1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
|
<!--
- Copyright (C) 2000, 2001 Internet Software Consortium.
-
- Permission to use, copy, modify, and distribute this software for any
- purpose with or without fee is hereby granted, provided that the above
- copyright notice and this permission notice appear in all copies.
-
- THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM
- DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
- IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL
- INTERNET SOFTWARE CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT,
- INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING
- FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
- NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
- WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
-->
<HTML
><HEAD
><TITLE
>lwres</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.61
"></HEAD
><BODY
CLASS="REFENTRY"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><H1
><A
NAME="AEN1"
>lwres</A
></H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN8"
></A
><H2
>Name</H2
>lwres -- introduction to the lightweight resolver library</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN11"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><A
NAME="AEN12"
></A
><P
></P
><PRE
CLASS="FUNCSYNOPSISINFO"
>#include <lwres/lwres.h></PRE
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN14"
></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
<B
CLASS="COMMAND"
>lwresd</B
>
running on the local host. The resover 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="REFSECT1"
><A
NAME="AEN18"
></A
><H2
>OVERVIEW</H2
><P
>The lwresd library implements multiple name service APIs.
The standard
<TT
CLASS="FUNCTION"
>gethostbyname()</TT
>,
<TT
CLASS="FUNCTION"
>gethostbyaddr()</TT
>,
<TT
CLASS="FUNCTION"
>gethostbyname_r()</TT
>,
<TT
CLASS="FUNCTION"
>gethostbyaddr_r()</TT
>,
<TT
CLASS="FUNCTION"
>getaddrinfo()</TT
>,
<TT
CLASS="FUNCTION"
>getipnodebyname()</TT
>,
and
<TT
CLASS="FUNCTION"
>getipnodebyaddr()</TT
>
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
<TT
CLASS="LITERAL"
>lwres_</TT
>.
To define the standard names, applications must include the
header file
<TT
CLASS="FILENAME"
><lwres/netdb.h></TT
>
which contains macro definitions mapping the standard function names
into
<TT
CLASS="LITERAL"
>lwres_</TT
>
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
<TT
CLASS="FUNCTION"
>lwres_getaddrsbyname()</TT
>
and
<TT
CLASS="FUNCTION"
>lwres_getnamebyaddr()</TT
>.
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
<TT
CLASS="FUNCTION"
>lwres_getaddrsbyname()</TT
>
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
<B
CLASS="COMMAND"
>lwresd</B
>
resolver daemon. The use of this low-level API in clients
and servers is outlined in the following sections.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN38"
></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 <TT
CLASS="VARNAME"
>pkt</TT
> below.</P
><P
>(2) Set <TT
CLASS="STRUCTFIELD"
><I
>pkt.recvlength</I
></TT
> 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
<TT
CLASS="FILENAME"
>lwres.h</TT
>: <TT
CLASS="CONSTANT"
>LWRES_RECVLENGTH = 4096</TT
>.</P
><P
>(3) Set <TT
CLASS="STRUCTFIELD"
><I
>pkt.serial</I
></TT
>
to a unique serial number. This value is echoed
back to the application by the remote server.</P
><P
>(4) Set <TT
CLASS="STRUCTFIELD"
><I
>pkt.pktflags</I
></TT
>. Usually this is set to 0.</P
><P
>(5) Set <TT
CLASS="STRUCTFIELD"
><I
>pkt.result</I
></TT
> to 0.</P
><P
>(6) Call <TT
CLASS="FUNCTION"
>lwres_*request_render()</TT
>,
or marshall in the data using the primitives
such as <TT
CLASS="FUNCTION"
>lwres_packet_render()</TT
>
and storing the packet data.</P
><P
>(7) Transmit the resulting buffer.</P
><P
>(8) Call <TT
CLASS="FUNCTION"
>lwres_*response_parse()</TT
>
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"
><A
NAME="AEN61"
></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 <TT
CLASS="FUNCTION"
>_parse()</TT
> and <TT
CLASS="FUNCTION"
>_render()</TT
> 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 <TT
CLASS="FUNCTION"
>lwres_*request_parse()</TT
> to
unmarshall it. This returns a <SPAN
CLASS="TYPE"
>lwres_packet_t</SPAN
> (also called <TT
CLASS="VARNAME"
>pkt</TT
>, 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 <TT
CLASS="STRUCTFIELD"
><I
>pkt.result</I
></TT
>,
<TT
CLASS="STRUCTFIELD"
><I
>pkt.recvlength</I
></TT
> as above. All other fields can
be left untouched since they were filled in by the <TT
CLASS="FUNCTION"
>*_parse()</TT
> call
above. If using <TT
CLASS="FUNCTION"
>lwres_*response_render()</TT
>,
<TT
CLASS="STRUCTFIELD"
><I
>pkt.pktflags</I
></TT
> will be set up
properly. Otherwise, the <TT
CLASS="CONSTANT"
>LWRES_LWPACKETFLAG_RESPONSE</TT
> bit should be
set.</P
><P
>(4) Call the data specific rendering function, such as
<TT
CLASS="FUNCTION"
>lwres_gabnresponse_render()</TT
>.</P
><P
>(5) Send the resulting packet to the client.</P
><P
></P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN85"
></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
></BODY
></HTML
>
|
