Detecting if a directory is a junction in Delphi

Question

I've been Google searching this I may be having some brain clouds because it just isn't working.

I need to detect if a folder is a junction so my recursive file search doesn't run off into an endless loop.

I could use a simple function like

IsJunction(attr: dword): boolean; 

where attr is dwFileAttributes from TWin32FindData;

I just can't seem to get it to work. Thanks!

Answer 1

dwFileAttributes of TWin32FindData does not have that information, you have to look to the dwReserved0 field. See documentation.

function IsJunction(const FileName: string): Boolean;
//  IO_REPARSE_TAG_MOUNT_POINT = $A0000003;
var
  FindHandle: THandle;
  FindData: TWin32FindData;
begin
  Result := False;
  FindHandle := FindFirstFile(PChar(FileName), FindData);
  if FindHandle <> INVALID_HANDLE_VALUE then begin
    Result := (Bool(FindData.dwFileAttributes and FILE_ATTRIBUTE_REPARSE_POINT))
              and Bool(FindData.dwReserved0 and $80000000) // MS bit
              and Bool(FindData.dwReserved0 and $20000000) // name surrogate bit
              and (LoWord(FindData.dwReserved0) = 3); // mount point value
    winapi.windows.FindClose(FindHandle);
  end else
    RaiseLastOSError;
end;