Windows UWP CreateFIle2 cannot read file in ApplicationData.LocalFolder - visual-c++

Question

I am trying to build UWP app in C#. My app has a native library written in C++. Whenever the app tries to read a file in ApplicationData.LocalFolder, CreateFile2 api is returning ERROR_NOT_SUPPORTED_IN_APPCONTAINER. The file exists in the path specified to this api.
This is the sequence of operation in my app.
Launch app. App creates file & writes some data
Later on based on user input app tries to read data in this file
Step 1 is working fine. App is able to create the file & write data in it. Only when app tries to access it later on, does it get this error.
I get the path to ApplicationData.LocalFolder using
Windows.Storage.ApplicationData.Current.LocalFolder.Path
This is the actual path I see in the app:
C:\Users\xxxxx\AppData\Local\Packages\ac7a11e4-c1d6-4d37-b9eb-a4b0dc8f67b8_yyjvd81p022em\LocalState\temp.txt
My code is as below:
CREATEFILE2_EXTENDED_PARAMETERS ms_param = {0};
ms_param.dwSize = sizeof(CREATEFILE2_EXTENDED_PARAMETERS);
ms_param.dwFileAttributes = FILE_ATTRIBUTE_READONLY;
ms_param.dwFileFlags = FILE_FLAG_NO_BUFFERING;
ms_param.dwSecurityQosFlags = SECURITY_DELEGATION;
ms_param.lpSecurityAttributes = NULL;
ms_param.hTemplateFile = NULL;
g_hfile = CreateFile2(filename, GENERIC_READ, FILE_SHARE_READ|FILE_SHARE_WRITE, OPEN_EXISTING, &ms_param);
if (g_hfile == INVALID_HANDLE_VALUE)
{
return GetLastError();
}
I tried CreateFile2 with both OPEN_EXISTING & OPEN_ALWAYS option for dwCreationDisposition parameter, but I see the same error in either case.
I had similar issue with CreateFile2 earlier. But that was an problem with my app & I have fixed that issue. This time though the file is available within the LocalFolder, still I get the error.

Answer 1

The problem here is related to the dwSecurityQosFlags you've set in CREATEFILE2_EXTENDED_PARAMETERS.
When called from a Windows Store app, CreateFile2 is simplified. You can open only files or directories inside the ApplicationData.LocalFolder or Package.InstalledLocation directories. You can't open named pipes or mailslots or create encrypted files (FILE_ATTRIBUTE_ENCRYPTED).
The dwSecurityQosFlags parameter specifies SQOS information. In Windows Stroe app, we can only set it to SECURITY_ANONYMOUS. Using other flag will raise ERROR_NOT_SUPPORTED_IN_APPCONTAINER exception. This indicates that it is not supported in UWP app.
Following is the code I used to test:
StorageFolder^ localFolder = ApplicationData::Current->LocalFolder;
String^ path = localFolder->Path;
path += L"\\MyFile.txt";
CREATEFILE2_EXTENDED_PARAMETERS ms_param = { 0 };
ms_param.dwSize = sizeof(CREATEFILE2_EXTENDED_PARAMETERS);
ms_param.dwFileAttributes = FILE_ATTRIBUTE_READONLY;
ms_param.dwFileFlags = FILE_FLAG_NO_BUFFERING;
ms_param.dwSecurityQosFlags = SECURITY_ANONYMOUS;
ms_param.lpSecurityAttributes = NULL;
ms_param.hTemplateFile = NULL;
HANDLE g_hfile = CreateFile2(path->Data(), GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, OPEN_EXISTING, &ms_param);
DWORD error = GetLastError();
If I don't have "MyFile.txt" under LocalFolder, I will get ERROR_FILE_NOT_FOUND exception, otherwise it will be ERROR_SUCCESS.