aboutsummaryrefslogtreecommitdiffstats
path: root/net/dns.lua
blob: 67eaa647adbf9c30f8c79c163fc39ff1ab1d52a3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
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
-- Prosody IM
-- This file is included with Prosody IM. It has modifications,
-- which are hereby placed in the public domain.


-- todo: quick (default) header generation
-- todo: nxdomain, error handling
-- todo: cache results of encodeName


-- reference: http://tools.ietf.org/html/rfc1035
-- reference: http://tools.ietf.org/html/rfc1876 (LOC)


local socket = require "socket";
local have_timer, timer = pcall(require, "util.timer");
local new_ip = require "util.ip".new_ip;
local have_util_net, util_net = pcall(require, "util.net");

local log = require "util.logger".init("dns");

local _, windows = pcall(require, "util.windows");
local is_windows = (_ and windows) or os.getenv("WINDIR");

local coroutine, io, math, string, table =
      coroutine, io, math, string, table;

local ipairs, next, pairs, print, setmetatable, tostring, assert, error, select, type =
      ipairs, next, pairs, print, setmetatable, tostring, assert, error, select, type;

local ztact = { -- public domain 20080404 lua@ztact.com
	get = function(parent, ...)
		local len = select('#', ...);
		for i=1,len do
			parent = parent[select(i, ...)];
			if parent == nil then break; end
		end
		return parent;
	end;
	set = function(parent, ...)
		local len = select('#', ...);
		local key, value = select(len-1, ...);
		local cutpoint, cutkey;

		for i=1,len-2 do
			local key = select (i, ...)
			local child = parent[key]

			if value == nil then
				if child == nil then
					return;
				elseif next(child, next(child)) then
					cutpoint = nil; cutkey = nil;
				elseif cutpoint == nil then
					cutpoint = parent; cutkey = key;
				end
			elseif child == nil then
				child = {};
				parent[key] = child;
			end
			parent = child
		end

		if value == nil and cutpoint then
			cutpoint[cutkey] = nil;
		else
			parent[key] = value;
			return value;
		end
	end;
};
local get, set = ztact.get, ztact.set;

local default_timeout = 15;

-------------------------------------------------- module dns
local _ENV = nil;
-- luacheck: std none
local dns = {};


-- dns type & class codes ------------------------------ dns type & class codes


local append = table.insert


local function highbyte(i)    -- - - - - - - - - - - - - - - - - - -  highbyte
	return (i-(i%0x100))/0x100;
end


local function augment (t, prefix)  -- - - - - - - - - - - - - - - - -  augment
	local a = {};
	for i,s in pairs(t) do
		a[i] = s;
		a[s] = s;
		a[string.lower(s)] = s;
	end
	setmetatable(a, {
		__index = function (_, i)
			if type(i) == "number" then
				return ("%s%d"):format(prefix, i);
			elseif type(i) == "string" then
				return i:upper();
			end
		end;
	})
	return a;
end


local function encode (t)    -- - - - - - - - - - - - - - - - - - - - -  encode
	local code = {};
	for i,s in pairs(t) do
		local word = string.char(highbyte(i), i%0x100);
		code[i] = word;
		code[s] = word;
		code[string.lower(s)] = word;
	end
	return code;
end


dns.types = {
	[1] = "A", -- a host address,[RFC1035],,
	[2] = "NS", -- an authoritative name server,[RFC1035],,
	[3] = "MD", -- a mail destination (OBSOLETE - use MX),[RFC1035],,
	[4] = "MF", -- a mail forwarder (OBSOLETE - use MX),[RFC1035],,
	[5] = "CNAME", -- the canonical name for an alias,[RFC1035],,
	[6] = "SOA", -- marks the start of a zone of authority,[RFC1035],,
	[7] = "MB", -- a mailbox domain name (EXPERIMENTAL),[RFC1035],,
	[8] = "MG", -- a mail group member (EXPERIMENTAL),[RFC1035],,
	[9] = "MR", -- a mail rename domain name (EXPERIMENTAL),[RFC1035],,
	[10] = "NULL", -- a null RR (EXPERIMENTAL),[RFC1035],,
	[11] = "WKS", -- a well known service description,[RFC1035],,
	[12] = "PTR", -- a domain name pointer,[RFC1035],,
	[13] = "HINFO", -- host information,[RFC1035],,
	[14] = "MINFO", -- mailbox or mail list information,[RFC1035],,
	[15] = "MX", -- mail exchange,[RFC1035],,
	[16] = "TXT", -- text strings,[RFC1035],,
	[17] = "RP", -- for Responsible Person,[RFC1183],,
	[18] = "AFSDB", -- for AFS Data Base location,[RFC1183][RFC5864],,
	[19] = "X25", -- for X.25 PSDN address,[RFC1183],,
	[20] = "ISDN", -- for ISDN address,[RFC1183],,
	[21] = "RT", -- for Route Through,[RFC1183],,
	[22] = "NSAP", -- "for NSAP address, NSAP style A record",[RFC1706],,
	[23] = "NSAP-PTR", -- "for domain name pointer, NSAP style",[RFC1348][RFC1637][RFC1706],,
	[24] = "SIG", -- for security signature,[RFC4034][RFC3755][RFC2535][RFC2536][RFC2537][RFC2931][RFC3110][RFC3008],,
	[25] = "KEY", -- for security key,[RFC4034][RFC3755][RFC2535][RFC2536][RFC2537][RFC2539][RFC3008][RFC3110],,
	[26] = "PX", -- X.400 mail mapping information,[RFC2163],,
	[27] = "GPOS", -- Geographical Position,[RFC1712],,
	[28] = "AAAA", -- IP6 Address,[RFC3596],,
	[29] = "LOC", -- Location Information,[RFC1876],,
	[30] = "NXT", -- Next Domain (OBSOLETE),[RFC3755][RFC2535],,
	[31] = "EID", -- Endpoint Identifier,[Michael_Patton][http://ana-3.lcs.mit.edu/~jnc/nimrod/dns.txt],,1995-06
	[32] = "NIMLOC", -- Nimrod Locator,[1][Michael_Patton][http://ana-3.lcs.mit.edu/~jnc/nimrod/dns.txt],,1995-06
	[33] = "SRV", -- Server Selection,[1][RFC2782],,
	[34] = "ATMA", -- ATM Address,"[ ATM Forum Technical Committee, ""ATM Name System, V2.0"", Doc ID: AF-DANS-0152.000, July 2000. Available from and held in escrow by IANA.]",,
	[35] = "NAPTR", -- Naming Authority Pointer,[RFC2915][RFC2168][RFC3403],,
	[36] = "KX", -- Key Exchanger,[RFC2230],,
	[37] = "CERT", -- CERT,[RFC4398],,
	[38] = "A6", -- A6 (OBSOLETE - use AAAA),[RFC3226][RFC2874][RFC6563],,
	[39] = "DNAME", -- DNAME,[RFC6672],,
	[40] = "SINK", -- SINK,[Donald_E_Eastlake][http://tools.ietf.org/html/draft-eastlake-kitchen-sink],,1997-11
	[41] = "OPT", -- OPT,[RFC6891][RFC3225],,
	[42] = "APL", -- APL,[RFC3123],,
	[43] = "DS", -- Delegation Signer,[RFC4034][RFC3658],,
	[44] = "SSHFP", -- SSH Key Fingerprint,[RFC4255],,
	[45] = "IPSECKEY", -- IPSECKEY,[RFC4025],,
	[46] = "RRSIG", -- RRSIG,[RFC4034][RFC3755],,
	[47] = "NSEC", -- NSEC,[RFC4034][RFC3755],,
	[48] = "DNSKEY", -- DNSKEY,[RFC4034][RFC3755],,
	[49] = "DHCID", -- DHCID,[RFC4701],,
	[50] = "NSEC3", -- NSEC3,[RFC5155],,
	[51] = "NSEC3PARAM", -- NSEC3PARAM,[RFC5155],,
	[52] = "TLSA", -- TLSA,[RFC6698],,
	[53] = "SMIMEA", -- S/MIME cert association,[RFC8162],SMIMEA/smimea-completed-template,2015-12-01
	-- [54] = "Unassigned", -- ,,,
	[55] = "HIP", -- Host Identity Protocol,[RFC8005],,
	[56] = "NINFO", -- NINFO,[Jim_Reid],NINFO/ninfo-completed-template,2008-01-21
	[57] = "RKEY", -- RKEY,[Jim_Reid],RKEY/rkey-completed-template,2008-01-21
	[58] = "TALINK", -- Trust Anchor LINK,[Wouter_Wijngaards],TALINK/talink-completed-template,2010-02-17
	[59] = "CDS", -- Child DS,[RFC7344],CDS/cds-completed-template,2011-06-06
	[60] = "CDNSKEY", -- DNSKEY(s) the Child wants reflected in DS,[RFC7344],,2014-06-16
	[61] = "OPENPGPKEY", -- OpenPGP Key,[RFC7929],OPENPGPKEY/openpgpkey-completed-template,2014-08-12
	[62] = "CSYNC", -- Child-To-Parent Synchronization,[RFC7477],,2015-01-27
	-- [63 .. 98] = "Unassigned", -- ,,,
	[99] = "SPF", -- ,[RFC7208],,
	[100] = "UINFO", -- ,[IANA-Reserved],,
	[101] = "UID", -- ,[IANA-Reserved],,
	[102] = "GID", -- ,[IANA-Reserved],,
	[103] = "UNSPEC", -- ,[IANA-Reserved],,
	[104] = "NID", -- ,[RFC6742],ILNP/nid-completed-template,
	[105] = "L32", -- ,[RFC6742],ILNP/l32-completed-template,
	[106] = "L64", -- ,[RFC6742],ILNP/l64-completed-template,
	[107] = "LP", -- ,[RFC6742],ILNP/lp-completed-template,
	[108] = "EUI48", -- an EUI-48 address,[RFC7043],EUI48/eui48-completed-template,2013-03-27
	[109] = "EUI64", -- an EUI-64 address,[RFC7043],EUI64/eui64-completed-template,2013-03-27
	-- [110 .. 248] = "Unassigned", -- ,,,
	[249] = "TKEY", -- Transaction Key,[RFC2930],,
	[250] = "TSIG", -- Transaction Signature,[RFC2845],,
	[251] = "IXFR", -- incremental transfer,[RFC1995],,
	[252] = "AXFR", -- transfer of an entire zone,[RFC1035][RFC5936],,
	[253] = "MAILB", -- "mailbox-related RRs (MB, MG or MR)",[RFC1035],,
	[254] = "MAILA", -- mail agent RRs (OBSOLETE - see MX),[RFC1035],,
	[255] = "*", -- A request for all records the server/cache has available,[RFC1035][RFC6895],,
	[256] = "URI", -- URI,[RFC7553],URI/uri-completed-template,2011-02-22
	[257] = "CAA", -- Certification Authority Restriction,[RFC6844],CAA/caa-completed-template,2011-04-07
	[258] = "AVC", -- Application Visibility and Control,[Wolfgang_Riedel],AVC/avc-completed-template,2016-02-26
	[259] = "DOA", -- Digital Object Architecture,[draft-durand-doa-over-dns],DOA/doa-completed-template,2017-08-30
	-- [260 .. 32767] = "Unassigned", -- ,,,
	[32768] = "TA", -- DNSSEC Trust Authorities,"[Sam_Weiler][http://cameo.library.cmu.edu/][ Deploying DNSSEC Without a Signed Root.  Technical Report 1999-19, Information Networking Institute, Carnegie Mellon University, April 2004.]",,2005-12-13
	[32769] = "DLV", -- DNSSEC Lookaside Validation,[RFC4431],,
	-- [32770 .. 65279] = "Unassigned", -- ,,,
	-- [65280 .. 65534] = "Private use", -- ,,,
	-- [65535] = "Reserved", -- ,,,
}

dns.classes = { 'IN', 'CS', 'CH', 'HS', [255] = '*' };


dns.type      = augment (dns.types, "TYPE");
dns.class     = augment (dns.classes, "CLASS");
dns.typecode  = encode  (dns.types);
dns.classcode = encode  (dns.classes);



local function standardize(qname, qtype, qclass)    -- - - - - - - standardize
	if string.byte(qname, -1) ~= 0x2E then qname = qname..'.';  end
	qname = string.lower(qname);
	return qname, dns.type[qtype or 'A'], dns.class[qclass or 'IN'];
end


local function prune(rrs, time, soft)    -- - - - - - - - - - - - - - -  prune
	time = time or socket.gettime();
	for i,rr in ipairs(rrs) do
		if rr.tod then
			if rr.tod < time then
				rrs[rr[rr.type:lower()]] = nil;
				table.remove(rrs, i);
				return prune(rrs, time, soft); -- Re-iterate
			end
		elseif soft == 'soft' then    -- What is this?  I forget!
			assert(rr.ttl == 0);
			rrs[rr[rr.type:lower()]] = nil;
			table.remove(rrs, i);
		end
	end
end


-- metatables & co. ------------------------------------------ metatables & co.


local resolver = {};
resolver.__index = resolver;

resolver.timeout = default_timeout;

local function default_rr_tostring(rr)
	local rr_val = rr.type and rr[rr.type:lower()];
	if type(rr_val) ~= "string" then
		return "<UNKNOWN RDATA TYPE>";
	end
	return rr_val;
end

local special_tostrings = {
	LOC = resolver.LOC_tostring;
	MX  = function (rr)
		return string.format('%2i %s', rr.pref, rr.mx);
	end;
	SRV = function (rr)
		local s = rr.srv;
		return string.format('%5d %5d %5d %s', s.priority, s.weight, s.port, s.target);
	end;
};

local rr_metatable = {};   -- - - - - - - - - - - - - - - - - - -  rr_metatable
function rr_metatable.__tostring(rr)
	local rr_string = (special_tostrings[rr.type] or default_rr_tostring)(rr);
	return string.format('%2s %-5s %6i %-28s %s', rr.class, rr.type, rr.ttl, rr.name, rr_string);
end


local rrs_metatable = {};    -- - - - - - - - - - - - - - - - - -  rrs_metatable
function rrs_metatable.__tostring(rrs)
	local t = {};
	for _, rr in ipairs(rrs) do
		append(t, tostring(rr)..'\n');
	end
	return table.concat(t);
end


local cache_metatable = {};    -- - - - - - - - - - - - - - - -  cache_metatable
function cache_metatable.__tostring(cache)
	local time = socket.gettime();
	local t = {};
	for class,types in pairs(cache) do
		for type,names in pairs(types) do
			for name,rrs in pairs(names) do
				prune(rrs, time);
				append(t, tostring(rrs));
			end
		end
	end
	return table.concat(t);
end


-- packet layer -------------------------------------------------- packet layer


function dns.random(...)    -- - - - - - - - - - - - - - - - - - -  dns.random
	math.randomseed(math.floor(10000*socket.gettime()) % 0x80000000);
	dns.random = math.random;
	return dns.random(...);
end


local function encodeHeader(o)    -- - - - - - - - - - - - - - -  encodeHeader
	o = o or {};
	o.id = o.id or dns.random(0, 0xffff); -- 16b	(random) id

	o.rd = o.rd or 1;		--  1b  1 recursion desired
	o.tc = o.tc or 0;		--  1b	1 truncated response
	o.aa = o.aa or 0;		--  1b	1 authoritative response
	o.opcode = o.opcode or 0;	--  4b	0 query
				--  1 inverse query
				--	2 server status request
				--	3-15 reserved
	o.qr = o.qr or 0;		--  1b	0 query, 1 response

	o.rcode = o.rcode or 0;	--  4b  0 no error
				--	1 format error
				--	2 server failure
				--	3 name error
				--	4 not implemented
				--	5 refused
				--	6-15 reserved
	o.z = o.z  or 0;		--  3b  0 resvered
	o.ra = o.ra or 0;		--  1b  1 recursion available

	o.qdcount = o.qdcount or 1;	-- 16b	number of question RRs
	o.ancount = o.ancount or 0;	-- 16b	number of answers RRs
	o.nscount = o.nscount or 0;	-- 16b	number of nameservers RRs
	o.arcount = o.arcount or 0;	-- 16b  number of additional RRs

	-- string.char() rounds, so prevent roundup with -0.4999
	local header = string.char(
		highbyte(o.id), o.id %0x100,
		o.rd + 2*o.tc + 4*o.aa + 8*o.opcode + 128*o.qr,
		o.rcode + 16*o.z + 128*o.ra,
		highbyte(o.qdcount),  o.qdcount %0x100,
		highbyte(o.ancount),  o.ancount %0x100,
		highbyte(o.nscount),  o.nscount %0x100,
		highbyte(o.arcount),  o.arcount %0x100
	);

	return header, o.id;
end


local function encodeName(name)    -- - - - - - - - - - - - - - - - encodeName
	local t = {};
	for part in string.gmatch(name, '[^.]+') do
		append(t, string.char(string.len(part)));
		append(t, part);
	end
	append(t, string.char(0));
	return table.concat(t);
end


local function encodeQuestion(qname, qtype, qclass)    -- - - - encodeQuestion
	qname  = encodeName(qname);
	qtype  = dns.typecode[qtype or 'a'];
	qclass = dns.classcode[qclass or 'in'];
	return qname..qtype..qclass;
end


function resolver:byte(len)    -- - - - - - - - - - - - - - - - - - - - - byte
	len = len or 1;
	local offset = self.offset;
	local last = offset + len - 1;
	if last > #self.packet then
		error(string.format('out of bounds: %i>%i', last, #self.packet));
	end
	self.offset = offset + len;
	return string.byte(self.packet, offset, last);
end


function resolver:word()    -- - - - - - - - - - - - - - - - - - - - - -  word
	local b1, b2 = self:byte(2);
	return 0x100*b1 + b2;
end


function resolver:dword ()    -- - - - - - - - - - - - - - - - - - - - -  dword
	local b1, b2, b3, b4 = self:byte(4);
	--print('dword', b1, b2, b3, b4);
	return 0x1000000*b1 + 0x10000*b2 + 0x100*b3 + b4;
end


function resolver:sub(len)    -- - - - - - - - - - - - - - - - - - - - - - sub
	len = len or 1;
	local s = string.sub(self.packet, self.offset, self.offset + len - 1);
	self.offset = self.offset + len;
	return s;
end


function resolver:header(force)    -- - - - - - - - - - - - - - - - - - header
	local id = self:word();
	--print(string.format(':header  id  %x', id));
	if not self.active[id] and not force then return nil; end

	local h = { id = id };

	local b1, b2 = self:byte(2);

	h.rd      = b1 %2;
	h.tc      = b1 /2%2;
	h.aa      = b1 /4%2;
	h.opcode  = b1 /8%16;
	h.qr      = b1 /128;

	h.rcode   = b2 %16;
	h.z       = b2 /16%8;
	h.ra      = b2 /128;

	h.qdcount = self:word();
	h.ancount = self:word();
	h.nscount = self:word();
	h.arcount = self:word();

	for k,v in pairs(h) do h[k] = v-v%1; end

	return h;
end


function resolver:name()    -- - - - - - - - - - - - - - - - - - - - - -  name
	local remember, pointers = nil, 0;
	local len = self:byte();
	local n = {};
	if len == 0 then return "." end -- Root label
	while len > 0 do
		if len >= 0xc0 then    -- name is "compressed"
			pointers = pointers + 1;
			if pointers >= 20 then error('dns error: 20 pointers'); end;
			local offset = ((len-0xc0)*0x100) + self:byte();
			remember = remember or self.offset;
			self.offset = offset + 1;    -- +1 for lua
		else    -- name is not compressed
			append(n, self:sub(len)..'.');
		end
		len = self:byte();
	end
	self.offset = remember or self.offset;
	return table.concat(n);
end


function resolver:question()    -- - - - - - - - - - - - - - - - - -  question
	local q = {};
	q.name  = self:name();
	q.type  = dns.type[self:word()];
	q.class = dns.class[self:word()];
	return q;
end


function resolver:A(rr)    -- - - - - - - - - - - - - - - - - - - - - - - -  A
	local b1, b2, b3, b4 = self:byte(4);
	rr.a = string.format('%i.%i.%i.%i', b1, b2, b3, b4);
end

if have_util_net and util_net.ntop then
	function resolver:A(rr)
		rr.a = util_net.ntop(self:sub(4));
	end
end

function resolver:AAAA(rr)
	local addr = {};
	for _ = 1, rr.rdlength, 2 do
		local b1, b2 = self:byte(2);
		table.insert(addr, ("%02x%02x"):format(b1, b2));
	end
	addr = table.concat(addr, ":"):gsub("%f[%x]0+(%x)","%1");
	local zeros = {};
	for item in addr:gmatch(":[0:]+:[0:]+:") do
		table.insert(zeros, item)
	end
	if #zeros == 0 then
		rr.aaaa = addr;
		return
	elseif #zeros > 1 then
		table.sort(zeros, function(a, b) return #a > #b end);
	end
	rr.aaaa = addr:gsub(zeros[1], "::", 1):gsub("^0::", "::"):gsub("::0$", "::");
end

if have_util_net and util_net.ntop then
	function resolver:AAAA(rr)
		rr.aaaa = util_net.ntop(self:sub(16));
	end
end

function resolver:CNAME(rr)    -- - - - - - - - - - - - - - - - - - - -  CNAME
	rr.cname = self:name();
end


function resolver:MX(rr)    -- - - - - - - - - - - - - - - - - - - - - - -  MX
	rr.pref = self:word();
	rr.mx   = self:name();
end


function resolver:LOC_nibble_power()    -- - - - - - - - - -  LOC_nibble_power
	local b = self:byte();
	--print('nibbles', ((b-(b%0x10))/0x10), (b%0x10));
	return ((b-(b%0x10))/0x10) * (10^(b%0x10));
end


function resolver:LOC(rr)    -- - - - - - - - - - - - - - - - - - - - - -  LOC
	rr.version = self:byte();
	if rr.version == 0 then
		rr.loc           = rr.loc or {};
		rr.loc.size      = self:LOC_nibble_power();
		rr.loc.horiz_pre = self:LOC_nibble_power();
		rr.loc.vert_pre  = self:LOC_nibble_power();
		rr.loc.latitude  = self:dword();
		rr.loc.longitude = self:dword();
		rr.loc.altitude  = self:dword();
	end
end


local function LOC_tostring_degrees(f, pos, neg)    -- - - - - - - - - - - - -
	f = f - 0x80000000;
	if f < 0 then pos = neg; f = -f; end
	local deg, min, msec;
	msec = f%60000;
	f    = (f-msec)/60000;
	min  = f%60;
	deg = (f-min)/60;
	return string.format('%3d %2d %2.3f %s', deg, min, msec/1000, pos);
end


function resolver.LOC_tostring(rr)    -- - - - - - - - - - - - -  LOC_tostring
	local t = {};

	--[[
	for k,name in pairs { 'size', 'horiz_pre', 'vert_pre', 'latitude', 'longitude', 'altitude' } do
		append(t, string.format('%4s%-10s: %12.0f\n', '', name, rr.loc[name]));
	end
	--]]

	append(t, string.format(
		'%s    %s    %.2fm %.2fm %.2fm %.2fm',
		LOC_tostring_degrees (rr.loc.latitude, 'N', 'S'),
		LOC_tostring_degrees (rr.loc.longitude, 'E', 'W'),
		(rr.loc.altitude - 10000000) / 100,
		rr.loc.size / 100,
		rr.loc.horiz_pre / 100,
		rr.loc.vert_pre / 100
	));

	return table.concat(t);
end


function resolver:NS(rr)    -- - - - - - - - - - - - - - - - - - - - - - -  NS
	rr.ns = self:name();
end


function resolver:SOA(rr)    -- - - - - - - - - - - - - - - - - - - - - -  SOA
end


function resolver:SRV(rr)    -- - - - - - - - - - - - - - - - - - - - - -  SRV
	  rr.srv = {};
	  rr.srv.priority = self:word();
	  rr.srv.weight   = self:word();
	  rr.srv.port     = self:word();
	  rr.srv.target   = self:name();
end

function resolver:PTR(rr)
	rr.ptr = self:name();
end

function resolver:TXT(rr)    -- - - - - - - - - - - - - - - - - - - - - -  TXT
	rr.txt = self:sub (self:byte());
end


function resolver:rr()    -- - - - - - - - - - - - - - - - - - - - - - - -  rr
	local rr = {};
	setmetatable(rr, rr_metatable);
	rr.name     = self:name(self);
	rr.type     = dns.type[self:word()] or rr.type;
	rr.class    = dns.class[self:word()] or rr.class;
	rr.ttl      = 0x10000*self:word() + self:word();
	rr.rdlength = self:word();

	rr.tod = self.time + math.max(rr.ttl, 1);

	local remember = self.offset;
	local rr_parser = self[dns.type[rr.type]];
	if rr_parser then rr_parser(self, rr); end
	self.offset = remember;
	rr.rdata = self:sub(rr.rdlength);
	return rr;
end


function resolver:rrs (count)    -- - - - - - - - - - - - - - - - - - - - - rrs
	local rrs = {};
	for _ = 1, count do append(rrs, self:rr()); end
	return rrs;
end


function resolver:decode(packet, force)    -- - - - - - - - - - - - - - decode
	self.packet, self.offset = packet, 1;
	local header = self:header(force);
	if not header then return nil; end
	local response = { header = header };

	response.question = {};
	local offset = self.offset;
	for _ = 1, response.header.qdcount do
		append(response.question, self:question());
	end
	response.question.raw = string.sub(self.packet, offset, self.offset - 1);

	if not force then
		if not self.active[response.header.id] or not self.active[response.header.id][response.question.raw] then
			self.active[response.header.id] = nil;
			return nil;
		end
	end

	response.answer     = self:rrs(response.header.ancount);
	response.authority  = self:rrs(response.header.nscount);
	response.additional = self:rrs(response.header.arcount);

	return response;
end


-- socket layer -------------------------------------------------- socket layer


resolver.delays = { 1, 3 };


function resolver:addnameserver(address)    -- - - - - - - - - - addnameserver
	self.server = self.server or {};
	append(self.server, address);
end


function resolver:setnameserver(address)    -- - - - - - - - - - setnameserver
	self.server = {};
	self:addnameserver(address);
end


function resolver:adddefaultnameservers()    -- - - - -  adddefaultnameservers
	if is_windows then
		if windows and windows.get_nameservers then
			for _, server in ipairs(windows.get_nameservers()) do
				self:addnameserver(server);
			end
		end
		if not self.server or #self.server == 0 then
			-- TODO log warning about no nameservers, adding opendns servers as fallback
			self:addnameserver("208.67.222.222");
			self:addnameserver("208.67.220.220");
		end
	else -- posix
		local resolv_conf = io.open("/etc/resolv.conf");
		if resolv_conf then
			for line in resolv_conf:lines() do
				line = line:gsub("#.*$", "")
					:match('^%s*nameserver%s+([%x:%.]*%%?%S*)%s*$');
				if line then
					local ip = new_ip(line);
					if ip then
						self:addnameserver(ip.addr);
					end
				end
			end
			resolv_conf:close();
		end
		if not self.server or #self.server == 0 then
			-- TODO log warning about no nameservers, adding localhost as the default nameserver
			self:addnameserver("127.0.0.1");
		end
	end
end


function resolver:getsocket(servernum)    -- - - - - - - - - - - - - getsocket
	self.socket = self.socket or {};
	self.socketset = self.socketset or {};

	local sock = self.socket[servernum];
	if sock then return sock; end

	local ok, err;
	local peer = self.server[servernum];
	if peer:find(":") then
		sock, err = socket.udp6();
	else
		sock, err = (socket.udp4 or socket.udp)();
	end
	if sock and self.socket_wrapper then sock, err = self.socket_wrapper(sock, self); end
	if not sock then
		return nil, err;
	end
	sock:settimeout(0);
	-- todo: attempt to use a random port, fallback to 0
	self.socket[servernum] = sock;
	self.socketset[sock] = servernum;
	-- set{sock,peer}name can fail, eg because of local routing table
	-- if so, try the next server
	ok, err = sock:setsockname('*', 0);
	if not ok then return self:servfail(sock, err); end
	ok, err = sock:setpeername(peer, 53);
	if not ok then return self:servfail(sock, err); end
	return sock;
end

function resolver:voidsocket(sock)
	if self.socket[sock] then
		self.socketset[self.socket[sock]] = nil;
		self.socket[sock] = nil;
	elseif self.socketset[sock] then
		self.socket[self.socketset[sock]] = nil;
		self.socketset[sock] = nil;
	end
	sock:close();
end

function resolver:socket_wrapper_set(func)  -- - - - - - - socket_wrapper_set
	self.socket_wrapper = func;
end


function resolver:closeall ()    -- - - - - - - - - - - - - - - - - -  closeall
	for i,sock in ipairs(self.socket) do
		self.socket[i] = nil;
		self.socketset[sock] = nil;
		sock:close();
	end
end


function resolver:remember(rr, type)    -- - - - - - - - - - - - - -  remember
	--print ('remember', type, rr.class, rr.type, rr.name)
	local qname, qtype, qclass = standardize(rr.name, rr.type, rr.class);

	if type ~= '*' then
		type = qtype;
		local all = get(self.cache, qclass, '*', qname);
		--print('remember all', all);
		if all then append(all, rr); end
	end

	self.cache = self.cache or setmetatable({}, cache_metatable);
	local rrs = get(self.cache, qclass, type, qname) or
		set(self.cache, qclass, type, qname, setmetatable({}, rrs_metatable));
	if rr[qtype:lower()] and not rrs[rr[qtype:lower()]] then
		rrs[rr[qtype:lower()]] = true;
		append(rrs, rr);
	end

	if type == 'MX' then self.unsorted[rrs] = true; end
end


local function comp_mx(a, b)    -- - - - - - - - - - - - - - - - - - - comp_mx
	return (a.pref == b.pref) and (a.mx < b.mx) or (a.pref < b.pref);
end


function resolver:peek (qname, qtype, qclass, n)    -- - - - - - - - - - - -  peek
	qname, qtype, qclass = standardize(qname, qtype, qclass);
	local rrs = get(self.cache, qclass, qtype, qname);
	if not rrs then
		if n then if n <= 0 then return end else n = 3 end
		rrs = get(self.cache, qclass, "CNAME", qname);
		if not (rrs and rrs[1]) then return end
		return self:peek(rrs[1].cname, qtype, qclass, n - 1);
	end
	if prune(rrs, socket.gettime()) and qtype == '*' or not next(rrs) then
		set(self.cache, qclass, qtype, qname, nil);
		return nil;
	end
	if self.unsorted[rrs] then table.sort (rrs, comp_mx); self.unsorted[rrs] = nil; end
	return rrs;
end


function resolver:purge(soft)    -- - - - - - - - - - - - - - - - - - -  purge
	if soft == 'soft' then
		self.time = socket.gettime();
		for class,types in pairs(self.cache or {}) do
			for type,names in pairs(types) do
				for name,rrs in pairs(names) do
					prune(rrs, self.time, 'soft')
				end
			end
		end
	else self.cache = setmetatable({}, cache_metatable); end
end


function resolver:query(qname, qtype, qclass)    -- - - - - - - - - - -- query
	qname, qtype, qclass = standardize(qname, qtype, qclass)

	local co = coroutine.running();
	local q = get(self.wanted, qclass, qtype, qname);
	if co and q then
		-- We are already waiting for a reply to an identical query.
		set(self.wanted, qclass, qtype, qname, co, true);
		return true;
	end

	if not self.server then self:adddefaultnameservers(); end

	local question = encodeQuestion(qname, qtype, qclass);
	local peek = self:peek (qname, qtype, qclass);
	if peek then return peek; end

	local header, id = encodeHeader();
	--print ('query  id', id, qclass, qtype, qname)
	local o = {
		packet = header..question,
		server = self.best_server,
		delay  = 1,
		retry  = socket.gettime() + self.delays[1]
	};

	-- remember the query
	self.active[id] = self.active[id] or {};
	self.active[id][question] = o;

	local conn, err = self:getsocket(o.server)
	if not conn then
		return nil, err;
	end
	conn:send (o.packet)

	-- remember which coroutine wants the answer
	if co then
		set(self.wanted, qclass, qtype, qname, co, true);
	end
	
	if have_timer and self.timeout then
		local num_servers = #self.server;
		local i = 1;
		timer.add_task(self.timeout, function ()
			if get(self.wanted, qclass, qtype, qname, co) then
				if i < num_servers then
				log("debug", "DNS request timeout %d/%d", i, num_servers)
					i = i + 1;
					self:servfail(conn);
					o.server = self.best_server;
					conn, err = self:getsocket(o.server);
					if conn then
						conn:send(o.packet);
						return self.timeout;
					end
				end
				-- Tried everything, failed
				self:cancel(qclass, qtype, qname);
			end
		end)
	end
	return true;
end

function resolver:servfail(sock, err)
	-- Resend all queries for this server

	local num = self.socketset[sock]

	-- Socket is dead now
	sock = self:voidsocket(sock);

	-- Find all requests to the down server, and retry on the next server
	self.time = socket.gettime();
	log("debug", "servfail %d (of %d)", num, #self.server);
	for id,queries in pairs(self.active) do
		for question,o in pairs(queries) do
			if o.server == num then -- This request was to the broken server
				o.server = o.server + 1 -- Use next server
				if o.server > #self.server then
					o.server = 1;
				end

				o.retries = (o.retries or 0) + 1;
				if o.retries >= #self.server then
					--print('timeout');
					queries[question] = nil;
				else
					sock, err = self:getsocket(o.server);
					if sock then sock:send(o.packet); end
				end
			end
		end
		if next(queries) == nil then
			self.active[id] = nil;
		end
	end

	if num == self.best_server then
		self.best_server = self.best_server + 1;
		if self.best_server > #self.server then
			-- Exhausted all servers, try first again
			self.best_server = 1;
		end
	end
	return sock, err;
end

function resolver:settimeout(seconds)
	self.timeout = seconds;
end

function resolver:receive(rset)    -- - - - - - - - - - - - - - - - -  receive
	--print('receive');  print(self.socket);
	self.time = socket.gettime();
	rset = rset or self.socket;

	local response;
	for _, sock in pairs(rset) do

		if self.socketset[sock] then
			local packet = sock:receive();
			if packet then
				response = self:decode(packet);
				if response and self.active[response.header.id]
					and self.active[response.header.id][response.question.raw] then
					--print('received response');
					--self.print(response);

					for _, rr in pairs(response.answer) do
						if rr.name:sub(-#response.question[1].name, -1) == response.question[1].name then
							self:remember(rr, response.question[1].type)
						end
					end

					-- retire the query
					local queries = self.active[response.header.id];
					queries[response.question.raw] = nil;
					
					if not next(queries) then self.active[response.header.id] = nil; end
					if not next(self.active) then self:closeall(); end

					-- was the query on the wanted list?
					local q = response.question[1];
					local cos = get(self.wanted, q.class, q.type, q.name);
					if cos then
						for co in pairs(cos) do
							if coroutine.status(co) == "suspended" then coroutine.resume(co); end
						end
						set(self.wanted, q.class, q.type, q.name, nil);
					end
				end
				
			end
		end
	end

	return response;
end


function resolver:feed(sock, packet, force)
	--print('receive'); print(self.socket);
	self.time = socket.gettime();

	local response = self:decode(packet, force);
	if response and self.active[response.header.id]
		and self.active[response.header.id][response.question.raw] then
		--print('received response');
		--self.print(response);

		for _, rr in pairs(response.answer) do
			self:remember(rr, rr.type);
		end

		for _, rr in pairs(response.additional) do
			self:remember(rr, rr.type);
		end

		-- retire the query
		local queries = self.active[response.header.id];
		queries[response.question.raw] = nil;
		if not next(queries) then self.active[response.header.id] = nil; end
		if not next(self.active) then self:closeall(); end

		-- was the query on the wanted list?
		local q = response.question[1];
		if q then
			local cos = get(self.wanted, q.class, q.type, q.name);
			if cos then
				for co in pairs(cos) do
					if coroutine.status(co) == "suspended" then coroutine.resume(co); end
				end
				set(self.wanted, q.class, q.type, q.name, nil);
			end
		end
	end

	return response;
end

function resolver:cancel(qclass, qtype, qname)
	local cos = get(self.wanted, qclass, qtype, qname);
	if cos then
		for co in pairs(cos) do
			if coroutine.status(co) == "suspended" then coroutine.resume(co); end
		end
		set(self.wanted, qclass, qtype, qname, nil);
	end
end

function resolver:pulse()    -- - - - - - - - - - - - - - - - - - - - -  pulse
	--print(':pulse');
	while self:receive() do end
	if not next(self.active) then return nil; end

	self.time = socket.gettime();
	for id,queries in pairs(self.active) do
		for question,o in pairs(queries) do
			if self.time >= o.retry then

				o.server = o.server + 1;
				if o.server > #self.server then
					o.server = 1;
					o.delay = o.delay + 1;
				end

				if o.delay > #self.delays then
					--print('timeout');
					queries[question] = nil;
					if not next(queries) then self.active[id] = nil; end
					if not next(self.active) then return nil; end
				else
					--print('retry', o.server, o.delay);
					local _a = self.socket[o.server];
					if _a then _a:send(o.packet); end
					o.retry = self.time + self.delays[o.delay];
				end
			end
		end
	end

	if next(self.active) then return true; end
	return nil;
end


function resolver:lookup(qname, qtype, qclass)    -- - - - - - - - - -  lookup
	self:query (qname, qtype, qclass)
	while self:pulse() do
		local recvt = {}
		for i, s in ipairs(self.socket) do
			recvt[i] = s
		end
		socket.select(recvt, nil, 4)
	end
	--print(self.cache);
	return self:peek(qname, qtype, qclass);
end

function resolver:lookupex(handler, qname, qtype, qclass)    -- - - - - - - - - -  lookup
	return self:peek(qname, qtype, qclass) or self:query(qname, qtype, qclass);
end

function resolver:tohostname(ip)
	return dns.lookup(ip:gsub("(%d+)%.(%d+)%.(%d+)%.(%d+)", "%4.%3.%2.%1.in-addr.arpa."), "PTR");
end

--print ---------------------------------------------------------------- print


local hints = {    -- - - - - - - - - - - - - - - - - - - - - - - - - - - hints
	qr = { [0]='query', 'response' },
	opcode = { [0]='query', 'inverse query', 'server status request' },
	aa = { [0]='non-authoritative', 'authoritative' },
	tc = { [0]='complete', 'truncated' },
	rd = { [0]='recursion not desired', 'recursion desired' },
	ra = { [0]='recursion not available', 'recursion available' },
	z  = { [0]='(reserved)' },
	rcode = { [0]='no error', 'format error', 'server failure', 'name error', 'not implemented' },

	type = dns.type,
	class = dns.class
};


local function hint(p, s)    -- - - - - - - - - - - - - - - - - - - - - - hint
	return (hints[s] and hints[s][p[s]]) or '';
end


function resolver.print(response)    -- - - - - - - - - - - - - resolver.print
	for _, s in pairs { 'id', 'qr', 'opcode', 'aa', 'tc', 'rd', 'ra', 'z',
						'rcode', 'qdcount', 'ancount', 'nscount', 'arcount' } do
		print( string.format('%-30s', 'header.'..s), response.header[s], hint(response.header, s) );
	end

	for i,question in ipairs(response.question) do
		print(string.format ('question[%i].name         ', i), question.name);
		print(string.format ('question[%i].type         ', i), question.type);
		print(string.format ('question[%i].class        ', i), question.class);
	end

	local common = { name=1, type=1, class=1, ttl=1, rdlength=1, rdata=1 };
	local tmp;
	for _, s in pairs({'answer', 'authority', 'additional'}) do
		for i,rr in pairs(response[s]) do
			for _, t in pairs({ 'name', 'type', 'class', 'ttl', 'rdlength' }) do
				tmp = string.format('%s[%i].%s', s, i, t);
				print(string.format('%-30s', tmp), rr[t], hint(rr, t));
			end
			for j,t in pairs(rr) do
				if not common[j] then
					tmp = string.format('%s[%i].%s', s, i, j);
					print(string.format('%-30s  %s', tostring(tmp), tostring(t)));
				end
			end
		end
	end
end


-- module api ------------------------------------------------------ module api


function dns.resolver ()    -- - - - - - - - - - - - - - - - - - - - - resolver
	local r = { active = {}, cache = {}, unsorted = {}, wanted = {}, best_server = 1 };
	setmetatable (r, resolver);
	setmetatable (r.cache, cache_metatable);
	setmetatable (r.unsorted, { __mode = 'kv' });
	return r;
end

local _resolver = dns.resolver();
dns._resolver = _resolver;

function dns.lookup(...)    -- - - - - - - - - - - - - - - - - - - - -  lookup
	return _resolver:lookup(...);
end

function dns.tohostname(...)
	return _resolver:tohostname(...);
end

function dns.purge(...)    -- - - - - - - - - - - - - - - - - - - - - -  purge
	return _resolver:purge(...);
end

function dns.peek(...)    -- - - - - - - - - - - - - - - - - - - - - - -  peek
	return _resolver:peek(...);
end

function dns.query(...)    -- - - - - - - - - - - - - - - - - - - - - -  query
	return _resolver:query(...);
end

function dns.feed(...)    -- - - - - - - - - - - - - - - - - - - - - - -  feed
	return _resolver:feed(...);
end

function dns.cancel(...)  -- - - - - - - - - - - - - - - - - - - - - -  cancel
	return _resolver:cancel(...);
end

function dns.settimeout(...)
	return _resolver:settimeout(...);
end

function dns.cache()
	return _resolver.cache;
end

function dns.socket_wrapper_set(...)    -- - - - - - - - -  socket_wrapper_set
	return _resolver:socket_wrapper_set(...);
end

return dns;