[Haskell-cafe] Encoding-aware System.Directory functions

Michael Snoyman michael at snoyman.com
Wed Mar 30 18:07:45 CEST 2011

On Wed, Mar 30, 2011 at 9:26 AM, Jason Dagit <dagitj at gmail.com> wrote:
> On Tue, Mar 29, 2011 at 11:52 PM, Michael Snoyman <michael at snoyman.com>
> wrote:
>> Hi all,
>> I think this is a well-known issue: it seems that there is no
>> character decoding performed on the values returned from the functions
>> in System.Directory (getDirectoryContents specifically). I could
>> manually do something like (utf8Decode . S8.pack), but that presumes
>> that the character encoding on the system in question is UTF8. So two
>> questions:
>> * Is there a package out there that handles all the gory details for
>> me automatically, and simply returns a properly decoded String (or
>> Text)?
>> * If not, is there a standard way to determine the character encoding
>> used by the filesystem, short of hard-coding in character encodings
>> used by the major ones?
> I started to write a thoughtful reply, but I found that the answers here sum
> up everything I was going to say:
> http://unix.stackexchange.com/questions/2089/what-charset-encoding-is-used-for-filenames-and-paths-on-linux
> This same issue comes up from time to time for darcs and, if I recall
> correctly, the solution has been to treat unix file paths as arbitrary bytes
> whenever possible and to escape non-ascii compatible bytes when they occur.
>  Otherwise it can be hard to encode them in textual patch descriptions or
> xml (where an encoding is required and I believe utf8 is a standard
> default).
> I wish you luck.  It's not as easy problem, at least on unix.  I've heard
> that windows has a much easier time here as MS has provided a standard for
> it.
> Jason

Thanks to you (and everyone else) for the informative responses. For
now, I've simply hard-coded in UTF-8 encoding for all non-Windows
systems. I'm not sure how this will play with OSes besides Windows and
Linux (especially Mac), but it's a good stop-gap measure.

I *do* think it would be incredibly useful to provide alternatives to
all the standard operations on FilePath which used opaque datatypes
and properly handles filename encoding. I noticed John Millikin's
system-filepath package[1]. Do people have experience with it? It
seems that adding a few functions like getDirectoryContents, plus
adding a version of toString which performs some character decoding,
would get us pretty far.


[1] http://hackage.haskell.org/package/system-filepath

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