Re: [libmicrohttpd] Patch to improve IPv6 support in libmicrohttpd

[Christian Grothoff]

On 01/16/2012 10:31 AM, Steinar H. Gunderson wrote:
> On Sun, Jan 15, 2012 at 05:11:14PM +0100, Christian Grothoff wrote:
> > 0.4.6? You got to be kidding me.  We're at 0.9.17, 0.4.6 is about 2
> > years old.
> That's the joy of being on Debian stable, I guess :-)
>
> > More importantly, the patch is overall not taking the
> > code in the right direction.  The modern, recommended way to do
> > dual-stack IPv6 is what MHD already supports: use two listen
> > sockets.
> I don't know who's been recommending this, but it's certainly not the
> majority opinion in the Internet community at large. However, I guess trying
> to convince you would not be a very productive endeavor -- it's a contendable
> point, and it's your code.

IPv4-compatible IPv6 addresses are used for the dualstack sockets you 
propose to use:
http://tools.ietf.org/html/rfc3493#page-22

But, IPv4-compatible IPv6 addresses are now deprecated:

http://tools.ietf.org/html/rfc4291#section-2.5.5

Also, as discussed here

http://stackoverflow.com/questions/2693709/what-was-the-motivation-for-adding-the-ipv6-v6only-flag

you will find that "Specifically Windows XP/2003 does not support 
dualstack sockets."

So for portability, having two sockets and using IPV6_ONLY is a good 
idea as well.


In conclusion, I cannot show that my decision is the "majority" of the 
Internet community at large (I'm pretty sure the majority has no opinion 
on this technical detail), but it is well-founded and in line with IETF 
recommendations.

> How would using two sockets look like from a client's point of view?
> Do you have an API example?

Now I do.  I've modified the "minimal_example.c" from src/examples/ to 
make it dual-stack.  As you can see, the changes are trivial.

Happy hacking,

-Christian

dual_stack_example.c
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