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From "Roy T. Fielding" <field...@gbiv.com>
Subject Re: apr_filepath_encoding on Darwin
Date Tue, 07 Aug 2007 00:11:25 GMT
On Aug 6, 2007, at 4:10 PM, Wilfredo Sánchez Vega wrote:

>   (Sorry for the lame reply latency.)
>
> On Jul 18, 2007, at 5:24 PM, Roy T. Fielding wrote:
>
>> A system less concerned with backwards compatibility is better off
>> with a requirement of utf-8, though OS X should have made the  
>> filename
>> encoding a mount option.
>
>   I disagree.  Having one encoding is far superior to every  
> application having to first find out what encoding the filesystem  
> is question is using then using that.
>
>   I see no value in having different mount points use different  
> encodings.

Well, neither do I (now that utf-8 exists), but the fact is that they do
and they aren't necessarily controlled by the same OS.

>> I assume that the ISO9660-Joliet (CD-ROM) driver does
>> some form of filename translation automatically from UCS-2.
>
>   The underlying volume format can use whatever it wants.  Ideally  
> the format defines what that is.  Unfortunately, that's not the  
> case, but for those that do, yes, converting to UTF-8 is the  
> responsibility of the file system at the VFS layer.
>
>   I suppose that a mount option to tell the filesystem that "this  
> UFS volume uses encoding X" would be useful, but I maintain that  
> above the kernel, you really want one encoding, not N.  Helping the  
> kernel know what's underneath is certainly useful.

I agree.  But is it the case that non-native mounted filesystems
are name-translated by the kernel?  I mean, if OS X did this  
consistently
for all mount points, then I would see it as being reasonable for the
OS X applications to reject anything else.

>> In any case, even with the convention, it is left to the application
>> to determine how it will treat encoded filenames.  The OS X decision
>> to treat them all as utf-8 is at least consistent.  OTOH, this
>> is just a display convention -- OS X apps should have been designed
>> to treat the filename internally as an opaque nul-terminated array,
>> rather than barfing on non-utf8 encodings.
>
>   This is difficult in practice.  When the open panel sees a file  
> that is not in UTF-8, there is no reliable way to display anything  
> sane to the user.  I suppose a Linux nerd might say "show me some  
> hex" or something, but most of our users are not Linux nerds.  I  
> agree that crashing is worse than hex, though.

Actually, it also crashes on valid utf-8 in normal form, because OS X
doesn't follow the standard on normalization.  See "man -s 5 utf8":

      If more than a single representation of a value exists (for  
example,
      0x00; 0xC0 0x80; 0xE0 0x80 0x80) the shortest representation is  
always
      used.  Longer ones are detected as an error as they pose a  
potential
      security risk, and destroy the 1:1 character:octet sequence  
mapping.

but OS X requires the longer composition characters over shorter ones.
My guess is that choice was driven by the way the UI allows such
characters to be composed (like "alt-u u" for uumlaut).

Of course, even with these issues, the Mac still kicks ass.

>   Basically, on Mac OS X, you can, in fact, use whatever characters  
> you like on UFS and BSD level software tends to cope with that. But  
> if you aren't using UTF-8, then you aren't writing file name that  
> are meant for user consumption.  ie. that may be OK for a database  
> (eg. fsfs), though I think that even in that case you can  
> reasonably stick to ASCII in many cases.
>
>> One thing I miss in OS X is an automated way for file archivers
>> (like unzip) to recognize and convert non-utf-8 filenames
>> when they are unarchived.  I frequently have to do that by hand
>> after unzipping something from China or Switzerland.
>
>   Again, same as with volume formats, if the zip file format  
> defines the encoding in zip files, then this should be easy  
> (insofar as encodings are easy) for the software to deal with.

Sadly, it doesn't (filenames are just null-terminated strings).  There
are options for conversion from EBCDIC, but nothing to transcode the
filenames in general as they are unzipped.  Maybe the zip command
maintainer will take that as an enhancement request.

>> Subversion
>> breaks on OS X whenever someone commits a filename with an e-grave,
>> which is a problem when your main product name is Communiqué.
>> I wonder if this change in APR would fix that error?
>
>   You still have to hope that the inbound encoding is correct (that  
> is, that svn somehow knows it).  On OS X, that's easy; it's UTF-8.   
> Once other operating systems come into the mix, it'll works as well  
> as the encodings are defined (and known to svn) on those systems.

What I do currently is define

    setenv  MM_CHARSET "utf-8"
    setenv  LANG       "en_US.utf-8"

in my shell init file.

....Roy


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