[Bug 4154] is_dns_available fails to loop as designed upon timeouts

[bu...@bugzilla.spamassassin.org]

http://bugzilla.spamassassin.org/show_bug.cgi?id=4154





------- Additional Comments From felicity@kluge.net  2005-02-24 10:15 -------
Subject: Re:   New: is_dns_available fails to loop as designed upon timeouts

On Thu, Feb 24, 2005 at 09:26:31AM -0800, bugzilla-daemon@bugzilla.spamassassin.org wrote:
> is_dns_available realizes this, and tries to loop, but the loop is coded wrong,
> because either a success or a failure breaks out of the loop!  A timeout in
> lookup_ns will result in $result defined, but containing no records, and that
> triggers the "failed horribly" clause, setting $IS_DNS_AVAILABLE to zero.  This,
> of course, results in many missed spams that are listedin DNSBLs.

Oh, I see what you're saying.  Basically, the loop in question:

  for(my $retry = 3; $retry > 0 and $#domains>-1; $retry--) {
    my $domain = splice(@domains, rand(@domains), 1);
    dbg ("trying ($retry) $domain...", "dnsavailable", -2);
[...]

tries to pick a random domain and try it.  but the section in question:

    if(defined $result && scalar @$result > 0) {
[...]
        $IS_DNS_AVAILABLE = 1;
        last;
[...]
    }     
    else {
      dbg ("NS lookup of $domain failed horribly => Perhaps your resolv.conf
isn't pointing at a valid server?", "dnsavailable", -1);
      $IS_DNS_AVAILABLE = 0; # should already be 0, but let's be sure.
      last; 
    } 

So "last" is called either way and we don't actually try 3 times, only once.

> And, you know, now that I look at it, it seems like is_dns_available uses
> lookup_ns to test general DNS availability, but lookup_ns has its own caching
> that would seem to defeat the point of the test if a site is ever hit twice! 

Judging by the code, the cache only exists for the lifetime of 1 message
check.  When rbl_finish() is called post-check, the cache is destroyed.





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