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21153816Sdougb<title>lwres</title>
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24153816Sdougb<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" lang="en">
25234010Sdougb<a name="id2476274"></a><div class="titlepage"></div>
26153816Sdougb<div class="refnamediv">
27153816Sdougb<h2>Name</h2>
28153816Sdougb<p>lwres &#8212; introduction to the lightweight resolver library</p>
29153816Sdougb</div>
30153816Sdougb<div class="refsynopsisdiv">
31153816Sdougb<h2>Synopsis</h2>
32153816Sdougb<div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;lwres/lwres.h&gt;</pre></div>
33153816Sdougb</div>
34153816Sdougb<div class="refsect1" lang="en">
35234010Sdougb<a name="id2543350"></a><h2>DESCRIPTION</h2>
36153816Sdougb<p>
37170222Sdougb      The BIND 9 lightweight resolver library is a simple, name service
38170222Sdougb      independent stub resolver library.  It provides hostname-to-address
39170222Sdougb      and address-to-hostname lookup services to applications by
40170222Sdougb      transmitting lookup requests to a resolver daemon
41170222Sdougb      <span><strong class="command">lwresd</strong></span>
42170222Sdougb      running on the local host. The resover daemon performs the
43170222Sdougb      lookup using the DNS or possibly other name service protocols,
44170222Sdougb      and returns the results to the application through the library.
45170222Sdougb      The library and resolver daemon communicate using a simple
46170222Sdougb      UDP-based protocol.
47170222Sdougb    </p>
48153816Sdougb</div>
49153816Sdougb<div class="refsect1" lang="en">
50234010Sdougb<a name="id2543363"></a><h2>OVERVIEW</h2>
51153816Sdougb<p>
52170222Sdougb      The lwresd library implements multiple name service APIs.
53170222Sdougb      The standard
54170222Sdougb      <code class="function">gethostbyname()</code>,
55170222Sdougb      <code class="function">gethostbyaddr()</code>,
56170222Sdougb      <code class="function">gethostbyname_r()</code>,
57170222Sdougb      <code class="function">gethostbyaddr_r()</code>,
58170222Sdougb      <code class="function">getaddrinfo()</code>,
59170222Sdougb      <code class="function">getipnodebyname()</code>,
60170222Sdougb      and
61170222Sdougb      <code class="function">getipnodebyaddr()</code>
62170222Sdougb      functions are all supported.  To allow the lwres library to coexist
63170222Sdougb      with system libraries that define functions of the same name,
64170222Sdougb      the library defines these functions with names prefixed by
65170222Sdougb      <code class="literal">lwres_</code>.
66170222Sdougb      To define the standard names, applications must include the
67170222Sdougb      header file
68170222Sdougb      <code class="filename">&lt;lwres/netdb.h&gt;</code>
69170222Sdougb      which contains macro definitions mapping the standard function names
70170222Sdougb      into
71170222Sdougb      <code class="literal">lwres_</code>
72170222Sdougb      prefixed ones.  Operating system vendors who integrate the lwres
73170222Sdougb      library into their base distributions should rename the functions
74170222Sdougb      in the library proper so that the renaming macros are not needed.
75170222Sdougb    </p>
76153816Sdougb<p>
77170222Sdougb      The library also provides a native API consisting of the functions
78170222Sdougb      <code class="function">lwres_getaddrsbyname()</code>
79170222Sdougb      and
80170222Sdougb      <code class="function">lwres_getnamebyaddr()</code>.
81170222Sdougb      These may be called by applications that require more detailed
82170222Sdougb      control over the lookup process than the standard functions
83170222Sdougb      provide.
84170222Sdougb    </p>
85153816Sdougb<p>
86170222Sdougb      In addition to these name service independent address lookup
87170222Sdougb      functions, the library implements a new, experimental API
88170222Sdougb      for looking up arbitrary DNS resource records, using the
89170222Sdougb      <code class="function">lwres_getaddrsbyname()</code>
90170222Sdougb      function.
91170222Sdougb    </p>
92153816Sdougb<p>
93170222Sdougb      Finally, there is a low-level API for converting lookup
94170222Sdougb      requests and responses to and from raw lwres protocol packets.
95170222Sdougb      This API can be used by clients requiring nonblocking operation,
96170222Sdougb      and is also used when implementing the server side of the lwres
97170222Sdougb      protocol, for example in the
98170222Sdougb      <span><strong class="command">lwresd</strong></span>
99170222Sdougb      resolver daemon.  The use of this low-level API in clients
100170222Sdougb      and servers is outlined in the following sections.
101170222Sdougb    </p>
102153816Sdougb</div>
103153816Sdougb<div class="refsect1" lang="en">
104234010Sdougb<a name="id2543427"></a><h2>CLIENT-SIDE LOW-LEVEL API CALL FLOW</h2>
105153816Sdougb<p>
106170222Sdougb      When a client program wishes to make an lwres request using the
107170222Sdougb      native low-level API, it typically performs the following
108170222Sdougb      sequence of actions.
109170222Sdougb    </p>
110153816Sdougb<p>
111170222Sdougb      (1) Allocate or use an existing <span class="type">lwres_packet_t</span>,
112170222Sdougb      called <code class="varname">pkt</code> below.
113170222Sdougb    </p>
114153816Sdougb<p>
115170222Sdougb      (2) Set <em class="structfield"><code>pkt.recvlength</code></em> to the maximum length
116170222Sdougb      we will accept.
117170222Sdougb      This is done so the receiver of our packets knows how large our receive
118170222Sdougb      buffer is.  The "default" is a constant in
119170222Sdougb      <code class="filename">lwres.h</code>: <code class="constant">LWRES_RECVLENGTH = 4096</code>.
120170222Sdougb    </p>
121153816Sdougb<p>
122170222Sdougb      (3) Set <em class="structfield"><code>pkt.serial</code></em>
123170222Sdougb      to a unique serial number.  This value is echoed
124170222Sdougb      back to the application by the remote server.
125170222Sdougb    </p>
126153816Sdougb<p>
127170222Sdougb      (4) Set <em class="structfield"><code>pkt.pktflags</code></em>.  Usually this is set to
128170222Sdougb      0.
129170222Sdougb    </p>
130153816Sdougb<p>
131170222Sdougb      (5) Set <em class="structfield"><code>pkt.result</code></em> to 0.
132170222Sdougb    </p>
133153816Sdougb<p>
134170222Sdougb      (6) Call <code class="function">lwres_*request_render()</code>,
135170222Sdougb      or marshall in the data using the primitives
136170222Sdougb      such as <code class="function">lwres_packet_render()</code>
137170222Sdougb      and storing the packet data.
138170222Sdougb    </p>
139153816Sdougb<p>
140170222Sdougb      (7) Transmit the resulting buffer.
141170222Sdougb    </p>
142153816Sdougb<p>
143170222Sdougb      (8) Call <code class="function">lwres_*response_parse()</code>
144170222Sdougb      to parse any packets received.
145170222Sdougb    </p>
146153816Sdougb<p>
147170222Sdougb      (9) Verify that the opcode and serial match a request, and process the
148170222Sdougb      packet specific information contained in the body.
149170222Sdougb    </p>
150153816Sdougb</div>
151153816Sdougb<div class="refsect1" lang="en">
152234010Sdougb<a name="id2543575"></a><h2>SERVER-SIDE LOW-LEVEL API CALL FLOW</h2>
153153816Sdougb<p>
154170222Sdougb      When implementing the server side of the lightweight resolver
155170222Sdougb      protocol using the lwres library, a sequence of actions like the
156170222Sdougb      following is typically involved in processing each request packet.
157170222Sdougb    </p>
158153816Sdougb<p>
159170222Sdougb      Note that the same <span class="type">lwres_packet_t</span> is used
160170222Sdougb      in both the <code class="function">_parse()</code> and <code class="function">_render()</code> calls,
161170222Sdougb      with only a few modifications made
162170222Sdougb      to the packet header's contents between uses.  This method is
163170222Sdougb      recommended
164170222Sdougb      as it keeps the serial, opcode, and other fields correct.
165170222Sdougb    </p>
166153816Sdougb<p>
167170222Sdougb      (1) When a packet is received, call <code class="function">lwres_*request_parse()</code> to
168170222Sdougb      unmarshall it.  This returns a <span class="type">lwres_packet_t</span> (also called <code class="varname">pkt</code>, below)
169170222Sdougb      as well as a data specific type, such as <span class="type">lwres_gabnrequest_t</span>.
170170222Sdougb    </p>
171153816Sdougb<p>
172170222Sdougb      (2) Process the request in the data specific type.
173170222Sdougb    </p>
174153816Sdougb<p>
175170222Sdougb      (3) Set the <em class="structfield"><code>pkt.result</code></em>,
176170222Sdougb      <em class="structfield"><code>pkt.recvlength</code></em> as above.  All other fields
177170222Sdougb      can
178170222Sdougb      be left untouched since they were filled in by the <code class="function">*_parse()</code> call
179170222Sdougb      above.  If using <code class="function">lwres_*response_render()</code>,
180170222Sdougb      <em class="structfield"><code>pkt.pktflags</code></em> will be set up
181170222Sdougb      properly.  Otherwise, the <code class="constant">LWRES_LWPACKETFLAG_RESPONSE</code> bit should be
182170222Sdougb      set.
183170222Sdougb    </p>
184153816Sdougb<p>
185170222Sdougb      (4) Call the data specific rendering function, such as
186170222Sdougb      <code class="function">lwres_gabnresponse_render()</code>.
187170222Sdougb    </p>
188153816Sdougb<p>
189170222Sdougb      (5) Send the resulting packet to the client.
190170222Sdougb    </p>
191170222Sdougb<p></p>
192153816Sdougb</div>
193153816Sdougb<div class="refsect1" lang="en">
194234010Sdougb<a name="id2543658"></a><h2>SEE ALSO</h2>
195170222Sdougb<p><span class="citerefentry"><span class="refentrytitle">lwres_gethostent</span>(3)</span>,
196135446Strhodes
197170222Sdougb      <span class="citerefentry"><span class="refentrytitle">lwres_getipnode</span>(3)</span>,
198135446Strhodes
199170222Sdougb      <span class="citerefentry"><span class="refentrytitle">lwres_getnameinfo</span>(3)</span>,
200135446Strhodes
201170222Sdougb      <span class="citerefentry"><span class="refentrytitle">lwres_noop</span>(3)</span>,
202135446Strhodes
203170222Sdougb      <span class="citerefentry"><span class="refentrytitle">lwres_gabn</span>(3)</span>,
204135446Strhodes
205170222Sdougb      <span class="citerefentry"><span class="refentrytitle">lwres_gnba</span>(3)</span>,
206135446Strhodes
207170222Sdougb      <span class="citerefentry"><span class="refentrytitle">lwres_context</span>(3)</span>,
208135446Strhodes
209170222Sdougb      <span class="citerefentry"><span class="refentrytitle">lwres_config</span>(3)</span>,
210135446Strhodes
211170222Sdougb      <span class="citerefentry"><span class="refentrytitle">resolver</span>(5)</span>,
212135446Strhodes
213170222Sdougb      <span class="citerefentry"><span class="refentrytitle">lwresd</span>(8)</span>.
214153816Sdougb
215170222Sdougb    </p>
216153816Sdougb</div>
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