644
--- a/src/corelib/io/qfile.cpp
+++ b/src/corelib/io/qfile.cpp
@@ -1036,8 +1036,11 @@ bool QFile::open(OpenMode mode)
 #endif
     {
         QIODevice::open(mode);
-        if (mode & Append)
-            seek(size());
+        if (mode & Append) {
+            //The file engine should have done this in open(),
+            //this is a workaround for backward compatibility
+            fileEngine()->seek(size());
+        }
         return true;
     }
     QFile::FileError err = d->fileEngine->error();
diff --git a/src/corelib/io/qfsfileengine_win.cpp b/src/corelib/io/qfsfileengine_win.cpp
index 8014720..a148fd9 100644
--- a/src/corelib/io/qfsfileengine_win.cpp
+++ b/src/corelib/io/qfsfileengine_win.cpp
@@ -144,6 +144,11 @@ bool QFSFileEnginePrivate::nativeOpen(QIODevice::OpenMode openMode)
     if (openMode & QIODevice::Truncate)
         q->setSize(0);
 
+    // Seek to the end when in Append mode.
+    if (openMode & QFile::Append) {
+        ::SetFilePointer(fileHandle, 0, 0, FILE_END);
+    }
+
     return true;
 }