contrib/bind9/lib/lwres/man/lwres.docbook

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  22
  23 <refentry>
  24 <refentryinfo>
  25
  26 <date>Jun 30, 2000</date>
  27 </refentryinfo>
  28 <refmeta>
  29 <refentrytitle>lwres</refentrytitle>
  30 <manvolnum>3</manvolnum>
  31 <refmiscinfo>BIND9</refmiscinfo>
  32 </refmeta>
  33
  34   <docinfo>
  35     <copyright>
  36       <year>2004</year>
  37       <year>2005</year>
  38       <holder>Internet Systems Consortium, Inc. ("ISC")</holder>
  39     </copyright>
  40     <copyright>
  41       <year>2000</year>
  42       <year>2001</year>
  43       <holder>Internet Software Consortium.</holder>
  44     </copyright>
  45   </docinfo>
  46
  47 <refnamediv>
  48 <refname>lwres</refname>
  49 <refpurpose>introduction to the lightweight resolver library</refpurpose>
  50 </refnamediv>
  51
  52 <refsynopsisdiv>
  53 <funcsynopsis>
  54 <funcsynopsisinfo>#include &lt;lwres/lwres.h&gt;</funcsynopsisinfo>
  55 </funcsynopsis>
  56 </refsynopsisdiv>
  57
  58 <refsect1>
  59 <title>DESCRIPTION</title>
  60 <para>
  61 The BIND 9 lightweight resolver library is a simple, name service
  62 independent stub resolver library.  It provides hostname-to-address
  63 and address-to-hostname lookup services to applications by
  64 transmitting lookup requests to a resolver daemon
  65 <command>lwresd</command>
  66 running on the local host. The resover daemon performs the
  67 lookup using the DNS or possibly other name service protocols,
  68 and returns the results to the application through the library.
  69 The library and resolver daemon communicate using a simple
  70 UDP-based protocol.
  71 </para>
  72 </refsect1>
  73
  74 <refsect1>
  75 <title>OVERVIEW</title>
  76 <para>
  77 The lwresd library implements multiple name service APIs.
  78 The standard
  79 <function>gethostbyname()</function>,
  80 <function>gethostbyaddr()</function>,
  81 <function>gethostbyname_r()</function>,
  82 <function>gethostbyaddr_r()</function>,
  83 <function>getaddrinfo()</function>,
  84 <function>getipnodebyname()</function>,
  85 and
  86 <function>getipnodebyaddr()</function>
  87 functions are all supported.  To allow the lwres library to coexist
  88 with system libraries that define functions of the same name,
  89 the library defines these functions with names prefixed by
  90 <literal>lwres_</literal>.
  91 To define the standard names, applications must include the
  92 header file
  93 <filename>&lt;lwres/netdb.h&gt;</filename>
  94 which contains macro definitions mapping the standard function names
  95 into
  96 <literal>lwres_</literal>
  97 prefixed ones.  Operating system vendors who integrate the lwres
  98 library into their base distributions should rename the functions
  99 in the library proper so that the renaming macros are not needed.
 100 </para>
 101 <para>
 102 The library also provides a native API consisting of the functions
 103 <function>lwres_getaddrsbyname()</function>
 104 and
 105 <function>lwres_getnamebyaddr()</function>.
 106 These may be called by applications that require more detailed
 107 control over the lookup process than the standard functions
 108 provide.
 109 </para>
 110 <para>
 111 In addition to these name service independent address lookup
 112 functions, the library implements a new, experimental API
 113 for looking up arbitrary DNS resource records, using the
 114 <function>lwres_getaddrsbyname()</function>
 115 function.
 116 </para>
 117 <para>
 118 Finally, there is a low-level API for converting lookup
 119 requests and responses to and from raw lwres protocol packets.
 120 This API can be used by clients requiring nonblocking operation,
 121 and is also used when implementing the server side of the lwres
 122 protocol, for example in the
 123 <command>lwresd</command>
 124 resolver daemon.  The use of this low-level API in clients
 125 and servers is outlined in the following sections.
 126 </para>
 127 </refsect1>
 128 <refsect1>
 129 <title>CLIENT-SIDE LOW-LEVEL API CALL FLOW</title>
 130 <para>
 131 When a client program wishes to make an lwres request using the
 132 native low-level API, it typically performs the following
 133 sequence of actions.
 134 </para>
 135 <para>
 136 (1) Allocate or use an existing <type>lwres_packet_t</type>,
 137 called <varname>pkt</varname> below.
 138 </para>
 139 <para>
 140 (2) Set <structfield>pkt.recvlength</structfield> to the maximum length we will accept.
 141 This is done so the receiver of our packets knows how large our receive
 142 buffer is.  The "default" is a constant in
 143 <filename>lwres.h</filename>: <constant>LWRES_RECVLENGTH = 4096</constant>.
 144 </para>
 145 <para>
 146 (3) Set <structfield>pkt.serial</structfield>
 147 to a unique serial number.  This value is echoed
 148 back to the application by the remote server.
 149 </para>
 150 <para>
 151 (4) Set <structfield>pkt.pktflags</structfield>.  Usually this is set to 0.
 152 </para>
 153 <para>
 154 (5) Set <structfield>pkt.result</structfield> to 0.
 155 </para>
 156 <para>
 157 (6) Call <function>lwres_*request_render()</function>,
 158 or marshall in the data using the primitives
 159 such as <function>lwres_packet_render()</function>
 160 and storing the packet data.
 161 </para>
 162 <para>
 163 (7) Transmit the resulting buffer.
 164 </para>
 165 <para>
 166 (8) Call <function>lwres_*response_parse()</function>
 167 to parse any packets received.
 168 </para>
 169 <para>
 170 (9) Verify that the opcode and serial match a request, and process the
 171 packet specific information contained in the body.
 172 </para>
 173 </refsect1>
 174 <refsect1>
 175 <title>SERVER-SIDE LOW-LEVEL API CALL FLOW</title>
 176 <para>
 177 When implementing the server side of the lightweight resolver
 178 protocol using the lwres library, a sequence of actions like the
 179 following is typically involved in processing each request packet.
 180 </para>
 181 <para>
 182 Note that the same <type>lwres_packet_t</type> is used
 183 in both the <function>_parse()</function> and <function>_render()</function> calls,
 184 with only a few modifications made
 185 to the packet header's contents between uses.  This method is recommended
 186 as it keeps the serial, opcode, and other fields correct.
 187 </para>
 188 <para>
 189 (1) When a packet is received, call <function>lwres_*request_parse()</function> to
 190 unmarshall it.  This returns a <type>lwres_packet_t</type> (also called <varname>pkt</varname>, below)
 191 as well as a data specific type, such as <type>lwres_gabnrequest_t</type>.
 192 </para>
 193 <para>
 194 (2) Process the request in the data specific type.
 195 </para>
 196 <para>
 197 (3) Set the <structfield>pkt.result</structfield>,
 198 <structfield>pkt.recvlength</structfield> as above.  All other fields can
 199 be left untouched since they were filled in by the <function>*_parse()</function> call
 200 above.  If using <function>lwres_*response_render()</function>,
 201 <structfield>pkt.pktflags</structfield> will be set up
 202 properly.  Otherwise, the <constant>LWRES_LWPACKETFLAG_RESPONSE</constant> bit should be
 203 set.
 204 </para>
 205 <para>
 206 (4) Call the data specific rendering function, such as
 207 <function>lwres_gabnresponse_render()</function>.
 208 </para>
 209 <para>
 210 (5) Send the resulting packet to the client.
 211 </para>
 212 <para>
 213 </para>
 214 </refsect1>
 215 <refsect1>
 216 <title>SEE ALSO</title>
 217 <para>
 218 <citerefentry>
 219 <refentrytitle>lwres_gethostent</refentrytitle><manvolnum>3</manvolnum>
 220 </citerefentry>,
 221
 222 <citerefentry>
 223 <refentrytitle>lwres_getipnode</refentrytitle><manvolnum>3</manvolnum>
 224 </citerefentry>,
 225
 226 <citerefentry>
 227 <refentrytitle>lwres_getnameinfo</refentrytitle><manvolnum>3</manvolnum>
 228 </citerefentry>,
 229
 230 <citerefentry>
 231 <refentrytitle>lwres_noop</refentrytitle><manvolnum>3</manvolnum>
 232 </citerefentry>,
 233
 234 <citerefentry>
 235 <refentrytitle>lwres_gabn</refentrytitle><manvolnum>3</manvolnum>
 236 </citerefentry>,
 237
 238 <citerefentry>
 239 <refentrytitle>lwres_gnba</refentrytitle><manvolnum>3</manvolnum>
 240 </citerefentry>,
 241
 242 <citerefentry>
 243 <refentrytitle>lwres_context</refentrytitle><manvolnum>3</manvolnum>
 244 </citerefentry>,
 245
 246 <citerefentry>
 247 <refentrytitle>lwres_config</refentrytitle><manvolnum>3</manvolnum>
 248 </citerefentry>,
 249
 250 <citerefentry>
 251 <refentrytitle>resolver</refentrytitle><manvolnum>5</manvolnum>
 252 </citerefentry>,
 253
 254 <citerefentry>
 255 <refentrytitle>lwresd</refentrytitle><manvolnum>8</manvolnum>
 256 </citerefentry>.
 257
 258 </para>
 259 </refsect1>
 260 </refentry>