1RESOLVER(3) BSD Library Functions Manual RESOLVER(3)
2
4 res_ninit, res_ourserver_p, fp_resstat, res_hostalias, res_pquery,
5 res_nquery, res_nsearch, res_nquerydomain, res_nmkquery, res_nsend,
6 res_nupdate, res_nmkupdate, res_nclose, res_nsendsigned, res_findzonecut,
7 res_getservers, res_setservers, dn_comp, dn_expand, hstrerror, res_init,
8 res_isourserver, fp_nquery, p_query, hostalias, res_query, res_search,
9 res_querydomain, res_mkquery, res_send, res_update, res_close, herror —
10 resolver routines
11
13 #include <sys/types.h>
14 #include <netinet/in.h>
15 #include <arpa/nameser.h>
16 #include <resolv.h>
17 #include <res_update.h>
18 typedef struct __res_state *res_state;
20 int
22 res_ninit(res_state statp);
23 int
25 res_ourserver_p(const res_state statp, const struct sockaddr_in *addr);
26 void
28 fp_resstat(const res_state statp, FILE *fp);
29 const char *
31 res_hostalias(const res_state statp, const char *name, char *buf,
32 size_t buflen);
33 int
35 res_pquery(const res_state statp, const u_char *msg, int msglen,
36 FILE *fp);
37 int
39 res_nquery(res_state statp, const char *dname, int class, int type,
40 u_char *answer, int anslen);
41 int
43 res_nsearch(res_state statp, const char *dname, int class, int type,
44 u_char * answer, int anslen);
45 int
47 res_nquerydomain(res_state statp, const char *name, const char *domain,
48 int class, int type, u_char *answer, int anslen);
49 int
51 res_nmkquery(res_state statp, int op, const char *dname, int class,
52 int type, const u_char *data, int datalen, const u_char *newrr,
53 u_char *buf, int buflen);
54 int
56 res_nsend(res_state statp, const u_char *msg, int msglen, u_char *answer,
57 int anslen);
58 int
60 res_nupdate(res_state statp, ns_updrec *rrecp_in);
61 int
63 res_nmkupdate(res_state statp, ns_updrec *rrecp_in, u_char *buf,
64 int buflen);
65 void
67 res_nclose(res_state statp);
68 int
70 res_nsendsigned(res_state statp, const u_char *msg, int msglen,
71 ns_tsig_key *key, u_char *answer, int anslen);
72 int
74 res_findzonecut(res_state statp, const char *dname, ns_class class,
75 int options, char *zname, size_t zsize, struct in_addr *addrs,
76 int naddrs);
77 int
79 res_getservers(res_state statp, union res_sockaddr_union *set, int cnt);
80 void
82 res_setservers(res_state statp, const union res_sockaddr_union *set,
83 int cnt);
84 int
86 dn_comp(const char *exp_dn, u_char *comp_dn, int length, u_char **dnptrs,
87 u_char **lastdnptr);
88 int
90 dn_expand(const u_char *msg, const u_char *eomorig,
91 const u_char *comp_dn, char *exp_dn, int length);
92 const char *
94 hstrerror(int err);
95 DEPRECATED
97 #include <sys/types.h>
98 #include <netinet/in.h>
99 #include <arpa/nameser.h>
100 #include <resolv.h>
101 #include <res_update.h>
102 int
104 res_init(void);
105 int
107 res_isourserver(const struct sockaddr_in *addr);
108 int
110 fp_nquery(const u_char *msg, int msglen, FILE *fp);
111 void
113 p_query(const u_char *msg, FILE *fp);
114 const char *
116 hostalias(const char *name);
117 int
119 res_query(const char *dname, int class, int type, u_char *answer,
120 int anslen);
121 int
123 res_search(const char *dname, int class, int type, u_char *answer,
124 int anslen);
125 int
127 res_querydomain(const char *name, const char *domain, int class,
128 int type, u_char *answer, int anslen);
129 int
131 res_mkquery(int op, const char *dname, int class, int type,
132 const char *data, int datalen, struct rrec *newrr, u_char *buf,
133 int buflen);
134 int
136 res_send(const u_char *msg, int msglen, u_char *answer, int anslen);
137 int
139 res_update(ns_updrec *rrecp_in);
140 void
142 res_close(void);
143 void
145 herror(const char *s);
146
148 These routines are used for making, sending and interpreting query and
149 reply messages with Internet domain name servers.
150 State information is kept in statp and is used to control the behavior of
152 these functions. statp should be set to all zeros prior to the first
153 call to any of these functions.
154 The functions res_init(), res_isourserver(), fp_nquery(), p_query(),
156 hostalias(), res_query(), res_search(), res_querydomain(), res_mkquery(),
157 res_send(), res_update(), res_close() and herror() are deprecated and are
158 supplied for compatability with old source code. They use global config‐
159 uration and state information that is kept in the structure _res rather
160 than that referenced through statp.
161 Most of the values in statp and _res are initialized on the first call to
163 res_ninit() / res_init() to reasonable defaults and can be ignored.
164 Options stored in statp->options / _res.options are defined in resolv.h
165 and are as follows. Options are stored as a simple bit mask containing
166 the bitwise “OR” of the options enabled.
167 RES_INIT
169 True if the initial name server address and default domain name
170 are initialized (i.e., res_ninit() / res_init() has been
171 called).
172 RES_DEBUG
174 Print debugging messages.
175 RES_AAONLY
177 Accept authoritative answers only. Should continue until it
178 finds an authoritative answer or finds an error. Currently this
179 is not implemented.
180 RES_USEVC
182 Use TCP connections for queries instead of UDP datagrams.
183 RES_STAYOPEN
185 Used with RES_USEVC to keep the TCP connection open between
186 queries. This is useful only in programs that regularly do many
187 queries. UDP should be the normal mode used.
188 RES_IGNTC
190 Ignore truncation errors, i.e., don't retry with TCP.
191 RES_RECURSE
193 Set the recursion-desired bit in queries. This is the default.
194 (res_nsend() / res_send() does not do iterative queries and
195 expects the name server to handle recursion.)
196 RES_DEFNAMES
198 If set, res_nsearch() / res_search() will append the default
199 domain name to single-component names (those that do not contain
200 a dot). This option is enabled by default.
201 RES_DNSRCH
203 If this option is set, res_nsearch() / res_search() will search
204 for host names in the current domain and in parent domains; see
205 hostname(7). This is used by the standard host lookup routine
206 gethostbyname(3). This option is enabled by default.
207 RES_NOALIASES
209 This option turns off the user level aliasing feature controlled
210 by the HOSTALIASES environment variable. Network daemons should
211 set this option.
212 RES_USE_INET6
214 This option causes gethostbyname(3) to look for AAAA records
215 before looking for A records if none are found.
216 RES_ROTATE
218 This options causes the res_nsend() / res_send() to rotate the
219 list of nameservers in statp->nsaddr_list / _res.nsaddr_list.
220 RES_KEEPTSIG
222 This option causes res_nsendsigned() to leave the message
223 unchanged after TSIG verification; otherwise the TSIG record
224 would be removed and the header updated.
225 RES_NOTLDQUERY
227 This option causes res_nsearch() to not attempt to resolve a
228 unqualified name as if it were a top level domain (TLD). This
229 option can cause problems if the site has "localhost" as a TLD
230 rather than having localhost on one or more elements of the
231 search list. This option has no effect if neither RES_DEFNAMES
232 or RES_DNSRCH is set.
233 The res_ninit() / res_init() routine reads the configuration file (if
235 any; see resolver(5)) to get the default domain name, search list and the
236 Internet address of the local name server(s). If no server is config‐
237 ured, the host running the resolver is tried. The current domain name is
238 defined by the hostname if not specified in the configuration file; it
239 can be overridden by the environment variable LOCALDOMAIN. This environ‐
240 ment variable may contain several blank-separated tokens if you wish to
241 override the “search list” on a per-process basis. This is similar to
242 the search command in the configuration file. Another environment vari‐
243 able (“RES_OPTIONS”) can be set to override certain internal resolver
244 options which are otherwise set by changing fields in the statp / _res
245 structure or are inherited from the configuration file's options command.
246 The syntax of the “RES_OPTIONS” environment variable is explained in
247 resolver(5). Initialization normally occurs on the first call to one of
248 the other resolver routines.
249 The res_nquery() / res_query() functions provides interfaces to the
251 server query mechanism. They constructs a query, sends it to the local
252 server, awaits a response, and makes preliminary checks on the reply.
253 The query requests information of the specified type and class for the
254 specified fully-qualified domain name dname. The reply message is left
255 in the answer buffer with length anslen supplied by the caller.
256 res_nquery() / res_query() return -1 on error or the length of the
257 answer.
258 The res_nsearch() / res_search() routines make a query and awaits a
260 response like res_nquery() / res_query(), but in addition, it implements
261 the default and search rules controlled by the RES_DEFNAMES and
262 RES_DNSRCH options. It returns the length of the first successful reply
263 which is stored in answer or -1 on error.
264 The remaining routines are lower-level routines used by res_nquery() /
266 res_query(). The res_nmkquery() / res_mkquery() functions constructs a
267 standard query message and places it in buf. It returns the size of the
268 query, or -1 if the query is larger than buflen. The query type op is
269 usually QUERY, but can be any of the query types defined in
270 <arpa/nameser.h>. The domain name for the query is given by dname.
271 Newrr is currently unused but is intended for making update messages.
272 The res_nsend() / res_send() / res_nsendsigned() routines sends a pre-
274 formatted query and returns an answer. It will call res_ninit() /
275 res_init() if RES_INIT is not set, send the query to the local name
276 server, and handle timeouts and retries. Additionally, res_nsendsigned()
277 will use TSIG signatures to add authentication to the query and verify
278 the response. In this case, only one nameserver will be contacted. The
279 length of the reply message is returned, or -1 if there were errors.
280 res_nquery() / res_query(), res_nsearch() / res_search() and res_nsend()
282 / res_send() return a length that may be bigger than anslen. In that
283 case the query should be retried with a bigger buffer. NOTE the answer
284 to the second query may be larger still so supplying a buffer that bigger
285 that the answer returned by the previous query is recommended.
286 answer MUST be big enough to receive a maximum UDP response from the
288 server or parts of the answer will be silently discarded. The default
289 maximum UDP response size is 512 bytes.
290 The function res_ourserver_p() returns true when inp is one of the
292 servers in statp->nsaddr_list / _res.nsaddr_list.
293 The functions fp_nquery() / p_query() print out the query and any answer
295 in msg on fp. p_query() is equivalent to fp_nquery() with msglen set to
296 512.
297 The function fp_resstat() prints out the active flag bits in
299 statp->options preceeded by the text ";; res options:" on file.
300 The functions res_hostalias() / hostalias() lookup up name in the file
302 referred to by the HOSTALIASES files return a fully qualified hostname if
303 found or NULL if not found or an error occurred. res_hostalias() uses
304 buf to store the result in, hostalias() uses a static buffer.
305 The functions res_getservers() and res_setservers() are used to get and
307 set the list of server to be queried.
308 The functions res_nupdate() / res_update() take a list of ns_updrec
310 rrecp_in. Identifies the containing zone for each record and groups the
311 records according to containing zone maintaining in zone order then sends
312 and update request to the servers for these zones. The number of zones
313 updated is returned or -1 on error. Note that res_nupdate() will perform
314 TSIG authenticated dynamic update operations if the key is not NULL.
315 The function res_findzonecut() discovers the closest enclosing zone cut
317 for a specified domain name, and finds the IP addresses of the zone's
318 master servers.
319 The functions res_nmkupdate() / res_mkupdate() take a linked list of
321 ns_updrec rrecp_in and construct a UPDATE message in buf.
322 res_nmkupdate() / res_mkupdate() return the length of the constructed
323 message on no error or one of the following error values.
324 -1 An error occurred parsing rrecp_in.
326 -2 The buffer buf was too small.
328 -3 The first record was not a zone section or there was a section order
330 problem. The section order is S_ZONE, S_PREREQ and S_UPDATE.
331 -4 A number overflow occurred.
333 -5 Unknown operation or no records.
335 The functions res_nclose() / res_close() close any open files referenced
337 through statp / _res.
338 The dn_comp() function compresses the domain name exp_dn and stores it in
340 comp_dn. The size of the compressed name is returned or -1 if there were
341 errors. The size of the array pointed to by comp_dn is given by length.
342 The compression uses an array of pointers dnptrs to previously-compressed
343 names in the current message. The first pointer points to to the begin‐
344 ning of the message and the list ends with NULL. The limit to the array
345 is specified by lastdnptr. A side effect of dn_comp() is to update the
346 list of pointers for labels inserted into the message as the name is com‐
347 pressed. If dnptr is NULL, names are not compressed. If lastdnptr is
348 NULL, the list of labels is not updated.
349 The dn_expand() entry expands the compressed domain name comp_dn to a
351 full domain name. The compressed name is contained in a query or reply
352 message; msg is a pointer to the beginning of the message. eomorig is a
353 pointer to the first location after the message. The uncompressed name
354 is placed in the buffer indicated by exp_dn which is of size length. The
355 size of compressed name is returned or -1 if there was an error.
356 The variables statp->res_h_errno / _res.res_h_errno and external variable
358 h_errno is set whenever an error occurs during resolver operation. The
359 following definitions are given in <netdb.h>:
360 #define NETDB_INTERNAL -1 /* see errno */
362 #define NETDB_SUCCESS 0 /* no problem */
363 #define HOST_NOT_FOUND 1 /* Authoritative Answer Host not found */
364 #define TRY_AGAIN 2 /* Non-Authoritative not found, or SERVFAIL */
365 #define NO_RECOVERY 3 /* Non-Recoverable: FORMERR, REFUSED, NOTIMP */
366 #define NO_DATA 4 /* Valid name, no data for requested type */
367 The herror() function writes a message to the diagnostic output consist‐
369 ing of the string parameter s, the constant string ": ", and a message
370 corresponding to the value of h_errno.
371 The hstrerror() function returns a string which is the message text cor‐
373 responding to the value of the err parameter.
374
376 /etc/resolv.conf See resolver(5).
377
379 gethostbyname(3), hostname(7), named(8), resolver(5); RFC1032, RFC1033,
380 RFC1034, RFC1035, RFC974; SMM:11, “Name Server Operations Guide for BIND”
3814th Berkeley Distribution July 4, 2000 4th Berkeley Distribution