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+<!--
+ - Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ -
+ - This Source Code Form is subject to the terms of the Mozilla Public
+ - License, v. 2.0. If a copy of the MPL was not distributed with this
+ - file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ -
+ - See the COPYRIGHT file distributed with this work for additional
+ - information regarding copyright ownership.
+-->
+
+<!-- Converted by db4-upgrade version 1.0 -->
+<refentry xmlns:db="http://docbook.org/ns/docbook" version="5.0">
+ <info>
+ <date>2007-06-18</date>
+ </info>
+ <refentryinfo>
+ <corpname>ISC</corpname>
+ <corpauthor>Internet Systems Consortium, Inc.</corpauthor>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>lwres</refentrytitle>
+ <manvolnum>3</manvolnum>
+ <refmiscinfo>BIND9</refmiscinfo>
+ </refmeta>
+ <refnamediv>
+ <refname>lwres</refname>
+ <refpurpose>introduction to the lightweight resolver library</refpurpose>
+ </refnamediv>
+
+ <docinfo>
+ <copyright>
+ <year>2000</year>
+ <year>2001</year>
+ <year>2004</year>
+ <year>2005</year>
+ <year>2007</year>
+ <year>2014</year>
+ <year>2015</year>
+ <year>2016</year>
+ <year>2018</year>
+ <year>2019</year>
+ <holder>Internet Systems Consortium, Inc. ("ISC")</holder>
+ </copyright>
+ </docinfo>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+<funcsynopsisinfo>#include &lt;lwres/lwres.h&gt;</funcsynopsisinfo>
+</funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsection><info><title>DESCRIPTION</title></info>
+
+ <para>
+ The BIND 9 lightweight resolver library is a simple, name service
+ independent stub resolver library. It provides hostname-to-address
+ and address-to-hostname lookup services to applications by
+ transmitting lookup requests to a resolver daemon
+ <command>lwresd</command>
+ running on the local host. The resolver daemon performs the
+ lookup using the DNS or possibly other name service protocols,
+ and returns the results to the application through the library.
+ The library and resolver daemon communicate using a simple
+ UDP-based protocol.
+ </para>
+ </refsection>
+
+ <refsection><info><title>OVERVIEW</title></info>
+
+ <para>
+ The lwresd library implements multiple name service APIs.
+ The standard
+ <function>gethostbyname()</function>,
+ <function>gethostbyaddr()</function>,
+ <function>gethostbyname_r()</function>,
+ <function>gethostbyaddr_r()</function>,
+ <function>getaddrinfo()</function>,
+ <function>getipnodebyname()</function>,
+ and
+ <function>getipnodebyaddr()</function>
+ functions are all supported. To allow the lwres library to coexist
+ with system libraries that define functions of the same name,
+ the library defines these functions with names prefixed by
+ <literal>lwres_</literal>.
+ To define the standard names, applications must include the
+ header file
+ <filename>&lt;lwres/netdb.h&gt;</filename>
+ which contains macro definitions mapping the standard function names
+ into
+ <literal>lwres_</literal>
+ prefixed ones. Operating system vendors who integrate the lwres
+ library into their base distributions should rename the functions
+ in the library proper so that the renaming macros are not needed.
+ </para>
+ <para>
+ The library also provides a native API consisting of the functions
+ <function>lwres_getaddrsbyname()</function>
+ and
+ <function>lwres_getnamebyaddr()</function>.
+ These may be called by applications that require more detailed
+ control over the lookup process than the standard functions
+ provide.
+ </para>
+ <para>
+ In addition to these name service independent address lookup
+ functions, the library implements a new, experimental API
+ for looking up arbitrary DNS resource records, using the
+ <function>lwres_getaddrsbyname()</function>
+ function.
+ </para>
+ <para>
+ Finally, there is a low-level API for converting lookup
+ requests and responses to and from raw lwres protocol packets.
+ This API can be used by clients requiring nonblocking operation,
+ and is also used when implementing the server side of the lwres
+ protocol, for example in the
+ <command>lwresd</command>
+ resolver daemon. The use of this low-level API in clients
+ and servers is outlined in the following sections.
+ </para>
+ </refsection>
+ <refsection><info><title>CLIENT-SIDE LOW-LEVEL API CALL FLOW</title></info>
+
+ <para>
+ When a client program wishes to make an lwres request using the
+ native low-level API, it typically performs the following
+ sequence of actions.
+ </para>
+ <para>
+ (1) Allocate or use an existing <type>lwres_packet_t</type>,
+ called <varname>pkt</varname> below.
+ </para>
+ <para>
+ (2) Set <varname remap="structfield">pkt.recvlength</varname> to the maximum length
+ we will accept.
+ This is done so the receiver of our packets knows how large our receive
+ buffer is. The "default" is a constant in
+ <filename>lwres.h</filename>: <constant>LWRES_RECVLENGTH = 4096</constant>.
+ </para>
+ <para>
+ (3) Set <varname remap="structfield">pkt.serial</varname>
+ to a unique serial number. This value is echoed
+ back to the application by the remote server.
+ </para>
+ <para>
+ (4) Set <varname remap="structfield">pkt.pktflags</varname>. Usually this is set to
+ 0.
+ </para>
+ <para>
+ (5) Set <varname remap="structfield">pkt.result</varname> to 0.
+ </para>
+ <para>
+ (6) Call <function>lwres_*request_render()</function>,
+ or marshall in the data using the primitives
+ such as <function>lwres_packet_render()</function>
+ and storing the packet data.
+ </para>
+ <para>
+ (7) Transmit the resulting buffer.
+ </para>
+ <para>
+ (8) Call <function>lwres_*response_parse()</function>
+ to parse any packets received.
+ </para>
+ <para>
+ (9) Verify that the opcode and serial match a request, and process the
+ packet specific information contained in the body.
+ </para>
+ </refsection>
+ <refsection><info><title>SERVER-SIDE LOW-LEVEL API CALL FLOW</title></info>
+
+ <para>
+ When implementing the server side of the lightweight resolver
+ protocol using the lwres library, a sequence of actions like the
+ following is typically involved in processing each request packet.
+ </para>
+ <para>
+ Note that the same <type>lwres_packet_t</type> is used
+ in both the <function>_parse()</function> and <function>_render()</function> calls,
+ with only a few modifications made
+ to the packet header's contents between uses. This method is
+ recommended
+ as it keeps the serial, opcode, and other fields correct.
+ </para>
+ <para>
+ (1) When a packet is received, call <function>lwres_*request_parse()</function> to
+ unmarshall it. This returns a <type>lwres_packet_t</type> (also called <varname>pkt</varname>, below)
+ as well as a data specific type, such as <type>lwres_gabnrequest_t</type>.
+ </para>
+ <para>
+ (2) Process the request in the data specific type.
+ </para>
+ <para>
+ (3) Set the <varname remap="structfield">pkt.result</varname>,
+ <varname remap="structfield">pkt.recvlength</varname> as above. All other fields
+ can
+ be left untouched since they were filled in by the <function>*_parse()</function> call
+ above. If using <function>lwres_*response_render()</function>,
+ <varname remap="structfield">pkt.pktflags</varname> will be set up
+ properly. Otherwise, the <constant>LWRES_LWPACKETFLAG_RESPONSE</constant> bit should be
+ set.
+ </para>
+ <para>
+ (4) Call the data specific rendering function, such as
+ <function>lwres_gabnresponse_render()</function>.
+ </para>
+ <para>
+ (5) Send the resulting packet to the client.
+ </para>
+ <para/>
+ </refsection>
+ <refsection><info><title>SEE ALSO</title></info>
+
+ <para><citerefentry>
+ <refentrytitle>lwres_gethostent</refentrytitle><manvolnum>3</manvolnum>
+ </citerefentry>,
+
+ <citerefentry>
+ <refentrytitle>lwres_getipnode</refentrytitle><manvolnum>3</manvolnum>
+ </citerefentry>,
+
+ <citerefentry>
+ <refentrytitle>lwres_getnameinfo</refentrytitle><manvolnum>3</manvolnum>
+ </citerefentry>,
+
+ <citerefentry>
+ <refentrytitle>lwres_noop</refentrytitle><manvolnum>3</manvolnum>
+ </citerefentry>,
+
+ <citerefentry>
+ <refentrytitle>lwres_gabn</refentrytitle><manvolnum>3</manvolnum>
+ </citerefentry>,
+
+ <citerefentry>
+ <refentrytitle>lwres_gnba</refentrytitle><manvolnum>3</manvolnum>
+ </citerefentry>,
+
+ <citerefentry>
+ <refentrytitle>lwres_context</refentrytitle><manvolnum>3</manvolnum>
+ </citerefentry>,
+
+ <citerefentry>
+ <refentrytitle>lwres_config</refentrytitle><manvolnum>3</manvolnum>
+ </citerefentry>,
+
+ <citerefentry>
+ <refentrytitle>resolver</refentrytitle><manvolnum>5</manvolnum>
+ </citerefentry>,
+
+ <citerefentry>
+ <refentrytitle>lwresd</refentrytitle><manvolnum>8</manvolnum>
+ </citerefentry>.
+
+ </para>
+ </refsection>
+</refentry>