NLS: Internationalized Domain Name Conversion Sample

The sample application described in this topic demonstrates how certain NLS functions can be used to convert internationalized domain names (IDNs). This application demonstrates the following NLS API functions:

• IdnToAscii
• IdnToNameprepUnicode
• IdnToUnicode

In the sample output, note that, "ExAmPlE.cOm" is converted to "русский.example.com" for the Cyrillic example.

// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF 
// ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO 
// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A 
// PARTICULAR PURPOSE. 
// 
// Copyright (c) Microsoft Corporation. All rights reserved. 
// 
// IdnConversion.cpp 

#include "stdafx.h"
#include "windows.h"
#include <stdio.h>
#include <tchar.h>

#define IDN_MAX_LENGTH 255

// Print out a string using code points for the non-ASCII values 
void DumpString(LPCWSTR pInput)
{
    while (*pInput != 0)
    {
        if (*pInput < 0x80)
            wprintf(L"%c", *pInput);
        else
            wprintf(L"\\x%4.4x", *pInput);
        pInput++;
    }
    wprintf(L"\n");
}

// Convert some IDN strings 
void IdnConvert(LPCWSTR strInput)
{
    // Show string we're converting 
    wprintf(L"Converting string: ");
    DumpString(strInput);

    // Convert it to IDN "Punycode" form.  Note that IDN names have a maximum length, 
    // so we'll just use a hard coded buffer size.  
    WCHAR pPunycode[IDN_MAX_LENGTH];
    if (IdnToAscii(0, strInput, -1, pPunycode, IDN_MAX_LENGTH) == 0)
    {
        wprintf(L"ERROR %d converting to Punycode\n", GetLastError());
    }
    else
    {
        // Output it, safe to just wprintf to console because it has to be ASCII 
        wprintf(L"   Punycode value: %s\n", pPunycode);

        // Convert it to IDN normalized Unicode 
        WCHAR pUnicode[IDN_MAX_LENGTH];
        if (IdnToNameprepUnicode(0, strInput, -1, pUnicode, IDN_MAX_LENGTH) == 0)
        {
            wprintf(L"ERROR %d converting to nameprep Unicode\n", GetLastError());
        }
        else
        {
            wprintf(L"   Nameprep value: ");
            DumpString(pUnicode);
        }

        // Convert the punycode string back to Unicode 
        if (IdnToUnicode(0, pPunycode, -1, pUnicode, IDN_MAX_LENGTH) == 0)
        {
            wprintf(L"ERROR %d converting back to Unicode\n", GetLastError());
        }
        else
        {
            // Note that this round-trip value should be the same as the nameprep value above 
            wprintf(L"    Unicode value: ");
            DumpString(pUnicode);
        }
    }

    wprintf(L"\n");
}

int __cdecl wmain(int argc, WCHAR* argv[])
{
    // Non-IDN names do not change 
    IdnConvert(L"ExAmPlE.cOm");
    
    // Show some idn conversions.  Note that some characters change 
    IdnConvert(L"&#1088;&#1091;&#1089;&#1089;&#1082;&#1080;&#1081;.ExAmPlE.cOm");
    IdnConvert(L"&#26085;&#26412;&#35486;.example.com");
    IdnConvert(L"&#65318;&#65365;&#65356;&#65356;&#65367;&#65353;&#65348;&#65364;&#65352;&#12290;example&#12290;com&#12290;");

    // Some characters are illegal in IDN names 
    IdnConvert(L"\x9fa5\x9fff\x00\x7f");
}

/* This code example produces the following output:

Converting string: ExAmPlE.cOm
   Punycode value: ExAmPlE.cOm
   Nameprep value: ExAmPlE.cOm
    Unicode value: ExAmPlE.cOm

Converting string: \x0440\x0443\x0441\x0441\x043a\x0438\x0439.ExAmPlE.cOm
   Punycode value: xn--h1acbxfam.example.com
   Nameprep value: \x0440\x0443\x0441\x0441\x043a\x0438\x0439.example.com
    Unicode value: \x0440\x0443\x0441\x0441\x043a\x0438\x0439.example.com

Converting string: \x65e5\x672c\x8a9e.example.com
   Punycode value: xn--wgv71a119e.example.com
   Nameprep value: \x65e5\x672c\x8a9e.example.com
    Unicode value: \x65e5\x672c\x8a9e.example.com

Converting string: \xff26\xff55\xff4c\xff4c\xff57\xff49\xff44\xff54\xff48\x3002example\x3002com\x3002
   Punycode value: fullwidth.example.com.
   Nameprep value: fullwidth.example.com.
    Unicode value: fullwidth.example.com.

Converting string: \x9fa5\x9fff
ERROR 123 converting to Punycode

*/