IDN Support in WinINet

Starting in Windows Server 2008 and Windows Vista, the host portion of the Unicode URL is converted to the Internationalized Domain Name (IDN). Separate portions of the Unicode URL encoding can also be modified by configurations set by the application. The ANSI versions of the WinINet API continue to send the URL over the wire as entered by the application, however the WinINet Unicode versions of the API now conform to the IDN standard (RFC3490) for URL encodings.

By default, when a URL is entered as a Unicode parameter, the host portion, for both proxy and direct connections, is converted to IDN format. The application has the option to disable IDN host formatting by setting the INTERNET_OPTION_IDN option. IDN host conversion can be enabled on only the direct or proxy connections by using the INTERNET_FLAG_IDN_DIRECT or INTERNET_FLAG_IDN_PROXY flags with INTERNET_OPTION_IDN.

The following code example shows how to disable IDN host conversion for both the proxy and direct connections.

DWORD IDN = 0; 
InternetSetOption( hRequest, 
                   INTERNET_OPTION_IDN,
                   &IDN, 
                   sizeof(DWORD) ); 

If IDN host formatting is disabled, the application has the option to specify the desired codepage using INTERNET_OPTION_CODEPAGE.

The following code example shows how to specify the Japanese code page.

DWORD CP_SHIFT_JIS = 932;  // ANSI/OEM  Japanese, Shift-JIS
InternetSetOption( hRequest, 
                   INTERNET_OPTION_CODEPAGE,
                   &CP_SHIFT_JIS, 
                   Sizeof(DWORD) ); 

The path portion of the URL is UTF8 encoded by default, and the remaining segments of the URL, the query or fragment, are converted to the default system code page (CP_ACP).

The following example shows how to specify the Korean language code page for the path portion of the URL.

DWORD CP_KOREAN = 949;   // ANSI/OEM Korean 
InternetSetOption( hRequest, 
                   INTERNET_OPTION_CODEPAGE_PATH,
                   &CP_KOREAN, 
                   sizeof(DWORD) );

The following table defines the options that support IDN. For more information, see the Option flags topic.