Propagator: Use FILE_SHARE_DELETE on Windows. #2070 #2597

src/libsync/filesystem.cpp

@@ -25,6 +25,7 @@
 #ifdef Q_OS_WIN
 #include <windef.h>
 #include <winbase.h>
+#include <fcntl.h>
 #endif
 
 // We use some internals of csync:
@@ -149,6 +150,62 @@ bool FileSystem::renameReplace(const QString& originFileName, const QString& des
     return true;
 }
 
+bool FileSystem::openFileSharedRead(QFile* file, QString* error)
+{
+    bool ok = false;
+    if (error) {
+        error->clear();
+    }
 
+#ifdef Q_OS_WIN
+    //
+    // The following code is adapted from Qt's QFSFileEnginePrivate::nativeOpen()
+    // by including the FILE_SHARE_DELETE share mode.
+    //
+
+    // Enable full sharing.
+    DWORD shareMode = FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE;
+
+    int accessRights = GENERIC_READ;
+    DWORD creationDisp = OPEN_EXISTING;
+
+    // Create the file handle.
+    SECURITY_ATTRIBUTES securityAtts = { sizeof(SECURITY_ATTRIBUTES), NULL, FALSE };
+    HANDLE fileHandle = CreateFileW(
+            (const wchar_t*)file->fileName().utf16(),
+            accessRights,
+            shareMode,
+            &securityAtts,
+            creationDisp,
+            FILE_ATTRIBUTE_NORMAL,
+            NULL);
+
+    // Bail out on error.
+    if (fileHandle == INVALID_HANDLE_VALUE) {
+        if (error) {
+            *error = qt_error_string();
+        }
+        return false;
+    }
+
+    // Convert the HANDLE to an fd and pass it to QFile's foreign-open
+    // function. The fd owns the handle, so when QFile later closes
+    // the fd the handle will be closed too.
+    int fd = _open_osfhandle((intptr_t)fileHandle, _O_RDONLY);
+    if (fd == -1) {
+        if (error) {
+            *error = "could not make fd from handle";
+        }
+        return false;
+    }
+    ok = file->open(fd, QIODevice::ReadOnly, QFile::AutoCloseHandle);
+#else
+    ok = file->open(QFile::ReadOnly);
+#endif
+    if (! ok && error) {
+        *error = file->errorString();
+    }
+    return ok;
+}
 
 }

src/libsync/filesystem.h

@@ -14,6 +14,7 @@
 #pragma once
 
 #include <QString>
+#include <QFile>
 #include <ctime>
 
 #include <owncloudlib.h>
@@ -49,4 +50,13 @@ bool setModTime(const QString &filename, time_t modTime);
 bool renameReplace(const QString &originFileName, const QString &destinationFileName,
                    QString *errorString);
 
+/**
+ * Replacement for QFile::open(ReadOnly) that sets a more permissive sharing mode
+ * on Windows.
+ *
+ * Warning: The resuting file may have an empty fileName and be unsuitable for use
+ * with QFileInfo!
+ */
+bool openFileSharedRead(QFile* file, QString* error);
+
 }}

src/libsync/propagateupload.cpp

@@ -348,9 +348,11 @@ void PropagateUploadFileQNAM::startNextChunk()
     QString path = _item._file;
 
     QFile file(_propagator->getFilePath(_item._file), this);
-    if (!file.open(QIODevice::ReadOnly)) {
+    QString openError;
+    // Warning: this clears file->fileName() and makes it unsuitable for QFileInfo!
+    if (!FileSystem::openFileSharedRead(&file, &openError)) {
         // Soft error because this is likely caused by the user modifying his files while syncing
-        abortWithError(SyncFileItem::SoftError, file.errorString());
+        abortWithError(SyncFileItem::SoftError, openError);
         return;
     }