Advanced, easy to use, asynchronous-capable DNS client library and utilities
Latest commit 6f29c34 Jul 2, 2009 Ian Jackson Ian Jackson committed with lucab Imported Upstream version 1.4


                                   GNU adns
   Advanced, easy to use, asynchronous-capable DNS client library and
   adns is a resolver library for C (and C++) programs, and a collection
   of useful DNS resolver utilities.
C library

   In contrast with the standard interfaces, gethostbyname et al and
   libresolv, it has the following features:
     * It is reasonably easy to use for simple programs which just want
       to translate names to addresses, look up MX records, etc.
     * It can be used in an asynchronous, non-blocking, manner. Many
       queries can be handled simultaneously.
     * Responses are decoded automatically into a natural representation
       for a C program - there is no need to deal with DNS packet
     * Sanity checking (eg, name syntax checking, reverse/forward
       correspondence, CNAME pointing to CNAME) is performed
     * Time-to-live, CNAME and other similar information is returned in
       an easy-to-use form, without getting in the way.
     * There is no global state in the library; resolver state is an
       opaque data structure which the client creates explicitly. A
       program can have several instances of the resolver.
     * Errors are reported to the application in a way that distinguishes
       the various causes of failure properly.
     * Understands conventional resolv.conf, but this can overridden by
       environment variables.
     * Flexibility. For example, the application can tell adns to: ignore
       environment variables (for setuid programs), disable hostname
       syntax sanity checks to return arbitrary data, override or ignore
       resolv.conf in favour of supplied configuration, etc.
     * Believed to be correct ! For example, will correctly back off to
       TCP in case of long replies or queries, or to other nameservers if
       several are available. It has sensible handling of bad responses
DNS utility programs

   adns also comes with a number of utility programs for use from the
   command line and in scripts:
     * adnslogres is a much faster version of Apache's logresolv program.
     * adnsresfilter is a filter which copies its input to its output,
       replacing IP addresses by the corresponding names, without unduly
       delaying the output. For example, you can usefully pipe the output
       of netstat -n, tcpdump -ln, and the like, into it.
     * adnshost is a general-purpose DNS lookup utility which can be used
       easily in from the command line and from shell scripts to do
       simple lookups. In a more advanced mode it can be used as a
       general-purpose DNS helper program for scripting languages which
       can invoke and communicate with subprocesses. See the [1]adnshost
       usage message for a summary of its capabilities.

   I hope that future versions may also have the following features:
     * The library should be useable by threads in a multithreaded
       program in a natural way. It should multiplex many threads'
       queries through a single query socket.
     * IPv6 support.
     * Some kind of awareness of DNSSEC.
     * Possibly some very limited caching behaviour.
     * There was, at one point, a draft native Perl interface from Tony

   I'm afraid there is no manual yet. However, competent C programmers
   should be able to use the library based on the [2]commented adns.h
   header file, and the usage messages for the programs should be

   I'd be pleased if you would let me know if you're using my library in
   your project, and what you think of it.
   If you are subscribed to adns-discuss please send feedback, including
   bug reports, there; otherwise send mail to If you'd prefer that your
   message wasn't forwarded to the adns-bugreports list, send it to

   I have set up mailinglists adns-announce and adns-discuss. The
   announcements list is moderated and will contain only announcements of
   important bugs, new versions, etc. The bug reports address mentioned
   above is also a mailing list; feel free to subscribe to it.
   There are [3]archives and subscription web pages, or you can subscribe
   by sending mail containing the word `subscribe' to or

   Available for download from [4] are:
     * The [5]current release as a gzipped tarfile.
     * [6]adns.h API header file with comments, and [7]usage message for
       adnshost (currently there is no manual, sorry).
     * All versions released so far are also available via [8]anonymous
       FTP and [9]HTTP.
   You can also access the project CVS repositories:
     * A mirror of the source code repository is available via rsync from (use FTP
       first to find your way around), or via [10]cvsweb.
     * This web page is maintained in [11]Savannah, where you can browse
       the [12]webpage CVS.
   adns is also available from the [13]GNU Project FTP servers and their
Technical note

   adns requires a real nameserver like [15]BIND or [16]Dents running on
   the same system or a nearby one, which must be willing to provide
   `recursive service'. I.e., adns is a `stub resolver'. All properly
   configured UN*X and GNU systems will already have such nameserver(s);
   they are usually listed in /etc/resolv.conf.
References and related projects

     * [17]Python bindings by Andy Dustman.
     * [18]Haskell bindings by Peter Simons.
     * [19]liboop event loop library (by Dan Egnor) has a built-in
       binding for adns.
     * [20]port to MS Visual Studio 6 C++ by Jarle Aase.
Copyright and licensing

   adns is Copyright 1997-2000,2003,2006 Ian Jackson, Copyright
   1999-2000,2003,2006 Tony Finch, and Copyright (C) 1991 Massachusetts
   Institute of Technology.
   adns is free software; you can redistribute it and/or modify it under
   the terms of the GNU General Public License as published by the Free
   Software Foundation; either version 2 of the License, or (at your
   option) any later version.
   This program and documentation is distributed in the hope that it will
   be useful, but without any warranty; without even the implied warranty
   of merchantability or fitness for a particular purpose. See the
   [21]GNU General Public License for more details.
   You should have received a copy of the GNU General Public License
   along with adns, or one should be available above; if not, write to
   the [22]Free Software Foundation, 59 Temple Place - Suite 330, Boston,
   MA 02111-1307, USA, or email
   [23]Ian Jackson / [24]; more [25]free
   software by me.
   [26]GNU home page; [27]chiark home page; [28]site or mirror home page
   This web page is Copyright (C)1996-2005 Ian Jackson. See the
   Use any browser - [30]Campaign for a non-browser-specific WWW


  28. file://localhost/