Add IDN support to existing net APIs

[Jonathan Lu]

Hi net-dev,

If a Java application tries to support International Domain Names (IDN)
[1], which was firstly brought in Java6,
 it has to write additional code or wrap java.net.IDN API [2] to make the
conversion each time it tries to resolve
a non-ASCII domain name, and use the converted punycode to make connections
to remote host, like:

    java.net.IDN.toASCII("电脑.info <http://xn--wnyy6w.info>");

It is easier for newly writen applications, since a wrappers can be made in
early design stage, but if
it comes to existing Java applications and third-party libraries, IDN
support would involve much more effort
like modifying the existing code base, inspecting libraries
interfaces/implementations, or even
re-implement some of the functions.

I'm wondering if it is possible to add IDN support into existing Java APIs,
like
java.net.InetAddress.getByName(), if JDK itself supports IDN, any existing
applications or libraries would
benefit from supporting IDN automatically without any source code
modifications.

Of course there's security risks regarding IDN homograph attacks [1][2], so
it may not be a
good idea to change the default behavior right now. But it would still work
if a simple switch can be
added into current JDK.
For example, by defining following the property in command like options
like

-Djava.net.AutoIDN=true

Any existing Java applications who wishes to support IDN feature will be
able to support IDN
without any changes to its source code or re-compilation.

What's your opinion on this ? any comment is welcome.

Thank you

- Jonathan Lu

-----------

[1] http://en.wikipedia.org/wiki/Internationalized_domain_name
[2] http://download.java.net/jdk8/docs/api/java/net/IDN.html
[3] http://www.unicode.org/reports/tr36/
[4] http://en.wikipedia.org/wiki/IDN_homograph_attack
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