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28 .\" @(#)resolver.3 8.1 (Berkeley) 6/4/93
30 .Dd September 15, 2022
56 .Fa "const char *dname"
64 .Fa "const char *dname"
73 .Fa "const char *dname"
76 .Fa "const u_char *data"
78 .Fa "const u_char *newrr_in"
84 .Fa "const u_char *msg"
93 .Fa "const char *exp_dn"
97 .Fa "u_char **lastdnptr"
101 .Fa "const u_char *msg"
102 .Fa "const u_char *eomorig"
103 .Fa "const u_char *comp_dn"
108 .Fn dn_skipname "const u_char *comp_dn" "const u_char *eom"
110 .Fn ns_get16 "const u_char *src"
112 .Fn ns_get32 "const u_char *src"
114 .Fn ns_put16 "u_int src" "u_char *dst"
116 .Fn ns_put32 "u_long src" "u_char *dst"
118 These routines are used for making, sending and interpreting
119 query and reply messages with Internet domain name servers.
121 Global configuration and state information that is used by the
122 resolver routines is kept in the structure
124 Most of the values have reasonable defaults and can be ignored.
131 Options are stored as a simple bit mask containing the bitwise ``or''
132 of the options enabled.
133 .Bl -tag -width RES_USE_INET6
135 True if the initial name server address and default domain name are
140 Print debugging messages.
142 Accept authoritative answers only.
145 should continue until it finds an authoritative answer or finds an error.
146 Currently this is not implemented.
150 connections for queries instead of
158 connection open between
160 This is useful only in programs that regularly do many queries.
162 should be the normal mode used.
164 Unused currently (ignore truncation errors, i.e., do not retry with
167 Set the recursion-desired bit in queries.
170 does not do iterative queries and expects the name server
171 to handle recursion.)
175 will append the default domain name to single-component names
176 (those that do not contain a dot).
177 This option is enabled by default.
179 If this option is set,
181 will search for host names in the current domain and in parent domains; see
183 This is used by the standard host lookup routine
184 .Xr gethostbyname 3 .
185 This option is enabled by default.
187 This option turns off the user level aliasing feature controlled by the
189 environment variable.
190 Network daemons should set this option.
192 Enables support for IPv6-only applications.
193 This causes IPv4 addresses to be returned as an IPv4 mapped address.
197 .Li ::ffff:10.1.1.1 .
198 The option is meaningful with certain kernel configuration only.
200 Enables support for OPT pseudo-RR for EDNS0 extension.
201 With the option, resolver code will attach OPT pseudo-RR into DNS queries,
202 to inform of our receive buffer size.
203 The option will allow DNS servers to take advantage of non-default receive
204 buffer size, and to send larger replies.
205 DNS query packets with EDNS0 extension is not compatible with
206 non-EDNS0 DNS servers.
212 reads the configuration file (if any; see
214 to get the default domain name,
216 the Internet address of the local name server(s).
217 If no server is configured, the host running
218 the resolver is tried.
219 The current domain name is defined by the hostname
220 if not specified in the configuration file;
221 it can be overridden by the environment variable
223 This environment variable may contain several blank-separated
224 tokens if you wish to override the
226 on a per-process basis.
227 This is similar to the
229 command in the configuration file.
230 Another environment variable
233 override certain internal resolver options which are otherwise
234 set by changing fields in the
236 structure or are inherited from the configuration file's
241 environment variable is explained in
243 Initialization normally occurs on the first call
244 to one of the following routines.
248 function provides an interface to the server query mechanism.
249 It constructs a query, sends it to the local server,
250 awaits a response, and makes preliminary checks on the reply.
251 The query requests information of the specified
255 for the specified fully-qualified domain name
257 The reply message is left in the
261 supplied by the caller.
265 routine makes a query and awaits a response like
267 but in addition, it implements the default and search rules
273 It returns the first successful reply.
275 The remaining routines are lower-level routines used by
280 constructs a standard query message and places it in
282 It returns the size of the query, or \-1 if the query is
289 but can be any of the query types defined in
291 The domain name for the query is given by
296 is currently unused but is intended for making update messages.
301 sends a pre-formatted query and returns an answer.
306 is not set, send the query to the local name server, and
307 handle timeouts and retries.
308 The length of the reply message is returned, or
309 \-1 if there were errors.
314 compresses the domain name
318 The size of the compressed name is returned or \-1 if there were errors.
319 The size of the array pointed to by
326 to previously-compressed names in the current message.
327 The first pointer points to
328 the beginning of the message and the list ends with
330 The limit to the array is specified by
334 is to update the list of pointers for
335 labels inserted into the message
336 as the name is compressed.
341 names are not compressed.
346 the list of labels is not updated.
351 expands the compressed domain name
353 to a full domain name
354 The compressed name is contained in a query or reply message;
356 is a pointer to the beginning of the message.
357 The uncompressed name is placed in the buffer indicated by
361 The size of compressed name is returned or \-1 if there was an error.
365 function skips over a compressed domain name, which starts at a location
368 The compressed name is contained in a query or reply message;
370 is a pointer to the end of the message.
371 The size of compressed name is returned or \-1 if there was
376 function gets a 16-bit quantity from a buffer pointed to by
381 function gets a 32-bit quantity from a buffer pointed to by
386 function puts a 16-bit quantity
388 to a buffer pointed to by
393 function puts a 32-bit quantity
395 to a buffer pointed to by
397 .Sh IMPLEMENTATION NOTES
398 This implementation of the resolver is thread-safe, but it will not
399 function properly if the programmer attempts to declare his or her own
401 structure in an attempt to replace the per-thread version referred to
404 The following compile-time option can be specified to change the default
405 behavior of resolver routines when necessary.
406 .Bl -tag -width RES_ENFORCE_RFC1034
407 .It Dv RES_ENFORCE_RFC1034
408 If this symbol is defined during compile-time,
410 will enforce RFC 1034 check, namely, disallow using of underscore character
412 This is used by the standard host lookup routines like
413 .Xr gethostbyname 3 .
414 For compatibility reasons this option is not enabled by default.
419 function will return 0 on success, or \-1 in a threaded program if
420 per-thread storage could not be allocated.
427 functions return the size of the response on success, or \-1 if an
431 may be checked to determine the reason for error.
434 for more information.
436 .Bl -tag -width /etc/resolv.conf
437 .It Pa /etc/resolv.conf
438 The configuration file,
443 .Xr gethostbyname 3 ,