1;;; dns.el --- Domain Name Service lookups 2 3;; Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc. 4 5;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org> 6;; Keywords: network 7 8;; This file is part of GNU Emacs. 9 10;; GNU Emacs is free software; you can redistribute it and/or modify 11;; it under the terms of the GNU General Public License as published by 12;; the Free Software Foundation; either version 2, or (at your option) 13;; any later version. 14 15;; GNU Emacs is distributed in the hope that it will be useful, 16;; but WITHOUT ANY WARRANTY; without even the implied warranty of 17;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 18;; GNU General Public License for more details. 19 20;; You should have received a copy of the GNU General Public License 21;; along with GNU Emacs; see the file COPYING. If not, write to the 22;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, 23;; Boston, MA 02110-1301, USA. 24 25;;; Commentary: 26 27;;; Code: 28 29(eval-when-compile (require 'cl)) 30 31(require 'mm-util) 32 33(defvar dns-timeout 5 34 "How many seconds to wait when doing DNS queries.") 35 36(defvar dns-servers nil 37 "Which DNS servers to query. 38If nil, /etc/resolv.conf will be consulted.") 39 40;;; Internal code: 41 42(defvar dns-query-types 43 '((A 1) 44 (NS 2) 45 (MD 3) 46 (MF 4) 47 (CNAME 5) 48 (SOA 6) 49 (MB 7) 50 (MG 8) 51 (MR 9) 52 (NULL 10) 53 (WKS 11) 54 (PRT 12) 55 (HINFO 13) 56 (MINFO 14) 57 (MX 15) 58 (TXT 16) 59 (AXFR 252) 60 (MAILB 253) 61 (MAILA 254) 62 (* 255)) 63 "Names of query types and their values.") 64 65(defvar dns-classes 66 '((IN 1) 67 (CS 2) 68 (CH 3) 69 (HS 4)) 70 "Classes of queries.") 71 72(defun dns-write-bytes (value &optional length) 73 (let (bytes) 74 (dotimes (i (or length 1)) 75 (push (% value 256) bytes) 76 (setq value (/ value 256))) 77 (dolist (byte bytes) 78 (insert byte)))) 79 80(defun dns-read-bytes (length) 81 (let ((value 0)) 82 (dotimes (i length) 83 (setq value (logior (* value 256) (following-char))) 84 (forward-char 1)) 85 value)) 86 87(defun dns-get (type spec) 88 (cadr (assq type spec))) 89 90(defun dns-inverse-get (value spec) 91 (let ((found nil)) 92 (while (and (not found) 93 spec) 94 (if (eq value (cadr (car spec))) 95 (setq found (caar spec)) 96 (pop spec))) 97 found)) 98 99(defun dns-write-name (name) 100 (dolist (part (split-string name "\\.")) 101 (dns-write-bytes (length part)) 102 (insert part)) 103 (dns-write-bytes 0)) 104 105(defun dns-read-string-name (string buffer) 106 (mm-with-unibyte-buffer 107 (insert string) 108 (goto-char (point-min)) 109 (dns-read-name buffer))) 110 111(defun dns-read-name (&optional buffer) 112 (let ((ended nil) 113 (name nil) 114 length) 115 (while (not ended) 116 (setq length (dns-read-bytes 1)) 117 (if (= 192 (logand length (lsh 3 6))) 118 (let ((offset (+ (* (logand 63 length) 256) 119 (dns-read-bytes 1)))) 120 (save-excursion 121 (when buffer 122 (set-buffer buffer)) 123 (goto-char (1+ offset)) 124 (setq ended (dns-read-name buffer)))) 125 (if (zerop length) 126 (setq ended t) 127 (push (buffer-substring (point) 128 (progn (forward-char length) (point))) 129 name)))) 130 (if (stringp ended) 131 (if (null name) 132 ended 133 (concat (mapconcat 'identity (nreverse name) ".") "." ended)) 134 (mapconcat 'identity (nreverse name) ".")))) 135 136(defun dns-write (spec &optional tcp-p) 137 "Write a DNS packet according to SPEC. 138If TCP-P, the first two bytes of the package with be the length field." 139 (with-temp-buffer 140 (dns-write-bytes (dns-get 'id spec) 2) 141 (dns-write-bytes 142 (logior 143 (lsh (if (dns-get 'response-p spec) 1 0) -7) 144 (lsh 145 (cond 146 ((eq (dns-get 'opcode spec) 'query) 0) 147 ((eq (dns-get 'opcode spec) 'inverse-query) 1) 148 ((eq (dns-get 'opcode spec) 'status) 2) 149 (t (error "No such opcode: %s" (dns-get 'opcode spec)))) 150 -3) 151 (lsh (if (dns-get 'authoritative-p spec) 1 0) -2) 152 (lsh (if (dns-get 'truncated-p spec) 1 0) -1) 153 (lsh (if (dns-get 'recursion-desired-p spec) 1 0) 0))) 154 (dns-write-bytes 155 (cond 156 ((eq (dns-get 'response-code spec) 'no-error) 0) 157 ((eq (dns-get 'response-code spec) 'format-error) 1) 158 ((eq (dns-get 'response-code spec) 'server-failure) 2) 159 ((eq (dns-get 'response-code spec) 'name-error) 3) 160 ((eq (dns-get 'response-code spec) 'not-implemented) 4) 161 ((eq (dns-get 'response-code spec) 'refused) 5) 162 (t 0))) 163 (dns-write-bytes (length (dns-get 'queries spec)) 2) 164 (dns-write-bytes (length (dns-get 'answers spec)) 2) 165 (dns-write-bytes (length (dns-get 'authorities spec)) 2) 166 (dns-write-bytes (length (dns-get 'additionals spec)) 2) 167 (dolist (query (dns-get 'queries spec)) 168 (dns-write-name (car query)) 169 (dns-write-bytes (cadr (assq (or (dns-get 'type query) 'A) 170 dns-query-types)) 2) 171 (dns-write-bytes (cadr (assq (or (dns-get 'class query) 'IN) 172 dns-classes)) 2)) 173 (dolist (slot '(answers authorities additionals)) 174 (dolist (resource (dns-get slot spec)) 175 (dns-write-name (car resource)) 176 (dns-write-bytes (cadr (assq (dns-get 'type resource) dns-query-types)) 177 2) 178 (dns-write-bytes (cadr (assq (dns-get 'class resource) dns-classes)) 179 2) 180 (dns-write-bytes (dns-get 'ttl resource) 4) 181 (dns-write-bytes (length (dns-get 'data resource)) 2) 182 (insert (dns-get 'data resource)))) 183 (when tcp-p 184 (goto-char (point-min)) 185 (dns-write-bytes (buffer-size) 2)) 186 (buffer-string))) 187 188(defun dns-read (packet) 189 (mm-with-unibyte-buffer 190 (let ((spec nil) 191 queries answers authorities additionals) 192 (insert packet) 193 (goto-char (point-min)) 194 (push (list 'id (dns-read-bytes 2)) spec) 195 (let ((byte (dns-read-bytes 1))) 196 (push (list 'response-p (if (zerop (logand byte (lsh 1 7))) nil t)) 197 spec) 198 (let ((opcode (logand byte (lsh 7 3)))) 199 (push (list 'opcode 200 (cond ((eq opcode 0) 'query) 201 ((eq opcode 1) 'inverse-query) 202 ((eq opcode 2) 'status))) 203 spec)) 204 (push (list 'authoritative-p (if (zerop (logand byte (lsh 1 2))) 205 nil t)) spec) 206 (push (list 'truncated-p (if (zerop (logand byte (lsh 1 2))) nil t)) 207 spec) 208 (push (list 'recursion-desired-p 209 (if (zerop (logand byte (lsh 1 0))) nil t)) spec)) 210 (let ((rc (logand (dns-read-bytes 1) 15))) 211 (push (list 'response-code 212 (cond 213 ((eq rc 0) 'no-error) 214 ((eq rc 1) 'format-error) 215 ((eq rc 2) 'server-failure) 216 ((eq rc 3) 'name-error) 217 ((eq rc 4) 'not-implemented) 218 ((eq rc 5) 'refused))) 219 spec)) 220 (setq queries (dns-read-bytes 2)) 221 (setq answers (dns-read-bytes 2)) 222 (setq authorities (dns-read-bytes 2)) 223 (setq additionals (dns-read-bytes 2)) 224 (let ((qs nil)) 225 (dotimes (i queries) 226 (push (list (dns-read-name) 227 (list 'type (dns-inverse-get (dns-read-bytes 2) 228 dns-query-types)) 229 (list 'class (dns-inverse-get (dns-read-bytes 2) 230 dns-classes))) 231 qs)) 232 (push (list 'queries qs) spec)) 233 (dolist (slot '(answers authorities additionals)) 234 (let ((qs nil) 235 type) 236 (dotimes (i (symbol-value slot)) 237 (push (list (dns-read-name) 238 (list 'type 239 (setq type (dns-inverse-get (dns-read-bytes 2) 240 dns-query-types))) 241 (list 'class (dns-inverse-get (dns-read-bytes 2) 242 dns-classes)) 243 (list 'ttl (dns-read-bytes 4)) 244 (let ((length (dns-read-bytes 2))) 245 (list 'data 246 (dns-read-type 247 (buffer-substring 248 (point) 249 (progn (forward-char length) (point))) 250 type)))) 251 qs)) 252 (push (list slot qs) spec))) 253 (nreverse spec)))) 254 255(defun dns-read-type (string type) 256 (let ((buffer (current-buffer)) 257 (point (point))) 258 (prog1 259 (mm-with-unibyte-buffer 260 (insert string) 261 (goto-char (point-min)) 262 (cond 263 ((eq type 'A) 264 (let ((bytes nil)) 265 (dotimes (i 4) 266 (push (dns-read-bytes 1) bytes)) 267 (mapconcat 'number-to-string (nreverse bytes) "."))) 268 ((eq type 'NS) 269 (dns-read-string-name string buffer)) 270 ((eq type 'CNAME) 271 (dns-read-string-name string buffer)) 272 (t string))) 273 (goto-char point)))) 274 275(defun dns-parse-resolv-conf () 276 (when (file-exists-p "/etc/resolv.conf") 277 (with-temp-buffer 278 (insert-file-contents "/etc/resolv.conf") 279 (goto-char (point-min)) 280 (while (re-search-forward "^nameserver[\t ]+\\([^ \t\n]+\\)" nil t) 281 (push (match-string 1) dns-servers)) 282 (setq dns-servers (nreverse dns-servers))))) 283 284;;; Interface functions. 285(eval-when-compile 286 (when (featurep 'xemacs) 287 (require 'gnus-xmas))) 288 289(defmacro dns-make-network-process (server) 290 (if (featurep 'xemacs) 291 `(let ((coding-system-for-read 'binary) 292 (coding-system-for-write 'binary)) 293 (gnus-xmas-open-network-stream "dns" (current-buffer) 294 ,server "domain" 'udp)) 295 `(let ((server ,server) 296 (coding-system-for-read 'binary) 297 (coding-system-for-write 'binary)) 298 (if (fboundp 'make-network-process) 299 (make-network-process 300 :name "dns" 301 :coding 'binary 302 :buffer (current-buffer) 303 :host server 304 :service "domain" 305 :type 'datagram) 306 ;; Older versions of Emacs doesn't have 307 ;; `make-network-process', so we fall back on opening a TCP 308 ;; connection to the DNS server. 309 (open-network-stream "dns" (current-buffer) server "domain"))))) 310 311(defun query-dns (name &optional type fullp) 312 "Query a DNS server for NAME of TYPE. 313If FULLP, return the entire record returned." 314 (setq type (or type 'A)) 315 (unless dns-servers 316 (dns-parse-resolv-conf)) 317 318 (if (not dns-servers) 319 (message "No DNS server configuration found") 320 (mm-with-unibyte-buffer 321 (let ((process (condition-case () 322 (dns-make-network-process (car dns-servers)) 323 (error 324 (message "dns: Got an error while trying to talk to %s" 325 (car dns-servers)) 326 nil))) 327 (tcp-p (and (not (fboundp 'make-network-process)) 328 (not (featurep 'xemacs)))) 329 (step 100) 330 (times (* dns-timeout 1000)) 331 (id (random 65000))) 332 (when process 333 (process-send-string 334 process 335 (dns-write `((id ,id) 336 (opcode query) 337 (queries ((,name (type ,type)))) 338 (recursion-desired-p t)) 339 tcp-p)) 340 (while (and (zerop (buffer-size)) 341 (> times 0)) 342 (accept-process-output process 0 step) 343 (decf times step)) 344 (ignore-errors 345 (delete-process process)) 346 (when (and tcp-p 347 (>= (buffer-size) 2)) 348 (goto-char (point-min)) 349 (delete-region (point) (+ (point) 2))) 350 (when (>= (buffer-size) 2) 351 (let ((result (dns-read (buffer-string)))) 352 (if fullp 353 result 354 (let ((answer (car (dns-get 'answers result)))) 355 (when (eq type (dns-get 'type answer)) 356 (dns-get 'data answer))))))))))) 357 358(provide 'dns) 359 360;;; arch-tag: d0edd0c4-4cce-4538-ae92-06c3356ee80a 361;;; dns.el ends here 362