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<h1 class="settitle">Libidn2 0.7</h1>
<div class="contents">
<h2>Table of Contents</h2>
<ul>
<li><a name="toc_Top" href="#Top">Libidn2</a>
<li><a name="toc_Introduction" href="#Introduction">1 Introduction</a>
<li><a name="toc_Library-Functions" href="#Library-Functions">2 Library Functions</a>
<ul>
<li><a href="#Library-Functions">2.1 Header file <code>idn2.h</code></a>
<li><a href="#Library-Functions">2.2 Core Functions</a>
<li><a href="#Library-Functions">2.3 Locale Functions</a>
<li><a href="#Library-Functions">2.4 Control Flags</a>
<li><a href="#Library-Functions">2.5 Error Handling</a>
<li><a href="#Library-Functions">2.6 Return Codes</a>
<li><a href="#Library-Functions">2.7 Memory Handling</a>
<li><a href="#Library-Functions">2.8 Version Check</a>
</li></ul>
<li><a name="toc_Examples" href="#Examples">3 Examples</a>
<ul>
<li><a href="#Lookup">3.1 Lookup</a>
<li><a href="#Register">3.2 Register</a>
</li></ul>
<li><a name="toc_Invoking-idn2" href="#Invoking-idn2">4 Invoking idn2</a>
<ul>
<li><a href="#Invoking-idn2">4.1 Options</a>
<li><a href="#Invoking-idn2">4.2 Environment Variables</a>
<li><a href="#Invoking-idn2">4.3 Examples</a>
<li><a href="#Invoking-idn2">4.4 Troubleshooting</a>
</li></ul>
<li><a name="toc_Interface-Index" href="#Interface-Index">Interface Index</a>
<li><a name="toc_Concept-Index" href="#Concept-Index">Concept Index</a>
</li></ul>
</div>
<div class="node">
<a name="Top"></a>
<p><hr>
Next: <a rel="next" accesskey="n" href="#Introduction">Introduction</a>,
Up: <a rel="up" accesskey="u" href="#dir">(dir)</a>
</div>
<h2 class="unnumbered">Libidn2</h2>
<p>This manual is for Libidn2 (version 0.7, 5 May 2011),
an implementation of IDNA2008 internationalized domain names.
<p>Copyright © 2011 Simon Josefsson
<ul class="menu">
<li><a accesskey="1" href="#Introduction">Introduction</a>: What is Libidn2?
<li><a accesskey="2" href="#Library-Functions">Library Functions</a>: Library functions.
<li><a accesskey="3" href="#Examples">Examples</a>: Demonstrate how to use the library.
<li><a accesskey="4" href="#Invoking-idn2">Invoking idn2</a>: Command line interface to the library.
<li><a accesskey="5" href="#Interface-Index">Interface Index</a>
<li><a accesskey="6" href="#Concept-Index">Concept Index</a>
</ul>
<div class="node">
<a name="Introduction"></a>
<p><hr>
Next: <a rel="next" accesskey="n" href="#Library-Functions">Library Functions</a>,
Previous: <a rel="previous" accesskey="p" href="#Top">Top</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">1 Introduction</h2>
<p>Libidn2 is a free software implementation of IDNA2008.
<div class="node">
<a name="Library-Functions"></a>
<p><hr>
Next: <a rel="next" accesskey="n" href="#Examples">Examples</a>,
Previous: <a rel="previous" accesskey="p" href="#Introduction">Introduction</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">2 Library Functions</h2>
<p><a name="index-Library-Functions-1"></a>
Below are the interfaces of the Libidn2 library documented.
<h3 class="section">2.1 Header file <code>idn2.h</code></h3>
<p>To use the functions documented in this chapter, you need to include
the file <samp><span class="file">idn2.h</span></samp> like this:
<pre class="example"> #include <idn2.h>
</pre>
<h3 class="section">2.2 Core Functions</h3>
<p>When you have the data encoded in UTF-8 form the direct interfaces to
the library are as follows.
<h4 class="subheading">idn2_lookup_u8</h4>
<p><a name="idn2_005flookup_005fu8"></a>
<div class="defun">
— Function: int <b>idn2_lookup_u8</b> (<var>const uint8_t * src, uint8_t ** lookupname, int flags</var>)<var><a name="index-idn2_005flookup_005fu8-2"></a></var><br>
<blockquote><p><var>src</var>: input zero-terminated UTF-8 string in Unicode NFC normalized form.
<p><var>lookupname</var>: newly allocated output variable with name to lookup in DNS.
<p><var>flags</var>: optional <code>idn2_flags</code> to modify behaviour.
<p>Perform IDNA2008 lookup string conversion on domain name <code>src</code>, 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.
<p>Pass <code>IDN2_NFC_INPUT</code> in <code>flags</code> to convert input to NFC form before
further processing. Pass <code>IDN2_ALABEL_ROUNDTRIP</code> in <code>flags</code> 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 example <code>IDN2_NFC_INPUT</code> | <code>IDN2_ALABEL_ROUNDTRIP</code>.
<p><strong>Returns:</strong> On successful conversion <code>IDN2_OK</code> is returned, if the
output domain or any label would have been too long
<code>IDN2_TOO_BIG_DOMAIN</code> or <code>IDN2_TOO_BIG_LABEL</code> is returned, or
another error code is returned.
</p></blockquote></div>
<h4 class="subheading">idn2_register_u8</h4>
<p><a name="idn2_005fregister_005fu8"></a>
<div class="defun">
— Function: int <b>idn2_register_u8</b> (<var>const uint8_t * ulabel, const uint8_t * alabel, uint8_t ** insertname, int flags</var>)<var><a name="index-idn2_005fregister_005fu8-3"></a></var><br>
<blockquote><p><var>ulabel</var>: input zero-terminated UTF-8 and Unicode NFC string, or NULL.
<p><var>alabel</var>: input zero-terminated ACE encoded string (xn–), or NULL.
<p><var>insertname</var>: newly allocated output variable with name to register in DNS.
<p><var>flags</var>: optional <code>idn2_flags</code> to modify behaviour.
<p>Perform IDNA2008 register string conversion on domain label <code>ulabel</code>
and <code>alabel</code>, as described in section 4 of RFC 5891. Note that the
input <code>ulabel</code> must be encoded in UTF-8 and be in Unicode NFC form.
<p>Pass <code>IDN2_NFC_INPUT</code> in <code>flags</code> to convert input <code>ulabel</code> to NFC form
before further processing.
<p>It is recommended to supply both <code>ulabel</code> and <code>alabel</code> for better
error checking, but supplying just one of them will work. Passing
in only <code>alabel</code> is better than only <code>ulabel</code>. See RFC 5891 section
4 for more information.
<p><strong>Returns:</strong> On successful conversion <code>IDN2_OK</code> is returned, when the
given <code>ulabel</code> and <code>alabel</code> does not match each other
<code>IDN2_UALABEL_MISMATCH</code> is returned, when either of the input
labels are too long <code>IDN2_TOO_BIG_LABEL</code> is returned, when <code>alabel</code>
does does not appear to be a proper A-label <code>IDN2_INVALID_ALABEL</code>
is returned, or another error code is returned.
</p></blockquote></div>
<h3 class="section">2.3 Locale Functions</h3>
<p>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.
<h4 class="subheading">idn2_lookup_ul</h4>
<p><a name="idn2_005flookup_005ful"></a>
<div class="defun">
— Function: int <b>idn2_lookup_ul</b> (<var>const char * src, char ** lookupname, int flags</var>)<var><a name="index-idn2_005flookup_005ful-4"></a></var><br>
<blockquote><p><var>src</var>: input zero-terminated locale encoded string.
<p><var>lookupname</var>: newly allocated output variable with name to lookup in DNS.
<p><var>flags</var>: optional <code>idn2_flags</code> to modify behaviour.
<p>Perform IDNA2008 lookup string conversion on domain name <code>src</code>, 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.
<p>Pass <code>IDN2_ALABEL_ROUNDTRIP</code> in <code>flags</code> to convert any input A-labels
to U-labels and perform additional testing.
<p><strong>Returns:</strong> On successful conversion <code>IDN2_OK</code> is returned, if
conversion from locale to UTF-8 fails then <code>IDN2_ICONV_FAIL</code> is
returned, if the output domain or any label would have been too
long <code>IDN2_TOO_BIG_DOMAIN</code> or <code>IDN2_TOO_BIG_LABEL</code> is returned, or
another error code is returned.
</p></blockquote></div>
<h4 class="subheading">idn2_register_ul</h4>
<p><a name="idn2_005fregister_005ful"></a>
<div class="defun">
— Function: int <b>idn2_register_ul</b> (<var>const char * ulabel, const char * alabel, char ** insertname, int flags</var>)<var><a name="index-idn2_005fregister_005ful-5"></a></var><br>
<blockquote><p><var>ulabel</var>: input zero-terminated locale encoded string, or NULL.
<p><var>alabel</var>: input zero-terminated ACE encoded string (xn–), or NULL.
<p><var>insertname</var>: newly allocated output variable with name to register in DNS.
<p><var>flags</var>: optional <code>idn2_flags</code> to modify behaviour.
<p>Perform IDNA2008 register string conversion on domain label <code>ulabel</code>
and <code>alabel</code>, as described in section 4 of RFC 5891. Note that the
input <code>ulabel</code> 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.
<p>It is recommended to supply both <code>ulabel</code> and <code>alabel</code> for better
error checking, but supplying just one of them will work. Passing
in only <code>alabel</code> is better than only <code>ulabel</code>. See RFC 5891 section
4 for more information.
<p><strong>Returns:</strong> On successful conversion <code>IDN2_OK</code> is returned, when the
given <code>ulabel</code> and <code>alabel</code> does not match each other
<code>IDN2_UALABEL_MISMATCH</code> is returned, when either of the input
labels are too long <code>IDN2_TOO_BIG_LABEL</code> is returned, when <code>alabel</code>
does does not appear to be a proper A-label <code>IDN2_INVALID_ALABEL</code>
is returned, or another error code is returned.
</p></blockquote></div>
<h3 class="section">2.4 Control Flags</h3>
<p>The <code>flags</code> parameter can take on the following values, or a
bit-wise inclusive or of any subset of the parameters:
<div class="defun">
— Global flag: idn2_flags <b>IDN2_NFC_INPUT</b><var><a name="index-IDN2_005fNFC_005fINPUT-6"></a></var><br>
<blockquote><p>Apply NFC normalization on input.
</p></blockquote></div>
<div class="defun">
— Global flag: idn2_flags <b>IDN2_ALABEL_ROUNDTRIP</b><var><a name="index-IDN2_005fALABEL_005fROUNDTRIP-7"></a></var><br>
<blockquote><p>Apply additional round-trip conversion of A-label inputs.
</p></blockquote></div>
<h3 class="section">2.5 Error Handling</h3>
<h4 class="subheading">idn2_strerror</h4>
<p><a name="idn2_005fstrerror"></a>
<div class="defun">
— Function: const char * <b>idn2_strerror</b> (<var>int rc</var>)<var><a name="index-idn2_005fstrerror-8"></a></var><br>
<blockquote><p><var>rc</var>: return code from another libidn2 function.
<p>Convert internal libidn2 error code to a humanly readable string.
The returned pointer must not be de-allocated by the caller.
<p><strong>Return value:</strong> A humanly readable string describing error.
</p></blockquote></div>
<h4 class="subheading">idn2_strerror_name</h4>
<p><a name="idn2_005fstrerror_005fname"></a>
<div class="defun">
— Function: const char * <b>idn2_strerror_name</b> (<var>int rc</var>)<var><a name="index-idn2_005fstrerror_005fname-9"></a></var><br>
<blockquote><p><var>rc</var>: return code from another libidn2 function.
<p>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".
<p>The caller must not attempt to de-allocate the returned string.
<p><strong>Return value:</strong> A string corresponding to error code symbol.
</p></blockquote></div>
<h3 class="section">2.6 Return Codes</h3>
<p>The functions normally return 0 on sucess or a negative error code.
<div class="defun">
— Return code: idn2_rc <b>IDN2_OK</b><var><a name="index-IDN2_005fOK-10"></a></var><br>
<blockquote><p>Successful return.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_MALLOC</b><var><a name="index-IDN2_005fMALLOC-11"></a></var><br>
<blockquote><p>Memory allocation error.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_NO_CODESET</b><var><a name="index-IDN2_005fNO_005fCODESET-12"></a></var><br>
<blockquote><p>Could not determine locale string encoding format.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_ICONV_FAIL</b><var><a name="index-IDN2_005fICONV_005fFAIL-13"></a></var><br>
<blockquote><p>Could not transcode locale string to UTF-8.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_ENCODING_ERROR</b><var><a name="index-IDN2_005fENCODING_005fERROR-14"></a></var><br>
<blockquote><p>Unicode data encoding error.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_NFC</b><var><a name="index-IDN2_005fNFC-15"></a></var><br>
<blockquote><p>Error normalizing string.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_PUNYCODE_BAD_INPUT</b><var><a name="index-IDN2_005fPUNYCODE_005fBAD_005fINPUT-16"></a></var><br>
<blockquote><p>Punycode invalid input.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_PUNYCODE_BIG_OUTPUT</b><var><a name="index-IDN2_005fPUNYCODE_005fBIG_005fOUTPUT-17"></a></var><br>
<blockquote><p>Punycode output buffer too small.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_PUNYCODE_OVERFLOW</b><var><a name="index-IDN2_005fPUNYCODE_005fOVERFLOW-18"></a></var><br>
<blockquote><p>Punycode conversion would overflow.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_TOO_BIG_DOMAIN</b><var><a name="index-IDN2_005fTOO_005fBIG_005fDOMAIN-19"></a></var><br>
<blockquote><p>Domain name longer than 255 characters.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_TOO_BIG_LABEL</b><var><a name="index-IDN2_005fTOO_005fBIG_005fLABEL-20"></a></var><br>
<blockquote><p>Domain label longer than 63 characters.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_INVALID_ALABEL</b><var><a name="index-IDN2_005fINVALID_005fALABEL-21"></a></var><br>
<blockquote><p>Input A-label is not valid.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_UALABEL_MISMATCH</b><var><a name="index-IDN2_005fUALABEL_005fMISMATCH-22"></a></var><br>
<blockquote><p>Input A-label and U-label does not match.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_NOT_NFC</b><var><a name="index-IDN2_005fNOT_005fNFC-23"></a></var><br>
<blockquote><p>String is not NFC.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_2HYPHEN</b><var><a name="index-IDN2_005f2HYPHEN-24"></a></var><br>
<blockquote><p>String has forbidden two hyphens.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_HYPHEN_STARTEND</b><var><a name="index-IDN2_005fHYPHEN_005fSTARTEND-25"></a></var><br>
<blockquote><p>String has forbidden starting/ending hyphen.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_LEADING_COMBINING</b><var><a name="index-IDN2_005fLEADING_005fCOMBINING-26"></a></var><br>
<blockquote><p>String has forbidden leading combining character.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_DISALLOWED</b><var><a name="index-IDN2_005fDISALLOWED-27"></a></var><br>
<blockquote><p>String has disallowed character.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_CONTEXTJ</b><var><a name="index-IDN2_005fCONTEXTJ-28"></a></var><br>
<blockquote><p>String has forbidden context-j character.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_CONTEXTJ_NO_RULE</b><var><a name="index-IDN2_005fCONTEXTJ_005fNO_005fRULE-29"></a></var><br>
<blockquote><p>String has context-j character with no rull.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_CONTEXTO</b><var><a name="index-IDN2_005fCONTEXTO-30"></a></var><br>
<blockquote><p>String has forbidden context-o character.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_CONTEXTO_NO_RULE</b><var><a name="index-IDN2_005fCONTEXTO_005fNO_005fRULE-31"></a></var><br>
<blockquote><p>String has context-o character with no rull.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_UNASSIGNED</b><var><a name="index-IDN2_005fUNASSIGNED-32"></a></var><br>
<blockquote><p>String has forbidden unassigned character.
</p></blockquote></div>
<div class="defun">
— Return code: idn2_rc <b>IDN2_BIDI</b><var><a name="index-IDN2_005fBIDI-33"></a></var><br>
<blockquote><p>String has forbidden bi-directional properties.
</p></blockquote></div>
<h3 class="section">2.7 Memory Handling</h3>
<h4 class="subheading">idn2_free</h4>
<p><a name="idn2_005ffree"></a>
<div class="defun">
— Function: void <b>idn2_free</b> (<var>void * ptr</var>)<var><a name="index-idn2_005ffree-34"></a></var><br>
<blockquote><p><var>ptr</var>: pointer to deallocate
<p>Call free(3) on the given pointer.
<p>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.
</p></blockquote></div>
<h3 class="section">2.8 Version Check</h3>
<p>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.
<h4 class="subheading">idn2_check_version</h4>
<p><a name="idn2_005fcheck_005fversion"></a>
<div class="defun">
— Function: const char * <b>idn2_check_version</b> (<var>const char * req_version</var>)<var><a name="index-idn2_005fcheck_005fversion-35"></a></var><br>
<blockquote><p><var>req_version</var>: version string to compare with, or NULL.
<p>Check IDN2 library version. This function can also be used to read
out the version of the library code used. See <code>IDN2_VERSION</code> for a
suitable <code>req_version</code> 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.
<p><strong>Return value:</strong> Check that the version of the library is at
minimum the one given as a string in <code>req_version</code> 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.
</p></blockquote></div>
<p>The normal way to use the function is to put something similar to the
following first in your <code>main</code>:
<pre class="example"> if (!idn2_check_version (IDN2_VERSION))
{
printf ("idn2_check_version() failed:\n"
"Header file incompatible with shared library.\n");
exit(EXIT_FAILURE);
}
</pre>
<div class="node">
<a name="Examples"></a>
<p><hr>
Next: <a rel="next" accesskey="n" href="#Invoking-idn2">Invoking idn2</a>,
Previous: <a rel="previous" accesskey="p" href="#Library-Functions">Library Functions</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">3 Examples</h2>
<p><a name="index-Examples-36"></a>
This chapter contains example code which illustrate how Libidn2 is
used when you write your own application.
<ul class="menu">
<li><a accesskey="1" href="#Lookup">Lookup</a>: Example IDNA2008 Lookup domain name operation.
<li><a accesskey="2" href="#Register">Register</a>: Example IDNA2008 Register label operation.
</ul>
<div class="node">
<a name="Lookup"></a>
<p><hr>
Next: <a rel="next" accesskey="n" href="#Register">Register</a>,
Up: <a rel="up" accesskey="u" href="#Examples">Examples</a>
</div>
<h3 class="section">3.1 Lookup</h3>
<p>This example demonstrates how a domain name is processed before it is
lookup in the DNS.
<pre class="verbatim">#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;
}
</pre>
<div class="node">
<a name="Register"></a>
<p><hr>
Previous: <a rel="previous" accesskey="p" href="#Lookup">Lookup</a>,
Up: <a rel="up" accesskey="u" href="#Examples">Examples</a>
</div>
<h3 class="section">3.2 Register</h3>
<p>This example demonstrates how a domain label is processed before it is
registered in the DNS.
<pre class="verbatim">#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;
}
</pre>
<div class="node">
<a name="Invoking-idn2"></a>
<p><hr>
Next: <a rel="next" accesskey="n" href="#Interface-Index">Interface Index</a>,
Previous: <a rel="previous" accesskey="p" href="#Examples">Examples</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="chapter">4 Invoking idn2</h2>
<p><a name="index-idn2-37"></a><a name="index-invoking-_0040command_007bidn2_007d-38"></a><a name="index-command-line-39"></a>
<samp><span class="command">idn2</span></samp> translates internationalized domain names to the
IDNA2008 encoded format, either for lookup or registration.
<p>If strings are specified on the command line, they are used as input
and the computed output is printed to standard output <code>stdout</code>.
If no strings are specified on the command line, the program read
data, line by line, from the standard input <code>stdin</code>, 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.
<p>All strings are expected to be encoded in the preferred charset used
by your locale. Use <code>--debug</code> to find out what this charset is.
On POSIX systems you may use the <code>LANG</code> environment variable to
specify a different locale.
<p>To process a string that starts with <code>-</code>, for example
<code>-foo</code>, use <code>--</code> to signal the end of parameters, as in
<code>idn2 -r -- -foo</code>.
<h3 class="section">4.1 Options</h3>
<p><code>idn2</code> recognizes these commands:
<pre class="verbatim"> -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
</pre>
<h3 class="section">4.2 Environment Variables</h3>
<p>On POSIX systems the <var>LANG</var> 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:
<pre class="example"> $ LANG=en_US.UTF-8 idn2
...
</pre>
<h3 class="section">4.3 Examples</h3>
<p>Standard usage, reading input from standard input and disabling
license and usage instructions:
<pre class="example"> jas@latte:~$ idn2 --quiet
räksmörgås.se
xn--rksmrgs-5wao1o.se
...
</pre>
<p>Reading input from the command line:
<pre class="example"> jas@latte:~$ idn2 räksmörgås.se blåbærgrød.no
xn--rksmrgs-5wao1o.se
xn--blbrgrd-fxak7p.no
jas@latte:~$
</pre>
<p>Testing the IDNA2008 Register function:
<pre class="example"> jas@latte:~$ idn2 --register fußball
xn--fuball-cta
jas@latte:~$
</pre>
<h3 class="section">4.4 Troubleshooting</h3>
<p>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 <code>UTF-8</code> together with <code>ISO-8859-1</code> or
<code>ISO-2022-JP</code>. 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.
<p>The first step to troubleshooting character encoding problems with
Libidn2 is to use the ‘<samp><span class="samp">--debug</span></samp>’ parameter to find out which
character set encoding ‘<samp><span class="samp">idn2</span></samp>’ believe your locale uses.
<pre class="example"> jas@latte:~$ idn2 --debug --quiet ""
Charset: UTF-8
jas@latte:~$
</pre>
<p>If it prints <code>ANSI_X3.4-1968</code> (i.e., <code>US-ASCII</code>), this
indicate you have not configured your locale properly. To configure
the locale, you can, for example, use ‘<samp><span class="samp">LANG=sv_SE.UTF-8; export
LANG</span></samp>’ at a <code>/bin/sh</code> prompt, to set up your locale for a Swedish
environment using <code>UTF-8</code> as the encoding.
<p>Sometimes ‘<samp><span class="samp">idn2</span></samp>’ appear to be unable to translate from your
system locale into <code>UTF-8</code> (which is used internally), and you
will get an error message like this:
<pre class="example"> idn2: lookup: could not convert string to UTF-8
</pre>
<p>One explanation is that you didn't install the ‘<samp><span class="samp">iconv</span></samp>’ conversion
tools. You can find it as a standalone library in GNU Libiconv
(<a href="http://www.gnu.org/software/libiconv/">http://www.gnu.org/software/libiconv/</a>). 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.
<p>Another explanation is that the error is correct and you are feeding
‘<samp><span class="samp">idn2</span></samp>’ invalid data. This can happen inadvertently if you are
not careful with the character set encoding you use. For example, if
your shell run in a <code>ISO-8859-1</code> environment, and you invoke
‘<samp><span class="samp">idn2</span></samp>’ with the ‘<samp><span class="samp">LANG</span></samp>’ environment variable as follows, you
will feed it <code>ISO-8859-1</code> characters but force it to believe they
are <code>UTF-8</code>. Naturally this will lead to an error, unless the
byte sequences happen to be valid <code>UTF-8</code>. Note that even if you
don't get an error, the output may be incorrect in this situation,
because <code>ISO-8859-1</code> and <code>UTF-8</code> does not in general encode
the same characters as the same byte sequences.
<pre class="example"> 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:~$
</pre>
<p>The sense moral here is to forget about ‘<samp><span class="samp">LANG</span></samp>’ (instead,
configure your system locale properly) unless you know what you are
doing, and if you want to use ‘<samp><span class="samp">LANG</span></samp>’, do it carefully and after
verifying with ‘<samp><span class="samp">--debug</span></samp>’ that you get the desired results.
<div class="node">
<a name="Interface-Index"></a>
<p><hr>
Next: <a rel="next" accesskey="n" href="#Concept-Index">Concept Index</a>,
Previous: <a rel="previous" accesskey="p" href="#Invoking-idn2">Invoking idn2</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="unnumbered">Interface Index</h2>
<ul class="index-fn" compact>
<li><a href="#index-idn2_005fcheck_005fversion-35"><code>idn2_check_version</code></a>: <a href="#Library-Functions">Library Functions</a></li>
<li><a href="#index-idn2_005ffree-34"><code>idn2_free</code></a>: <a href="#Library-Functions">Library Functions</a></li>
<li><a href="#index-idn2_005flookup_005fu8-2"><code>idn2_lookup_u8</code></a>: <a href="#Library-Functions">Library Functions</a></li>
<li><a href="#index-idn2_005flookup_005ful-4"><code>idn2_lookup_ul</code></a>: <a href="#Library-Functions">Library Functions</a></li>
<li><a href="#index-idn2_005fregister_005fu8-3"><code>idn2_register_u8</code></a>: <a href="#Library-Functions">Library Functions</a></li>
<li><a href="#index-idn2_005fregister_005ful-5"><code>idn2_register_ul</code></a>: <a href="#Library-Functions">Library Functions</a></li>
<li><a href="#index-idn2_005fstrerror-8"><code>idn2_strerror</code></a>: <a href="#Library-Functions">Library Functions</a></li>
<li><a href="#index-idn2_005fstrerror_005fname-9"><code>idn2_strerror_name</code></a>: <a href="#Library-Functions">Library Functions</a></li>
</ul><div class="node">
<a name="Concept-Index"></a>
<p><hr>
Previous: <a rel="previous" accesskey="p" href="#Interface-Index">Interface Index</a>,
Up: <a rel="up" accesskey="u" href="#Top">Top</a>
</div>
<h2 class="unnumbered">Concept Index</h2>
<ul class="index-cp" compact>
<li><a href="#index-command-line-39">command line</a>: <a href="#Invoking-idn2">Invoking idn2</a></li>
<li><a href="#index-Examples-36">Examples</a>: <a href="#Examples">Examples</a></li>
<li><a href="#index-idn2-37"><code>idn2</code></a>: <a href="#Invoking-idn2">Invoking idn2</a></li>
<li><a href="#index-invoking-_0040command_007bidn2_007d-38">invoking <samp><span class="command">idn2</span></samp></a>: <a href="#Invoking-idn2">Invoking idn2</a></li>
<li><a href="#index-Library-Functions-1">Library Functions</a>: <a href="#Library-Functions">Library Functions</a></li>
</ul></body></html>
