[1.7] Proposal: the filename encoding in C locale uses UTF-8 instead of SO/UTF-8

[IWAMURO Motonori]

Hi.

My idea is as follows:

1)  separate mbtowc/wctomb function entries to library usage and
system usage. (__mbtowc/__wctomb & __sys_mbtowc/__sys_wctomb)

2) If call setlocale(LC_CTYPE) by locale != "C", then lib == sys.

3) If call setlocale(LC_CTYPE) by locale == "C", then sys is set by
LC_ALL/LC_CTYPE/LANG. If LC_ALL/LC_CTYPE/LANG are not set, use UTF-8
converter.

Cygwin startup call setlocale(LC_CTYPE, "C") at winsup/cygwin/dcrt0.cc.

I think that the result is as follows:

1) LANG=C
   lib = ascii converter, sys = UTF-8 converter.

2) LANG=xx_XX.ENCODING & not call setlocale.
   lib = ascii converter, sys = ENCODING converter.

3) LANG=xx_XX.ENCODING & call setlocale(LC_ALL, "").
   lib = ENCODING converter, sys = ENCODING converter.

I think that [cat `read_dir_entry_and_print_app`] works correctly above all.

I am writing this patch and test code now.

> One problem can't be solved this way:  If an application fetches
> and stores a filename, then switches the locale, and then tries
> to use the filename in another system call, the filename is
> potentially broken.

If the application switches the encoding while processing, I think
that the problem is a responsibility of the application.

2009/5/13 Corinna Vinschen <corinna-cygwin@cygwin.com>:
> On May 12 19:37, Corinna Vinschen wrote:
>> On May 13 02:29, IWAMURO Motonori wrote:
>> > I propose that the filename encoding in C locale uses UTF-8 instead of SO/UTF-8.
>> >
>> > There are three reasons:
>>
>> That's an interesting thought.  Do you have a patch and, if so, did you
>> try it?  Does it, for instance, help for the issue reported in the
>> thread starting at http://cygwin.com/ml/cygwin/2009-05/msg00245.html?
>
> After examining the issue Lenik reported in the above thread, I'm at
> a loss how to solve this problem in a generic way.
>
> The problem is that the filename changes dependent on the character
> set used in $LANG.  The reason is that every time a multibyte filename
> has to be generated, it has to be converted from UTF-16 to multibyte.
>
> For instance, taking one of the filename from Lenik's example.  It's
> stored on the filesystem as the UTF-16 sequence \u684c \u9762.  If I set
> LANG to en_US.UTF-8, a readdir(2) call returns the multibyte sequence
>
>  0xe6 0xa1 0x8c 0xe9 0x9d 0xa2
>
> If I set LANG to en_US.GBK, `ls' returns the filename
>
>  0xd7 0xc0 0xc3 0xe6
>
> And in case LANG=C, `ls' returns
>
>  0x0e 0xe6 0xa1 0x8c 0x0e 0xe9 0x9d 0xa2
>
> So, dependent on the character set setting in the application, the idea
> of the filename differs.  That's not exactly helpful for interoperability
> between different applications.
>
> I can think of two potential solutions to fix this problem:
>
> (1) Always return filenames in UTF-8 encoding and pretend that UTF-8
>    is the way files are stored on disk.  That results in unchangable
>    filenames which are always valid.
>
>    But what if an application sets LANG="xxxx.SJIS" and tries to create
>    a file using SJIS character encoding?  Should the file be created
>    using the SJIS->UTF-16 conversion or should open fail with EILSEQ?
>    That's not good.
>
> (2) If none of $LC_ALL/$LC_CTYPE/$LANG is set in the environment, then
>    Cygwin uses the LC_CTYPE setting which corresponds to the current
>    codepage.  If one of $LC_ALL/$LC_CTYPE/$LANG is set in the environment,
>    Cygwin uses that to convert pathnames.  If the application uses
>    setlocale, Cygwin uses that setting to convert pathnames.
>
>    One problem can't be solved this way:  If an application fetches
>    and stores a filename, then switches the locale, and then tries
>    to use the filename in another system call, the filename is
>    potentially broken.
>
> Any better ideas?
>
>
> Corinna
>
> --
> Corinna Vinschen                  Please, send mails regarding Cygwin to
> Cygwin Project Co-Leader          cygwin AT cygwin DOT com
> Red Hat
>
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>



-- 
IWAMURO Motnori <http://vmi.jp/>

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