Copyright © 2002, 2003, 2004 Simon Josefsson.
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".
Indices
Appendices
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 iSCSI, Kerberos 5, Nameprep, SASL and XMPP are included. Punycode and ASCII Compatible Encoding (ACE) via IDNA are supported.
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 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.
This manual documents the library programming interface. All functions and data types provided by the library are explained.
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.
Libidn has at some point in time been tested on the following platforms.
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.
GCC 2.95.1 and GNU Make. armv4l-unknown-linux-gnu.
Tru64 UNIX C compiler and Tru64 Make. alphaev67-dec-osf5.1,
alphaev68-dec-osf5.1.
GCC 2.96 and GNU Make. alphaev6-unknown-linux-gnu,
alphaev67-unknown-linux-gnu.
GCC 3.0 and GNU Make. ia64-unknown-linux-gnu.
GCC 3.2.2 and GNU Make. x86_64-unknown-linux-gnu (AMD64
Opteron “Melody”).
GCC 2.96 and GNU Make. alphaev6-unknown-linux-gnu,
alphaev67-unknown-linux-gnu, ia64-unknown-linux-gnu.
GCC 3.2 and GNU Make. i686-pc-linux-gnu.
GCC 2.96 and GNU Make. i686-pc-linux-gnu.
GCC 2.95.3 and GNU Make. i686-pc-linux-gnu.
GCC 3.2 and GNU Make. i686-pc-linux-gnu.
MIPS C compiler, IRIX Make. mips-sgi-irix6.5.
IBM C for AIX compiler, AIX Make. rs6000-ibm-aix4.3.2.0.
GCC 3.2, GNU make. i686-pc-cygwin.
HP-UX C compiler and HP Make. ia64-hp-hpux11.22,
hppa2.0w-hp-hpux11.11.
Sun WorkShop Compiler C 6.0 and SUN Make. sparc-sun-solaris2.8.
Sun Forte Developer 7 C compiler and GNU
Make. sparc-sun-solaris2.9.
GCC 2.95.3 and GNU Make. alpha-unknown-netbsd1.6,
i386-unknown-netbsdelf1.6.
GCC 2.95.3 and GNU Make. alpha-unknown-openbsd3.1,
i386-unknown-openbsd3.1.
GCC 2.95.4 and GNU Make. alpha-unknown-freebsd4.7,
alpha-unknown-freebsd4.8, i386-unknown-freebsd4.7,
i386-unknown-freebsd4.8.
GCC 3.1 and GNU Make. powerpc-apple-darwin6.5.
If you use Libidn on, or port Libidn to, a new platform please report it to the author.
Commercial support is available for users of GNU Libidn. The kind of support that can be purchased may include:
If you are interested, please write to:
Simon Josefsson Datakonsult Drottningholmsv. 70 112 42 Stockholm Sweden E-mail: simon@josefsson.org
If your company provide support related to GNU Libidn and would like to be mentioned here, contact the author (see Bug Reports).
The package can be downloaded from several places, including
<http://josefsson.org/libidn/releases/>. The latest version is
stored in a file, e.g., libidn-0.3.7.tar.gz where the
0.3.7 indicate the highest version number.
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-0.3.7.tar.gz
$ tar xfz libidn-0.3.7.tar.gz
$ cd libidn-0.3.7/
$ ./configure
...
$ make
...
$ make install
...
After that Libidn should be properly installed and ready for use.
If you think you have found a bug in Libidn, please investigate it and report it.
Please make an effort to produce a self-contained report, with something definite that can be tested or debugged. Vague queries or piecemeal messages are difficult to act on and don't help the development effort.
If your bug report is good, we will do our best to help you to get a corrected version of the software; if the bug report is poor, we won't do anything about it (apart from asking you to send better bug reports).
If you think something in this manual is unclear, or downright incorrect, or if the language needs to be improved, please also send a note.
Send your bug report to:
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.
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:
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 the same name
prefixes with one prepended underscore are reserved for internal use
and should never be used by an application.
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 the same name prefixes with one
prepended underscore are reserved for internal use and should never be
used by an application.
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 the same name prefixes with one prepended
underscore are reserved for internal use and should never be used by
an application.
Libidn is stateless and does not need any initialization.
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.
req_version: Required version number, or NULL.
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:
gcc -o foo foo.c `pkg-config libidn --cflags --libs`
If you work on a project that uses Autoconf (see GNU Autoconf) to help find installed libraries, the suggestions in the previous section are not the entire story. There are a few methods to detect and incorporate Libidn into your Autoconf based package.
If your audience is a typical GNU/Linux desktop, you can often assume they have the pkg-config tool installed, in which you can use its Autoconf M4 macro to find and set up your package for use with Shishi. The following illustrate this scenario.
AC_ARG_ENABLE(idn,
AC_HELP_STRING([--disable-idn],
[Don't use Libidn]),
libidn=$enableval)
if test "$libidn" != "no" ; then
PKG_CHECK_MODULES(LIBIDN, libidn >= 0.0.0,
[libidn=yes],
[libidn=no])
if test "$libidn" != "yes" ; then
libidn=no
AC_MSG_WARN([Libidn not found])
else
libidn=yes
AC_DEFINE(USE_LIBIDN, 1, [Define to 1 if you want Libidn.])
fi
fi
AC_MSG_CHECKING([if Libidn should be used])
AC_MSG_RESULT($libidn)
The following illustrate a standalone autconf test, that work regardless of if your project Libtool (see GNU Libtool) or not. It is the most portable solution, and is recommended.
AC_CHECK_HEADER(idna.h,
AC_CHECK_LIB(idn, stringprep_check_version,
[libidn=yes AC_SUBST(SHISHI_LIBS, -lidn)],
libidn=no),
kerberos5=no)
AC_ARG_ENABLE(idn, AC_HELP_STRING([--disable-idn], [Don't use Libidn]),
libidn=$enableval)
if test "$libidn" != "no" ; then
AC_DEFINE(USE_LIBIDN, 1, [Define to 1 if you want Libidn.])
else
AC_MSG_WARN([Libidn not found])
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.
stringprep.hTo use the functions explained in this chapter, you need to include the file stringprep.h using:
#include <stringprep.h>
p: a pointer to Unicode character encoded as UTF-8
Converts a sequence of bytes encoded as UTF-8 to a Unicode character.
If p does not point to a valid UTF-8 encoded character, results are
undefined.
Return value: the resulting character.
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.
Converts a single character to UTF-8.
Return value: number of bytes written.
p: a pointer to Unicode character encoded as UTF-8
Converts a sequence of bytes encoded as UTF-8 to a Unicode character.
If p does not point to a valid UTF-8 encoded character, results are
undefined.
Return value: the resulting character.
str: a UCS-4 encoded string
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.
str: a UTF-8 encoded string
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().
str: a Unicode string.
len: length of str array, or -1 if str is nul-terminated.
Converts UCS4 string into UTF-8 and runs
stringprep_utf8_nfkc_normalize().
Return value: a newly allocated Unicode string, that is the NFKC
normalized form of str.
str: a UTF-8 encoded string.
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 system locale charset.
Note that this function return what it believe the SYSTEM is using as a locale, not what locale the program is currently in (modified, e.g., by a setlocale(LC_CTYPE, "ISO-8859-1")). The reason is that data read from argv[], stdin etc comes from the system, and is more likely to be encoded using the system locale than the program locale.
You can set the environment variable CHARSET to override the value returned. Note that this function caches the result, so you will have to modify CHARSET before calling (even indirectly) any stringprep functions, e.g., by setting it when invoking the application.
Return value: Return the character set used by the system locale. It will never return NULL, but use "ASCII" as a fallback.
str: input zero-terminated string.
to_codeset: name of destination character set.
from_codeset: name of origin character set, as used by str.
Convert the string from one character set to another using the
system's iconv() function.
Return value: Returns newly allocated zero-terminated string which
is str transcoded into to_codeset.
str: input zero terminated string.
Convert string encoded in the locale's character set into UTF-8 by
using stringprep_convert().
Return value: Returns newly allocated zero-terminated string which
is str transcoded into UTF-8.
str: input zero terminated string.
Convert string encoded in UTF-8 into the locale's character set by
using stringprep_convert().
Return value: Returns newly allocated zero-terminated string which
is str transcoded into the locale's character set.
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.
stringprep.hTo use the functions explained in this chapter, you need to include the file stringprep.h using:
#include <stringprep.h>
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.
All functions return a code of the Stringprep_rc
enumerated type:
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.
String contain unassigned Unicode code points, which is forbidden by the profile.
String contain code points prohibited by the profile.
String contain code points with conflicting bidirection category.
Leading and trailing character in string not of proper bidirectional category.
Contains prohibited code points detected by bidirectional code.
Buffer handed to function was too small. This usually indicate a problem in the calling application.
The stringprep profile was inconsistent. This usually indicate an internal error in the library.
The supplied flag conflicted with profile. This usually indicate a problem in the calling application.
The supplied profile name was not known to the library.
The Unicode NFKC operation failed. This usually indicate an internal error in the library.
The malloc was out of memory. This is usually a fatal error.
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.
Disable the BIDI step. Usually the profile specifies BIDI and NFKC settings, and applications should not override it unless in special situations.
Make the library return with an error if string contains unassigned characters according to profile.
ucs4: input/output array with string to prepare.
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: stringprep profile flags, 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, or 0.
The profile contain the 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.
ucs4: input/output array with zero terminated string to prepare.
maxucs4len: maximum length of input/output array.
flags: stringprep profile flags, 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, or 0.
The profile contain the 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.
in: input/ouput array with string to prepare.
maxlen: maximum length of input/output array.
flags: stringprep profile flags, 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, or 0.
The profile contain the 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.
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: stringprep profile flags, 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, 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.
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.
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.
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 Kerberos5 stringprep profile. Returns 0 iff successful, or an error code.
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.
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.
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.
punycode.hTo use the functions explained in this chapter, you need to include the file punycode.h using:
#include <punycode.h>
All functions return a code of the Punycode_status enumerated
type:
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.
Input is invalid.
Output would exceed the space provided.
Input needs wider integers to process.
The punycode function uses a special type to denote Unicode code points. It is guaranteed to always be a 32 bit unsigned integer.
A unsigned integer that hold Unicode code points.
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.
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.
idna.hTo use the functions explained in this chapter, you need to include the file idna.h using:
#include <idna.h>
All functions return a exit code:
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.
Error during string preparation.
Error during punycode operation.
For IDNA_USE_STD3_ASCII_RULES, indicate that the string contains non-LDH ASCII characters.
For IDNA_USE_STD3_ASCII_RULES, indicate that the string contains a leading or trailing hyphen-minus (U+002D).
The final output string is not within the (inclusive) range 1 to 63 characters.
The string does not contain the ACE prefix (for ToUnicode).
The ToASCII operation on output string does not equal the input.
The input contains the ACE prefix (for ToASCII).
Could not convert string in locale encoding.
Could not allocate buffer (this is typically a fatal error).
The IDNA flags parameter can take on the following values, or a
bit-wise inclusive or of any subset of the parameters:
Allow unassigned Unicode code points.
Check output to make sure it is a STD3 conforming host name.
String with the official IDNA prefix, xn--.
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:
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: IDNA flags, 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 error code.
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: IDNA flags, 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 ToUnicode output never contains more code points than its input. 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 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.
input: zero terminated input Unicode string.
output: pointer to newly allocated output string.
flags: IDNA flags, 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.
input: zero terminated input UTF-8 string.
output: pointer to newly allocated output string.
flags: IDNA flags, 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.
input: zero terminated input UTF-8 string.
output: pointer to newly allocated output string.
flags: IDNA flags, 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.
input: zero-terminated Unicode string.
output: pointer to newly allocated output Unicode string.
flags: IDNA flags, 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.
input: zero-terminated UTF-8 string.
output: pointer to newly allocated output Unicode string.
flags: IDNA flags, 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.
input: zero-terminated UTF-8 string.
output: pointer to newly allocated output UTF-8 string.
flags: IDNA flags, 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.
input: zero-terminated UTF-8 string.
output: pointer to newly allocated output string encoded in the current locale's character set.
flags: IDNA flags, 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.
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: IDNA flags, 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.
This chapter contains example code which illustrate how `Libidn' can be used when writing your own application.
This example demonstrates how the stringprep functions are used.
/* example.c Example code showing how to use stringprep().
* Copyright (C) 2002, 2003 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 <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;
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 with rc %d...\n", 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 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
*
*/
/*
* 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];
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 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 <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;
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\n", 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 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 <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;
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\n", 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;
}
GNU Libidn (idn) – Internationalized Domain Names command line tool
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.
To process a string that starts with -, for example
-foo, use -- to signal the end of parameters, as in
idn --quiet -a -- -foo.
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)
-p, --profile=STRING Use specified stringprep profile instead
Valid stringprep profiles are `Nameprep', `KRBprep', `Nodeprep',
`Resourceprep', `plain', `trace', `SASLprep', and `iSCSI'.
--debug Print debugging information (default=off)
--quiet Silent operation (default=off)
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
...
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
xn--rksmrgs-5wao1o
jas@latte:~$
Reading input from command line, and disabling copyright and license information:
jas@latte:~$ idn --quiet räksmörgås blåbærgrød
xn--rksmrgs-5wao1o
xn--blbrgrd-fxak7p
jas@latte:~$
Accessing a specific StringPrep profile directly:
jas@latte:~$ idn --quiet --profile=SASLprep --stringprep teßtª
teßta
jas@latte:~$
Getting the character set encoding issues can be difficult, especially if you use more than one encoding in your environment (e.g., UTF-8 together with ISO-8859-1 or ISO-2022-JP). The first step is to use the --debug parameter to find out which character set encoding idn believe your locale uses.
jas@latte:~$ idn --debug --quiet ""
system locale uses charset `UTF-8'.
jas@latte:~$
If it prints ANSI_X3.4-1968 (i.e., US-ASCII), this indicate you have not configured your locale properly. Use, e.g., LANG=sv_SE.UTF-8; export LANG 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), i.e., you get an error like:
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).
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.
jas@latte:~$ idn --quiet --debug ""
system locale uses charset `ISO-8859-1'.
jas@latte:~$ CHARSET=UTF-8 idn --quiet --debug räksmörgås
system locale uses charset `UTF-8'.
input[0] = U+0072
input[1] = U+4af3
input[2] = U+006d
input[3] = U+1b29e5
input[4] = U+0073
output[0] = U+0078
output[1] = U+006e
output[2] = U+002d
output[3] = U+002d
output[4] = U+0072
output[5] = U+006d
output[6] = U+0073
output[7] = U+002d
output[8] = U+0068
output[9] = U+0069
output[10] = U+0036
output[11] = U+0064
output[12] = U+0035
output[13] = U+0039
output[14] = U+0037
output[15] = U+0035
output[16] = U+0035
output[17] = U+0032
output[18] = U+0061
xn--rms-hi6d597552a
jas@latte:~$
The sense moral is to forget about CHARSET 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.
Name of the GNU Libidn idn application. The default is idn. This variable can be customized.
List of environment variable definitions prepended to process-environment. The default is ("CHARSET=UTF-8"). This variable can be customized.
List of parameters passed to punycode-program to invoke punycode encoding mode. The default is ("--quiet" "--punycode-encode"). This variable can be customized.
Parameters passed to punycode-program to invoke punycode decoding mode. The default is ("--quiet" "--punycode-decode"). This variable can be customized.
Returns a Punycode encoding of the string, after converting the input into UTF-8.
Returns a possibly multibyte string which is the decoding of the string which is a punycode encoded string.
Name of the GNU Libidn idn application. The default is idn. This variable can be customized.
List of environment variable definitions prepended to process-environment. The default is ("CHARSET=UTF-8"). This variable can be customized.
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.
Parameters passed idna-program to invoke IDNA ToUnicode mode. The default is ("--quiet" "--idna-to-unicode" "--usestd3asciirules"). This variable can be customized.
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.
Returns a possibly multibyte string which is the output of the IDNA ToUnicode operation computed on the input string.
The punycode code was taken from the IETF IDN Punycode specification, by Adam M. Costello.
Some functions (see nfkc.c and toutf8.c) has been borrowed from GLib downloaded from www.gtk.org.
Several people reported bugs, sent patches or suggested improvements, see the file THANKS.
idn: Invoking idn
idna-to-ascii: Emacs API
idna-to-unicode: Emacs API
idna_to_ascii_4i: IDNA Functions
idna_to_ascii_4z: IDNA Functions
idna_to_ascii_8z: IDNA Functions
idna_to_ascii_lz: IDNA Functions
idna_to_unicode_44i: IDNA Functions
idna_to_unicode_4z4z: IDNA Functions
idna_to_unicode_8z4z: IDNA Functions
idna_to_unicode_8z8z: IDNA Functions
idna_to_unicode_8zlz: IDNA Functions
idna_to_unicode_lzlz: IDNA Functions
punycode-decode: Emacs API
punycode-encode: Emacs API
punycode_decode: Punycode Functions
punycode_encode: Punycode Functions
stringprep: Stringprep Functions
stringprep_4i: Stringprep Functions
stringprep_4zi: Stringprep Functions
stringprep_check_version: Version Check
stringprep_convert: Utility Functions
stringprep_iscsi: Stringprep Functions
stringprep_kerberos5: Stringprep Functions
stringprep_locale_charset: Utility Functions
stringprep_locale_to_utf8: Utility Functions
stringprep_nameprep_no_unassigned: Stringprep Functions
stringprep_plain: Stringprep Functions
stringprep_profile: Stringprep Functions
stringprep_ucs4_nfkc_normalize: Utility Functions
stringprep_ucs4_to_utf8: Utility Functions
stringprep_unichar_to_utf8: Utility Functions
stringprep_utf8_nfkc_normalize: Utility Functions
stringprep_utf8_to_locale: Utility Functions
stringprep_utf8_to_ucs4: Utility Functions
stringprep_utf8_to_unichar: Utility Functions
stringprep_xmpp_nodeprep: Stringprep Functions
stringprep_xmpp_resourceprep: Stringprep Functions
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