aboutsummaryrefslogtreecommitdiffstats
path: root/net/dns.lua
blob: d6462031a85de7be38c374c8381c4e148989a72b (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
-- Prosody IM
-- This file is included with Prosody IM. It has modifications,
-- which are hereby placed in the public domain.

-- public domain 20080404 lua@ztact.com


-- 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)


require 'socket'
local ztact = require 'util.ztact'
local require = require
local os = os;

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

local ipairs, next, pairs, print, setmetatable, tostring, assert, error, unpack =
      ipairs, next, pairs, print, setmetatable, tostring, assert, error, unpack

local get, set = ztact.get, ztact.set


-------------------------------------------------- module dns
module ('dns')
local dns = _M;


-- 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)    -- - - - - - - - - - - - - - - - - - - -  augment
  local a = {}
  for i,s in pairs (t) do  a[i] = s  a[s] = s  a[string.lower (s)] = s  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 = {
  'A', 'NS', 'MD', 'MF', 'CNAME', 'SOA', 'MB', 'MG', 'MR', 'NULL', 'WKS',
  'PTR', 'HINFO', 'MINFO', 'MX', 'TXT',
  [ 28] = 'AAAA', [ 29] = 'LOC',   [ 33] = 'SRV',
  [252] = 'AXFR', [253] = 'MAILB', [254] = 'MAILA', [255] = '*' }


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


dns.type      = augment (dns.types)
dns.class     = augment (dns.classes)
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 pairs (rrs) do

    if rr.tod then
      -- rr.tod = rr.tod - 50    -- accelerated decripitude
      rr.ttl = math.floor (rr.tod - time)
      if rr.ttl <= 0 then
        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[i] = nil
      end  end  end


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


local resolver = {}
resolver.__index = resolver


local SRV_tostring


local rr_metatable = {}    -- - - - - - - - - - - - - - - - - - -  rr_metatable
function rr_metatable.__tostring (rr)
  local s0 = string.format (
    '%2s %-5s %6i %-28s', rr.class, rr.type, rr.ttl, rr.name )
  local s1 = ''
  if rr.type == 'A' then  s1 = ' '..rr.a
  elseif rr.type == 'MX' then
    s1 = string.format (' %2i %s', rr.pref, rr.mx)
  elseif rr.type == 'CNAME' then  s1 = ' '..rr.cname
  elseif rr.type == 'LOC'   then  s1 = ' '..resolver.LOC_tostring (rr)
  elseif rr.type == 'NS'    then  s1 = ' '..rr.ns
  elseif rr.type == 'SRV'   then  s1 = ' '..SRV_tostring (rr)
  elseif rr.type == 'TXT'   then  s1 = ' '..rr.txt
  else  s1 = ' <UNKNOWN RDATA TYPE>'  end
  return s0..s1
  end


local rrs_metatable = {}    -- - - - - - - - - - - - - - - - - -  rrs_metatable
function rrs_metatable.__tostring (rrs)
  local t = {}
  for i,rr in pairs (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


function resolver:new ()    -- - - - - - - - - - - - - - - - - - - - - resolver
  local r = { active = {}, cache = {}, unsorted = {} }
  setmetatable (r, resolver)
  setmetatable (r.cache, cache_metatable)
  setmetatable (r.unsorted, { __mode = 'kv' })
  return r
  end


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


function dns.random (...)    -- - - - - - - - - - - - - - - - - - -  dns.random
  math.randomseed (10000*socket.gettime ())
  dns.random = math.random
  return dns.random (...)
  end


local function encodeHeader (o)    -- - - - - - - - - - - - - - -  encodeHeader

  o = o or {}

  o.id = o.id or		-- 16b	(random) id
    dns.random (0, 0xffff)

  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 = {}
  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


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 SRV_tostring (rr)    -- - - - - - - - - - - - - - - - - - SRV_tostring
  local s = rr.srv
  return string.format ( '%5d %5d %5d %s',
                         s.priority, s.weight, s.port, s.target )
  end


function resolver:TXT (rr)    -- - - - - - - - - - - - - - - - - - - - - -  TXT
  rr.txt = self:sub (rr.rdlength)
  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 ()

  if rr.ttl == 0 then  -- pass
  else  rr.tod = self.time + rr.ttl  end

  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 i = 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 i = 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
      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
  local resolv_conf = io.open("/etc/resolv.conf");
  if resolv_conf then
	  for line in resolv_conf:lines() do
		local address = string.match (line, '^%s*nameserver%s+(%d+%.%d+%.%d+%.%d+)%s*$')
		if address then self:addnameserver (address)  end
	  end
  elseif os.getenv("WINDIR") then
  	self:addnameserver ("208.67.222.222")
  	self:addnameserver ("208.67.220.220")  	
  end
  if not self.server or #self.server == 0 then
  	self:addnameserver("127.0.0.1");
  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

  sock = socket.udp ()
  if self.socket_wrapper then  sock = self.socket_wrapper (sock, self)  end
  sock:settimeout (0)
  -- todo: attempt to use a random port, fallback to 0
  sock:setsockname ('*', 0)
  sock:setpeername (self.server[servernum], 53)
  self.socket[servernum] = sock
  self.socketset[sock] = servernum
  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
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]:close ()  end
  self.socket = {}
  end


function resolver:remember (rr, type)    -- - - - - - - - - - - - - -  remember

  --print ('remember', type, rr.class, rr.type, rr.name)

  if type ~= '*' then
    type = rr.type
    local all = get (self.cache, rr.class, '*', rr.name)
    --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, rr.class, type, rr.name) or
    set (self.cache, rr.class, type, rr.name, setmetatable ({}, rrs_metatable))
  append (rrs, rr)

  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)    -- - - - - - - - - - - -  peek
  qname, qtype, qclass = standardize (qname, qtype, qclass)
  local rrs = get (self.cache, qclass, qtype, qname)
  if not rrs then  return nil  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)  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 = {}  end
  end


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

  qname, qtype, qclass = standardize (qname, qtype, qclass)

  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

  -- remember which coroutine wants the answer
  local co = coroutine.running ()
  if co then
    set (self.wanted, qclass, qtype, qname, co, true)
    --set (self.yielded, co, qclass, qtype, qname, true)
  end
  
  self:getsocket (o.server):send (o.packet)

end

function resolver:servfail(sock)
  -- Resend all queries for this server
  
  local num = self.socketset[sock]
  
  -- Socket is dead now
  self:voidsocket(sock);
  
  -- Find all requests to the down server, and retry on the next server
  self.time = socket.gettime ()
  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
          local _a = self:getsocket(o.server);
          if _a then _a:send (o.packet) end
        end
      end
    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
end

function resolver:receive (rset)    -- - - - - - - - - - - - - - - - -  receive

  --print 'receive'  print (self.socket)
  self.time = socket.gettime ()
  rset = rset or self.socket

  local response
  for i,sock in pairs (rset) do

    if self.socketset[sock] then
    local packet = sock:receive ()
    if packet then

    response = self:decode (packet)
    if response then
    --print 'received response'
    --self.print (response)

    for i,section in pairs { 'answer', 'authority', 'additional' } do
      for j,rr in pairs (response[section]) do
        self:remember (rr, response.question[1].type)  end  end

    -- retire the query
    local queries = self.active[response.header.id]
    if queries[response.question.raw] then
      queries[response.question.raw] = nil  end
    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
    local cos = get (self.wanted, q.class, q.type, q.name)
    if cos then
      for co in pairs (cos) do
        set (self.yielded, co, q.class, q.type, q.name, nil)
	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)
  --print 'receive'  print (self.socket)
  self.time = socket.gettime ()

  local response = self:decode (packet)
  if response then
    --print 'received response'
    --self.print (response)

    for i,section in pairs { 'answer', 'authority', 'additional' } do
      for j,rr in pairs (response[section]) do
        self:remember (rr, response.question[1].type)
      end
    end

    -- retire the query
    local queries = self.active[response.header.id]
    if queries[response.question.raw] then
      queries[response.question.raw] = nil
    end
    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
          set (self.yielded, co, q.class, q.type, q.name, nil)
          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(data)
	local cos = get (self.wanted, unpack(data, 1, 3))
	if cos then
		cos[data[4]] = 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  socket.select (self.socket, 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


--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,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,s in pairs {'answer', 'authority', 'additional'} do
    for i,rr in pairs (response[s]) do
      for j,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


local function resolve (func, ...)    -- - - - - - - - - - - - - - resolver_get
  dns._resolver = dns._resolver or dns.resolver ()
  return func (dns._resolver, ...)
  end


function dns.resolver ()    -- - - - - - - - - - - - - - - - - - - - - resolver

  -- this function seems to be redundant with resolver.new ()

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


function dns.lookup (...)    -- - - - - - - - - - - - - - - - - - - - -  lookup
  return resolve (resolver.lookup, ...)  end


function dns.purge (...)    -- - - - - - - - - - - - - - - - - - - - - -  purge
  return resolve (resolver.purge, ...)  end

function dns.peek (...)    -- - - - - - - - - - - - - - - - - - - - - - -  peek
  return resolve (resolver.peek, ...)  end


function dns.query (...)    -- - - - - - - - - - - - - - - - - - - - - -  query
  return resolve (resolver.query, ...)  end

function dns.feed (...)    -- - - - - - - - - - - - - - - - - - - - - -  feed
  return resolve (resolver.feed, ...)  end

function dns.cancel(...)   -- - - - - - - - - - - - - - - - - - - - - -  cancel
  return resolve(resolver.cancel, ...) end

function dns:socket_wrapper_set (...)    -- - - - - - - - -  socket_wrapper_set
  return resolve (resolver.socket_wrapper_set, ...)  end


return dns