path: root/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](http://po4a.alioth.debian.org/).

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
---------

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:

1. updates the POT file and the PO files for the "slave" languages;
   the updated PO files are then put under version control;
2. 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
----------------

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.

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.

TODO
====

Security checks
---------------

### Security history

The only past security issues I could find in GNU gettext and po4a
are:

- [CVE-2004-0966](http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2004-0966),
  *i.e.* [Debian bug #278283](http://bugs.debian.org/cgi-bin/bugreport.cgi?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](http://cve.mitre.org/cgi-bin/cvename.cgi?name=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](http://www.gnu.org/software/gettext/manual/gettext.html#PO-Files)
> 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; we
  currently only use the `Text` module
- the `Text` module does not run any external program
- check that no module is loaded by `Chooser.pm`, when we tell it to
  load the `Text` one
- `nsgmls` is used by `Sgml.pm`

##### Text::WrapI18N

`Text::WrapI18N` can cause DoS (see the
[Debian bug #470250](http://bugs.debian.org/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]]

##### 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]]

### 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](http://fusil.hachoir.org/trac/browser/trunk/fuzzers/fusil-gettext),
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]]

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.

Misc. improvements
------------------

### page titles

Use nice page titles from meta plugin in links, as inline already
does. This is actually a duplicate for
[[bugs/pagetitle_function_does_not_respect_meta_titles]], which might
be fixed by something like [[todo/using_meta_titles_for_parentlinks]].

### source files format

Markdown is supported, great, but what about others? The set of file
formats supported both in ikiwiki and po4a probably is greater than
`{markdown}`. Warning: the po4a modules are the place where one can
expect security issues.

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.