\input texinfo   @c -*- mode: texinfo; coding: us-ascii; -*-
@c This file is part of GNU Libidn.
@c See below for copyright and license.

@setfilename libidn.info
@documentencoding UTF-8
@include version.texi
@settitle GNU Libidn @value{VERSION}
@finalout

@syncodeindex pg cp

@copying
This manual is last updated @value{UPDATED} for version
@value{VERSION} of GNU Libidn.

Copyright @copyright{} 2002--2025 Simon Josefsson.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.  A
copy of the license is included in the section entitled ``GNU Free
Documentation License''.
@end quotation
@end copying

@dircategory Software libraries
@direntry
* libidn: (libidn).	Internationalized string processing library.
@end direntry

@dircategory Localization
@direntry
* idn: (libidn)Invoking idn.	Internationalized Domain Name (IDN) string conversion.
@end direntry

@dircategory Emacs
@direntry
* IDN Library: (libidn)Emacs API.	Emacs API for IDN functions.
@end direntry

@titlepage
@title GNU Libidn
@subtitle Internationalized string processing for the GNU system
@subtitle for version @value{VERSION}, @value{UPDATED}
@author Simon Josefsson
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@contents

@ifnottex
@node Top
@top GNU Libidn

@insertcopying
@end ifnottex

@menu
* Introduction::		How to use this manual.
* Preparation::			What you should do before using the library.
* Utility Functions::		Unicode transformation utility functions.
* Stringprep Functions::	Stringprep functions.
* Punycode Functions::		Punycode functions.
* IDNA Functions::		IDNA functions.
* TLD Functions::		TLD functions.
* PR29 Functions::		Detect strings non-idempotent under NFKC.
* Examples::                    Demonstrate how to use the library.
* Invoking idn::		Command line interface to the library.
* Emacs API::                   Emacs Lisp API for Libidn.
* Java API::                    Notes on the Java port of Libidn.
* C# API::                      Notes on the C# port of Libidn.
* Acknowledgements::            Whom to blame.
* History::                     Rough outline of development history.

Appendices

* PR29 discussion::             Implementation aspects of the PR29 flaw.
* On Label Separators::         Discussions of a flaw in the IDNA spec.

Copying This Manual

* GNU Free Documentation License::     Copying and sharing this manual

Indices

* Function and Variable Index::
* Concept Index::

@end menu


@node Introduction
@chapter Introduction

GNU Libidn is a fully documented implementation of the Stringprep,
Punycode and IDNA specifications.  Libidn's purpose is to encode and
decode internationalized domain name strings.  There are native C, C#
and Java libraries.

The C library contains a generic Stringprep implementation.  Profiles
for Nameprep, iSCSI, SASL, XMPP and Kerberos V5 are included.
Punycode and ASCII Compatible Encoding (ACE) via IDNA are supported.
A mechanism to define Top-Level Domain (TLD) specific validation
tables, and to compare strings against those tables, is included.
Default tables for some TLDs are also included.

The Stringprep API consists of two main functions, one for converting
data from the system's native representation into UTF-8, and one
function to perform the Stringprep processing.  Adding a new
Stringprep profile for your application within the API is
straightforward.  The Punycode API consists of one encoding function
and one decoding function.  The IDNA API consists of the ToASCII and
ToUnicode functions, as well as an high-level interface for converting
entire domain names to and from the ACE encoded form.  The TLD API
consists of one set of functions to extract the TLD name from a domain
string, one set of functions to locate the proper TLD table to use
based on the TLD name, and core functions to validate a string against
a TLD table, and some utility wrappers to perform all the steps in one
call.

The library is used by, e.g., GNU SASL and Shishi to process user
names and passwords.  Libidn can be built into GNU Libc to enable a
new system-wide getaddrinfo flag for IDN processing.

Libidn is developed for the GNU/Linux system, but runs on over 20 Unix
platforms (including Solaris, IRIX, AIX, and Tru64) and Windows.  The
library is written in C and (parts of) the API is also accessible from
C++, Emacs Lisp, Python and Java.  A native Java and C# port is
included.

Also included is a command line tool, several self tests, code
examples, and more.

@menu
* Getting Started::
* Features::
* Library Overview::
* Supported Platforms::
* Getting help::
* Commercial Support::
* Downloading and Installing::
* Bug Reports::
* Contributing::
@end menu

@node Getting Started
@section Getting Started

This manual documents the library programming interface.  All
functions and data types provided by the library are explained.
Included are also examples, and documentation for the command line
tool @file{idn} that provide a quick interface to the library.  The
Emacs Lisp bindings for the library is also discussed.

The reader is assumed to possess basic familiarity with
internationalization concepts and network programming in C or C++.

This manual can be used in several ways.  If read from the beginning
to the end, it gives a good introduction into the library and how it
can be used in an application.  Forward references are included where
necessary.  Later on, the manual can be used as a reference manual to
get just the information needed about any particular interface of the
library.  Experienced programmers might want to start looking at the
examples at the end of the manual (@pxref{Examples}), and then only
read up those parts of the interface which are unclear.

@node Features
@section Features

This library might have a couple of advantages over other libraries
doing a similar job.

@table @asis
@item It's Free Software
Anybody can use, modify, and redistribute it under the terms of a free
software license.

@item It's thread-safe
No global state is kept in the library.  All functions are re-entrant.

@item It's portable
The code is intended to be written in pure ANSI C89.  It has been
tested on many Unix like operating systems, and Windows.

@item It's modularized
The library is composed of several modules, and the only interaction
between modules is through each modules' public API.  If you only need
one piece of functionality, it is possible to take the files you need
and incorporate them into your own project.

@item It's not bloated
The design of the library is based on the smallest API necessary to
implement the basic functionality.  It has been carefully extended
with a small number of high-level wrappers to make it comfortable to
use the library.  However, it does not implement additional
functionality just for the sake of completeness.

@item It's documented
Sadly, not all software comes with documentation these days.  This one
does.

@end table

@node Library Overview
@section Library Overview

The following illustration show the components that make up Libidn,
and how your application relates to the library.  In the illustration,
various components are shown as boxes.  You see the generic StringPrep
component, the various StringPrep profiles including Nameprep, the
Punycode component, the IDNA component, and the TLD component.  The
arrows indicate aggregation, e.g., IDNA uses Punycode and Nameprep,
and in turn Nameprep uses the generic StringPrep interface.  The
interfaces to all components are available for applications, no
component within the library is hidden from the application.

@image{libidn-components}

@node Supported Platforms
@section Supported Platforms

Libidn has at some point in time been tested on the following
platforms.  Build reports for each platforms and Libidn version is
available at @url{http://autobuild.josefsson.org/libidn/}.

@enumerate

@item Debian GNU/Linux 3.0 (Woody)
@cindex Debian

GCC 2.95.4 and GNU Make. This is the main development platform.
@code{alphaev67-unknown-linux-gnu}, @code{alphaev6-unknown-linux-gnu},
@code{arm-unknown-linux-gnu}, @code{armv4l-unknown-linux-gnu},
@code{hppa-unknown-linux-gnu}, @code{hppa64-unknown-linux-gnu},
@code{i686-pc-linux-gnu}, @code{ia64-unknown-linux-gnu},
@code{m68k-unknown-linux-gnu}, @code{mips-unknown-linux-gnu},
@code{mipsel-unknown-linux-gnu}, @code{powerpc-unknown-linux-gnu},
@code{s390-ibm-linux-gnu}, @code{sparc-unknown-linux-gnu},
@code{sparc64-unknown-linux-gnu}.

@item Debian GNU/Linux 2.1
@cindex Debian

GCC 2.95.1 and GNU Make. @code{armv4l-unknown-linux-gnu}.

@item Tru64 UNIX
@cindex Tru64

Tru64 UNIX C compiler and Tru64 Make. @code{alphaev67-dec-osf5.1},
@code{alphaev68-dec-osf5.1}.

@item SuSE Linux 7.1
@cindex SuSE

GCC 2.96 and GNU Make. @code{alphaev6-unknown-linux-gnu},
@code{alphaev67-unknown-linux-gnu}.

@item SuSE Linux 7.2a
@cindex SuSE Linux

GCC 3.0 and GNU Make. @code{ia64-unknown-linux-gnu}.

@item SuSE Linux
@cindex SuSE Linux

GCC 3.2.2 and GNU Make.  @code{x86_64-unknown-linux-gnu} (AMD64
Opteron ``Melody'').

@item SuSE Enterprise Server 9 on IBM OpenPower 720
@cindex SuSE Linux
@cindex OpenPower 720

GCC 3.3.3 and GNU Make.  @code{powerpc64-unknown-linux-gnu}.

@item RedHat Linux 7.2
@cindex RedHat

GCC 2.96 and GNU Make. @code{alphaev6-unknown-linux-gnu},
@code{alphaev67-unknown-linux-gnu}, @code{ia64-unknown-linux-gnu}.

@item RedHat Linux 8.0
@cindex RedHat

GCC 3.2 and GNU Make. @code{i686-pc-linux-gnu}.

@item RedHat Advanced Server 2.1
@cindex RedHat Advanced Server

GCC 2.96 and GNU Make. @code{i686-pc-linux-gnu}.

@item Slackware Linux 8.0.01
@cindex RedHat

GCC 2.95.3 and GNU Make. @code{i686-pc-linux-gnu}.

@item Mandrake Linux 9.0
@cindex Mandrake

GCC 3.2 and GNU Make. @code{i686-pc-linux-gnu}.

@item IRIX 6.5
@cindex IRIX

MIPS C compiler, IRIX Make. @code{mips-sgi-irix6.5}.

@item AIX 4.3.2
@cindex AIX

IBM C for AIX compiler, AIX Make.  @code{rs6000-ibm-aix4.3.2.0}.

@item Microsoft Windows 2000 (Cygwin)
@cindex Windows

GCC 3.2, GNU make. @code{i686-pc-cygwin}.

@item HP-UX 11
@cindex HP-UX

HP-UX C compiler and HP Make. @code{ia64-hp-hpux11.22},
@code{hppa2.0w-hp-hpux11.11}.

@item SUN Solaris 2.7
@cindex Solaris

GCC 3.0.4 and GNU Make. @code{sparc-sun-solaris2.7}.

@item SUN Solaris 2.8
@cindex Solaris

Sun WorkShop Compiler C 6.0 and SUN Make. @code{sparc-sun-solaris2.8}.

@item SUN Solaris 2.9
@cindex Solaris

Sun Forte Developer 7 C compiler and GNU
Make. @code{sparc-sun-solaris2.9}.

@item NetBSD 1.6
@cindex NetBSD

GCC 2.95.3 and GNU Make. @code{alpha-unknown-netbsd1.6},
@code{i386-unknown-netbsdelf1.6}.

@item OpenBSD 3.1 and 3.2
@cindex OpenBSD

GCC 2.95.3 and GNU Make. @code{alpha-unknown-openbsd3.1},
@code{i386-unknown-openbsd3.1}.

@item FreeBSD 4.7 and 4.8
@cindex FreeBSD

GCC 2.95.4 and GNU Make. @code{alpha-unknown-freebsd4.7},
@code{alpha-unknown-freebsd4.8}, @code{i386-unknown-freebsd4.7},
@code{i386-unknown-freebsd4.8}.

@item MacOS X 10.2 Server Edition
@cindex MacOS X

GCC 3.1 and GNU Make. @code{powerpc-apple-darwin6.5}.

@item MacOS X 10.4 ``Tiger'' with Xcode 2.0
@cindex MacOS X

GCC 4.0 and GNU Make. @code{powerpc-apple-darwin8.0}.

@item Cross compiled to uClinux/uClibc on Motorola Coldfire
@cindex Motorola Coldfire
@cindex uClinux
@cindex uClibc

GCC 3.4 and GNU Make @code{m68k-uclinux-elf}.

@item Cross compiled to ARM using Glibc
@cindex ARM

GCC 2.95 and GNU Make @code{arm-linux}.

@item Cross compiled to Mingw32.
@cindex Windows
@cindex Microsoft
@cindex mingw32

GCC 3.4.4 and GNU Make @code{i586-mingw32msvc}.

@item OS/2
@cindex OS/2
@cindex IBM

GCC.

@end enumerate

If you use Libidn on, or port Libidn to, a new platform please report
it to the author.

@node Getting help
@section Getting help

A mailing list where users of Libidn may help each other exists, and
you can reach it by sending e-mail to @email{help-libidn@@gnu.org}.
Archives of the mailing list discussions, and an interface to manage
subscriptions, is available through the World Wide Web at
@url{http://lists.gnu.org/mailman/listinfo/help-libidn}.

@node Commercial Support
@section Commercial Support

Commercial support is available for users of GNU Libidn.  The kind of
support that can be purchased may include:

@itemize

@item Implement new features.
Such as country code specific profiling to support a restricted subset
of Unicode.

@item Port Libidn to new platforms.
This could include porting Libidn to an embedded platforms that may
need memory or size optimization.

@item Integrating IDN support in your existing project.

@item System design of components related to IDN.

@end itemize

If you are interested, please write to:

@verbatim
Simon Josefsson Datakonsult AB
Hagagatan 24
113 47 Stockholm
Sweden

E-mail: simon@josefsson.org
@end verbatim

If your company provides support related to GNU Libidn and would like
to be mentioned here, contact the author (@pxref{Bug Reports}).

@node Downloading and Installing
@section Downloading and Installing
@cindex Installation
@cindex Download

The package can be downloaded from several places, including:

@url{ftp://alpha.gnu.org/pub/gnu/libidn/}

The latest version is stored in a file, e.g.,
@samp{libidn-@value{VERSION}.tar.gz} where the @samp{@value{VERSION}}
value is the highest version number in the directory.

The package is then extracted, configured and built like many other
packages that use Autoconf.  For detailed information on configuring
and building it, refer to the @file{INSTALL} file that is part of the
distribution archive.

Here is an example terminal session that download, configure, build
and install the package.  You will need a few basic tools, such as
@samp{sh}, @samp{make} and @samp{cc}.

@example
$ wget -q ftp://alpha.gnu.org/pub/gnu/libidn/libidn-@value{VERSION}.tar.gz
$ tar xfz libidn-@value{VERSION}.tar.gz
$ cd libidn-@value{VERSION}/
$ ./configure
...
$ make
...
$ make install
...
@end example

After that Libidn should be properly installed and ready for use.

A few @code{configure} options may be relevant, summarized in the
table.

@table @code

@item --enable-java
Build the Java port into a *.JAR file.  @xref{Java API}, for more
information.

@item --disable-tld
Disable the TLD module.  This would typically only be useful if you
are building on a memory restricted platforms.  @xref{TLD Functions},
for more information.

@item --enable-csharp[=IMPL]
Build the @code{C#} port into a @code{*.DLL} file.  @xref{C# API}, for
more information.  Here, @code{IMPL} is @code{pnet} or @code{mono},
indicating whether the PNET @command{cscc} compiler or the Mono
@command{mcs} compiler should be used, respectively.

@item --disable-valgrind-tests
Disable running the self-checks under Valgrind
(@url{http://valgrind.org/}).  Normally Valgrind does not cause
problems and can detect some severe memory errors.  If you are getting
errors from Valgrind that are caused by the compiler or libc (possibly
as a result of special optimization flags), you may use this option to
disable the use of Valgrind.

@end table

For the complete list, refer to the output from @code{configure
--help}.

@menu
* Installing under Windows::    Windows specific build instructions.
@end menu

@node Installing under Windows
@subsection Installing under Windows

There are two ways to build Libidn on Windows: via MinGW or via Visual
Studio.

With MinGW, you can build a Libidn DLL and use it from other
applications.  After installing MinGW (@url{http://mingw.org/}) follow
the generic installation instructions (@pxref{Downloading and
Installing}).  The DLL is installed by default.

For information on how to use the DLL in other applications, see:
@url{http://www.mingw.org/mingwfaq.shtml#faq-msvcdll}.

You can build Libidn as a native Visual Studio C++ project.  This
allows you to build the code for other platforms that VS supports,
such as Windows Mobile.  You need Visual Studio 2005 or later.

First download and unpack the archive as described in the generic
installation instructions (@pxref{Downloading and Installing}).  Don't
run @code{./configure}.  Instead, start Visual Studio and open the
project file @file{windows/libidn.sln} inside the Libidn directory.  You
should be able to build the project using Build Project.

Output libraries will be written into the @code{windows/lib} (or
@code{windows/lib/debug} for Debug versions) folder.

When working with Windows you may want to look into the special memory
handling functions that may be needed (@pxref{Memory handling under
Windows}).

@node Bug Reports
@section Bug Reports
@cindex Reporting Bugs

If you think you have found a bug in Libidn, please investigate it and
report it.

@itemize @bullet

@item Please make sure that the bug is really in Libidn, and
preferably also check that it hasn't already been fixed in the latest
version.

@item You have to send us a test case that makes it possible for us to
reproduce the bug.

@item You also have to explain what is wrong; if you get a crash, or
if the results printed are not good and in that case, in what way.
Make sure that the bug report includes all information you would need
to fix this kind of bug for someone else.

@end itemize

Please make an effort to produce a self-contained report, with
something definite that can be tested or debugged.  Vague queries or
piecemeal messages are difficult to act on and don't help the
development effort.

If your bug report is good, we will do our best to help you to get a
corrected version of the software; if the bug report is poor, we won't
do anything about it (apart from asking you to send better bug
reports).

If you think something in this manual is unclear, or downright
incorrect, or if the language needs to be improved, please also send a
note.

Send your bug report to:

@center @samp{bug-libidn@@gnu.org}


@node Contributing
@section Contributing
@cindex Contributing
@cindex Hacking

If you want to submit a patch for inclusion -- from solve a typo you
discovered, up to adding support for a new feature -- you should
submit it as a bug report (@pxref{Bug Reports}).  There are some
things that you can do to increase the chances for it to be included
in the official package.

Unless your patch is very small (say, under 10 lines) we require that
you assign the copyright of your work to the Free Software Foundation.
This is to protect the freedom of the project.  If you have not
already signed papers, we will send you the necessary information when
you submit your contribution.

For contributions that doesn't consist of actual programming code, the
only guidelines are common sense.  Use it.

For code contributions, a number of style guides will help you:

@itemize @bullet

@item Coding Style.
Follow the GNU Standards document (@pxref{top, GNU Coding Standards,,
standards}).

If you normally code using another coding standard, there is no
problem, but you should use @samp{indent} to reformat the code
(@pxref{top, GNU Indent,, indent}) before submitting your work.

@item Use the unified diff format @samp{diff -u}.

@item Return errors.
No reason whatsoever should abort the execution of the library.  Even
memory allocation errors, e.g. when malloc return NULL, should work
although result in an error code.

@item Design with thread safety in mind.
Don't use global variables and the like.

@item Avoid using the C math library.
It causes problems for embedded implementations, and in most
situations it is very easy to avoid using it.

@item Document your functions.
Use comments before each function headers, that, if properly
formatted, are extracted into GTK-DOC web pages.  Don't forget to
update the Texinfo manual as well.

@item Supply a ChangeLog and NEWS entries, where appropriate.

@end itemize

@c **********************************************************
@c *******************  Preparation  ************************
@c **********************************************************
@node Preparation
@chapter Preparation

To use `Libidn', you have to perform some changes to your sources and
the build system.  The necessary changes are small and explained in
the following sections.  At the end of this chapter, it is described
how the library is initialized, and how the requirements of the
library are verified.

A faster way to find out how to adapt your application for use with
`Libidn' may be to look at the examples at the end of this manual
(@pxref{Examples}).

@menu
* Header::
* Initialization::
* Version Check::
* Building the source::
* Autoconf tests::
* Memory handling under Windows::
@end menu

@node Header
@section Header

The library contains a few independent parts, and each part export the
interfaces (data types and functions) in a header file.  You must
include the appropriate header files in all programs using the
library, either directly or through some other header file, like this:

@example
#include <stringprep.h>
@end example

The header files and the functions they define are categorized as
follows:

@table @asis
@item stringprep.h

The low-level stringprep API entry point.  For IDN applications, this
is usually invoked via IDNA. Some applications, specifically non-IDN
ones, may want to prepare strings directly though, and should include
this header file.

The name space of the stringprep part of Libidn is @code{stringprep*}
for function names, @code{Stringprep*} for data types and
@code{STRINGPREP_*} for other symbols.  In addition,
@code{_stringprep*} is reserved for internal use and should never be
used by applications.

@item punycode.h

The entry point to Punycode encoding and decoding functions.  Normally
punycode is used via the idna.h interface, but some application may
want to perform raw punycode operations.

The name space of the punycode part of Libidn is @code{punycode_*} for
function names, @code{Punycode*} for data types and @code{PUNYCODE_*}
for other symbols.  In addition, @code{_punycode*} is reserved for
internal use and should never be used by applications.
@item idna.h

The entry point to the IDNA functions.  This is the normal entry point
for applications that need IDN functionality.

The name space of the IDNA part of Libidn is @code{idna_*} for
function names, @code{Idna*} for data types and @code{IDNA_*} for
other symbols.  In addition, @code{_idna*} is reserved for internal
use and should never be used by applications.

@item tld.h

The entry point to the TLD functions.  Normal applications are not
expected to need this functionality, but it is present for
applications that are used by TLDs to validate customer input.

The name space of the TLD part of Libidn is @code{tld_*} for function
names, @code{Tld_*} for data types and @code{TLD_*} for other symbols.
In addition, @code{_tld*} is reserved for internal use and should
never be used by applications.

@item pr29.h

The entry point to the PR29 functions.  These functions are used to
detect ``problem sequences'' (@pxref{PR29 Functions}), mostly for use
in security critical applications.

The name space of the PR29 part of Libidn is @code{pr29_*} for
function names, @code{Pr29_*} for data types and @code{PR29_*} for
other symbols.  In addition, @code{_pr29*} is reserved for internal
use and should never be used by applications.

@item idn-free.h

The entry point to the Windows memory de-allocation function
(@pxref{Memory handling under Windows}).  It contains only one
function @code{idn_free}.

@end table

All header files defined and use the symbol @code{IDNAPI} to decorate
the API functions.

@node Initialization
@section Initialization

Libidn is stateless and does not need any initialization.

@node Version Check
@section Version Check

It is often desirable to check that the version of `Libidn' used is
indeed one which fits all requirements.  Even with binary
compatibility new features may have been introduced but due to problem
with the dynamic linker an old version is actually used.  So you may
want to check that the version is okay right after program startup.

@include texi/stringprep_check_version.texi

The normal way to use the function is to put something similar to the
following first in your @code{main}:

@example
  if (!stringprep_check_version (STRINGPREP_VERSION))
    @{
      printf ("stringprep_check_version() failed:\n"
              "Header file incompatible with shared library.\n");
      exit(EXIT_FAILURE);
    @}
@end example

@node Building the source
@section Building the source
@cindex Compiling your application

If you want to compile a source file including e.g. the `idna.h' header
file, you must make sure that the compiler can find it in the
directory hierarchy.  This is accomplished by adding the path to the
directory in which the header file is located to the compilers include
file search path (via the @option{-I} option).

However, the path to the include file is determined at the time the
source is configured.  To solve this problem, `Libidn' uses the
external package @command{pkg-config} that knows the path to the
include file and other configuration options.  The options that need
to be added to the compiler invocation at compile time are output by
the @option{--cflags} option to @command{pkg-config libidn}.  The
following example shows how it can be used at the command line:

@example
gcc -c foo.c `pkg-config libidn --cflags`
@end example

Adding the output of @samp{pkg-config libidn --cflags} to the
compilers command line will ensure that the compiler can find e.g. the
idna.h header file.

A similar problem occurs when linking the program with the library.
Again, the compiler has to find the library files.  For this to work,
the path to the library files has to be added to the library search
path (via the @option{-L} option).  For this, the option
@option{--libs} to @command{pkg-config libidn} can be used.  For
convenience, this option also outputs all other options that are
required to link the program with the `libidn' library.  The example
shows how to link @file{foo.o} with the `libidn' library to a program
@command{foo}.

@example
gcc -o foo foo.o `pkg-config libidn --libs`
@end example

Of course you can also combine both examples to a single command by
specifying both options to @command{pkg-config}:

@example
gcc -o foo foo.c `pkg-config libidn --cflags --libs`
@end example

@node Autoconf tests
@section Autoconf tests
@cindex Autoconf tests
@cindex Configure tests

If your project uses Autoconf (@pxref{top, GNU Autoconf,, autoconf})
to check for installed libraries, you might find the following snippet
illustrative.  It add a new @file{configure} parameter
@code{--with-libidn}, and check for @file{idna.h} and @samp{-lidn}
(possibly below the directory specified as the optional argument to
@code{--with-libidn}), and define the CPP symbol @code{LIBIDN} if the
library is found.  The default behaviour is to search for the library
and enable the functionality (that is, define the symbol) when the
library is found, but if you wish to make the default behaviour of
your package be that Libidn is not used (even if it is installed on
the system), change @samp{libidn=yes} to @samp{libidn=no} on the third
line.

@example
AC_ARG_WITH(libidn, AS_HELP_STRING([--with-libidn=[DIR]],
                                [Support IDN (needs GNU Libidn)]),
  libidn=$withval, libidn=yes)
if test "$libidn" != "no"; then
  if test "$libidn" != "yes"; then
    LDFLAGS="$@{LDFLAGS@} -L$libidn/lib"
    CPPFLAGS="$@{CPPFLAGS@} -I$libidn/include"
  fi
  AC_CHECK_HEADER(idna.h,
    AC_CHECK_LIB(idn, stringprep_check_version,
      [libidn=yes LIBS="$@{LIBS@} -lidn"], libidn=no),
    libidn=no)
fi
if test "$libidn" != "no" ; then
  AC_DEFINE(LIBIDN, 1, [Define to 1 if you want IDN support.])
else
  AC_MSG_WARN([Libidn not found])
fi
AC_MSG_CHECKING([if Libidn should be used])
AC_MSG_RESULT($libidn)
@end example

If you require that your users have installed @code{pkg-config} (which
I cannot recommend generally), the above can be done more easily as
follows.

@example
AC_ARG_WITH(libidn, AS_HELP_STRING([--with-libidn=[DIR]],
                                [Support IDN (needs GNU Libidn)]),
  libidn=$withval, libidn=yes)
if test "$libidn" != "no" ; then
  PKG_CHECK_MODULES(LIBIDN, libidn >= 0.0.0, [libidn=yes], [libidn=no])
  if test "$libidn" != "yes" ; then
    libidn=no
    AC_MSG_WARN([Libidn not found])
  else
    libidn=yes
    AC_DEFINE(LIBIDN, 1, [Define to 1 if you want Libidn.])
  fi
fi
AC_MSG_CHECKING([if Libidn should be used])
AC_MSG_RESULT($libidn)
@end example

@node Memory handling under Windows
@section Memory handling under Windows
@cindex free
@cindex Memory handling
@cindex de-allocation
@cindex heap memory

Several functions in the library allocates memory.  The memory is
expected to be de-allocated using the @code{free} function.  Under
Windows, it is sometimes necessary to de-allocate memory in the same
module that allocated a memory region.  The reason is that different
modules use separate heap memory regions.  To solve this problem we
provide a function to de-allocate memory inside the library.

Note that we do not recommend using this interface generally if you do
not care about Windows portability.

@section Header file @code{idn-free.h}

To use the function explained in this chapter, you need to include the
file @file{idn-free.h} using:

@example
#include <idn-free.h>
@end example

@section Memory de-allocation function

@include texi/idn_free.texi

@c **********************************************************
@c ********************  Utility Functions ******************
@c **********************************************************
@node Utility Functions
@chapter Utility Functions
@cindex Utility Functions

The rest of this library makes extensive use of Unicode characters.
In order to interface this library with the outside world, your
application may need to make various Unicode transformations.

@section Header file @code{stringprep.h}

To use the functions explained in this chapter, you need to include
the file @file{stringprep.h} using:

@example
#include <stringprep.h>
@end example

@section Unicode Encoding Transformation

@include texi/stringprep_unichar_to_utf8.texi
@include texi/stringprep_utf8_to_unichar.texi
@include texi/stringprep_ucs4_to_utf8.texi
@include texi/stringprep_utf8_to_ucs4.texi

@section Unicode Normalization

@include texi/stringprep_ucs4_nfkc_normalize.texi
@include texi/stringprep_utf8_nfkc_normalize.texi

@section Character Set Conversion

@include texi/stringprep_locale_charset.texi
@include texi/stringprep_convert.texi
@include texi/stringprep_locale_to_utf8.texi
@include texi/stringprep_utf8_to_locale.texi


@c **********************************************************
@c ******************  Stringprep Functions *****************
@c **********************************************************
@node Stringprep Functions
@chapter Stringprep Functions
@cindex Stringprep Functions

Stringprep describes a framework for preparing Unicode text strings in
order to increase the likelihood that string input and string
comparison work in ways that make sense for typical users throughout
the world. The stringprep protocol is useful for protocol identifier
values, company and personal names, internationalized domain names,
and other text strings.

@section Header file @code{stringprep.h}

To use the functions explained in this chapter, you need to include
the file @file{stringprep.h} using:

@example
#include <stringprep.h>
@end example

@section Defining A Stringprep Profile

Further types and structures are defined for applications that want to
specify their own stringprep profile.  As these are fairly obscure,
and by necessity tied to the implementation, we do not document them
here.  Look into the @file{stringprep.h} header file, and the
@file{profiles.c} source code for the details.

@section Control Flags

@deftypevr {Stringprep flags} {Stringprep_profile_flags} {STRINGPREP_NO_NFKC}
Disable the NFKC normalization, as well as selecting the non-NFKC case
folding tables.  Usually the profile specifies BIDI and NFKC settings,
and applications should not override it unless in special situations.
@end deftypevr

@deftypevr {Stringprep flags} {Stringprep_profile_flags} {STRINGPREP_NO_BIDI}
Disable the BIDI step.  Usually the profile specifies BIDI and NFKC
settings, and applications should not override it unless in special
situations.
@end deftypevr

@deftypevr {Stringprep flags} {Stringprep_profile_flags} {STRINGPREP_NO_UNASSIGNED}
Make the library return with an error if string contains unassigned
characters according to profile.
@end deftypevr

@section Core Functions

@include texi/stringprep_4i.texi
@include texi/stringprep_4zi.texi
@include texi/stringprep.texi
@include texi/stringprep_profile.texi

@section Error Handling

@include texi/stringprep_strerror.texi

@section Stringprep Profile Macros

@deftypefun {int} stringprep_nameprep_no_unassigned (char * @var{in}, int @var{maxlen})

@var{in}: input/output array with string to prepare.

@var{maxlen}: maximum length of input/output array.

Prepare the input UTF-8 string according to the nameprep profile.  The
AllowUnassigned flag is false, use @code{stringprep_nameprep} for
true AllowUnassigned.  Returns 0 iff successful, or an error code.
@end deftypefun

@deftypefun {int} stringprep_iscsi (char * @var{in}, int @var{maxlen})

@var{in}: input/output array with string to prepare.

@var{maxlen}: maximum length of input/output array.

Prepare the input UTF-8 string according to the draft iSCSI stringprep
profile.  Returns 0 iff successful, or an error code.
@end deftypefun

@deftypefun {int} stringprep_plain (char * @var{in}, int @var{maxlen})

@var{in}: input/output array with string to prepare.

@var{maxlen}: maximum length of input/output array.

Prepare the input UTF-8 string according to the draft SASL ANONYMOUS
profile.  Returns 0 iff successful, or an error code.
@end deftypefun

@deftypefun {int} stringprep_xmpp_nodeprep (char * @var{in}, int @var{maxlen})

@var{in}: input/output array with string to prepare.

@var{maxlen}: maximum length of input/output array.

Prepare the input UTF-8 string according to the draft XMPP node
identifier profile.  Returns 0 iff successful, or an error code.
@end deftypefun

@deftypefun {int} stringprep_xmpp_resourceprep (char * @var{in}, int @var{maxlen})

@var{in}: input/output array with string to prepare.

@var{maxlen}: maximum length of input/output array.

Prepare the input UTF-8 string according to the draft XMPP resource
identifier profile.  Returns 0 iff successful, or an error code.
@end deftypefun

@c **********************************************************
@c *******************  Punycode Functions ******************
@c **********************************************************
@node Punycode Functions
@chapter Punycode Functions
@cindex Punycode Functions

Punycode is a simple and efficient transfer encoding syntax designed
for use with Internationalized Domain Names in Applications. It
uniquely and reversibly transforms a Unicode string into an ASCII
string. ASCII characters in the Unicode string are represented
literally, and non-ASCII characters are represented by ASCII
characters that are allowed in host name labels (letters, digits, and
hyphens). A general algorithm called Bootstring allows a string of
basic code points to uniquely represent any string of code points
drawn from a larger set. Punycode is an instance of Bootstring that
uses particular parameter values, appropriate for IDNA.

@section Header file @code{punycode.h}

To use the functions explained in this chapter, you need to include
the file @file{punycode.h} using:

@example
#include <punycode.h>
@end example

@section Unicode Code Point Data Type

The punycode function uses a special type to denote Unicode code
points.  It is guaranteed to always be a 32 bit unsigned integer.

@deftypevr {Punycode Unicode code point} uint32_t punycode_uint
A unsigned integer that hold Unicode code points.
@end deftypevr

@section Core Functions

Note that the current implementation will fail if the
@code{input_length} exceed 4294967295 (the size of
@code{punycode_uint}).  This restriction may be removed in the future.
Meanwhile applications are encouraged to not depend on this problem,
and use @code{sizeof} to initialize @code{input_length} and
@code{output_length}.

The functions provided are the following two entry points:

@include texi/punycode_encode.texi
@include texi/punycode_decode.texi

@section Error Handling

@include texi/punycode_strerror.texi

@c **********************************************************
@c ********************* IDNA Functions *********************
@c **********************************************************
@node IDNA Functions
@chapter IDNA Functions
@cindex IDNA Functions

Until now, there has been no standard method for domain names to use
characters outside the ASCII repertoire. The IDNA document defines
internationalized domain names (IDNs) and a mechanism called IDNA for
handling them in a standard fashion. IDNs use characters drawn from a
large repertoire (Unicode), but IDNA allows the non-ASCII characters
to be represented using only the ASCII characters already allowed in
so-called host names today. This backward-compatible representation is
required in existing protocols like DNS, so that IDNs can be
introduced with no changes to the existing infrastructure. IDNA is
only meant for processing domain names, not free text.

@section Header file @code{idna.h}

To use the functions explained in this chapter, you need to include
the file @file{idna.h} using:

@example
#include <idna.h>
@end example

@section Control Flags

The IDNA @code{flags} parameter can take on the following values, or a
bit-wise inclusive or of any subset of the parameters:

@deftypevr {Return code} {Idna_flags} IDNA_ALLOW_UNASSIGNED
Allow unassigned Unicode code points.
@end deftypevr

@deftypevr {Return code} {Idna_flags} IDNA_USE_STD3_ASCII_RULES
Check output to make sure it is a STD3 conforming host name.
@end deftypevr

@section Prefix String

@deftypevr {Macro} {#define} IDNA_ACE_PREFIX
String with the official IDNA prefix, @code{xn--}.
@end deftypevr

@section Core Functions

The idea behind the IDNA function names are as follows: the
@code{idna_to_ascii_4i} and @code{idna_to_unicode_44i} functions are
the core IDNA primitives.  The @code{4} indicate that the function
takes UCS-4 strings (i.e., Unicode code points encoded in a 32-bit
unsigned integer type) of the specified length.  The @code{i} indicate
that the data is written ``inline'' into the buffer.  This means the
caller is responsible for allocating (and de-allocating) the string,
and providing the library with the allocated length of the string.
The output length is written in the output length variable.  The
remaining functions all contain the @code{z} indicator, which means
the strings are zero terminated.  All output strings are allocated by
the library, and must be de-allocated by the caller.  The @code{4}
indicator again means that the string is UCS-4, the @code{8} means the
strings are UTF-8 and the @code{l} indicator means the strings are
encoded in the encoding used by the current locale.

The functions provided are the following entry points:

@include texi/idna_to_ascii_4i.texi
@include texi/idna_to_unicode_44i.texi

@section Simplified ToASCII Interface

@include texi/idna_to_ascii_4z.texi
@include texi/idna_to_ascii_8z.texi
@include texi/idna_to_ascii_lz.texi

@section Simplified ToUnicode Interface

@include texi/idna_to_unicode_4z4z.texi
@include texi/idna_to_unicode_8z4z.texi
@include texi/idna_to_unicode_8z8z.texi
@include texi/idna_to_unicode_8zlz.texi
@include texi/idna_to_unicode_lzlz.texi

@section Error Handling

@include texi/idna_strerror.texi

@c **********************************************************
@c ********************** TLD Functions *********************
@c **********************************************************
@node TLD Functions
@chapter TLD Functions
@cindex TLD Functions

Organizations that manage some Top Level Domains (TLDs) have published
tables with characters they accept within the domain.  The reason may
be to reduce complexity that come from using the full Unicode range,
and to protect themselves from future (backwards incompatible) changes
in the IDN or Unicode specifications.  Libidn implement an
infrastructure for defining and checking strings against such tables.
Libidn also ship some tables from TLDs that we have managed to get
permission to use them from.  Because these tables are even less
static than Unicode or StringPrep tables, it is likely that they will
be updated from time to time (even in backwards incompatible ways).
The Libidn interface provide a ``version'' field for each TLD table,
which can be compared for equality to guarantee the same operation
over time.

From a design point of view, you can regard the TLD tables for IDN as
the ``localization'' step that come after the ``internationalization''
step provided by the IETF standards.

The TLD functionality rely on up-to-date tables.  The latest version
of Libidn aim to provide these, but tables with unclear copying
conditions, or generally experimental tables, are not included.  Some
such tables can be found at @url{https://github.com/gnuthor/tldchk}.

@section Header file @code{tld.h}

To use the functions explained in this chapter, you need to include
the file @file{tld.h} using:

@example
#include <tld.h>
@end example

@c @section Data Types
@c
@c @deftp {Data type} {Tld_table_element} @var{start} @var{end}
@c @example
@c /* Interval of valid code points in the TLD. */
@c struct Tld_table_element
@c @{
@c   uint32_t start;		/* Start of range. */
@c   uint32_t end;		/* End of range, end == start if single. */
@c @};
@c typedef struct Tld_table_element Tld_table_element;
@c @end example
@c This @code{struct} contain the @var{start} and @var{end} positions
@c (inclusive) of a range.  If the range is a single (i.e., starts and
@c ends in the same character), then set @var{end} to the same as
@c @var{start}.  This structure is normally used as an array.
@c @end deftp
@c
@c @deftp {Data type} {Tld_table} @var{name} @var{version} @var{nvalid} @var{valid}
@c @example
@c /* List valid code points in a TLD. */
@c struct Tld_table
@c @{
@c   char *name;			/* TLD name, e.g., "no". */
@c   char *version;		/* Version string from TLD file. */
@c   size_t nvalid;		/* Number of entries in data. */
@c   Tld_table_element *valid[];	/* Sorted array of valid code points. */
@c @};
@c typedef struct Tld_table Tld_table;
@c @end example
@c In this @code{struct}, the @var{name} field is a string (@samp{char*})
@c indicating the TLD name (e.g., ``no'').  The @var{version} field is a
@c string (@samp{char*}) containing a free form humanly readable string
@c that can be used for equality comparison to compare different versions
@c of the table.  The @var{nvalid} field indicate how many entries there
@c are in @var{valid}, which brings us finally to @var{valid} that
@c contain the actual code points that are valid for this TLD (see
@c @code{Tld_table_element} above).
@c @end deftp

@section Core Functions

@include texi/tld_check_4t.texi
@include texi/tld_check_4tz.texi

@section Utility Functions

@include texi/tld_get_4.texi
@include texi/tld_get_4z.texi
@include texi/tld_get_z.texi
@include texi/tld_get_table.texi
@include texi/tld_default_table.texi

@section High-Level Wrapper Functions

@include texi/tld_check_4.texi
@include texi/tld_check_4z.texi
@include texi/tld_check_8z.texi
@include texi/tld_check_lz.texi

@section Error Handling

@include texi/tld_strerror.texi

@c **********************************************************
@c ********************** PR29 Functions ********************
@c **********************************************************
@node PR29 Functions
@chapter PR29 Functions
@cindex PR29 Functions

A deficiency in the specification of Unicode Normalization Forms has
been found.  The consequence is that some strings can be normalized
into different strings by different implementations.  In other words,
two different implementations may return different output for the same
input (because the interpretation of the specification is
ambiguous). Further, an implementation invoked again on the one of the
output strings may return a different string (because one of the
interpretation of the ambiguous specification make normalization
non-idempotent).  Fortunately, only a select few character sequence
exhibit this problem, and none of them are expected to occur in
natural languages (due to different linguistic uses of the involved
characters).

A full discussion of the problem may be found at:

@url{http://www.unicode.org/review/pr-29.html}

The PR29 functions below allow you to detect the problem sequence.  So
when would you want to use these functions?  For most applications,
such as those using Nameprep for IDN, this is likely only to be an
interoperability problem.  Thus, you may not want to care about it, as
the character sequences will rarely occur naturally.  However, if you
are using a profile, such as SASLPrep, to process authentication
tokens; authorization tokens; or passwords, there is a real danger
that attackers may try to use the peculiarities in these strings to
attack parts of your system.  As only a small number of strings, and
no naturally occurring strings, exhibit this problem, the conservative
approach of rejecting the strings is recommended.  If this approach is
not used, you should instead verify that all parts of your system,
that process the tokens and passwords, use a NFKC implementation that
produce the same output for the same input.

Technically inclined readers may be interested in knowing more about
the implementation aspects of the PR29 flaw. @xref{PR29 discussion}.

@section Header file @code{pr29.h}

To use the functions explained in this chapter, you need to include
the file @file{pr29.h} using:

@example
#include <pr29.h>
@end example

@section Core Functions

@include texi/pr29_4.texi

@section Utility Functions

@include texi/pr29_4z.texi
@include texi/pr29_8z.texi

@section Error Handling

@include texi/pr29_strerror.texi

@c **********************************************************
@c ***********************  Examples  ***********************
@c **********************************************************
@node Examples
@chapter Examples
@cindex Examples

This chapter contains example code which illustrate how `Libidn' can
be used when writing your own application.

@menu
* Example 1::		Example using stringprep.
* Example 2::		Example using punycode.
* Example 3::		Example using IDNA ToASCII.
* Example 4::		Example using IDNA ToUnicode.
* Example 5::		Example using TLD checking.
@end menu

@node Example 1
@section Example 1

This example demonstrates how the stringprep functions are used.

@verbatiminclude example.txt

@node Example 2
@section Example 2

This example demonstrates how the punycode functions are used.

@verbatiminclude example2.txt

@node Example 3
@section Example 3

This example demonstrates how the library is used to convert
internationalized domain names into ASCII compatible names.

@verbatiminclude example3.txt

@node Example 4
@section Example 4

This example demonstrates how the library is used to convert ASCII
compatible names to internationalized domain names.

@verbatiminclude example4.txt

@node Example 5
@section Example 5

This example demonstrates how the library is used to check a string
for invalid characters within a specific TLD.

@verbatiminclude example5.txt

@c **********************************************************
@c *********************  Invoking idn  *********************
@c **********************************************************
@node Invoking idn
@chapter Invoking idn

@pindex idn
@cindex invoking @command{idn}
@cindex command line

@section Name

GNU Libidn (idn) -- Internationalized Domain Names command line tool

@section Description
@code{idn} allows internationalized string preparation
(@samp{stringprep}), encoding and decoding of punycode data, and IDNA
ToASCII/ToUnicode operations to be performed on the command line.

If strings are specified on the command line, they are used as input
and the computed output is printed to standard output @code{stdout}.
If no strings are specified on the command line, the program read
data, line by line, from the standard input @code{stdin}, and print
the computed output to standard output.  What processing is performed
(e.g., ToASCII, or Punycode encode) is indicated by options.  If any
errors are encountered, the execution of the applications is aborted.

All strings are expected to be encoded in the preferred charset used
by your locale.  Use @code{--debug} to find out what this charset is.
You can override the charset used by setting environment variable
@code{CHARSET}.

To process a string that starts with @code{-}, for example
@code{-foo}, use @code{--} to signal the end of parameters, as in
@code{idn --quiet -a -- -foo}.

@section Options
@code{idn} recognizes these commands:

@verbatiminclude idn-help.texi

@section Environment Variables

The @var{CHARSET} environment variable can be used to override what
character set to be used for decoding incoming data (i.e., on the
command line or on the standard input stream), and to encode data to
the standard output.  If your system is set up correctly, however, the
application will guess which character set is used automatically.
Example usage:

@example
$ CHARSET=ISO-8859-1 idn --punycode-encode
...
@end example

@section Examples

Standard usage, reading input from standard input.  The parameter
@code{--quiet} disable printing copyright, license and usage
instructions.

@example
jas@@latte:~$ idn --quiet
r@"aksm@"org@aa{}s.se
xn--rksmrgs-5wao1o.se
jas@@latte:~$
@end example

Reading input from command line:

@example
jas@@latte:~$ idn --quiet r@"aksm@"org@aa{}s.se bl@aa{}b@ae{}rgr@o{}d.no
xn--rksmrgs-5wao1o.se
xn--blbrgrd-fxak7p.no
jas@@latte:~$
@end example

Accessing a specific StringPrep profile directly:

@example
jas@@latte:~$ idn --quiet --profile=SASLprep --stringprep te@ss{}t@ordf{}
te@ss{}ta
jas@@latte:~$
@end example

@section Troubleshooting

Getting character data encoded right, and making sure Libidn use the
same encoding, can be difficult.  The reason for this is that most
systems encode character data in more than one character encoding,
i.e., using @code{UTF-8} together with @code{ISO-8859-1} or
@code{ISO-2022-JP}.  This problem is likely to continue to exist until
only one character encoding come out as the evolutionary winner, or
(more likely, at least to some extents) forever.

The first step to troubleshooting character encoding problems with
Libidn is to use the @samp{--debug} parameter to find out which
character set encoding @samp{idn} believe your locale uses.

@example
jas@@latte:~$ idn --debug --quiet ""
system locale uses charset `UTF-8'.

jas@@latte:~$
@end example

If it prints @code{ANSI_X3.4-1968} (i.e., @code{US-ASCII}), this
indicate you have not configured your locale properly.  To configure
the locale, you can, for example, use @samp{LANG=sv_SE.UTF-8; export
LANG} at a @code{/bin/sh} prompt, to set up your locale for a Swedish
environment using @code{UTF-8} as the encoding.

Sometimes @samp{idn} appear to be unable to translate from your system
locale into @code{UTF-8} (which is used internally), and you get an
error like the following:

@example
jas@@latte:~$ idn --quiet foo
idn: could not convert from ISO-8859-1 to UTF-8.
jas@@latte:~$
@end example

The simplest explanation is that you haven't installed the
@samp{iconv} conversion tools.  You can find it as a standalone
library in GNU Libiconv
(@uref{https://www.gnu.org/software/libiconv/}).  On many GNU/Linux
systems, this library is part of the system, but you may have to
install additional packages (e.g., @samp{glibc-locale} for Debian) to
be able to use it.

Another explanation is that the error is correct and you are feeding
@samp{idn} invalid data.  This can happen inadvertently if you are not
careful with the character set encoding you use.  For example, if your
shell run in a @code{ISO-8859-1} environment, and you invoke
@samp{idn} with the @samp{CHARSET} environment variable as follows,
you will feed it @code{ISO-8859-1} characters but force it to believe
they are @code{UTF-8}.  Naturally this will lead to an error, unless
the byte sequences happen to be valid @code{UTF-8}.  Note that even if
you don't get an error, the output may be incorrect in this situation,
because @code{ISO-8859-1} and @code{UTF-8} does not in general encode
the same characters as the same byte sequences.

@example
jas@@latte:~$ idn --quiet --debug ""
system locale uses charset `ISO-8859-1'.

jas@@latte:~$ CHARSET=UTF-8 idn --quiet --debug r@"aksm@"org@aa{}s
system locale uses charset `UTF-8'.
input[0] = U+0072
input[1] = U+4af3
input[2] = U+006d
input[3] = U+1b29e5
input[4] = U+0073
output[0] = U+0078
output[1] = U+006e
output[2] = U+002d
output[3] = U+002d
output[4] = U+0072
output[5] = U+006d
output[6] = U+0073
output[7] = U+002d
output[8] = U+0068
output[9] = U+0069
output[10] = U+0036
output[11] = U+0064
output[12] = U+0035
output[13] = U+0039
output[14] = U+0037
output[15] = U+0035
output[16] = U+0035
output[17] = U+0032
output[18] = U+0061
xn--rms-hi6d597552a
jas@@latte:~$
@end example

The sense moral here is to forget about @samp{CHARSET} (configure your
locales properly instead) unless you know what you are doing, and if
you want to use it, do it carefully, after verifying with
@samp{--debug} that you get the desired results.

@node Emacs API
@chapter Emacs API

Included in Libidn are @file{punycode.el} and @file{idna.el} that
provides an Emacs Lisp API to (a limited set of) the Libidn API.  This
section describes the API.  Currently the IDNA API always set the
@code{UseSTD3ASCIIRules} flag and clear the @code{AllowUnassigned}
flag, in the future there may be functionality to specify these flags
via the API.

@section Punycode Emacs API

@defvar punycode-program
Name of the GNU Libidn @file{idn} application.  The default is
@samp{idn}.  This variable can be customized.
@end defvar

@defvar punycode-environment
List of environment variable definitions prepended to
@samp{process-environment}.  The default is @samp{("CHARSET=UTF-8")}.
This variable can be customized.
@end defvar

@defvar punycode-encode-parameters
List of parameters passed to @var{punycode-program} to invoke punycode
encoding mode.  The default is @samp{("--quiet" "--punycode-encode")}.
This variable can be customized.
@end defvar

@defvar punycode-decode-parameters
Parameters passed to @var{punycode-program} to invoke punycode
decoding mode.  The default is @samp{("--quiet" "--punycode-decode")}.
This variable can be customized.
@end defvar

@defun punycode-encode string
Returns a Punycode encoding of the @var{string}, after converting the
input into UTF-8.
@end defun

@defun punycode-decode string
Returns a possibly multibyte string which is the decoding of the
@var{string} which is a punycode encoded string.
@end defun

@section IDNA Emacs API

@defvar idna-program
Name of the GNU Libidn @file{idn} application.  The default is
@samp{idn}.  This variable can be customized.
@end defvar

@defvar idna-environment
List of environment variable definitions prepended to
@samp{process-environment}.  The default is @samp{("CHARSET=UTF-8")}.
This variable can be customized.
@end defvar

@defvar idna-to-ascii-parameters
List of parameters passed to @var{idna-program} to invoke IDNA ToASCII
mode.  The default is @samp{("--quiet" "--idna-to-ascii"
"--usestd3asciirules")}.  This variable can be customized.
@end defvar

@defvar idna-to-unicode-parameters
Parameters passed @var{idna-program} to invoke IDNA ToUnicode mode.
The default is @samp{("--quiet" "--idna-to-unicode"
"--usestd3asciirules")}.  This variable can be customized.
@end defvar

@defun idna-to-ascii string
Returns an ASCII Compatible Encoding (ACE) of the string computed by
the IDNA ToASCII operation on the input @var{string}, after converting
the input to UTF-8.
@end defun

@defun idna-to-unicode string
Returns a possibly multibyte string which is the output of the IDNA
ToUnicode operation computed on the input @var{string}.
@end defun

@node Java API
@chapter Java API

Libidn has been ported to the Java programming language, and as a
consequence most of the API is available to native Java applications.
This section contain notes on this support, complete documentation is
pending.

The Java library, if Libidn has been built with Java support
(@pxref{Downloading and Installing}), will be placed in
@file{java/libidn-@value{VERSION}.jar}.  The source code is below
@file{java/} in Maven directory layout, and there is a Maven
@file{pom.xml} build script as well.  Source code files are in
@file{java/src/main/java/gnu/inet/encoding/}.

@section Overview

This package provides a Java implementation of the Internationalized
Domain Names in Applications (IDNA) standard. It is written entirely
in Java and does not require any additional libraries to be set up.

The gnu.inet.encoding.IDNA class offers two public functions, toASCII
and toUnicode which can be used as follows:

@example
gnu.inet.encoding.IDNA.toASCII("bl@"ods.z@"ug");
gnu.inet.encoding.IDNA.toUnicode("xn--blds-6qa.xn--zg-xka");
@end example

@section Miscellaneous Programs

The @file{java/src/util/java/} directory contains several programs that
are related to the Java part of GNU Libidn, but that don't need to be
included in the main source tree or the JAR file.

@subsection GenerateRFC3454

This program parses RFC3454 and creates the RFC3454.java program that
is required during the StringPrep phase.

The RFC can be found at various locations, for example at
@url{http://www.ietf.org/rfc/rfc3454.txt}.

Invoke the program as follows:

@example
$ java GenerateRFC3454
Creating RFC3454.java... Ok.
@end example

@subsection GenerateNFKC

The GenerateNFKC program parses the Unicode character database file
and generates all the tables required for NFKC. This program requires
the two files UnicodeData.txt and CompositionExclusions.txt of version
3.2 of the Unicode files. Note that RFC3454 (Stringprep) defines that
Unicode version 3.2 is to be used, not the latest version.

The Unicode data files can be found at
@url{http://www.unicode.org/Public/}.

Invoke the program as follows:

@example
$ java GenerateNFKC
Creating CombiningClass.java... Ok.
Creating DecompositionKeys.java... Ok.
Creating DecompositionMappings.java... Ok.
Creating Composition.java... Ok.
@end example

@subsection TestIDNA

The TestIDNA program allows to test the IDNA implementation manually
or against Simon Josefsson's test vectors.

The test vectors can be found at the Libidn homepage,
@url{https://www.gnu.org/software/libidn/}.

To test the transformation manually, use:

@example
$ java -cp .:/usr/share/java/libidn.jar TestIDNA -a <string to test>
Input: <string to test>
Output: <toASCII(string to test)>
$ java -cp .:/usr/share/java/libidn.jar TestIDNA -u <string to test>
Input: <string to test>
Output: <toUnicode(string to test)>
@end example

To test against draft-josefsson-idn-test-vectors.html, use:

@example
$ java -cp .:/usr/share/java/libidn/libidn.jar TestIDNA -t
No errors detected!
@end example

@subsection TestNFKC

The TestNFKC program allows to test the NFKC implementation manually
or against the NormalizationTest.txt file from the Unicode data files.

To test the normalization manually, use:

@example
$ java -cp .:/usr/share/java/libidn.jar TestNFKC <string to test>
Input: <string to test>
Output: <nfkc version of the string to test>
@end example

To test against NormalizationTest.txt:

@example
$ java -cp .:/usr/share/java/libidn.jar TestNFKC
No errors detected!
@end example

@section Possible Problems

Beware of Bugs: This Java API needs a lot more testing, especially
with "exotic" character sets. While it works for me, it may not work
for you.

Encoding of your Java sources: If you are using non-ASCII characters
in your Java source code, make sure javac compiles your programs with
the correct encoding. If necessary specify the encoding using the
-encoding parameter.

Java Unicode handling: Java 1.4 only handles 16-bit Unicode code
points (i.e. characters in the Basic Multilingual Plane), this
implementation therefore ignores all references to so-called
Supplementary Characters (U+10000 to U+10FFFF). Starting from Java
1.5, these characters will also be supported by Java, but this will
require changes to this library.  See also the next section.

@section A Note on Java and Unicode

This library uses Java's built-in 'char' datatype. Up to Java 1.4, this
datatype only supports 16-bit Unicode code points, also called the
Basic Multilingual Plane. For this reason, this library doesn't work
for Supplementary Characters (i.e. characters from U+10000 to
U+10FFFF). All references to such characters are silently ignored.

Starting from Java 1.5, also Supplementary Characters will be
supported. However, this will require changes in the present version
of the library. Java 1.5 is currently in beta status.

For more information refer to the documentation of java.lang.Character
in the JDK API.

@node C# API
@chapter C# API

The Libidn library has been ported to the C# language.  The port
reside in the top-level @file{csharp/} directory.  Currently, no
further documentation about the implementation or the API is
available.  However, the C# port was based on the Java port, and the
API is exactly the same as in the Java version.  The help files for
the Java API may thus be useful.

@c **********************************************************
@c *******************  Acknowledgements  *******************
@c **********************************************************
@node Acknowledgements
@chapter Acknowledgements

The punycode implementation was taken from the IETF IDN Punycode
specification, by Adam M. Costello.  The TLD code was contributed by
Thomas Jacob.  The Java implementation was contributed by Oliver Hitz.
The C# implementation was contributed by Alexander Gnauck.  The
Unicode tables were provided by Unicode, Inc.  Some functions for
dealing with Unicode (see nfkc.c and toutf8.c) were borrowed from
GLib, downloaded from @url{http://www.gtk.org/}.  The manual borrowed
text from Libgcrypt by Werner Koch.

Inspiration for many things that, consciously or not, have gone into
this package is due to a number of free software package that the
author has been exposed to.  The author wishes to acknowledge the free
software community in general, for giving an example on what role
software development can play in the modern society.

Several people reported bugs, sent patches or suggested improvements,
see the file THANKS in the top-level directory of the source code.

@c **********************************************************
@c ************************  History  ***********************
@c **********************************************************
@node History
@chapter History

The complete history of user visible changes is stored in the file
@file{NEWS} in the top-level directory of the source code tree.  The
complete history of modifications to each file is stored in the file
@file{ChangeLog} in the same directory.  This section contain a
condensed version of that information, in the form of ``milestones''
for the project.

@table @asis
@item Stringprep implementation.
Version 0.0.0 released on 2002-11-05.

@item IDNA and Punycode implementations, part of the GNU project.
Version 0.1.0 released on 2003-01-05.

@item Uses official IDNA ACE prefix @code{xn--}.
Version 0.1.7 released on 2003-02-12.

@item Command line interface.
Version 0.1.11 released on 2003-02-26.

@item GNU Libc add-on proposed.
Version 0.1.12 released on 2003-03-06.

@item Interoperability testing during IDNConnect.
Version 0.3.1 released on 2003-10-02.

@item TLD restriction testing.
Version 0.4.0 released on 2004-02-28.

@item GNU Libc add-on integrated.
Version 0.4.1 released on 2004-03-08.

@item Native Java implementation.
Version 0.4.2-0.4.9 released between 2004-03-20 and 2004-06-11.

@item PR-29 functions for ``problem sequences''.
Version 0.5.0 released on 2004-06-26.

@item Many small portability fixes and wider use.
Version 0.5.1 through 0.5.20, released between 2004-07-09 and
2005-10-23.

@item Native C# implementation.
Version 0.6.0 released on 2005-12-03.

@item Windows support through cross-compilation.
Version 0.6.1 released on 2006-01-20.

@item Library declared stable by releasing v1.0.
Version 1.0 released on 2007-07-31.

@end table

@node PR29 discussion
@appendix PR29 discussion

If you wish to experiment with a modified Unicode NFKC implementation
according to the PR29 proposal, you may find the following bug report
useful.  However, I have not verified that the suggested modifications
are correct.  For reference, I'm including my response to the report
as well.

@verbatim
From: Rick McGowan <rick@unicode.org>
Subject: Possible bug and status of PR 29 change(s)
To: bug-libidn@gnu.org
Date: Wed, 27 Oct 2004 14:49:17 -0700

Hello. On behalf of the Unicode Consortium editorial committee, I would
like to find out more information about the PR 29 fixes, if any, and
functions in Libidn. Your implementation was listed in the text of PR29 as
needing investigation, so I am following up on several implementations.

The UTC has accepted the proposed fix to D2 as outlined in PR29, and a new
draft of UAX #15 has been issued.

I have looked at Libidn 0.5.8 (today), and there may still be a possible
bug in NFKC.java and nfkc.c.

------------------------------------------------------

1. In NFKC.java, this line in canonicalOrdering():

      if (i > 0 && (last_cc == 0 || last_cc != cc)) {

should perhaps be changed to:

      if (i > 0 && (last_cc == 0 || last_cc < cc)) {

but I'm not sure of the sense of this comparison.

------------------------------------------------------

2. In nfkc.c, function _g_utf8_normalize_wc() has this code:

	  if (i > 0 &&
	      (last_cc == 0 || last_cc != cc) &&
	      combine (wc_buffer[last_start], wc_buffer[i],
		       &wc_buffer[last_start]))
	    {

This appears to have the same bug as the current Python implementation (in
Python 2.3.4). The code should be checking, as per new rule D2 UAX #15
update, that the next combining character is the same or HIGHER than the
current one. It now checks to see if it's non-zero and not equal.

The above line(s) should perhaps be changed to:

	  if (i > 0 &&
	      (last_cc == 0 || last_cc < cc) &&
	      combine (wc_buffer[last_start], wc_buffer[i],
		       &wc_buffer[last_start]))
	    {

but I'm not sure of the sense of the comparison (< or > or <=?) here.

In the text of PR29, I will be marking Libidn as "needs change" and adding
the version number that I checked. If any further change is made, please
let me know the release version, and I'll update again.

Regards,
	Rick McGowan
@end verbatim

@verbatim
From: Simon Josefsson <jas@extundo.com>
Subject: Re: Possible bug and status of PR 29 change(s)
To: Rick McGowan <rick@unicode.org>
Cc: bug-libidn@gnu.org
Date: Thu, 28 Oct 2004 09:47:47 +0200

Rick McGowan <rick@unicode.org> writes:

> Hello. On behalf of the Unicode Consortium editorial committee, I would
> like to find out more information about the PR 29 fixes, if any, and
> functions in Libidn. Your implementation was listed in the text of PR29 as
> needing investigation, so I am following up on several implementations.
>
> The UTC has accepted the proposed fix to D2 as outlined in PR29, and a new
> draft of UAX #15 has been issued.
>
> I have looked at Libidn 0.5.8 (today), and there may still be a possible
> bug in NFKC.java and nfkc.c.

Hello Rick.

I believe the current behavior is intentional.  Libidn do not aim to
implement latest-and-greatest NFKC, it aim to implement the NFKC
functionality required for StringPrep and IDN.  As you may know,
StringPrep/IDN reference Unicode 3.2.0, and explicitly says any later
changes (which I consider PR29 as) do not apply.

In fact, I believe that would I incorporate the changes suggested in
PR29, I would in fact be violating the IDN specifications.

Thanks for looking into the code and finding the place where the
change could be made.  I'll see if I can mention this in the manual
somewhere, for technically interested readers.

Regards,
Simon
@end verbatim

@node On Label Separators
@appendix On Label Separators

Some strings contains characters whose NFKC normalized form contain
the ASCII dot (0x2E, ``.'').  Examples of these characters are U+2024
(ONE DOT LEADER) and U+248C (DIGIT FIVE FULL STOP).  The strings have
the interesting property that their IDNA ToASCII output will contain
embedded dots.  For example:

@example
ToASCII (hi U+248C com) = hi5.com
ToASCII (r@"aksm@"org@aa{}s U+2024 com) = xn--rksmrgs.com-l8as9u
@end example

This demonstrate the two general cases: The first where the ASCII dot
is part of an output that do not begin with the IDN prefix
@code{xn--}.  The second example illustrate when the dot is part of
IDN prefixed with @code{xn--}.

The input strings are, from the DNS point of view, a single label.
The IDNA algorithm translate one label at a time.  Thus, the output is
expected to be only one label.  What is important here is to make sure
the DNS resolver receives the correct query.  The DNS protocol does
not use the dot to delimit labels on the wire, rather it uses
length-value pairs.  Thus the correct query would be for
@code{@{7@}hi5.com} and @code{@{22@}xn--rksmrgs.com-l8as9u}
respectively.

Some implementations @footnote{Notably Microsoft's Internet Explorer
and Mozilla's Firefox, but not Apple's Safari.} have decided that
these inputs strings are potentially confusing for the user.  The
string @code{hi U+248C com} looks like @code{hi5.com} on systems that
support Unicode properly.  These implementations do not follow RFC
3490.  They yield:

@example
ToASCII (hi U+248C com) = hi5.com
ToASCII (r@"aksm@"org@aa{}s U+2024 com) = xn--rksmrgs-5wao1o.com
@end example

The DNS query they perform are @code{@{3@}hi5@{3@}com} and
@code{@{18@}xn--rksmrgs-5wao1o@{3@}com} respectively.  Arguably, this
leads to a better user experience, and suggests that the IDNA
specification is sub-optimal in this area.

@section Recommended Workaround

It has been suggested to normalize the entire input string using NFKC
before passing it to IDNA ToASCII.  You may use
@code{stringprep_utf8_nfkc_normalize} or
@code{stringprep_ucs4_nfkc_normalize}.  This appears to lead to
similar behaviour as IE/Firefox, which would avoid the problem, but
this needs to be confirmed.  Feel free to discuss the issue with us.

Alternative workarounds are being considered.  Eventually Libidn may
implement a new flag to the @code{idna_*} functions that implements a
recommended way to work around this problem.

@node GNU Free Documentation License
@appendix GNU Free Documentation License

@include fdl-1.3.texi

@node Function and Variable Index
@unnumbered Function and Variable Index

@printindex fn

@node Concept Index
@unnumbered Concept Index

@printindex cp

@bye

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