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+<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
+<title>lwres</title>
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+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry">
+<a name="id-1"></a><div class="titlepage"></div>
+
+
+
+
+ <div class="refnamediv">
+<h2>Name</h2>
+<p>
+ lwres
+ &#8212; introduction to the lightweight resolver library
+ </p>
+</div>
+
+
+
+ <div class="refsynopsisdiv">
+<h2>Synopsis</h2>
+ <div class="funcsynopsis">
+<pre class="funcsynopsisinfo">#include &lt;lwres/lwres.h&gt;</pre>
+</div>
+ </div>
+
+ <div class="refsection">
+<a name="id-1.7"></a><h2>DESCRIPTION</h2>
+
+ <p>
+ 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
+ <span class="command"><strong>lwresd</strong></span>
+ 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.
+ </p>
+ </div>
+
+ <div class="refsection">
+<a name="id-1.8"></a><h2>OVERVIEW</h2>
+
+ <p>
+ The lwresd library implements multiple name service APIs.
+ The standard
+ <code class="function">gethostbyname()</code>,
+ <code class="function">gethostbyaddr()</code>,
+ <code class="function">gethostbyname_r()</code>,
+ <code class="function">gethostbyaddr_r()</code>,
+ <code class="function">getaddrinfo()</code>,
+ <code class="function">getipnodebyname()</code>,
+ and
+ <code class="function">getipnodebyaddr()</code>
+ 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
+ <code class="literal">lwres_</code>.
+ To define the standard names, applications must include the
+ header file
+ <code class="filename">&lt;lwres/netdb.h&gt;</code>
+ which contains macro definitions mapping the standard function names
+ into
+ <code class="literal">lwres_</code>
+ 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.
+ </p>
+ <p>
+ The library also provides a native API consisting of the functions
+ <code class="function">lwres_getaddrsbyname()</code>
+ and
+ <code class="function">lwres_getnamebyaddr()</code>.
+ These may be called by applications that require more detailed
+ control over the lookup process than the standard functions
+ provide.
+ </p>
+ <p>
+ 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
+ <code class="function">lwres_getaddrsbyname()</code>
+ function.
+ </p>
+ <p>
+ 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
+ <span class="command"><strong>lwresd</strong></span>
+ resolver daemon. The use of this low-level API in clients
+ and servers is outlined in the following sections.
+ </p>
+ </div>
+ <div class="refsection">
+<a name="id-1.9"></a><h2>CLIENT-SIDE LOW-LEVEL API CALL FLOW</h2>
+
+ <p>
+ When a client program wishes to make an lwres request using the
+ native low-level API, it typically performs the following
+ sequence of actions.
+ </p>
+ <p>
+ (1) Allocate or use an existing <span class="type">lwres_packet_t</span>,
+ called <code class="varname">pkt</code> below.
+ </p>
+ <p>
+ (2) Set <code class="varname">pkt.recvlength</code> 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 <code class="varname">pkt.serial</code>
+ to a unique serial number. This value is echoed
+ back to the application by the remote server.
+ </p>
+ <p>
+ (4) Set <code class="varname">pkt.pktflags</code>. Usually this is set to
+ 0.
+ </p>
+ <p>
+ (5) Set <code class="varname">pkt.result</code> 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="refsection">
+<a name="id-1.10"></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 <code class="varname">pkt.result</code>,
+ <code class="varname">pkt.recvlength</code> 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>,
+ <code class="varname">pkt.pktflags</code> 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="refsection">
+<a name="id-1.11"></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>
+</div></body>
+</html>