R devel - Aug 2023 - R-4.3 version list.files function could not work correctly in chinese

Found it! Looks like a buffer length problem. This isn't limited to
Chinese, just more likely to happen when a character takes three bytes
to represent in UTF-8. (Any filename containing characters which take
more than one byte to represent in UTF-8 may fail.)

If a directory contains a file with a sufficiently long name,
FindNextFile() fails with ERROR_MORE_DATA (0xEA, 234), making
R_readdir() return NULL, stopping list_files() prematurely:

# everything seems to work fine...

list.files("????")
# [1] "????-non-utf8-?????
????????????????????????????????????????????????????.txt"
# [2] "????-non-utf8-?????.txt"
# [3] "????-utf-8.txt"

# now create a file with an even longer name

list.files("????")
# [1] "????-non-utf8-?????
????????????????????????????????????????????????????.txt"

# the files are still there, but not visible to list.files():

system("cmd /c dir /s *.txt")
#  Volume in drive C has no label.
#  Volume Serial Number is A85A-AA74
#
#  Directory of C:\R\R-4.3.1\bin\x64\????
#
# 08/12/2023  07:57 AM                22 ????-non-utf8-?????
????????????????????????????????????????????????????.txt
# 08/12/2023 07:57 AM                22 ????-non-utf8-?????
????????????????????????????????????????????????????????????????????????????????????????????????????????.txt
# 08/12/2023  07:57 AM                22 ????-non-utf8-?????.txt
# 08/12/2023  07:56 AM                18 ????-utf-8.txt
# 4 File(s)             84 bytes
# 
#       Total Files Listed:
#                4 File(s)             84 bytes
#                0 Dir(s)  29,281,538,048 bytes free
# [1] 0

Increasing the path length limits [*] doesn't help, since it's the
filename length limit that we're bumping against. While both
WIN32_FIND_DATAA and WIN32_FIND_DATAW contain fixed-size buffers, a
valid filename may take more than MAX_PATH bytes to represent in UTF-8
while still being under the limit of MAX_PATH wide characters. This may
mean having to rewrite list_files in terms of R_wopendir()/R_wreaddir()
for Windows. As a workaround, we may use the short filename (which
sometimes may not exist, alas) when FindNextFile() fails with
ERROR_MORE_DATA.

-- 
Best regards,
Ivan

[*]
https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation

On 8/13/23 13:16, Ivan Krylov wrote:
> Found it! Looks like a buffer length problem. This isn't limited to
> Chinese, just more likely to happen when a character takes three bytes
> to represent in UTF-8. (Any filename containing characters which take
> more than one byte to represent in UTF-8 may fail.)
>
> If a directory contains a file with a sufficiently long name,
> FindNextFile() fails with ERROR_MORE_DATA (0xEA, 234), making
> R_readdir() return NULL, stopping list_files() prematurely:
>
> # everything seems to work fine...
>
> list.files("????")
> # [1] "????-non-utf8-?????
> ????????????????????????????????????????????????????.txt"
> # [2] "????-non-utf8-?????.txt"
> # [3] "????-utf-8.txt"
>
> # now create a file with an even longer name
>
> list.files("????")
> # [1] "????-non-utf8-?????
> ????????????????????????????????????????????????????.txt"
>
> # the files are still there, but not visible to list.files():
Thanks, Ivan, could you please turn this into a complete minimal 
reproducible example, ideally with only ASCII characters (if enough to 
trigger)? Or any reproducible example would do. I would have a look 
later today.
>
> system("cmd /c dir /s *.txt")
> #  Volume in drive C has no label.
> #  Volume Serial Number is A85A-AA74
> #
> #  Directory of C:\R\R-4.3.1\bin\x64\????
> #
> # 08/12/2023  07:57 AM                22 ????-non-utf8-?????
> ????????????????????????????????????????????????????.txt
> # 08/12/2023 07:57 AM                22 ????-non-utf8-?????
>
????????????????????????????????????????????????????????????????????????????????????????????????????????.txt
> # 08/12/2023  07:57 AM                22 ????-non-utf8-?????.txt
> # 08/12/2023  07:56 AM                18 ????-utf-8.txt
> # 4 File(s)             84 bytes
> #
> #       Total Files Listed:
> #                4 File(s)             84 bytes
> #                0 Dir(s)  29,281,538,048 bytes free
> # [1] 0
>
> Increasing the path length limits [*] doesn't help, since it's the
> filename length limit that we're bumping against. While both
> WIN32_FIND_DATAA and WIN32_FIND_DATAW contain fixed-size buffers, a
> valid filename may take more than MAX_PATH bytes to represent in UTF-8
> while still being under the limit of MAX_PATH wide characters. This may
> mean having to rewrite list_files in terms of R_wopendir()/R_wreaddir()
> for Windows. As a workaround, we may use the short filename (which
> sometimes may not exist, alas) when FindNextFile() fails with
> ERROR_MORE_DATA.
I admit I didn't get your analysis. However, I've rewritten this code 
for R 4.3 to support long paths (when enabled in the system), more in 
https://blog.r-project.org/2023/03/07/path-length-limit-on-windows/index.html. 
As this was reported to be regression in 4.3, it is entirely possible 
this change came with a regression (though a bit surprising we didn't 
catch it earlier by testing), so it would be a great help if I could 
have the example and debug it.

Thanks,
Tomas