Alan Bateman wrote:
Alan,
I don't think it's a significant change, since that's how getByName()
acts when the cache entries time out, so changing it would make it act
a lot more consistently.
Actually, I think it's worth debating whether or not InetAddress
should cache lookups at all, I think it's more fitting to delegate
that to the underlying OS.
Search for a ~1996 paper on DNS spoofing attacks from Princeton
University as that gives useful background on this topic and is the
original reason for the caching. When a security manager is set then it
caches forever and getByName will always return the same address. There
was some capitulation on this topic in jdk6 so that it doesn't cache
forever when there isn't a security manager. There was analysis done at
the time on the implications of the change but I don't know if that
included changing the behavior of the getByName method (Michael?).
Thanks for the background info. Incidentally, that brings us to a third
inconsistent operating mode of getByName(), so we're up to three
different behaviours:
1. When running under a security manager, we cache forever
2. When not running under a security manager, with more than ten seconds
between name lookups, we return random answers (at least if the dns
reply is delivered randomized to java)
3. When not running under a security manager, with less than ten seconds
between name lookups, we return the same answer on every query.
As far as I can see from what I've been able to google, the problem lies
in that applets may be cheated in connecting to a different host, and
that this makes it easier (actually invisible) to the applet author that
there may be more than one record in the dns reply.
I may not have a lot of say in this, but I still don't feel this is the
right solution. Do you perhaps have some more resources to any previous
discussion on the subject?
I think I'd prefer breaking compatibility and introducing a caching
InetAddress implementation for applet programmers and make InetAddress
work as expected. But then again, I don't have to do the required cleanup :)
--
Andreas
