Let's improve IPv6 support

[Jun-ya Kato]

> However, I'm also aware of three "hard problems" that would require
> new features, and significant changes to current behavior:
> - Address selection: https://bugs.openjdk.java.net/browse/JDK-8170568

JDK-8170568 is not IPv6 specific problem.

Even if target-host has multiple IP addresses,
java.net.Socket("target-host", port) constructor trys to connect to
the only first one.

Service provider often assigns IP addresses on his edge nodes for
load balancing and reliabilty.  For example, I could easily find
that "amazon.com" DNS record has six IPv4 addresses.

  Name:	amazon.com
  Address: 54.239.17.6
  Name:	amazon.com
  Address: 54.239.17.7
  Name:	amazon.com
  Address: 54.239.25.192
  Name:	amazon.com
  Address: 54.239.25.200
  Name:	amazon.com
  Address: 54.239.25.208
  Name:	amazon.com
  Address: 54.239.26.128



Most common Linux/UNIX network commands such as telnet, ssh, or netcat
implement multiple addresses manuplation that trys all possible
addresses until connetion is established.  This behavior is useful
for java.net.Socket(String hostname, int port) constructor.  I also think
that RFC6555 is more better solution.

--
J. Kato
kato at win6.jp






From: Paul Marks <pmarks at google.com>
Subject: Re: Let's improve IPv6 support
Date: Mon, 27 Mar 2017 15:34:10 +0900 (JST)

> On Fri, Mar 17, 2017 at 11:47 AM, Martin Buchholz <martinrb at google.com> wrote:
>> Google cares a lot about IPv6, and not only because Vint Cerf works at
>> Google.
>>
>> We have some local modifications and some networking expertise and intend to
>> port/contribute that to openjdk10.
>>
>> Most of this is the work of my colleagues Alexander Smundak and Paul Marks.
>>
>> We hope we can do most of this work without asking too much of other net-dev
>> engineers, but we will likely need help with porting to non-Linux platforms,
>> running JPRT, and perhaps CCC/JEP process.
>>
>> We expect to make a large number of commits.  Should there be a JEP to cover
>> this?  Is there a current net-dev engineer who feels they "own" this problem
>> (Chris?)?
> 
> I should point out that the current batch of changes are focused on
> support for systems where 127.0.0.1 doesn't exist, which is relatively
> straightforward and unexciting.
> 
> However, I'm also aware of three "hard problems" that would require
> new features, and significant changes to current behavior:
> - Address selection: https://bugs.openjdk.java.net/browse/JDK-8170568
> - Default IP address formatting ("0:0:0:0:0:0:0:1" vs. RFC 5952)
> - Parsing and formatting of host:port strings, e.g. "[::1]:80"
> 
>