forked from abrasive/shairport
-
Notifications
You must be signed in to change notification settings - Fork 0
/
tinysvcmdns.c
1676 lines (1350 loc) · 54 KB
/
tinysvcmdns.c
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
// This file is the concatenation of mdnsd.c and mdns.c
// from tinysvcmdns with minor modifications
// The code was taken from https://bitbucket.org/geekman/tinysvcmdns at revision e34b562
/*
* tinysvcmdns - a tiny MDNS implementation for publishing services
* Copyright (C) 2011 Darell Tan
* 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.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
*/
#include "tinysvcmdns.h"
#include "common.h"
#define DEBUG_PRINTF(...) debug(1, __VA_ARGS__)
#define log_message(level, ...) \
do { \
switch(level) \
{ \
case LOG_ERR: \
warn(__VA_ARGS__); \
break; \
default: \
debug(1, __VA_ARGS__); \
} \
} while (0)
//******************************************************//
// mdns.c //
//******************************************************//
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>
#ifdef _WIN32
#include <winsock.h>
#include <in6addr.h>
#else
#include <netinet/in.h>
#endif
#define DEFAULT_TTL 120
struct name_comp {
uint8_t *label; // label
size_t pos; // position in msg
struct name_comp *next;
};
// ----- label functions -----
// duplicates a name
inline uint8_t *dup_nlabel(const uint8_t *n) {
assert(n[0] <= 63); // prevent mis-use
return (uint8_t *) strdup((char *) n);
}
// duplicates a label
uint8_t *dup_label(const uint8_t *label) {
int len = *label + 1;
if (len > 63)
return NULL;
uint8_t *newlabel = malloc(len + 1);
strncpy((char *) newlabel, (char *) label, len);
newlabel[len] = '\0';
return newlabel;
}
uint8_t *join_nlabel(const uint8_t *n1, const uint8_t *n2) {
int len1, len2;
uint8_t *s;
assert(n1[0] <= 63 && n2[0] <= 63); // detect misuse
len1 = strlen((char *) n1);
len2 = strlen((char *) n2);
s = malloc(len1 + len2 + 1);
strncpy((char *) s, (char *) n1, len1);
strncpy((char *) s+len1, (char *) n2, len2);
s[len1 + len2] = '\0';
return s;
}
// returns a human-readable name label in dotted form
char *nlabel_to_str(const uint8_t *name) {
char *label, *labelp;
const uint8_t *p;
assert(name != NULL);
label = labelp = malloc(256);
for (p = name; *p; p++) {
strncpy(labelp, (char *) p + 1, *p);
labelp += *p;
*labelp = '.';
labelp++;
p += *p;
}
*labelp = '\0';
return label;
}
// returns the length of a label field
// does NOT uncompress the field, so it could be as small as 2 bytes
// or 1 for the root
static size_t label_len(uint8_t *pkt_buf, size_t pkt_len, size_t off) {
uint8_t *p;
uint8_t *e = pkt_buf + pkt_len;
size_t len = 0;
for (p = pkt_buf + off; p < e; p++) {
if (*p == 0) {
return len + 1;
} else if ((*p & 0xC0) == 0xC0) {
return len + 2;
} else {
len += *p + 1;
p += *p;
}
}
return len;
}
// creates a label
// free() after use
uint8_t *create_label(const char *txt) {
int len;
uint8_t *s;
assert(txt != NULL);
len = strlen(txt);
if (len > 63)
return NULL;
s = malloc(len + 2);
s[0] = len;
strncpy((char *) s + 1, txt, len);
s[len + 1] = '\0';
return s;
}
// creates a uncompressed name label given a DNS name like "apple.b.com"
// free() after use
uint8_t *create_nlabel(const char *name) {
char *label;
char *p, *e, *lenpos;
int len = 0;
assert(name != NULL);
len = strlen(name);
label = malloc(len + 1 + 1);
if (label == NULL)
return NULL;
strncpy((char *) label + 1, name, len);
label[len + 1] = '\0';
p = label;
e = p + len;
lenpos = p;
while (p < e) {
*lenpos = 0;
char *dot = memchr(p + 1, '.', e - p - 1);
if (dot == NULL)
dot = e + 1;
*lenpos = dot - p - 1;
p = dot;
lenpos = dot;
}
return (uint8_t *) label;
}
// copies a label from the buffer into a newly-allocated string
// free() after use
static uint8_t *copy_label(uint8_t *pkt_buf, size_t pkt_len, size_t off) {
int len;
if (off > pkt_len)
return NULL;
len = pkt_buf[off] + 1;
if (off + len > pkt_len) {
DEBUG_PRINTF("label length exceeds packet buffer\n");
return NULL;
}
return dup_label(pkt_buf + off);
}
// uncompresses a name
// free() after use
static uint8_t *uncompress_nlabel(uint8_t *pkt_buf, size_t pkt_len, size_t off) {
uint8_t *p;
uint8_t *e = pkt_buf + pkt_len;
size_t len = 0;
char *str, *sp;
if (off >= pkt_len)
return NULL;
// calculate length of uncompressed label
for (p = pkt_buf + off; *p && p < e; p++) {
size_t llen = 0;
if ((*p & 0xC0) == 0xC0) {
uint8_t *p2 = pkt_buf + (((p[0] & ~0xC0) << 8) | p[1]);
llen = *p2 + 1;
p = p2 + llen - 1;
} else {
llen = *p + 1;
p += llen - 1;
}
len += llen;
}
str = sp = malloc(len + 1);
if (str == NULL)
return NULL;
// FIXME: must merge this with above code
for (p = pkt_buf + off; *p && p < e; p++) {
size_t llen = 0;
if ((*p & 0xC0) == 0xC0) {
uint8_t *p2 = pkt_buf + (((p[0] & ~0xC0) << 8) | p[1]);
llen = *p2 + 1;
strncpy(sp, (char *) p2, llen);
p = p2 + llen - 1;
} else {
llen = *p + 1;
strncpy(sp, (char *) p, llen);
p += llen - 1;
}
sp += llen;
}
*sp = '\0';
return (uint8_t *) str;
}
// ----- RR list & group functions -----
const char *rr_get_type_name(enum rr_type type) {
switch (type) {
case RR_A: return "A";
case RR_PTR: return "PTR";
case RR_TXT: return "TXT";
case RR_AAAA: return "AAAA";
case RR_SRV: return "SRV";
case RR_NSEC: return "NSEC";
case RR_ANY: return "ANY";
}
return NULL;
}
void rr_entry_destroy(struct rr_entry *rr) {
struct rr_data_txt *txt_rec;
assert(rr);
// check rr_type and free data elements
switch (rr->type) {
case RR_PTR:
if (rr->data.PTR.name)
free(rr->data.PTR.name);
// don't free entry
break;
case RR_TXT:
txt_rec = &rr->data.TXT;
while (txt_rec) {
struct rr_data_txt *next = txt_rec->next;
if (txt_rec->txt)
free(txt_rec->txt);
// only free() if it wasn't part of the struct
if (txt_rec != &rr->data.TXT)
free(txt_rec);
txt_rec = next;
}
break;
case RR_SRV:
if (rr->data.SRV.target)
free(rr->data.SRV.target);
break;
default:
// nothing to free
break;
}
free(rr->name);
free(rr);
}
// destroys an RR list (and optionally, items)
void rr_list_destroy(struct rr_list *rr, char destroy_items) {
struct rr_list *rr_next;
for (; rr; rr = rr_next) {
rr_next = rr->next;
if (destroy_items)
rr_entry_destroy(rr->e);
free(rr);
}
}
int rr_list_count(struct rr_list *rr) {
int i = 0;
for (; rr; i++, rr = rr->next);
return i;
}
struct rr_entry *rr_list_remove(struct rr_list **rr_head, struct rr_entry *rr) {
struct rr_list *le = *rr_head, *pe = NULL;
for (; le; le = le->next) {
if (le->e == rr) {
if (pe == NULL) {
*rr_head = le->next;
free(le);
return rr;
} else {
pe->next = le->next;
free(le);
return rr;
}
}
pe = le;
}
return NULL;
}
// appends an rr_entry to an RR list
// if the RR is already in the list, it will not be added
// RRs are compared by memory location - not its contents
// return value of 0 means item not added
int rr_list_append(struct rr_list **rr_head, struct rr_entry *rr) {
struct rr_list *node = malloc(sizeof(struct rr_list));
node->e = rr;
node->next = NULL;
if (*rr_head == NULL) {
*rr_head = node;
} else {
struct rr_list *e = *rr_head, *taile;
for (; e; e = e->next) {
// already in list - don't add
if (e->e == rr) {
free(node);
return 0;
}
if (e->next == NULL)
taile = e;
}
taile->next = node;
}
return 1;
}
#define FILL_RR_ENTRY(rr, _name, _type) \
rr->name = _name; \
rr->type = _type; \
rr->ttl = DEFAULT_TTL; \
rr->cache_flush = 1; \
rr->rr_class = 1;
struct rr_entry *rr_create_a(uint8_t *name, uint32_t addr) {
DECL_MALLOC_ZERO_STRUCT(rr, rr_entry);
FILL_RR_ENTRY(rr, name, RR_A);
rr->data.A.addr = addr;
return rr;
}
struct rr_entry *rr_create_aaaa(uint8_t *name, struct in6_addr *addr) {
DECL_MALLOC_ZERO_STRUCT(rr, rr_entry);
FILL_RR_ENTRY(rr, name, RR_AAAA);
rr->data.AAAA.addr = addr;
return rr;
}
struct rr_entry *rr_create_srv(uint8_t *name, uint16_t port, uint8_t *target) {
DECL_MALLOC_ZERO_STRUCT(rr, rr_entry);
FILL_RR_ENTRY(rr, name, RR_SRV);
rr->data.SRV.port = port;
rr->data.SRV.target = target;
return rr;
}
struct rr_entry *rr_create_ptr(uint8_t *name, struct rr_entry *d_rr) {
DECL_MALLOC_ZERO_STRUCT(rr, rr_entry);
FILL_RR_ENTRY(rr, name, RR_PTR);
rr->cache_flush = 0; // PTRs shouldn't have their cache flush bit set
rr->data.PTR.entry = d_rr;
return rr;
}
struct rr_entry *rr_create(uint8_t *name, enum rr_type type) {
DECL_MALLOC_ZERO_STRUCT(rr, rr_entry);
FILL_RR_ENTRY(rr, name, type);
return rr;
}
void rr_set_nsec(struct rr_entry *rr_nsec, enum rr_type type) {
assert(rr_nsec->type = RR_NSEC);
assert((type / 8) < sizeof(rr_nsec->data.NSEC.bitmap));
rr_nsec->data.NSEC.bitmap[ type / 8 ] = 1 << (7 - (type % 8));
}
void rr_add_txt(struct rr_entry *rr_txt, const char *txt) {
struct rr_data_txt *txt_rec;
assert(rr_txt->type == RR_TXT);
txt_rec = &rr_txt->data.TXT;
// is current data filled?
if (txt_rec->txt == NULL) {
txt_rec->txt = create_label(txt);
return;
}
// find the last node
for (; txt_rec->next; txt_rec = txt_rec->next);
// create a new empty node
txt_rec->next = malloc(sizeof(struct rr_data_txt));
txt_rec = txt_rec->next;
txt_rec->txt = create_label(txt);
txt_rec->next = NULL;
}
// adds a record to an rr_group
void rr_group_add(struct rr_group **group, struct rr_entry *rr) {
struct rr_group *g;
assert(rr != NULL);
if (*group) {
g = rr_group_find(*group, rr->name);
if (g) {
rr_list_append(&g->rr, rr);
return;
}
}
MALLOC_ZERO_STRUCT(g, rr_group);
g->name = dup_nlabel(rr->name);
rr_list_append(&g->rr, rr);
// prepend to list
g->next = *group;
*group = g;
}
// finds a rr_group matching the given name
struct rr_group *rr_group_find(struct rr_group* g, uint8_t *name) {
for (; g; g = g->next) {
if (cmp_nlabel(g->name, name) == 0)
return g;
}
return NULL;
}
struct rr_entry *rr_entry_find(struct rr_list *rr_list, uint8_t *name, uint16_t type) {
struct rr_list *rr = rr_list;
for (; rr; rr = rr->next) {
if (rr->e->type == type && cmp_nlabel(rr->e->name, name) == 0)
return rr->e;
}
return NULL;
}
// looks for a matching entry in rr_list
// if entry is a PTR, we need to check if the PTR target also matches
struct rr_entry *rr_entry_match(struct rr_list *rr_list, struct rr_entry *entry) {
struct rr_list *rr = rr_list;
for (; rr; rr = rr->next) {
if (rr->e->type == entry->type && cmp_nlabel(rr->e->name, entry->name) == 0) {
if (entry->type != RR_PTR) {
return rr->e;
} else if (cmp_nlabel(MDNS_RR_GET_PTR_NAME(entry), MDNS_RR_GET_PTR_NAME(rr->e)) == 0) {
// if it's a PTR, we need to make sure PTR target also matches
return rr->e;
}
}
}
return NULL;
}
void rr_group_destroy(struct rr_group *group) {
struct rr_group *g = group;
while (g) {
struct rr_group *nextg = g->next;
free(g->name);
rr_list_destroy(g->rr, 1);
free(g);
g = nextg;
}
}
uint8_t *mdns_write_u16(uint8_t *ptr, const uint16_t v) {
*ptr++ = (uint8_t) (v >> 8) & 0xFF;
*ptr++ = (uint8_t) (v >> 0) & 0xFF;
return ptr;
}
uint8_t *mdns_write_u32(uint8_t *ptr, const uint32_t v) {
*ptr++ = (uint8_t) (v >> 24) & 0xFF;
*ptr++ = (uint8_t) (v >> 16) & 0xFF;
*ptr++ = (uint8_t) (v >> 8) & 0xFF;
*ptr++ = (uint8_t) (v >> 0) & 0xFF;
return ptr;
}
uint16_t mdns_read_u16(const uint8_t *ptr) {
return ((ptr[0] & 0xFF) << 8) |
((ptr[1] & 0xFF) << 0);
}
uint32_t mdns_read_u32(const uint8_t *ptr) {
return ((ptr[0] & 0xFF) << 24) |
((ptr[1] & 0xFF) << 16) |
((ptr[2] & 0xFF) << 8) |
((ptr[3] & 0xFF) << 0);
}
// initialize the packet for reply
// clears the packet of list structures but not its list items
void mdns_init_reply(struct mdns_pkt *pkt, uint16_t id) {
// copy transaction ID
pkt->id = id;
// response flags
pkt->flags = MDNS_FLAG_RESP | MDNS_FLAG_AA;
rr_list_destroy(pkt->rr_qn, 0);
rr_list_destroy(pkt->rr_ans, 0);
rr_list_destroy(pkt->rr_auth, 0);
rr_list_destroy(pkt->rr_add, 0);
pkt->rr_qn = NULL;
pkt->rr_ans = NULL;
pkt->rr_auth = NULL;
pkt->rr_add = NULL;
pkt->num_qn = 0;
pkt->num_ans_rr = 0;
pkt->num_auth_rr = 0;
pkt->num_add_rr = 0;
}
// destroys an mdns_pkt struct, including its contents
void mdns_pkt_destroy(struct mdns_pkt *p) {
rr_list_destroy(p->rr_qn, 1);
rr_list_destroy(p->rr_ans, 1);
rr_list_destroy(p->rr_auth, 1);
rr_list_destroy(p->rr_add, 1);
free(p);
}
// parse the MDNS questions section
// stores the parsed data in the given mdns_pkt struct
static size_t mdns_parse_qn(uint8_t *pkt_buf, size_t pkt_len, size_t off,
struct mdns_pkt *pkt) {
const uint8_t *p = pkt_buf + off;
struct rr_entry *rr;
uint8_t *name;
assert(pkt != NULL);
rr = malloc(sizeof(struct rr_entry));
memset(rr, 0, sizeof(struct rr_entry));
name = uncompress_nlabel(pkt_buf, pkt_len, off);
p += label_len(pkt_buf, pkt_len, off);
rr->name = name;
rr->type = mdns_read_u16(p);
p += sizeof(uint16_t);
rr->unicast_query = (*p & 0x80) == 0x80;
rr->rr_class = mdns_read_u16(p) & ~0x80;
p += sizeof(uint16_t);
rr_list_append(&pkt->rr_qn, rr);
return p - (pkt_buf + off);
}
// parse the MDNS RR section
// stores the parsed data in the given mdns_pkt struct
static size_t mdns_parse_rr(uint8_t *pkt_buf, size_t pkt_len, size_t off,
struct mdns_pkt *pkt) {
const uint8_t *p = pkt_buf + off;
const uint8_t *e = pkt_buf + pkt_len;
struct rr_entry *rr;
uint8_t *name;
size_t rr_data_len = 0;
struct rr_data_txt *txt_rec;
int parse_error = 0;
assert(pkt != NULL);
if (off > pkt_len)
return 0;
rr = malloc(sizeof(struct rr_entry));
memset(rr, 0, sizeof(struct rr_entry));
name = uncompress_nlabel(pkt_buf, pkt_len, off);
p += label_len(pkt_buf, pkt_len, off);
rr->name = name;
rr->type = mdns_read_u16(p);
p += sizeof(uint16_t);
rr->cache_flush = (*p & 0x80) == 0x80;
rr->rr_class = mdns_read_u16(p) & ~0x80;
p += sizeof(uint16_t);
rr->ttl = mdns_read_u32(p);
p += sizeof(uint32_t);
// RR data
rr_data_len = mdns_read_u16(p);
p += sizeof(uint16_t);
if (p + rr_data_len > e) {
DEBUG_PRINTF("rr_data_len goes beyond packet buffer: %lu > %lu\n", rr_data_len, e - p);
rr_entry_destroy(rr);
return 0;
}
e = p + rr_data_len;
// see if we can parse the RR data
switch (rr->type) {
case RR_A:
if (rr_data_len < sizeof(uint32_t)) {
DEBUG_PRINTF("invalid rr_data_len=%lu for A record\n", rr_data_len);
parse_error = 1;
break;
}
rr->data.A.addr = ntohl(mdns_read_u32(p)); /* addr already in net order */
p += sizeof(uint32_t);
break;
case RR_AAAA:
if (rr_data_len < sizeof(struct in6_addr)) {
DEBUG_PRINTF("invalid rr_data_len=%lu for AAAA record\n", rr_data_len);
parse_error = 1;
break;
}
rr->data.AAAA.addr = malloc(sizeof(struct in6_addr));
int i;
for (i = 0; i < sizeof(struct in6_addr); i++)
rr->data.AAAA.addr->s6_addr[i] = p[i];
p += sizeof(struct in6_addr);
break;
case RR_PTR:
rr->data.PTR.name = uncompress_nlabel(pkt_buf, pkt_len, p - pkt_buf);
if (rr->data.PTR.name == NULL) {
DEBUG_PRINTF("unable to parse/uncompress label for PTR name\n");
parse_error = 1;
break;
}
p += rr_data_len;
break;
case RR_TXT:
txt_rec = &rr->data.TXT;
// not supposed to happen, but we should handle it
if (rr_data_len == 0) {
DEBUG_PRINTF("WARN: rr_data_len for TXT is 0\n");
txt_rec->txt = create_label("");
break;
}
while (1) {
txt_rec->txt = copy_label(pkt_buf, pkt_len, p - pkt_buf);
if (txt_rec->txt == NULL) {
DEBUG_PRINTF("unable to copy label for TXT record\n");
parse_error = 1;
break;
}
p += txt_rec->txt[0] + 1;
if (p >= e)
break;
// allocate another record
txt_rec->next = malloc(sizeof(struct rr_data_txt));
txt_rec = txt_rec->next;
txt_rec->next = NULL;
}
break;
default:
// skip to end of RR data
p = e;
}
// if there was a parse error, destroy partial rr_entry
if (parse_error) {
rr_entry_destroy(rr);
return 0;
}
rr_list_append(&pkt->rr_ans, rr);
return p - (pkt_buf + off);
}
// parse a MDNS packet into an mdns_pkt struct
struct mdns_pkt *mdns_parse_pkt(uint8_t *pkt_buf, size_t pkt_len) {
uint8_t *p = pkt_buf;
size_t off;
struct mdns_pkt *pkt;
int i;
if (pkt_len < 12)
return NULL;
MALLOC_ZERO_STRUCT(pkt, mdns_pkt);
// parse header
pkt->id = mdns_read_u16(p); p += sizeof(uint16_t);
pkt->flags = mdns_read_u16(p); p += sizeof(uint16_t);
pkt->num_qn = mdns_read_u16(p); p += sizeof(uint16_t);
pkt->num_ans_rr = mdns_read_u16(p); p += sizeof(uint16_t);
pkt->num_auth_rr = mdns_read_u16(p); p += sizeof(uint16_t);
pkt->num_add_rr = mdns_read_u16(p); p += sizeof(uint16_t);
off = p - pkt_buf;
// parse questions
for (i = 0; i < pkt->num_qn; i++) {
size_t l = mdns_parse_qn(pkt_buf, pkt_len, off, pkt);
if (! l) {
DEBUG_PRINTF("error parsing question #%d\n", i);
mdns_pkt_destroy(pkt);
return NULL;
}
off += l;
}
// parse answer RRs
for (i = 0; i < pkt->num_ans_rr; i++) {
size_t l = mdns_parse_rr(pkt_buf, pkt_len, off, pkt);
if (! l) {
DEBUG_PRINTF("error parsing answer #%d\n", i);
mdns_pkt_destroy(pkt);
return NULL;
}
off += l;
}
// TODO: parse the authority and additional RR sections
return pkt;
}
// encodes a name (label) into a packet using the name compression scheme
// encoded names will be added to the compression list for subsequent use
static size_t mdns_encode_name(uint8_t *pkt_buf, size_t pkt_len, size_t off,
const uint8_t *name, struct name_comp *comp) {
struct name_comp *c, *c_tail = NULL;
uint8_t *p = pkt_buf + off;
size_t len = 0;
if (name) {
while (*name) {
// find match for compression
for (c = comp; c; c = c->next) {
if (cmp_nlabel(name, c->label) == 0) {
mdns_write_u16(p, 0xC000 | (c->pos & ~0xC000));
return len + sizeof(uint16_t);
}
if (c->next == NULL)
c_tail = c;
}
// copy this segment
int segment_len = *name + 1;
strncpy((char *) p, (char *) name, segment_len);
// cache the name for subsequent compression
DECL_MALLOC_ZERO_STRUCT(new_c, name_comp);
new_c->label = (uint8_t *) name;
new_c->pos = p - pkt_buf;
c_tail->next = new_c;
// advance to next name segment
p += segment_len;
len += segment_len;
name += segment_len;
}
}
*p = '\0'; // root "label"
len += 1;
return len;
}
// encodes an RR entry at the given offset
// returns the size of the entire RR entry
static size_t mdns_encode_rr(uint8_t *pkt_buf, size_t pkt_len, size_t off,
struct rr_entry *rr, struct name_comp *comp) {
uint8_t *p = pkt_buf + off, *p_data;
size_t l;
struct rr_data_txt *txt_rec;
uint8_t *label;
int i;
assert(off < pkt_len);
// name
l = mdns_encode_name(pkt_buf, pkt_len, off, rr->name, comp);
assert(l != 0);
p += l;
// type
p = mdns_write_u16(p, rr->type);
// class & cache flush
p = mdns_write_u16(p, (rr->rr_class & ~0x8000) | (rr->cache_flush << 15));
// TTL
p = mdns_write_u32(p, rr->ttl);
// data length (filled in later)
p += sizeof(uint16_t);
// start of data marker
p_data = p;
switch (rr->type) {
case RR_A:
/* htonl() needed coz addr already in net order */
p = mdns_write_u32(p, htonl(rr->data.A.addr));
break;
case RR_AAAA:
for (i = 0; i < sizeof(struct in6_addr); i++)
*p++ = rr->data.AAAA.addr->s6_addr[i];
break;
case RR_PTR:
label = rr->data.PTR.name ?
rr->data.PTR.name :
rr->data.PTR.entry->name;
p += mdns_encode_name(pkt_buf, pkt_len, p - pkt_buf, label, comp);
break;
case RR_TXT:
txt_rec = &rr->data.TXT;
for (; txt_rec; txt_rec = txt_rec->next) {
int len = txt_rec->txt[0] + 1;
strncpy((char *) p, (char *) txt_rec->txt, len);
p += len;
}
break;
case RR_SRV:
p = mdns_write_u16(p, rr->data.SRV.priority);
p = mdns_write_u16(p, rr->data.SRV.weight);
p = mdns_write_u16(p, rr->data.SRV.port);
p += mdns_encode_name(pkt_buf, pkt_len, p - pkt_buf,
rr->data.SRV.target, comp);
break;
case RR_NSEC:
p += mdns_encode_name(pkt_buf, pkt_len, p - pkt_buf,
rr->name, comp);
*p++ = 0; // bitmap window/block number
*p++ = sizeof(rr->data.NSEC.bitmap); // bitmap length
for (i = 0; i < sizeof(rr->data.NSEC.bitmap); i++)
*p++ = rr->data.NSEC.bitmap[i];
break;
default:
DEBUG_PRINTF("unhandled rr type 0x%02x\n", rr->type);
}
// calculate data length based on p
l = p - p_data;
// fill in the length
mdns_write_u16(p - l - sizeof(uint16_t), l);
return p - pkt_buf - off;
}
// encodes a MDNS packet from the given mdns_pkt struct into a buffer
// returns the size of the entire MDNS packet
size_t mdns_encode_pkt(struct mdns_pkt *answer, uint8_t *pkt_buf, size_t pkt_len) {
struct name_comp *comp;
uint8_t *p = pkt_buf;
//uint8_t *e = pkt_buf + pkt_len;
size_t off;
int i;
assert(answer != NULL);
assert(pkt_len >= 12);
if (p == NULL)
return -1;
// this is an Answer - number of qns should be zero
assert(answer->num_qn == 0);
p = mdns_write_u16(p, answer->id);
p = mdns_write_u16(p, answer->flags);
p = mdns_write_u16(p, answer->num_qn);
p = mdns_write_u16(p, answer->num_ans_rr);
p = mdns_write_u16(p, answer->num_auth_rr);
p = mdns_write_u16(p, answer->num_add_rr);
off = p - pkt_buf;
// allocate list for name compression
comp = malloc(sizeof(struct name_comp));
if (comp == NULL)
return -1;
memset(comp, 0, sizeof(struct name_comp));
// dummy entry
comp->label = (uint8_t *) "";
comp->pos = 0;
// skip encoding of qn
struct rr_list *rr_set[] = {
answer->rr_ans,
answer->rr_auth,
answer->rr_add
};
// encode answer, authority and additional RRs
for (i = 0; i < sizeof(rr_set) / sizeof(rr_set[0]); i++) {
struct rr_list *rr = rr_set[i];
for (; rr; rr = rr->next) {
size_t l = mdns_encode_rr(pkt_buf, pkt_len, off, rr->e, comp);
off += l;
if (off >= pkt_len) {