aboutsummaryrefslogtreecommitdiff
path: root/ares/ares_init.c
blob: 7246bc48474feb104fb433fcc18a642503ea1e95 (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
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
/* $Id$ */

/* Copyright 1998 by the Massachusetts Institute of Technology.
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting
 * documentation, and that the name of M.I.T. not be used in
 * advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 */

#include "setup.h"
#include <sys/types.h>

#if defined(WIN32) && !defined(WATT32)
#include "nameser.h"
#include <iphlpapi.h>
#include <malloc.h>

#else
#include <sys/param.h>
#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

#ifdef HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif

#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <arpa/nameser.h>
#ifdef HAVE_ARPA_NAMESER_COMPAT_H
#include <arpa/nameser_compat.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <time.h>
#include <errno.h>
#include "ares.h"
#include "ares_private.h"
#include "inet_net_pton.h"

#ifdef WATT32
#undef WIN32  /* Redefined in MingW/MSVC headers */
#endif

static int init_by_options(ares_channel channel, struct ares_options *options,
                           int optmask);
static int init_by_environment(ares_channel channel);
static int init_by_resolv_conf(ares_channel channel);
static int init_by_defaults(ares_channel channel);

static int config_nameserver(struct server_state **servers, int *nservers,
                             char *str);
static int set_search(ares_channel channel, const char *str);
static int set_options(ares_channel channel, const char *str);
static const char *try_option(const char *p, const char *q, const char *opt);
#ifndef WIN32
static int sortlist_alloc(struct apattern **sortlist, int *nsort, struct apattern *pat);
static int ip_addr(const char *s, int len, struct in_addr *addr);
static void natural_mask(struct apattern *pat);
static int config_domain(ares_channel channel, char *str);
static int config_lookup(ares_channel channel, const char *str,
                         const char *bindch, const char *filech);
static int config_sortlist(struct apattern **sortlist, int *nsort,
                           const char *str);
static char *try_config(char *s, const char *opt);
#endif

int ares_init(ares_channel *channelptr)
{
  return ares_init_options(channelptr, NULL, 0);
}

int ares_init_options(ares_channel *channelptr, struct ares_options *options,
                      int optmask)
{
  ares_channel channel;
  int i, status;
  struct server_state *server;
  struct timeval tv;

#ifdef CURLDEBUG
  const char *env = getenv("CARES_MEMDEBUG");

  if (env)
    curl_memdebug(env);
  env = getenv("CARES_MEMLIMIT");
  if (env)
    curl_memlimit(atoi(env));
#endif

  channel = malloc(sizeof(struct ares_channeldata));
  if (!channel)
    return ARES_ENOMEM;

  /* Set everything to distinguished values so we know they haven't
   * been set yet.
   */
  channel->flags = -1;
  channel->timeout = -1;
  channel->tries = -1;
  channel->ndots = -1;
  channel->udp_port = -1;
  channel->tcp_port = -1;
  channel->nservers = -1;
  channel->ndomains = -1;
  channel->nsort = -1;
  channel->lookups = NULL;
  channel->queries = NULL;
  channel->domains = NULL;
  channel->sortlist = NULL;
  channel->servers = NULL;
  channel->sock_state_cb = NULL;
  channel->sock_state_cb_data = NULL;

  /* Initialize configuration by each of the four sources, from highest
   * precedence to lowest.
   */
  status = init_by_options(channel, options, optmask);
  if (status == ARES_SUCCESS)
    status = init_by_environment(channel);
  if (status == ARES_SUCCESS)
    status = init_by_resolv_conf(channel);
  if (status == ARES_SUCCESS)
    status = init_by_defaults(channel);
  if (status != ARES_SUCCESS)
    {
      /* Something failed; clean up memory we may have allocated. */
      if (channel->servers)
        free(channel->servers);
      if (channel->domains)
        {
          for (i = 0; i < channel->ndomains; i++)
            free(channel->domains[i]);
          free(channel->domains);
        }
      if (channel->sortlist)
        free(channel->sortlist);
      if(channel->lookups)
        free(channel->lookups);
      free(channel);
      return status;
    }

  /* Trim to one server if ARES_FLAG_PRIMARY is set. */
  if ((channel->flags & ARES_FLAG_PRIMARY) && channel->nservers > 1)
    channel->nservers = 1;

  /* Initialize server states. */
  for (i = 0; i < channel->nservers; i++)
    {
      server = &channel->servers[i];
      server->udp_socket = ARES_SOCKET_BAD;
      server->tcp_socket = ARES_SOCKET_BAD;
      server->tcp_lenbuf_pos = 0;
      server->tcp_buffer = NULL;
      server->qhead = NULL;
      server->qtail = NULL;
    }

  /* Choose a somewhat random query ID.  The main point is to avoid
   * collisions with stale queries.  An attacker trying to spoof a DNS
   * answer also has to guess the query ID, but it's only a 16-bit
   * field, so there's not much to be done about that.
   */
  gettimeofday(&tv, NULL);
  channel->next_id = (unsigned short)
    (tv.tv_sec ^ tv.tv_usec ^ getpid()) & 0xffff;

  channel->queries = NULL;

  *channelptr = channel;
  return ARES_SUCCESS;
}

static int init_by_options(ares_channel channel, struct ares_options *options,
                           int optmask)
{
  int i;

  /* Easy stuff. */
  if ((optmask & ARES_OPT_FLAGS) && channel->flags == -1)
    channel->flags = options->flags;
  if ((optmask & ARES_OPT_TIMEOUT) && channel->timeout == -1)
    channel->timeout = options->timeout;
  if ((optmask & ARES_OPT_TRIES) && channel->tries == -1)
    channel->tries = options->tries;
  if ((optmask & ARES_OPT_NDOTS) && channel->ndots == -1)
    channel->ndots = options->ndots;
  if ((optmask & ARES_OPT_UDP_PORT) && channel->udp_port == -1)
    channel->udp_port = options->udp_port;
  if ((optmask & ARES_OPT_TCP_PORT) && channel->tcp_port == -1)
    channel->tcp_port = options->tcp_port;
  if ((optmask & ARES_OPT_SOCK_STATE_CB) && channel->sock_state_cb == NULL)
    {
      channel->sock_state_cb = options->sock_state_cb;
      channel->sock_state_cb_data = options->sock_state_cb_data;
    }

  /* Copy the servers, if given. */
  if ((optmask & ARES_OPT_SERVERS) && channel->nservers == -1)
    {
      /* Avoid zero size allocations at any cost */
      if (options->nservers > 0)
        {
          channel->servers =
            malloc(options->nservers * sizeof(struct server_state));
          if (!channel->servers)
            return ARES_ENOMEM;
          for (i = 0; i < options->nservers; i++)
            channel->servers[i].addr = options->servers[i];
        }
      channel->nservers = options->nservers;
    }

  /* Copy the domains, if given.  Keep channel->ndomains consistent so
   * we can clean up in case of error.
   */
  if ((optmask & ARES_OPT_DOMAINS) && channel->ndomains == -1)
    {
      /* Avoid zero size allocations at any cost */
      if (options->ndomains > 0)
      {
        channel->domains = malloc(options->ndomains * sizeof(char *));
        if (!channel->domains)
          return ARES_ENOMEM;
        for (i = 0; i < options->ndomains; i++)
          {
            channel->ndomains = i;
            channel->domains[i] = strdup(options->domains[i]);
            if (!channel->domains[i])
              return ARES_ENOMEM;
          }
      }
      channel->ndomains = options->ndomains;
    }

  /* Set lookups, if given. */
  if ((optmask & ARES_OPT_LOOKUPS) && !channel->lookups)
    {
      channel->lookups = strdup(options->lookups);
      if (!channel->lookups)
        return ARES_ENOMEM;
    }

  return ARES_SUCCESS;
}

static int init_by_environment(ares_channel channel)
{
  const char *localdomain, *res_options;
  int status;

  localdomain = getenv("LOCALDOMAIN");
  if (localdomain && channel->ndomains == -1)
    {
      status = set_search(channel, localdomain);
      if (status != ARES_SUCCESS)
        return status;
    }

  res_options = getenv("RES_OPTIONS");
  if (res_options)
    {
      status = set_options(channel, res_options);
      if (status != ARES_SUCCESS)
        return status;
    }

  return ARES_SUCCESS;
}

#ifdef WIN32
/*
 * Warning: returns a dynamically allocated buffer, the user MUST
 * use free() if the function returns 1
 */
static int get_res_nt(HKEY hKey, const char *subkey, char **obuf)
{
  /* Test for the size we need */
  DWORD size = 0;
  int result;

  result = RegQueryValueEx(hKey, subkey, 0, NULL, NULL, &size);
  if ((result != ERROR_SUCCESS && result != ERROR_MORE_DATA) || !size)
    return 0;
  *obuf = malloc(size+1);
  if (!*obuf)
    return 0;

  if (RegQueryValueEx(hKey, subkey, 0, NULL,
                      (LPBYTE)*obuf, &size) != ERROR_SUCCESS)
  {
    free(*obuf);
    return 0;
  }
  if (size == 1)
  {
    free(*obuf);
    return 0;
  }
  return 1;
}

static int get_res_interfaces_nt(HKEY hKey, const char *subkey, char **obuf)
{
  char enumbuf[39]; /* GUIDs are 38 chars + 1 for NULL */
  DWORD enum_size = 39;
  int idx = 0;
  HKEY hVal;

  while (RegEnumKeyEx(hKey, idx++, enumbuf, &enum_size, 0,
                      NULL, NULL, NULL) != ERROR_NO_MORE_ITEMS)
  {
    int rc;

    enum_size = 39;
    if (RegOpenKeyEx(hKey, enumbuf, 0, KEY_QUERY_VALUE, &hVal) !=
        ERROR_SUCCESS)
      continue;
    rc = get_res_nt(hVal, subkey, obuf);
      RegCloseKey(hVal);
    if (rc)
      return 1;
    }
  return 0;
}

static int get_iphlpapi_dns_info (char *ret_buf, size_t ret_size)
{
  FIXED_INFO    *fi   = alloca (sizeof(*fi));
  DWORD          size = sizeof (*fi);
  typedef DWORD (WINAPI* get_net_param_func) (FIXED_INFO*, DWORD*);
  get_net_param_func GetNetworkParams;  /* available only on Win-98/2000+ */
  HMODULE        handle;
  IP_ADDR_STRING *ipAddr;
  int            i, count = 0;
  int            debug  = 0;
  size_t         ip_size = sizeof("255.255.255.255,")-1;
  size_t         left = ret_size;
  char          *ret = ret_buf;
  HRESULT        res;

  if (!fi)
     return (0);

  handle = LoadLibrary ("iphlpapi.dll");
  if (!handle)
     return (0);

  GetNetworkParams = (get_net_param_func) GetProcAddress (handle, "GetNetworkParams");
  if (!GetNetworkParams)
     goto quit;

  res = (*GetNetworkParams) (fi, &size);
  if ((res != ERROR_BUFFER_OVERFLOW) && (res != ERROR_SUCCESS))
     goto quit;

  fi = alloca (size);
  if (!fi || (*GetNetworkParams) (fi, &size) != ERROR_SUCCESS)
     goto quit;

  if (debug)
  {
    printf ("Host Name: %s\n", fi->HostName);
    printf ("Domain Name: %s\n", fi->DomainName);
    printf ("DNS Servers:\n"
            "    %s (primary)\n", fi->DnsServerList.IpAddress.String);
  }
  if (strlen(fi->DnsServerList.IpAddress.String) > 0 &&
      inet_addr(fi->DnsServerList.IpAddress.String) != INADDR_NONE &&
      left > ip_size)
  {
    ret += sprintf (ret, "%s,", fi->DnsServerList.IpAddress.String);
    left -= ret - ret_buf;
    count++;
  }

  for (i = 0, ipAddr = fi->DnsServerList.Next; ipAddr && left > ip_size;
       ipAddr = ipAddr->Next, i++)
  {
    if (inet_addr(ipAddr->IpAddress.String) != INADDR_NONE)
    {
       ret += sprintf (ret, "%s,", ipAddr->IpAddress.String);
       left -= ret - ret_buf;
       count++;
    }
    if (debug)
       printf ("    %s (secondary %d)\n", ipAddr->IpAddress.String, i+1);
  }

quit:
  if (handle)
     FreeLibrary (handle);

  if (debug && left <= ip_size)
     printf ("Too many nameservers. Truncating to %d addressess", count);
  if (ret > ret_buf)
     ret[-1] = '\0';
  return (count);
}
#endif

static int init_by_resolv_conf(ares_channel channel)
{
  char *line = NULL;
  int status = -1, nservers = 0, nsort = 0;
  struct server_state *servers = NULL;
  struct apattern *sortlist = NULL;

#ifdef WIN32

    /*
  NameServer info via IPHLPAPI (IP helper API):
    GetNetworkParams() should be the trusted source for this.
    Available in Win-98/2000 and later. If that fail, fall-back to
    registry information.

  NameServer Registry:

   On Windows 9X, the DNS server can be found in:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\MSTCP\NameServer

        On Windows NT/2000/XP/2003:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\NameServer
        or
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\DhcpNameServer
        or
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\{AdapterID}\
NameServer
        or
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\{AdapterID}\
DhcpNameServer
   */

  HKEY mykey;
  HKEY subkey;
  DWORD data_type;
  DWORD bytes;
  DWORD result;
  char  buf[256];

  if (channel->nservers > -1)  /* don't override ARES_OPT_SERVER */
     return ARES_SUCCESS;

  if (get_iphlpapi_dns_info(buf,sizeof(buf)) > 0)
  {
    status = config_nameserver(&servers, &nservers, buf);
    if (status == ARES_SUCCESS)
      goto okay;
  }

  if (IS_NT())
  {
    if (RegOpenKeyEx(
          HKEY_LOCAL_MACHINE, WIN_NS_NT_KEY, 0,
          KEY_READ, &mykey
          ) == ERROR_SUCCESS)
    {
      RegOpenKeyEx(mykey, "Interfaces", 0,
                   KEY_QUERY_VALUE|KEY_ENUMERATE_SUB_KEYS, &subkey);
      if (get_res_nt(mykey, NAMESERVER, &line))
      {
        status = config_nameserver(&servers, &nservers, line);
        free(line);
      }
      else if (get_res_nt(mykey, DHCPNAMESERVER, &line))
      {
        status = config_nameserver(&servers, &nservers, line);
        free(line);
      }
      /* Try the interfaces */
      else if (get_res_interfaces_nt(subkey, NAMESERVER, &line))
      {
        status = config_nameserver(&servers, &nservers, line);
        free(line);
      }
      else if (get_res_interfaces_nt(subkey, DHCPNAMESERVER, &line))
      {
        status = config_nameserver(&servers, &nservers, line);
        free(line);
      }
      RegCloseKey(subkey);
      RegCloseKey(mykey);
    }
  }
  else
  {
    if (RegOpenKeyEx(
          HKEY_LOCAL_MACHINE, WIN_NS_9X, 0,
          KEY_READ, &mykey
          ) == ERROR_SUCCESS)
    {
      if ((result = RegQueryValueEx(
             mykey, NAMESERVER, NULL, &data_type,
             NULL, &bytes
             )
            ) == ERROR_SUCCESS ||
          result == ERROR_MORE_DATA)
      {
        if (bytes)
        {
          line = (char *)malloc(bytes+1);
          if (RegQueryValueEx(mykey, NAMESERVER, NULL, &data_type,
                              (unsigned char *)line, &bytes) ==
              ERROR_SUCCESS)
          {
            status = config_nameserver(&servers, &nservers, line);
          }
          free(line);
        }
      }
    }
    RegCloseKey(mykey);
  }

  if (status == ARES_SUCCESS)
    status = ARES_EOF;

#elif defined(__riscos__)

  /* Under RISC OS, name servers are listed in the
     system variable Inet$Resolvers, space separated. */

  line = getenv("Inet$Resolvers");
  status = ARES_EOF;
  if (line) {
    char *resolvers = strdup(line), *pos, *space;

    if (!resolvers)
      return ARES_ENOMEM;

    pos = resolvers;
    do {
      space = strchr(pos, ' ');
      if (space)
        *space = 0;
      status = config_nameserver(&servers, &nservers, pos);
      if (status != ARES_SUCCESS)
        break;
      pos = space + 1;
    } while (space);

    if (status == ARES_SUCCESS)
      status = ARES_EOF;

    free(resolvers);
  }

#elif defined(WATT32)
  int i;

  sock_init();
  for (i = 0; def_nameservers[i]; i++)
      ;
  if (i == 0)
    return ARES_SUCCESS; /* use localhost DNS server */

  nservers = i;
  servers = calloc(sizeof(*servers), i);
  if (!servers)
     return ARES_ENOMEM;

  for (i = 0; def_nameservers[i]; i++)
      servers[i].addr.s_addr = htonl(def_nameservers[i]);
  status = ARES_EOF;

#else
  {
    char *p;
    FILE *fp;
    int linesize;

    fp = fopen(PATH_RESOLV_CONF, "r");
    if (!fp)
      return (errno == ENOENT) ? ARES_SUCCESS : ARES_EFILE;
    while ((status = ares__read_line(fp, &line, &linesize)) == ARES_SUCCESS)
    {
      if ((p = try_config(line, "domain")))
        status = config_domain(channel, p);
      else if ((p = try_config(line, "lookup")) && !channel->lookups)
        status = config_lookup(channel, p, "bind", "file");
      else if ((p = try_config(line, "search")))
        status = set_search(channel, p);
      else if ((p = try_config(line, "nameserver")) && channel->nservers == -1)
        status = config_nameserver(&servers, &nservers, p);
      else if ((p = try_config(line, "sortlist")) && channel->nsort == -1)
        status = config_sortlist(&sortlist, &nsort, p);
      else if ((p = try_config(line, "options")))
        status = set_options(channel, p);
      else
        status = ARES_SUCCESS;
      if (status != ARES_SUCCESS)
        break;
    }
    fclose(fp);

    if (!channel->lookups) {
      /* Many systems (Solaris, Linux, BSD's) use nsswitch.conf */
      fp = fopen("/etc/nsswitch.conf", "r");
      if (fp) {
        while ((status = ares__read_line(fp, &line, &linesize)) == ARES_SUCCESS)
        {
          if ((p = try_config(line, "hosts:")) && !channel->lookups)
            status = config_lookup(channel, p, "dns", "files");
        }
        fclose(fp);
      }
    }

    if (!channel->lookups) {
      /* Linux / GNU libc 2.x and possibly others have host.conf */
      fp = fopen("/etc/host.conf", "r");
      if (fp) {
        while ((status = ares__read_line(fp, &line, &linesize)) == ARES_SUCCESS)
        {
          if ((p = try_config(line, "order")) && !channel->lookups)
            status = config_lookup(channel, p, "bind", "hosts");
        }
        fclose(fp);
      }
    }

    if (!channel->lookups) {
      /* Tru64 uses /etc/svc.conf */
      fp = fopen("/etc/svc.conf", "r");
      if (fp) {
        while ((status = ares__read_line(fp, &line, &linesize)) == ARES_SUCCESS)
        {
          if ((p = try_config(line, "hosts=")) && !channel->lookups)
            status = config_lookup(channel, p, "bind", "local");
        }
        fclose(fp);
      }
    }

    if(line)
      free(line);
  }

#endif

  /* Handle errors. */
  if (status != ARES_EOF)
    {
      if (servers != NULL)
        free(servers);
      if (sortlist != NULL)
        free(sortlist);
      return status;
    }

  /* If we got any name server entries, fill them in. */
#ifdef WIN32
okay:
#endif
  if (servers)
    {
      channel->servers = servers;
      channel->nservers = nservers;
    }

  /* If we got any sortlist entries, fill them in. */
  if (sortlist)
    {
      channel->sortlist = sortlist;
      channel->nsort = nsort;
    }

  return ARES_SUCCESS;
}

static int init_by_defaults(ares_channel channel)
{
  char hostname[MAXHOSTNAMELEN + 1];

  if (channel->flags == -1)
    channel->flags = 0;
  if (channel->timeout == -1)
    channel->timeout = DEFAULT_TIMEOUT;
  if (channel->tries == -1)
    channel->tries = DEFAULT_TRIES;
  if (channel->ndots == -1)
    channel->ndots = 1;
  if (channel->udp_port == -1)
    channel->udp_port = htons(NAMESERVER_PORT);
  if (channel->tcp_port == -1)
    channel->tcp_port = htons(NAMESERVER_PORT);

  if (channel->nservers == -1)
    {
      /* If nobody specified servers, try a local named. */
      channel->servers = malloc(sizeof(struct server_state));
      if (!channel->servers)
        return ARES_ENOMEM;
      channel->servers[0].addr.s_addr = htonl(INADDR_LOOPBACK);
      channel->nservers = 1;
    }

  if (channel->ndomains == -1)
    {
      /* Derive a default domain search list from the kernel hostname,
       * or set it to empty if the hostname isn't helpful.
       */
      if (gethostname(hostname, sizeof(hostname)) == -1
          || !strchr(hostname, '.'))
        {
          channel->ndomains = 0;
        }
      else
        {
          channel->domains = malloc(sizeof(char *));
          if (!channel->domains)
            return ARES_ENOMEM;
          channel->ndomains = 0;
          channel->domains[0] = strdup(strchr(hostname, '.') + 1);
          if (!channel->domains[0])
            return ARES_ENOMEM;
          channel->ndomains = 1;
        }
    }

  if (channel->nsort == -1)
    {
      channel->sortlist = NULL;
      channel->nsort = 0;
    }

  if (!channel->lookups)
    {
      channel->lookups = strdup("fb");
      if (!channel->lookups)
        return ARES_ENOMEM;
    }

  return ARES_SUCCESS;
}

#ifndef WIN32
static int config_domain(ares_channel channel, char *str)
{
  char *q;

  /* Set a single search domain. */
  q = str;
  while (*q && !ISSPACE(*q))
    q++;
  *q = 0;
  return set_search(channel, str);
}

static int config_lookup(ares_channel channel, const char *str,
                         const char *bindch, const char *filech)
{
  char lookups[3], *l;
  const char *p;

  /* Set the lookup order.  Only the first letter of each work
   * is relevant, and it has to be "b" for DNS or "f" for the
   * host file.  Ignore everything else.
   */
  l = lookups;
  p = str;
  while (*p)
    {
      if ((*p == *bindch || *p == *filech) && l < lookups + 2) {
        if (*p == *bindch) *l++ = 'b';
        else *l++ = 'f';
      }
      while (*p && !ISSPACE(*p) && (*p != ','))
        p++;
      while (*p && (ISSPACE(*p) || (*p == ',')))
        p++;
    }
  *l = 0;
  channel->lookups = strdup(lookups);
  return (channel->lookups) ? ARES_SUCCESS : ARES_ENOMEM;
}

#endif

static int config_nameserver(struct server_state **servers, int *nservers,
                             char *str)
{
  struct in_addr addr;
  struct server_state *newserv;
  /* On Windows, there may be more than one nameserver specified in the same
   * registry key, so we parse it as a space or comma seperated list.
   */
#ifdef WIN32
  char *p = str;
  char *begin = str;
  int more = 1;
  while (more)
  {
    more = 0;
    while (*p && !ISSPACE(*p) && *p != ',')
      p++;

    if (*p)
    {
      *p = 0;
      more = 1;
    }

    /* Skip multiple spaces or trailing spaces */
    if (!*begin)
    {
      begin = ++p;
      continue;
    }

    /* This is the part that actually sets the nameserver */
    addr.s_addr = inet_addr(begin);
    if (addr.s_addr == INADDR_NONE)
      continue;
    newserv = realloc(*servers, (*nservers + 1) * sizeof(struct server_state));
    if (!newserv)
      return ARES_ENOMEM;
    newserv[*nservers].addr = addr;
    *servers = newserv;
    (*nservers)++;

    if (!more)
      break;
    begin = ++p;
  }
#else
  /* Add a nameserver entry, if this is a valid address. */
  addr.s_addr = inet_addr(str);
  if (addr.s_addr == INADDR_NONE)
    return ARES_SUCCESS;
  newserv = realloc(*servers, (*nservers + 1) * sizeof(struct server_state));
  if (!newserv)
    return ARES_ENOMEM;
  newserv[*nservers].addr = addr;
  *servers = newserv;
  (*nservers)++;
#endif
  return ARES_SUCCESS;
}

#ifndef WIN32
static int config_sortlist(struct apattern **sortlist, int *nsort,
                           const char *str)
{
  struct apattern pat;
  const char *q;

  /* Add sortlist entries. */
  while (*str && *str != ';')
    {
      int bits;
      char ipbuf[16], ipbufpfx[32];
      /* Find just the IP */
      q = str;
      while (*q && *q != '/' && *q != ';' && !ISSPACE(*q))
        q++;
      memcpy(ipbuf, str, (int)(q-str));
      ipbuf[(int)(q-str)] = 0;
      /* Find the prefix */
      if (*q == '/')
        {
          const char *str2 = q+1;
          while (*q && *q != ';' && !ISSPACE(*q))
            q++;
          memcpy(ipbufpfx, str, (int)(q-str));
          ipbufpfx[(int)(q-str)] = 0;
          str = str2;
        }
      else
        ipbufpfx[0] = 0;
      /* Lets see if it is CIDR */
      /* First we'll try IPv6 */
      if ((bits = ares_inet_net_pton(AF_INET6, ipbufpfx ? ipbufpfx : ipbuf,
                                     &pat.addr.addr6,
                                     sizeof(pat.addr.addr6))) > 0)
        {
          pat.type = PATTERN_CIDR;
          pat.mask.bits = bits;
          pat.family = AF_INET6;
          if (!sortlist_alloc(sortlist, nsort, &pat))
            return ARES_ENOMEM;
        }
      if (ipbufpfx &&
          (bits = ares_inet_net_pton(AF_INET, ipbufpfx, &pat.addr.addr4,
                                     sizeof(pat.addr.addr4))) > 0)
        {
          pat.type = PATTERN_CIDR;
          pat.mask.bits = bits;
          pat.family = AF_INET;
          if (!sortlist_alloc(sortlist, nsort, &pat))
            return ARES_ENOMEM;
        }
      /* See if it is just a regular IP */
      else if (ip_addr(ipbuf, (int)(q-str), &pat.addr.addr4) == 0)
        {
          if (ipbufpfx)
            {
              memcpy(ipbuf, str, (int)(q-str));
              ipbuf[(int)(q-str)] = 0;
              if (ip_addr(ipbuf, (int)(q - str), &pat.mask.addr.addr4) != 0)
                natural_mask(&pat);
            }
          else
            natural_mask(&pat);
          pat.family = AF_INET;
          pat.type = PATTERN_MASK;
          if (!sortlist_alloc(sortlist, nsort, &pat))
            return ARES_ENOMEM;
        }
      else
        {
          while (*q && *q != ';' && !ISSPACE(*q))
            q++;
        }
      str = q;
      while (ISSPACE(*str))
        str++;
    }

  return ARES_SUCCESS;
}
#endif

static int set_search(ares_channel channel, const char *str)
{
  int n;
  const char *p, *q;

  if(channel->ndomains != -1) {
    /* if we already have some domains present, free them first */
    for(n=0; n < channel->ndomains; n++)
      free(channel->domains[n]);
    free(channel->domains);
    channel->domains = NULL;
    channel->ndomains = -1;
  }

  /* Count the domains given. */
  n = 0;
  p = str;
  while (*p)
    {
      while (*p && !ISSPACE(*p))
        p++;
      while (ISSPACE(*p))
        p++;
      n++;
    }

  if (!n)
    {
      channel->ndomains = 0;
      return ARES_SUCCESS;
    }

  channel->domains = malloc(n * sizeof(char *));
  if (!channel->domains)
    return ARES_ENOMEM;

  /* Now copy the domains. */
  n = 0;
  p = str;
  while (*p)
    {
      channel->ndomains = n;
      q = p;
      while (*q && !ISSPACE(*q))
        q++;
      channel->domains[n] = malloc(q - p + 1);
      if (!channel->domains[n])
        return ARES_ENOMEM;
      memcpy(channel->domains[n], p, q - p);
      channel->domains[n][q - p] = 0;
      p = q;
      while (ISSPACE(*p))
        p++;
      n++;
    }
  channel->ndomains = n;

  return ARES_SUCCESS;
}

static int set_options(ares_channel channel, const char *str)
{
  const char *p, *q, *val;

  p = str;
  while (*p)
    {
      q = p;
      while (*q && !ISSPACE(*q))
        q++;
      val = try_option(p, q, "ndots:");
      if (val && channel->ndots == -1)
        channel->ndots = atoi(val);
      val = try_option(p, q, "retrans:");
      if (val && channel->timeout == -1)
        channel->timeout = atoi(val);
      val = try_option(p, q, "retry:");
      if (val && channel->tries == -1)
        channel->tries = atoi(val);
      p = q;
      while (ISSPACE(*p))
        p++;
    }

  return ARES_SUCCESS;
}

#ifndef WIN32
static char *try_config(char *s, const char *opt)
{
  size_t len;

  len = strlen(opt);
  if (strncmp(s, opt, len) != 0 || !ISSPACE(s[len]))
    return NULL;
  s += len;
  while (ISSPACE(*s))
    s++;
  return s;
}

#endif

static const char *try_option(const char *p, const char *q, const char *opt)
{
  size_t len = strlen(opt);
  return ((size_t)(q - p) > len && !strncmp(p, opt, len)) ? &p[len] : NULL;
}

#ifndef WIN32
static int sortlist_alloc(struct apattern **sortlist, int *nsort,
                          struct apattern *pat)
{
  struct apattern *newsort;
  newsort = realloc(*sortlist, (*nsort + 1) * sizeof(struct apattern));
  if (!newsort)
    return 0;
  newsort[*nsort] = *pat;
  *sortlist = newsort;
  (*nsort)++;
  return 1;
}

static int ip_addr(const char *ipbuf, int len, struct in_addr *addr)
{

  /* Four octets and three periods yields at most 15 characters. */
  if (len > 15)
    return -1;

  addr->s_addr = inet_addr(ipbuf);
  if (addr->s_addr == INADDR_NONE && strcmp(ipbuf, "255.255.255.255") != 0)
    return -1;
  return 0;
}

static void natural_mask(struct apattern *pat)
{
  struct in_addr addr;

  /* Store a host-byte-order copy of pat in a struct in_addr.  Icky,
   * but portable.
   */
  addr.s_addr = ntohl(pat->addr.addr4.s_addr);

  /* This is out of date in the CIDR world, but some people might
   * still rely on it.
   */
  if (IN_CLASSA(addr.s_addr))
    pat->mask.addr.addr4.s_addr = htonl(IN_CLASSA_NET);
  else if (IN_CLASSB(addr.s_addr))
    pat->mask.addr.addr4.s_addr = htonl(IN_CLASSB_NET);
  else
    pat->mask.addr.addr4.s_addr = htonl(IN_CLASSC_NET);
}
#endif