summaryrefslogtreecommitdiff
path: root/lib/doh.c
blob: 98b201462f4b3f9fc81196432e5e18f7f823652d (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
/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 2018 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at https://curl.haxx.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ***************************************************************************/

#include "curl_setup.h"

#ifndef CURL_DISABLE_DOH

#include "urldata.h"
#include "curl_addrinfo.h"
#include "doh.h"

#include "sendf.h"
#include "multiif.h"
#include "url.h"
#include "share.h"
#include "curl_base64.h"
#include "connect.h"
#include "strdup.h"
#include "dynbuf.h"
/* The last 3 #include files should be in this order */
#include "curl_printf.h"
#include "curl_memory.h"
#include "memdebug.h"

#define DNS_CLASS_IN 0x01

#ifndef CURL_DISABLE_VERBOSE_STRINGS
static const char * const errors[]={
  "",
  "Bad label",
  "Out of range",
  "Label loop",
  "Too small",
  "Out of memory",
  "RDATA length",
  "Malformat",
  "Bad RCODE",
  "Unexpected TYPE",
  "Unexpected CLASS",
  "No content",
  "Bad ID"
};

static const char *doh_strerror(DOHcode code)
{
  if((code >= DOH_OK) && (code <= DOH_DNS_BAD_ID))
    return errors[code];
  return "bad error code";
}
#endif

#ifdef DEBUGBUILD
#define UNITTEST
#else
#define UNITTEST static
#endif

/* @unittest 1655
 */
UNITTEST DOHcode doh_encode(const char *host,
                            DNStype dnstype,
                            unsigned char *dnsp, /* buffer */
                            size_t len,  /* buffer size */
                            size_t *olen) /* output length */
{
  const size_t hostlen = strlen(host);
  unsigned char *orig = dnsp;
  const char *hostp = host;

  /* The expected output length is 16 bytes more than the length of
   * the QNAME-encoding of the host name.
   *
   * A valid DNS name may not contain a zero-length label, except at
   * the end.  For this reason, a name beginning with a dot, or
   * containing a sequence of two or more consecutive dots, is invalid
   * and cannot be encoded as a QNAME.
   *
   * If the host name ends with a trailing dot, the corresponding
   * QNAME-encoding is one byte longer than the host name. If (as is
   * also valid) the hostname is shortened by the omission of the
   * trailing dot, then its QNAME-encoding will be two bytes longer
   * than the host name.
   *
   * Each [ label, dot ] pair is encoded as [ length, label ],
   * preserving overall length.  A final [ label ] without a dot is
   * also encoded as [ length, label ], increasing overall length
   * by one. The encoding is completed by appending a zero byte,
   * representing the zero-length root label, again increasing
   * the overall length by one.
   */

  size_t expected_len;
  DEBUGASSERT(hostlen);
  expected_len = 12 + 1 + hostlen + 4;
  if(host[hostlen-1]!='.')
    expected_len++;

  if(expected_len > (256 + 16)) /* RFCs 1034, 1035 */
    return DOH_DNS_NAME_TOO_LONG;

  if(len < expected_len)
    return DOH_TOO_SMALL_BUFFER;

  *dnsp++ = 0; /* 16 bit id */
  *dnsp++ = 0;
  *dnsp++ = 0x01; /* |QR|   Opcode  |AA|TC|RD| Set the RD bit */
  *dnsp++ = '\0'; /* |RA|   Z    |   RCODE   |                */
  *dnsp++ = '\0';
  *dnsp++ = 1;    /* QDCOUNT (number of entries in the question section) */
  *dnsp++ = '\0';
  *dnsp++ = '\0'; /* ANCOUNT */
  *dnsp++ = '\0';
  *dnsp++ = '\0'; /* NSCOUNT */
  *dnsp++ = '\0';
  *dnsp++ = '\0'; /* ARCOUNT */

  /* encode each label and store it in the QNAME */
  while(*hostp) {
    size_t labellen;
    char *dot = strchr(hostp, '.');
    if(dot)
      labellen = dot - hostp;
    else
      labellen = strlen(hostp);
    if((labellen > 63) || (!labellen)) {
      /* label is too long or too short, error out */
      *olen = 0;
      return DOH_DNS_BAD_LABEL;
    }
    /* label is non-empty, process it */
    *dnsp++ = (unsigned char)labellen;
    memcpy(dnsp, hostp, labellen);
    dnsp += labellen;
    hostp += labellen;
    /* advance past dot, but only if there is one */
    if(dot)
      hostp++;
  } /* next label */

  *dnsp++ = 0; /* append zero-length label for root */

  /* There are assigned TYPE codes beyond 255: use range [1..65535]  */
  *dnsp++ = (unsigned char)(255 & (dnstype>>8)); /* upper 8 bit TYPE */
  *dnsp++ = (unsigned char)(255 & dnstype);      /* lower 8 bit TYPE */

  *dnsp++ = '\0'; /* upper 8 bit CLASS */
  *dnsp++ = DNS_CLASS_IN; /* IN - "the Internet" */

  *olen = dnsp - orig;

  /* verify that our estimation of length is valid, since
   * this has led to buffer overflows in this function */
  DEBUGASSERT(*olen == expected_len);
  return DOH_OK;
}

static size_t
doh_write_cb(const void *contents, size_t size, size_t nmemb, void *userp)
{
  size_t realsize = size * nmemb;
  struct dynbuf *mem = (struct dynbuf *)userp;

  if(Curl_dyn_addn(mem, contents, realsize))
    return 0;

  return realsize;
}

/* called from multi.c when this DOH transfer is complete */
static int Curl_doh_done(struct Curl_easy *doh, CURLcode result)
{
  struct Curl_easy *data = doh->set.dohfor;
  /* so one of the DOH request done for the 'data' transfer is now complete! */
  data->req.doh.pending--;
  infof(data, "a DOH request is completed, %u to go\n", data->req.doh.pending);
  if(result)
    infof(data, "DOH request %s\n", curl_easy_strerror(result));

  if(!data->req.doh.pending) {
    /* DOH completed */
    curl_slist_free_all(data->req.doh.headers);
    data->req.doh.headers = NULL;
    Curl_expire(data, 0, EXPIRE_RUN_NOW);
  }
  return 0;
}

#define ERROR_CHECK_SETOPT(x,y) \
do {                                      \
  result = curl_easy_setopt(doh, x, y);   \
  if(result)                              \
    goto error;                           \
} while(0)

static CURLcode dohprobe(struct Curl_easy *data,
                         struct dnsprobe *p, DNStype dnstype,
                         const char *host,
                         const char *url, CURLM *multi,
                         struct curl_slist *headers)
{
  struct Curl_easy *doh = NULL;
  char *nurl = NULL;
  CURLcode result = CURLE_OK;
  timediff_t timeout_ms;
  DOHcode d = doh_encode(host, dnstype, p->dohbuffer, sizeof(p->dohbuffer),
                         &p->dohlen);
  if(d) {
    failf(data, "Failed to encode DOH packet [%d]\n", d);
    return CURLE_OUT_OF_MEMORY;
  }

  p->dnstype = dnstype;
  Curl_dyn_init(&p->serverdoh, DYN_DOH_RESPONSE);

  /* Note: this is code for sending the DoH request with GET but there's still
     no logic that actually enables this. We should either add that ability or
     yank out the GET code. Discuss! */
  if(data->set.doh_get) {
    char *b64;
    size_t b64len;
    result = Curl_base64url_encode(data, (char *)p->dohbuffer, p->dohlen,
                                   &b64, &b64len);
    if(result)
      goto error;
    nurl = aprintf("%s?dns=%s", url, b64);
    free(b64);
    if(!nurl) {
      result = CURLE_OUT_OF_MEMORY;
      goto error;
    }
    url = nurl;
  }

  timeout_ms = Curl_timeleft(data, NULL, TRUE);
  if(timeout_ms <= 0) {
    result = CURLE_OPERATION_TIMEDOUT;
    goto error;
  }
  /* Curl_open() is the internal version of curl_easy_init() */
  result = Curl_open(&doh);
  if(!result) {
    /* pass in the struct pointer via a local variable to please coverity and
       the gcc typecheck helpers */
    struct dynbuf *resp = &p->serverdoh;
    ERROR_CHECK_SETOPT(CURLOPT_URL, url);
    ERROR_CHECK_SETOPT(CURLOPT_WRITEFUNCTION, doh_write_cb);
    ERROR_CHECK_SETOPT(CURLOPT_WRITEDATA, resp);
    if(!data->set.doh_get) {
      ERROR_CHECK_SETOPT(CURLOPT_POSTFIELDS, p->dohbuffer);
      ERROR_CHECK_SETOPT(CURLOPT_POSTFIELDSIZE, (long)p->dohlen);
    }
    ERROR_CHECK_SETOPT(CURLOPT_HTTPHEADER, headers);
#ifdef USE_NGHTTP2
    ERROR_CHECK_SETOPT(CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2TLS);
#endif
#ifndef CURLDEBUG
    /* enforce HTTPS if not debug */
    ERROR_CHECK_SETOPT(CURLOPT_PROTOCOLS, CURLPROTO_HTTPS);
#else
    /* in debug mode, also allow http */
    ERROR_CHECK_SETOPT(CURLOPT_PROTOCOLS, CURLPROTO_HTTP|CURLPROTO_HTTPS);
#endif
    ERROR_CHECK_SETOPT(CURLOPT_TIMEOUT_MS, (long)timeout_ms);
    if(data->set.verbose)
      ERROR_CHECK_SETOPT(CURLOPT_VERBOSE, 1L);
    if(data->set.no_signal)
      ERROR_CHECK_SETOPT(CURLOPT_NOSIGNAL, 1L);

    /* Inherit *some* SSL options from the user's transfer. This is a
       best-guess as to which options are needed for compatibility. #3661 */
    if(data->set.ssl.falsestart)
      ERROR_CHECK_SETOPT(CURLOPT_SSL_FALSESTART, 1L);
    if(data->set.ssl.primary.verifyhost)
      ERROR_CHECK_SETOPT(CURLOPT_SSL_VERIFYHOST, 2L);
#ifndef CURL_DISABLE_PROXY
    if(data->set.proxy_ssl.primary.verifyhost)
      ERROR_CHECK_SETOPT(CURLOPT_PROXY_SSL_VERIFYHOST, 2L);
    if(data->set.proxy_ssl.primary.verifypeer)
      ERROR_CHECK_SETOPT(CURLOPT_PROXY_SSL_VERIFYPEER, 1L);
    if(data->set.str[STRING_SSL_CAFILE_PROXY]) {
      ERROR_CHECK_SETOPT(CURLOPT_PROXY_CAINFO,
        data->set.str[STRING_SSL_CAFILE_PROXY]);
    }
    if(data->set.str[STRING_SSL_CRLFILE_PROXY]) {
      ERROR_CHECK_SETOPT(CURLOPT_PROXY_CRLFILE,
        data->set.str[STRING_SSL_CRLFILE_PROXY]);
    }
    if(data->set.proxy_ssl.no_revoke)
      ERROR_CHECK_SETOPT(CURLOPT_PROXY_SSL_OPTIONS, CURLSSLOPT_NO_REVOKE);
    else if(data->set.proxy_ssl.revoke_best_effort)
      ERROR_CHECK_SETOPT(CURLOPT_PROXY_SSL_OPTIONS,
                         CURLSSLOPT_REVOKE_BEST_EFFORT);
    if(data->set.str[STRING_SSL_CAPATH_PROXY]) {
      ERROR_CHECK_SETOPT(CURLOPT_PROXY_CAPATH,
        data->set.str[STRING_SSL_CAPATH_PROXY]);
    }
#endif
    if(data->set.ssl.primary.verifypeer)
      ERROR_CHECK_SETOPT(CURLOPT_SSL_VERIFYPEER, 1L);
    if(data->set.ssl.primary.verifystatus)
      ERROR_CHECK_SETOPT(CURLOPT_SSL_VERIFYSTATUS, 1L);
    if(data->set.str[STRING_SSL_CAFILE_ORIG]) {
      ERROR_CHECK_SETOPT(CURLOPT_CAINFO,
        data->set.str[STRING_SSL_CAFILE_ORIG]);
    }
    if(data->set.str[STRING_SSL_CAPATH_ORIG]) {
      ERROR_CHECK_SETOPT(CURLOPT_CAPATH,
        data->set.str[STRING_SSL_CAPATH_ORIG]);
    }
    if(data->set.str[STRING_SSL_CRLFILE_ORIG]) {
      ERROR_CHECK_SETOPT(CURLOPT_CRLFILE,
        data->set.str[STRING_SSL_CRLFILE_ORIG]);
    }
    if(data->set.ssl.certinfo)
      ERROR_CHECK_SETOPT(CURLOPT_CERTINFO, 1L);
    if(data->set.str[STRING_SSL_RANDOM_FILE]) {
      ERROR_CHECK_SETOPT(CURLOPT_RANDOM_FILE,
        data->set.str[STRING_SSL_RANDOM_FILE]);
    }
    if(data->set.str[STRING_SSL_EGDSOCKET]) {
      ERROR_CHECK_SETOPT(CURLOPT_EGDSOCKET,
        data->set.str[STRING_SSL_EGDSOCKET]);
    }
    if(data->set.ssl.no_revoke)
      ERROR_CHECK_SETOPT(CURLOPT_SSL_OPTIONS, CURLSSLOPT_NO_REVOKE);
    else if(data->set.ssl.revoke_best_effort)
      ERROR_CHECK_SETOPT(CURLOPT_SSL_OPTIONS, CURLSSLOPT_REVOKE_BEST_EFFORT);
    if(data->set.ssl.fsslctx)
      ERROR_CHECK_SETOPT(CURLOPT_SSL_CTX_FUNCTION, data->set.ssl.fsslctx);
    if(data->set.ssl.fsslctxp)
      ERROR_CHECK_SETOPT(CURLOPT_SSL_CTX_DATA, data->set.ssl.fsslctxp);

    doh->set.fmultidone = Curl_doh_done;
    doh->set.dohfor = data; /* identify for which transfer this is done */
    p->easy = doh;

    /* add this transfer to the multi handle */
    if(curl_multi_add_handle(multi, doh))
      goto error;
  }
  else
    goto error;
  free(nurl);
  return CURLE_OK;

  error:
  free(nurl);
  Curl_close(&doh);
  return result;
}

/*
 * Curl_doh() resolves a name using DOH. It resolves a name and returns a
 * 'Curl_addrinfo *' with the address information.
 */

struct Curl_addrinfo *Curl_doh(struct connectdata *conn,
                               const char *hostname,
                               int port,
                               int *waitp)
{
  struct Curl_easy *data = conn->data;
  CURLcode result = CURLE_OK;
  int slot;
  *waitp = TRUE; /* this never returns synchronously */
  (void)conn;
  (void)hostname;
  (void)port;

  /* start clean, consider allocating this struct on demand */
  memset(&data->req.doh, 0, sizeof(struct dohdata));

  data->req.doh.host = hostname;
  data->req.doh.port = port;
  data->req.doh.headers =
    curl_slist_append(NULL,
                      "Content-Type: application/dns-message");
  if(!data->req.doh.headers)
    goto error;

  if(conn->ip_version != CURL_IPRESOLVE_V6) {
    /* create IPv4 DOH request */
    result = dohprobe(data, &data->req.doh.probe[DOH_PROBE_SLOT_IPADDR_V4],
                      DNS_TYPE_A, hostname, data->set.str[STRING_DOH],
                      data->multi, data->req.doh.headers);
    if(result)
      goto error;
    data->req.doh.pending++;
  }

  if(conn->ip_version != CURL_IPRESOLVE_V4) {
    /* create IPv6 DOH request */
    result = dohprobe(data, &data->req.doh.probe[DOH_PROBE_SLOT_IPADDR_V6],
                      DNS_TYPE_AAAA, hostname, data->set.str[STRING_DOH],
                      data->multi, data->req.doh.headers);
    if(result)
      goto error;
    data->req.doh.pending++;
  }
  return NULL;

  error:
  curl_slist_free_all(data->req.doh.headers);
  data->req.doh.headers = NULL;
  for(slot = 0; slot < DOH_PROBE_SLOTS; slot++) {
    Curl_close(&data->req.doh.probe[slot].easy);
  }
  return NULL;
}

static DOHcode skipqname(const unsigned char *doh, size_t dohlen,
                         unsigned int *indexp)
{
  unsigned char length;
  do {
    if(dohlen < (*indexp + 1))
      return DOH_DNS_OUT_OF_RANGE;
    length = doh[*indexp];
    if((length & 0xc0) == 0xc0) {
      /* name pointer, advance over it and be done */
      if(dohlen < (*indexp + 2))
        return DOH_DNS_OUT_OF_RANGE;
      *indexp += 2;
      break;
    }
    if(length & 0xc0)
      return DOH_DNS_BAD_LABEL;
    if(dohlen < (*indexp + 1 + length))
      return DOH_DNS_OUT_OF_RANGE;
    *indexp += 1 + length;
  } while(length);
  return DOH_OK;
}

static unsigned short get16bit(const unsigned char *doh, int index)
{
  return (unsigned short)((doh[index] << 8) | doh[index + 1]);
}

static unsigned int get32bit(const unsigned char *doh, int index)
{
   /* make clang and gcc optimize this to bswap by incrementing
      the pointer first. */
   doh += index;

   /* avoid undefined behaviour by casting to unsigned before shifting
      24 bits, possibly into the sign bit. codegen is same, but
      ub sanitizer won't be upset */
  return ( (unsigned)doh[0] << 24) | (doh[1] << 16) |(doh[2] << 8) | doh[3];
}

static DOHcode store_a(const unsigned char *doh, int index, struct dohentry *d)
{
  /* silently ignore addresses over the limit */
  if(d->numaddr < DOH_MAX_ADDR) {
    struct dohaddr *a = &d->addr[d->numaddr];
    a->type = DNS_TYPE_A;
    memcpy(&a->ip.v4, &doh[index], 4);
    d->numaddr++;
  }
  return DOH_OK;
}

static DOHcode store_aaaa(const unsigned char *doh,
                          int index,
                          struct dohentry *d)
{
  /* silently ignore addresses over the limit */
  if(d->numaddr < DOH_MAX_ADDR) {
    struct dohaddr *a = &d->addr[d->numaddr];
    a->type = DNS_TYPE_AAAA;
    memcpy(&a->ip.v6, &doh[index], 16);
    d->numaddr++;
  }
  return DOH_OK;
}

static DOHcode store_cname(const unsigned char *doh,
                           size_t dohlen,
                           unsigned int index,
                           struct dohentry *d)
{
  struct dynbuf *c;
  unsigned int loop = 128; /* a valid DNS name can never loop this much */
  unsigned char length;

  if(d->numcname == DOH_MAX_CNAME)
    return DOH_OK; /* skip! */

  c = &d->cname[d->numcname++];
  do {
    if(index >= dohlen)
      return DOH_DNS_OUT_OF_RANGE;
    length = doh[index];
    if((length & 0xc0) == 0xc0) {
      int newpos;
      /* name pointer, get the new offset (14 bits) */
      if((index + 1) >= dohlen)
        return DOH_DNS_OUT_OF_RANGE;

      /* move to the new index */
      newpos = (length & 0x3f) << 8 | doh[index + 1];
      index = newpos;
      continue;
    }
    else if(length & 0xc0)
      return DOH_DNS_BAD_LABEL; /* bad input */
    else
      index++;

    if(length) {
      if(Curl_dyn_len(c)) {
        if(Curl_dyn_add(c, "."))
          return DOH_OUT_OF_MEM;
      }
      if((index + length) > dohlen)
        return DOH_DNS_BAD_LABEL;

      if(Curl_dyn_addn(c, &doh[index], length))
        return DOH_OUT_OF_MEM;
      index += length;
    }
  } while(length && --loop);

  if(!loop)
    return DOH_DNS_LABEL_LOOP;
  return DOH_OK;
}

static DOHcode rdata(const unsigned char *doh,
                     size_t dohlen,
                     unsigned short rdlength,
                     unsigned short type,
                     int index,
                     struct dohentry *d)
{
  /* RDATA
     - A (TYPE 1):  4 bytes
     - AAAA (TYPE 28): 16 bytes
     - NS (TYPE 2): N bytes */
  DOHcode rc;

  switch(type) {
  case DNS_TYPE_A:
    if(rdlength != 4)
      return DOH_DNS_RDATA_LEN;
    rc = store_a(doh, index, d);
    if(rc)
      return rc;
    break;
  case DNS_TYPE_AAAA:
    if(rdlength != 16)
      return DOH_DNS_RDATA_LEN;
    rc = store_aaaa(doh, index, d);
    if(rc)
      return rc;
    break;
  case DNS_TYPE_CNAME:
    rc = store_cname(doh, dohlen, index, d);
    if(rc)
      return rc;
    break;
  case DNS_TYPE_DNAME:
    /* explicit for clarity; just skip; rely on synthesized CNAME  */
    break;
  default:
    /* unsupported type, just skip it */
    break;
  }
  return DOH_OK;
}

UNITTEST void de_init(struct dohentry *de)
{
  int i;
  memset(de, 0, sizeof(*de));
  de->ttl = INT_MAX;
  for(i = 0; i < DOH_MAX_CNAME; i++)
    Curl_dyn_init(&de->cname[i], DYN_DOH_CNAME);
}


UNITTEST DOHcode doh_decode(const unsigned char *doh,
                            size_t dohlen,
                            DNStype dnstype,
                            struct dohentry *d)
{
  unsigned char rcode;
  unsigned short qdcount;
  unsigned short ancount;
  unsigned short type = 0;
  unsigned short rdlength;
  unsigned short nscount;
  unsigned short arcount;
  unsigned int index = 12;
  DOHcode rc;

  if(dohlen < 12)
    return DOH_TOO_SMALL_BUFFER; /* too small */
  if(!doh || doh[0] || doh[1])
    return DOH_DNS_BAD_ID; /* bad ID */
  rcode = doh[3] & 0x0f;
  if(rcode)
    return DOH_DNS_BAD_RCODE; /* bad rcode */

  qdcount = get16bit(doh, 4);
  while(qdcount) {
    rc = skipqname(doh, dohlen, &index);
    if(rc)
      return rc; /* bad qname */
    if(dohlen < (index + 4))
      return DOH_DNS_OUT_OF_RANGE;
    index += 4; /* skip question's type and class */
    qdcount--;
  }

  ancount = get16bit(doh, 6);
  while(ancount) {
    unsigned short class;
    unsigned int ttl;

    rc = skipqname(doh, dohlen, &index);
    if(rc)
      return rc; /* bad qname */

    if(dohlen < (index + 2))
      return DOH_DNS_OUT_OF_RANGE;

    type = get16bit(doh, index);
    if((type != DNS_TYPE_CNAME)    /* may be synthesized from DNAME */
       && (type != DNS_TYPE_DNAME) /* if present, accept and ignore */
       && (type != dnstype))
      /* Not the same type as was asked for nor CNAME nor DNAME */
      return DOH_DNS_UNEXPECTED_TYPE;
    index += 2;

    if(dohlen < (index + 2))
      return DOH_DNS_OUT_OF_RANGE;
    class = get16bit(doh, index);
    if(DNS_CLASS_IN != class)
      return DOH_DNS_UNEXPECTED_CLASS; /* unsupported */
    index += 2;

    if(dohlen < (index + 4))
      return DOH_DNS_OUT_OF_RANGE;

    ttl = get32bit(doh, index);
    if(ttl < d->ttl)
      d->ttl = ttl;
    index += 4;

    if(dohlen < (index + 2))
      return DOH_DNS_OUT_OF_RANGE;

    rdlength = get16bit(doh, index);
    index += 2;
    if(dohlen < (index + rdlength))
      return DOH_DNS_OUT_OF_RANGE;

    rc = rdata(doh, dohlen, rdlength, type, index, d);
    if(rc)
      return rc; /* bad rdata */
    index += rdlength;
    ancount--;
  }

  nscount = get16bit(doh, 8);
  while(nscount) {
    rc = skipqname(doh, dohlen, &index);
    if(rc)
      return rc; /* bad qname */

    if(dohlen < (index + 8))
      return DOH_DNS_OUT_OF_RANGE;

    index += 2 + 2 + 4; /* type, class and ttl */

    if(dohlen < (index + 2))
      return DOH_DNS_OUT_OF_RANGE;

    rdlength = get16bit(doh, index);
    index += 2;
    if(dohlen < (index + rdlength))
      return DOH_DNS_OUT_OF_RANGE;
    index += rdlength;
    nscount--;
  }

  arcount = get16bit(doh, 10);
  while(arcount) {
    rc = skipqname(doh, dohlen, &index);
    if(rc)
      return rc; /* bad qname */

    if(dohlen < (index + 8))
      return DOH_DNS_OUT_OF_RANGE;

    index += 2 + 2 + 4; /* type, class and ttl */

    if(dohlen < (index + 2))
      return DOH_DNS_OUT_OF_RANGE;

    rdlength = get16bit(doh, index);
    index += 2;
    if(dohlen < (index + rdlength))
      return DOH_DNS_OUT_OF_RANGE;
    index += rdlength;
    arcount--;
  }

  if(index != dohlen)
    return DOH_DNS_MALFORMAT; /* something is wrong */

  if((type != DNS_TYPE_NS) && !d->numcname && !d->numaddr)
    /* nothing stored! */
    return DOH_NO_CONTENT;

  return DOH_OK; /* ok */
}

#ifndef CURL_DISABLE_VERBOSE_STRINGS
static void showdoh(struct Curl_easy *data,
                    const struct dohentry *d)
{
  int i;
  infof(data, "TTL: %u seconds\n", d->ttl);
  for(i = 0; i < d->numaddr; i++) {
    const struct dohaddr *a = &d->addr[i];
    if(a->type == DNS_TYPE_A) {
      infof(data, "DOH A: %u.%u.%u.%u\n",
            a->ip.v4[0], a->ip.v4[1],
            a->ip.v4[2], a->ip.v4[3]);
    }
    else if(a->type == DNS_TYPE_AAAA) {
      int j;
      char buffer[128];
      char *ptr;
      size_t len;
      msnprintf(buffer, 128, "DOH AAAA: ");
      ptr = &buffer[10];
      len = 118;
      for(j = 0; j < 16; j += 2) {
        size_t l;
        msnprintf(ptr, len, "%s%02x%02x", j?":":"", d->addr[i].ip.v6[j],
                  d->addr[i].ip.v6[j + 1]);
        l = strlen(ptr);
        len -= l;
        ptr += l;
      }
      infof(data, "%s\n", buffer);
    }
  }
  for(i = 0; i < d->numcname; i++) {
    infof(data, "CNAME: %s\n", Curl_dyn_ptr(&d->cname[i]));
  }
}
#else
#define showdoh(x,y)
#endif

/*
 * doh2ai()
 *
 * This function returns a pointer to the first element of a newly allocated
 * Curl_addrinfo struct linked list filled with the data from a set of DOH
 * lookups.  Curl_addrinfo is meant to work like the addrinfo struct does for
 * a IPv6 stack, but usable also for IPv4, all hosts and environments.
 *
 * The memory allocated by this function *MUST* be free'd later on calling
 * Curl_freeaddrinfo().  For each successful call to this function there
 * must be an associated call later to Curl_freeaddrinfo().
 */

static struct Curl_addrinfo *
doh2ai(const struct dohentry *de, const char *hostname, int port)
{
  struct Curl_addrinfo *ai;
  struct Curl_addrinfo *prevai = NULL;
  struct Curl_addrinfo *firstai = NULL;
  struct sockaddr_in *addr;
#ifdef ENABLE_IPV6
  struct sockaddr_in6 *addr6;
#endif
  CURLcode result = CURLE_OK;
  int i;

  if(!de)
    /* no input == no output! */
    return NULL;

  for(i = 0; i < de->numaddr; i++) {
    size_t ss_size;
    CURL_SA_FAMILY_T addrtype;
    if(de->addr[i].type == DNS_TYPE_AAAA) {
#ifndef ENABLE_IPV6
      /* we can't handle IPv6 addresses */
      continue;
#else
      ss_size = sizeof(struct sockaddr_in6);
      addrtype = AF_INET6;
#endif
    }
    else {
      ss_size = sizeof(struct sockaddr_in);
      addrtype = AF_INET;
    }

    ai = calloc(1, sizeof(struct Curl_addrinfo));
    if(!ai) {
      result = CURLE_OUT_OF_MEMORY;
      break;
    }
    ai->ai_canonname = strdup(hostname);
    if(!ai->ai_canonname) {
      result = CURLE_OUT_OF_MEMORY;
      free(ai);
      break;
    }
    ai->ai_addr = calloc(1, ss_size);
    if(!ai->ai_addr) {
      result = CURLE_OUT_OF_MEMORY;
      free(ai->ai_canonname);
      free(ai);
      break;
    }

    if(!firstai)
      /* store the pointer we want to return from this function */
      firstai = ai;

    if(prevai)
      /* make the previous entry point to this */
      prevai->ai_next = ai;

    ai->ai_family = addrtype;

    /* we return all names as STREAM, so when using this address for TFTP
       the type must be ignored and conn->socktype be used instead! */
    ai->ai_socktype = SOCK_STREAM;

    ai->ai_addrlen = (curl_socklen_t)ss_size;

    /* leave the rest of the struct filled with zero */

    switch(ai->ai_family) {
    case AF_INET:
      addr = (void *)ai->ai_addr; /* storage area for this info */
      DEBUGASSERT(sizeof(struct in_addr) == sizeof(de->addr[i].ip.v4));
      memcpy(&addr->sin_addr, &de->addr[i].ip.v4, sizeof(struct in_addr));
      addr->sin_family = (CURL_SA_FAMILY_T)addrtype;
      addr->sin_port = htons((unsigned short)port);
      break;

#ifdef ENABLE_IPV6
    case AF_INET6:
      addr6 = (void *)ai->ai_addr; /* storage area for this info */
      DEBUGASSERT(sizeof(struct in6_addr) == sizeof(de->addr[i].ip.v6));
      memcpy(&addr6->sin6_addr, &de->addr[i].ip.v6, sizeof(struct in6_addr));
      addr6->sin6_family = (CURL_SA_FAMILY_T)addrtype;
      addr6->sin6_port = htons((unsigned short)port);
      break;
#endif
    }

    prevai = ai;
  }

  if(result) {
    Curl_freeaddrinfo(firstai);
    firstai = NULL;
  }

  return firstai;
}

#ifndef CURL_DISABLE_VERBOSE_STRINGS
static const char *type2name(DNStype dnstype)
{
  return (dnstype == DNS_TYPE_A)?"A":"AAAA";
}
#endif

UNITTEST void de_cleanup(struct dohentry *d)
{
  int i = 0;
  for(i = 0; i < d->numcname; i++) {
    Curl_dyn_free(&d->cname[i]);
  }
}

CURLcode Curl_doh_is_resolved(struct connectdata *conn,
                              struct Curl_dns_entry **dnsp)
{
  CURLcode result;
  struct Curl_easy *data = conn->data;
  *dnsp = NULL; /* defaults to no response */

  if(!data->req.doh.probe[DOH_PROBE_SLOT_IPADDR_V4].easy &&
     !data->req.doh.probe[DOH_PROBE_SLOT_IPADDR_V6].easy) {
    failf(data, "Could not DOH-resolve: %s", conn->async.hostname);
    return conn->bits.proxy?CURLE_COULDNT_RESOLVE_PROXY:
      CURLE_COULDNT_RESOLVE_HOST;
  }
  else if(!data->req.doh.pending) {
    DOHcode rc[DOH_PROBE_SLOTS] = {
      DOH_OK, DOH_OK
    };
    struct dohentry de;
    int slot;
    /* remove DOH handles from multi handle and close them */
    for(slot = 0; slot < DOH_PROBE_SLOTS; slot++) {
      curl_multi_remove_handle(data->multi, data->req.doh.probe[slot].easy);
      Curl_close(&data->req.doh.probe[slot].easy);
    }
    /* parse the responses, create the struct and return it! */
    de_init(&de);
    for(slot = 0; slot < DOH_PROBE_SLOTS; slot++) {
      struct dnsprobe *p = &data->req.doh.probe[slot];
      if(!p->dnstype)
        continue;
      rc[slot] = doh_decode(Curl_dyn_uptr(&p->serverdoh),
                            Curl_dyn_len(&p->serverdoh),
                            p->dnstype,
                            &de);
      Curl_dyn_free(&p->serverdoh);
      if(rc[slot]) {
        infof(data, "DOH: %s type %s for %s\n", doh_strerror(rc[slot]),
              type2name(p->dnstype), data->req.doh.host);
      }
    } /* next slot */

    result = CURLE_COULDNT_RESOLVE_HOST; /* until we know better */
    if(!rc[DOH_PROBE_SLOT_IPADDR_V4] || !rc[DOH_PROBE_SLOT_IPADDR_V6]) {
      /* we have an address, of one kind or other */
      struct Curl_dns_entry *dns;
      struct Curl_addrinfo *ai;

      infof(data, "DOH Host name: %s\n", data->req.doh.host);
      showdoh(data, &de);

      ai = doh2ai(&de, data->req.doh.host, data->req.doh.port);
      if(!ai) {
        de_cleanup(&de);
        return CURLE_OUT_OF_MEMORY;
      }

      if(data->share)
        Curl_share_lock(data, CURL_LOCK_DATA_DNS, CURL_LOCK_ACCESS_SINGLE);

      /* we got a response, store it in the cache */
      dns = Curl_cache_addr(data, ai, data->req.doh.host, data->req.doh.port);

      if(data->share)
        Curl_share_unlock(data, CURL_LOCK_DATA_DNS);

      if(!dns) {
        /* returned failure, bail out nicely */
        Curl_freeaddrinfo(ai);
      }
      else {
        conn->async.dns = dns;
        *dnsp = dns;
        result = CURLE_OK;      /* address resolution OK */
      }
    } /* address processing done */

    /* Now process any build-specific attributes retrieved from DNS */

    /* All done */
    de_cleanup(&de);
    return result;

  } /* !data->req.doh.pending */

  /* else wait for pending DOH transactions to complete */
  return CURLE_OK;
}

#endif /* CURL_DISABLE_DOH */