doc/plugins/po.mdwn



[[!template id=plugin name=po core=0 author="[[intrigeri]]"]]
[[!tag type/format]]
This plugin adds support for multi-lingual wikis, translated with
gettext, using po4a.
It depends on the Perl Locale::Po4a::Po library (apt-get install po4a).
[[!toc levels=2]]
Introduction
A language is chosen as the "master" one, and any other supported
language is a "slave" one.
A page written in the "master" language is a "master" page. It can be
of any page type supported by ikiwiki, except po. It does not have to be
named a special way: migration to this plugin does not imply any page
renaming work.
Example: bla/page.mdwn is a "master" Markdown page written in
English; if usedirs is enabled, it is rendered as
bla/page/index.en.html, else as bla/page.en.html.
Any translation of a "master" page into a "slave" language is called
a "slave" page; it is written in the gettext PO format. po is now
a page type supported by ikiwiki.
Example: bla/page.fr.po is the PO "message catalog" used to
translate bla/page.mdwn into French; if usedirs is enabled, it is
rendered as bla/page/index.fr.html, else as bla/page.fr.html
Configuration
Supported languages
po_master_language is used to set the "master" language in
ikiwiki.setup, such as:
    po_master_language => { 'code' => 'en', 'name' => 'English' }

po_slave_languages is used to set the list of supported "slave"
languages, such as:
    po_slave_languages => { 'fr' => 'Français',
                            'es' => 'Castellano',
                            'de' => 'Deutsch',
    }

Decide which pages are translatable
The po_translatable_pages setting configures what pages are
translatable. It is a [[ikiwiki/PageSpec]], so you have lots of
control over what kind of pages are translatable.
The .po files are not considered as being translatable, so you don't need to
worry about excluding them explicitly from this [[ikiwiki/PageSpec]].
Internal links
The po_link_to option in ikiwiki.setup is used to decide how
internal links should be generated, depending on web server features
and site-specific preferences.
Default linking behavior
If po_link_to is unset, or set to default, ikiwiki's default
linking behavior is preserved: \[[destpage]] links to the master
language's page.
Link to current language
If po_link_to is set to current, \[[destpage]] links to the
destpage's version written in the current page's language, if
available, i.e.:

foo/destpage/index.LL.html if usedirs is enabled
foo/destpage.LL.html if usedirs is disabled

Link to negotiated language
If po_link_to is set to negotiated, \[[page]] links to the
negotiated preferred language, i.e. foo/page/.
(In)compatibility notes:

if usedirs is disabled, it does not make sense to set po_link_to
to negotiated; this option combination is neither implemented
nor allowed.
if the web server does not support Content Negotiation, setting
po_link_to to negotiated will produce a unusable website.

Server support
Apache
Using Apache mod_negotiation makes it really easy to have Apache
serve any page in the client's preferred language, if available.
This is the default Debian Apache configuration.
When usedirs is enabled, one has to set DirectoryIndex index for
the wiki context.
Setting DefaultLanguage LL (replace LL with your default MIME
language code) for the wiki context can help to ensure
bla/page/index.en.html is served as Content-Language: LL.
lighttpd
lighttpd unfortunately does not support content negotiation.
FIXME: does mod_magnet provide the functionality needed to
emulate this?
Usage
Templates
When po_link_to is not set to negotiated, one should replace some
occurrences of BASEURL with HOMEPAGEURL to get correct links to
the wiki homepage.
The ISTRANSLATION and ISTRANSLATABLE variables can be used to
display things only on translatable or translation pages.
Display page's versions in other languages
The OTHERLANGUAGES loop provides ways to display other languages'
versions of the same page, and the translations' status.
One typically adds the following code to templates/page.tmpl:
<TMPL_IF NAME="OTHERLANGUAGES">
<div id="otherlanguages">
  <ul>
  <TMPL_LOOP NAME="OTHERLANGUAGES">
    <li>
      <a href="<TMPL_VAR NAME="URL">"><TMPL_VAR NAME="LANGUAGE"></a>
      <TMPL_UNLESS NAME="MASTER">
        (<TMPL_VAR NAME="PERCENT">&nbsp;%)
      </TMPL_UNLESS>
    </li>
  </TMPL_LOOP>
  </ul>
</div>
</TMPL_IF>

The following variables are available inside the loop (for every page in):

URL - url to the page
CODE - two-letters language code
LANGUAGE - language name (as defined in po_slave_languages)
MASTER - is true (1) if, and only if the page is a "master" page
PERCENT - for "slave" pages, is set to the translation completeness, in percents

Display the current translation status
The PERCENTTRANSLATED variable is set to the translation
completeness, expressed in percent, on "slave" pages.
One can use it this way:
<TMPL_IF NAME="ISTRANSLATION">
<div id="percenttranslated">
  <TMPL_VAR NAME="PERCENTTRANSLATED">
</div>
</TMPL_IF>

Additional PageSpec tests
This plugin enhances the regular [[ikiwiki/PageSpec]] syntax with some
additional tests that are documented [[here|ikiwiki/pagespec/po]].
Automatic PO file update
Committing changes to a "master" page:

updates the POT file and the PO files for the "slave" languages;
the updated PO files are then put under version control;
triggers a refresh of the corresponding HTML slave pages.

Also, when the plugin has just been enabled, or when a page has just
been declared as being translatable, the needed POT and PO files are
created, and the PO files are checked into version control.
Discussion pages and other sub-pages
Discussion should happen in the language in which the pages are
written for real, i.e. the "master" one. If discussion pages are
enabled, "slave" pages therefore link to the "master" page's
discussion page.
Likewise, "slave" pages are not supposed to have sub-pages;
[[WikiLinks|wikilink]] that appear on a "slave" page therefore link to
the master page's sub-pages.
Translating
One can edit the PO files using ikiwiki's CGI (a message-by-message
interface could also be implemented at some point).
If [[tips/untrusted_git_push]] is setup, one can edit the PO files in one's
preferred $EDITOR, without needing to be online.
Markup languages support
Markdown is well supported. Some other markup languages supported by
ikiwiki mostly work, but some pieces of syntax are not rendered
correctly on the slave pages:

[[reStructuredText|rst]]: anonymous hyperlinks and internal
cross-references
[[wikitext]]: conversion of newlines to paragraphs
[[creole]]: verbatim text is wrapped, tables are broken
[[html]] and LaTeX: not supported yet; the dedicated po4a modules
could be used to support them, but they would need a security audit
other markup languages have not been tested.

TODO
Security checks
Security history
The only past security issues I could find in GNU gettext and po4a
are:

CVE-2004-0966,
i.e. Debian bug #278283:
the autopoint and gettextize scripts in the GNU gettext package
1.14 and later versions, as used in Trustix Secure Linux 1.5
through 2.1 and other operating systems, allows local users to
overwrite files via a symlink attack on temporary files.
CVE-2007-4462:
lib/Locale/Po4a/Po.pm in po4a before 0.32 allows local users to
overwrite arbitrary files via a symlink attack on the
gettextization.failed.po temporary file.

FIXME: check whether this plugin would have been a possible attack
vector to exploit these vulnerabilities.
Depending on my mood, the lack of found security issues can either
indicate that there are none, or reveal that no-one ever bothered to
find (and publish) them.
PO file features
Can any sort of directives be put in po files that will cause mischief
(ie, include other files, run commands, crash gettext, whatever)?

No documented
directive is supposed to do so. [[--intrigeri]]

Running po4a on untrusted content
Are there any security issues on running po4a on untrusted content?
To say the least, this issue is not well covered, at least publicly:

the documentation does not talk about it;
grep'ing the source code for security or trust gives no answer.

On the other hand, a po4a developer answered my questions in
a convincing manner, stating that processing untrusted content was not
an initial goal, and analysing in detail the possible issues.
Already checked

the core (Po.pm, Transtractor.pm) should be safe
po4a source code was fully checked for other potential symlink
attacks, after discovery of one such issue
the only external program run by the core is diff, in Po.pm (in
parts of its code we don't use)
Locale::gettext: only used to display translated error messages
Nicolas François "hopes" DynaLoader is safe, and has "no reason to
think that Encode is not safe"
Nicolas François has "no reason to think that Encode::Guess is not
safe". The po plugin nevertheless avoids using it by defining the
input charset (file_in_charset) before asking Transtractor to
read any file. NB: this hack depends on po4a internals to stay
the same.

To be checked
Locale::Po4a modules
The modules we want to use have to be checked, as not all are safe
(e.g. the LaTeX module's behaviour is changed by commands included in
the content); they may use regexps generated from the content.
Chooser.pm only loads the plugin we tell it too: currently, this
means the Text module only.
Text module (I checked the CVS version):


it does not run any external program


only do_paragraph() builds regexp's that expand untrusted
variables; they seem safe to me, but someone more expert than me
will need to check. Joey?

Freaky code, but seems ok due to use of quotementa.


Text::WrapI18N
Text::WrapI18N can cause DoS (see the
Debian bug #470250), but it is
optional and we do not need the features it provides.
It is loaded if available by Locale::Po4a::Common; looking at the
code, I'm not sure we can prevent this at all, but maybe some symbol
table manipulation tricks could work; overriding
Locale::Po4a::Common::wrapi18n may be easier. I'm no expert at all
in this field. Joey? [[--intrigeri]]

Update: Nicolas François suggests we add an option to po4a to
disable it. It would do the trick, but only for people running
a brand new po4a (probably too late for Lenny). Anyway, this option
would have to take effect in a BEGIN / eval that I'm not
familiar with. I can learn and do it, in case no Perl wizard
volunteers to provide the po4a patch. [[--intrigeri]]


That doesn't really need to be in a BEGIN. This patch moves it to
import, and makes this disable wrap18n:
use Locale::Po4a::Common q{nowrapi18n} --[[Joey]]


Term::ReadKey
Term::ReadKey is not a hard dependency in our case, i.e. po4a
works nicely without it. But the po4a Debian package recommends
libterm-readkey-perl, so it will probably be installed on most
systems using the po plugin.
If $ENV{COLUMNS} is not set, Locale::Po4a::Common uses
Term::ReadKey::GetTerminalSize() to get the terminal size. How safe
is this?
Part of Term::ReadKey is written in C. Depending on the runtime
platform, this function use ioctl, environment, or C library function
calls, and may end up running the resize command (without
arguments).
IMHO, using Term::ReadKey has too far reaching implications for us to
be able to guarantee anything wrt. security. Since it is anyway of no
use in our case, I suggest we define ENV{COLUMNS} before loading
Locale::Po4a::Common, just to be on the safe side. Joey?
[[--intrigeri]]

Update: adding an option to disable Text::WrapI18N, as Nicolas
François suggested, would as a bonus disable Term::ReadKey
as well. [[--intrigeri]]

msgmerge
refreshpofiles() runs this external program. A po4a developer
answered he does "not expect any security issues from it".
Fuzzing input
I was not able to find any public information about gettext or po4a
having been tested with a fuzzing program, such as zzuf or fusil.
Moreover, some gettext parsers seem to be quite
easy to crash,
so it might be useful to bang msgmerge/po4a's heads against such
a program in order to easily detect some of the most obvious DoS.
[[--intrigeri]]

po4a was not fuzzy-tested, but according to one of its developers,
"it would be really appreciated". [[--intrigeri]]

Test conditions:

a 21M file containing 100 concatenated copies of all the files in my
/usr/share/common-licenses/; I had no existing PO file or
translated versions at hand, which renders these tests
quite incomplete.
po4a was the Debian 0.34-2 package; the same tests were also run
after replacing the Text module with the CVS one (the core was not
changed in CVS since 0.34-2 was released), without any significant
difference in the results.
Perl 5.10.0-16

po4a-gettextize
po4a-gettextize uses more or less the same po4a features as our
refreshpot function.
Without specifying an input charset, zzuf'ed po4a-gettextize quickly
errors out, complaining it was not able to detect the input charset;
it leaves no incomplete file on disk.
So I had to pretend the input was in UTF-8, as does the po plugin.
Two ways of crashing were revealed by this command-line:
    zzuf -vc -s 0:100 -r 0.1:0.5 \
      po4a-gettextize -f text -o markdown -M utf-8 -L utf-8 \
        -m LICENSES >/dev/null

They are:
    Malformed UTF-8 character (UTF-16 surrogate 0xdcc9) in substitution iterator at /usr/share/perl5/Locale/Po4a/Po.pm line 1443.
    Malformed UTF-8 character (fatal) at /usr/share/perl5/Locale/Po4a/Po.pm line 1443.

and
    Malformed UTF-8 character (UTF-16 surrogate 0xdcec) in substitution (s///) at /usr/share/perl5/Locale/Po4a/Po.pm line 1443.
    Malformed UTF-8 character (fatal) at /usr/share/perl5/Locale/Po4a/Po.pm line 1443.

Perl seems to exit cleanly, and an incomplete PO file is written on
disk. I not sure whether if this is a bug in Perl or in Po.pm.

It's fairly standard perl behavior when fed malformed utf-8. As long as it doesn't
crash ikiwiki, it's probably acceptable. Ikiwiki can do some similar things itself when fed malformed utf-8 (doesn't crash tho) --[[Joey]]

po4a-translate
po4a-translate uses more or less the same po4a features as our
filter function.
Without specifying an input charset, same behaviour as
po4a-gettextize, so let's specify UTF-8 as input charset as of now.
    zzuf -cv \
      po4a-translate -d -f text -o markdown -M utf-8 -L utf-8 \
        -k 0 -m LICENSES -p LICENSES.fr.po -l test.fr

... prints tons of occurences of the following error, but a complete
translated document is written (obviously with some weird chars
inside):
    Use of uninitialized value in string ne at /usr/share/perl5/Locale/Po4a/TransTractor.pm line 854.
    Use of uninitialized value in string ne at /usr/share/perl5/Locale/Po4a/TransTractor.pm line 840.
    Use of uninitialized value in pattern match (m//) at /usr/share/perl5/Locale/Po4a/Po.pm line 1002.

While:
    zzuf -cv -s 0:10 -r 0.001:0.3 \
      po4a-translate -d -f text -o markdown -M utf-8 -L utf-8 \
        -k 0 -m LICENSES -p LICENSES.fr.po -l test.fr

... seems to lose the fight, at the readpo(LICENSES.fr.po) step,
against some kind of infinite loop, deadlock, or any similar beast.
It does not seem to eat memory, though.
Whatever format module is used does not change anything. This is thus
probably a bug in po4a's core or in a lib it depends on.
The sub read, in TransTractor.pm, seems to be a good debugging
starting point.
msgmerge
msgmerge is run in our refreshpofiles function. I did not manage
to crash it with zzuf.
gettext/po4a rough corners

fix infinite loop when synchronizing two ikiwiki (when checkouts
live in different directories): say bla.fr.po has been updated in
repo2; pulling repo2 from repo1 seems to trigger a PO update, that
changes bla.fr.po in repo1; then pushing repo1 to repo2 triggers
a PO update, that changes bla.fr.po in repo2; etc.; quickly fixed in
629968fc89bced6727981c0a1138072631751fee, by disabling references
in Pot files. Using Locale::Po4a::write_if_needed might be
a cleaner solution. (warning: this function runs the external
diff program, have to check security)
new translations created in the web interface must get proper
charset/encoding gettext metadata, else the next automatic PO update
removes any non-ascii chars; possible solution: put such metadata
into the Pot file, and let it propagate; should be fixed in
773de05a7a1ee68d2bed173367cf5e716884945a, time will tell.

Better links
Page title in links
Using the fix to
[[bugs/pagetitle_function_does_not_respect_meta_titles]] from
[[intrigeri]]'s meta branch, the generated links' text is based on
the page titles set with the [[meta|plugins/meta]] plugin. This has to
be merged upstream, though.
Translation quality assurance
Modifying a PO file via the CGI must be forbidden if the new version
is not a valid PO file. As a bonus, check that it provides a more
complete translation than the existing one.
A new cansave type of hook would be needed to implement this.
Note: committing to the underlying repository is a way to bypass
this check.
Creating new pages on the web
See [[contrib/po|contrib/po]].
Renaming/deleting pages
Renaming or deleting a translation in the CGI should be forbidden.
Implementing this requires two new hooks: canrename and canremove,
that would be run respectively by the rename and the remove plugins.
Robustness tests
Disabling the plugin

enabling the plugin with po_translatable_pages set
enabling the plugin without po_translatable_pages set: OK
disabling the plugin: OK

Changing the plugin config

adding existing pages to po_translatable_pages: OK
removing existing pages from po_translatable_pages: OK
adding a language to po_slave_languages: OK
removing a language from po_slave_languages: OK
changing po_master_language: OK
replacing po_master_language with a language previously part of
po_slave_languages: needs two rebuilds, but OK (this is quite
a perverse test actually)

Creating pages

creating a master page via RCS: OK
creating a master page via CGI: OK

Deleting pages

removing a master page via RCS: OK
removing a translation via RCS: OK
removing a master page via CGI: OK
removing a translation via CGI: OK

Renaming pages

renaming a master page via RCS: OK (but the old translations
are lost, because not all RCS track file renaming)
renaming a master page and its translations via RCS: OK
renaming a master page via CGI: OK
renaming a translation via RCS
renaming a translation via CGI

Misc

general test with usedirs disabled: OK
general test with indexpages enabled
general test with po_link_to=default

Documentation
Maybe write separate documentation depending on the people it targets:
translators, wiki administrators, hackers. This plugin may be complex
enough to deserve this.