IDNA Convert: Convert from and to IDNA Punycode domain names

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*                    IDNA Convert (idna_convert.class.php)                    *
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* http://idnaconv.phlymail.de                     mailto:phlymail@phlylabs.de *
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* (c) 2004-2011 phlyLabs, Berlin                                              *
* This file is encoded in UTF-8                                               *
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Introduction
------------

The class idna_convert allows to convert internationalized domain names
(see RFC 3490, 3491, 3492 and 3454 for detials) as they can be used with various
registries worldwide to be translated between their original (localized) form
and their encoded form as it will be used in the DNS (Domain Name System).

The class provides two public methods, encode() and decode(), which do exactly
what you would expect them to do. You are allowed to use complete domain names,
simple strings and complete email addresses as well. That means, that you might
use any of the following notations:

- www.nörgler.com
- xn--nrgler-wxa
- xn--brse-5qa.xn--knrz-1ra.info

Errors, incorrectly encoded or invalid strings will lead to either a FALSE
response (when in strict mode) or to only partially converted strings.
You can query the occured error by calling the method get_last_error().

Unicode strings are expected to be either UTF-8 strings, UCS-4 strings or UCS-4
arrays. The default format is UTF-8. For setting different encodings, you can
call the method setParams() - please see the inline documentation for details.
ACE strings (the Punycode form) are always 7bit ASCII strings.

ATTENTION: As of version 0.6.0 this class is written in the OOP style of PHP5.
Since PHP4 is no longer actively maintained, you should switch to PHP5 as fast as
possible.
We expect to see no compatibility issues with the upcoming PHP6, too.

ATTENTION: BC break! As of version 0.6.4 the class per default allows the German
ligature ß to be encoded as the DeNIC, the registry for .DE allows domains
containing ß.
In older builds "ß" was mapped to "ss". Should you still need this behaviour,
see example 5 below.

ATTENTION: As of version 0.8.0 the class fully supports IDNA 2008. Thus the 
aforementioned parameter is deprecated and replaced by a parameter to switch
between the standards. See the updated example 5 below.

Files
-----
idna_convert.class.php         - The actual class
example.php                    - An example web page for converting
transcode_wrapper.php          - Convert various encodings, see below
uctc.php                       - phlyLabs' Unicode Transcoder, see below
ReadMe.txt                     - This file
LICENCE                        - The LGPL licence file

The class is contained in idna_convert.class.php.


Examples
--------
1. Say we wish to encode the domain name nörgler.com:

// Include the class
require_once('idna_convert.class.php');
// Instantiate it
$IDN = new idna_convert();
// The input string, if input is not UTF-8 or UCS-4, it must be converted before
$input = utf8_encode('nörgler.com');
// Encode it to its punycode presentation
$output = $IDN->encode($input);
// Output, what we got now
echo $output; // This will read: xn--nrgler-wxa.com


2. We received an email from a punycoded domain and are willing to learn, how
   the domain name reads originally

// Include the class
require_once('idna_convert.class.php');
// Instantiate it
$IDN = new idna_convert();
// The input string
$input = 'andre@xn--brse-5qa.xn--knrz-1ra.info';
// Encode it to its punycode presentation
$output = $IDN->decode($input);
// Output, what we got now, if output should be in a format different to UTF-8
// or UCS-4, you will have to convert it before outputting it
echo utf8_decode($output); // This will read: andre@börse.knörz.info


3. The input is read from a UCS-4 coded file and encoded line by line. By
   appending the optional second parameter we tell enode() about the input
   format to be used

// Include the class
require_once('idna_convert.class.php');
// Instantiate it
$IDN = new dinca_convert();
// Iterate through the input file line by line
foreach (file('ucs4-domains.txt') as $line) {
    echo $IDN->encode(trim($line), 'ucs4_string');
    echo "\n";
}


4. We wish to convert a whole URI into the IDNA form, but leave the path or
   query string component of it alone. Just using encode() would lead to mangled
   paths or query strings. Here the public method encode_uri() comes into play:

// Include the class
require_once('idna_convert.class.php');
// Instantiate it
$IDN = new idna_convert();
// The input string, a whole URI in UTF-8 (!)
$input = 'http://nörgler:secret@nörgler.com/my_päth_is_not_ÄSCII/');
// Encode it to its punycode presentation
$output = $IDN->encode_uri($input);
// Output, what we got now
echo $output; // http://nörgler:secret@xn--nrgler-wxa.com/my_päth_is_not_ÄSCII/


5. To support IDNA 2008, the class needs to be invoked with an additional
   parameter. This can also be achieved on an instance.

// Include the class
require_once('idna_convert.class.php');
// Instantiate it
$IDN = new idna_convert(array('idn_version' => 2008));
// Sth. containing the German letter ß
$input = 'meine-straße.de');
// Encode it to its punycode presentation
$output = $IDN->encode_uri($input);
// Output, what we got now
echo $output; // xn--meine-strae-46a.de
// Switch back to old IDNA 2003, the original standard
$IDN->set_parameter('idn_version', 2003);
// Sth. containing the German letter ß
$input = 'meine-straße.de');
// Encode it to its punycode presentation
$output = $IDN->encode_uri($input);
// Output, what we got now
echo $output; // meine-strasse.de


Transcode wrapper
-----------------
In case you have strings in different encoding than ISO-8859-1 and UTF-8 you might need to
translate these strings to UTF-8 before feeding the IDNA converter with it.
PHP's built in functions utf8_encode() and utf8_decode() can only deal with ISO-8859-1.
Use the file transcode_wrapper.php for the conversion. It requires either iconv, libiconv
or mbstring installed together with one of the relevant PHP extensions.
The functions you will find useful are
encode_utf8() as a replacement for utf8_encode() and
decode_utf8() as a replacement for utf8_decode().

Example usage:
<?php
require_once('idna_convert.class.php');
require_once('transcode_wrapper.php');
$mystring = '<something in e.g. ISO-8859-15';
$mystring = encode_utf8($mystring, 'ISO-8859-15');
echo $IDN->encode($mystring);
?>


UCTC - Unicode Transcoder
-------------------------
Another class you might find useful when dealing with one or more of the Unicode encoding
flavours. The class is static, it requires PHP5. It can transcode into each other:
- UCS-4 string / array
- UTF-8
- UTF-7
- UTF-7 IMAP (modified UTF-7)
All encodings expect / return a string in the given format, with one major exception:
UCS-4 array is jsut an array, where each value represents one codepoint in the string, i.e.
every value is a 32bit integer value.

Example usage:
<?php
require_once('uctc.php');
$mystring = 'nörgler.com';
echo uctc::convert($mystring, 'utf8', 'utf7imap');
?>


Contact us
----------
In case of errors, bugs, questions, wishes, please don't hesitate to contact us
under the email address above.

The team of phlyLabs
http://phlylabs.de
mailto:phlymail@phlylabs.de