(Classic ASP) Punycode Encoding / Decoding

Punycode is an encoding standard for representing Unicode characters using only the 7bit us-ascii characters that are permitted in network host names. Punycode is used for internationalized domain names -- i.e. IDN or IDNA (Internationalizing Domain Names in Applications).

Punycode is defined in RFC 3492. Converting to/from punycode does not include the "xn--" prefix. The "xn--" prefix is to signify that punycode follows. For example, the string " café.com" is converted to "caf-dma.com" in punycode. The punycode domain name is "xn--caf-dma.com".

Converting an email address to punycode would be as follows. Suppose the email address is "coffee@café.com". The punycode representation is "coffee@xn--caf-dma.com". The RFC 3492 punycode representation of "café.com" is simply "caf-dma.com", but the punycode domain name is "xn--caf-dma.com".

The "xn--" is a constant. It is the same regardless of the domain. For example, the punycode URL representation of "mañana.com" is "xn--maana-pta.com".

Chilkat ActiveX Downloads

ActiveX for 32-bit and 64-bit Windows

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
<%

' For versions of Chilkat < 10.0.0, use CreateObject("Chilkat_9_5_0.StringBuilder")
set sb = Server.CreateObject("Chilkat.StringBuilder")

' Load the string "café" from a utf-8 text file.
success = sb.LoadFile("qa_data/txt/cafe.txt","utf-8")

success = sb.PunyEncode()
Response.Write "<pre>" & Server.HTMLEncode( sb.GetAsString()) & "</pre>"

success = sb.PunyDecode()
Response.Write "<pre>" & Server.HTMLEncode( sb.GetAsString()) & "</pre>"

' The output is:
' 
' caf-dma
' café

%>
</body>
</html>