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03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<!--
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03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<title>lwres</title>
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03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" lang="en">
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<a name="id2456972"></a><div class="titlepage"></div>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<div class="refnamediv">
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<h2>Name</h2>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<p>lwres &#8212; introduction to the lightweight resolver library</p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync</div>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<div class="refsynopsisdiv">
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<h2>Synopsis</h2>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;lwres/lwres.h&gt;</pre></div>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync</div>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<div class="refsect1" lang="en">
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<a name="id2514515"></a><h2>DESCRIPTION</h2>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync The BIND 9 lightweight resolver library is a simple, name service
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync independent stub resolver library. It provides hostname-to-address
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync and address-to-hostname lookup services to applications by
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync transmitting lookup requests to a resolver daemon
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <span><strong class="command">lwresd</strong></span>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync running on the local host. The resover daemon performs the
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync lookup using the DNS or possibly other name service protocols,
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync and returns the results to the application through the library.
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync The library and resolver daemon communicate using a simple
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync UDP-based protocol.
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync </p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync</div>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<div class="refsect1" lang="en">
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<a name="id2514528"></a><h2>OVERVIEW</h2>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync The lwresd library implements multiple name service APIs.
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync The standard
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <code class="function">gethostbyname()</code>,
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <code class="function">gethostbyaddr()</code>,
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <code class="function">gethostbyname_r()</code>,
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <code class="function">gethostbyaddr_r()</code>,
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <code class="function">getaddrinfo()</code>,
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <code class="function">getipnodebyname()</code>,
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync and
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <code class="function">getipnodebyaddr()</code>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync functions are all supported. To allow the lwres library to coexist
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync with system libraries that define functions of the same name,
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync the library defines these functions with names prefixed by
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <code class="literal">lwres_</code>.
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync To define the standard names, applications must include the
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync header file
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <code class="filename">&lt;lwres/netdb.h&gt;</code>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync which contains macro definitions mapping the standard function names
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync into
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <code class="literal">lwres_</code>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync prefixed ones. Operating system vendors who integrate the lwres
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync library into their base distributions should rename the functions
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync in the library proper so that the renaming macros are not needed.
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync </p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync The library also provides a native API consisting of the functions
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <code class="function">lwres_getaddrsbyname()</code>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync and
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <code class="function">lwres_getnamebyaddr()</code>.
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync These may be called by applications that require more detailed
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync control over the lookup process than the standard functions
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync provide.
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync </p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync In addition to these name service independent address lookup
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync functions, the library implements a new, experimental API
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync for looking up arbitrary DNS resource records, using the
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <code class="function">lwres_getaddrsbyname()</code>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync function.
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync </p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync Finally, there is a low-level API for converting lookup
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync requests and responses to and from raw lwres protocol packets.
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync This API can be used by clients requiring nonblocking operation,
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync and is also used when implementing the server side of the lwres
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync protocol, for example in the
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync <span><strong class="command">lwresd</strong></span>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync resolver daemon. The use of this low-level API in clients
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync and servers is outlined in the following sections.
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync </p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync</div>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<div class="refsect1" lang="en">
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<a name="id2514660"></a><h2>CLIENT-SIDE LOW-LEVEL API CALL FLOW</h2>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync When a client program wishes to make an lwres request using the
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync native low-level API, it typically performs the following
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync sequence of actions.
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync </p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync (1) Allocate or use an existing <span class="type">lwres_packet_t</span>,
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync called <code class="varname">pkt</code> below.
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync </p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync<p>
03532efdc331b598d3dedc8cc7477641c3b0dd12vboxsync (2) Set <em class="structfield"><code>pkt.recvlength</code></em> 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
<code class="filename">lwres.h</code>: <code class="constant">LWRES_RECVLENGTH = 4096</code>.
</p>
<p>
(3) Set <em class="structfield"><code>pkt.serial</code></em>
to a unique serial number. This value is echoed
back to the application by the remote server.
</p>
<p>
(4) Set <em class="structfield"><code>pkt.pktflags</code></em>. Usually this is set to
0.
</p>
<p>
(5) Set <em class="structfield"><code>pkt.result</code></em> to 0.
</p>
<p>
(6) Call <code class="function">lwres_*request_render()</code>,
or marshall in the data using the primitives
such as <code class="function">lwres_packet_render()</code>
and storing the packet data.
</p>
<p>
(7) Transmit the resulting buffer.
</p>
<p>
(8) Call <code class="function">lwres_*response_parse()</code>
to parse any packets received.
</p>
<p>
(9) Verify that the opcode and serial match a request, and process the
packet specific information contained in the body.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2514876"></a><h2>SERVER-SIDE LOW-LEVEL API CALL FLOW</h2>
<p>
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.
</p>
<p>
Note that the same <span class="type">lwres_packet_t</span> is used
in both the <code class="function">_parse()</code> and <code class="function">_render()</code> 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.
</p>
<p>
(1) When a packet is received, call <code class="function">lwres_*request_parse()</code> to
unmarshall it. This returns a <span class="type">lwres_packet_t</span> (also called <code class="varname">pkt</code>, below)
as well as a data specific type, such as <span class="type">lwres_gabnrequest_t</span>.
</p>
<p>
(2) Process the request in the data specific type.
</p>
<p>
(3) Set the <em class="structfield"><code>pkt.result</code></em>,
<em class="structfield"><code>pkt.recvlength</code></em> as above. All other fields
can
be left untouched since they were filled in by the <code class="function">*_parse()</code> call
above. If using <code class="function">lwres_*response_render()</code>,
<em class="structfield"><code>pkt.pktflags</code></em> will be set up
properly. Otherwise, the <code class="constant">LWRES_LWPACKETFLAG_RESPONSE</code> bit should be
set.
</p>
<p>
(4) Call the data specific rendering function, such as
<code class="function">lwres_gabnresponse_render()</code>.
</p>
<p>
(5) Send the resulting packet to the client.
</p>
<p></p>
</div>
<div class="refsect1" lang="en">
<a name="id2514960"></a><h2>SEE ALSO</h2>
<p><span class="citerefentry"><span class="refentrytitle">lwres_gethostent</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_getipnode</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_getnameinfo</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_noop</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_gabn</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_gnba</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_context</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">lwres_config</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">resolver</span>(5)</span>,
<span class="citerefentry"><span class="refentrytitle">lwresd</span>(8)</span>.
</p>
</div>
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