IPv6 in Perl

A lot of people are talking about IPv6 lately. And perhaps with good reason - it's been years in coming, but finally we're really starting to run out of IPv4 addresses. Tools like the IPv4 Address Report may put a certain amount of panic on things with their realtime Flash-based countdown widget, but the problem is real and does need sorting.

The latest development release of Perl; perl-5.13.9, now has full support for IPv6, and the new address handling functions specified in RFC 2553. The new functions all live in Socket.

As well as the low-level AF_INET6 constant, and the pack_sockaddr_in6 and unpack_sockaddr_in6 structure functions (already in place in 5.13.8 in fact), there is now the full set of getaddrinfo, getnameinfo and associated constants. These allow fully protocol-agnostic handling of connections and addresses. There is now enough in core to support IO::Socket::IP. This is a fully protocol-agnostic replacement of IO::Socket::INET.

use IO::Socket::IP;

my $sock = IO::Socket::IP->new(
   PeerHost    => "www.google.com",
   PeerService => "www",
) or die "Cannot construct socket - $@";

printf "Now connected to %s:%s\n", $sock->peerhost_service;

...

What could be simpler?

Perhaps now is the time to make a case for putting IO::Socket::IP itself in the core distribution, such that when perl-5.14.0 comes out, it will be properly ready for the next 30 years of the Internet?

IO::Socket::IP's API is designed to be a drop-in replacement for the IPv4-only IO::Socket::INET. Any program currently using INET ought to work exactly the same, by simply substituting IP instead, and now will also work on IPv6.

If you maintain a distribution that uses IO::Socket::INET, please try out IO::Socket::IP instead. I'd be very keen to hear from anyone who finds it doesn't JustWork in their situation.

See also my earlier post on the subject; Perl - IO::Socket::IP

General Updates

I have no big specific updates today. Instead, a list of lots of little things I've been working on:

• IO::Socket::IP now has preliminary non-blocking connect support (version 0.05_003). This isn't quite a perfect solution because of blocking name resolvers, but see also Net::LibAsyncNS below.


• Created a new CPAN dist, wrapping libasyncns, called Net::LibAsyncNS. This allows a simple way to asynchronise name resolver lookups.


• Have fixed a few bugs in IO::KQueue, relating to dodgy handling of Perl scalars in the udata field. Some memory leak bugs still exist, but I believe these to be the kernel's fault. See below.


• Spent some time on Freebsd-hackers@ arguing about kqueue and managing user data pointers. Long story short I believe kqueue API itself is missing a feature, making generic wrapping of it impossible from any high-level language, or properly by C libraries also.


• Both talks I submitted for LPW2010 were accepted; on the subjects of CPS and IO::Async.


• Net::Async::HTTP now has SSL support and can stream response body content as it arrives, rather than waiting for the whole response (version 0.08).

That's all for a quick update, but I may write about any or all of these topics in more detail later...

Perl - IO::Socket::IP

IO::Socket::IP is a subclass of IO::Socket that provides a protocol-independent way to use IPv4 and IPv6 sockets. It provides an API compatible with the IPv4-only IO::Socket::INET, but does so in a way that ensures properly transparent IPv6 support.

The following example shows it has an identical API to the ::INET module:

use IO::Socket::IP;

my $sock = IO::Socket::IP->new(
   PeerHost => "www.google.com",
   PeerPort => "www",
) or die "Cannot construct socket - $@";

At this point, $sock is just another IO::Socket-derived filehandle, and supports all the usual methods and IO functionality. The only difference here is that, where IO::Socket::INET would have used a legacy gethostbyname call and made a PF_INET socket, IO::Socket::IP will use getaddrinfo (via Socket::GetAddrInfo), and will use either PF_INET or PF_INET6 as appropriate.

It's not yet a complete 100% API clone of ::INET though. While it supports all the methods, there are a few constructor arguments not yet supported, being Blocking and Timeout. The way that getaddrinfo returns a list of candidate addresses, to be tried in order, makes nonblocking support hard to do, and complicates the model for what timeout really means. For nonblocking connect support, better solutions already exist, such as IO::Async's Connector, which has always supported IPv6 via getaddrinfo. As for timeouts, eventually IO::Socket::IP should support it, but for now a local'ised $SIG{ALRM} and alarm call should suffice.

For almost all use cases, switching to using IO::Socket::IP should be a simple matter, because of the API similarities. Just adding an extra dependency (because ::IP isn't core), and substituting the package name in source should be enough.

Finally, in case you don't want to pull in an extra hard dependency, you might consider the following fragment I've used quite successfully:

   my $class = eval { require IO::Socket::IP
                         and "IO::Socket::IP" } ||
               do   { require IO::Socket::INET
                         and "IO::Socket::INET" };

   $socket = $class->new(
      PeerHost => $host,
      PeerPort => $port,
   ) or die "Cannot connect - $@\n";

There. Now you have no excuse for not being IPv6-ready.