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1 .\" $NetBSD: resolver.3,v 1.28 2013/11/14 00:13:41 wiz Exp $
2 .\" Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
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33 .\" @(#)resolver.3 6.5 (Berkeley) 6/23/90
34 .\" Id: resolver.man3,v 1.2 2009/01/21 00:12:34 each Exp
35 .\"
36 .Dd November 13, 2013
37 .Dt RESOLVER 3
38 .Os
39 .Sh NAME
40 .Nm res_ninit ,
41 .Nm res_ourserver_p ,
42 .Nm fp_resstat ,
43 .Nm res_hostalias ,
44 .Nm res_pquery ,
45 .Nm res_nquery ,
46 .Nm res_nsearch ,
47 .Nm res_nquerydomain ,
48 .Nm res_nmkquery ,
49 .Nm res_nsend ,
50 .Nm res_nupdate ,
51 .Nm res_nmkupdate ,
52 .Nm res_nclose ,
53 .Nm res_nsendsigned ,
54 .Nm res_findzonecut ,
55 .Nm res_getservers ,
56 .Nm res_setservers ,
57 .Nm res_ndestroy ,
58 .Nm dn_comp ,
59 .Nm dn_expand ,
60 .\" .Nm hstrerror ,
61 .Nm res_init ,
62 .Nm res_isourserver ,
63 .Nm fp_nquery ,
64 .Nm p_query ,
65 .Nm hostalias ,
66 .Nm res_query ,
67 .Nm res_search ,
68 .Nm res_querydomain ,
69 .Nm res_mkquery ,
70 .Nm res_send ,
71 .Nm res_update ,
72 .Nm res_close ,
73 .\" .Nm herror
74 .Nd resolver routines
75 .Sh LIBRARY
76 .Lb libc
77 .Lb libresolv
78 .Sh SYNOPSIS
79 .In resolv.h
80 .In res_update.h
81 .Vt typedef struct __res_state *res_state ;
82 .Pp
83 .Ft int
84 .Fn res_ninit "res_state statp"
85 .Ft int
86 .Fn res_ourserver_p "const res_state statp" "const struct sockaddr_in *addr"
87 .Ft void
88 .Fn fp_resstat "const res_state statp" "FILE *fp"
89 .Ft "const char *"
90 .Fn res_hostalias "const res_state statp" "const char *name" "char *buf" "size_t buflen"
91 .Ft int
92 .Fn res_pquery "const res_state statp" "const u_char *msg" "int msglen" "FILE *fp"
93 .Ft int
94 .Fn res_nquery "res_state statp" "const char *dname" "int class" "int type" "u_char *answer" "int anslen"
95 .Ft int
96 .Fn res_nsearch "res_state statp" "const char *dname" "int class" "int type" "u_char * answer" "int anslen"
97 .Ft int
98 .Fn res_nquerydomain "res_state statp" "const char *name" "const char *domain" "int class" "int type" "u_char *answer" "int anslen"
99 .Ft int
100 .Fo res_nmkquery
101 .Fa "res_state statp"
102 .Fa "int op"
103 .Fa "const char *dname"
104 .Fa "int class"
105 .Fa "int type"
106 .Fa "const u_char *data"
107 .Fa "int datalen"
108 .Fa "const u_char *newrr"
109 .Fa "u_char *buf"
110 .Fa "int buflen"
111 .Fc
112 .Ft int
113 .Fn res_nsend "res_state statp" "const u_char *msg" "int msglen" "u_char *answer" "int anslen"
114 .Ft int
115 .Fn res_nupdate "res_state statp" "ns_updrec *rrecp_in"
116 .Ft int
117 .Fn res_nmkupdate "res_state statp" "ns_updrec *rrecp_in" "u_char *buf" "int buflen"
118 .Ft void
119 .Fn res_nclose "res_state statp"
120 .Ft int
121 .Fn res_nsendsigned "res_state statp" "const u_char *msg" "int msglen" "ns_tsig_key *key" "u_char *answer" "int anslen"
122 .Ft int
123 .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"
124 .Ft int
125 .Fn res_getservers "res_state statp" "union res_sockaddr_union *set" "int cnt"
126 .Ft void
127 .Fn res_setservers "res_state statp" "const union res_sockaddr_union *set" "int cnt"
128 .Ft void
129 .Fn res_ndestroy "res_state statp"
130 .Ft int
131 .Fn dn_comp "const char *exp_dn" "u_char *comp_dn" "int length" "u_char **dnptrs" "u_char **lastdnptr"
132 .Ft int
133 .Fn dn_expand "const u_char *msg" "const u_char *eomorig" "const u_char *comp_dn" "char *exp_dn" "int length"
134 .\" .Ft "const char *"
135 .\" .Fn hstrerror "int err"
136 .Ss DEPRECATED
137 .In sys/types.h
138 .In netinet/in.h
139 .In arpa/nameser.h
140 .In resolv.h
141 .In res_update.h
142 .Ft int
143 .Fn res_init "void"
144 .Ft int
145 .Fn res_isourserver "const struct sockaddr_in *addr"
146 .Ft int
147 .Fn fp_nquery "const u_char *msg" "int msglen" "FILE *fp"
148 .Ft void
149 .Fn p_query "const u_char *msg" "FILE *fp"
150 .Ft "const char *"
151 .Fn hostalias "const char *name"
152 .Ft int
153 .Fn res_query "const char *dname" "int class" "int type" "u_char *answer" "int anslen"
154 .Ft int
155 .Fn res_search "const char *dname" "int class" "int type" "u_char *answer" "int anslen"
156 .Ft int
157 .Fn res_querydomain "const char *name" "const char *domain" "int class" "int type" "u_char *answer" "int anslen"
158 .Ft int
159 .Fo res_mkquery
160 .Fa "int op"
161 .Fa "const char *dname"
162 .Fa "int class"
163 .Fa "int type"
164 .Fa "const char *data"
165 .Fa "int datalen"
166 .Fa "struct rrec *newrr"
167 .Fa "u_char *buf"
168 .Fa "int buflen"
169 .Fc
170 .Ft int
171 .Fn res_send "const u_char *msg" "int msglen" "u_char *answer" "int anslen"
172 .Ft int
173 .Fn res_update "ns_updrec *rrecp_in"
174 .Ft void
175 .Fn res_close "void"
176 .\" .Ft void
177 .\" .Fn herror "const char *s"
178 .Sh DESCRIPTION
179 These routines are used for making, sending and interpreting
180 query and reply messages with Internet domain name servers.
181 .Pp
182 State information is kept in
183 .Fa statp
184 and is used to control the behavior of these functions.
185 .Fa statp
186 should be set to all zeros prior to the first call to any of these functions.
187 .Pp
188 The functions
189 .Fn res_init ,
190 .Fn res_isourserver ,
191 .Fn fp_nquery ,
192 .Fn p_query ,
193 .Fn hostalias ,
194 .Fn res_query ,
195 .Fn res_search ,
196 .Fn res_querydomain ,
197 .Fn res_mkquery ,
198 .Fn res_send ,
199 .Fn res_update ,
200 .Fn res_close
201 .\" and
202 .\" .Fn herror
203 are deprecated and are supplied for compatability with old source
204 code.
205 They use global configuration and state information that is
206 kept in the structure
207 .Ft _res
208 rather than that referenced through
209 .Ft statp .
210 .Pp
211 Most of the values in
212 .Ft statp
213 and
214 .Ft _res
215 are initialized on the first call to
216 .Fn res_ninit
217 /
218 .Fn res_init
219 to reasonable defaults and can be ignored.
220 Options
221 stored in
222 .Ft statp->options
223 /
224 .Ft _res.options
225 are defined in
226 .Pa resolv.h
227 and are as follows.
228 Options are stored as a simple bit mask containing the bitwise
229 .Dq OR
230 of the options enabled.
231 .Bl -tag -width "RES_USE_INET6"
232 .It Dv RES_INIT
233 True if the initial name server address and default domain name are
234 initialized (i.e.,
235 .Fn res_ninit
236 /
237 .Fn res_init
238 has been called).
239 .It Dv RES_DEBUG
240 Print debugging messages.
241 .It Dv RES_AAONLY
242 Accept authoritative answers only.
243 Should continue until it finds an authoritative answer or finds an error.
244 Currently this is not implemented.
245 .It Dv RES_USEVC
246 Use TCP connections for queries instead of UDP datagrams.
247 .It Dv RES_STAYOPEN
248 Used with
249 .Dv RES_USEVC
250 to keep the TCP connection open between queries.
251 This is useful only in programs that regularly do many queries.
252 UDP should be the normal mode used.
253 .It Dv RES_IGNTC
254 Ignore truncation errors, i.e., don't retry with TCP.
255 .It Dv RES_RECURSE
256 Set the recursion-desired bit in queries.
257 This is the default.
258 (\c
259 .Fn res_nsend
260 /
261 .Fn res_send
262 does not do iterative queries and expects the name server
263 to handle recursion.)
264 .It Dv RES_DEFNAMES
265 If set,
266 .Fn res_nsearch
267 /
268 .Fn res_search
269 will append the default domain name to single-component names
270 (those that do not contain a dot).
271 This option is enabled by default.
272 .It Dv RES_DNSRCH
273 If this option is set,
274 .Fn res_nsearch
275 /
276 .Fn res_search
277 will search for host names in the current domain and in parent domains; see
278 .Xr hostname 7 .
279 This is used by the standard host lookup routine
280 .Xr gethostbyname 3 .
281 This option is enabled by default.
282 .It Dv RES_USE_INET6
283 Enables support for IPv6-only applications.
284 This causes IPv4 addresses to be returned as an IPv4 mapped address.
285 For example, 10.1.1.1 will be returned as ::ffff:10.1.1.1.
286 The option is meaningful with certain kernel configuration only.
287 .It Dv RES_USE_EDNS0
288 Enables support for OPT pseudo-RR for EDNS0 extension.
289 With the option, resolver code will attach OPT pseudo-RR into DNS queries,
290 to inform of our receive buffer size.
291 The option will allow DNS servers to take advantage of non-default receive
292 buffer size, and to send larger replies.
293 DNS query packets with EDNS0 extension is not compatible with
294 non-EDNS0 DNS servers.
295 .It Dv RES_NOALIASES
296 This option turns off the user level aliasing feature controlled by
297 the
298 .Ev HOSTALIASES
299 environment variable.
300 Network daemons should set this option.
301 .It Dv RES_ROTATE
302 This options causes the
303 .Fn res_nsend
304 /
305 .Fn res_send
306 to rotate the list of nameservers in
307 .Fa statp->nsaddr_list
308 /
309 .Fa _res.nsaddr_list .
310 .It Dv RES_KEEPTSIG
311 This option causes
312 .Fn res_nsendsigned
313 to leave the message unchanged after TSIG verification; otherwise the TSIG
314 record would be removed and the header updated.
315 .It Dv RES_NOTLDQUERY
316 This option causes
317 .Fn res_nsearch
318 to not attempt to resolve an unqualified name as if it were a top level
319 domain (TLD).
320 This option can cause problems if the site has "localhost" as a TLD rather
321 than having localhost on one or more elements of the search list.
322 This option has no effect if neither
323 .Dv RES_DEFNAMES
324 or
325 .Dv RES_DNSRCH
326 is set.
327 .El
328 .Pp
329 The
330 .Fn res_ninit
331 /
332 .Fn res_init
333 routine
334 reads the configuration file (if any; see
335 .Xr resolv.conf 5 )
336 to get the default domain name, search list and
337 the Internet address of the local name server(s).
338 If no server is configured, the host running the resolver is tried.
339 The current domain name is defined by the hostname
340 if not specified in the configuration file;
341 it can be overridden by the environment variable
342 .Ev LOCALDOMAIN .
343 This environment variable may contain several blank-separated
344 tokens if you wish to override the
345 .Fa search list
346 on a per-process basis.
347 This is similar to the
348 .Fa search
349 command in the configuration file.
350 Another environment variable
351 .Ev RES_OPTIONS
352 can be set to override certain internal resolver options which are otherwise
353 set by changing fields in the
354 .Ft statp
355 /
356 .Ft _res
357 structure or are inherited from the configuration file's
358 .Fa options
359 command.
360 The syntax of the
361 .Ev RES_OPTIONS
362 environment variable is explained in
363 .Xr resolv.conf 5 .
364 Initialization normally occurs on the first call
365 to one of the other resolver routines.
366 .Pp
367 In
368 .Nx
369 the initialization code also sets up a
370 .Xr kqueue 2
371 and creates a
372 .Xr kevent 2
373 watching a file descriptor that points to the resolver file.
374 Every resolver function calls the internal function
375 .Fn __res_check
376 which checks for a new
377 .Xr kevent 2
378 related to the
379 .Xr resolv.conf 5
380 file, and reloads the file if necessary.
381 This does not work if the file is accessed through a symlink and the symlink
382 changes to point to a different file.
383 To fix the symlink issue one could add a system call per resolver call to
384 get the current time, and reload every so often.
385 This is not done currently, but it is under consideration.
386 .Pp
387 The memory referred to by
388 .Ft statp
389 must be set to all zeros prior to the first call to
390 .Fn res_ninit .
391 .Fn res_ndestroy
392 should be call to free memory allocated by
393 .Fn res_ninit
394 after last use.
395 .Pp
396 The
397 .Fn res_nquery
398 /
399 .Fn res_query
400 functions provides interfaces to the server query mechanism.
401 They constructs a query, sends it to the local server,
402 awaits a response, and makes preliminary checks on the reply.
403 The query requests information of the specified
404 .Fa type
405 and
406 .Fa class
407 for the specified fully-qualified domain name
408 .Fa dname .
409 The reply message is left in the
410 .Fa answer
411 buffer with length
412 .Fa anslen
413 supplied by the caller.
414 .Fn res_nquery
415 /
416 .Fn res_query
417 return \-1 on error or the length of the answer.
418 .Pp
419 The
420 .Fn res_nsearch
421 /
422 .Fn res_search
423 routines make a query and awaits a response like
424 .Fn res_nquery
425 /
426 .Fn res_query ,
427 but in addition, it implements the default and search rules
428 controlled by the
429 .Dv RES_DEFNAMES
430 and
431 .Dv RES_DNSRCH
432 options.
433 It returns the length of the first successful reply which is stored in
434 .Ft answer
435 or \-1 on error.
436 .Pp
437 The remaining routines are lower-level routines used by
438 .Fn res_nquery
439 /
440 .Fn res_query .
441 The
442 .Fn res_nmkquery
443 /
444 .Fn res_mkquery
445 functions
446 constructs a standard query message and places it in
447 .Fa buf .
448 It returns the size of the query, or \-1 if the query is
449 larger than
450 .Fa buflen .
451 The query type
452 .Fa op
453 is usually
454 .Dv QUERY ,
455 but can be any of the query types defined in
456 .Aq Pa arpa/nameser.h .
457 The domain name for the query is given by
458 .Fa dname .
459 .Fa newrr
460 is currently unused but is intended for making update messages.
461 .Pp
462 The
463 .Fn res_nsend
464 /
465 .Fn res_send
466 /
467 .Fn res_nsendsigned
468 routines
469 sends a pre-formatted query and returns an answer.
470 It will call
471 .Fn res_ninit
472 /
473 .Fn res_init
474 if
475 .Dv RES_INIT
476 is not set, send the query to the local name server, and
477 handle timeouts and retries.
478 Additionally,
479 .Fn res_nsendsigned
480 will use TSIG signatures to add authentication to the query and verify the
481 response.
482 In this case, only one nameserver will be contacted.
483 The length of the reply message is returned, or \-1 if there were errors.
484 .Pp
485 .Fn res_nquery
486 /
487 .Fn res_query ,
488 .Fn res_nsearch
489 /
490 .Fn res_search
491 and
492 .Fn res_nsend
493 /
494 .Fn res_send
495 return a length that may be bigger than
496 .Fa anslen .
497 In that case the query should be retried with a bigger buffer.
498 NOTE the answer to the second query may be larger still so supplying
499 a buffer that bigger that the answer returned by the previous
500 query is recommended.
501 .Pp
502 .Fa answer
503 MUST be big enough to receive a maximum UDP response from the server or
504 parts of the answer will be silently discarded.
505 The default maximum UDP response size is 512 bytes.
506 .Pp
507 The function
508 .Fn res_ourserver_p
509 returns true when
510 .Fa inp
511 is one of the servers in
512 .Fa statp->nsaddr_list
513 /
514 .Fa _res.nsaddr_list .
515 .Pp
516 The functions
517 .Fn fp_nquery
518 /
519 .Fn p_query
520 print out the query and any answer in
521 .Fa msg
522 on
523 .Fa fp .
524 .Fn p_query
525 is equivalent to
526 .Fn fp_nquery
527 with
528 .Fa msglen
529 set to 512.
530 .Pp
531 The function
532 .Fn fp_resstat
533 prints out the active flag bits in
534 .Fa statp->options
535 preceeded by the text ";; res options:" on
536 .Fa file .
537 .Pp
538 The functions
539 .Fn res_hostalias
540 /
541 .Fn hostalias
542 lookup up name in the file referred to by the
543 .Ev HOSTALIASES
544 files return a fully qualified hostname if found or NULL if
545 not found or an error occurred.
546 .Fn res_hostalias
547 uses
548 .Fa buf
549 to store the result in,
550 .Fn hostalias
551 uses a static buffer.
552 .Pp
553 The functions
554 .Fn res_getservers
555 and
556 .Fn res_setservers
557 are used to get and set the list of server to be queried.
558 .Pp
559 The functions
560 .Fn res_nupdate
561 /
562 .Fn res_update
563 take a list of ns_updrec
564 .Fa rrecp_in .
565 Identifies the containing zone for each record and groups the records
566 according to containing zone maintaining in zone order then sends and update
567 request to the servers for these zones.
568 The number of zones updated is returned or \-1 on error.
569 Note that
570 .Fn res_nupdate
571 will perform TSIG authenticated dynamic update operations if the key is not
572 NULL.
573 .Pp
574 The function
575 .Fn res_findzonecut
576 discovers the closest enclosing zone cut for a specified domain name,
577 and finds the IP addresses of the zone's master servers.
578 .Pp
579 The functions
580 .Fn res_nmkupdate
581 /
582 .Fn res_mkupdate
583 take a linked list of ns_updrec
584 .Fa rrecp_in
585 and construct a UPDATE message in
586 .Fa buf .
587 .Fn res_nmkupdate
588 /
589 .Fn res_mkupdate
590 return the length of the constructed message on no error or one of the
591 following error values.
592 .Bl -inset -width "-5"
593 .It \-1
594 An error occurred parsing
595 .Fa rrecp_in .
596 .It \-2
597 The buffer
598 .Fa buf
599 was too small.
600 .It \-3
601 The first record was not a zone section or there was a section order problem.
602 The section order is S_ZONE, S_PREREQ and S_UPDATE.
603 .It \-4
604 A number overflow occurred.
605 .It \-5
606 Unknown operation or no records.
607 .El
608 .Pp
609 The functions
610 .Fn res_nclose
611 /
612 .Fn res_close
613 close any open files referenced through
614 .Fa statp
615 /
616 .Fa _res .
617 .Pp
618 The function
619 .Fn res_ndestroy
620 calls
621 .Fn res_nclose
622 then frees any memory allocated by
623 .Fn res_ninit .
624 .Pp
625 The
626 .Fn dn_comp
627 function
628 compresses the domain name
629 .Fa exp_dn
630 and stores it in
631 .Fa comp_dn .
632 The size of the compressed name is returned or \-1 if there were errors.
633 The size of the array pointed to by
634 .Fa comp_dn
635 is given by
636 .Fa length .
637 The compression uses
638 an array of pointers
639 .Fa dnptrs
640 to previously-compressed names in the current message.
641 The first pointer points to
642 the beginning of the message and the list ends with
643 .Dv NULL .
644 The limit to the array is specified by
645 .Fa lastdnptr .
646 A side effect of
647 .Fn dn_comp
648 is to update the list of pointers for labels inserted into the message
649 as the name is compressed.
650 If
651 .Fa dnptr
652 is
653 .Dv NULL ,
654 names are not compressed.
655 If
656 .Fa lastdnptr
657 is
658 .Dv NULL ,
659 the list of labels is not updated.
660 .Pp
661 The
662 .Fn dn_expand
663 entry expands the compressed domain name
664 .Fa comp_dn
665 to a full domain name.
666 The compressed name is contained in a query or reply message;
667 .Fa msg
668 is a pointer to the beginning of the message.
669 .Fa eomorig
670 is a pointer to the first location after the message.
671 The uncompressed name is placed in the buffer indicated by
672 .Fa exp_dn
673 which is of size
674 .Fa length .
675 The size of compressed name is returned or \-1 if there was an error.
676 .Pp
677 The variables
678 .Ft statp->res_h_errno
679 /
680 .Ft _res.res_h_errno
681 and external variable
682 .Ft h_errno
683 is set whenever an error occurs during resolver operation.
684 The following
685 definitions are given in
686 .Aq Pa netdb.h :
687 .Bd -literal
688 #define NETDB_INTERNAL -1
689 /* see errno */
690 #define NETDB_SUCCESS 0
691 /* no problem */
692 #define HOST_NOT_FOUND 1
693 /* Authoritative Answer Host not found */
694 #define TRY_AGAIN 2
695 /* Non-Authoritative not found, or SERVFAIL */
696 #define NO_RECOVERY 3
697 /* Non-Recoverable: FORMERR, REFUSED, NOTIMP */
698 #define NO_DATA 4
699 /* Valid name, no data for requested type */
700 .Ed
701 .\" .Pp
702 .\" The
703 .\" .Fn herror
704 .\" function writes a message to the diagnostic output consisting of the string
705 .\" parameter
706 .\" .Fa s ,
707 .\" the constant string ": ", and a message corresponding to the value of
708 .\" .Ft h_errno .
709 .\" .Pp
710 .\" The
711 .\" .Fn hstrerror
712 .\" function returns a string which is the message text corresponding to the
713 .\" value of the
714 .\" .Fa err
715 .\" parameter.
716 .Pp
717 The following functions are only in
718 .Dv libresolv :
719 .Fn res_findzonecut ,
720 .Fn res_nmkupdate ,
721 .Fn res_nsendsigned ,
722 and
723 .Fn res_nupdate .
724 All the rest are in both
725 .Dv libc
726 and
727 .Dv libresolv .
728 .Sh FILES
729 .Bl -tag -width "/etc/resolv.conf "
730 .It Pa /etc/resolv.conf
731 The configuration file, see
732 .Xr resolv.conf 5 .
733 .El
734 .Sh SEE ALSO
735 .Xr getaddrinfo 3 ,
736 .Xr gethostbyaddr 3 ,
737 .Xr gethostbyname 3 ,
738 .Xr getnameinfo 3 ,
739 .Xr resolv.conf 5 ,
740 .Xr hostname 7 ,
741 .Xr named 8
742 .Pp
743 .%T RFC 974 ,
744 .%T RFC 1032 ,
745 .%T RFC 1033 ,
746 .%T RFC 1034 ,
747 .%T RFC 1035 ,
748 .%T RFC 1535
749 .Rs
750 .%T "Name Server Operations Guide for BIND"
751 .Re
752 .Sh HISTORY
753 The
754 .Nm
755 function appeared in
756 .Bx 4.3 .