summaryrefslogtreecommitdiffstats
path: root/lib/libc/net/resolver.3
blob: 83167b28712d20e6d10e7db0a6abff2b6669f553 (plain)
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
.\" Copyright (c) 1985, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)resolver.3	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt RESOLVER 3
.Os BSD 4.3
.Sh NAME
.Nm res_query ,
.Nm res_search ,
.Nm res_mkquery ,
.Nm res_send ,
.Nm res_init ,
.Nm dn_comp ,
.Nm dn_expand
.Nd resolver routines
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <netinet/in.h>
.Fd #include <arpa/nameser.h>
.Fd #include <resolv.h>
.Ft int
.Fo res_query
.Fa "const char *dname"
.Fa "int class"
.Fa "int type"
.Fa "u_char *answer"
.Fa "int anslen"
.Fc
.Ft int
.Fo res_search
.Fa "const char *dname"
.Fa "int class"
.Fa "int type"
.Fa "u_char *answer"
.Fa "int anslen"
.Fc
.Ft int
.Fo res_mkquery
.Fa "int op"
.Fa "const char *dname"
.Fa "int class"
.Fa "int type"
.Fa "const u_char *data"
.Fa "int datalen"
.Fa "const u_char *newrr_in"
.Fa "u_char *buf"
.Fa "int buflen"
.Fc
.Ft int
.Fo res_send
.Fa "const u_char *msg"
.Fa "int msglen"
.Fa "u_char *answer"
.Fa "int anslen"
.Fc
.Ft int
.Fn res_init 
.Fo dn_comp
.Fa "const char *exp_dn"
.Fa "u_char *comp_dn"
.Fa "int length"
.Fa "u_char **dnptrs"
.Fa "u_char **lastdnptr"
.Fc
.Ft int
.Fo dn_expand
.Fa "const u_char *msg"
.Fa "const u_char *eomorig"
.Fa "const u_char *comp_dn"
.Fa "char *exp_dn"
.Fa "int length"
.Fc
.Sh DESCRIPTION
These routines are used for making, sending and interpreting
query and reply messages with Internet domain name servers.
.Pp
Global configuration and state information that is used by the
resolver routines is kept in the structure
.Em _res .
Most of the values have reasonable defaults and can be ignored.
Options
stored in
.Em _res.options
are defined in
.Pa resolv.h
and are as follows.
Options are stored as a simple bit mask containing the bitwise ``or''
of the options enabled.
.Bl -tag -width RES_DEFNAMES
.It Dv RES_INIT
True if the initial name server address and default domain name are
initialized (i.e.,
.Fn res_init
has been called).
.It Dv RES_DEBUG
Print debugging messages.
.It Dv RES_AAONLY
Accept authoritative answers only.
With this option,
.Fn res_send
should continue until it finds an authoritative answer or finds an error.
Currently this is not implemented.
.It Dv RES_USEVC
Use
.Tn TCP
connections for queries instead of
.Tn UDP
datagrams.
.It Dv RES_STAYOPEN
Used with
.Dv RES_USEVC
to keep the
.Tn TCP
connection open between
queries.
This is useful only in programs that regularly do many queries.
.Tn UDP
should be the normal mode used.
.It Dv RES_IGNTC
Unused currently (ignore truncation errors, i.e., don't retry with
.Tn TCP ) .
.It Dv RES_RECURSE
Set the recursion-desired bit in queries.
This is the default.
.Pf ( Fn res_send
does not do iterative queries and expects the name server
to handle recursion.)
.It Dv RES_DEFNAMES
If set,
.Fn res_search
will append the default domain name to single-component names
(those that do not contain a dot).
This option is enabled by default.
.It Dv RES_DNSRCH
If this option is set,
.Fn res_search
will search for host names in the current domain and in parent domains; see
.Xr hostname 7 .
This is used by the standard host lookup routine
.Xr gethostbyname 3 .
This option is enabled by default.
.It Dv RES_NOALIASES
This option turns off the user level aliasing feature controlled by the
.Dq Ev HOSTALIASES
environment variable.  Network daemons should set this option.
.El
.Pp
The
.Fn res_init
routine
reads the configuration file (if any; see
.Xr resolver 5 )
to get the default domain name,
search list and
the Internet address of the local name server(s).
If no server is configured, the host running
the resolver is tried.
The current domain name is defined by the hostname
if not specified in the configuration file;
it can be overridden by the environment variable
.Ev LOCALDOMAIN .
This environment variable may contain several blank-separated
tokens if you wish to override the
.Em "search list"
on a per-process basis.  This is similar to the
.Em search
command in the configuration file.
Another environment variable (
.Dq Ev RES_OPTIONS
can be set to
override certain internal resolver options which are otherwise
set by changing fields in the
.Em _res
structure or are inherited from the configuration file's
.Em options
command.  The syntax of the
.Dq Ev RES_OPTIONS
environment variable is explained in
.Xr resolver 5 .
Initialization normally occurs on the first call
to one of the following routines.
.Pp
The
.Fn res_query
function provides an interface to the server query mechanism.
It constructs a query, sends it to the local server,
awaits a response, and makes preliminary checks on the reply.
The query requests information of the specified
.Fa type
and
.Fa class
for the specified fully-qualified domain name
.Fa dname .
The reply message is left in the
.Fa answer
buffer with length
.Fa anslen
supplied by the caller.
.Pp
The
.Fn res_search
routine makes a query and awaits a response like
.Fn res_query ,
but in addition, it implements the default and search rules
controlled by the
.Dv RES_DEFNAMES
and
.Dv RES_DNSRCH
options.
It returns the first successful reply.
.Pp
The remaining routines are lower-level routines used by
.Fn res_query .
The
.Fn res_mkquery
function
constructs a standard query message and places it in
.Fa buf .
It returns the size of the query, or \-1 if the query is
larger than
.Fa buflen .
The query type
.Fa op
is usually
.Dv QUERY ,
but can be any of the query types defined in
.Aq Pa arpa/nameser.h .
The domain name for the query is given by
.Fa dname .
.Fa Newrr
is currently unused but is intended for making update messages.
.Pp
The
.Fn res_send
routine
sends a pre-formatted query and returns an answer.
It will call
.Fn res_init
if
.Dv RES_INIT
is not set, send the query to the local name server, and
handle timeouts and retries.
The length of the reply message is returned, or
\-1 if there were errors.
.Pp
The
.Fn dn_comp
function
compresses the domain name
.Fa exp_dn
and stores it in
.Fa comp_dn .
The size of the compressed name is returned or \-1 if there were errors.
The size of the array pointed to by
.Fa comp_dn
is given by
.Fa length .
The compression uses
an array of pointers
.Fa dnptrs
to previously-compressed names in the current message.
The first pointer points to
the beginning of the message and the list ends with
.Dv NULL .
The limit to the array is specified by
.Fa lastdnptr .
A side effect of
.Fn dn_comp
is to update the list of pointers for
labels inserted into the message
as the name is compressed.
If
.Em dnptr
is
.Dv NULL, names are not compressed.
If
.Fa lastdnptr
is
.Dv NULL ,
the list of labels is not updated.
.Pp
The
.Fn dn_expand
entry
expands the compressed domain name
.Fa comp_dn
to a full domain name
The compressed name is contained in a query or reply message;
.Fa msg
is a pointer to the beginning of the message.
The uncompressed name is placed in the buffer indicated by
.Fa exp_dn
which is of size
.Fa length .
The size of compressed name is returned or \-1 if there was an error.
.Sh FILES
.Bl -tag -width Pa
/etc/resolv.conf
The configuration file
see
.Xr resolver 5 .
.El
.Sh SEE ALSO
.Xr gethostbyname 3 ,
.Xr resolver 5 ,
.Xr hostname 7 ,
.Xr named 8
.Pp
.%T RFC1032 ,
.%T RFC1033 ,
.%T RFC1034 ,
.%T RFC1035 ,
.%T RFC974
.Rs
.%T "Name Server Operations Guide for BIND"
.Re
.Sh HISTORY
The
.Nm
function appeared in 
.Bx 4.3 .
OpenPOWER on IntegriCloud