<i18n dev> Reading Linux filenames in a way that will map back the same on open?

[Martin Buchholz]

On Wed, Sep 10, 2008 at 17:50, Dan Stromberg <strombrg at gmail.com> wrote:
>
>
> Would you believe that I'm getting file not found errors even with
> ISO-8859-1?

The software world is full of suprises.

Try
export LANG=C LC_ALL=C LC_CTYPE=C
java ... -Dfile.encoding=ISO-8859-1 ...

You could also be explicit about the
encoding used when doing any kind of char<->byte
conversion, e.g. reading from stdin or writing to stdout.

Oh, and this is only traditional Unix systems like
Linux and Solaris.  Windows and MacOSX
(at least should) act very differently in this area.

Martin

> (Naoto: My program doesn't know what encoding to expect - I'm afraid I
> probably have different applications writing filenames in different
> encodings on my Ubuntu system.  I'd been thinking I wanted to treat
> filenames as just a sequence of bytes, and let the terminal emulator
> interpret the encoding (hopefully) correctly on output).
>
>
>
> This gives two file not found tracebacks:
>
> export LC_ALL='ISO-8859-1'
> export LC_CTYPE="$LC_ALL"
> export LANG="$LC_ALL"
>
> find 'test-files' -type f -print | java -Xmx512M -Dfile.encoding=ISO-8859-1
> -jar equivs.jar equivs.main
>
> find ~/Sound/Music -type f -print | java -Xmx512M -Dfile.encoding=ISO-8859-1
> -jar equivs.jar equivs.main
>
>
>
> I'm reading the filenames like (please forgive the weird indentation) :
>
> try                                                        {
>
> while((line = stdin.readLine()) != null)
>        {
>                            // System.out.println(line);
>           // System.out.flush();
> lst.add(new Sortable_file(line));
> }
> }
> catch(java.io.IOException e)
> {
> System.err.println("**** exception " + e);
> e.printStackTrace();                                                     }
>
>
>
> Where Sortable_file's constructor just looks like:
>
>   public Sortable_file(String filename)
>      {
>      this.filename = filename;
>      /*
>      Java doesn't have a stat function without doing some fancy stuff, so we
> skip this
>      optimization.  It really only helps with hard links anyway.
>      this.device = -1
>      this.inode = -1
>      */
>      File file = new File(this.filename);
>      this.size = file.length();
>      // It bothers a little that we can't close this, but perhaps it's
> unnecessary.  That'll
>      // be determined in large tests.
>      // file.close();
>      this.have_prefix = false;
>      this.have_hash = false;
>      }
>
>
>
> ..and the part that actually blows up looks like:
>
>   private void get_prefix()
>      {
>      byte[] buffer = new byte[128];
>      try
>         {
>         // The next line is the one that gives file not found
>         FileInputStream file = new FileInputStream(this.filename);
>         file.read(buffer);
>         // System.out.println("this.prefix.length " + this.prefix.length);
>         file.close();
>         }
>      catch (IOException ioe)
>         {
>         // System.out.println( "IO error: " + ioe );
>         ioe.printStackTrace();
>         System.exit(1);
>         }
>      this.prefix = new String(buffer);
>      this.have_prefix = true;
>      }
>
>
>
> Interestingly, it's already tried to get the file's length without an error
> when it goes to read data from the file and has trouble.
>
> I don't -think- I'm doing anything screwy in there - could it be that
> ISO-8859-1 isn't giving good round-trip conversions in practice?  Would this
> be an attribute of the java runtime in question, or could it be a matter of
> the locale files on my Ubuntu system being a little off?  It would seem the
> locale files would be a better explanation (or a bug in my program I'm not
> seeing!), since I get the same errors with both OpenJDK and gcj.
>
> Martin Buchholz wrote:
>>
>> ISO-8859-1 guarantees round-trip conversion between bytes and chars,
>> guarateeing no loss of data, or getting apparently impossible situations
>> where the JDK gives you a list of files in a directory, but you get
>> File not found when you try to open them.
>>
>> If you want to show the file names to users, you can always take
>> your ISO-8859-1 decoded strings, turn them back into byte[],
>> and decode using UTF-8 later, if you so desired.
>> (The basic OS interfaces in the JDK are not so flexible.
>> They are hard-coded to use the one charset specified by file.encoding)
>>
>> Martin
>>
>> On Wed, Sep 10, 2008 at 14:54, Naoto Sato <Naoto.Sato at sun.com> wrote:
>>>
>>> Why ISO-8859-1?  CJK filenames are guaranteed to fail in that case.  I'd
>>> rather choose UTF-8, as the default encoding on recent Unix/Linux are all
>>> UTF-8 so the filenames are likely in UTF-8.
>>>
>>> Naoto
>>>
>>> Martin Buchholz wrote:
>>>>
>>>> Java made the decision to use String as an abstraction
>>>> for many OS-specific objects, like filenames (or environment variables).
>>>> Most of the time this works fine, but occasionally you can notice
>>>> that the underlying OS (in the case of Unix) actually uses
>>>> arbitrary byte arrays as filenames.
>>>>
>>>> It would have been much more confusing to provide an interface
>>>> to filenames that is sometimes a sequence of char, sometimes a
>>>> sequence of byte.
>>>>
>>>> So this is unlikely to change.
>>>>
>>>> But if all you want is reliable reversible conversion,
>>>> using java -Dfile.encoding=ISO-8859-1
>>>> should do the trick.
>>>>
>>>> Martin
>>>>
>>>> On Tue, Sep 9, 2008 at 17:39, Dan Stromberg <dstromberglists at gmail.com>
>>>> wrote:
>>>>>
>>>>> Sorry if this is the wrong list for this question.  I tried asking it
>>>>> on comp.lang.java, but didn't get very far there.
>>>>>
>>>>> I've been wanting to expand my horizons a bit by taking one of my
>>>>> programs and rewriting it into a number of other languages.  It
>>>>> started life in python, and I've recoded it into perl
>>>>> (http://stromberg.dnsalias.org/~strombrg/equivalence-classes.html).
>>>>> Next on my list is java.  After that I'll probably do Haskell and
>>>>> Eiffel/Sather.
>>>>>
>>>>> So the python and perl versions were pretty easy, but I'm finding that
>>>>> the java version has a somewhat solution-resistant problem with
>>>>> non-ASCII filenames.
>>>>>
>>>>> The program just reads filenames from stdin (usually generated with
>>>>> the *ix find command), and then compares those files, dividing them up
>>>>> into equal groups.
>>>>>
>>>>> The problem with the java version, which manifests both with OpenJDK
>>>>> and gcj, is that the filenames being read from disk are 8 bit, and the
>>>>> filenames opened by the OpenJDK JVM or gcj-compiled binary are 8 bit,
>>>>> but as far as the java language is concerned, those filenames are made
>>>>> up of 16 bit characters.  That's fine, but going from 8 to 16 bit and
>>>>> back to 8 bit seems to be non-information-preserving in this case,
>>>>> which isn't so fine - I can clearly see the program, in an strace,
>>>>> reading with one sequence of bytes, but then trying to open
>>>>> another-though-related sequence of bytes.  To be perfectly clear: It's
>>>>> getting file not found errors.
>>>>>
>>>>> By playing with $LC_ALL, $LC_CTYPE and $LANG, it appears I can get the
>>>>> program to handle files with one encoding, but not another.  I've
>>>>> tried a bunch of values in these variables, including ISO-8859-1, C,
>>>>> POSIX, UTF-8, and so on.
>>>>>
>>>>> Is there such a thing as a filename encoding that will map 8 bit
>>>>> filenames to 16 bit characters, but only using the low 8 bits of those
>>>>> 16, and then map back to 8 bit filenames only using those low 8 bits
>>>>> again?
>>>>>
>>>>> Is there some other way of making a Java program on Linux able to read
>>>>> filenames from stdin and later open those filenames?
>>>>>
>>>>> Thanks!
>>>>>
>>>
>>> --
>>> Naoto Sato
>>>
>
>