about summary refs log tree commit diff
path: root/resolv/res_send.c
blob: 6b9c73f82081552fb31bbfe23a5d0cad5b80e4be (plain) (blame)
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
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
/* Copyright (C) 2016-2019 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
   <https://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.
 */

/*
 * Send query to name server and wait for reply.
 */

#include <assert.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <sys/uio.h>
#include <sys/poll.h>

#include <netinet/in.h>
#include <arpa/nameser.h>
#include <arpa/inet.h>
#include <sys/ioctl.h>

#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#include <resolv/resolv-internal.h>
#include <resolv/resolv_context.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <kernel-features.h>
#include <libc-diag.h>
#include <random-bits.h>

#if PACKETSZ > 65536
#define MAXPACKET       PACKETSZ
#else
#define MAXPACKET       65536
#endif

/* From ev_streams.c.  */

static inline void
__attribute ((always_inline))
evConsIovec(void *buf, size_t cnt, struct iovec *vec) {
	memset(vec, 0xf5, sizeof (*vec));
	vec->iov_base = buf;
	vec->iov_len = cnt;
}

/* From ev_timers.c.  */

#define BILLION 1000000000

static inline void
evConsTime(struct timespec *res, time_t sec, long nsec) {
	res->tv_sec = sec;
	res->tv_nsec = nsec;
}

static inline void
evAddTime(struct timespec *res, const struct timespec *addend1,
	  const struct timespec *addend2) {
	res->tv_sec = addend1->tv_sec + addend2->tv_sec;
	res->tv_nsec = addend1->tv_nsec + addend2->tv_nsec;
	if (res->tv_nsec >= BILLION) {
		res->tv_sec++;
		res->tv_nsec -= BILLION;
	}
}

static inline void
evSubTime(struct timespec *res, const struct timespec *minuend,
	  const struct timespec *subtrahend) {
       res->tv_sec = minuend->tv_sec - subtrahend->tv_sec;
	if (minuend->tv_nsec >= subtrahend->tv_nsec)
		res->tv_nsec = minuend->tv_nsec - subtrahend->tv_nsec;
	else {
		res->tv_nsec = (BILLION
				- subtrahend->tv_nsec + minuend->tv_nsec);
		res->tv_sec--;
	}
}

static int
evCmpTime(struct timespec a, struct timespec b) {
	long x = a.tv_sec - b.tv_sec;

	if (x == 0L)
		x = a.tv_nsec - b.tv_nsec;
	return (x < 0L ? (-1) : x > 0L ? (1) : (0));
}

static void
evNowTime(struct timespec *res) {
	struct timeval now;

	if (gettimeofday(&now, NULL) < 0)
		evConsTime(res, 0, 0);
	else
		TIMEVAL_TO_TIMESPEC (&now, res);
}


#define EXT(res) ((res)->_u._ext)

/* Forward. */

static struct sockaddr *get_nsaddr (res_state, unsigned int);
static int		send_vc(res_state, const u_char *, int,
				const u_char *, int,
				u_char **, int *, int *, int, u_char **,
				u_char **, int *, int *, int *);
static int		send_dg(res_state, const u_char *, int,
				const u_char *, int,
				u_char **, int *, int *, int,
				int *, int *, u_char **,
				u_char **, int *, int *, int *);
static int		sock_eq(struct sockaddr_in6 *, struct sockaddr_in6 *);

/* Public. */

/* int
 * res_isourserver(ina)
 *	looks up "ina" in _res.ns_addr_list[]
 * returns:
 *	0  : not found
 *	>0 : found
 * author:
 *	paul vixie, 29may94
 */
int
res_ourserver_p(const res_state statp, const struct sockaddr_in6 *inp)
{
	int ns;

	if (inp->sin6_family == AF_INET) {
	    struct sockaddr_in *in4p = (struct sockaddr_in *) inp;
	    in_port_t port = in4p->sin_port;
	    in_addr_t addr = in4p->sin_addr.s_addr;

	    for (ns = 0;  ns < statp->nscount;  ns++) {
		const struct sockaddr_in *srv =
		    (struct sockaddr_in *) get_nsaddr (statp, ns);

		if ((srv->sin_family == AF_INET) &&
		    (srv->sin_port == port) &&
		    (srv->sin_addr.s_addr == INADDR_ANY ||
		     srv->sin_addr.s_addr == addr))
		    return (1);
	    }
	} else if (inp->sin6_family == AF_INET6) {
	    for (ns = 0;  ns < statp->nscount;  ns++) {
		const struct sockaddr_in6 *srv
		  = (struct sockaddr_in6 *) get_nsaddr (statp, ns);
		if ((srv->sin6_family == AF_INET6) &&
		    (srv->sin6_port == inp->sin6_port) &&
		    !(memcmp(&srv->sin6_addr, &in6addr_any,
			     sizeof (struct in6_addr)) &&
		      memcmp(&srv->sin6_addr, &inp->sin6_addr,
			     sizeof (struct in6_addr))))
		    return (1);
	    }
	}
	return (0);
}

int
res_isourserver (const struct sockaddr_in *inp)
{
  return res_ourserver_p (&_res, (const struct sockaddr_in6 *) inp);
}

/* int
 * res_nameinquery(name, type, class, buf, eom)
 *	look for (name,type,class) in the query section of packet (buf,eom)
 * requires:
 *	buf + HFIXEDSZ <= eom
 * returns:
 *	-1 : format error
 *	0  : not found
 *	>0 : found
 * author:
 *	paul vixie, 29may94
 */
int
res_nameinquery(const char *name, int type, int class,
		const u_char *buf, const u_char *eom)
{
	const u_char *cp = buf + HFIXEDSZ;
	int qdcount = ntohs(((HEADER*)buf)->qdcount);

	while (qdcount-- > 0) {
		char tname[MAXDNAME+1];
		int n, ttype, tclass;

		n = dn_expand(buf, eom, cp, tname, sizeof tname);
		if (n < 0)
			return (-1);
		cp += n;
		if (cp + 2 * INT16SZ > eom)
			return (-1);
		NS_GET16(ttype, cp);
		NS_GET16(tclass, cp);
		if (ttype == type && tclass == class &&
		    ns_samename(tname, name) == 1)
			return (1);
	}
	return (0);
}
libresolv_hidden_def (res_nameinquery)

/* Returns a shift value for the name server index.  Used to implement
   RES_ROTATE.  */
static unsigned int
nameserver_offset (struct __res_state *statp)
{
  /* If we only have one name server or rotation is disabled, return
     offset 0 (no rotation).  */
  unsigned int nscount = statp->nscount;
  if (nscount <= 1 || !(statp->options & RES_ROTATE))
    return 0;

  /* Global offset.  The lowest bit indicates whether the offset has
     been initialized with a random value.  Use relaxed MO to access
     global_offset because all we need is a sequence of roughly
     sequential value.  */
  static unsigned int global_offset;
  unsigned int offset = atomic_fetch_add_relaxed (&global_offset, 2);
  if ((offset & 1) == 0)
    {
      /* Initialization is required.  */
      offset = random_bits ();
      /* The lowest bit is the most random.  Preserve it.  */
      offset <<= 1;

      /* Store the new starting value.  atomic_fetch_add_relaxed
	 returns the old value, so emulate that by storing the new
	 (incremented) value.  Concurrent initialization with
	 different random values is harmless.  */
      atomic_store_relaxed (&global_offset, (offset | 1) + 2);
    }

  /* Remove the initialization bit.  */
  offset >>= 1;

  /* Avoid the division in the most common cases.  */
  switch (nscount)
    {
    case 2:
      return offset & 1;
    case 3:
      return offset % 3;
    case 4:
      return offset & 3;
    default:
      return offset % nscount;
    }
}

/* int
 * res_queriesmatch(buf1, eom1, buf2, eom2)
 *	is there a 1:1 mapping of (name,type,class)
 *	in (buf1,eom1) and (buf2,eom2)?
 * returns:
 *	-1 : format error
 *	0  : not a 1:1 mapping
 *	>0 : is a 1:1 mapping
 * author:
 *	paul vixie, 29may94
 */
int
res_queriesmatch(const u_char *buf1, const u_char *eom1,
		 const u_char *buf2, const u_char *eom2)
{
	if (buf1 + HFIXEDSZ > eom1 || buf2 + HFIXEDSZ > eom2)
		return (-1);

	/*
	 * Only header section present in replies to
	 * dynamic update packets.
	 */
	if ((((HEADER *)buf1)->opcode == ns_o_update) &&
	    (((HEADER *)buf2)->opcode == ns_o_update))
		return (1);

	/* Note that we initially do not convert QDCOUNT to the host byte
	   order.  We can compare it with the second buffer's QDCOUNT
	   value without doing this.  */
	int qdcount = ((HEADER*)buf1)->qdcount;
	if (qdcount != ((HEADER*)buf2)->qdcount)
		return (0);

	qdcount = htons (qdcount);
	const u_char *cp = buf1 + HFIXEDSZ;

	while (qdcount-- > 0) {
		char tname[MAXDNAME+1];
		int n, ttype, tclass;

		n = dn_expand(buf1, eom1, cp, tname, sizeof tname);
		if (n < 0)
			return (-1);
		cp += n;
		if (cp + 2 * INT16SZ > eom1)
			return (-1);
		NS_GET16(ttype, cp);
		NS_GET16(tclass, cp);
		if (!res_nameinquery(tname, ttype, tclass, buf2, eom2))
			return (0);
	}
	return (1);
}
libresolv_hidden_def (res_queriesmatch)

int
__res_context_send (struct resolv_context *ctx,
		    const unsigned char *buf, int buflen,
		    const unsigned char *buf2, int buflen2,
		    unsigned char *ans, int anssiz,
		    unsigned char **ansp, unsigned char **ansp2,
		    int *nansp2, int *resplen2, int *ansp2_malloced)
{
	struct __res_state *statp = ctx->resp;
	int gotsomewhere, terrno, try, v_circuit, resplen;
	/* On some architectures send_vc is inlined and the compiler might emit
	   a warning indicating 'resplen' may be used uninitialized.  Note that
	   the warning belongs to resplen in send_vc which is used as return
	   value!  There the maybe-uninitialized warning is already ignored as
	   it is a false-positive - see comment in send_vc.
	   Here the variable n is set to the return value of send_vc.
	   See below.  */
	DIAG_PUSH_NEEDS_COMMENT;
	DIAG_IGNORE_NEEDS_COMMENT (9, "-Wmaybe-uninitialized");
	int n;
	DIAG_POP_NEEDS_COMMENT;

	if (statp->nscount == 0) {
		__set_errno (ESRCH);
		return (-1);
	}

	if (anssiz < (buf2 == NULL ? 1 : 2) * HFIXEDSZ) {
		__set_errno (EINVAL);
		return (-1);
	}

	v_circuit = ((statp->options & RES_USEVC)
		     || buflen > PACKETSZ
		     || buflen2 > PACKETSZ);
	gotsomewhere = 0;
	terrno = ETIMEDOUT;

	/*
	 * If the ns_addr_list in the resolver context has changed, then
	 * invalidate our cached copy and the associated timing data.
	 */
	if (EXT(statp).nscount != 0) {
		int needclose = 0;

		if (EXT(statp).nscount != statp->nscount)
			needclose++;
		else
			for (unsigned int ns = 0; ns < statp->nscount; ns++) {
				if (statp->nsaddr_list[ns].sin_family != 0
				    && !sock_eq((struct sockaddr_in6 *)
						&statp->nsaddr_list[ns],
						EXT(statp).nsaddrs[ns]))
				{
					needclose++;
					break;
				}
			}
		if (needclose) {
			__res_iclose(statp, false);
			EXT(statp).nscount = 0;
		}
	}

	/*
	 * Maybe initialize our private copy of the ns_addr_list.
	 */
	if (EXT(statp).nscount == 0) {
		for (unsigned int ns = 0; ns < statp->nscount; ns++) {
			EXT(statp).nssocks[ns] = -1;
			if (statp->nsaddr_list[ns].sin_family == 0)
				continue;
			if (EXT(statp).nsaddrs[ns] == NULL)
				EXT(statp).nsaddrs[ns] =
				    malloc(sizeof (struct sockaddr_in6));
			if (EXT(statp).nsaddrs[ns] != NULL)
				memset (mempcpy(EXT(statp).nsaddrs[ns],
						&statp->nsaddr_list[ns],
						sizeof (struct sockaddr_in)),
					'\0',
					sizeof (struct sockaddr_in6)
					- sizeof (struct sockaddr_in));
			else
				return -1;
		}
		EXT(statp).nscount = statp->nscount;
	}

	/* Name server index offset.  Used to implement
	   RES_ROTATE.  */
	unsigned int ns_offset = nameserver_offset (statp);

	/*
	 * Send request, RETRY times, or until successful.
	 */
	for (try = 0; try < statp->retry; try++) {
	    for (unsigned ns_shift = 0; ns_shift < statp->nscount; ns_shift++)
	    {
		/* The actual name server index.  This implements
		   RES_ROTATE.  */
		unsigned int ns = ns_shift + ns_offset;
		if (ns >= statp->nscount)
			ns -= statp->nscount;

	    same_ns:
		if (__glibc_unlikely (v_circuit))       {
			/* Use VC; at most one attempt per server. */
			try = statp->retry;
			n = send_vc(statp, buf, buflen, buf2, buflen2,
				    &ans, &anssiz, &terrno,
				    ns, ansp, ansp2, nansp2, resplen2,
				    ansp2_malloced);
			if (n < 0)
				return (-1);
			/* See comment at the declaration of n.  */
			DIAG_PUSH_NEEDS_COMMENT;
			DIAG_IGNORE_NEEDS_COMMENT (9, "-Wmaybe-uninitialized");
			if (n == 0 && (buf2 == NULL || *resplen2 == 0))
				goto next_ns;
			DIAG_POP_NEEDS_COMMENT;
		} else {
			/* Use datagrams. */
			n = send_dg(statp, buf, buflen, buf2, buflen2,
				    &ans, &anssiz, &terrno,
				    ns, &v_circuit, &gotsomewhere, ansp,
				    ansp2, nansp2, resplen2, ansp2_malloced);
			if (n < 0)
				return (-1);
			if (n == 0 && (buf2 == NULL || *resplen2 == 0))
				goto next_ns;
			if (v_circuit)
			  // XXX Check whether both requests failed or
			  // XXX whether one has been answered successfully
				goto same_ns;
		}

		resplen = n;

		/*
		 * If we have temporarily opened a virtual circuit,
		 * or if we haven't been asked to keep a socket open,
		 * close the socket.
		 */
		if ((v_circuit && (statp->options & RES_USEVC) == 0) ||
		    (statp->options & RES_STAYOPEN) == 0) {
			__res_iclose(statp, false);
		}
		return (resplen);
 next_ns: ;
	   } /*foreach ns*/
	} /*foreach retry*/
	__res_iclose(statp, false);
	if (!v_circuit) {
		if (!gotsomewhere)
			__set_errno (ECONNREFUSED);	/* no nameservers found */
		else
			__set_errno (ETIMEDOUT);	/* no answer obtained */
	} else
		__set_errno (terrno);
	return (-1);
}

/* Common part of res_nsend and res_send.  */
static int
context_send_common (struct resolv_context *ctx,
		     const unsigned char *buf, int buflen,
		     unsigned char *ans, int anssiz)
{
  if (ctx == NULL)
    {
      RES_SET_H_ERRNO (&_res, NETDB_INTERNAL);
      return -1;
    }
  int result = __res_context_send (ctx, buf, buflen, NULL, 0, ans, anssiz,
				   NULL, NULL, NULL, NULL, NULL);
  __resolv_context_put (ctx);
  return result;
}

int
res_nsend (res_state statp, const unsigned char *buf, int buflen,
	   unsigned char *ans, int anssiz)
{
  return context_send_common
    (__resolv_context_get_override (statp), buf, buflen, ans, anssiz);
}

int
res_send (const unsigned char *buf, int buflen, unsigned char *ans, int anssiz)
{
  return context_send_common
    (__resolv_context_get (), buf, buflen, ans, anssiz);
}

/* Private */

static struct sockaddr *
get_nsaddr (res_state statp, unsigned int n)
{
  assert (n < statp->nscount);

  if (statp->nsaddr_list[n].sin_family == 0 && EXT(statp).nsaddrs[n] != NULL)
    /* EXT(statp).nsaddrs[n] holds an address that is larger than
       struct sockaddr, and user code did not update
       statp->nsaddr_list[n].  */
    return (struct sockaddr *) EXT(statp).nsaddrs[n];
  else
    /* User code updated statp->nsaddr_list[n], or statp->nsaddr_list[n]
       has the same content as EXT(statp).nsaddrs[n].  */
    return (struct sockaddr *) (void *) &statp->nsaddr_list[n];
}

/* Close the resolver structure, assign zero to *RESPLEN2 if RESPLEN2
   is not NULL, and return zero.  */
static int
__attribute__ ((warn_unused_result))
close_and_return_error (res_state statp, int *resplen2)
{
  __res_iclose(statp, false);
  if (resplen2 != NULL)
    *resplen2 = 0;
  return 0;
}

/* The send_vc function is responsible for sending a DNS query over TCP
   to the nameserver numbered NS from the res_state STATP i.e.
   EXT(statp).nssocks[ns].  The function supports sending both IPv4 and
   IPv6 queries at the same serially on the same socket.

   Please note that for TCP there is no way to disable sending both
   queries, unlike UDP, which honours RES_SNGLKUP and RES_SNGLKUPREOP
   and sends the queries serially and waits for the result after each
   sent query.  This implementation should be corrected to honour these
   options.

   Please also note that for TCP we send both queries over the same
   socket one after another.  This technically violates best practice
   since the server is allowed to read the first query, respond, and
   then close the socket (to service another client).  If the server
   does this, then the remaining second query in the socket data buffer
   will cause the server to send the client an RST which will arrive
   asynchronously and the client's OS will likely tear down the socket
   receive buffer resulting in a potentially short read and lost
   response data.  This will force the client to retry the query again,
   and this process may repeat until all servers and connection resets
   are exhausted and then the query will fail.  It's not known if this
   happens with any frequency in real DNS server implementations.  This
   implementation should be corrected to use two sockets by default for
   parallel queries.

   The query stored in BUF of BUFLEN length is sent first followed by
   the query stored in BUF2 of BUFLEN2 length.  Queries are sent
   serially on the same socket.

   Answers to the query are stored firstly in *ANSP up to a max of
   *ANSSIZP bytes.  If more than *ANSSIZP bytes are needed and ANSCP
   is non-NULL (to indicate that modifying the answer buffer is allowed)
   then malloc is used to allocate a new response buffer and ANSCP and
   ANSP will both point to the new buffer.  If more than *ANSSIZP bytes
   are needed but ANSCP is NULL, then as much of the response as
   possible is read into the buffer, but the results will be truncated.
   When truncation happens because of a small answer buffer the DNS
   packets header field TC will bet set to 1, indicating a truncated
   message and the rest of the socket data will be read and discarded.

   Answers to the query are stored secondly in *ANSP2 up to a max of
   *ANSSIZP2 bytes, with the actual response length stored in
   *RESPLEN2.  If more than *ANSSIZP bytes are needed and ANSP2
   is non-NULL (required for a second query) then malloc is used to
   allocate a new response buffer, *ANSSIZP2 is set to the new buffer
   size and *ANSP2_MALLOCED is set to 1.

   The ANSP2_MALLOCED argument will eventually be removed as the
   change in buffer pointer can be used to detect the buffer has
   changed and that the caller should use free on the new buffer.

   Note that the answers may arrive in any order from the server and
   therefore the first and second answer buffers may not correspond to
   the first and second queries.

   It is not supported to call this function with a non-NULL ANSP2
   but a NULL ANSCP.  Put another way, you can call send_vc with a
   single unmodifiable buffer or two modifiable buffers, but no other
   combination is supported.

   It is the caller's responsibility to free the malloc allocated
   buffers by detecting that the pointers have changed from their
   original values i.e. *ANSCP or *ANSP2 has changed.

   If errors are encountered then *TERRNO is set to an appropriate
   errno value and a zero result is returned for a recoverable error,
   and a less-than zero result is returned for a non-recoverable error.

   If no errors are encountered then *TERRNO is left unmodified and
   a the length of the first response in bytes is returned.  */
static int
send_vc(res_state statp,
	const u_char *buf, int buflen, const u_char *buf2, int buflen2,
	u_char **ansp, int *anssizp,
	int *terrno, int ns, u_char **anscp, u_char **ansp2, int *anssizp2,
	int *resplen2, int *ansp2_malloced)
{
	const HEADER *hp = (HEADER *) buf;
	const HEADER *hp2 = (HEADER *) buf2;
	HEADER *anhp = (HEADER *) *ansp;
	struct sockaddr *nsap = get_nsaddr (statp, ns);
	int truncating, connreset, n;
	/* On some architectures compiler might emit a warning indicating
	   'resplen' may be used uninitialized.  However if buf2 == NULL
	   then this code won't be executed; if buf2 != NULL, then first
	   time round the loop recvresp1 and recvresp2 will be 0 so this
	   code won't be executed but "thisresplenp = &resplen;" followed
	   by "*thisresplenp = rlen;" will be executed so that subsequent
	   times round the loop resplen has been initialized.  So this is
	   a false-positive.
	 */
	DIAG_PUSH_NEEDS_COMMENT;
	DIAG_IGNORE_NEEDS_COMMENT (5, "-Wmaybe-uninitialized");
	int resplen;
	DIAG_POP_NEEDS_COMMENT;
	struct iovec iov[4];
	u_short len;
	u_short len2;
	u_char *cp;

	connreset = 0;
 same_ns:
	truncating = 0;

	/* Are we still talking to whom we want to talk to? */
	if (statp->_vcsock >= 0 && (statp->_flags & RES_F_VC) != 0) {
		struct sockaddr_in6 peer;
		socklen_t size = sizeof peer;

		if (getpeername(statp->_vcsock,
				(struct sockaddr *)&peer, &size) < 0 ||
		    !sock_eq(&peer, (struct sockaddr_in6 *) nsap)) {
			__res_iclose(statp, false);
			statp->_flags &= ~RES_F_VC;
		}
	}

	if (statp->_vcsock < 0 || (statp->_flags & RES_F_VC) == 0) {
		if (statp->_vcsock >= 0)
		  __res_iclose(statp, false);

		statp->_vcsock = socket
		  (nsap->sa_family, SOCK_STREAM | SOCK_CLOEXEC, 0);
		if (statp->_vcsock < 0) {
			*terrno = errno;
			if (resplen2 != NULL)
			  *resplen2 = 0;
			return (-1);
		}
		__set_errno (0);
		if (connect(statp->_vcsock, nsap,
			    nsap->sa_family == AF_INET
			    ? sizeof (struct sockaddr_in)
			    : sizeof (struct sockaddr_in6)) < 0) {
			*terrno = errno;
			return close_and_return_error (statp, resplen2);
		}
		statp->_flags |= RES_F_VC;
	}

	/*
	 * Send length & message
	 */
	len = htons ((u_short) buflen);
	evConsIovec(&len, INT16SZ, &iov[0]);
	evConsIovec((void*)buf, buflen, &iov[1]);
	int niov = 2;
	ssize_t explen = INT16SZ + buflen;
	if (buf2 != NULL) {
		len2 = htons ((u_short) buflen2);
		evConsIovec(&len2, INT16SZ, &iov[2]);
		evConsIovec((void*)buf2, buflen2, &iov[3]);
		niov = 4;
		explen += INT16SZ + buflen2;
	}
	if (TEMP_FAILURE_RETRY (writev(statp->_vcsock, iov, niov)) != explen) {
		*terrno = errno;
		return close_and_return_error (statp, resplen2);
	}
	/*
	 * Receive length & response
	 */
	int recvresp1 = 0;
	/* Skip the second response if there is no second query.
	   To do that we mark the second response as received.  */
	int recvresp2 = buf2 == NULL;
	uint16_t rlen16;
 read_len:
	cp = (u_char *)&rlen16;
	len = sizeof(rlen16);
	while ((n = TEMP_FAILURE_RETRY (read(statp->_vcsock, cp,
					     (int)len))) > 0) {
		cp += n;
		if ((len -= n) <= 0)
			break;
	}
	if (n <= 0) {
		*terrno = errno;
		/*
		 * A long running process might get its TCP
		 * connection reset if the remote server was
		 * restarted.  Requery the server instead of
		 * trying a new one.  When there is only one
		 * server, this means that a query might work
		 * instead of failing.  We only allow one reset
		 * per query to prevent looping.
		 */
		if (*terrno == ECONNRESET && !connreset)
		  {
		    __res_iclose (statp, false);
		    connreset = 1;
		    goto same_ns;
		  }
		return close_and_return_error (statp, resplen2);
	}
	int rlen = ntohs (rlen16);

	int *thisanssizp;
	u_char **thisansp;
	int *thisresplenp;
	if ((recvresp1 | recvresp2) == 0 || buf2 == NULL) {
		/* We have not received any responses
		   yet or we only have one response to
		   receive.  */
		thisanssizp = anssizp;
		thisansp = anscp ?: ansp;
		assert (anscp != NULL || ansp2 == NULL);
		thisresplenp = &resplen;
	} else {
		thisanssizp = anssizp2;
		thisansp = ansp2;
		thisresplenp = resplen2;
	}
	anhp = (HEADER *) *thisansp;

	*thisresplenp = rlen;
	/* Is the answer buffer too small?  */
	if (*thisanssizp < rlen) {
		/* If the current buffer is not the the static
		   user-supplied buffer then we can reallocate
		   it.  */
		if (thisansp != NULL && thisansp != ansp) {
			/* Always allocate MAXPACKET, callers expect
			   this specific size.  */
			u_char *newp = malloc (MAXPACKET);
			if (newp == NULL)
			  {
			    *terrno = ENOMEM;
			    return close_and_return_error (statp, resplen2);
			  }
			*thisanssizp = MAXPACKET;
			*thisansp = newp;
			if (thisansp == ansp2)
			  *ansp2_malloced = 1;
			anhp = (HEADER *) newp;
			/* A uint16_t can't be larger than MAXPACKET
			   thus it's safe to allocate MAXPACKET but
			   read RLEN bytes instead.  */
			len = rlen;
		} else {
			truncating = 1;
			len = *thisanssizp;
		}
	} else
		len = rlen;

	if (__glibc_unlikely (len < HFIXEDSZ))       {
		/*
		 * Undersized message.
		 */
		*terrno = EMSGSIZE;
		return close_and_return_error (statp, resplen2);
	}

	cp = *thisansp;
	while (len != 0 && (n = read(statp->_vcsock, (char *)cp, (int)len)) > 0){
		cp += n;
		len -= n;
	}
	if (__glibc_unlikely (n <= 0))       {
		*terrno = errno;
		return close_and_return_error (statp, resplen2);
	}
	if (__glibc_unlikely (truncating))       {
		/*
		 * Flush rest of answer so connection stays in synch.
		 */
		anhp->tc = 1;
		len = rlen - *thisanssizp;
		while (len != 0) {
			char junk[PACKETSZ];

			n = read(statp->_vcsock, junk,
				 (len > sizeof junk) ? sizeof junk : len);
			if (n > 0)
				len -= n;
			else
				break;
		}
	}
	/*
	 * If the calling application has bailed out of
	 * a previous call and failed to arrange to have
	 * the circuit closed or the server has got
	 * itself confused, then drop the packet and
	 * wait for the correct one.
	 */
	if ((recvresp1 || hp->id != anhp->id)
	    && (recvresp2 || hp2->id != anhp->id))
		goto read_len;

	/* Mark which reply we received.  */
	if (recvresp1 == 0 && hp->id == anhp->id)
	  recvresp1 = 1;
	else
	  recvresp2 = 1;
	/* Repeat waiting if we have a second answer to arrive.  */
	if ((recvresp1 & recvresp2) == 0)
		goto read_len;

	/*
	 * All is well, or the error is fatal.  Signal that the
	 * next nameserver ought not be tried.
	 */
	return resplen;
}

static int
reopen (res_state statp, int *terrno, int ns)
{
	if (EXT(statp).nssocks[ns] == -1) {
		struct sockaddr *nsap = get_nsaddr (statp, ns);
		socklen_t slen;

		/* only try IPv6 if IPv6 NS and if not failed before */
		if (nsap->sa_family == AF_INET6 && !statp->ipv6_unavail) {
			EXT(statp).nssocks[ns] = socket
			  (PF_INET6,
			   SOCK_DGRAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0);
			if (EXT(statp).nssocks[ns] < 0)
			    statp->ipv6_unavail = errno == EAFNOSUPPORT;
			slen = sizeof (struct sockaddr_in6);
		} else if (nsap->sa_family == AF_INET) {
			EXT(statp).nssocks[ns] = socket
			  (PF_INET,
			   SOCK_DGRAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0);
			slen = sizeof (struct sockaddr_in);
		}
		if (EXT(statp).nssocks[ns] < 0) {
			*terrno = errno;
			return (-1);
		}

		/* Enable full ICMP error reporting for this
		   socket.  */
		if (__res_enable_icmp (nsap->sa_family,
				       EXT (statp).nssocks[ns]) < 0)
		  {
		    int saved_errno = errno;
		    __res_iclose (statp, false);
		    __set_errno (saved_errno);
		    *terrno = saved_errno;
		    return -1;
		  }

		/*
		 * On a 4.3BSD+ machine (client and server,
		 * actually), sending to a nameserver datagram
		 * port with no nameserver will cause an
		 * ICMP port unreachable message to be returned.
		 * If our datagram socket is "connected" to the
		 * server, we get an ECONNREFUSED error on the next
		 * socket operation, and select returns if the
		 * error message is received.  We can thus detect
		 * the absence of a nameserver without timing out.
		 */
		/* With GCC 5.3 when compiling with -Os the compiler
		   emits a warning that slen may be used uninitialized,
		   but that is never true.  Both slen and
		   EXT(statp).nssocks[ns] are initialized together or
		   the function return -1 before control flow reaches
		   the call to connect with slen.  */
		DIAG_PUSH_NEEDS_COMMENT;
		DIAG_IGNORE_Os_NEEDS_COMMENT (5, "-Wmaybe-uninitialized");
		if (connect(EXT(statp).nssocks[ns], nsap, slen) < 0) {
		DIAG_POP_NEEDS_COMMENT;
			__res_iclose(statp, false);
			return (0);
		}
	}

	return 1;
}

/* The send_dg function is responsible for sending a DNS query over UDP
   to the nameserver numbered NS from the res_state STATP i.e.
   EXT(statp).nssocks[ns].  The function supports IPv4 and IPv6 queries
   along with the ability to send the query in parallel for both stacks
   (default) or serially (RES_SINGLKUP).  It also supports serial lookup
   with a close and reopen of the socket used to talk to the server
   (RES_SNGLKUPREOP) to work around broken name servers.

   The query stored in BUF of BUFLEN length is sent first followed by
   the query stored in BUF2 of BUFLEN2 length.  Queries are sent
   in parallel (default) or serially (RES_SINGLKUP or RES_SNGLKUPREOP).

   Answers to the query are stored firstly in *ANSP up to a max of
   *ANSSIZP bytes.  If more than *ANSSIZP bytes are needed and ANSCP
   is non-NULL (to indicate that modifying the answer buffer is allowed)
   then malloc is used to allocate a new response buffer and ANSCP and
   ANSP will both point to the new buffer.  If more than *ANSSIZP bytes
   are needed but ANSCP is NULL, then as much of the response as
   possible is read into the buffer, but the results will be truncated.
   When truncation happens because of a small answer buffer the DNS
   packets header field TC will bet set to 1, indicating a truncated
   message, while the rest of the UDP packet is discarded.

   Answers to the query are stored secondly in *ANSP2 up to a max of
   *ANSSIZP2 bytes, with the actual response length stored in
   *RESPLEN2.  If more than *ANSSIZP bytes are needed and ANSP2
   is non-NULL (required for a second query) then malloc is used to
   allocate a new response buffer, *ANSSIZP2 is set to the new buffer
   size and *ANSP2_MALLOCED is set to 1.

   The ANSP2_MALLOCED argument will eventually be removed as the
   change in buffer pointer can be used to detect the buffer has
   changed and that the caller should use free on the new buffer.

   Note that the answers may arrive in any order from the server and
   therefore the first and second answer buffers may not correspond to
   the first and second queries.

   It is not supported to call this function with a non-NULL ANSP2
   but a NULL ANSCP.  Put another way, you can call send_vc with a
   single unmodifiable buffer or two modifiable buffers, but no other
   combination is supported.

   It is the caller's responsibility to free the malloc allocated
   buffers by detecting that the pointers have changed from their
   original values i.e. *ANSCP or *ANSP2 has changed.

   If an answer is truncated because of UDP datagram DNS limits then
   *V_CIRCUIT is set to 1 and the return value non-zero to indicate to
   the caller to retry with TCP.  The value *GOTSOMEWHERE is set to 1
   if any progress was made reading a response from the nameserver and
   is used by the caller to distinguish between ECONNREFUSED and
   ETIMEDOUT (the latter if *GOTSOMEWHERE is 1).

   If errors are encountered then *TERRNO is set to an appropriate
   errno value and a zero result is returned for a recoverable error,
   and a less-than zero result is returned for a non-recoverable error.

   If no errors are encountered then *TERRNO is left unmodified and
   a the length of the first response in bytes is returned.  */
static int
send_dg(res_state statp,
	const u_char *buf, int buflen, const u_char *buf2, int buflen2,
	u_char **ansp, int *anssizp,
	int *terrno, int ns, int *v_circuit, int *gotsomewhere, u_char **anscp,
	u_char **ansp2, int *anssizp2, int *resplen2, int *ansp2_malloced)
{
	const HEADER *hp = (HEADER *) buf;
	const HEADER *hp2 = (HEADER *) buf2;
	struct timespec now, timeout, finish;
	struct pollfd pfd[1];
	int ptimeout;
	struct sockaddr_in6 from;
	int resplen = 0;
	int n;

	/*
	 * Compute time for the total operation.
	 */
	int seconds = (statp->retrans << ns);
	if (ns > 0)
		seconds /= statp->nscount;
	if (seconds <= 0)
		seconds = 1;
	bool single_request_reopen = (statp->options & RES_SNGLKUPREOP) != 0;
	bool single_request = (((statp->options & RES_SNGLKUP) != 0)
			       | single_request_reopen);
	int save_gotsomewhere = *gotsomewhere;

	int retval;
 retry_reopen:
	retval = reopen (statp, terrno, ns);
	if (retval <= 0)
	  {
	    if (resplen2 != NULL)
	      *resplen2 = 0;
	    return retval;
	  }
 retry:
	evNowTime(&now);
	evConsTime(&timeout, seconds, 0);
	evAddTime(&finish, &now, &timeout);
	int need_recompute = 0;
	int nwritten = 0;
	int recvresp1 = 0;
	/* Skip the second response if there is no second query.
	   To do that we mark the second response as received.  */
	int recvresp2 = buf2 == NULL;
	pfd[0].fd = EXT(statp).nssocks[ns];
	pfd[0].events = POLLOUT;
 wait:
	if (need_recompute) {
	recompute_resend:
		evNowTime(&now);
		if (evCmpTime(finish, now) <= 0) {
		poll_err_out:
			return close_and_return_error (statp, resplen2);
		}
		evSubTime(&timeout, &finish, &now);
		need_recompute = 0;
	}
	/* Convert struct timespec in milliseconds.  */
	ptimeout = timeout.tv_sec * 1000 + timeout.tv_nsec / 1000000;

	n = 0;
	if (nwritten == 0)
	  n = __poll (pfd, 1, 0);
	if (__glibc_unlikely (n == 0))       {
		n = __poll (pfd, 1, ptimeout);
		need_recompute = 1;
	}
	if (n == 0) {
		if (resplen > 1 && (recvresp1 || (buf2 != NULL && recvresp2)))
		  {
		    /* There are quite a few broken name servers out
		       there which don't handle two outstanding
		       requests from the same source.  There are also
		       broken firewall settings.  If we time out after
		       having received one answer switch to the mode
		       where we send the second request only once we
		       have received the first answer.  */
		    if (!single_request)
		      {
			statp->options |= RES_SNGLKUP;
			single_request = true;
			*gotsomewhere = save_gotsomewhere;
			goto retry;
		      }
		    else if (!single_request_reopen)
		      {
			statp->options |= RES_SNGLKUPREOP;
			single_request_reopen = true;
			*gotsomewhere = save_gotsomewhere;
			__res_iclose (statp, false);
			goto retry_reopen;
		      }

		    *resplen2 = 1;
		    return resplen;
		  }

		*gotsomewhere = 1;
		if (resplen2 != NULL)
		  *resplen2 = 0;
		return 0;
	}
	if (n < 0) {
		if (errno == EINTR)
			goto recompute_resend;

		goto poll_err_out;
	}
	__set_errno (0);
	if (pfd[0].revents & POLLOUT) {
#ifndef __ASSUME_SENDMMSG
		static int have_sendmmsg;
#else
# define have_sendmmsg 1
#endif
		if (have_sendmmsg >= 0 && nwritten == 0 && buf2 != NULL
		    && !single_request)
		  {
		    struct iovec iov =
		      { .iov_base = (void *) buf, .iov_len = buflen };
		    struct iovec iov2 =
		      { .iov_base = (void *) buf2, .iov_len = buflen2 };
		    struct mmsghdr reqs[2] =
		      {
			{
			  .msg_hdr =
			    {
			      .msg_iov = &iov,
			      .msg_iovlen = 1,
			    },
			},
			{
			  .msg_hdr =
			    {
			      .msg_iov = &iov2,
			      .msg_iovlen = 1,
			    }
			},
		      };

		    int ndg = __sendmmsg (pfd[0].fd, reqs, 2, MSG_NOSIGNAL);
		    if (__glibc_likely (ndg == 2))
		      {
			if (reqs[0].msg_len != buflen
			    || reqs[1].msg_len != buflen2)
			  goto fail_sendmmsg;

			pfd[0].events = POLLIN;
			nwritten += 2;
		      }
		    else if (ndg == 1 && reqs[0].msg_len == buflen)
		      goto just_one;
		    else if (ndg < 0 && (errno == EINTR || errno == EAGAIN))
		      goto recompute_resend;
		    else
		      {
#ifndef __ASSUME_SENDMMSG
			if (__glibc_unlikely (have_sendmmsg == 0))
			  {
			    if (ndg < 0 && errno == ENOSYS)
			      {
				have_sendmmsg = -1;
				goto try_send;
			      }
			    have_sendmmsg = 1;
			  }
#endif

		      fail_sendmmsg:
			return close_and_return_error (statp, resplen2);
		      }
		  }
		else
		  {
		    ssize_t sr;
#ifndef __ASSUME_SENDMMSG
		  try_send:
#endif
		    if (nwritten != 0)
		      sr = send (pfd[0].fd, buf2, buflen2, MSG_NOSIGNAL);
		    else
		      sr = send (pfd[0].fd, buf, buflen, MSG_NOSIGNAL);

		    if (sr != (nwritten != 0 ? buflen2 : buflen)) {
		      if (errno == EINTR || errno == EAGAIN)
			goto recompute_resend;
		      return close_and_return_error (statp, resplen2);
		    }
		  just_one:
		    if (nwritten != 0 || buf2 == NULL || single_request)
		      pfd[0].events = POLLIN;
		    else
		      pfd[0].events = POLLIN | POLLOUT;
		    ++nwritten;
		  }
		goto wait;
	} else if (pfd[0].revents & POLLIN) {
		int *thisanssizp;
		u_char **thisansp;
		int *thisresplenp;

		if ((recvresp1 | recvresp2) == 0 || buf2 == NULL) {
			/* We have not received any responses
			   yet or we only have one response to
			   receive.  */
			thisanssizp = anssizp;
			thisansp = anscp ?: ansp;
			assert (anscp != NULL || ansp2 == NULL);
			thisresplenp = &resplen;
		} else {
			thisanssizp = anssizp2;
			thisansp = ansp2;
			thisresplenp = resplen2;
		}

		if (*thisanssizp < MAXPACKET
		    /* If the current buffer is not the the static
		       user-supplied buffer then we can reallocate
		       it.  */
		    && (thisansp != NULL && thisansp != ansp)
#ifdef FIONREAD
		    /* Is the size too small?  */
		    && (ioctl (pfd[0].fd, FIONREAD, thisresplenp) < 0
			|| *thisanssizp < *thisresplenp)
#endif
                    ) {
			/* Always allocate MAXPACKET, callers expect
			   this specific size.  */
			u_char *newp = malloc (MAXPACKET);
			if (newp != NULL) {
				*thisanssizp = MAXPACKET;
				*thisansp = newp;
				if (thisansp == ansp2)
				  *ansp2_malloced = 1;
			}
		}
		/* We could end up with truncation if anscp was NULL
		   (not allowed to change caller's buffer) and the
		   response buffer size is too small.  This isn't a
		   reliable way to detect truncation because the ioctl
		   may be an inaccurate report of the UDP message size.
		   Therefore we use this only to issue debug output.
		   To do truncation accurately with UDP we need
		   MSG_TRUNC which is only available on Linux.  We
		   can abstract out the Linux-specific feature in the
		   future to detect truncation.  */
		HEADER *anhp = (HEADER *) *thisansp;
		socklen_t fromlen = sizeof(struct sockaddr_in6);
		assert (sizeof(from) <= fromlen);
		*thisresplenp = recvfrom(pfd[0].fd, (char*)*thisansp,
					 *thisanssizp, 0,
					(struct sockaddr *)&from, &fromlen);
		if (__glibc_unlikely (*thisresplenp <= 0))       {
			if (errno == EINTR || errno == EAGAIN) {
				need_recompute = 1;
				goto wait;
			}
			return close_and_return_error (statp, resplen2);
		}
		*gotsomewhere = 1;
		if (__glibc_unlikely (*thisresplenp < HFIXEDSZ))       {
			/*
			 * Undersized message.
			 */
			*terrno = EMSGSIZE;
			return close_and_return_error (statp, resplen2);
		}
		if ((recvresp1 || hp->id != anhp->id)
		    && (recvresp2 || hp2->id != anhp->id)) {
			/*
			 * response from old query, ignore it.
			 * XXX - potential security hazard could
			 *	 be detected here.
			 */
			goto wait;
		}

		/* Paranoia check.  Due to the connected UDP socket,
		   the kernel has already filtered invalid addresses
		   for us.  */
		if (!res_ourserver_p(statp, &from))
		  goto wait;

		/* Check for the correct header layout and a matching
		   question.  */
		if ((recvresp1 || !res_queriesmatch(buf, buf + buflen,
						       *thisansp,
						       *thisansp
						       + *thisanssizp))
		    && (recvresp2 || !res_queriesmatch(buf2, buf2 + buflen2,
						       *thisansp,
						       *thisansp
						       + *thisanssizp)))
		  goto wait;

		if (anhp->rcode == SERVFAIL ||
		    anhp->rcode == NOTIMP ||
		    anhp->rcode == REFUSED) {
		next_ns:
			if (recvresp1 || (buf2 != NULL && recvresp2)) {
			  *resplen2 = 0;
			  return resplen;
			}
			if (buf2 != NULL)
			  {
			    /* No data from the first reply.  */
			    resplen = 0;
			    /* We are waiting for a possible second reply.  */
			    if (hp->id == anhp->id)
			      recvresp1 = 1;
			    else
			      recvresp2 = 1;

			    goto wait;
			  }

			/* don't retry if called from dig */
			if (!statp->pfcode)
			  return close_and_return_error (statp, resplen2);
			__res_iclose(statp, false);
		}
		if (anhp->rcode == NOERROR && anhp->ancount == 0
		    && anhp->aa == 0 && anhp->ra == 0 && anhp->arcount == 0) {
			goto next_ns;
		}
		if (!(statp->options & RES_IGNTC) && anhp->tc) {
			/*
			 * To get the rest of answer,
			 * use TCP with same server.
			 */
			*v_circuit = 1;
			__res_iclose(statp, false);
			// XXX if we have received one reply we could
			// XXX use it and not repeat it over TCP...
			if (resplen2 != NULL)
			  *resplen2 = 0;
			return (1);
		}
		/* Mark which reply we received.  */
		if (recvresp1 == 0 && hp->id == anhp->id)
			recvresp1 = 1;
		else
			recvresp2 = 1;
		/* Repeat waiting if we have a second answer to arrive.  */
		if ((recvresp1 & recvresp2) == 0) {
			if (single_request) {
				pfd[0].events = POLLOUT;
				if (single_request_reopen) {
					__res_iclose (statp, false);
					retval = reopen (statp, terrno, ns);
					if (retval <= 0)
					  {
					    if (resplen2 != NULL)
					      *resplen2 = 0;
					    return retval;
					  }
					pfd[0].fd = EXT(statp).nssocks[ns];
				}
			}
			goto wait;
		}
		/* All is well.  We have received both responses (if
		   two responses were requested).  */
		return (resplen);
	} else if (pfd[0].revents & (POLLERR | POLLHUP | POLLNVAL))
	  /* Something went wrong.  We can stop trying.  */
	  return close_and_return_error (statp, resplen2);
	else {
		/* poll should not have returned > 0 in this case.  */
		abort ();
	}
}

static int
sock_eq(struct sockaddr_in6 *a1, struct sockaddr_in6 *a2) {
	if (a1->sin6_family == a2->sin6_family) {
		if (a1->sin6_family == AF_INET)
			return ((((struct sockaddr_in *)a1)->sin_port ==
				 ((struct sockaddr_in *)a2)->sin_port) &&
				(((struct sockaddr_in *)a1)->sin_addr.s_addr ==
				 ((struct sockaddr_in *)a2)->sin_addr.s_addr));
		else
			return ((a1->sin6_port == a2->sin6_port) &&
				!memcmp(&a1->sin6_addr, &a2->sin6_addr,
					sizeof (struct in6_addr)));
	}
	if (a1->sin6_family == AF_INET) {
		struct sockaddr_in6 *sap = a1;
		a1 = a2;
		a2 = sap;
	} /* assumes that AF_INET and AF_INET6 are the only possibilities */
	return ((a1->sin6_port == ((struct sockaddr_in *)a2)->sin_port) &&
		IN6_IS_ADDR_V4MAPPED(&a1->sin6_addr) &&
		(a1->sin6_addr.s6_addr32[3] ==
		 ((struct sockaddr_in *)a2)->sin_addr.s_addr));
}