[Bug 8511] New: DragQueryFile returns wrong string length

[Wine Bugs]

http://bugs.winehq.org/show_bug.cgi?id=8511

Summary: DragQueryFile returns wrong string length
           Product: Wine
           Version: 0.9.33.
          Platform: Other
        OS/Version: other
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: wine-shell32
        AssignedTo: [e-mail]
        ReportedBy: [e-mail]

Hi,

A friend of mine tried to run a win32 software I made, which relies on
drag-and-drop features. My software is currently not working on Wine. We tracked
the problem down to the DragQueryFileW function.

Here is a reminder of the declaration:
UINT DragQueryFileW(HDROP hDrop, UINT iFile, LPWSTR lpszFile, UINT nBufferSize);

To get the needed length to store the file path, I call this function with 
lpszFile set to NULL:

UINT nNeededLength = DragQueryFileW(hDrop, iFile, NULL, 0);

nNeededLength is the total number of characters, not including the terminating
null character, as stated by the function documentation in MSDN.

Then I call the function again with a dynamically allocated buffer:
UINT nRet = DragQueryFileW(hDrop, iFile, pszFilePath, nNeededLength + 1);

The "+ 1" is because DragQueryFileW expects a buffer size that counts the
terminating null character. The return value, nRet, is equal to nNeededLength on
a real Windows.

On Wine 0.9.33 instead, we get the expected length + 1. I made a test I ran on
Windows 2000 then on Wine 0.9.33 that confirms the unexpected behavior.

By looking at Wine source code it looks like the same problem exists with
DragQueryFileA and DragQueryFile16 in shell.c and shellole.c

A possible test case in a WM_DROPFILES handler:

wchar szSuperBuffer[260];
UINT nFile = 0;
UINT nLengthNeeded = DragQueryFileW(hDrop, nFile, NULL, 0);
UINT nRet = DragQueryFileW(hDrop, nFile, szSuperBuffer, sizeof(szSuperBuffer));
UINT nLengthGot = strlenW(szSuperBuffer);
    	
if( !(nLengthNeeded == nRet && nLengthNeeded == nLengthGot))
{
    // ERROR ! (message box, error trace, or whatever)
}