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32 .\" @(#)resolver.3 8.1 (Berkeley) 6/4/93
33 .\" $FreeBSD: src/lib/libc/net/resolver.3,v 1.21 2001/10/01 16:08:56 ru Exp $
34 .\"
35 .Dd June 4, 1993
36 .Dt RESOLVER 3
37 .Os
38 .Sh NAME
39 .Nm res_query ,
40 .Nm res_search ,
41 .Nm res_mkquery ,
42 .Nm res_send ,
43 .Nm res_init ,
44 .Nm dn_comp ,
45 .Nm dn_expand ,
46 .Nm dn_skipname ,
47 .Nm ns_get16 ,
48 .Nm ns_get32 ,
49 .Nm ns_put16 ,
50 .Nm ns_put32
51 .Nd resolver routines
52 .Sh LIBRARY
53 .Lb libresolv
54 .Sh SYNOPSIS
55 .In sys/types.h
56 .In netinet/in.h
57 .In arpa/nameser.h
58 .In resolv.h
59 .Ft int
60 .Fo res_query
61 .Fa "const char *dname"
62 .Fa "int class"
63 .Fa "int type"
64 .Fa "u_char *answer"
65 .Fa "int anslen"
66 .Fc
67 .Ft int
68 .Fo res_search
69 .Fa "const char *dname"
70 .Fa "int class"
71 .Fa "int type"
72 .Fa "u_char *answer"
73 .Fa "int anslen"
74 .Fc
75 .Ft int
76 .Fo res_mkquery
77 .Fa "int op"
78 .Fa "const char *dname"
79 .Fa "int class"
80 .Fa "int type"
81 .Fa "const u_char *data"
82 .Fa "int datalen"
83 .Fa "const u_char *newrr_in"
84 .Fa "u_char *buf"
85 .Fa "int buflen"
86 .Fc
87 .Ft int
88 .Fo res_send
89 .Fa "const u_char *msg"
90 .Fa "int msglen"
91 .Fa "u_char *answer"
92 .Fa "int anslen"
93 .Fc
94 .Ft int
95 .Fn res_init
96 .Ft int
97 .Fo dn_comp
98 .Fa "const char *exp_dn"
99 .Fa "u_char *comp_dn"
100 .Fa "int length"
101 .Fa "u_char **dnptrs"
102 .Fa "u_char **lastdnptr"
103 .Fc
104 .Ft int
105 .Fo dn_expand
106 .Fa "const u_char *msg"
107 .Fa "const u_char *eomorig"
108 .Fa "const u_char *comp_dn"
109 .Fa "char *exp_dn"
110 .Fa "int length"
111 .Fc
112 .Ft int
113 .Fn dn_skipname "const u_char *comp_dn" "const u_char *eom"
114 .Ft u_int
115 .Fn ns_get16 "const u_char *src"
116 .Ft u_long
117 .Fn ns_get32 "const u_char *src"
118 .Ft void
119 .Fn ns_put16 "u_int src" "u_char *dst"
120 .Ft void
121 .Fn ns_put32 "u_long src" "u_char *dst"
122 .Sh DESCRIPTION
123 These routines are used for making, sending and interpreting
124 query and reply messages with Internet domain name servers.
125 .Pp
126 Global configuration and state information that is used by the
127 resolver routines is kept in the structure
128 .Em _res .
129 Most of the values have reasonable defaults and can be ignored.
130 Options
131 stored in
132 .Em _res.options
133 are defined in
134 .Pa resolv.h
135 and are as follows.
136 Options are stored as a simple bit mask containing the bitwise ``or''
137 of the options enabled.
138 .Bl -tag -width RES_USE_INET6
139 .It Dv RES_INIT
140 True if the initial name server address and default domain name are
141 initialized (i.e.,
142 .Fn res_init
143 has been called).
144 .It Dv RES_DEBUG
145 Print debugging messages.
146 .It Dv RES_AAONLY
147 Accept authoritative answers only.
148 With this option,
149 .Fn res_send
150 should continue until it finds an authoritative answer or finds an error.
151 Currently this is not implemented.
152 .It Dv RES_USEVC
153 Use
154 .Tn TCP
155 connections for queries instead of
156 .Tn UDP
157 datagrams.
158 .It Dv RES_STAYOPEN
159 Used with
160 .Dv RES_USEVC
161 to keep the
162 .Tn TCP
163 connection open between
164 queries.
165 This is useful only in programs that regularly do many queries.
166 .Tn UDP
167 should be the normal mode used.
168 .It Dv RES_IGNTC
169 Unused currently (ignore truncation errors, i.e., don't retry with
170 .Tn TCP ) .
171 .It Dv RES_RECURSE
172 Set the recursion-desired bit in queries.
173 This is the default.
174 .Pf ( Fn res_send
175 does not do iterative queries and expects the name server
176 to handle recursion.)
177 .It Dv RES_DEFNAMES
178 If set,
179 .Fn res_search
180 will append the default domain name to single-component names
181 (those that do not contain a dot).
182 This option is enabled by default.
183 .It Dv RES_DNSRCH
184 If this option is set,
185 .Fn res_search
186 will search for host names in the current domain and in parent domains; see
187 .Xr hostname 7 .
188 This is used by the standard host lookup routine
189 .Xr gethostbyname 3 .
190 This option is enabled by default.
191 .It Dv RES_NOALIASES
192 This option turns off the user level aliasing feature controlled by the
193 .Dq Ev HOSTALIASES
194 environment variable. Network daemons should set this option.
195 .It Dv RES_USE_INET6
196 Enables support for IPv6-only applications.
197 This causes IPv4 addresses to be returned as an IPv4 mapped address.
198 For example,
199 .Li 10.1.1.1
200 will be returned as
201 .Li ::ffff:10.1.1.1 .
202 The option is meaningful with certain kernel configuration only.
203 .It Dv RES_USE_EDNS0
204 Enables support for OPT pseudo-RR for EDNS0 extension.
205 With the option, resolver code will attach OPT pseudo-RR into DNS queries,
206 to inform of our receive buffer size.
207 The option will allow DNS servers to take advantage of non-default receive
208 buffer size, and to send larger replies.
209 DNS query packets with EDNS0 extension is not compatible with
210 non-EDNS0 DNS servers.
211 .El
212 .Pp
213 The
214 .Fn res_init
215 routine
216 reads the configuration file (if any; see
217 .Xr resolver 5 )
218 to get the default domain name,
219 search list and
220 the Internet address of the local name server(s).
221 If no server is configured, the host running
222 the resolver is tried.
223 The current domain name is defined by the hostname
224 if not specified in the configuration file;
225 it can be overridden by the environment variable
226 .Ev LOCALDOMAIN .
227 This environment variable may contain several blank-separated
228 tokens if you wish to override the
229 .Em "search list"
230 on a per-process basis. This is similar to the
231 .Em search
232 command in the configuration file.
233 Another environment variable
234 .Dq Ev RES_OPTIONS
235 can be set to
236 override certain internal resolver options which are otherwise
237 set by changing fields in the
238 .Em _res
239 structure or are inherited from the configuration file's
240 .Em options
241 command. The syntax of the
242 .Dq Ev RES_OPTIONS
243 environment variable is explained in
244 .Xr resolver 5 .
245 Initialization normally occurs on the first call
246 to one of the following routines.
247 .Pp
248 The
249 .Fn res_query
250 function provides an interface to the server query mechanism.
251 It constructs a query, sends it to the local server,
252 awaits a response, and makes preliminary checks on the reply.
253 The query requests information of the specified
254 .Fa type
255 and
256 .Fa class
257 for the specified fully-qualified domain name
258 .Fa dname .
259 The reply message is left in the
260 .Fa answer
261 buffer with length
262 .Fa anslen
263 supplied by the caller. Constants for
264 .Fa type
265 and
266 .Fa class
267 are defined in
268 .Aq Pa arpa/nameser.h .
269 .Pp
270 The
271 .Fn res_search
272 routine makes a query and awaits a response like
273 .Fn res_query ,
274 but in addition, it implements the default and search rules
275 controlled by the
276 .Dv RES_DEFNAMES
277 and
278 .Dv RES_DNSRCH
279 options.
280 It returns the first successful reply.
281 .Pp
282 The remaining routines are lower-level routines used by
283 .Fn res_query .
284 The
285 .Fn res_mkquery
286 function
287 constructs a standard query message and places it in
288 .Fa buf .
289 It returns the size of the query, or \-1 if the query is
290 larger than
291 .Fa buflen .
292 The query type
293 .Fa op
294 is usually
295 .Dv QUERY ,
296 but can be any of the query types defined in
297 .Aq Pa arpa/nameser.h .
298 The domain name for the query is given by
299 .Fa dname .
300 .Fa Newrr
301 is currently unused but is intended for making update messages.
302 .Pp
303 The
304 .Fn res_send
305 routine
306 sends a pre-formatted query and returns an answer.
307 It will call
308 .Fn res_init
309 if
310 .Dv RES_INIT
311 is not set, send the query to the local name server, and
312 handle timeouts and retries.
313 The length of the reply message is returned, or
314 \-1 if there were errors.
315 .Pp
316 The
317 .Fn dn_comp
318 function
319 compresses the domain name
320 .Fa exp_dn
321 and stores it in
322 .Fa comp_dn .
323 The size of the compressed name is returned or \-1 if there were errors.
324 The size of the array pointed to by
325 .Fa comp_dn
326 is given by
327 .Fa length .
328 The compression uses
329 an array of pointers
330 .Fa dnptrs
331 to previously-compressed names in the current message.
332 The first pointer points to
333 the beginning of the message and the list ends with
334 .Dv NULL .
335 The limit to the array is specified by
336 .Fa lastdnptr .
337 A side effect of
338 .Fn dn_comp
339 is to update the list of pointers for
340 labels inserted into the message
341 as the name is compressed.
342 If
343 .Em dnptr
344 is
345 .Dv NULL ,
346 names are not compressed.
347 If
348 .Fa lastdnptr
349 is
350 .Dv NULL ,
351 the list of labels is not updated.
352 .Pp
353 The
354 .Fn dn_expand
355 entry
356 expands the compressed domain name
357 .Fa comp_dn
358 to a full domain name.
359 The compressed name is contained in a query or reply message;
360 .Fa msg
361 is a pointer to the beginning of the message.
362 The uncompressed name is placed in the buffer indicated by
363 .Fa exp_dn
364 which is of size
365 .Fa length .
366 The size of compressed name is returned or \-1 if there was an error.
367 .Pp
368 The
369 .Fn dn_skipname
370 function skips over a compressed domain name, which starts at a location
371 pointed to by
372 .Fa comp_dn .
373 The compressed name is contained in a query or reply message;
374 .Fa eom
375 is a pointer to the end of the message.
376 The size of compressed name is returned or \-1 if there was
377 an error.
378 .Pp
379 The
380 .Fn ns_get16
381 function gets a 16-bit quantity from a buffer pointed to by
382 .Fa src .
383 .Pp
384 The
385 .Fn ns_get32
386 function gets a 32-bit quantity from a buffer pointed to by
387 .Fa src .
388 .Pp
389 The
390 .Fn ns_put16
391 function puts a 16-bit quantity
392 .Fa src
393 to a buffer pointed to by
394 .Fa dst .
395 .Pp
396 The
397 .Fn ns_put32
398 function puts a 32-bit quantity
399 .Fa src
400 to a buffer pointed to by
401 .Fa dst .
402 .Sh FILES
403 .Bl -tag -width /etc/resolv.conf
404 .It Pa /etc/resolv.conf
405 The configuration file,
406 see
407 .Xr resolver 5 .
408 .El
409 .Sh SEE ALSO
410 .Xr gethostbyname 3 ,
411 .Xr resolver 5 ,
412 .Xr hostname 7 ,
413 .Xr named 8
414 .Pp
415 .%T RFC1032 ,
416 .%T RFC1033 ,
417 .%T RFC1034 ,
418 .%T RFC1035 ,
419 .%T RFC974
420 .Rs
421 .%T "Name Server Operations Guide for BIND"
422 .Re
423 .Sh HISTORY
424 The
425 .Nm
426 function appeared in
427 .Bx 4.3 .