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
|
;;; dns.el --- Domain Name Service lookups
;; Copyright (C) 2002-2017 Free Software Foundation, Inc.
;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
;; Keywords: network comm
;; This file is part of GNU Emacs.
;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
;;; Commentary:
;;; Code:
(defvar dns-timeout 5
"How many seconds to wait when doing DNS queries.")
(defvar dns-servers nil
"List of DNS servers to query.
If nil, /etc/resolv.conf and nslookup will be consulted.")
(defvar dns-servers-valid-for-interfaces nil
"The return value of `network-interface-list' when `dns-servers' was set.
If the set of network interfaces and/or their IP addresses
change, then presumably the list of DNS servers needs to be
updated. Set this variable to t to disable the check.")
;;; Internal code:
(defvar dns-query-types
'((A 1)
(NS 2)
(MD 3)
(MF 4)
(CNAME 5)
(SOA 6)
(MB 7)
(MG 8)
(MR 9)
(NULL 10)
(WKS 11)
(PTR 12)
(HINFO 13)
(MINFO 14)
(MX 15)
(TXT 16)
(AAAA 28) ; RFC3596
(SRV 33) ; RFC2782
(AXFR 252)
(MAILB 253)
(MAILA 254)
(* 255))
"Names of query types and their values.")
(defvar dns-classes
'((IN 1)
(CS 2)
(CH 3)
(HS 4))
"Classes of queries.")
(defun dns-write-bytes (value &optional length)
(let (bytes)
(dotimes (i (or length 1))
(push (% value 256) bytes)
(setq value (/ value 256)))
(dolist (byte bytes)
(insert byte))))
(defun dns-read-bytes (length)
(let ((value 0))
(dotimes (i length)
(setq value (logior (* value 256) (following-char)))
(forward-char 1))
value))
(defun dns-get (type spec)
(cadr (assq type spec)))
(defun dns-inverse-get (value spec)
(let ((found nil))
(while (and (not found)
spec)
(if (eq value (cadr (car spec)))
(setq found (caar spec))
(pop spec)))
found))
(defun dns-write-name (name)
(dolist (part (split-string name "\\."))
(dns-write-bytes (length part))
(insert part))
(dns-write-bytes 0))
(defun dns-read-string-name (string buffer)
(with-temp-buffer
(unless (featurep 'xemacs) (set-buffer-multibyte nil))
(insert string)
(goto-char (point-min))
(dns-read-name buffer)))
(defun dns-read-name (&optional buffer)
(let ((ended nil)
(name nil)
length)
(while (not ended)
(setq length (dns-read-bytes 1))
(if (= 192 (logand length (lsh 3 6)))
(let ((offset (+ (* (logand 63 length) 256)
(dns-read-bytes 1))))
(save-excursion
(when buffer
(set-buffer buffer))
(goto-char (1+ offset))
(setq ended (dns-read-name buffer))))
(if (zerop length)
(setq ended t)
(push (buffer-substring (point)
(progn (forward-char length) (point)))
name))))
(if (stringp ended)
(if (null name)
ended
(concat (mapconcat 'identity (nreverse name) ".") "." ended))
(mapconcat 'identity (nreverse name) "."))))
(defun dns-write (spec &optional tcp-p)
"Write a DNS packet according to SPEC.
If TCP-P, the first two bytes of the package with be the length field."
(with-temp-buffer
(unless (featurep 'xemacs) (set-buffer-multibyte nil))
(dns-write-bytes (dns-get 'id spec) 2)
(dns-write-bytes
(logior
(lsh (if (dns-get 'response-p spec) 1 0) -7)
(lsh
(cond
((eq (dns-get 'opcode spec) 'query) 0)
((eq (dns-get 'opcode spec) 'inverse-query) 1)
((eq (dns-get 'opcode spec) 'status) 2)
(t (error "No such opcode: %s" (dns-get 'opcode spec))))
-3)
(lsh (if (dns-get 'authoritative-p spec) 1 0) -2)
(lsh (if (dns-get 'truncated-p spec) 1 0) -1)
(lsh (if (dns-get 'recursion-desired-p spec) 1 0) 0)))
(dns-write-bytes
(cond
((eq (dns-get 'response-code spec) 'no-error) 0)
((eq (dns-get 'response-code spec) 'format-error) 1)
((eq (dns-get 'response-code spec) 'server-failure) 2)
((eq (dns-get 'response-code spec) 'name-error) 3)
((eq (dns-get 'response-code spec) 'not-implemented) 4)
((eq (dns-get 'response-code spec) 'refused) 5)
(t 0)))
(dns-write-bytes (length (dns-get 'queries spec)) 2)
(dns-write-bytes (length (dns-get 'answers spec)) 2)
(dns-write-bytes (length (dns-get 'authorities spec)) 2)
(dns-write-bytes (length (dns-get 'additionals spec)) 2)
(dolist (query (dns-get 'queries spec))
(dns-write-name (car query))
(dns-write-bytes (cadr (assq (or (dns-get 'type query) 'A)
dns-query-types)) 2)
(dns-write-bytes (cadr (assq (or (dns-get 'class query) 'IN)
dns-classes)) 2))
(dolist (slot '(answers authorities additionals))
(dolist (resource (dns-get slot spec))
(dns-write-name (car resource))
(dns-write-bytes (cadr (assq (dns-get 'type resource) dns-query-types))
2)
(dns-write-bytes (cadr (assq (dns-get 'class resource) dns-classes))
2)
(dns-write-bytes (dns-get 'ttl resource) 4)
(dns-write-bytes (length (dns-get 'data resource)) 2)
(insert (dns-get 'data resource))))
(when tcp-p
(goto-char (point-min))
(dns-write-bytes (buffer-size) 2))
(buffer-string)))
(defun dns-read (packet)
(with-temp-buffer
(unless (featurep 'xemacs) (set-buffer-multibyte nil))
(let ((spec nil)
queries answers authorities additionals)
(insert packet)
(goto-char (point-min))
(push (list 'id (dns-read-bytes 2)) spec)
(let ((byte (dns-read-bytes 1)))
(push (list 'response-p (if (zerop (logand byte (lsh 1 7))) nil t))
spec)
(let ((opcode (logand byte (lsh 7 3))))
(push (list 'opcode
(cond ((eq opcode 0) 'query)
((eq opcode 1) 'inverse-query)
((eq opcode 2) 'status)))
spec))
(push (list 'authoritative-p (if (zerop (logand byte (lsh 1 2)))
nil t)) spec)
(push (list 'truncated-p (if (zerop (logand byte (lsh 1 2))) nil t))
spec)
(push (list 'recursion-desired-p
(if (zerop (logand byte (lsh 1 0))) nil t)) spec))
(let ((rc (logand (dns-read-bytes 1) 15)))
(push (list 'response-code
(cond
((eq rc 0) 'no-error)
((eq rc 1) 'format-error)
((eq rc 2) 'server-failure)
((eq rc 3) 'name-error)
((eq rc 4) 'not-implemented)
((eq rc 5) 'refused)))
spec))
(setq queries (dns-read-bytes 2))
(setq answers (dns-read-bytes 2))
(setq authorities (dns-read-bytes 2))
(setq additionals (dns-read-bytes 2))
(let ((qs nil))
(dotimes (i queries)
(push (list (dns-read-name)
(list 'type (dns-inverse-get (dns-read-bytes 2)
dns-query-types))
(list 'class (dns-inverse-get (dns-read-bytes 2)
dns-classes)))
qs))
(push (list 'queries qs) spec))
(dolist (slot '(answers authorities additionals))
(let ((qs nil)
type)
(dotimes (i (symbol-value slot))
(push (list (dns-read-name)
(list 'type
(setq type (dns-inverse-get (dns-read-bytes 2)
dns-query-types)))
(list 'class (dns-inverse-get (dns-read-bytes 2)
dns-classes))
(list 'ttl (dns-read-bytes 4))
(let ((length (dns-read-bytes 2)))
(list 'data
(dns-read-type
(buffer-substring
(point)
(progn (forward-char length) (point)))
type))))
qs))
(push (list slot qs) spec)))
(nreverse spec))))
(defun dns-read-int32 ()
;; Full 32 bit Integers can't be handled by 32-bit Emacsen. If we
;; use floats, it works.
(format "%.0f" (+ (* (dns-read-bytes 1) 16777216.0)
(dns-read-bytes 3))))
(defun dns-read-type (string type)
(let ((buffer (current-buffer))
(point (point)))
(prog1
(with-temp-buffer
(unless (featurep 'xemacs) (set-buffer-multibyte nil))
(insert string)
(goto-char (point-min))
(cond
((eq type 'A)
(let ((bytes nil))
(dotimes (i 4)
(push (dns-read-bytes 1) bytes))
(mapconcat 'number-to-string (nreverse bytes) ".")))
((eq type 'AAAA)
(let (hextets)
(dotimes (i 8)
(push (dns-read-bytes 2) hextets))
(mapconcat (lambda (n) (format "%x" n))
(nreverse hextets) ":")))
((eq type 'SOA)
(list (list 'mname (dns-read-name buffer))
(list 'rname (dns-read-name buffer))
(list 'serial (dns-read-int32))
(list 'refresh (dns-read-int32))
(list 'retry (dns-read-int32))
(list 'expire (dns-read-int32))
(list 'minimum (dns-read-int32))))
((eq type 'SRV)
(list (list 'priority (dns-read-bytes 2))
(list 'weight (dns-read-bytes 2))
(list 'port (dns-read-bytes 2))
(list 'target (dns-read-name buffer))))
((eq type 'MX)
(cons (dns-read-bytes 2) (dns-read-name buffer)))
((or (eq type 'CNAME) (eq type 'NS) (eq type 'PTR))
(dns-read-string-name string buffer))
(t string)))
(goto-char point))))
(declare-function network-interface-list "process.c")
(defun dns-servers-up-to-date-p ()
"Return false if we need to recheck the list of DNS servers."
(and dns-servers
(or (eq dns-servers-valid-for-interfaces t)
;; `network-interface-list' was introduced in Emacs 22.1.
(not (fboundp 'network-interface-list))
(equal dns-servers-valid-for-interfaces
(network-interface-list)))))
(defun dns-set-servers ()
"Set `dns-servers' to a list of DNS servers or nil if none are found.
Parses \"/etc/resolv.conf\" or calls \"nslookup\"."
(or (when (file-exists-p "/etc/resolv.conf")
(setq dns-servers nil)
(with-temp-buffer
(insert-file-contents "/etc/resolv.conf")
(goto-char (point-min))
(while (re-search-forward "^nameserver[\t ]+\\([^ \t\n]+\\)" nil t)
(push (match-string 1) dns-servers))
(setq dns-servers (nreverse dns-servers))))
(when (executable-find "nslookup")
(with-temp-buffer
(call-process "nslookup" nil t nil "localhost")
(goto-char (point-min))
(re-search-forward
"^Address:[ \t]*\\([0-9]+\\.[0-9]+\\.[0-9]+\\.[0-9]+\\)" nil t)
(setq dns-servers (list (match-string 1))))))
(when (fboundp 'network-interface-list)
(setq dns-servers-valid-for-interfaces (network-interface-list))))
(defun dns-read-txt (string)
(if (> (length string) 1)
(substring string 1)
string))
(defun dns-get-txt-answer (answers)
(let ((result "")
(do-next nil))
(dolist (answer answers)
(dolist (elem answer)
(when (consp elem)
(cond
((eq (car elem) 'type)
(setq do-next (eq (cadr elem) 'TXT)))
((eq (car elem) 'data)
(when do-next
(setq result (concat result (dns-read-txt (cadr elem))))))))))
result))
;;; Interface functions.
(defmacro dns-make-network-process (server)
(if (featurep 'xemacs)
`(let ((coding-system-for-read 'binary)
(coding-system-for-write 'binary))
(open-network-stream "dns" (current-buffer)
,server "domain" 'udp))
`(let ((server ,server)
(coding-system-for-read 'binary)
(coding-system-for-write 'binary))
(if (fboundp 'make-network-process)
(make-network-process
:name "dns"
:coding 'binary
:buffer (current-buffer)
:host server
:service "domain"
:type 'datagram)
;; Older versions of Emacs doesn't have
;; `make-network-process', so we fall back on opening a TCP
;; connection to the DNS server.
(open-network-stream "dns" (current-buffer) server "domain")))))
(defvar dns-cache (make-vector 4096 0))
(defun dns-query-cached (name &optional type fullp reversep)
(let* ((key (format "%s:%s:%s:%s" name type fullp reversep))
(sym (intern-soft key dns-cache)))
(if (and sym
(boundp sym))
(symbol-value sym)
(let ((result (dns-query name type fullp reversep)))
(set (intern key dns-cache) result)
result))))
;; The old names `query-dns' and `query-dns-cached' weren't used in Emacs 23
;; yet, so no alias are provided. --rsteib
(defun dns-query (name &optional type fullp reversep)
"Query a DNS server for NAME of TYPE.
If FULLP, return the entire record returned.
If REVERSEP, look up an IP address."
(setq type (or type 'A))
(unless (dns-servers-up-to-date-p)
(dns-set-servers))
(when reversep
(setq name (concat
(mapconcat 'identity (nreverse (split-string name "\\.")) ".")
".in-addr.arpa")
type 'PTR))
(if (not dns-servers)
(message "No DNS server configuration found")
(with-temp-buffer
(unless (featurep 'xemacs) (set-buffer-multibyte nil))
(let ((process (condition-case ()
(dns-make-network-process (car dns-servers))
(error
(message
"dns: Got an error while trying to talk to %s"
(car dns-servers))
nil)))
(tcp-p (and (not (fboundp 'make-network-process))
(not (featurep 'xemacs))))
(step 100)
(times (* dns-timeout 1000))
(id (random 65000)))
(when process
(process-send-string
process
(dns-write `((id ,id)
(opcode query)
(queries ((,name (type ,type))))
(recursion-desired-p t))
tcp-p))
(while (and (zerop (buffer-size))
(> times 0))
(sit-for (/ step 1000.0))
(accept-process-output process 0 step)
(setq times (- times step)))
(condition-case nil
(delete-process process)
(error nil))
(when (and tcp-p
(>= (buffer-size) 2))
(goto-char (point-min))
(delete-region (point) (+ (point) 2)))
(when (and (>= (buffer-size) 2)
;; We had a time-out.
(> times 0))
(let ((result (dns-read (buffer-string))))
(if fullp
result
(let ((answer (car (dns-get 'answers result))))
(when (eq type (dns-get 'type answer))
(if (eq type 'TXT)
(dns-get-txt-answer (dns-get 'answers result))
(dns-get 'data answer))))))))))))
(provide 'dns)
;;; dns.el ends here
|
