Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with the
Invariant Sections being “Commercial Support”, no Front-Cover Texts,
and no Back-Cover Texts. A copy of the license is included in the
section entitled “GNU Free Documentation License”.
GNU Libidn is an implementation of the Stringprep, Punycode and IDNA
specifications defined by the IETF Internationalized Domain Names
(IDN) working group, used for internationalized domain names. The
package is available under the GNU Lesser General Public License.
The library contains a generic Stringprep implementation that does
Unicode 3.2 NFKC normalization, mapping and prohibitation of
characters, and bidirectional character handling. Profiles for
Nameprep, iSCSI, SASL and XMPP 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.
Libidn is written in C and (parts of) the API is accessible from C,
C++, Emacs Lisp, Python and Java. An experimental native Java API is
also available.
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 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 (see Examples), and then only
read up those parts of the interface which are unclear.
This library might have a couple of advantages over other libraries
doing a similar job.
It's Free Software
Anybody can use, modify, and redistribute it under the terms of the
GNU Lesser General Public License.
It's thread-safe
No global state is kept in the library. All functions are reentrant.
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.
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.
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.
It's documented
Sadly, not all software comes with documentation these days. This one
does.
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.
Libidn has at some point in time been tested on the following
platforms.
Debian GNU/Linux 3.0 (Woody)
GCC 2.95.4 and GNU Make. This is the main development platform.
alphaev67-unknown-linux-gnu, alphaev6-unknown-linux-gnu,
arm-unknown-linux-gnu, armv4l-unknown-linux-gnu,
hppa-unknown-linux-gnu, hppa64-unknown-linux-gnu,
i686-pc-linux-gnu, ia64-unknown-linux-gnu,
m68k-unknown-linux-gnu, mips-unknown-linux-gnu,
mipsel-unknown-linux-gnu, powerpc-unknown-linux-gnu,
s390-ibm-linux-gnu, sparc-unknown-linux-gnu,
sparc64-unknown-linux-gnu.
Debian GNU/Linux 2.1
GCC 2.95.1 and GNU Make. armv4l-unknown-linux-gnu.
Tru64 UNIX
Tru64 UNIX C compiler and Tru64 Make. alphaev67-dec-osf5.1,
alphaev68-dec-osf5.1.
SuSE Linux 7.1
GCC 2.96 and GNU Make. alphaev6-unknown-linux-gnu,
alphaev67-unknown-linux-gnu.
SuSE Linux 7.2a
GCC 3.0 and GNU Make. ia64-unknown-linux-gnu.
SuSE Linux
GCC 3.2.2 and GNU Make. x86_64-unknown-linux-gnu (AMD64
Opteron “Melody”).
RedHat Linux 7.2
GCC 2.96 and GNU Make. alphaev6-unknown-linux-gnu,
alphaev67-unknown-linux-gnu, ia64-unknown-linux-gnu.
RedHat Linux 8.0
GCC 3.2 and GNU Make. i686-pc-linux-gnu.
RedHat Advanced Server 2.1
GCC 2.96 and GNU Make. i686-pc-linux-gnu.
Slackware Linux 8.0.01
GCC 2.95.3 and GNU Make. i686-pc-linux-gnu.
Mandrake Linux 9.0
GCC 3.2 and GNU Make. i686-pc-linux-gnu.
IRIX 6.5
MIPS C compiler, IRIX Make. mips-sgi-irix6.5.
AIX 4.3.2
IBM C for AIX compiler, AIX Make. rs6000-ibm-aix4.3.2.0.
Microsoft Windows 2000 (Cygwin)
GCC 3.2, GNU make. i686-pc-cygwin.
HP-UX 11
HP-UX C compiler and HP Make. ia64-hp-hpux11.22,
hppa2.0w-hp-hpux11.11.
SUN Solaris 2.7
GCC 3.0.4 and GNU Make. sparc-sun-solaris2.7.
SUN Solaris 2.8
Sun WorkShop Compiler C 6.0 and SUN Make. sparc-sun-solaris2.8.
SUN Solaris 2.9
Sun Forte Developer 7 C compiler and GNU
Make. sparc-sun-solaris2.9.
NetBSD 1.6
GCC 2.95.3 and GNU Make. alpha-unknown-netbsd1.6,
i386-unknown-netbsdelf1.6.
OpenBSD 3.1 and 3.2
GCC 2.95.3 and GNU Make. alpha-unknown-openbsd3.1,
i386-unknown-openbsd3.1.
FreeBSD 4.7 and 4.8
GCC 2.95.4 and GNU Make. alpha-unknown-freebsd4.7,
alpha-unknown-freebsd4.8, i386-unknown-freebsd4.7,
i386-unknown-freebsd4.8.
MacOS X 10.2 Server Edition
GCC 3.1 and GNU Make. powerpc-apple-darwin6.5.
Cross compiled to uClinux/uClibc on Motorola Coldfire
GCC 3.4 and GNU Make m68k-uclinux-elf.
Cross compiled to ARM using Glibc
GCC 2.95 and GNU Make arm-linux.
If you use Libidn on, or port Libidn to, a new platform please report
it to the author.
The latest version is stored in a file, e.g.,
`gsasl-0.5.15.tar.gz' where the `0.5.15'
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 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
`sh', `make' and `cc'.
$ wget -q http://josefsson.org/libidn/releases/libidn-0.5.15.tar.gz
$ tar xfz libidn-0.5.15.tar.gz
$ cd libidn-0.5.15/
$ ./configure
...
$ make
...
$ make install
...
After that Libidn should be properly installed and ready for use.
A few configure options may be relevant, summarized in the
table.
--enable-java
Build the Java port into a *.JAR file. See Java API, for more
information.
--disable-tld
Disable the TLD module. This would typically only be useful if you
are building on a memory restricted platforms. See TLD Functions,
for more information.
For the complete list, refer to the output from configure
--help.
If you think you have found a bug in Libidn, please investigate it and
report it.
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.
You have to send us a test case that makes it possible for us to
reproduce the bug.
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.
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.
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 (see 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:
If you normally code using another coding standard, there is no
problem, but you should use `indent' to reformat the code
(see GNU Indent) before submitting your work.
Use the unified diff format `diff -u'.
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.
Design with thread safety in mind.
Don't use global variables and the like.
Avoid using the C math library.
It causes problems for embedded implementations, and in most
situations it is very easy to avoid using it.
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.
Supply a ChangeLog and NEWS entries, where appropriate.
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
(see Examples).
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:
#include <stringprep.h>
The header files and the functions they define are categorized as
follows:
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 stringprep*
for function names, Stringprep* for data types and
STRINGPREP_* for other symbols. In addition,
_stringprep* is reserved for internal use and should never be
used by applications.
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 punycode_* for
function names, Punycode* for data types and PUNYCODE_*
for other symbols. In addition, _punycode* is reserved for
internal use and should never be used by applications.
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 idna_* for
function names, Idna* for data types and IDNA_* for
other symbols. In addition, _idna* is reserved for internal
use and should never be used by applications.
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 tld_* for function
names, Tld_* for data types and TLD_* for other symbols.
In addition, _tld* is reserved for internal use and should
never be used by applications.
pr29.h
The entry point to the PR29 functions. These functions are used to
detect “problem sequences” (see PR29 Functions), mostly for use
in security critical applications.
The name space of the PR29 part of Libidn is pr29_* for
function names, Pr29_* for data types and PR29_* for
other symbols. In addition, _pr29* is reserved for internal
use and should never be used by applications.
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.
Check that the the version of the library is at minimum the requested one
and return the version string; return NULL if the condition is not
satisfied. If a NULL is passed to this function, no check is done,
but the version string is simply returned.
See STRINGPREP_VERSION for a suitable req_version string.
Return value: Version string of run-time library, or NULL if the
run-time library does not meet the required version number.
The normal way to use the function is to put something similar to the
following first in your main:
if (!stringprep_check_version (STRINGPREP_VERSION))
{
printf ("stringprep_check_version() failed:\n"
"Header file incompatible with shared library.\n");
exit(1);
}
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 -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 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 --cflags option to pkg-config libidn. The
following example shows how it can be used at the command line:
gcc -c foo.c `pkg-config libidn --cflags`
Adding the output of `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 -L option). For this, the option
--libs to 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' libarary. The example
shows how to link foo.o with the `libidn' library to a program
foo.
gcc -o foo foo.o `pkg-config libidn --libs`
Of course you can also combine both examples to a single command by
specifying both options to pkg-config:
If your project uses Autoconf (see GNU Autoconf)
to check for installed libraries, you might find the following snippet
illustrative. It add a new configure parameter
--with-libidn, and check for idna.h and `-lidn'
(possibly below the directory specified as the optional argument to
--with-libidn), and define the CPP symbol
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 `libidn=yes' to
`libidn=no' on the third line.
AC_ARG_WITH(libidn, AC_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)
If you require that your users have installed pkg-config (which
I cannot recommend generally), the above can be done more easily as
follows.
AC_ARG_WITH(libidn, AC_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)
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.
3.1 Header file stringprep.h
To use the functions explained in this chapter, you need to include
the file stringprep.h using:
#include <stringprep.h>
3.2 Unicode Encoding Transformation
— Function: int stringprep_unichar_to_utf8 (uint32_t c, char * outbuf)
c: a ISO10646 character code
outbuf: output buffer, must have at least 6 bytes of space.
If NULL, the length will be computed and returned
and nothing will be written to outbuf.
len: the maximum length of str to use. If len < 0, then
the string is terminated with a 0 character.
items_read: location to store number of characters read read, or NULL.
items_written: location to store number of bytes written or NULL.
The value here stored does not include the trailing 0
byte.
Convert a string from a 32-bit fixed width representation as UCS-4.
to UTF-8. The result will be terminated with a 0 byte.
Return value: a pointer to a newly allocated UTF-8 string.
This value must be freed with free(). If an
error occurs, NULL will be returned and
error set.
len: the maximum length of str to use. If len < 0, then
the string is nul-terminated.
items_written: location to store the number of characters in the
result, or NULL.
Convert a string from UTF-8 to a 32-bit fixed width
representation as UCS-4, assuming valid UTF-8 input.
This function does no error checking on the input.
Return value: a pointer to a newly allocated UCS-4 string.
This value must be freed with free().
len: length of str, in bytes, or -1 if str is nul-terminated.
Converts a string into canonical form, standardizing
such issues as whether a character with an accent
is represented as a base character and combining
accent or as a single precomposed character.
The normalization mode is NFKC (ALL COMPOSE). It standardizes
differences that do not affect the text content, such as the
above-mentioned accent representation. It standardizes the
"compatibility" characters in Unicode, such as SUPERSCRIPT THREE to
the standard forms (in this case DIGIT THREE). Formatting
information may be lost but for most text operations such
characters should be considered the same. It returns a result with
composed forms rather than a maximally decomposed form.
Return value: a newly allocated string, that is the
NFKC normalized form of str.
Find out current locale charset. The function respect the CHARSET
environment variable, but typically uses nl_langinfo(CODESET) when
it is supported. It fall back on "ASCII" if CHARSET isn't set and
nl_langinfo isn't supported or return anything.
Note that this function return the application's locale's preferred
charset (or thread's locale's preffered charset, if your system
support thread-specific locales). It does not return what the
system may be using. Thus, if you receive data from external
sources you cannot in general use this function to guess what
charset it is encoded in. Use stringprep_convert from the external
representation into the charset returned by this function, to have
data in the locale encoding.
Return value: Return the character set used by the current locale.
It will never return NULL, but use "ASCII" as a fallback.
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.
4.1 Header file stringprep.h
To use the functions explained in this chapter, you need to include
the file stringprep.h using:
#include <stringprep.h>
4.2 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 stringprep.h header file, and the
profiles.c source code for the details.
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.
len: on input, length of input array with Unicode code points,
on exit, length of output array with Unicode code points.
maxucs4len: maximum length of input/output array.
flags: a Stringprep_profile_flags value, or 0.
profile: pointer to Stringprep_profile to use.
Prepare the input UCS-4 string according to the stringprep profile,
and write back the result to the input string.
The input is not required to be zero terminated (ucs4[len] = 0).
The output will not be zero terminated unless ucs4[len] = 0.
Instead, see stringprep_4zi() if your input is zero terminated or
if you want the output to be.
Since the stringprep operation can expand the string, maxucs4len
indicate how large the buffer holding the string is. This function
will not read or write to code points outside that size.
The flags are one of Stringprep_profile_flags values, or 0.
The profile contain the Stringprep_profile instructions to
perform. Your application can define new profiles, possibly
re-using the generic stringprep tables that always will be part of
the library, or use one of the currently supported profiles.
Return value: Returns STRINGPREP_OK iff successful, or an
Stringprep_rc error code.
ucs4: input/output array with zero terminated string to prepare.
maxucs4len: maximum length of input/output array.
flags: a Stringprep_profile_flags value, or 0.
profile: pointer to Stringprep_profile to use.
Prepare the input zero terminated UCS-4 string according to the
stringprep profile, and write back the result to the input string.
Since the stringprep operation can expand the string, maxucs4len
indicate how large the buffer holding the string is. This function
will not read or write to code points outside that size.
The flags are one of Stringprep_profile_flags values, or 0.
The profile contain the Stringprep_profile instructions to
perform. Your application can define new profiles, possibly
re-using the generic stringprep tables that always will be part of
the library, or use one of the currently supported profiles.
Return value: Returns STRINGPREP_OK iff successful, or an
Stringprep_rc error code.
— Function: int stringprep (char * in, size_t maxlen, Stringprep_profile_flags flags, const Stringprep_profile * profile)
in: input/ouput array with string to prepare.
maxlen: maximum length of input/output array.
flags: a Stringprep_profile_flags value, or 0.
profile: pointer to Stringprep_profile to use.
Prepare the input zero terminated UTF-8 string according to the
stringprep profile, and write back the result to the input string.
Note that you must convert strings entered in the systems locale
into UTF-8 before using this function, see
stringprep_locale_to_utf8().
Since the stringprep operation can expand the string, maxlen
indicate how large the buffer holding the string is. This function
will not read or write to characters outside that size.
The flags are one of Stringprep_profile_flags values, or 0.
The profile contain the Stringprep_profile instructions to
perform. Your application can define new profiles, possibly
re-using the generic stringprep tables that always will be part of
the library, or use one of the currently supported profiles.
Return value: Returns STRINGPREP_OK iff successful, or an error code.
— Function: int stringprep_profile (const char * in, char ** out, const char * profile, Stringprep_profile_flags flags)
in: input array with UTF-8 string to prepare.
out: output variable with pointer to newly allocate string.
profile: name of stringprep profile to use.
flags: a Stringprep_profile_flags value, or 0.
Prepare the input zero terminated UTF-8 string according to the
stringprep profile, and return the result in a newly allocated
variable.
Note that you must convert strings entered in the systems locale
into UTF-8 before using this function, see
stringprep_locale_to_utf8().
The output out variable must be deallocated by the caller.
The flags are one of Stringprep_profile_flags values, or 0.
The profile specifies the name of the stringprep profile to use.
It must be one of the internally supported stringprep profiles.
Return value: Returns STRINGPREP_OK iff successful, or an error code.
Convert a return code integer to a text string. This string can be
used to output a diagnostic message to the user.
STRINGPREP_OK: Successful operation. This value is guaranteed to
always be zero, the remaining ones are only guaranteed to hold
non-zero values, for logical comparison purposes.
STRINGPREP_CONTAINS_UNASSIGNED: String contain unassigned Unicode
code points, which is forbidden by the profile.
STRINGPREP_CONTAINS_PROHIBITED: String contain code points
prohibited by the profile.
STRINGPREP_BIDI_BOTH_L_AND_RAL: String contain code points with
conflicting bidirection category.
STRINGPREP_BIDI_LEADTRAIL_NOT_RAL: Leading and trailing character
in string not of proper bidirectional category.
STRINGPREP_BIDI_CONTAINS_PROHIBITED: Contains prohibited code
points detected by bidirectional code.
STRINGPREP_TOO_SMALL_BUFFER: Buffer handed to function was too
small. This usually indicate a problem in the calling
application.
STRINGPREP_PROFILE_ERROR: The stringprep profile was inconsistent.
This usually indicate an internal error in the library.
STRINGPREP_FLAG_ERROR: The supplied flag conflicted with profile.
This usually indicate a problem in the calling application.
STRINGPREP_UNKNOWN_PROFILE: The supplied profile name was not
known to the library.
STRINGPREP_NFKC_FAILED: The Unicode NFKC operation failed. This
usually indicate an internal error in the library.
STRINGPREP_MALLOC_ERROR: The malloc() was out of memory. This is
usually a fatal error.
Return value: Returns a pointer to a statically allocated string
containing a description of the error with the return code rc.
4.6 Stringprep Profile Macros
— Function: int stringprep_nameprep_no_unassigned (char * in, int maxlen)
in: input/ouput array with string to prepare.
maxlen: maximum length of input/output array.
Prepare the input UTF-8 string according to the nameprep profile. The
AllowUnassigned flag is false, use stringprep_nameprep for
true AllowUnassigned. Returns 0 iff successful, or an error code.
— Function: int stringprep_iscsi (char * in, int maxlen)
in: input/ouput array with string to prepare.
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.
— Function: int stringprep_plain (char * in, int maxlen)
in: input/ouput array with string to prepare.
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.
— Function: int stringprep_xmpp_nodeprep (char * in, int maxlen)
in: input/ouput array with string to prepare.
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.
— Function: int stringprep_xmpp_resourceprep (char * in, int maxlen)
in: input/ouput array with string to prepare.
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.
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.
5.1 Header file punycode.h
To use the functions explained in this chapter, you need to include
the file punycode.h using:
#include <punycode.h>
5.2 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.
Note that the current implementation will fail if the
input_length exceed 4294967295 (the size of
punycode_uint). This restriction may be removed in the future.
Meanwhile applications are encouraged to not depend on this problem,
and use sizeof to initialize input_length and
output_length.
The functions provided are the following two entry points:
input_length: The number of code points in the input array and
the number of flags in the case_flags array.
input: An array of code points. They are presumed to be Unicode
code points, but that is not strictly REQUIRED. The array
contains code points, not code units. UTF-16 uses code units
D800 through DFFF to refer to code points 10000..10FFFF. The
code points D800..DFFF do not occur in any valid Unicode string.
The code points that can occur in Unicode strings (0..D7FF and
E000..10FFFF) are also called Unicode scalar values.
case_flags: A NULL pointer or an array of boolean values parallel
to the input array. Nonzero (true, flagged) suggests that the
corresponding Unicode character be forced to uppercase after
being decoded (if possible), and zero (false, unflagged) suggests
that it be forced to lowercase (if possible). ASCII code points
(0..7F) are encoded literally, except that ASCII letters are
forced to uppercase or lowercase according to the corresponding
case flags. If case_flags is a NULL pointer then ASCII letters
are left as they are, and other code points are treated as
unflagged.
output_length: The caller passes in the maximum number of ASCII
code points that it can receive. On successful return it will
contain the number of ASCII code points actually output.
output: An array of ASCII code points. It is *not*
null-terminated; it will contain zeros if and only if the input
contains zeros. (Of course the caller can leave room for a
terminator and add one if needed.)
Converts a sequence of code points (presumed to be Unicode code
points) to Punycode.
Return value: The return value can be any of the Punycode_status
values defined above except PUNYCODE_BAD_INPUT. If not
PUNYCODE_SUCCESS, then output_size and output might contain
garbage.
input_length: The number of ASCII code points in the input array.
input: An array of ASCII code points (0..7F).
output_length: The caller passes in the maximum number of code
points that it can receive into the output array (which is also
the maximum number of flags that it can receive into the
case_flags array, if case_flags is not a NULL pointer). On
successful return it will contain the number of code points
actually output (which is also the number of flags actually
output, if case_flags is not a null pointer). The decoder will
never need to output more code points than the number of ASCII
code points in the input, because of the way the encoding is
defined. The number of code points output cannot exceed the
maximum possible value of a punycode_uint, even if the supplied
output_length is greater than that.
output: An array of code points like the input argument of
punycode_encode() (see above).
case_flags: A NULL pointer (if the flags are not needed by the
caller) or an array of boolean values parallel to the output
array. Nonzero (true, flagged) suggests that the corresponding
Unicode character be forced to uppercase by the caller (if
possible), and zero (false, unflagged) suggests that it be forced
to lowercase (if possible). ASCII code points (0..7F) are output
already in the proper case, but their flags will be set
appropriately so that applying the flags would be harmless.
Converts Punycode to a sequence of code points (presumed to be
Unicode code points).
Return value: The return value can be any of the Punycode_status
values defined above. If not PUNYCODE_SUCCESS, then
output_length, output, and case_flags might contain garbage.
Convert a return code integer to a text string. This string can be
used to output a diagnostic message to the user.
PUNYCODE_SUCCESS: Successful operation. This value is guaranteed
to always be zero, the remaining ones are only guaranteed to hold
non-zero values, for logical comparison purposes.
PUNYCODE_BAD_INPUT: Input is invalid.
PUNYCODE_BIG_OUTPUT: Output would exceed the space provided.
PUNYCODE_OVERFLOW: Input needs wider integers to process.
Return value: Returns a pointer to a statically allocated string
containing a description of the error with the return code rc.
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.
6.1 Header file idna.h
To use the functions explained in this chapter, you need to include
the file idna.h using:
#include <idna.h>
6.2 Control Flags
The IDNA flags parameter can take on the following values, or a
bit-wise inclusive or of any subset of the parameters:
Check output to make sure it is a STD3 conforming host name.
6.3 Prefix String
— Macro: #define IDNA_ACE_PREFIX
String with the official IDNA prefix, xn--.
6.4 Core Functions
The idea behind the IDNA function names are as follows: the
idna_to_ascii_4i and idna_to_unicode_44i functions are
the core IDNA primitives. The 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 i indicate
that the data is written “inline” into the buffer. This means the
caller is responsible for allocating (and deallocating) 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 z indicator, which means
the strings are zero terminated. All output strings are allocated by
the library, and must be deallocated by the caller. The 4
indicator again means that the string is UCS-4, the 8 means the
strings are UTF-8 and the l indicator means the strings are
encoded in the encoding used by the current locale.
The functions provided are the following entry points:
— Function: int idna_to_ascii_4i (const uint32_t * in, size_t inlen, char * out, int flags)
in: input array with unicode code points.
inlen: length of input array with unicode code points.
out: output zero terminated string that must have room for at
least 63 characters plus the terminating zero.
flags: an Idna_flags value, e.g., IDNA_ALLOW_UNASSIGNED or
IDNA_USE_STD3_ASCII_RULES.
The ToASCII operation takes a sequence of Unicode code points that make
up one label and transforms it into a sequence of code points in the
ASCII range (0..7F). If ToASCII succeeds, the original sequence and the
resulting sequence are equivalent labels.
It is important to note that the ToASCII operation can fail. ToASCII
fails if any step of it fails. If any step of the ToASCII operation
fails on any label in a domain name, that domain name MUST NOT be used
as an internationalized domain name. The method for deadling with this
failure is application-specific.
The inputs to ToASCII are a sequence of code points, the AllowUnassigned
flag, and the UseSTD3ASCIIRules flag. The output of ToASCII is either a
sequence of ASCII code points or a failure condition.
ToASCII never alters a sequence of code points that are all in the ASCII
range to begin with (although it could fail). Applying the ToASCII
operation multiple times has exactly the same effect as applying it just
once.
Return value: Returns 0 on success, or an Idna_rc error code.
— Function: int idna_to_unicode_44i (const uint32_t * in, size_t inlen, uint32_t * out, size_t * outlen, int flags)
in: input array with unicode code points.
inlen: length of input array with unicode code points.
out: output array with unicode code points.
outlen: on input, maximum size of output array with unicode code points,
on exit, actual size of output array with unicode code points.
flags: an Idna_flags value, e.g., IDNA_ALLOW_UNASSIGNED or
IDNA_USE_STD3_ASCII_RULES.
The ToUnicode operation takes a sequence of Unicode code points
that make up one label and returns a sequence of Unicode code
points. If the input sequence is a label in ACE form, then the
result is an equivalent internationalized label that is not in ACE
form, otherwise the original sequence is returned unaltered.
ToUnicode never fails. If any step fails, then the original input
sequence is returned immediately in that step.
The Punycode decoder can never output more code points than it
inputs, but Nameprep can, and therefore ToUnicode can. Note that
the number of octets needed to represent a sequence of code points
depends on the particular character encoding used.
The inputs to ToUnicode are a sequence of code points, the
AllowUnassigned flag, and the UseSTD3ASCIIRules flag. The output of
ToUnicode is always a sequence of Unicode code points.
Return value: Returns Idna_rc error condition, but it must only be
used for debugging purposes. The output buffer is always
guaranteed to contain the correct data according to the
specification (sans malloc induced errors). NB! This means that
you normally ignore the return code from this function, as
checking it means breaking the standard.
6.5 Simplified ToASCII Interface
— Function: int idna_to_ascii_4z (const uint32_t * input, char ** output, int flags)
input: zero terminated input Unicode string.
output: pointer to newly allocated output string.
flags: an Idna_flags value, e.g., IDNA_ALLOW_UNASSIGNED or
IDNA_USE_STD3_ASCII_RULES.
Convert UCS-4 domain name to ASCII string. The domain name may
contain several labels, separated by dots. The output buffer must
be deallocated by the caller.
Return value: Returns IDNA_SUCCESS on success, or error code.
— Function: int idna_to_ascii_8z (const char * input, char ** output, int flags)
input: zero terminated input UTF-8 string.
output: pointer to newly allocated output string.
flags: an Idna_flags value, e.g., IDNA_ALLOW_UNASSIGNED or
IDNA_USE_STD3_ASCII_RULES.
Convert UTF-8 domain name to ASCII string. The domain name may
contain several labels, separated by dots. The output buffer must
be deallocated by the caller.
Return value: Returns IDNA_SUCCESS on success, or error code.
— Function: int idna_to_ascii_lz (const char * input, char ** output, int flags)
input: zero terminated input string encoded in the current locale's
character set.
output: pointer to newly allocated output string.
flags: an Idna_flags value, e.g., IDNA_ALLOW_UNASSIGNED or
IDNA_USE_STD3_ASCII_RULES.
Convert domain name in the locale's encoding to ASCII string. The
domain name may contain several labels, separated by dots. The
output buffer must be deallocated by the caller.
Return value: Returns IDNA_SUCCESS on success, or error code.
6.6 Simplified ToUnicode Interface
— Function: int idna_to_unicode_4z4z (const uint32_t * input, uint32_t ** output, int flags)
input: zero-terminated Unicode string.
output: pointer to newly allocated output Unicode string.
flags: an Idna_flags value, e.g., IDNA_ALLOW_UNASSIGNED or
IDNA_USE_STD3_ASCII_RULES.
Convert possibly ACE encoded domain name in UCS-4 format into a
UCS-4 string. The domain name may contain several labels,
separated by dots. The output buffer must be deallocated by the
caller.
Return value: Returns IDNA_SUCCESS on success, or error code.
— Function: int idna_to_unicode_8z4z (const char * input, uint32_t ** output, int flags)
input: zero-terminated UTF-8 string.
output: pointer to newly allocated output Unicode string.
flags: an Idna_flags value, e.g., IDNA_ALLOW_UNASSIGNED or
IDNA_USE_STD3_ASCII_RULES.
Convert possibly ACE encoded domain name in UTF-8 format into a
UCS-4 string. The domain name may contain several labels,
separated by dots. The output buffer must be deallocated by the
caller.
Return value: Returns IDNA_SUCCESS on success, or error code.
— Function: int idna_to_unicode_8z8z (const char * input, char ** output, int flags)
input: zero-terminated UTF-8 string.
output: pointer to newly allocated output UTF-8 string.
flags: an Idna_flags value, e.g., IDNA_ALLOW_UNASSIGNED or
IDNA_USE_STD3_ASCII_RULES.
Convert possibly ACE encoded domain name in UTF-8 format into a
UTF-8 string. The domain name may contain several labels,
separated by dots. The output buffer must be deallocated by the
caller.
Return value: Returns IDNA_SUCCESS on success, or error code.
— Function: int idna_to_unicode_8zlz (const char * input, char ** output, int flags)
input: zero-terminated UTF-8 string.
output: pointer to newly allocated output string encoded in the
current locale's character set.
flags: an Idna_flags value, e.g., IDNA_ALLOW_UNASSIGNED or
IDNA_USE_STD3_ASCII_RULES.
Convert possibly ACE encoded domain name in UTF-8 format into a
string encoded in the current locale's character set. The domain
name may contain several labels, separated by dots. The output
buffer must be deallocated by the caller.
Return value: Returns IDNA_SUCCESS on success, or error code.
— Function: int idna_to_unicode_lzlz (const char * input, char ** output, int flags)
input: zero-terminated string encoded in the current locale's
character set.
output: pointer to newly allocated output string encoded in the
current locale's character set.
flags: an Idna_flags value, e.g., IDNA_ALLOW_UNASSIGNED or
IDNA_USE_STD3_ASCII_RULES.
Convert possibly ACE encoded domain name in the locale's character
set into a string encoded in the current locale's character set.
The domain name may contain several labels, separated by dots. The
output buffer must be deallocated by the caller.
Return value: Returns IDNA_SUCCESS on success, or error code.
Convert a return code integer to a text string. This string can be
used to output a diagnostic message to the user.
IDNA_SUCCESS: Successful operation. This value is guaranteed to
always be zero, the remaining ones are only guaranteed to hold
non-zero values, for logical comparison purposes.
IDNA_STRINGPREP_ERROR: Error during string preparation.
IDNA_PUNYCODE_ERROR: Error during punycode operation.
IDNA_CONTAINS_NON_LDH: For IDNA_USE_STD3_ASCII_RULES, indicate that
the string contains non-LDH ASCII characters.
IDNA_CONTAINS_MINUS: For IDNA_USE_STD3_ASCII_RULES, indicate that
the string contains a leading or trailing hyphen-minus (U+002D).
IDNA_INVALID_LENGTH: The final output string is not within the
(inclusive) range 1 to 63 characters.
IDNA_NO_ACE_PREFIX: The string does not contain the ACE prefix
(for ToUnicode).
IDNA_ROUNDTRIP_VERIFY_ERROR: The ToASCII operation on output
string does not equal the input.
IDNA_CONTAINS_ACE_PREFIX: The input contains the ACE prefix (for
ToASCII).
IDNA_ICONV_ERROR: Could not convert string in locale encoding.
IDNA_MALLOC_ERROR: Could not allocate buffer (this is typically a
fatal error).
IDNA_DLOPEN_ERROR: Could not dlopen the libcidn DSO (only used
internally in libc).
Return value: Returns a pointer to a statically allocated string
containing a description of the error with the return code rc.
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
incompatibe 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 http://tldchk.berlios.de.
7.1 Header file tld.h
To use the functions explained in this chapter, you need to include
the file tld.h using:
#include <tld.h>
7.2 Core Functions
— Function: int tld_check_4t (const uint32_t * in, size_t inlen, size_t * errpos, const Tld_table * tld)
in: Array of unicode code points to process. Does not need to be
zero terminated.
inlen: Number of unicode code points.
errpos: Position of offending character is returned here.
tld: A Tld_table data structure representing the restrictions for
which the input should be tested.
Test each of the code points in in for whether or not
they are allowed by the data structure in tld, return
the position of the first character for which this is not
the case in errpos.
Return value: Returns the Tld_rc value TLD_SUCCESS if all code
points are valid or when tld is null, TLD_INVALID if a
character is not allowed, or additional error codes on general
failure conditions.
— Function: int tld_check_4tz (const uint32_t * in, size_t * errpos, const Tld_table * tld)
in: Zero terminated array of unicode code points to process.
errpos: Position of offending character is returned here.
tld: A Tld_table data structure representing the restrictions for
which the input should be tested.
Test each of the code points in in for whether or not
they are allowed by the data structure in tld, return
the position of the first character for which this is not
the case in errpos.
Return value: Returns the Tld_rc value TLD_SUCCESS if all code
points are valid or when tld is null, TLD_INVALID if a
character is not allowed, or additional error codes on general
failure conditions.
7.3 Utility Functions
— Function: int tld_get_4 (const uint32_t * in, size_t inlen, char ** out)
in: Array of unicode code points to process. Does not need to be
zero terminated.
inlen: Number of unicode code points.
out: Zero terminated ascii result string pointer.
Isolate the top-level domain of in and return it as an ASCII
string in out.
Return value: Return TLD_SUCCESS on success, or the corresponding
Tld_rc error code otherwise.
— Function: int tld_get_4z (const uint32_t * in, char ** out)
in: Zero terminated array of unicode code points to process.
out: Zero terminated ascii result string pointer.
Isolate the top-level domain of in and return it as an ASCII
string in out.
Return value: Return TLD_SUCCESS on success, or the corresponding
Tld_rc error code otherwise.
— Function: int tld_get_z (const char * in, char ** out)
in: Zero terminated character array to process.
out: Zero terminated ascii result string pointer.
Isolate the top-level domain of in and return it as an ASCII
string in out. The input string in may be UTF-8, ISO-8859-1 or
any ASCII compatible character encoding.
Return value: Return TLD_SUCCESS on success, or the corresponding
Tld_rc error code otherwise.
tld: TLD name (e.g. "com") as zero terminated ASCII byte string.
overrides: Additional zero terminated array of Tld_table
info-structures for TLDs, or NULL to only use library deault
tables.
Get the TLD table for a named TLD, using the internal defaults,
possibly overrided by the (optional) supplied tables.
Return value: Return structure corresponding to TLD tld_str, first
looking through overrides then thru built-in list, or NULL if
no such structure found.
7.4 High-Level Wrapper Functions
— Function: int tld_check_4 (const uint32_t * in, size_t inlen, size_t * errpos, const Tld_table ** overrides)
in: Array of unicode code points to process. Does not need to be
zero terminated.
inlen: Number of unicode code points.
errpos: Position of offending character is returned here.
overrides: A Tld_table array of additional domain restriction
structures that complement and supersede the built-in information.
Test each of the code points in in for whether or not they are
allowed by the information in overrides or by the built-in TLD
restriction data. When data for the same TLD is available both
internally and in overrides, the information in overrides takes
precedence. If several entries for a specific TLD are found, the
first one is used. If overrides is NULL, only the built-in
information is used. The position of the first offending character
is returned in errpos.
Return value: Returns the Tld_rc value TLD_SUCCESS if all code
points are valid or when tld is null, TLD_INVALID if a
character is not allowed, or additional error codes on general
failure conditions.
— Function: int tld_check_4z (const uint32_t * in, size_t * errpos, const Tld_table ** overrides)
in: Zero-terminated array of unicode code points to process.
errpos: Position of offending character is returned here.
overrides: A Tld_table array of additional domain restriction
structures that complement and supersede the built-in information.
Test each of the code points in in for whether or not they are
allowed by the information in overrides or by the built-in TLD
restriction data. When data for the same TLD is available both
internally and in overrides, the information in overrides takes
precedence. If several entries for a specific TLD are found, the
first one is used. If overrides is NULL, only the built-in
information is used. The position of the first offending character
is returned in errpos.
Return value: Returns the Tld_rc value TLD_SUCCESS if all code
points are valid or when tld is null, TLD_INVALID if a
character is not allowed, or additional error codes on general
failure conditions.
— Function: int tld_check_8z (const char * in, size_t * errpos, const Tld_table ** overrides)
in: Zero-terminated UTF8 string to process.
errpos: Position of offending character is returned here.
overrides: A Tld_table array of additional domain restriction
structures that complement and supersede the built-in information.
Test each of the characters in in for whether or not they are
allowed by the information in overrides or by the built-in TLD
restriction data. When data for the same TLD is available both
internally and in overrides, the information in overrides takes
precedence. If several entries for a specific TLD are found, the
first one is used. If overrides is NULL, only the built-in
information is used. The position of the first offending character
is returned in errpos. Note that the error position refers to the
decoded character offset rather than the byte position in the
string.
Return value: Returns the Tld_rc value TLD_SUCCESS if all
characters are valid or when tld is null, TLD_INVALID if a
character is not allowed, or additional error codes on general
failure conditions.
— Function: int tld_check_lz (const char * in, size_t * errpos, const Tld_table ** overrides)
in: Zero-terminated string in the current locales encoding to process.
errpos: Position of offending character is returned here.
overrides: A Tld_table array of additional domain restriction
structures that complement and supersede the built-in information.
Test each of the characters in in for whether or not they are
allowed by the information in overrides or by the built-in TLD
restriction data. When data for the same TLD is available both
internally and in overrides, the information in overrides takes
precedence. If several entries for a specific TLD are found, the
first one is used. If overrides is NULL, only the built-in
information is used. The position of the first offending character
is returned in errpos. Note that the error position refers to the
decoded character offset rather than the byte position in the
string.
Return value: Returns the Tld_rc value TLD_SUCCESS if all
characters are valid or when tld is null, TLD_INVALID if a
character is not allowed, or additional error codes on general
failure conditions.
7.5 Error Handling
— Function: const char * tld_strerror (Tld_rc rc)
rc: tld return code
Convert a return code integer to a text string. This string can be
used to output a diagnostic message to the user.
TLD_SUCCESS: Successful operation. This value is guaranteed to
always be zero, the remaining ones are only guaranteed to hold
non-zero values, for logical comparison purposes.
TLD_INVALID: Invalid character found.
TLD_NODATA: No input data was provided.
TLD_MALLOC_ERROR: Error during memory allocation.
TLD_ICONV_ERROR: Error during iconv string conversion.
TLD_NO_TLD: No top-level domain found in domain string.
Return value: Returns a pointer to a statically allocated string
containing a description of the error with the return code rc.
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).
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. See PR29 discussion.
8.1 Header file pr29.h
To use the functions explained in this chapter, you need to include
the file pr29.h using:
#include <pr29.h>
8.2 Core Functions
— Function: int pr29_4 (const uint32_t * in, size_t len)
in: input array with unicode code points.
len: length of input array with unicode code points.
Check the input to see if it may be normalized into different
strings by different NFKC implementations, due to an anomaly in the
NFKC specifications.
Return value: Returns the Pr29_rc value PR29_SUCCESS on success,
and PR29_PROBLEM if the input sequence is a "problem sequence"
(i.e., may be normalized into different strings by different
implementations).
8.3 Utility Functions
— Function: int pr29_4z (const uint32_t * in)
in: zero terminated array of Unicode code points.
Check the input to see if it may be normalized into different
strings by different NFKC implementations, due to an anomaly in the
NFKC specifications.
Return value: Returns the Pr29_rc value PR29_SUCCESS on success,
and PR29_PROBLEM if the input sequence is a "problem sequence"
(i.e., may be normalized into different strings by different
implementations).
— Function: int pr29_8z (const char * in)
in: zero terminated input UTF-8 string.
Check the input to see if it may be normalized into different
strings by different NFKC implementations, due to an anomaly in the
NFKC specifications.
Return value: Returns the Pr29_rc value PR29_SUCCESS on success,
and PR29_PROBLEM if the input sequence is a "problem sequence"
(i.e., may be normalized into different strings by different
implementations), or PR29_STRINGPREP_ERROR if there was a
problem converting the string from UTF-8 to UCS-4.
Convert a return code integer to a text string. This string can be
used to output a diagnostic message to the user.
PR29_SUCCESS: Successful operation. This value is guaranteed to
always be zero, the remaining ones are only guaranteed to hold
non-zero values, for logical comparison purposes.
PR29_PROBLEM: A problem sequence was encountered.
PR29_STRINGPREP_ERROR: The character set conversion failed (only
for pr29_8() and pr29_8z()).
Return value: Returns a pointer to a statically allocated string
containing a description of the error with the return code rc.
This example demonstrates how the stringprep functions are used.
/* example.c --- Example code showing how to use stringprep().
* Copyright (C) 2002, 2003, 2004 Simon Josefsson
*
* This file is part of GNU Libidn.
*
* GNU Libidn is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* GNU Libidn is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with GNU Libidn; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <locale.h> /* setlocale() */
#include <stringprep.h>
/*
* Compiling using libtool and pkg-config is recommended:
*
* $ libtool cc -o example example.c `pkg-config --cflags --libs libidn`
* $ ./example
* Input string encoded as `ISO-8859-1': ª
* Before locale2utf8 (length 2): aa 0a
* Before stringprep (length 3): c2 aa 0a
* After stringprep (length 2): 61 0a
* $
*
*/
int
main (int argc, char *argv[])
{
char buf[BUFSIZ];
char *p;
int rc;
size_t i;
setlocale (LC_ALL, "");
printf ("Input string encoded as `%s': ", stringprep_locale_charset ());
fflush (stdout);
fgets (buf, BUFSIZ, stdin);
printf ("Before locale2utf8 (length %d): ", strlen (buf));
for (i = 0; i < strlen (buf); i++)
printf ("%02x ", buf[i] & 0xFF);
printf ("\n");
p = stringprep_locale_to_utf8 (buf);
if (p)
{
strcpy (buf, p);
free (p);
}
else
printf ("Could not convert string to UTF-8, continuing anyway...\n");
printf ("Before stringprep (length %d): ", strlen (buf));
for (i = 0; i < strlen (buf); i++)
printf ("%02x ", buf[i] & 0xFF);
printf ("\n");
rc = stringprep (buf, BUFSIZ, 0, stringprep_nameprep);
if (rc != STRINGPREP_OK)
printf ("Stringprep failed (%d): %s\n", rc, stringprep_strerror (rc));
else
{
printf ("After stringprep (length %d): ", strlen (buf));
for (i = 0; i < strlen (buf); i++)
printf ("%02x ", buf[i] & 0xFF);
printf ("\n");
}
return 0;
}
This example demonstrates how the punycode functions are used.
/* example2.c --- Example code showing how to use punycode.
* Copyright (C) 2002, 2003, 2004 Simon Josefsson
* Copyright (C) 2002 Adam M. Costello
*
* This file is part of GNU Libidn.
*
* GNU Libidn is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* GNU Libidn is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with GNU Libidn; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/
#include <locale.h> /* setlocale() */
/*
* This file is derived from RFC 3492 written by Adam M. Costello.
*
* Disclaimer and license: Regarding this entire document or any
* portion of it (including the pseudocode and C code), the author
* makes no guarantees and is not responsible for any damage resulting
* from its use. The author grants irrevocable permission to anyone
* to use, modify, and distribute it in any way that does not diminish
* the rights of anyone else to use, modify, and distribute it,
* provided that redistributed derivative works do not contain
* misleading author or version information. Derivative works need
* not be licensed under similar terms.
*
*/
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <punycode.h>
/* For testing, we'll just set some compile-time limits rather than */
/* use malloc(), and set a compile-time option rather than using a */
/* command-line option. */
enum
{
unicode_max_length = 256,
ace_max_length = 256
};
static void
usage (char **argv)
{
fprintf (stderr,
"\n"
"%s -e reads code points and writes a Punycode string.\n"
"%s -d reads a Punycode string and writes code points.\n"
"\n"
"Input and output are plain text in the native character set.\n"
"Code points are in the form u+hex separated by whitespace.\n"
"Although the specification allows Punycode strings to contain\n"
"any characters from the ASCII repertoire, this test code\n"
"supports only the printable characters, and needs the Punycode\n"
"string to be followed by a newline.\n"
"The case of the u in u+hex is the force-to-uppercase flag.\n",
argv[0], argv[0]);
exit (EXIT_FAILURE);
}
static void
fail (const char *msg)
{
fputs (msg, stderr);
exit (EXIT_FAILURE);
}
static const char too_big[] =
"input or output is too large, recompile with larger limits\n";
static const char invalid_input[] = "invalid input\n";
static const char overflow[] = "arithmetic overflow\n";
static const char io_error[] = "I/O error\n";
/* The following string is used to convert printable */
/* characters between ASCII and the native charset: */
static const char print_ascii[] = "\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n" "\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n" " !\"#$%&'()*+,-./" "0123456789:;<=>?" "\0x40" /* at sign */
"ABCDEFGHIJKLMNO"
"PQRSTUVWXYZ[\\]^_" "`abcdefghijklmno" "pqrstuvwxyz{|}~\n";
int
main (int argc, char **argv)
{
enum punycode_status status;
int r;
size_t input_length, output_length, j;
unsigned char case_flags[unicode_max_length];
setlocale (LC_ALL, "");
if (argc != 2)
usage (argv);
if (argv[1][0] != '-')
usage (argv);
if (argv[1][2] != 0)
usage (argv);
if (argv[1][1] == 'e')
{
uint32_t input[unicode_max_length];
unsigned long codept;
char output[ace_max_length + 1], uplus[3];
int c;
/* Read the input code points: */
input_length = 0;
for (;;)
{
r = scanf ("%2s%lx", uplus, &codept);
if (ferror (stdin))
fail (io_error);
if (r == EOF || r == 0)
break;
if (r != 2 || uplus[1] != '+' || codept > (uint32_t) - 1)
{
fail (invalid_input);
}
if (input_length == unicode_max_length)
fail (too_big);
if (uplus[0] == 'u')
case_flags[input_length] = 0;
else if (uplus[0] == 'U')
case_flags[input_length] = 1;
else
fail (invalid_input);
input[input_length++] = codept;
}
/* Encode: */
output_length = ace_max_length;
status = punycode_encode (input_length, input, case_flags,
&output_length, output);
if (status == punycode_bad_input)
fail (invalid_input);
if (status == punycode_big_output)
fail (too_big);
if (status == punycode_overflow)
fail (overflow);
assert (status == punycode_success);
/* Convert to native charset and output: */
for (j = 0; j < output_length; ++j)
{
c = output[j];
assert (c >= 0 && c <= 127);
if (print_ascii[c] == 0)
fail (invalid_input);
output[j] = print_ascii[c];
}
output[j] = 0;
r = puts (output);
if (r == EOF)
fail (io_error);
return EXIT_SUCCESS;
}
if (argv[1][1] == 'd')
{
char input[ace_max_length + 2], *p, *pp;
uint32_t output[unicode_max_length];
/* Read the Punycode input string and convert to ASCII: */
fgets (input, ace_max_length + 2, stdin);
if (ferror (stdin))
fail (io_error);
if (feof (stdin))
fail (invalid_input);
input_length = strlen (input) - 1;
if (input[input_length] != '\n')
fail (too_big);
input[input_length] = 0;
for (p = input; *p != 0; ++p)
{
pp = strchr (print_ascii, *p);
if (pp == 0)
fail (invalid_input);
*p = pp - print_ascii;
}
/* Decode: */
output_length = unicode_max_length;
status = punycode_decode (input_length, input, &output_length,
output, case_flags);
if (status == punycode_bad_input)
fail (invalid_input);
if (status == punycode_big_output)
fail (too_big);
if (status == punycode_overflow)
fail (overflow);
assert (status == punycode_success);
/* Output the result: */
for (j = 0; j < output_length; ++j)
{
r = printf ("%s+%04lX\n",
case_flags[j] ? "U" : "u", (unsigned long) output[j]);
if (r < 0)
fail (io_error);
}
return EXIT_SUCCESS;
}
usage (argv);
return EXIT_SUCCESS; /* not reached, but quiets compiler warning */
}
This example demonstrates how the library is used to convert
internationalized domain names into ASCII compatible names.
/* example3.c --- Example ToASCII() code showing how to use Libidn.
* Copyright (C) 2002, 2003, 2004 Simon Josefsson
*
* This file is part of GNU Libidn.
*
* GNU Libidn is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* GNU Libidn is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with GNU Libidn; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <locale.h> /* setlocale() */
#include <stringprep.h> /* stringprep_locale_charset() */
#include <idna.h> /* idna_to_ascii_lz() */
/*
* Compiling using libtool and pkg-config is recommended:
*
* $ libtool cc -o example3 example3.c `pkg-config --cflags --libs libidn`
* $ ./example3
* Input domain encoded as `ISO-8859-1': www.räksmörgåsª.example
* Read string (length 23): 77 77 77 2e 72 e4 6b 73 6d f6 72 67 e5 73 aa 2e 65 78 61 6d 70 6c 65
* ACE label (length 33): 'www.xn--rksmrgsa-0zap8p.example'
* 77 77 77 2e 78 6e 2d 2d 72 6b 73 6d 72 67 73 61 2d 30 7a 61 70 38 70 2e 65 78 61 6d 70 6c 65
* $
*
*/
int
main (int argc, char *argv[])
{
char buf[BUFSIZ];
char *p;
int rc;
size_t i;
setlocale (LC_ALL, "");
printf ("Input domain encoded as `%s': ", stringprep_locale_charset ());
fflush (stdout);
fgets (buf, BUFSIZ, stdin);
buf[strlen (buf) - 1] = '\0';
printf ("Read string (length %d): ", strlen (buf));
for (i = 0; i < strlen (buf); i++)
printf ("%02x ", buf[i] & 0xFF);
printf ("\n");
rc = idna_to_ascii_lz (buf, &p, 0);
if (rc != IDNA_SUCCESS)
{
printf ("ToASCII() failed (%d): %s\n", rc, idna_strerror (rc));
exit (1);
}
printf ("ACE label (length %d): '%s'\n", strlen (p), p);
for (i = 0; i < strlen (p); i++)
printf ("%02x ", p[i] & 0xFF);
printf ("\n");
free (p);
return 0;
}
This example demonstrates how the library is used to convert ASCII
compatible names to internationalized domain names.
/* example4.c --- Example ToUnicode() code showing how to use Libidn.
* Copyright (C) 2002, 2003, 2004 Simon Josefsson
*
* This file is part of GNU Libidn.
*
* GNU Libidn is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* GNU Libidn is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with GNU Libidn; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <locale.h> /* setlocale() */
#include <stringprep.h> /* stringprep_locale_charset() */
#include <idna.h> /* idna_to_unicode_lzlz() */
/*
* Compiling using libtool and pkg-config is recommended:
*
* $ libtool cc -o example4 example4.c `pkg-config --cflags --libs libidn`
* $ ./example4
* Input domain encoded as `ISO-8859-1': www.xn--rksmrgsa-0zap8p.example
* Read string (length 33): 77 77 77 2e 78 6e 2d 2d 72 6b 73 6d 72 67 73 61 2d 30 7a 61 70 38 70 2e 65 78 61 6d 70 6c 65
* ACE label (length 23): 'www.räksmörgåsa.example'
* 77 77 77 2e 72 e4 6b 73 6d f6 72 67 e5 73 61 2e 65 78 61 6d 70 6c 65
* $
*
*/
int
main (int argc, char *argv[])
{
char buf[BUFSIZ];
char *p;
int rc;
size_t i;
setlocale (LC_ALL, "");
printf ("Input domain encoded as `%s': ", stringprep_locale_charset ());
fflush (stdout);
fgets (buf, BUFSIZ, stdin);
buf[strlen (buf) - 1] = '\0';
printf ("Read string (length %d): ", strlen (buf));
for (i = 0; i < strlen (buf); i++)
printf ("%02x ", buf[i] & 0xFF);
printf ("\n");
rc = idna_to_unicode_lzlz (buf, &p, 0);
if (rc != IDNA_SUCCESS)
{
printf ("ToUnicode() failed (%d): %s\n", rc, idna_strerror (rc));
exit (1);
}
printf ("ACE label (length %d): '%s'\n", strlen (p), p);
for (i = 0; i < strlen (p); i++)
printf ("%02x ", p[i] & 0xFF);
printf ("\n");
free (p);
return 0;
}
This example demonstrates how the library is used to check a string
for invalid characters within a specific TLD.
/* example5.c --- Example TLD checking.
* Copyright (C) 2004 Simon Josefsson
*
* This file is part of GNU Libidn.
*
* GNU Libidn is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* GNU Libidn is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with GNU Libidn; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* Get stringprep_locale_charset, etc. */
#include <stringprep.h>
/* Get idna_to_ascii_8z, etc. */
#include <idna.h>
/* Get tld_check_4z. */
#include <tld.h>
/*
* Compiling using libtool and pkg-config is recommended:
*
* $ libtool cc -o example5 example5.c `pkg-config --cflags --libs libidn`
* $ ./example5
* Input domain encoded as `UTF-8': fooß.no
* Read string (length 8): 66 6f 6f c3 9f 2e 6e 6f
* ToASCII string (length 8): fooss.no
* ToUnicode string: U+0066 U+006f U+006f U+0073 U+0073 U+002e U+006e U+006f
* Domain accepted by TLD check
*
* $ ./example5
* Input domain encoded as `UTF-8': gr€€n.no
* Read string (length 12): 67 72 e2 82 ac e2 82 ac 6e 2e 6e 6f
* ToASCII string (length 16): xn--grn-l50aa.no
* ToUnicode string: U+0067 U+0072 U+20ac U+20ac U+006e U+002e U+006e U+006f
* Domain rejected by TLD check, Unicode position 2
*
*/
int
main (int argc, char *argv[])
{
char buf[BUFSIZ];
char *p;
uint32_t *r;
int rc;
size_t errpos, i;
printf ("Input domain encoded as `%s': ", stringprep_locale_charset ());
fflush (stdout);
fgets (buf, BUFSIZ, stdin);
buf[strlen (buf) - 1] = '\0';
printf ("Read string (length %d): ", strlen (buf));
for (i = 0; i < strlen (buf); i++)
printf ("%02x ", buf[i] & 0xFF);
printf ("\n");
p = stringprep_locale_to_utf8 (buf);
if (p)
{
strcpy (buf, p);
free (p);
}
else
printf ("Could not convert string to UTF-8, continuing anyway...\n");
rc = idna_to_ascii_8z (buf, &p, 0);
if (rc != IDNA_SUCCESS)
{
printf ("idna_to_ascii_8z failed (%d): %s\n", rc, idna_strerror (rc));
return 2;
}
printf ("ToASCII string (length %d): %s\n", strlen (p), p);
rc = idna_to_unicode_8z4z (p, &r, 0);
free (p);
if (rc != IDNA_SUCCESS)
{
printf ("idna_to_unicode_8z4z failed (%d): %s\n",
rc, idna_strerror (rc));
return 2;
}
printf ("ToUnicode string: ");
for (i = 0; r[i]; i++)
printf ("U+%04x ", r[i]);
printf ("\n");
rc = tld_check_4z (r, &errpos, NULL);
free (r);
if (rc == TLD_INVALID)
{
printf ("Domain rejected by TLD check, Unicode position %d\n", errpos);
return 1;
}
else if (rc != TLD_SUCCESS)
{
printf ("tld_check_4z() failed (%d): %s\n", rc, tld_strerror (rc));
return 2;
}
printf ("Domain accepted by TLD check\n");
return 0;
}
GNU Libidn (idn) – Internationalized Domain Names command line tool
10.2 Description
idn allows internationalized string preparation
(`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 stdout.
If no strings are specified on the command line, the program read
data, line by line, from the standard input 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 --debug to find out what this charset is.
You can override the charset used by setting environment variable
CHARSET.
To process a string that starts with -, for example
-foo, use -- to signal the end of parameters, as in
idn --quiet -a -- -foo.
10.3 Options
idn recognizes these commands:
-h, --help Print help and exit
-V, --version Print version and exit
-s, --stringprep Prepare string according to nameprep profile
-d, --punycode-decode Decode Punycode
-e, --punycode-encode Encode Punycode
-a, --idna-to-ascii Convert to ACE according to IDNA (default)
-u, --idna-to-unicode Convert from ACE according to IDNA
--allow-unassigned Toggle IDNA AllowUnassigned flag (default=off)
--usestd3asciirules Toggle IDNA UseSTD3ASCIIRules flag (default=off)
-t, --tld Check string for TLD specific rules
Only for --idna-to-ascii and --idna-to-unicode
(default=on)
-p, --profile=STRING Use specified stringprep profile instead
Valid stringprep profiles are `Nameprep',
`iSCSI', `Nodeprep', `Resourceprep', `trace', and
`SASLprep'.
--debug Print debugging information (default=off)
--quiet Silent operation (default=off)
10.4 Environment Variables
The 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:
$ CHARSET=ISO-8859-1 idn --punycode-encode
...
10.5 Examples
Standard usage, reading input from standard input:
jas@latte:~$ idn
libidn 0.3.5
Copyright 2002, 2003 Simon Josefsson.
GNU Libidn comes with NO WARRANTY, to the extent permitted by law.
You may redistribute copies of GNU Libidn under the terms of
the GNU Lesser General Public License. For more information
about these matters, see the file named COPYING.LIB.
Type each input string on a line by itself, terminated by a newline character.
räksmörgås.se
xn--rksmrgs-5wao1o.se
jas@latte:~$
Reading input from command line, and disabling copyright and license
information:
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 UTF-8 together with ISO-8859-1 or
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 `--debug' parameter to find out which
character set encoding `idn' believe your locale uses.
If it prints ANSI_X3.4-1968 (i.e., US-ASCII), this
indicate you have not configured your locale properly. To configure
the locale, you can, for example, use `LANG=sv_SE.UTF-8; export
LANG' at a /bin/sh prompt, to set up your locale for a Swedish
environment using UTF-8 as the encoding.
Sometimes `idn' appear to be unable to translate from your system
locale into UTF-8 (which is used internally), and you get an
error like the following:
jas@latte:~$ idn --quiet foo
idn: could not convert from ISO-8859-1 to UTF-8.
jas@latte:~$
The simplest explanation is that you haven't installed the
`iconv' conversion tools. You can find it as a standalone
library in GNU Libiconv
(http://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., `glibc-locale'
for Debian) to be able to use it.
Another explanation is that the error is correct and you are feeding
`idn' invalid data. This can happen inadvertently if you are not
careful with the character set encodings you use. For example, if
your shell run in a ISO-8859-1 environment, and you invoke
`idn' with the `CHARSET' environment variable as follows,
you will feed it ISO-8859-1 characters but force it to believe
they are UTF-8. Naturally this will lead to an error, unless
the byte sequences happen to be parsable as UTF-8. Note that
even if you don't get an error, the output may be incorrect in this
situation, because ISO-8859-1 and UTF-8 does not in
general encode the same characters as the same byte sequences.
The sense moral here is to forget about `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
`--debug' that you get the desired results.
Included in Libidn are punycode.el and 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
UseSTD3ASCIIRules flag and clear the AllowUnassigned
flag, in the future there may be functionality to specify these flags
via the API.
11.1 Punycode Emacs API
— Variable: punycode-program
Name of the GNU Libidn idn application. The default is
`idn'. This variable can be customized.
— Variable: punycode-environment
List of environment variable definitions prepended to
`process-environment'. The default is `("CHARSET=UTF-8")'.
This variable can be customized.
— Variable: punycode-encode-parameters
List of parameters passed to punycode-program to invoke punycode
encoding mode. The default is `("--quiet" "--punycode-encode")'.
This variable can be customized.
— Variable: punycode-decode-parameters
Parameters passed to punycode-program to invoke punycode
decoding mode. The default is `("--quiet" "--punycode-decode")'.
This variable can be customized.
— Function: punycode-encode string
Returns a Punycode encoding of the string, after converting the
input into UTF-8.
— Function: punycode-decode string
Returns a possibly multibyte string which is the decoding of the
string which is a punycode encoded string.
11.2 IDNA Emacs API
— Variable: idna-program
Name of the GNU Libidn idn application. The default is
`idn'. This variable can be customized.
— Variable: idna-environment
List of environment variable definitions prepended to
`process-environment'. The default is `("CHARSET=UTF-8")'.
This variable can be customized.
— Variable: idna-to-ascii-parameters
List of parameters passed to idna-program to invoke IDNA ToASCII
mode. The default is `("--quiet" "--idna-to-ascii"
"--usestd3asciirules")'. This variable can be customized.
— Variable: idna-to-unicode-parameters
Parameters passed idna-program to invoke IDNA ToUnicode mode.
The default is `("--quiet" "--idna-to-unicode"
"--usestd3asciirules")'. This variable can be customized.
— Function: idna-to-ascii string
Returns an ASCII Compatible Encoding (ACE) of the string computed by
the IDNA ToASCII operation on the input string, after converting
the input to UTF-8.
— Function: idna-to-unicode string
Returns a possibly multibyte string which is the output of the IDNA
ToUnicode operation computed on the input string.
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
(see Downloading and Installing), will be placed in
java/libidn.jar. The source code is located in
java/gnu/inet/encoding/.
12.1 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:
The misc/ 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.
12.2.1 GenerateRFC3454
This program parses RFC3454 and creates the RFC3454.java program that
is required during the StringPrep phase.
$ java GenerateRFC3454
Creating RFC3454.java... Ok.
12.2.2 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.
$ java GenerateNFKC
Creating CombiningClass.java... Ok.
Creating DecompositionKeys.java... Ok.
Creating DecompositionMappings.java... Ok.
Creating Composition.java... Ok.
12.2.3 TestIDNA
The TestIDNA program allows to test the IDNA implementation manually
or against Simon Josefsson's test vectors.
$ java -cp .:../libidn.jar TestIDNA -a <string to test>
Input: <string to test>
Output: <toASCII(string to test)>
$ java -cp .:../libidn.jar TestIDNA -u <string to test>
Input: <string to test>
Output: <toUnicode(string to test)>
To test against draft-josefsson-idn-test-vectors.html, use:
$ java -cp .:../libidn.jar TestIDNA -t
No errors detected!
12.2.4 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:
$ java -cp .:../libidn.jar TestNFKC <string to test>
Input: <string to test>
Output: <nfkc version of the string to test>
To test against NormalizationTest.txt:
$ java -cp .:../libidn.jar TestNFKC
No errors detected!
12.3 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.
12.4 A Note on Java and Unicode
This library uses Java's builtin '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.
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 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 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.
The complete history of user visible changes is stored in the 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
ChangeLog in the same directory. This section contain a
condensed version of that information, in the form of “milestones”
for the project.
Stringprep implementation.
Version 0.0.0 released on 2002-11-05.
IDNA and Punycode implementations, part of the GNU project.
Version 0.1.0 released on 2003-01-05.
Uses official IDNA ACE prefix 'xn–'.
Version 0.1.7 released on 2003-02-12.
Command line interface.
Version 0.1.11 released on 2003-02-26.
GNU Libc add-on proposed.
Version 0.1.12 released on 2003-03-06.
Interoperability testing during IDNConnect.
Version 0.3.1 released on 2003-10-02.
TLD restriction testing.
Version 0.4.0 released on 2004-02-28.
GNU Libc add-on integrated.
Version 0.4.1 released on 2004-03-08.
Native Java implementation.
Version 0.4.2-0.4.9 released between 2004-03-20 and 2004-06-11.
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.
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
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
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If the distribution and/or use of the Library is restricted in
certain countries either by patents or by copyrighted interfaces, the
original copyright holder who places the Library under this License may add
an explicit geographical distribution limitation excluding those countries,
so that distribution is permitted only in or among countries not thus
excluded. In such case, this License incorporates the limitation as if
written in the body of this License.
The Free Software Foundation may publish revised and/or new
versions of the Lesser General Public License from time to time.
Such new versions will be similar in spirit to the present version,
but may differ in detail to address new problems or concerns.
Each version is given a distinguishing version number. If the Library
specifies a version number of this License which applies to it and
“any later version”, you have the option of following the terms and
conditions either of that version or of any later version published by
the Free Software Foundation. If the Library does not specify a
license version number, you may choose any version ever published by
the Free Software Foundation.
If you wish to incorporate parts of the Library into other free
programs whose distribution conditions are incompatible with these,
write to the author to ask for permission. For software which is
copyrighted by the Free Software Foundation, write to the Free
Software Foundation; we sometimes make exceptions for this. Our
decision will be guided by the two goals of preserving the free status
of all derivatives of our free software and of promoting the sharing
and reuse of software generally.
BECAUSE THE LIBRARY IS LICENSED FREE OF CHARGE, THERE IS NO
WARRANTY FOR THE LIBRARY, TO THE EXTENT PERMITTED BY APPLICABLE LAW.
EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR
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KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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LIBRARY IS WITH YOU. SHOULD THE LIBRARY PROVE DEFECTIVE, YOU ASSUME
THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY
AND/OR REDISTRIBUTE THE LIBRARY AS PERMITTED ABOVE, BE LIABLE TO YOU
FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR
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FAILURE OF THE LIBRARY TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF
SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
DAMAGES.
B.2 How to Apply These Terms to Your New Libraries
If you develop a new library, and you want it to be of the greatest
possible use to the public, we recommend making it free software that
everyone can redistribute and change. You can do so by permitting
redistribution under these terms (or, alternatively, under the terms of the
ordinary General Public License).
To apply these terms, attach the following notices to the library. It is
safest to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least the
“copyright” line and a pointer to where the full notice is found.
one line to give the library's name and an idea of what it does.
Copyright (C) yearname of author
This library is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or (at
your option) any later version.
This library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307,
USA.
Also add information on how to contact you by electronic and paper mail.
You should also get your employer (if you work as a programmer) or your
school, if any, to sign a “copyright disclaimer” for the library, if
necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the library
`Frob' (a library for tweaking knobs) written by James Random Hacker.
signature of Ty Coon, 1 April 1990
Ty Coon, President of Vice
The purpose of this License is to make a manual, textbook, or other
functional and useful document free in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or noncommercially.
Secondarily, this License preserves for the author and publisher a way
to get credit for their work, while not being considered responsible
for modifications made by others.
This License is a kind of “copyleft”, which means that derivative
works of the document must themselves be free in the same sense. It
complements the GNU General Public License, which is a copyleft
license designed for free software.
We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free
program should come with manuals providing the same freedoms that the
software does. But this License is not limited to software manuals;
it can be used for any textual work, regardless of subject matter or
whether it is published as a printed book. We recommend this License
principally for works whose purpose is instruction or reference.
APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium, that
contains a notice placed by the copyright holder saying it can be
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A “Modified Version” of the Document means any work containing the
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A “Secondary Section” is a named appendix or a front-matter section
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The “Invariant Sections” are certain Secondary Sections whose titles
are designated, as being those of Invariant Sections, in the notice
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The “Cover Texts” are certain short passages of text that are listed,
as Front-Cover Texts or Back-Cover Texts, in the notice that says that
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A “Transparent” copy of the Document means a machine-readable copy,
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or discourage subsequent modification by readers is not Transparent.
An image format is not Transparent if used for any substantial amount
of text. A copy that is not “Transparent” is called “Opaque”.
Examples of suitable formats for Transparent copies include plain
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read and edited only by proprietary word processors, SGML or
XML for which the DTD and/or processing tools are
not generally available, and the machine-generated HTML,
PostScript or PDF produced by some word processors for
output purposes only.
The “Title Page” means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the material
this License requires to appear in the title page. For works in
formats which do not have any title page as such, “Title Page” means
the text near the most prominent appearance of the work's title,
preceding the beginning of the body of the text.
A section “Entitled XYZ” means a named subunit of the Document whose
title either is precisely XYZ or contains XYZ in parentheses following
text that translates XYZ in another language. (Here XYZ stands for a
specific section name mentioned below, such as “Acknowledgements”,
“Dedications”, “Endorsements”, or “History”.) To “Preserve the Title”
of such a section when you modify the Document means that it remains a
section “Entitled XYZ” according to this definition.
The Document may include Warranty Disclaimers next to the notice which
states that this License applies to the Document. These Warranty
Disclaimers are considered to be included by reference in this
License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and has
no effect on the meaning of this License.
VERBATIM COPYING
You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License applies
to the Document are reproduced in all copies, and that you add no other
conditions whatsoever to those of this License. You may not use
technical measures to obstruct or control the reading or further
copying of the copies you make or distribute. However, you may accept
compensation in exchange for copies. If you distribute a large enough
number of copies you must also follow the conditions in section 3.
You may also lend copies, under the same conditions stated above, and
you may publicly display copies.
COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly have
printed covers) of the Document, numbering more than 100, and the
Document's license notice requires Cover Texts, you must enclose the
copies in covers that carry, clearly and legibly, all these Cover
Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
the back cover. Both covers must also clearly and legibly identify
you as the publisher of these copies. The front cover must present
the full title with all words of the title equally prominent and
visible. You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve
the title of the Document and satisfy these conditions, can be treated
as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto adjacent
pages.
If you publish or distribute Opaque copies of the Document numbering
more than 100, you must either include a machine-readable Transparent
copy along with each Opaque copy, or state in or with each Opaque copy
a computer-network location from which the general network-using
public has access to download using public-standard network protocols
a complete Transparent copy of the Document, free of added material.
If you use the latter option, you must take reasonably prudent steps,
when you begin distribution of Opaque copies in quantity, to ensure
that this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you distribute an
Opaque copy (directly or through your agents or retailers) of that
edition to the public.
It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give
them a chance to provide you with an updated version of the Document.
MODIFICATIONS
You may copy and distribute a Modified Version of the Document under
the conditions of sections 2 and 3 above, provided that you release
the Modified Version under precisely this License, with the Modified
Version filling the role of the Document, thus licensing distribution
and modification of the Modified Version to whoever possesses a copy
of it. In addition, you must do these things in the Modified Version:
Use in the Title Page (and on the covers, if any) a title distinct
from that of the Document, and from those of previous versions
(which should, if there were any, be listed in the History section
of the Document). You may use the same title as a previous version
if the original publisher of that version gives permission.
List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified
Version, together with at least five of the principal authors of the
Document (all of its principal authors, if it has fewer than five),
unless they release you from this requirement.
State on the Title page the name of the publisher of the
Modified Version, as the publisher.
Preserve all the copyright notices of the Document.
Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
Include, immediately after the copyright notices, a license notice
giving the public permission to use the Modified Version under the
terms of this License, in the form shown in the Addendum below.
Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document's license notice.
Include an unaltered copy of this License.
Preserve the section Entitled “History”, Preserve its Title, and add
to it an item stating at least the title, year, new authors, and
publisher of the Modified Version as given on the Title Page. If
there is no section Entitled “History” in the Document, create one
stating the title, year, authors, and publisher of the Document as
given on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.
Preserve the network location, if any, given in the Document for
public access to a Transparent copy of the Document, and likewise
the network locations given in the Document for previous versions
it was based on. These may be placed in the “History” section.
You may omit a network location for a work that was published at
least four years before the Document itself, or if the original
publisher of the version it refers to gives permission.
For any section Entitled “Acknowledgements” or “Dedications”, Preserve
the Title of the section, and preserve in the section all the
substance and tone of each of the contributor acknowledgements and/or
dedications given therein.
Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles. Section numbers
or the equivalent are not considered part of the section titles.
Delete any section Entitled “Endorsements”. Such a section
may not be included in the Modified Version.
Do not retitle any existing section to be Entitled “Endorsements” or
to conflict in title with any Invariant Section.
Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no material
copied from the Document, you may at your option designate some or all
of these sections as invariant. To do this, add their titles to the
list of Invariant Sections in the Modified Version's license notice.
These titles must be distinct from any other section titles.
You may add a section Entitled “Endorsements”, provided it contains
nothing but endorsements of your Modified Version by various
parties—for example, statements of peer review or that the text has
been approved by an organization as the authoritative definition of a
standard.
You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list
of Cover Texts in the Modified Version. Only one passage of
Front-Cover Text and one of Back-Cover Text may be added by (or
through arrangements made by) any one entity. If the Document already
includes a cover text for the same cover, previously added by you or
by arrangement made by the same entity you are acting on behalf of,
you may not add another; but you may replace the old one, on explicit
permission from the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License
give permission to use their names for publicity for or to assert or
imply endorsement of any Modified Version.
COMBINING DOCUMENTS
You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified
versions, provided that you include in the combination all of the
Invariant Sections of all of the original documents, unmodified, and
list them all as Invariant Sections of your combined work in its
license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy. If there are multiple Invariant Sections with the same name but
different contents, make the title of each such section unique by
adding at the end of it, in parentheses, the name of the original
author or publisher of that section if known, or else a unique number.
Make the same adjustment to the section titles in the list of
Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled “History”
in the various original documents, forming one section Entitled
“History”; likewise combine any sections Entitled “Acknowledgements”,
and any sections Entitled “Dedications”. You must delete all
sections Entitled “Endorsements.”
COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in
the collection, provided that you follow the rules of this License for
verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute
it individually under this License, provided you insert a copy of this
License into the extracted document, and follow this License in all
other respects regarding verbatim copying of that document.
AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate
and independent documents or works, in or on a volume of a storage or
distribution medium, is called an “aggregate” if the copyright
resulting from the compilation is not used to limit the legal rights
of the compilation's users beyond what the individual works permit.
When the Document is included in an aggregate, this License does not
apply to the other works in the aggregate which are not themselves
derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half of
the entire aggregate, the Document's Cover Texts may be placed on
covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic form.
Otherwise they must appear on printed covers that bracket the whole
aggregate.
TRANSLATION
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section 4.
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also include
the original English version of this License and the original versions
of those notices and disclaimers. In case of a disagreement between
the translation and the original version of this License or a notice
or disclaimer, the original version will prevail.
If a section in the Document is Entitled “Acknowledgements”,
“Dedications”, or “History”, the requirement (section 4) to Preserve
its Title (section 1) will typically require changing the actual
title.
TERMINATION
You may not copy, modify, sublicense, or distribute the Document except
as expressly provided for under this License. Any other attempt to
copy, modify, sublicense or distribute the Document is void, and will
automatically terminate your rights under this License. However,
parties who have received copies, or rights, from you under this
License will not have their licenses terminated so long as such
parties remain in full compliance.
FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions
of the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number.
If the Document specifies that a particular numbered version of this
License “or any later version” applies to it, you have the option of
following the terms and conditions either of that specified version or
of any later version that has been published (not as a draft) by the
Free Software Foundation. If the Document does not specify a version
number of this License, you may choose any version ever published (not
as a draft) by the Free Software Foundation.
C.1.1 ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:
Copyright (C) yearyour name.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2
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''.
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the “with...Texts.” line with this:
with the Invariant Sections being list their titles, with
the Front-Cover Texts being list, and with the Back-Cover Texts
being list.
If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.
If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License,
to permit their use in free software.
