Re: back branches vs. VS 2008

On 01/03/2011 12:15 PM, I wrote:
>
> The following patch allows me to build the 8.3 and 8.4 branches using 
> Visual Studio 2008, once the build system is patched. But I don't 
> really know why. HEAD and 9.0 build fine without it. But those 
> branches branches fail with a complaint about IPPROTO_IPV6 being 
> undefined.
>
> The patch seems harmless enough. But I'd like to know why it's 
> happening. Does anyone have a clue?
>
>
> -#ifdef IPV6_V6ONLY
> +#if defined(IPV6_V6ONLY) && defined(IPPROTO_IPV6)
>         if (addr->ai_family == AF_INET6)
>         {
>             if (setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY,


OK, what's going here is that, in the newer SDK, IPV6_V6ONLY is defined 
unconditionally, but IPPROTO_IPV6 is only defined if _WIN32_WINNT is set 
to 0x0501 or higher. We defined _WIN32_WINNT as 0x0500 until 9.0, when 
we changed it specifically to allow use of the right IPV6 settings.

This seems to me like a clear error in the MS headers. I don't think it 
makes any sense to define the settings constant but not the context 
constant. The fix I have suggested above doesn't seem unreasonable or 
terribly unsafe in these circumstances. The code clearly contemplates 
the setsockopt() call in question not having been run, as shown in this 
comment:
        /*         * Note: This might fail on some OS's, like Linux older than         * 2.4.21-pre3, that don't have
theIPV6_V6ONLY socket option, 
 
and map         * ipv4 addresses to ipv6.  It will show ::ffff:ipv4 for all ipv4         * connections.         */


cheers

andrew