| blob | b5f3d23c181c754412cdac79bba8b30a7f2731cf |
1 .\" $NetBSD$
2 .\"
3 .\" Copyright (C) 2009 Internet Systems Consortium, Inc. ("ISC")
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17 .\" Id: resolver.3,v 1.3 2009/01/22 23:49:23 tbox Exp
18 .\"
19 .Dd July 4, 2000
20 .Dt RESOLVER @LIB_NETWORK_EXT_U@
21 .Os BSD 4
22 .Sh NAME
23 .Nm res_ninit ,
24 .Nm res_ourserver_p ,
25 .Nm fp_resstat ,
26 .Nm res_hostalias ,
27 .Nm res_pquery ,
28 .Nm res_nquery ,
29 .Nm res_nsearch ,
30 .Nm res_nquerydomain ,
31 .Nm res_nmkquery ,
32 .Nm res_nsend ,
33 .Nm res_nupdate ,
34 .Nm res_nmkupdate ,
35 .Nm res_nclose ,
36 .Nm res_nsendsigned ,
37 .Nm res_findzonecut ,
38 .Nm res_getservers ,
39 .Nm res_setservers ,
40 .Nm res_ndestroy ,
41 .Nm dn_comp ,
42 .Nm dn_expand ,
43 .Nm hstrerror ,
44 .Nm res_init ,
45 .Nm res_isourserver ,
46 .Nm fp_nquery ,
47 .Nm p_query ,
48 .Nm hostalias ,
49 .Nm res_query ,
50 .Nm res_search ,
51 .Nm res_querydomain ,
52 .Nm res_mkquery ,
53 .Nm res_send ,
54 .Nm res_update ,
55 .Nm res_close ,
56 .Nm herror
57 .Nd resolver routines
58 .Sh SYNOPSIS
59 .Fd #include <sys/types.h>
60 .Fd #include <netinet/in.h>
61 .Fd #include <arpa/nameser.h>
62 .Fd #include <resolv.h>
63 .Fd #include <res_update.h>
64 .Vt typedef struct __res_state *res_state ;
65 .Pp
66 .Ft int
67 .Fn res_ninit "res_state statp"
68 .Ft int
69 .Fn res_ourserver_p "const res_state statp" "const struct sockaddr_in *addr"
70 .Ft void
71 .Fn fp_resstat "const res_state statp" "FILE *fp"
72 .Ft "const char *"
73 .Fn res_hostalias "const res_state statp" "const char *name" "char *buf" "size_t buflen"
74 .Ft int
75 .Fn res_pquery "const res_state statp" "const u_char *msg" "int msglen" "FILE *fp"
76 .Ft int
77 .Fn res_nquery "res_state statp" "const char *dname" "int class" "int type" "u_char *answer" "int anslen"
78 .Ft int
79 .Fn res_nsearch "res_state statp" "const char *dname" "int class" "int type" "u_char * answer" "int anslen"
80 .Ft int
81 .Fn res_nquerydomain "res_state statp" "const char *name" "const char *domain" "int class" "int type" "u_char *answer" "int anslen"
82 .Ft int
83 .Fo res_nmkquery
84 .Fa "res_state statp"
85 .Fa "int op"
86 .Fa "const char *dname"
87 .Fa "int class"
88 .Fa "int type"
89 .Fa "const u_char *data"
90 .Fa "int datalen"
91 .Fa "const u_char *newrr"
92 .Fa "u_char *buf"
93 .Fa "int buflen"
94 .Fc
95 .Ft int
96 .Fn res_nsend "res_state statp" "const u_char *msg" "int msglen" "u_char *answer" "int anslen"
97 .Ft int
98 .Fn res_nupdate "res_state statp" "ns_updrec *rrecp_in"
99 .Ft int
100 .Fn res_nmkupdate "res_state statp" "ns_updrec *rrecp_in" "u_char *buf" "int buflen"
101 .Ft void
102 .Fn res_nclose "res_state statp"
103 .Ft int
104 .Fn res_nsendsigned "res_state statp" "const u_char *msg" "int msglen" "ns_tsig_key *key" "u_char *answer" "int anslen"
105 .Ft int
106 .Fn res_findzonecut "res_state statp" "const char *dname" "ns_class class" "int options" "char *zname" "size_t zsize" "struct in_addr *addrs" "int naddrs"
107 .Ft int
108 .Fn res_getservers "res_state statp" "union res_sockaddr_union *set" "int cnt"
109 .Ft void
110 .Fn res_setservers "res_state statp" "const union res_sockaddr_union *set" "int cnt"
111 .Ft void
112 .Fn res_ndestroy "res_state statp"
113 .Ft int
114 .Fn dn_comp "const char *exp_dn" "u_char *comp_dn" "int length" "u_char **dnptrs" "u_char **lastdnptr"
115 .Ft int
116 .Fn dn_expand "const u_char *msg" "const u_char *eomorig" "const u_char *comp_dn" "char *exp_dn" "int length"
117 .Ft "const char *"
118 .Fn hstrerror "int err"
119 .Ss DEPRECATED
120 .Fd #include <sys/types.h>
121 .Fd #include <netinet/in.h>
122 .Fd #include <arpa/nameser.h>
123 .Fd #include <resolv.h>
124 .Fd #include <res_update.h>
125 .Ft int
126 .Fn res_init "void"
127 .Ft int
128 .Fn res_isourserver "const struct sockaddr_in *addr"
129 .Ft int
130 .Fn fp_nquery "const u_char *msg" "int msglen" "FILE *fp"
131 .Ft void
132 .Fn p_query "const u_char *msg" "FILE *fp"
133 .Ft "const char *"
134 .Fn hostalias "const char *name"
135 .Ft int
136 .Fn res_query "const char *dname" "int class" "int type" "u_char *answer" "int anslen"
137 .Ft int
138 .Fn res_search "const char *dname" "int class" "int type" "u_char *answer" "int anslen"
139 .Ft int
140 .Fn res_querydomain "const char *name" "const char *domain" "int class" "int type" "u_char *answer" "int anslen"
141 .Ft int
142 .Fo res_mkquery
143 .Fa "int op"
144 .Fa "const char *dname"
145 .Fa "int class"
146 .Fa "int type"
147 .Fa "const char *data"
148 .Fa "int datalen"
149 .Fa "struct rrec *newrr"
150 .Fa "u_char *buf"
151 .Fa "int buflen"
152 .Fc
153 .Ft int
154 .Fn res_send "const u_char *msg" "int msglen" "u_char *answer" "int anslen"
155 .Ft int
156 .Fn res_update "ns_updrec *rrecp_in"
157 .Ft void
158 .Fn res_close "void"
159 .Ft void
160 .Fn herror "const char *s"
161 .Sh DESCRIPTION
162 These routines are used for making, sending and interpreting
163 query and reply messages with Internet domain name servers.
164 .Pp
165 State information is kept in
166 .Fa statp
167 and is used to control the behavior of these functions.
168 .Fa statp
169 should be set to all zeros prior to the first call to any of these functions.
170 .Pp
171 The functions
172 .Fn res_init ,
173 .Fn res_isourserver ,
174 .Fn fp_nquery ,
175 .Fn p_query ,
176 .Fn hostalias ,
177 .Fn res_query ,
178 .Fn res_search ,
179 .Fn res_querydomain ,
180 .Fn res_mkquery ,
181 .Fn res_send ,
182 .Fn res_update ,
183 .Fn res_close
184 and
185 .Fn herror
186 are deprecated and are supplied for compatability with old source
187 code.
188 They use global configuration and state information that is
189 kept in the structure
190 .Ft _res
191 rather than that referenced through
192 .Ft statp .
193 .Pp
194 Most of the values in
195 .Ft statp
196 and
197 .Ft _res
198 are initialized on the first call to
199 .Fn res_ninit
200 /
201 .Fn res_init
202 to reasonable defaults and can be ignored.
203 Options
204 stored in
205 .Ft statp->options
206 /
207 .Ft _res.options
208 are defined in
209 .Pa resolv.h
210 and are as follows.
211 Options are stored as a simple bit mask containing the bitwise
212 .Dq OR
213 of the options enabled.
214 .Bl -tag -width "RES_DEB"
215 .It Dv RES_INIT
216 True if the initial name server address and default domain name are
217 initialized (i.e.,
218 .Fn res_ninit
219 /
220 .Fn res_init
221 has been called).
222 .It Dv RES_DEBUG
223 Print debugging messages.
224 .It Dv RES_AAONLY
225 Accept authoritative answers only.
226 Should continue until it finds an authoritative answer or finds an error.
227 Currently this is not implemented.
228 .It Dv RES_USEVC
229 Use TCP connections for queries instead of UDP datagrams.
230 .It Dv RES_STAYOPEN
231 Used with
232 .Dv RES_USEVC
233 to keep the TCP connection open between queries.
234 This is useful only in programs that regularly do many queries.
235 UDP should be the normal mode used.
236 .It Dv RES_IGNTC
237 Ignore truncation errors, i.e., don't retry with TCP.
238 .It Dv RES_RECURSE
239 Set the recursion-desired bit in queries.
240 This is the default.
241 (\c
242 .Fn res_nsend
243 /
244 .Fn res_send
245 does not do iterative queries and expects the name server
246 to handle recursion.)
247 .It Dv RES_DEFNAMES
248 If set,
249 .Fn res_nsearch
250 /
251 .Fn res_search
252 will append the default domain name to single-component names
253 (those that do not contain a dot).
254 This option is enabled by default.
255 .It Dv RES_DNSRCH
256 If this option is set,
257 .Fn res_nsearch
258 /
259 .Fn res_search
260 will search for host names in the current domain and in parent domains; see
261 .Xr hostname @DESC_EXT@ .
262 This is used by the standard host lookup routine
263 .Xr gethostbyname @LIB_NETWORK_EXT@ .
264 This option is enabled by default.
265 .It Dv RES_NOALIASES
266 This option turns off the user level aliasing feature controlled by
267 the
268 .Ev HOSTALIASES
269 environment variable.
270 Network daemons should set this option.
271 .It Dv RES_USE_INET6
272 This option causes
273 .Xr gethostbyname @LIB_NETWORK_EXT@
274 to look for AAAA records before looking for A records if none are found.
275 .It Dv RES_ROTATE
276 This options causes the
277 .Fn res_nsend
278 /
279 .Fn res_send
280 to rotate the list of nameservers in
281 .Fa statp->nsaddr_list
282 /
283 .Fa _res.nsaddr_list .
284 .It Dv RES_KEEPTSIG
285 This option causes
286 .Fn res_nsendsigned
287 to leave the message unchanged after TSIG verification; otherwise the TSIG
288 record would be removed and the header updated.
289 .It Dv RES_NOTLDQUERY
290 This option causes
291 .Fn res_nsearch
292 to not attempt to resolve a unqualified name as if it were a top level
293 domain (TLD).
294 This option can cause problems if the site has "localhost" as a TLD rather
295 than having localhost on one or more elements of the search list.
296 This option has no effect if neither
297 .Dv RES_DEFNAMES
298 or
299 .Dv RES_DNSRCH
300 is set.
301 .El
302 .Pp
303 The
304 .Fn res_ninit
305 /
306 .Fn res_init
307 routine
308 reads the configuration file (if any; see
309 .Xr resolver @FORMAT_EXT@ )
310 to get the default domain name, search list and
311 the Internet address of the local name server(s).
312 If no server is configured, the host running the resolver is tried.
313 The current domain name is defined by the hostname
314 if not specified in the configuration file;
315 it can be overridden by the environment variable
316 .Ev LOCALDOMAIN .
317 This environment variable may contain several blank-separated
318 tokens if you wish to override the
319 .Dq search list
320 on a per-process basis. This is similar to the
321 .Ic search
322 command in the configuration file.
323 Another environment variable
324 .Pq Dq Ev RES_OPTIONS
325 can be set to override certain internal resolver options which are otherwise
326 set by changing fields in the
327 .Ft statp
328 /
329 .Ft _res
330 structure or are inherited from the configuration file's
331 .Ic options
332 command. The syntax of the
333 .Dq Ev RES_OPTIONS
334 environment variable is explained in
335 .Xr resolver @FORMAT_EXT@ .
336 Initialization normally occurs on the first call
337 to one of the other resolver routines.
338 .Pp
339 The memory referred to by
340 .Ft statp
341 must be set to all zeros prior to the first call to
342 .Fn res_ninit .
343 .Fn res_ndestroy
344 should be call to free memory allocated by
345 .Fn res_ninit
346 after last use.
347 .Pp
348 The
349 .Fn res_nquery
350 /
351 .Fn res_query
352 functions provides interfaces to the server query mechanism.
353 They constructs a query, sends it to the local server,
354 awaits a response, and makes preliminary checks on the reply.
355 The query requests information of the specified
356 .Fa type
357 and
358 .Fa class
359 for the specified fully-qualified domain name
360 .Fa dname .
361 The reply message is left in the
362 .Fa answer
363 buffer with length
364 .Fa anslen
365 supplied by the caller.
366 .Fn res_nquery
367 /
368 .Fn res_query
369 return -1 on error or the length of the answer.
370 .Pp
371 The
372 .Fn res_nsearch
373 /
374 .Fn res_search
375 routines make a query and awaits a response like
376 .Fn res_nquery
377 /
378 .Fn res_query ,
379 but in addition, it implements the default and search rules
380 controlled by the
381 .Dv RES_DEFNAMES
382 and
383 .Dv RES_DNSRCH
384 options.
385 It returns the length of the first successful reply which is stored in
386 .Ft answer
387 or -1 on error.
388 .Pp
389 The remaining routines are lower-level routines used by
390 .Fn res_nquery
391 /
392 .Fn res_query .
393 The
394 .Fn res_nmkquery
395 /
396 .Fn res_mkquery
397 functions
398 constructs a standard query message and places it in
399 .Fa buf .
400 It returns the size of the query, or \-1 if the query is
401 larger than
402 .Fa buflen .
403 The query type
404 .Fa op
405 is usually
406 .Dv QUERY ,
407 but can be any of the query types defined in
408 .Pa <arpa/nameser.h> .
409 The domain name for the query is given by
410 .Fa dname .
411 .Fa Newrr
412 is currently unused but is intended for making update messages.
413 .Pp
414 The
415 .Fn res_nsend
416 /
417 .Fn res_send
418 /
419 .Fn res_nsendsigned
420 routines
421 sends a pre-formatted query and returns an answer.
422 It will call
423 .Fn res_ninit
424 /
425 .Fn res_init
426 if
427 .Dv RES_INIT
428 is not set, send the query to the local name server, and
429 handle timeouts and retries. Additionally,
430 .Fn res_nsendsigned
431 will use TSIG signatures to add authentication to the query and verify the
432 response. In this case, only one nameserver will be contacted.
433 The length of the reply message is returned, or \-1 if there were errors.
434 .Pp
435 .Fn res_nquery
436 /
437 .Fn res_query ,
438 .Fn res_nsearch
439 /
440 .Fn res_search
441 and
442 .Fn res_nsend
443 /
444 .Fn res_send
445 return a length that may be bigger than
446 .Fa anslen .
447 In that case the query should be retried with a bigger buffer.
448 NOTE the answer to the second query may be larger still so supplying
449 a buffer that bigger that the answer returned by the previous
450 query is recommended.
451 .Pp
452 .Fa answer
453 MUST be big enough to receive a maximum UDP response from the server or
454 parts of the answer will be silently discarded.
455 The default maximum UDP response size is 512 bytes.
456 .Pp
457 The function
458 .Fn res_ourserver_p
459 returns true when
460 .Fa inp
461 is one of the servers in
462 .Fa statp->nsaddr_list
463 /
464 .Fa _res.nsaddr_list .
465 .Pp
466 The functions
467 .Fn fp_nquery
468 /
469 .Fn p_query
470 print out the query and any answer in
471 .Fa msg
472 on
473 .Fa fp .
474 .Fn p_query
475 is equivalent to
476 .Fn fp_nquery
477 with
478 .Fa msglen
479 set to 512.
480 .Pp
481 The function
482 .Fn fp_resstat
483 prints out the active flag bits in
484 .Fa statp->options
485 preceeded by the text ";; res options:" on
486 .Fa file .
487 .Pp
488 The functions
489 .Fn res_hostalias
490 /
491 .Fn hostalias
492 lookup up name in the file referred to by the
493 .Ev HOSTALIASES
494 files return a fully qualified hostname if found or NULL if
495 not found or an error occurred.
496 .Fn res_hostalias
497 uses
498 .Fa buf
499 to store the result in,
500 .Fn hostalias
501 uses a static buffer.
502 .Pp
503 The functions
504 .Fn res_getservers
505 and
506 .Fn res_setservers
507 are used to get and set the list of server to be queried.
508 .Pp
509 The functions
510 .Fn res_nupdate
511 /
512 .Fn res_update
513 take a list of ns_updrec
514 .Fa rrecp_in .
515 Identifies the containing zone for each record and groups the records
516 according to containing zone maintaining in zone order then sends and update
517 request to the servers for these zones. The number of zones updated is
518 returned or -1 on error. Note that
519 .Fn res_nupdate
520 will perform TSIG authenticated dynamic update operations if the key is not
521 NULL.
522 .Pp
523 The function
524 .Fn res_findzonecut
525 discovers the closest enclosing zone cut for a specified domain name,
526 and finds the IP addresses of the zone's master servers.
527 .Pp
528 The functions
529 .Fn res_nmkupdate
530 /
531 .Fn res_mkupdate
532 take a linked list of ns_updrec
533 .Fa rrecp_in
534 and construct a UPDATE message in
535 .Fa buf .
536 .Fn res_nmkupdate
537 /
538 .Fn res_mkupdate
539 return the length of the constructed message on no error or one of the
540 following error values.
541 .Bl -inset -width "-5"
542 .It -1
543 An error occurred parsing
544 .Fa rrecp_in .
545 .It -2
546 The buffer
547 .Fa buf
548 was too small.
549 .It -3
550 The first record was not a zone section or there was a section order problem.
551 The section order is S_ZONE, S_PREREQ and S_UPDATE.
552 .It -4
553 A number overflow occurred.
554 .It -5
555 Unknown operation or no records.
556 .El
557 .Pp
558 The functions
559 .Fn res_nclose
560 /
561 .Fn res_close
562 close any open files referenced through
563 .Fa statp
564 /
565 .Fa _res .
566 .Pp
567 The function
568 .Fn res_ndestroy
569 calls
570 .Fn res_nclose
571 then frees any memory allocated by
572 .Fn res_ninit .
573 .Pp
574 The
575 .Fn dn_comp
576 function
577 compresses the domain name
578 .Fa exp_dn
579 and stores it in
580 .Fa comp_dn .
581 The size of the compressed name is returned or \-1 if there were errors.
582 The size of the array pointed to by
583 .Fa comp_dn
584 is given by
585 .Fa length .
586 The compression uses
587 an array of pointers
588 .Fa dnptrs
589 to previously-compressed names in the current message.
590 The first pointer points to
591 to the beginning of the message and the list ends with
592 .Dv NULL .
593 The limit to the array is specified by
594 .Fa lastdnptr .
595 A side effect of
596 .Fn dn_comp
597 is to update the list of pointers for labels inserted into the message
598 as the name is compressed. If
599 .Fa dnptr
600 is
601 .Dv NULL ,
602 names are not compressed. If
603 .Fa lastdnptr
604 is
605 .Dv NULL ,
606 the list of labels is not updated.
607 .Pp
608 The
609 .Fn dn_expand
610 entry
611 expands the compressed domain name
612 .Fa comp_dn
613 to a full domain name.
614 The compressed name is contained in a query or reply message;
615 .Fa msg
616 is a pointer to the beginning of the message.
617 .Fa eomorig
618 is a pointer to the first location after the message.
619 The uncompressed name is placed in the buffer indicated by
620 .Fa exp_dn
621 which is of size
622 .Fa length .
623 The size of compressed name is returned or \-1 if there was an error.
624 .Pp
625 The variables
626 .Ft statp->res_h_errno
627 /
628 .Ft _res.res_h_errno
629 and external variable
630 .Ft h_errno
631 is set whenever an error occurs during resolver operation. The following
632 definitions are given in
633 .Pa <netdb.h> :
634 .Bd -literal
635 #define NETDB_INTERNAL -1 /* see errno */
636 #define NETDB_SUCCESS 0 /* no problem */
637 #define HOST_NOT_FOUND 1 /* Authoritative Answer Host not found */
638 #define TRY_AGAIN 2 /* Non-Authoritative not found, or SERVFAIL */
639 #define NO_RECOVERY 3 /* Non-Recoverable: FORMERR, REFUSED, NOTIMP */
640 #define NO_DATA 4 /* Valid name, no data for requested type */
641 .Ed
642 .Pp
643 The
644 .Fn herror
645 function writes a message to the diagnostic output consisting of the string
646 parameter
647 .Fa s ,
648 the constant string ": ", and a message corresponding to the value of
649 .Ft h_errno .
650 .Pp
651 The
652 .Fn hstrerror
653 function returns a string which is the message text corresponding to the
654 value of the
655 .Fa err
656 parameter.
657 .Sh FILES
658 .Bl -tag -width "/etc/resolv.conf "
659 .It Pa /etc/resolv.conf
660 See
661 .Xr resolver @FORMAT_EXT@ .
662 .El
663 .Sh SEE ALSO
664 .Xr gethostbyname @LIB_NETWORK_EXT@ ,
665 .Xr hostname @DESC_EXT@ ,
666 .Xr resolver @FORMAT_EXT@ ;
667 RFC1032, RFC1033, RFC1034, RFC1035, RFC974;
668 SMM:11,
669 .Dq Name Server Operations Guide for BIND