Re: [perl #75630] IO::Socket does not provide the IPV6_V6ONLY constant

On Thu, Jun 10, 2010 at 09:29:10AM +0100, Nicholas Clark wrote:
> I'm not certain either. The counter argument is that Socket is called
> Socket, not Socket4, and (I think) is intended to provide general
> functionality, not just IPv4.

Ah; a fair point.

> Plus, I think (and I'm assuming a rough consensus here, until proven
> otherwise) the perl core should be shipping complete IPv6 functionality
> (well, as complete as it currently ships IPv4).

Would be nice. ;) See e.g. my repeated attempts to get my
Socket::GetAddrInfo module into core; or something like it (original bug
report was using it).

> I right in guessing that without this constant exposed *somewhere* by a
> module shipping in the perl core, we'd not meet that goal?

Complicated.

There's two camps in IPv6 land; those who say 'v6 is an extension of
'v4, and those who don't. Some OSes take the view that bind()ing a
PF_INET6 to an AF_INET6 TCP port, say, should also grab the IPv4 one as
well. Some don't.

Those in the former camp do a single

  socket(PF_INET6,...) && bind(..., pack_sockaddr_in6())

to grab both. Those in the latter camp do two

  socket(AF_INET6,...) && bind(..., pack_sockaddr_in6())
  socket(AF_INET, ...) && bind(..., pack_sockaddr_in())

The IPV6_BINDV6ONLY sockopt was an attempt to appease both camps - to
allow mixed v4+6 stacks to perform either behaviour, for various
programs written to one style or the other, by setting that option to
what they'd prefer.

We don't -strictly- need it, as any application can attempt to create
both sockets, and if binding the AF_INET one fails on EADDRINUSE, it's
likely because the AF_INET6 was already in place.

But perhaps it's a good idea to provide it anyway...

-- 
Paul "LeoNerd" Evans

[email protected]
ICQ# 4135350       |  Registered Linux# 179460
http://www.leonerd.org.uk/

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