Another issue revealed during testing is that older Windows systems
cannot handle the reserved file names well. While Windows 8 and 10 are
fine (they silently abort the file transfer), using reserved names with
Windows 7 can flat out crash explorer.exe or result into weird error
messages like "fatal error: 0x00000000 ERROR_SUCCESS".
This is not required by MS-RDPECLIP specification, but we should try to
avoid this issue as not using reserved file names seems to be assumed
a common sense in Windows protocols.
The most convenient way to handle the issue would be on wClipboard level
so that WinPR's clients do not bother with it. We should prohibit the
reserved names from being used in FILEDESCRIPTOR, failing the conversion
if we see such a file.
POSIX subsystem (the only one at the moment) handles remote file names
in two places so move the Unicode conversion and the new validation
check into a separate function.
The reserved file name predicate is placed into <winpr/file.h> so that
it can be used in other places too. For example, other wClipboard local
file subsystems will need it. (It would be really nice to enforce this
check somewhere in the common code, so that the subsystems can't miss
it, but other places can miss some errors thus we're doing it here, as
early as possible.)
The predicate acts on separate file name components rather than full
file names because the backslash is a reserved character too. If we
process full file names this can result in phantom directory entry in
the remote file name. Not to say that handling ready-made components
spares us from splitting the full file name to extract them :)
The implementation is... a bit verbose, but that's fine by me. In the
absence of functions for case-insensitive wide string comparison and
the need to check for the [0-9] at the end of some file names this is
quite readable. Thanks to FAT and NTFS for being case-insensitive and
to MS-DOS for having reserved file names in the first place.
