This manual is for Libidn2 (version 0.10, 25 June 2014), an implementation of IDNA2008 internationalized domain names.
Copyright © 2011-2014 Simon Josefsson
Libidn2 is a free software implementation of IDNA2008.
Below are the interfaces of the Libidn2 library documented.
idn2.h
To use the functions documented in this chapter, you need to include the file idn2.h like this:
#include <idn2.h>
When you have the data encoded in UTF-8 form the direct interfaces to the library are as follows.
src: input zero-terminated UTF-8 string in Unicode NFC normalized form.
lookupname: newly allocated output variable with name to lookup in DNS.
flags: optional
idn2_flags
to modify behaviour.Perform IDNA2008 lookup string conversion on domain name
src
, as described in section 5 of RFC 5891. Note that the input string must be encoded in UTF-8 and be in Unicode NFC form.Pass
IDN2_NFC_INPUT
inflags
to convert input to NFC form before further processing. PassIDN2_ALABEL_ROUNDTRIP
inflags
to convert any input A-labels to U-labels and perform additional testing. Multiple flags may be specified by binary or:ing them together, for exampleIDN2_NFC_INPUT
|IDN2_ALABEL_ROUNDTRIP
.Returns: On successful conversion
IDN2_OK
is returned, if the output domain or any label would have been too longIDN2_TOO_BIG_DOMAIN
orIDN2_TOO_BIG_LABEL
is returned, or another error code is returned.
ulabel: input zero-terminated UTF-8 and Unicode NFC string, or NULL.
alabel: input zero-terminated ACE encoded string (xn–), or NULL.
insertname: newly allocated output variable with name to register in DNS.
flags: optional
idn2_flags
to modify behaviour.Perform IDNA2008 register string conversion on domain label
ulabel
andalabel
, as described in section 4 of RFC 5891. Note that the inputulabel
must be encoded in UTF-8 and be in Unicode NFC form.Pass
IDN2_NFC_INPUT
inflags
to convert inputulabel
to NFC form before further processing.It is recommended to supply both
ulabel
andalabel
for better error checking, but supplying just one of them will work. Passing in onlyalabel
is better than onlyulabel
. See RFC 5891 section 4 for more information.Returns: On successful conversion
IDN2_OK
is returned, when the givenulabel
andalabel
does not match each otherIDN2_UALABEL_MISMATCH
is returned, when either of the input labels are too longIDN2_TOO_BIG_LABEL
is returned, whenalabel
does does not appear to be a proper A-labelIDN2_INVALID_ALABEL
is returned, or another error code is returned.
As a convenience, the following functions are provided that will convert the input from the locale encoding format to UTF-8 and normalize the string using NFC, and then apply the core functions described earlier.
src: input zero-terminated locale encoded string.
lookupname: newly allocated output variable with name to lookup in DNS.
flags: optional
idn2_flags
to modify behaviour.Perform IDNA2008 lookup string conversion on domain name
src
, as described in section 5 of RFC 5891. Note that the input is assumed to be encoded in the locale's default coding system, and will be transcoded to UTF-8 and NFC normalized by this function.Pass
IDN2_ALABEL_ROUNDTRIP
inflags
to convert any input A-labels to U-labels and perform additional testing.Returns: On successful conversion
IDN2_OK
is returned, if conversion from locale to UTF-8 fails thenIDN2_ICONV_FAIL
is returned, if the output domain or any label would have been too longIDN2_TOO_BIG_DOMAIN
orIDN2_TOO_BIG_LABEL
is returned, or another error code is returned.
ulabel: input zero-terminated locale encoded string, or NULL.
alabel: input zero-terminated ACE encoded string (xn–), or NULL.
insertname: newly allocated output variable with name to register in DNS.
flags: optional
idn2_flags
to modify behaviour.Perform IDNA2008 register string conversion on domain label
ulabel
andalabel
, as described in section 4 of RFC 5891. Note that the inputulabel
is assumed to be encoded in the locale's default coding system, and will be transcoded to UTF-8 and NFC normalized by this function.It is recommended to supply both
ulabel
andalabel
for better error checking, but supplying just one of them will work. Passing in onlyalabel
is better than onlyulabel
. See RFC 5891 section 4 for more information.Returns: On successful conversion
IDN2_OK
is returned, when the givenulabel
andalabel
does not match each otherIDN2_UALABEL_MISMATCH
is returned, when either of the input labels are too longIDN2_TOO_BIG_LABEL
is returned, whenalabel
does does not appear to be a proper A-labelIDN2_INVALID_ALABEL
is returned, or another error code is returned.
The flags
parameter can take on the following values, or a
bit-wise inclusive or of any subset of the parameters:
Apply additional round-trip conversion of A-label inputs.
rc: return code from another libidn2 function.
Convert internal libidn2 error code to a humanly readable string. The returned pointer must not be de-allocated by the caller.
Return value: A humanly readable string describing error.
rc: return code from another libidn2 function.
Convert internal libidn2 error code to a string corresponding to internal header file symbols. For example, idn2_strerror_name(IDN2_MALLOC) will return the string "IDN2_MALLOC".
The caller must not attempt to de-allocate the returned string.
Return value: A string corresponding to error code symbol.
The functions normally return 0 on sucess or a negative error code.
ptr: pointer to deallocate
Call free(3) on the given pointer.
This function is typically only useful on systems where the library malloc heap is different from the library caller malloc heap, which happens on Windows when the library is a separate DLL.
It is often desirable to check that the version of Libidn2 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: version string to compare with, or NULL.
Check IDN2 library version. This function can also be used to read out the version of the library code used. See
IDN2_VERSION
for a suitablereq_version
string, it corresponds to the idn2.h header file version. Normally these two version numbers match, but if you are using an application built against an older libidn2 with a newer libidn2 shared library they will be different.Return value: Check that the version of the library is at minimum the one given as a string in
req_version
and return the actual version string of the library; return NULL if the condition is not met. If NULL is passed to this function no check is done and only the version string is returned.
The normal way to use the function is to put something similar to the
following first in your main
:
if (!idn2_check_version (IDN2_VERSION)) { printf ("idn2_check_version() failed:\n" "Header file incompatible with shared library.\n"); exit(EXIT_FAILURE); }
This chapter contains example code which illustrate how Libidn2 is used when you write your own application.
This example demonstrates how a domain name is processed before it is lookup in the DNS.
#include <stdio.h> /* printf, fflush, fgets, stdin, perror, fprintf */ #include <string.h> /* strlen */ #include <locale.h> /* setlocale */ #include <stdlib.h> /* free */ #include <idn2.h> /* idn2_lookup_ul, IDN2_OK, idn2_strerror, idn2_strerror_name */ int main (int argc, char *argv[]) { int rc; char src[BUFSIZ]; char *lookupname; setlocale (LC_ALL, ""); printf ("Enter (possibly non-ASCII) domain name to lookup: "); fflush (stdout); if (!fgets (src, sizeof (src), stdin)) { perror ("fgets"); return 1; } src[strlen (src) - 1] = '\0'; rc = idn2_lookup_ul (src, &lookupname, 0); if (rc != IDN2_OK) { fprintf (stderr, "error: %s (%s, %d)\n", idn2_strerror (rc), idn2_strerror_name (rc), rc); return 1; } printf ("IDNA2008 domain name to lookup in DNS: %s\n", lookupname); free (lookupname); return 0; }
This example demonstrates how a domain label is processed before it is registered in the DNS.
#include <stdio.h> /* printf, fflush, fgets, stdin, perror, fprintf */ #include <string.h> /* strlen */ #include <locale.h> /* setlocale */ #include <stdlib.h> /* free */ #include <idn2.h> /* idn2_register_ul, IDN2_OK, idn2_strerror, idn2_strerror_name */ int main (int argc, char *argv[]) { int rc; char src[BUFSIZ]; char *insertname; setlocale (LC_ALL, ""); printf ("Enter (possibly non-ASCII) label to register: "); fflush (stdout); if (!fgets (src, sizeof (src), stdin)) { perror ("fgets"); return 1; } src[strlen (src) - 1] = '\0'; rc = idn2_register_ul (src, NULL, &insertname, 0); if (rc != IDN2_OK) { fprintf (stderr, "error: %s (%s, %d)\n", idn2_strerror (rc), idn2_strerror_name (rc), rc); return 1; } printf ("IDNA2008 label to register in DNS: %s\n", insertname); free (insertname); return 0; }
idn2 translates internationalized domain names to the IDNA2008 encoded format, either for lookup or registration.
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., lookup or register) 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.
On POSIX systems you may use the LANG
environment variable to
specify a different locale.
To process a string that starts with -
, for example
-foo
, use --
to signal the end of parameters, as in
idn2 -r -- -foo
.
idn2
recognizes these commands:
-h, --help Print help and exit -V, --version Print version and exit -l, --lookup Lookup domain name (default) -r, --register Register label --debug Print debugging information --quiet Silent operation
On POSIX systems the LANG environment variable can be used to override the system locale for the command being invoked. The system locale may influence what character set is used to decode data (i.e., strings on the command line or data read from the standard input stream), and to encode data to the standard output. If your system is set up correctly, however, the application will use the correct locale and character set automatically. Example usage:
$ LANG=en_US.UTF-8 idn2 ...
Standard usage, reading input from standard input and disabling license and usage instructions:
jas@latte:~$ idn2 --quiet räksmörgås.se xn--rksmrgs-5wao1o.se ...
Reading input from the command line:
jas@latte:~$ idn2 räksmörgås.se blåbærgrød.no xn--rksmrgs-5wao1o.se xn--blbrgrd-fxak7p.no jas@latte:~$
Testing the IDNA2008 Register function:
jas@latte:~$ idn2 --register fußball xn--fuball-cta jas@latte:~$
Getting character data encoded right, and making sure Libidn2 use the
same encoding, can be difficult. The reason for this is that most
systems may 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 Libidn2 is to use the ‘--debug’ parameter to find out which character set encoding ‘idn2’ believe your locale uses.
jas@latte:~$ idn2 --debug --quiet "" 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. 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 ‘idn2’ appear to be unable to translate from your
system locale into UTF-8
(which is used internally), and you
will get an error message like this:
idn2: lookup: could not convert string to UTF-8
One explanation is that you didn't install 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 to be able to use it.
Another explanation is that the error is correct and you are feeding
‘idn2’ invalid data. This can happen inadvertently if you are
not careful with the character set encoding you use. For example, if
your shell run in a ISO-8859-1
environment, and you invoke
‘idn2’ with the ‘LANG’ 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 valid 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:~$ idn2 --quiet --debug "" Charset: ISO-8859-1 jas@latte:~$ LANG=sv_SE.UTF-8 idn2 --debug räksmörgås Charset: UTF-8 input[0] = 0x72 input[1] = 0xc3 input[2] = 0xa4 input[3] = 0xc3 input[4] = 0xa4 input[5] = 0x6b input[6] = 0x73 input[7] = 0x6d input[8] = 0xc3 input[9] = 0xb6 input[10] = 0x72 input[11] = 0x67 input[12] = 0xc3 input[13] = 0xa5 input[14] = 0x73 UCS-4 input[0] = U+0072 UCS-4 input[1] = U+00e4 UCS-4 input[2] = U+00e4 UCS-4 input[3] = U+006b UCS-4 input[4] = U+0073 UCS-4 input[5] = U+006d UCS-4 input[6] = U+00f6 UCS-4 input[7] = U+0072 UCS-4 input[8] = U+0067 UCS-4 input[9] = U+00e5 UCS-4 input[10] = U+0073 output[0] = 0x72 output[1] = 0xc3 output[2] = 0xa4 output[3] = 0xc3 output[4] = 0xa4 output[5] = 0x6b output[6] = 0x73 output[7] = 0x6d output[8] = 0xc3 output[9] = 0xb6 output[10] = 0x72 output[11] = 0x67 output[12] = 0xc3 output[13] = 0xa5 output[14] = 0x73 UCS-4 output[0] = U+0072 UCS-4 output[1] = U+00e4 UCS-4 output[2] = U+00e4 UCS-4 output[3] = U+006b UCS-4 output[4] = U+0073 UCS-4 output[5] = U+006d UCS-4 output[6] = U+00f6 UCS-4 output[7] = U+0072 UCS-4 output[8] = U+0067 UCS-4 output[9] = U+00e5 UCS-4 output[10] = U+0073 xn--rksmrgs-5waap8p jas@latte:~$
The sense moral here is to forget about ‘LANG’ (instead, configure your system locale properly) unless you know what you are doing, and if you want to use ‘LANG’, do it carefully and after verifying with ‘--debug’ that you get the desired results.
idn2_check_version
: Library Functionsidn2_free
: Library Functionsidn2_lookup_u8
: Library Functionsidn2_lookup_ul
: Library Functionsidn2_register_u8
: Library Functionsidn2_register_ul
: Library Functionsidn2_strerror
: Library Functionsidn2_strerror_name
: Library Functions