Re: lynx-dev z (was Re: Timeout parameter?)

[Kari E. Hurtta]

Bela Lubkin:
> Kari E. Hurtta wrote:
> 
> > Bela Lubkin:
> 
> (a long time ago)
> 
> > > brian j. pardy wrote:
> > > 
> > > > IIRC, gethost[by]name() (whichever lynx uses, no source in front of me) 
> > > > blocks when looking up a hostname, making it impossible to interrupt it.
> > > > That's why forking it away allows an interrupt.
> > > 
> > > gethostbyname() comes from the BIND resolver library [dunno about under
> > > Windows or VMS].  In older 4.8/4.9 versions of the library, there are
> > > timeout parameters which can be modified.  Unfortunately, they're in an
> > > internal structure which isn't documented or intended to be exposed.
> > > (I'm talking about struct __res_state _res, fields "retrans" and
> > > "retry".)  I don't know whether this situation has changed in the
> > > current BIND 8.x versions.
> > 
> > yes. Sendmail uses lot of code like:
> > 
> > #if NAMED_BIND
> >         /* unless interactive, try twice, over a minute */
> >         if (OpMode == MD_DAEMON || OpMode == MD_SMTP)
> >         {
> >                 _res.retrans = 30;
> >                 _res.retry = 2;
> >         }
> > #endif
> > 
> > As far I know many have compiled sendmail with BIND 8.
> 
> That's inconclusive (to me, not knowing the sendmail build environment):
> "NAMED_BIND" might be defined only for BIND 4.x, not 8.x.

NAMED_BIND is always defined as 1:

| NAMED_BIND      If non-zero, include DNS (name daemon) support, including
|                 MX support.  The specs say you must use this if you run
|                 SMTP.  You don't have to be running a name server daemon
|                 on your machine to need this -- any use of the DNS resolver,
|                 including remote access to another machine, requires this
|                 option.  Defined by default in conf.h.  Define it to zero
|                 ONLY on machines that do not use DNS in any way.

I do not have used BIND 8, so I do not is there some tricks needed.
What sendmail does is:

#if NAMED_BIND
#include <resolv.h>
#endif

(And I can guess that this is not native interface of BIND 8.)

> > Lynx is of course availabe much more systems that BSD (or Open Source) 
> > Sendmail :-)
> 
> Right, and this is no longer relevant since Lynx is using fork() and
> select() to control the duration of DNS lookups.  We could conceivably
> also, or alternatively, use BIND retrans/retry, but I don't see much
> point in it.

Yes. fork() + select() is perhaps available about same platforms than for which
there is Sendmail available :-) So there is no advantages.

/ Kari Hurtta