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432 lines
14 KiB
EmacsLisp
432 lines
14 KiB
EmacsLisp
;;; dns.el --- Domain Name Service lookups
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;; Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008
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;; Free Software Foundation, Inc.
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;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
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;; Keywords: network
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;; This file is part of GNU Emacs.
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;; GNU Emacs is free software; you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation; either version 3, or (at your option)
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;; any later version.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; You should have received a copy of the GNU General Public License
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;; along with GNU Emacs; see the file COPYING. If not, write to the
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;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
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;; Boston, MA 02110-1301, USA.
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;;; Commentary:
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;;; Code:
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(defvar dns-timeout 5
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"How many seconds to wait when doing DNS queries.")
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(defvar dns-servers nil
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"Which DNS servers to query.
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If nil, /etc/resolv.conf will be consulted.")
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;;; Internal code:
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(defvar dns-query-types
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'((A 1)
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(NS 2)
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(MD 3)
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(MF 4)
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(CNAME 5)
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(SOA 6)
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(MB 7)
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(MG 8)
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(MR 9)
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(NULL 10)
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(WKS 11)
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(PTR 12)
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(HINFO 13)
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(MINFO 14)
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(MX 15)
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(TXT 16)
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(AAAA 28) ; RFC3596
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(SRV 33) ; RFC2782
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(AXFR 252)
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(MAILB 253)
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(MAILA 254)
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(* 255))
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"Names of query types and their values.")
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(defvar dns-classes
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'((IN 1)
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(CS 2)
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(CH 3)
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(HS 4))
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"Classes of queries.")
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(defun dns-write-bytes (value &optional length)
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(let (bytes)
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(dotimes (i (or length 1))
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(push (% value 256) bytes)
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(setq value (/ value 256)))
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(dolist (byte bytes)
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(insert byte))))
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(defun dns-read-bytes (length)
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(let ((value 0))
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(dotimes (i length)
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(setq value (logior (* value 256) (following-char)))
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(forward-char 1))
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value))
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(defun dns-get (type spec)
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(cadr (assq type spec)))
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(defun dns-inverse-get (value spec)
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(let ((found nil))
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(while (and (not found)
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spec)
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(if (eq value (cadr (car spec)))
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(setq found (caar spec))
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(pop spec)))
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found))
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(defun dns-write-name (name)
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(dolist (part (split-string name "\\."))
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(dns-write-bytes (length part))
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(insert part))
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(dns-write-bytes 0))
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(defun dns-read-string-name (string buffer)
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(with-temp-buffer
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(set-buffer-multibyte nil)
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(insert string)
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(goto-char (point-min))
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(dns-read-name buffer)))
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(defun dns-read-name (&optional buffer)
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(let ((ended nil)
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(name nil)
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length)
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(while (not ended)
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(setq length (dns-read-bytes 1))
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(if (= 192 (logand length (lsh 3 6)))
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(let ((offset (+ (* (logand 63 length) 256)
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(dns-read-bytes 1))))
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(save-excursion
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(when buffer
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(set-buffer buffer))
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(goto-char (1+ offset))
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(setq ended (dns-read-name buffer))))
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(if (zerop length)
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(setq ended t)
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(push (buffer-substring (point)
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(progn (forward-char length) (point)))
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name))))
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(if (stringp ended)
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(if (null name)
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ended
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(concat (mapconcat 'identity (nreverse name) ".") "." ended))
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(mapconcat 'identity (nreverse name) "."))))
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(defun dns-write (spec &optional tcp-p)
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"Write a DNS packet according to SPEC.
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If TCP-P, the first two bytes of the package with be the length field."
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(with-temp-buffer
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(set-buffer-multibyte nil)
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(dns-write-bytes (dns-get 'id spec) 2)
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(dns-write-bytes
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(logior
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(lsh (if (dns-get 'response-p spec) 1 0) -7)
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(lsh
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(cond
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((eq (dns-get 'opcode spec) 'query) 0)
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((eq (dns-get 'opcode spec) 'inverse-query) 1)
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((eq (dns-get 'opcode spec) 'status) 2)
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(t (error "No such opcode: %s" (dns-get 'opcode spec))))
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-3)
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(lsh (if (dns-get 'authoritative-p spec) 1 0) -2)
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(lsh (if (dns-get 'truncated-p spec) 1 0) -1)
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(lsh (if (dns-get 'recursion-desired-p spec) 1 0) 0)))
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(dns-write-bytes
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(cond
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((eq (dns-get 'response-code spec) 'no-error) 0)
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((eq (dns-get 'response-code spec) 'format-error) 1)
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((eq (dns-get 'response-code spec) 'server-failure) 2)
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((eq (dns-get 'response-code spec) 'name-error) 3)
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((eq (dns-get 'response-code spec) 'not-implemented) 4)
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((eq (dns-get 'response-code spec) 'refused) 5)
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(t 0)))
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(dns-write-bytes (length (dns-get 'queries spec)) 2)
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(dns-write-bytes (length (dns-get 'answers spec)) 2)
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(dns-write-bytes (length (dns-get 'authorities spec)) 2)
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(dns-write-bytes (length (dns-get 'additionals spec)) 2)
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(dolist (query (dns-get 'queries spec))
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(dns-write-name (car query))
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(dns-write-bytes (cadr (assq (or (dns-get 'type query) 'A)
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dns-query-types)) 2)
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(dns-write-bytes (cadr (assq (or (dns-get 'class query) 'IN)
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dns-classes)) 2))
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(dolist (slot '(answers authorities additionals))
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(dolist (resource (dns-get slot spec))
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(dns-write-name (car resource))
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(dns-write-bytes (cadr (assq (dns-get 'type resource) dns-query-types))
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2)
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(dns-write-bytes (cadr (assq (dns-get 'class resource) dns-classes))
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2)
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(dns-write-bytes (dns-get 'ttl resource) 4)
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(dns-write-bytes (length (dns-get 'data resource)) 2)
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(insert (dns-get 'data resource))))
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(when tcp-p
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(goto-char (point-min))
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(dns-write-bytes (buffer-size) 2))
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(buffer-string)))
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(defun dns-read (packet)
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(with-temp-buffer
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(set-buffer-multibyte nil)
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(let ((spec nil)
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queries answers authorities additionals)
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(insert packet)
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(goto-char (point-min))
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(push (list 'id (dns-read-bytes 2)) spec)
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(let ((byte (dns-read-bytes 1)))
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(push (list 'response-p (if (zerop (logand byte (lsh 1 7))) nil t))
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spec)
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(let ((opcode (logand byte (lsh 7 3))))
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(push (list 'opcode
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(cond ((eq opcode 0) 'query)
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((eq opcode 1) 'inverse-query)
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((eq opcode 2) 'status)))
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spec))
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(push (list 'authoritative-p (if (zerop (logand byte (lsh 1 2)))
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nil t)) spec)
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(push (list 'truncated-p (if (zerop (logand byte (lsh 1 2))) nil t))
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spec)
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(push (list 'recursion-desired-p
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(if (zerop (logand byte (lsh 1 0))) nil t)) spec))
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(let ((rc (logand (dns-read-bytes 1) 15)))
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(push (list 'response-code
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(cond
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((eq rc 0) 'no-error)
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((eq rc 1) 'format-error)
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((eq rc 2) 'server-failure)
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((eq rc 3) 'name-error)
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((eq rc 4) 'not-implemented)
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((eq rc 5) 'refused)))
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spec))
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(setq queries (dns-read-bytes 2))
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(setq answers (dns-read-bytes 2))
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(setq authorities (dns-read-bytes 2))
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(setq additionals (dns-read-bytes 2))
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(let ((qs nil))
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(dotimes (i queries)
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(push (list (dns-read-name)
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(list 'type (dns-inverse-get (dns-read-bytes 2)
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dns-query-types))
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(list 'class (dns-inverse-get (dns-read-bytes 2)
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dns-classes)))
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qs))
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(push (list 'queries qs) spec))
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(dolist (slot '(answers authorities additionals))
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(let ((qs nil)
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type)
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(dotimes (i (symbol-value slot))
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(push (list (dns-read-name)
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(list 'type
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(setq type (dns-inverse-get (dns-read-bytes 2)
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dns-query-types)))
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(list 'class (dns-inverse-get (dns-read-bytes 2)
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dns-classes))
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(list 'ttl (dns-read-bytes 4))
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(let ((length (dns-read-bytes 2)))
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(list 'data
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(dns-read-type
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(buffer-substring
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(point)
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(progn (forward-char length) (point)))
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type))))
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qs))
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(push (list slot qs) spec)))
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(nreverse spec))))
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(defun dns-read-int32 ()
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;; Full 32 bit Integers can't be handled by Emacs. If we use
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;; floats, it works.
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(format "%.0f" (+ (* (dns-read-bytes 1) 16777216.0)
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(dns-read-bytes 3))))
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(defun dns-read-type (string type)
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(let ((buffer (current-buffer))
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(point (point)))
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(prog1
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(with-temp-buffer
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(set-buffer-multibyte nil)
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(insert string)
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(goto-char (point-min))
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(cond
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((eq type 'A)
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(let ((bytes nil))
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(dotimes (i 4)
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(push (dns-read-bytes 1) bytes))
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(mapconcat 'number-to-string (nreverse bytes) ".")))
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((eq type 'AAAA)
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(let (hextets)
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(dotimes (i 8)
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(push (dns-read-bytes 2) hextets))
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(mapconcat (lambda (n) (format "%x" n))
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(nreverse hextets) ":")))
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((eq type 'SOA)
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(list (list 'mname (dns-read-name buffer))
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(list 'rname (dns-read-name buffer))
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(list 'serial (dns-read-int32))
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(list 'refresh (dns-read-int32))
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(list 'retry (dns-read-int32))
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(list 'expire (dns-read-int32))
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(list 'minimum (dns-read-int32))))
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((eq type 'SRV)
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(list (list 'priority (dns-read-bytes 2))
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(list 'weight (dns-read-bytes 2))
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(list 'port (dns-read-bytes 2))
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(list 'target (dns-read-name buffer))))
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((eq type 'MX)
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(cons (dns-read-bytes 2) (dns-read-name buffer)))
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((or (eq type 'CNAME) (eq type 'NS) (eq type 'PTR))
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(dns-read-string-name string buffer))
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(t string)))
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(goto-char point))))
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(defun dns-parse-resolv-conf ()
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(when (file-exists-p "/etc/resolv.conf")
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(with-temp-buffer
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(insert-file-contents "/etc/resolv.conf")
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(goto-char (point-min))
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(while (re-search-forward "^nameserver[\t ]+\\([^ \t\n]+\\)" nil t)
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(push (match-string 1) dns-servers))
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(setq dns-servers (nreverse dns-servers)))))
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(defun dns-read-txt (string)
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(if (> (length string) 1)
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(substring string 1)
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string))
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(defun dns-get-txt-answer (answers)
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(let ((result "")
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(do-next nil))
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(dolist (answer answers)
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(dolist (elem answer)
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(when (consp elem)
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(cond
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((eq (car elem) 'type)
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(setq do-next (eq (cadr elem) 'TXT)))
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((eq (car elem) 'data)
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(when do-next
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(setq result (concat result (dns-read-txt (cadr elem))))))))))
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result))
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;;; Interface functions.
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(defmacro dns-make-network-process (server)
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(if (featurep 'xemacs)
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`(let ((coding-system-for-read 'binary)
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(coding-system-for-write 'binary))
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(open-network-stream "dns" (current-buffer)
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,server "domain" 'udp))
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`(let ((server ,server)
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(coding-system-for-read 'binary)
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(coding-system-for-write 'binary))
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(if (fboundp 'make-network-process)
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(make-network-process
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:name "dns"
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:coding 'binary
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:buffer (current-buffer)
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:host server
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:service "domain"
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:type 'datagram)
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;; Older versions of Emacs doesn't have
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;; `make-network-process', so we fall back on opening a TCP
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;; connection to the DNS server.
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(open-network-stream "dns" (current-buffer) server "domain")))))
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(defvar dns-cache (make-vector 4096 0))
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(defun query-dns-cached (name &optional type fullp reversep)
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(let* ((key (format "%s:%s:%s:%s" name type fullp reversep))
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(sym (intern-soft key dns-cache)))
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(if (and sym
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(boundp sym))
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(symbol-value sym)
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(let ((result (query-dns name type fullp reversep)))
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(set (intern key dns-cache) result)
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result))))
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(defun query-dns (name &optional type fullp reversep)
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"Query a DNS server for NAME of TYPE.
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If FULLP, return the entire record returned.
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If REVERSEP, look up an IP address."
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(setq type (or type 'A))
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(unless dns-servers
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(dns-parse-resolv-conf))
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(when reversep
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(setq name (concat
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(mapconcat 'identity (nreverse (split-string name "\\.")) ".")
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".in-addr.arpa")
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type 'PTR))
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(if (not dns-servers)
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(message "No DNS server configuration found")
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(with-temp-buffer
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(set-buffer-multibyte nil)
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(let ((process (condition-case ()
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(dns-make-network-process (car dns-servers))
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(error
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(message
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"dns: Got an error while trying to talk to %s"
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(car dns-servers))
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nil)))
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(tcp-p (and (not (fboundp 'make-network-process))
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(not (featurep 'xemacs))))
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(step 100)
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(times (* dns-timeout 1000))
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(id (random 65000)))
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(when process
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(process-send-string
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process
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(dns-write `((id ,id)
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(opcode query)
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(queries ((,name (type ,type))))
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(recursion-desired-p t))
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tcp-p))
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(while (and (zerop (buffer-size))
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(> times 0))
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(sit-for (/ step 1000.0))
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(accept-process-output process 0 step)
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(setq times (- times step)))
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(condition-case nil
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(delete-process process)
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(error nil))
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(when (and tcp-p
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(>= (buffer-size) 2))
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(goto-char (point-min))
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(delete-region (point) (+ (point) 2)))
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(when (and (>= (buffer-size) 2)
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;; We had a time-out.
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(> times 0))
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(let ((result (dns-read (buffer-string))))
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(if fullp
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result
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(let ((answer (car (dns-get 'answers result))))
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(when (eq type (dns-get 'type answer))
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(if (eq type 'TXT)
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(dns-get-txt-answer (dns-get 'answers result))
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(dns-get 'data answer))))))))))))
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(provide 'dns)
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;; arch-tag: d0edd0c4-4cce-4538-ae92-06c3356ee80a
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;;; dns.el ends here
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