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<title>adns - advanced, alternative, asynchronous resolver</title>
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<link rev="made" href="mailto:adns-maint@chiark.greenend.org.uk">
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<strong>Advanced, easy to use, asynchronous-capable DNS client
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library and utilities.</strong>
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<!-- Note: this file is maintained in Ian Jackson's private CVS. -->
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<!-- It is served on the GNU site and also from my own system, -->
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<!-- under the URL http://www.chiark.greenend.org.uk/adns/ -->
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<!-- Please ensure that all links continine to be correct -->
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<!-- both for www.gnu.org and chiark. -->
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<!-- $Id: README.html,v 1.5 2000/09/17 14:09:22 ian Exp $ -->
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adns is a resolver library for C (and C++) programs, and a collection
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of useful DNS resolver utilities.
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In contrast with the standard interfaces, gethostbyname et al and
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libresolv, it has the following features:
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<li>It is reasonably easy to use for simple programs which just want
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to translate names to addresses, look up MX records, etc.
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<li>It can be used in an asynchronous, non-blocking, manner. Many
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queries can be handled simultaneously.
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<li>Responses are decoded automatically into a natural representation
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for a C program - there is no need to deal with DNS packet formats.
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<li>Sanity checking (eg, name syntax checking, reverse/forward
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correspondence, CNAME pointing to CNAME) is performed automatically.
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<li>Time-to-live, CNAME and other similar information is returned in
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an easy-to-use form, without getting in the way.
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<li>There is no global state in the library; resolver state is an
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opaque data structure which the client creates explicitly. A program
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can have several instances of the resolver.
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<li>Errors are reported to the application in a way that distinguishes
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the various causes of failure properly.
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<li>Understands conventional resolv.conf, but this can overridden by
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environment variables.
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<li>Flexibility. For example, the application can tell adns to:
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ignore environment variables (for setuid programs), disable hostname
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syntax sanity checks to return arbitrary data, override or ignore
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resolv.conf in favour of supplied configuration, etc.
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<li>Believed to be correct ! For example, will correctly back off to
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TCP in case of long replies or queries, or to other nameservers if
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several are available. It has sensible handling of bad responses etc.
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<h2>DNS utility programs</h2>
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adns also comes with a number of utility programs for use from the
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command line and in scripts:
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<li><code>adnslogres</code> is a much faster version of Apache's
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<li><code>adnsresfilter</code> is a filter which copies its input to
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its output, replacing IP addresses by the corresponding names, without
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unduly delaying the output. For example, you can usefully pipe the
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output of netstat -n, tcpdump -ln, and the like, into it.
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<li><code>adnshost</code> is a general-purpose DNS lookup utility
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which can be used easily in from the command line and from shell
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scripts to do simple lookups. In a more advanced mode it can be used
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as a general-purpose DNS helper program for scripting languages which
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can invoke and communicate with subprocesses. See the
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<A href="http://www.chiark.greenend.org.uk/~ian/adns/adnshost.txt">adnshost
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usage message</A> for a summary of its capabilities.
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<h2>Documentation</h2>
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I'm afraid there is no manual yet. However, competent C programmers
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should be able to use the library based on the
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<A href="http://www.chiark.greenend.org.uk/~ian/adns/adns.h.txt">commented
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adns.h header file</A>, and the usage messages for the programs should
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I'd be pleased if you would let me know if you're using my library in
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your project, and what you think of it.
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If you are subscribed to <code>adns-discuss</code> please send
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feedback, including bug reports, there; otherwise send mail to
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<code>adns-bugreports@chiark.greenend.org.uk</code>. If you'd prefer
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that your message wasn't forwarded to the <code>adns-bugreports</code>
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list, send it to <code>adns-maint@chiark.greenend.org.uk</code>.
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<h2>Mailinglists</h2>
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I have set up mailinglists <code>adns-announce</code> and
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<code>adns-discuss</code>. The announcements list is moderated and
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will contain only announcements of important bugs, new versions, etc.
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The bug reports address mentioned above is also a mailing list; feel
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free to subscribe to it.
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<A href="http://www.chiark.greenend.org.uk/mailman/listinfo">archives
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and subscription web pages</A>, or you can subscribe by sending mail
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containing the word `subscribe' to
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<code>adns-announce-REQUEST@chiark.greenend.org.uk</code> or
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<code>adns-discuss-REQUEST@chiark.greenend.org.uk</code>.
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Available for download from
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<A href="http://www.chiark.greenend.org.uk/~ian/adns/">chiark.greenend.org.uk</A>
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<li>The <A href="http://www.chiark.greenend.org.uk/~ian/adns/adns.tar.gz">current
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release</A> as a gzipped tarfile.
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<li><A href="http://www.chiark.greenend.org.uk/~ian/adns/adns.h.txt">adns.h</A>
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API header file with comments, and
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<A href="http://www.chiark.greenend.org.uk/~ian/adns/adnshost.txt">usage
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message for adnshost</A> (currently there is no manual, sorry).
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<li>All versions released so far are also available via
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<A href="ftp://ftp.chiark.greenend.org.uk/users/ian/adns/">anonymous
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FTP</A> and <A href="http://www.chiark.greenend.org.uk/~ian/adns/ftp/">HTTP</A>,
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<li>A mirror of my CVS repository is available via rsync from
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<code>rsync.chiark.greenend.org.uk::ftp/users/ian/cvs-pub/adns</code>
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(use FTP first to find your way around), or via
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<A href="http://www.chiark.greenend.org.uk/ucgi/~ijackson/cvsweb/adns/">cvsweb</A>.
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adns is also available from the
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<A href="http://www.gnu.org/">GNU Project</A> FTP servers and their
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<A href="http://www.gnu.org/order/ftp.html">mirrors</A>.
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<h2>Technical note</h2>
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adns requires a real nameserver like
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<A href="http://www.isc.org/view.cgi?/products/BIND/index.phtml">BIND</A>
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<A href="http://www.dents.org/">Dents</A> running on
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the same system or a nearby one, which must be willing to provide
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`recursive service'. I.e., adns is a `stub resolver'. All properly
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configured UN*X and GNU systems will already have such nameserver(s);
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they are usually listed in /etc/resolv.conf.
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<h2>Copyright and licensing</h2>
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<kbd>adns</kbd> is Copyright 1997-2000 Ian Jackson, Copyright
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1999-2000 Tony Finch, and Copyright (C) 1991 Massachusetts Institute
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<kbd>adns</kbd> is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or (at
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your option) any later version.
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This program and documentation is distributed in the hope that it will
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be useful, but <em>without any warranty</em>; without even the implied
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warranty of <em>merchantability</em> or <em>fitness for a particular
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purpose</em>. See the
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<A href="http://www.chiark.greenend.org.uk/~ian/COPYING.txt">GNU
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General Public License</A> for more details.
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You should have received a copy of the GNU General Public License
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along with <kbd>adns</kbd>, or one should be available above; if not,
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<A href="http://www.fsf.org/">Free Software Foundation</A>,
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59 Temple Place - Suite 330, Boston, MA 02111-1307, USA,
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or email <code>adns-maint@chiark.greenend.org.uk</code>.
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<A href="http://www.chiark.greenend.org.uk/">Ian Jackson</A> /
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<A href="mailto:adns-maint@chiark.greenend.org.uk"><tt>adns-maint@chiark.greenend.org.uk</tt></A>;
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more <A href="http://www.chiark.greenend.org.uk/~ian/software/">free
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<A href="http://www.gnu.org/">GNU home page</A>;
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<A href="http://www.chiark.greenend.org.uk/">chiark home page</A>;
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<A href="/">site or mirror home page</A>
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This web page is Copyright (C)1996-2000 Ian Jackson. See the
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<A href="http://www.chiark.greenend.org.uk/~ian/sw-www-copy.html">Copyright/acknowledgements</A>.
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