Milter-greylist

BTW, we had this strangeness on topic already back in Oct 2008, see
http://tech.groups.yahoo.com/group/milter-greylist/message/4805

The conclusion was that we need a autoconf rule that handles
res_ninit() existence in a proper way. My promise to provide
such a beast never came to reality ...
Well, I'll give them a 2nd try.

On Thu, Feb 18, 2010 at 11:40:07AM +0100, manu@... wrote:
[..]
> This means that any successful call to res_ninit() must have a
> corresponding res_ndestroy() call.
> 
> In dnsrbl_check_source, once res_ninit() is called, there is no way out
> of the function without executing res_ndestroy(). But the trick is that
> res_ninit() and res_ndestroy() may be macros in milter-greylist, so that
> we can cope with older BIND resolvers without having #ifdef's everywhere
> in our code.
> 
> In some situation,  milter-greylist can define res_ndestroy() as
> res_nclose(), and this is a problem, because at least in NetBSD's
> resolver, res_ndestroy() does free statp->_u._ext.ext  whereas
> res_nclose() does not.
> 
> Hence, here is the offending code in dnsrbl.c
> 
> #if (defined(res_ninit) || (__RES >= 19991006) )
> #define HAVE_RESN       1
> #ifndef res_ndestroy
> #define res_ndestroy(res)       res_nclose(res)   /* <--- XXXhereXXX */
> #endif
> #else   
> #define res_ninit(res) \
>         ((_res.options & RES_INIT) == 0 && res_init())
> #define res_nquery(res, req, class, type, ans, anslen)  \
>         res_query(req, class, type, ans, anslen)
> #define res_ndestroy(res)
> #endif  
> 
> The ifdef on res_ninit and res_ndestroy is an error, it will never be
> evaluated as true. Please try this instead, and tell us if you get the
> warning at compile time.

I'm not sure.
The origin in some 4.0 alpha version was

[..]
#ifdef res_ninit
#define HAVE_RESN     1
#ifndef res_ndestroy
#define res_ndestroy(res)     res_nclose(res)
[..]

This tried to discover if a threaded version of res_ninit() do exist. But
this works only in environments which implement a macro layer for res_n* calls.
This is trues at least for Linux, NetBSD (AFAIK) but this will never hold on
systems which has real library functions for this (like Solaris).
The __RES condition was only added as a simply hack to this work for systems
with a newer Bind resolver (for which we can asume that the thread-safe
variants do exist).


> 
> #if (__RES >= 19991006) )
> #define HAVE_RESN       1
> #else   
> #warn "no res_ninit!"
> #define res_ninit(res) \
>         ((_res.options & RES_INIT) == 0 && res_init())
> #define res_nquery(res, req, class, type, ans, anslen)  \
>         res_query(req, class, type, ans, anslen)
> #define res_ndestroy(res)
> #endif  
> 
> Handling the BIND versions where res_nclose() exists but not
> res_ndestroy() must be done by an autoconf test.

Maybe the check for __RES is sufficient (at least if we asume that
mostly Bind resolver are in use). But to get it really clean res_ninit()
should be also checked by autoconf ...

Johann E. K.