/contrib/bind9/lib/lwres/man/lwres.docbook
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1<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" 2 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" 3 [<!ENTITY mdash "—">]> 4<!-- 5 - Copyright (C) 2004, 2005, 2007 Internet Systems Consortium, Inc. ("ISC") 6 - Copyright (C) 2000, 2001 Internet Software Consortium. 7 - 8 - Permission to use, copy, modify, and/or distribute this software for any 9 - purpose with or without fee is hereby granted, provided that the above 10 - copyright notice and this permission notice appear in all copies. 11 - 12 - THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH 13 - REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY 14 - AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT, 15 - INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM 16 - LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE 17 - OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR 18 - PERFORMANCE OF THIS SOFTWARE. 19--> 20 21<!-- $Id: lwres.docbook,v 1.10 2007/06/18 23:47:51 tbox Exp $ --> 22<refentry> 23 24 <refentryinfo> 25 <date>Jun 30, 2000</date> 26 </refentryinfo> 27 28 <refmeta> 29 <refentrytitle>lwres</refentrytitle> 30 <manvolnum>3</manvolnum> 31 <refmiscinfo>BIND9</refmiscinfo> 32 </refmeta> 33 <refnamediv> 34 <refname>lwres</refname> 35 <refpurpose>introduction to the lightweight resolver library</refpurpose> 36 </refnamediv> 37 38 <docinfo> 39 <copyright> 40 <year>2004</year> 41 <year>2005</year> 42 <year>2007</year> 43 <holder>Internet Systems Consortium, Inc. ("ISC")</holder> 44 </copyright> 45 <copyright> 46 <year>2000</year> 47 <year>2001</year> 48 <holder>Internet Software Consortium.</holder> 49 </copyright> 50 </docinfo> 51 52 <refsynopsisdiv> 53 <funcsynopsis> 54<funcsynopsisinfo>#include <lwres/lwres.h></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><lwres/netdb.h></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 141 we will accept. 142 This is done so the receiver of our packets knows how large our receive 143 buffer is. The "default" is a constant in 144 <filename>lwres.h</filename>: <constant>LWRES_RECVLENGTH = 4096</constant>. 145 </para> 146 <para> 147 (3) Set <structfield>pkt.serial</structfield> 148 to a unique serial number. This value is echoed 149 back to the application by the remote server. 150 </para> 151 <para> 152 (4) Set <structfield>pkt.pktflags</structfield>. Usually this is set to 153 0. 154 </para> 155 <para> 156 (5) Set <structfield>pkt.result</structfield> to 0. 157 </para> 158 <para> 159 (6) Call <function>lwres_*request_render()</function>, 160 or marshall in the data using the primitives 161 such as <function>lwres_packet_render()</function> 162 and storing the packet data. 163 </para> 164 <para> 165 (7) Transmit the resulting buffer. 166 </para> 167 <para> 168 (8) Call <function>lwres_*response_parse()</function> 169 to parse any packets received. 170 </para> 171 <para> 172 (9) Verify that the opcode and serial match a request, and process the 173 packet specific information contained in the body. 174 </para> 175 </refsect1> 176 <refsect1> 177 <title>SERVER-SIDE LOW-LEVEL API CALL FLOW</title> 178 <para> 179 When implementing the server side of the lightweight resolver 180 protocol using the lwres library, a sequence of actions like the 181 following is typically involved in processing each request packet. 182 </para> 183 <para> 184 Note that the same <type>lwres_packet_t</type> is used 185 in both the <function>_parse()</function> and <function>_render()</function> calls, 186 with only a few modifications made 187 to the packet header's contents between uses. This method is 188 recommended 189 as it keeps the serial, opcode, and other fields correct. 190 </para> 191 <para> 192 (1) When a packet is received, call <function>lwres_*request_parse()</function> to 193 unmarshall it. This returns a <type>lwres_packet_t</type> (also called <varname>pkt</varname>, below) 194 as well as a data specific type, such as <type>lwres_gabnrequest_t</type>. 195 </para> 196 <para> 197 (2) Process the request in the data specific type. 198 </para> 199 <para> 200 (3) Set the <structfield>pkt.result</structfield>, 201 <structfield>pkt.recvlength</structfield> as above. All other fields 202 can 203 be left untouched since they were filled in by the <function>*_parse()</function> call 204 above. If using <function>lwres_*response_render()</function>, 205 <structfield>pkt.pktflags</structfield> will be set up 206 properly. Otherwise, the <constant>LWRES_LWPACKETFLAG_RESPONSE</constant> bit should be 207 set. 208 </para> 209 <para> 210 (4) Call the data specific rendering function, such as 211 <function>lwres_gabnresponse_render()</function>. 212 </para> 213 <para> 214 (5) Send the resulting packet to the client. 215 </para> 216 <para></para> 217 </refsect1> 218 <refsect1> 219 <title>SEE ALSO</title> 220 <para><citerefentry> 221 <refentrytitle>lwres_gethostent</refentrytitle><manvolnum>3</manvolnum> 222 </citerefentry>, 223 224 <citerefentry> 225 <refentrytitle>lwres_getipnode</refentrytitle><manvolnum>3</manvolnum> 226 </citerefentry>, 227 228 <citerefentry> 229 <refentrytitle>lwres_getnameinfo</refentrytitle><manvolnum>3</manvolnum> 230 </citerefentry>, 231 232 <citerefentry> 233 <refentrytitle>lwres_noop</refentrytitle><manvolnum>3</manvolnum> 234 </citerefentry>, 235 236 <citerefentry> 237 <refentrytitle>lwres_gabn</refentrytitle><manvolnum>3</manvolnum> 238 </citerefentry>, 239 240 <citerefentry> 241 <refentrytitle>lwres_gnba</refentrytitle><manvolnum>3</manvolnum> 242 </citerefentry>, 243 244 <citerefentry> 245 <refentrytitle>lwres_context</refentrytitle><manvolnum>3</manvolnum> 246 </citerefentry>, 247 248 <citerefentry> 249 <refentrytitle>lwres_config</refentrytitle><manvolnum>3</manvolnum> 250 </citerefentry>, 251 252 <citerefentry> 253 <refentrytitle>resolver</refentrytitle><manvolnum>5</manvolnum> 254 </citerefentry>, 255 256 <citerefentry> 257 <refentrytitle>lwresd</refentrytitle><manvolnum>8</manvolnum> 258 </citerefentry>. 259 260 </para> 261 </refsect1> 262</refentry><!-- 263 - Local variables: 264 - mode: sgml 265 - End: 266-->