From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <3401d69f41053824dc944b92ffb0f3f1@plan9.bell-labs.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] csipinfo
Date: Wed, 18 Oct 2006 17:29:01 -0400
From: geoff@plan9.bell-labs.com
In-Reply-To: <365a3b8e0ce821506adb926ac1001503@plan9.jp>
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smtpd does a lot of this sort of DNS lookup.  If all you want is to
map an IP address back to a domainname, this one line from
/sys/src/cmd/upas/smtp/greylist.c:265 should suffice:

	fqdn = csgetvalue(nil, "ip", nci->rsys, "dom", nil);

where nci->rsys is a string containing a dotted-quad address like
"135.104.9.82" for IPv4.