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

[Christian Grothoff]

On 01/15/2012 04:41 PM, Steinar H. Gunderson wrote:
> Hi,
>
> Apologies for not using the bug tracker, but I really couldn't get it to
> work; on one of my email addresses, it never sent a notification, and in
> another one, I got a notification but as soon as I had created an account and
> set a password, I was logged right out and denied access back in :-)

Very strange.  I saw some account creation e-mails (I get 
notifications), and it works for others.

> Anyway, included is a patch to improve the IPv6 support in libmicrohttpd;
> it supports a “dual-stack” mode that allows for both IPv4 and IPv6
> connections on the same socket. The MHD_USE_IPv6 mode already does this
> more-or-less by accident on some operating systems, but on Linux it depends
> on a sysctl, and on *BSD you won't get it at all. Also, MHD_USE_IPv6 does not
> fall back to IPv4 if IPv6 is unavailable, making it a less attractive option
> for application developers -- MHD_USE_DUALSTACK should be safe for general
> use unless you specifically do not want IPv6.
>
> The patch also includes a fix so that if you _do_ receive an IPv4 connection
> on the dual-stack socket, you get back the proper IPv4 address (e.g.
> 127.0.0.1) and not the mapped-v4 address (::ffff:127.0.0.1).
>
> I've tested this on Debian, with XBMC as the user (that's what I wanted it
> for in the first place :-) ). Thus, the patch is against 0.4.6. Let me know
> if there are any questions.

0.4.6? You got to be kidding me.  We're at 0.9.17, 0.4.6 is about 2 
years old.  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.  Your 
approach may work on some systems (see: need for sysctl) but is again 
not how it should be done.  There've been discussions about this on the 
MHD mailinglist in the past.  Maybe I'll need to put something more 
explicit into the documentation...

Anyway, you *can* do your style of dual-stack with MHD 0.9.x using the 
MHD_OPTION_LISTEN_SOCKET (you'll need to move some of the code from your 
patch, specifically the code doing SOCKET + SETSOCKOPT) before 
MHD_start_daemon and pass the resulting listen socket to 
MHD_start_daemon.  However, I won't accept a patch to put explicit 
support for this style into the code as it is not the recommended way to 
dual-stack modern applications and thus we should not encourage the use 
of a socket bound to both IPv4 and IPv6.

Happy hacking!

Christian

libmicrohttpd-dualstack.diff
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