1resolver(3RESOLV) Resolver Library Functions resolver(3RESOLV)
2
6 resolver, res_ninit, fp_resstat, res_hostalias, res_nquery,
7 res_nsearch, res_nquerydomain, res_nmkquery, res_nsend, res_nclose,
8 res_nsendsigned, dn_comp, dn_expand, hstrerror, res_init, res_query,
9 res_search, res_mkquery, res_send, herror, res_getservers, res_set‐
10 servers, res_ndestroy - resolver routines
11
13 BIND 8.2.2 Interfaces
14 cc [ flag ... ] file ... -lresolv -lsocket -lnsl [ library ... ]
17 #include <sys/types.h>
18 #include <netinet/in.h>
19 #include <arpa/nameser.h>
20 #include <resolv.h>
21 #include <netdb.h>
22 int res_ninit(res_state statp);
24 void res_ndestroy(res_state statp);
27 void fp_resstat(const res_state statp, FILE *fp);
30 const char *res_hostalias(const res_state statp, const char *name,
33 char * name, char *buf, size_tbuflen);
34 int res_nquery(res_state statp, const char *dname, int class, int type,
37 u_char *answer, int datalen, int anslen);
38 int res_nsearch(res_state statp, const char *dname, int class, int type,
41 u_char *answer, int anslen);
42 int res_nquerydomain(res_state statp, const char *name,
45 const char *domain, int class, int type,
46 u_char *answer, int anslen);
47 int res_nmkquery(res_state statp, int op, const char *dname, int class,
50 int type, u_char *answer, int datalen,
51 int anslen);
52 int res_nsend(res_state statp, const u_char *msg, int msglen,
55 u_char *answer, int anslen);
56 void res_nclose(res_state statp);
59 int res_snendsigned(res_state statp, const u_char *msg,
62 int msglen, ns_tsig_key *key, u_char *answer, int anslen);
63 int dn_comp(const char *exp_dn, u_char *comp_dn, int length,
66 u_char **dnptrs, **lastdnptr);
67 int dn_expand(const u_char *msg, *eomorig, *comp_dn, char *exp_dn,
70 int length);
71 const char *hstrerror(int err);
74 void res_setservers(res_state statp, const union res_sockaddr_union *set,
77 int cnt);
78 int res_getservers(res_state statp, union res_sockaddr_union *set,
81 int cnt);
82 Deprecated Interfaces
85 cc [ flag ... ] file ... -lresolv -lsocket -lnsl [ library ... ]
88 #include <sys/types.h>
89 #include <netinet/in.h>
90 #include <arpa/nameser.h>
91 #include <resolv.h>
92 #include <netdb.h>
93 int res_init(void)
95 int res_query(const char *dname, int class,
98 int type, u_char *answer,
99 int anslen);
100 int res_search(const char *dname, int class,
103 int type, u_char *answer, int anslen);
104 int res_mkquery(int op, const char *dname, int class,
107 int type, const char *data,int datalen,
108 struct rrec *newrr, u_char *buf, int buflen);
109 int res_send(const u_char *msg, int msglen, u_char *answer,
112 int anslen);
113 void herror(const char *s);
116
119 These routines are used for making, sending, and interpreting query and
120 reply messages with Internet domain name servers.
121 State information is kept in statp and is used to control the behavior
124 of these functions. Set statp to all zeros prior to making the first
125 call to any of these functions.
126 The res_ndestroy() function should be called to free memory allocated
129 by res_ninit() after the last use of statp.
130 The functions res_init(), res_query(), res_search(), res_mkquery(),
133 res_send(), and herror() are deprecated. They are supplied for back‐
134 wards compatability. They use global configuration and state informa‐
135 tion that is kept in the structure _res rather than state information
136 referenced through statp.
137 Most of the values in statp and _res are initialized to reasonable
140 defaults on the first call to res_ninit() or res_init() and can be
141 ignored. Options stored in statp->options or _res.options are defined
142 in <resolv.h>. They are stored as a simple bit mask containing the bit‐
143 wise OR of the options enabled.
144 RES_INIT True if the initial name server address and default
146 domain name are initialized, that is, res_init() or
147 res_ninit() has been called.
148 RES_DEBUG Print debugging messages.
151 RES_AAONLY Accept authoritative answers only. With this option,
154 res_send() will continue until it finds an authorita‐
155 tive answer or finds an error. Currently this option
156 is not implemented.
157 RES_USEVC Use TCP connections for queries instead of UDP data‐
160 grams.
161 RES_STAYOPEN Use with RES_USEVC to keep the TCP connection open
164 between queries. This is a useful option for programs
165 that regularly do many queries. The normal mode used
166 should be UDP.
167 RES_IGNTC Ignore truncation errors; that is, do not retry with
170 TCP.
171 RES_RECURSE Set the recursion-desired bit in queries. This is the
174 default. res_send() and res_nsend() do not do itera‐
175 tive queries and expect the name server to handle
176 recursion.
177 RES_DEFNAMES If set, res_search() and res_nsearch() append the
180 default domain name to single-component names, that
181 is, names that do not contain a dot. This option is
182 enabled by default.
183 RES_DNSRCH If this option is set, res_search() and res_nsearch()
186 search for host names in the current domain and in
187 parent domains. See hostname(1). This option is used
188 by the standard host lookup routine gethostby‐
189 name(3NSL). This option is enabled by default.
190 RES_NOALIASES This option turns off the user level aliasing feature
193 controlled by the HOSTALIASES environment variable.
194 Network daemons should set this option.
195 RES_BLAST If the RES_BLAST option is defined, resolver() queries
198 will be sent to all servers. If the RES_BLAST option
199 is not defined, but RES_ROTATE is , the list of name‐
200 servers are rotated according to a round-robin scheme.
201 RES_BLAST overrides RES_ROTATE.
202 RES_ROTATE This option causes res_nsend() and res_send() to
205 rotate the list of nameservers in statp->nsaddr_list
206 or _res.nsaddr_list.
207 RES_KEEPTSIG This option causes res_nsendsigned() to leave the mes‐
210 sage unchanged after TSIG verification. Otherwise the
211 TSIG record would be removed and the header would be
212 updated.
213 res_ninit(), res_init()
216 The res_ninit() and res_init() routines read the configuration file, if
217 any is present, to get the default domain name, search list and the
218 Internet address of the local name server(s). See resolv.conf(4). If no
219 server is configured, res_init() or res_ninit() will try to obtain name
220 resolution services from the host on which it is running. The current
221 domain name is defined by domainname(1M), or by the hostname if it is
222 not specified in the configuration file. Use the environment variable
223 LOCALDOMAIN to override the domain name. This environment variable may
224 contain several blank-separated tokens if you wish to override the
225 search list on a per-process basis. This is similar to the search com‐
226 mand in the configuration file. You can set the RES_OPTIONS environment
227 variable to override certain internal resolver options. You can other‐
228 wise set them by changing fields in the statp /_res structure. Alterna‐
229 tively, they are inherited from the configuration file's options com‐
230 mand. See resolv.conf(4) for information regarding the syntax of the
231 RES_OPTIONS environment variable. Initialization normally occurs on the
232 first call to one of the other resolver routines.
233 res_nquery(), res_query()
235 The res_nquery() and res_query() functions provide interfaces to the
236 server query mechanism. They construct a query, send it to the local
237 server, await a response, and make preliminary checks on the reply. The
238 query requests information of the specified type and class for the
239 specified fully-qualified domain name dname. The reply message is left
240 in the answer buffer with length anslen supplied by the caller.
241 res_nquery() and res_query() return the length of the answer, or -1
242 upon error.
243 The res_nquery() and res_query() routines return a length that may be
246 bigger than anslen. In that case, retry the query with a larger buf.
247 The answer to the second query may be larger still], so it is recom‐
248 mended that you supply a buf larger than the answer returned by the
249 previous query. answer must be large enough to receive a maximum UDP
250 response from the server or parts of the answer will be silently dis‐
251 carded. The default maximum UDP response size is 512 bytes.
252 res_nsearch(), res_search()
254 The res_nsearch() and res_search() routines make a query and await a
255 response, just like like res_nquery() and res_query(). In addition,
256 they implement the default and search rules controlled by the RES_DEF‐
257 NAMES and RES_DNSRCH options. They return the length of the first suc‐
258 cessful reply which is stored in answer. On error, they reurn -1.
259 The res_nsearch() and res_search() routines return a length that may be
262 bigger than anslen. In that case, retry the query with a larger buf.
263 The answer to the second query may be larger still], so it is recom‐
264 mended that you supply a buf larger than the answer returned by the
265 previous query. answer must be large enough to receive a maximum UDP
266 response from the server or parts of the answer will be silently dis‐
267 carded. The default maximum UDP response size is 512 bytes.
268 res_nquerydomain()
270 The res_nquerydomain() function calls res_query() on the concatenation
271 of name and domain, removing a trailing dot from name if domain is
272 NULL.
273 res_nmkquery(), res_mkquery()
275 These routines are used by res_nquery() and res_query(). The res_nmk‐
276 query() and res_mkquery() functions construct a standard query message
277 and place it in buf. The routine returns the size of the query, or -1
278 if the query is larger than buflen. The query type op is usually QUERY,
279 but can be any of the query types defined in <arpa/nameser.h>. The
280 domain name for the query is given by dname. newrr is currently unused
281 but is intended for making update messages.
282 res_nsend(), res_send(), res_nsendsigned()
284 The res_nsend(), res_send(), and res_nsendsigned() routines send a pre-
285 formatted query that returns an answer. The routine calls res_ninit()
286 or res_init(). If RES_INIT is not set, the routine sends the query to
287 the local name server and handles timeouts and retries. Additionally,
288 the res_nsendsigned() uses TSIG signatures to add authentication to the
289 query and verify the response. In this case, only one name server will
290 be contacted. The routines return the length of the reply message, or
291 -1 if there are errors.
292 The res_nsend() and res_send() routines return a length that may be
295 bigger than anslen. In that case, retry the query with a larger buf.
296 The answer to the second query may be larger still], so it is recom‐
297 mended that you supply a buf larger than the answer returned by the
298 previous query. answer must be large enough to receive a maximum UDP
299 response from the server or parts of the answer will be silently dis‐
300 carded. The default maximum UDP response size is 512 bytes.
301 fp_resstat()
303 The function fp_resstat() prints out the active flag bits in
304 statp->options preceded by the text ";; res options:" on file.
305 res_hostalias()
307 The function res_hostalias() looks up name in the file referred to by
308 the HOSTALIASES environment variable and returns the fully qualified
309 host name. If name is not found or an error occurs, NULL is returned.
310 res_hostalias() stores the result in buf.
311 res_nclose()
313 The res_nclose() function closes any open files referenced through
314 statp.
315 res_ndestroy()
317 The res_ndestroy() function calls res_nclose(), then frees any memory
318 allocated by res_ninit() referenced through statp.
319 dn_comp()
321 The dn_comp() function compresses the domain name exp_dn and stores it
322 in comp_dn. The dn_comp() function returns the size of the compressed
323 name, or −1 if there were errors. length is the size of the array
324 pointed to by comp_dn.
325 The dnptrs parameter is a pointer to the head of the list of pointers
328 to previously compressed names in the current message. The first
329 pointer must point to the beginning of the message. The list ends with
330 NULL. The limit to the array is specified by lastdnptr.
331 A side effect of calling dn_comp() is to update the list of pointers
334 for labels inserted into the message by dn_comp() as the name is com‐
335 pressed. If dnptrs is NULL, names are not compressed. If lastdnptr is
336 NULL, dn_comp() does not update the list of labels.
337 dn_expand()
339 The dn_expand() function expands the compressed domain name comp_dn to
340 a full domain name. The compressed name is contained in a query or
341 reply message. msg is a pointer to the beginning of that message. The
342 uncompressed name is placed in the buffer indicated by exp_dn, which is
343 of size length. The dn_expand() function returns the size of the com‐
344 pressed name, or −1 if there was an error.
345 hstrerror(), herror()
347 The variables statp->res_h_errno and _res.res_h_errno and external
348 variable h_errno are set whenever an error occurs during a resolver
349 operation. The following definitions are given in <netdb.h>:
350 #define NETDB_INTERNAL -1 /* see errno */
352 #define NETDB_SUCCESS 0 /* no problem */
353 #define HOST_NOT_FOUND 1 /* Authoritative Answer Host not found */
354 #define TRY_AGAIN 2 /* Non-Authoritative not found, or SERVFAIL */
355 #define NO_RECOVERY 3 /* Non-Recoverable: FORMERR, REFUSED, NOTIMP*/
356 #define NO_DATA 4 /* Valid name, no data for requested type */
357 The herror() function writes a message to the diagnostic output con‐
362 sisting of the string parameters, the constant string ":", and a mes‐
363 sage corresponding to the value of h_errno.
364 The hstrerror() function returns a string, which is the message text
367 that corresponds to the value of the err parameter.
368 res_setservers(), res_getservers()
370 The functions res_getservers() and res_setservers() are used to get and
371 set the list of servers to be queried.
372
374 /etc/resolv.conf resolver configuration file
375
378 See attributes(5) for descriptions of the following attributes:
379 ┌─────────────────────────────┬─────────────────────────────┐
384 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
385 ├─────────────────────────────┼─────────────────────────────┤
386 │Availability │SUNWcsl (32-bit) │
387 │ │SUNWcslx (64-bit) │
388 ├─────────────────────────────┼─────────────────────────────┤
389 │Interface Stability │Committed │
390 ├─────────────────────────────┼─────────────────────────────┤
391 │MT-Level │Unsafe for deprecated │
392 │ │interfaces; MT-Safe for all │
393 │ │others. │
394 └─────────────────────────────┴─────────────────────────────┘
395
397 domainname(1M), gethostbyname(3NSL), libresolv(3LIB), resolv.conf(4),
398 attributes(5)
399 Lottor, M. RFC 1033, Domain Administrators Operations Guide. Network
402 Working Group. November 1987.
403 Mockapetris, Paul. RFC 1034, Domain Names - Concepts and Facilities.
406 Network Working Group. November 1987.
407 Mockapetris, Paul. RFC 1035, Domain Names - Implementation and Specifi‐
410 cation. Network Working Group. November 1987.
411 Partridge, Craig. RFC 974, Mail Routing and the Domain System. Network
414 Working Group. January 1986.
415 Stahl, M. RFC 1032, Domain Administrators Guide. Network Working Group.
418 November 1987.
419 Vixie, Paul, Dunlap, Kevin J., Karels, Michael J. Name Server Opera‐
422 tions Guide for BIND. Internet Software Consortium, 1996.
423
425 When the caller supplies a work buffer, for example the answer buffer
426 argument to res_nsend() or res_send(), the buffer should be aligned on
427 an eight byte boundary. Otherwise, an error such as a SIGBUS may
428 result.
429SunOS 5.11 26 Dec 2006 resolver(3RESOLV)