aboutsummaryrefslogtreecommitdiff
path: root/resolv/res_init.c
blob: fa46ce7813c1f8af1418c5a99cfe4e414d575142 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
/* Resolver state initialization and resolv.conf parsing.
   Copyright (C) 1995-2017 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

/*
 * Copyright (c) 1985, 1989, 1993
 *    The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * Portions Copyright (c) 1993 by Digital Equipment Corporation.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies, and that
 * the name of Digital Equipment Corporation not be used in advertising or
 * publicity pertaining to distribution of the document or software without
 * specific, written prior permission.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND DIGITAL EQUIPMENT CORP. DISCLAIMS ALL
 * WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS.   IN NO EVENT SHALL DIGITAL EQUIPMENT
 * CORPORATION BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

/*
 * Portions Copyright (c) 1996-1999 by Internet Software Consortium.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
 * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
 * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

#include <ctype.h>
#include <netdb.h>
#include <resolv/resolv-internal.h>
#include <res_hconf.h>
#include <stdio.h>
#include <stdio_ext.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdint.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>
#include <net/if.h>
#include <netinet/in.h>
#include <sys/param.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/types.h>
#include <inet/net-internal.h>
#include <errno.h>
#include <resolv_conf.h>

static uint32_t net_mask (struct in_addr);

int
res_ninit (res_state statp)
{
  return __res_vinit (statp, 0);
}
libc_hidden_def (__res_ninit)

/* Return true if CH separates the netmask in the "sortlist"
   directive.  */
static inline bool
is_sort_mask (char ch)
{
  return ch == '/' || ch == '&';
}

/* Array of name server addresses.  */
#define DYNARRAY_STRUCT nameserver_list
#define DYNARRAY_ELEMENT const struct sockaddr *
#define DYNARRAY_ELEMENT_FREE(e) free ((struct sockaddr *) *(e))
#define DYNARRAY_INITIAL_SIZE 3
#define DYNARRAY_PREFIX nameserver_list_
#include <malloc/dynarray-skeleton.c>

/* Array of strings for the search array.  The backing store is
   managed separately.  */
#define DYNARRAY_STRUCT search_list
#define DYNARRAY_ELEMENT const char *
#define DYNARRAY_INITIAL_SIZE 6
#define DYNARRAY_PREFIX search_list_
#include <malloc/dynarray-skeleton.c>

/* Array of name server addresses.  */
#define DYNARRAY_STRUCT sort_list
#define DYNARRAY_ELEMENT struct resolv_sortlist_entry
#define DYNARRAY_INITIAL_SIZE 0
#define DYNARRAY_PREFIX sort_list_
#include <malloc/dynarray-skeleton.c>

/* resolv.conf parser state and results.  */
struct resolv_conf_parser
{
  char *buffer;            /* Temporary buffer for reading lines.  */

  struct nameserver_list nameserver_list; /* Nameserver addresses.  */

  char *search_list_store; /* Backing storage for search list entries.  */
  struct search_list search_list; /* Points into search_list_store.  */

  struct sort_list sort_list;   /* Address preference sorting list.  */

  /* Configuration template.  The non-array elements are filled in
     directly.  The array elements are updated prior to the call to
     __resolv_conf_attach.  */
  struct resolv_conf template;
};

/* Return true if *PREINIT contains actual preinitialization.  */
static bool
has_preinit_values (const struct __res_state *preinit)
{
  return (preinit->retrans != 0 && preinit->retrans != RES_TIMEOUT)
    || (preinit->retry != 0 && preinit->retry != RES_DFLRETRY)
    || (preinit->options != 0
        && (preinit->options & ~RES_INIT) != RES_DEFAULT);
}

static void
resolv_conf_parser_init (struct resolv_conf_parser *parser,
                         const struct __res_state *preinit)
{
  parser->buffer = NULL;
  parser->search_list_store = NULL;
  nameserver_list_init (&parser->nameserver_list);
  search_list_init (&parser->search_list);
  sort_list_init (&parser->sort_list);

  if (preinit != NULL)
    {
      parser->template.retrans = preinit->retrans;
      parser->template.retry = preinit->retry;
      parser->template.options = preinit->options | RES_INIT;
    }
  else
    {
      parser->template.retrans = RES_TIMEOUT;
      parser->template.retry = RES_DFLRETRY;
      parser->template.options = RES_DEFAULT | RES_INIT;
    }
  parser->template.ndots = 1;
}

static void
resolv_conf_parser_free (struct resolv_conf_parser *parser)
{
  free (parser->buffer);
  free (parser->search_list_store);
  nameserver_list_free (&parser->nameserver_list);
  search_list_free (&parser->search_list);
  sort_list_free (&parser->sort_list);
}

/* Allocate a struct sockaddr_in object on the heap, with the
   specified address and port.  */
static struct sockaddr *
allocate_address_v4 (struct in_addr a, uint16_t port)
{
  struct sockaddr_in *sa4 = malloc (sizeof (*sa4));
  if (sa4 == NULL)
    return NULL;
  sa4->sin_family = AF_INET;
  sa4->sin_addr = a;
  sa4->sin_port = htons (port);
  return (struct sockaddr *) sa4;
}

/* Try to obtain the domain name from the host name and store it in
   *RESULT.  Return false on memory allocation failure.  If the domain
   name cannot be determined for any other reason, write NULL to
   *RESULT and return true.  */
static bool
domain_from_hostname (char **result)
{
  char buf[256];
  /* gethostbyname may not terminate the buffer.  */
  buf[sizeof (buf) - 1] = '\0';
  if (__gethostname (buf, sizeof (buf) - 1) == 0)
    {
      char *dot = strchr (buf, '.');
      if (dot != NULL)
        {
          *result = __strdup (dot + 1);
          if (*result == NULL)
            return false;
          return true;
        }
    }
  *result = NULL;
  return true;
}

static void res_setoptions (struct resolv_conf_parser *, const char *options);

/* Internal helper function for __res_vinit, to aid with resource
   deallocation and error handling.  Return true on success, false on
   failure.  */
static bool
res_vinit_1 (FILE *fp, struct resolv_conf_parser *parser)
{
  char *cp;
  size_t buffer_size = 0;
  bool haveenv = false;

  /* Allow user to override the local domain definition.  */
  if ((cp = getenv ("LOCALDOMAIN")) != NULL)
    {
      /* The code below splits the string in place.  */
      cp = __strdup (cp);
      if (cp == NULL)
        return false;
      free (parser->search_list_store);
      parser->search_list_store = cp;
      haveenv = true;

      /* The string will be truncated as needed below.  */
      search_list_add (&parser->search_list, cp);

      /* Set search list to be blank-separated strings from rest of
         env value.  Permits users of LOCALDOMAIN to still have a
         search list, and anyone to set the one that they want to use
         as an individual (even more important now that the rfc1535
         stuff restricts searches).  */
      for (bool in_name = true; *cp != '\0'; cp++)
        {
          if (*cp == '\n')
            {
              *cp = '\0';
              break;
            }
          else if (*cp == ' ' || *cp == '\t')
            {
              *cp = '\0';
              in_name = false;
            }
          else if (!in_name)
            {
              search_list_add (&parser->search_list, cp);
              in_name = true;
            }
        }
    }

#define MATCH(line, name)                       \
  (!strncmp ((line), name, sizeof (name) - 1)     \
   && ((line)[sizeof (name) - 1] == ' '           \
       || (line)[sizeof (name) - 1] == '\t'))

  if (fp != NULL)
    {
      /* No threads use this stream.  */
      __fsetlocking (fp, FSETLOCKING_BYCALLER);
      /* Read the config file.  */
      while (true)
        {
          {
            ssize_t ret = __getline (&parser->buffer, &buffer_size, fp);
            if (ret <= 0)
              {
                if (_IO_ferror_unlocked (fp))
                  return false;
                else
                  break;
              }
          }

          /* Skip comments.  */
          if (*parser->buffer == ';' || *parser->buffer == '#')
            continue;
          /* Read default domain name.  */
          if (MATCH (parser->buffer, "domain"))
            {
              if (haveenv)
                /* LOCALDOMAIN overrides the configuration file.  */
                continue;
              cp = parser->buffer + sizeof ("domain") - 1;
              while (*cp == ' ' || *cp == '\t')
                cp++;
              if ((*cp == '\0') || (*cp == '\n'))
                continue;

              cp = __strdup (cp);
              if (cp == NULL)
                return false;
              free (parser->search_list_store);
              parser->search_list_store = cp;
              search_list_clear (&parser->search_list);
              search_list_add (&parser->search_list, cp);
              /* Replace trailing whitespace.  */
              if ((cp = strpbrk (cp, " \t\n")) != NULL)
                *cp = '\0';
              continue;
            }
          /* Set search list.  */
          if (MATCH (parser->buffer, "search"))
            {
              if (haveenv)
                /* LOCALDOMAIN overrides the configuration file.  */
                continue;
              cp = parser->buffer + sizeof ("search") - 1;
              while (*cp == ' ' || *cp == '\t')
                cp++;
              if ((*cp == '\0') || (*cp == '\n'))
                continue;

              {
                char *p = strchr (cp, '\n');
                if (p != NULL)
                  *p = '\0';
              }
              cp = __strdup (cp);
              if (cp == NULL)
                return false;
              free (parser->search_list_store);
              parser->search_list_store = cp;

              /* The string is truncated below.  */
              search_list_clear (&parser->search_list);
              search_list_add (&parser->search_list, cp);

              /* Set search list to be blank-separated strings on rest
                 of line.  */
              for (bool in_name = true; *cp != '\0'; cp++)
                {
                  if (*cp == ' ' || *cp == '\t')
                    {
                      *cp = '\0';
                      in_name = false;
                    }
                  else if (!in_name)
                    {
                      search_list_add (&parser->search_list, cp);
                      in_name = true;
                    }
                }
              continue;
            }
          /* Read nameservers to query.  */
          if (MATCH (parser->buffer, "nameserver"))
            {
              struct in_addr a;

              cp = parser->buffer + sizeof ("nameserver") - 1;
              while (*cp == ' ' || *cp == '\t')
                cp++;
              struct sockaddr *sa;
              if ((*cp != '\0') && (*cp != '\n') && __inet_aton (cp, &a))
                {
                  sa = allocate_address_v4 (a, NAMESERVER_PORT);
                  if (sa == NULL)
                    return false;
                }
              else
                {
                  struct in6_addr a6;
                  char *el;

                  if ((el = strpbrk (cp, " \t\n")) != NULL)
                    *el = '\0';
                  if ((el = strchr (cp, SCOPE_DELIMITER)) != NULL)
                    *el = '\0';
                  if ((*cp != '\0') && (__inet_pton (AF_INET6, cp, &a6) > 0))
                    {
                      struct sockaddr_in6 *sa6;

                      sa6 = malloc (sizeof (*sa6));
                      if (sa6 == NULL)
                        return false;

                      sa6->sin6_family = AF_INET6;
                      sa6->sin6_port = htons (NAMESERVER_PORT);
                      sa6->sin6_flowinfo = 0;
                      sa6->sin6_addr = a6;

                      sa6->sin6_scope_id = 0;
                      if (__glibc_likely (el != NULL))
                        /* Ignore errors, for backwards
                           compatibility.  */
                        __inet6_scopeid_pton
                          (&a6, el + 1, &sa6->sin6_scope_id);
                      sa = (struct sockaddr *) sa6;
                    }
                  else
                    /* IPv6 address parse failure.  */
                    sa = NULL;
                }
              if (sa != NULL)
                {
                  const struct sockaddr **p = nameserver_list_emplace
                    (&parser->nameserver_list);
                  if (p != NULL)
                    *p = sa;
                }
              continue;
            }
          if (MATCH (parser->buffer, "sortlist"))
            {
              struct in_addr a;

              cp = parser->buffer + sizeof ("sortlist") - 1;
              while (true)
                {
                  while (*cp == ' ' || *cp == '\t')
                    cp++;
                  if (*cp == '\0' || *cp == '\n' || *cp == ';')
                    break;
                  char *net = cp;
                  while (*cp && !is_sort_mask (*cp) && *cp != ';'
                         && isascii (*cp) && !isspace (*cp))
                    cp++;
                  char separator = *cp;
                  *cp = 0;
                  struct resolv_sortlist_entry e;
                  if (__inet_aton (net, &a))
                    {
                      e.addr = a;
                      if (is_sort_mask (separator))
                        {
                          *cp++ = separator;
                          net = cp;
                          while (*cp && *cp != ';'
                                 && isascii (*cp) && !isspace (*cp))
                            cp++;
                          separator = *cp;
                          *cp = 0;
                          if (__inet_aton (net, &a))
                            e.mask = a.s_addr;
                          else
                            e.mask = net_mask (e.addr);
                        }
                      else
                        e.mask = net_mask (e.addr);
                      sort_list_add (&parser->sort_list, e);
                    }
                  *cp = separator;
                }
              continue;
            }
          if (MATCH (parser->buffer, "options"))
            {
              res_setoptions (parser, parser->buffer + sizeof ("options") - 1);
              continue;
            }
        }
      fclose (fp);
    }
  if (__glibc_unlikely (nameserver_list_size (&parser->nameserver_list) == 0))
    {
      const struct sockaddr **p
        = nameserver_list_emplace (&parser->nameserver_list);
      if (p == NULL)
        return false;
      *p = allocate_address_v4 (__inet_makeaddr (IN_LOOPBACKNET, 1),
                                NAMESERVER_PORT);
      if (*p == NULL)
        return false;
    }

  if (search_list_size (&parser->search_list) == 0)
    {
      char *domain;
      if (!domain_from_hostname (&domain))
        return false;
      if (domain != NULL)
        {
          free (parser->search_list_store);
          parser->search_list_store = domain;
          search_list_add (&parser->search_list, domain);
        }
    }

  if ((cp = getenv ("RES_OPTIONS")) != NULL)
    res_setoptions (parser, cp);

  if (nameserver_list_has_failed (&parser->nameserver_list)
      || search_list_has_failed (&parser->search_list)
      || sort_list_has_failed (&parser->sort_list))
    {
      __set_errno (ENOMEM);
      return false;
    }

  return true;
}

struct resolv_conf *
__resolv_conf_load (struct __res_state *preinit)
{
  /* Ensure that /etc/hosts.conf has been loaded (once).  */
  _res_hconf_init ();

  FILE *fp = fopen (_PATH_RESCONF, "rce");
  if (fp == NULL)
    switch (errno)
      {
      case EACCES:
      case EISDIR:
      case ELOOP:
      case ENOENT:
      case ENOTDIR:
      case EPERM:
        /* Ignore these errors.  They are persistent errors caused
           by file system contents.  */
        break;
      default:
        /* Other errors refer to resource allocation problems and
           need to be handled by the application.  */
        return NULL;
      }

  struct resolv_conf_parser parser;
  resolv_conf_parser_init (&parser, preinit);

  struct resolv_conf *conf = NULL;
  if (res_vinit_1 (fp, &parser))
    {
      parser.template.nameserver_list
        = nameserver_list_begin (&parser.nameserver_list);
      parser.template.nameserver_list_size
        = nameserver_list_size (&parser.nameserver_list);
      parser.template.search_list = search_list_begin (&parser.search_list);
      parser.template.search_list_size
        = search_list_size (&parser.search_list);
      parser.template.sort_list = sort_list_begin (&parser.sort_list);
      parser.template.sort_list_size = sort_list_size (&parser.sort_list);
      conf = __resolv_conf_allocate (&parser.template);
    }
  resolv_conf_parser_free (&parser);

  return conf;
}

/* Set up default settings.  If the /etc/resolv.conf configuration
   file exist, the values there will have precedence.  Otherwise, the
   server address is set to INADDR_LOOPBACK and the default domain
   name comes from gethostname.  The RES_OPTIONS and LOCALDOMAIN
   environment variables can be used to override some settings.
   Return 0 if completes successfully, -1 on error.  */
int
__res_vinit (res_state statp, int preinit)
{
  struct resolv_conf *conf;
  if (preinit && has_preinit_values (statp))
    /* For the preinit case, we cannot use the cached configuration
       because some settings could be different.  */
    conf = __resolv_conf_load (statp);
  else
    conf = __resolv_conf_get_current ();
  if (conf == NULL)
    return -1;

  bool ok = __resolv_conf_attach (statp, conf);
  __resolv_conf_put (conf);
  if (ok)
    {
      if (preinit)
        statp->id = res_randomid ();
      return 0;
    }
  else
    return -1;
}

static void
res_setoptions (struct resolv_conf_parser *parser, const char *options)
{
  const char *cp = options;

  while (*cp)
    {
      /* Skip leading and inner runs of spaces.  */
      while (*cp == ' ' || *cp == '\t')
        cp++;
      /* Search for and process individual options.  */
      if (!strncmp (cp, "ndots:", sizeof ("ndots:") - 1))
        {
          int i = atoi (cp + sizeof ("ndots:") - 1);
          if (i <= RES_MAXNDOTS)
            parser->template.ndots = i;
          else
            parser->template.ndots = RES_MAXNDOTS;
        }
      else if (!strncmp (cp, "timeout:", sizeof ("timeout:") - 1))
        {
          int i = atoi (cp + sizeof ("timeout:") - 1);
          if (i <= RES_MAXRETRANS)
            parser->template.retrans = i;
          else
            parser->template.retrans = RES_MAXRETRANS;
        }
      else if (!strncmp (cp, "attempts:", sizeof ("attempts:") - 1))
        {
          int i = atoi (cp + sizeof ("attempts:") - 1);
          if (i <= RES_MAXRETRY)
            parser->template.retry = i;
          else
            parser->template.retry = RES_MAXRETRY;
        }
      else
        {
          static const struct
          {
            char str[22];
            uint8_t len;
            uint8_t clear;
            unsigned long int flag;
          } options[] = {
#define STRnLEN(str) str, sizeof (str) - 1
            { STRnLEN ("inet6"), 0, DEPRECATED_RES_USE_INET6 },
            { STRnLEN ("rotate"), 0, RES_ROTATE },
            { STRnLEN ("edns0"), 0, RES_USE_EDNS0 },
            { STRnLEN ("single-request-reopen"), 0, RES_SNGLKUPREOP },
            { STRnLEN ("single-request"), 0, RES_SNGLKUP },
            { STRnLEN ("no_tld_query"), 0, RES_NOTLDQUERY },
            { STRnLEN ("no-tld-query"), 0, RES_NOTLDQUERY },
            { STRnLEN ("no-reload"), 0, RES_NORELOAD },
            { STRnLEN ("use-vc"), 0, RES_USEVC }
          };
#define noptions (sizeof (options) / sizeof (options[0]))
          for (int i = 0; i < noptions; ++i)
            if (strncmp (cp, options[i].str, options[i].len) == 0)
              {
                if (options[i].clear)
                  parser->template.options &= options[i].flag;
                else
                  parser->template.options |= options[i].flag;
                break;
              }
        }
      /* Skip to next run of spaces.  */
      while (*cp && *cp != ' ' && *cp != '\t')
        cp++;
    }
}

static uint32_t
net_mask (struct in_addr in)
{
  uint32_t i = ntohl (in.s_addr);

  if (IN_CLASSA (i))
    return htonl (IN_CLASSA_NET);
  else if (IN_CLASSB (i))
    return htonl (IN_CLASSB_NET);
  return htonl (IN_CLASSC_NET);
}